https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why not use a cc diode or a depletion fet?
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages.
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
Bill Sloman <bill.sloman@ieee.org> wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages. >>
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
The comments below the article answer Steve Woodwards question about
startup - the author says leakage. I?d be tempted to throw in 10megohm >resistor to guarantee that - but I don?t think I would use that circuit >anyway.
Author probably got his startup leakage from silly white protoboard?
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages.
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages. >>
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages. >>>
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that,
unless you bought a lot of them. Two monolithic pairs might be a dollar >each, and the resistors are going to very cheap surface mount parts.
EDN already posted the circuit. Working out what you might drive with it >would take longer, and why would I bother?
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages. >>>
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that, unless you bought a lot of them. Two monolithic pairs might be
a dollar each, and the resistors are going to very cheap surface mount parts.
EDN already posted the circuit. Working out what you might drive with it would take longer, and why would I bother?
--
Bill Sloman, Sydney
On Sat, 4 Apr 2026 03:10:18 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages. >>>>
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs >>>> and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that,
unless you bought a lot of them. Two monolithic pairs might be a dollar
each, and the resistors are going to very cheap surface mount parts.
Where is there a monolithic transistor pair for a dollar?
On 4/04/2026 3:29 am, john larkin wrote:
On Sat, 4 Apr 2026 03:10:18 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/ >>>>>>
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages.
The circuit has more parts than a constant current diode equivalent - >>>>> you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs >>>>> and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that,
unless you bought a lot of them. Two monolithic pairs might be a dollar
each, and the resistors are going to very cheap surface mount parts.
Where is there a monolithic transistor pair for a dollar?
TOSHIBA Transistor Silicon Npn Epitaxial Type (PCT Process)
HN1C03FU
is stocked by element-14 in Australia for $A0.55 ($US0.38) each -
minimum order five. It's not monolithic, but both transistors are in a >single package, which is close enough for the application.
They've also got the Nexperia BC847BS NPN for about the same price, and
the Nexperia BC857BS PNP part even cheaper.
<snipped the usual snark>
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qoopn$27kr$1@dont-email.me...
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages. >>>>
The circuit has more parts than a constant current diode equivalent -
you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs >>>> and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that, unless you bought a lot of them. Two monolithic pairs might be
a dollar each, and the resistors are going to very cheap surface mount parts.
EDN already posted the circuit. Working out what you might drive with it would take longer, and why would I bother?
You'd clearly think twice now because there's a small risk you might make an erroneous claim.
And then instead of being happy to be corrected by others who have the necessary
information, you might come across as a being just a little vindictive towards those
who pointed out your error.
Did you enjoy the capacitor film article JM posted?
On Sat, 4 Apr 2026 04:48:22 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 3:29 am, john larkin wrote:
On Sat, 4 Apr 2026 03:10:18 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/ >>>>>>>
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages.
The circuit has more parts than a constant current diode equivalent - >>>>>> you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs >>>>>> and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that,
unless you bought a lot of them. Two monolithic pairs might be a dollar >>>> each, and the resistors are going to very cheap surface mount parts.
Where is there a monolithic transistor pair for a dollar?
TOSHIBA Transistor Silicon Npn Epitaxial Type (PCT Process)
HN1C03FU
is stocked by element-14 in Australia for $A0.55 ($US0.38) each -
minimum order five. It's not monolithic, but both transistors are in a
single package, which is close enough for the application.
The data sheet says upfront that it's two devices in one package. Not monolithic.
I've tested some of those dual-chip things. The thermal coupling
between chips is ghastly.
https://www.dropbox.com/scl/fi/keyzn812hvjp7atomp9im/NEC_dual_transistor.jpg?rlkey=84hp3m9n2uyw53y7k2s7klq7t&raw=1
Hardly better than two SOT-23s on a board, but worse theta.
They've also got the Nexperia BC847BS NPN for about the same price, and
the Nexperia BC857BS PNP part even cheaper.
<snipped the usual snark>
Post your circuit.
On 4/04/2026 8:07 am, john larkin wrote:
On Sat, 4 Apr 2026 04:48:22 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 3:29 am, john larkin wrote:
On Sat, 4 Apr 2026 03:10:18 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 2:20 am, john larkin wrote:
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/ >>>>>>>>
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages.
The circuit has more parts than a constant current diode equivalent - >>>>>>> you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs >>>>>>> and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that,
unless you bought a lot of them. Two monolithic pairs might be a dollar >>>>> each, and the resistors are going to very cheap surface mount parts.
Where is there a monolithic transistor pair for a dollar?
TOSHIBA Transistor Silicon Npn Epitaxial Type (PCT Process)
HN1C03FU
is stocked by element-14 in Australia for $A0.55 ($US0.38) each -
minimum order five. It's not monolithic, but both transistors are in a
single package, which is close enough for the application.
The data sheet says upfront that it's two devices in one package. Not
monolithic.
I've tested some of those dual-chip things. The thermal coupling
between chips is ghastly.
But better than the thermal coupling of the chips to the board they are >mounted on.
https://www.dropbox.com/scl/fi/keyzn812hvjp7atomp9im/NEC_dual_transistor.jpg?rlkey=84hp3m9n2uyw53y7k2s7klq7t&raw=1
Hardly better than two SOT-23s on a board, but worse theta.
So what. Two SOT-23's would have to be mounted very close to each other
to do almost as well, and the application doesn't need particularly high >performance.
They've also got the Nexperia BC847BS NPN for about the same price, and
the Nexperia BC857BS PNP part even cheaper.
<snipped the usual snark>
Post your circuit.
To make you happy? Not exactly a compelling motivation. And the circuit
is intended to drive a bunch of LEDS. Until you specify the nature and
the number of the LEDs there's no point in getting into detailed design.
On Sat, 4 Apr 2026 17:33:54 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 8:07 am, john larkin wrote:
On Sat, 4 Apr 2026 04:48:22 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 4/04/2026 3:29 am, john larkin wrote:
On Sat, 4 Apr 2026 03:10:18 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 4/04/2026 2:20 am, john larkin wrote:Where is there a monolithic transistor pair for a dollar?
On Fri, 3 Apr 2026 16:45:29 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 3/04/2026 7:56 am, john larkin wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/ >>>>>>>>>
Why does it even start?
Why wouldn't it?
Why not use a cc diode or a depletion fet?
Constant current diodes are depletion FETs.
Current mirrors are more predictable, and they start up at lower voltages.
The circuit has more parts than a constant current diode equivalent - >>>>>>>> you'd use monolithic pairs for Q1 and Q2, and Q3 and Q4 so it two pairs
and three resistors - but might well be cheaper.
Cool. Post a circuit. Try to keep the cost below $60.
Any printed circuit board you put it on could cost more than that, >>>>>> unless you bought a lot of them. Two monolithic pairs might be a dollar >>>>>> each, and the resistors are going to very cheap surface mount parts. >>>>>
TOSHIBA Transistor Silicon Npn Epitaxial Type (PCT Process)
HN1C03FU
is stocked by element-14 in Australia for $A0.55 ($US0.38) each -
minimum order five. It's not monolithic, but both transistors are in a >>>> single package, which is close enough for the application.
The data sheet says upfront that it's two devices in one package. Not
monolithic.
I've tested some of those dual-chip things. The thermal coupling
between chips is ghastly.
But better than the thermal coupling of the chips to the board they are
mounted on.
If you are saying that the theta between chips is nonzero, I wouldn't
argue the claim. But the dual-chip things will make terrible current
mirrors.
I have noticed that scientific types have a universal affection for
current mirrors, and design terrible current mirrors.
Hardly better than two SOT-23s on a board, but worse theta.
So what. Two SOT-23's would have to be mounted very close to each other
to do almost as well, and the application doesn't need particularly high
performance.
See comment about current mirror fetishes. The output transistor
typically dissipates a lot more power than the input transistor, so
the thermals suck. Lots of papers in RSI have mirrors with separate transistors!
They've also got the Nexperia BC847BS NPN for about the same price, and >>>> the Nexperia BC857BS PNP part even cheaper.
<snipped the usual snark>
Post your circuit.
To make you happy? Not exactly a compelling motivation. And the circuit
is intended to drive a bunch of LEDS. Until you specify the nature and
the number of the LEDs there's no point in getting into detailed design.
Your circuits designs do make me happy. I wish you would post more.
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why not use a cc diode or a depletion fet?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why not use a cc diode or a depletion fet?
That circuit may be very inefficient, depending on the LEDs and the
input voItage range, and could fry those dinky little transistors. It
should be a switcher. That could be done with 4 or 5 parts for about
35 cents.
It wouldn't be a constant-current block of course; constant-power.
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why not use a cc diode or a depletion fet?
That circuit may be very inefficient, depending on the LEDs and the
input voItage range, and could fry those dinky little transistors. It
should be a switcher. That could be done with 4 or 5 parts for about
35 cents.
EDN doesn't specify the transistors at all.
They don't have to be dinky.
A practical design couldn't start until the nature and number of LEDs
being driven had been specified. If the designer was remarkably
incompetent they could put together something that might fry the >transistors. Since John Larkin may select his staff on their willingness
to flatter him it might happen. None of the people I've worked with have >ever been that silly - they made less obvious mistakes.
It wouldn't be a constant-current block of course; constant-power.
Why? You could do either. What you want from LEDs is constant
brightness, which equates to constant current. The voltage drop across a
LED isn't linearly dependent on the current through them, so that does
come pretty close to constant power.
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why not use a cc diode or a depletion fet?
That circuit may be very inefficient, depending on the LEDs and the
input voItage range, and could fry those dinky little transistors. It
should be a switcher. That could be done with 4 or 5 parts for about
35 cents.
EDN doesn't specify the transistors at all.
??????
It sure does, in plain sight. Silly little TO-92s.
They don't have to be dinky.
No, but they are.
A practical design couldn't start until the nature and number of LEDs
being driven had been specified. If the designer was remarkably
incompetent they could put together something that might fry the
transistors. Since John Larkin may select his staff on their willingness
to flatter him it might happen. None of the people I've worked with have
ever been that silly - they made less obvious mistakes.
Conservation of energy requires that the circuit dissipate I*(Vsupply-Vled)... unless you use a switcher.
It wouldn't be a constant-current block of course; constant-power.
Why? You could do either. What you want from LEDs is constant
brightness, which equates to constant current. The voltage drop across a
LED isn't linearly dependent on the current through them, so that does
come pretty close to constant power.
A switcher would be constant power in and constant current out. And
very efficient.
Give it a try.
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/
Why does it even start?
Why not use a cc diode or a depletion fet?
That circuit may be very inefficient, depending on the LEDs and the
input voItage range, and could fry those dinky little transistors. It
should be a switcher. That could be done with 4 or 5 parts for about
35 cents.
EDN doesn't specify the transistors at all.
??????
It sure does, in plain sight. Silly little TO-92s.
Oops. My mistake. Also EDNs. They didn't specify the LEDs to be driven, or with what current so specifying specific transistors
was a mistake.
They don't have to be dinky.
No, but they are.
A practical design couldn't start until the nature and number of LEDs
being driven had been specified. If the designer was remarkably
incompetent they could put together something that might fry the
transistors. Since John Larkin may select his staff on their willingness >>> to flatter him it might happen. None of the people I've worked with have >>> ever been that silly - they made less obvious mistakes.
Conservation of energy requires that the circuit dissipate
I*(Vsupply-Vled)... unless you use a switcher.
So what?
It wouldn't be a constant-current block of course; constant-power.
Why? You could do either. What you want from LEDs is constant
brightness, which equates to constant current. The voltage drop across a >>> LED isn't linearly dependent on the current through them, so that does
come pretty close to constant power.
A switcher would be constant power in and constant current out. And
very efficient.
It might be. Switching losses are real, and inept design can make them quite large.
Give it a try.
Specify the LEDs you want to drive, and the current you want to drive them at, and I might. Without that information the problem
is undefined and perfectly insoluble. Since you wouldn't build the device, it would a waste of effort even if you produced a
specification of what you wanted.
--
Bill Sloman, Sydney
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>> wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/ >>>>>>
Why does it even start?
Why not use a cc diode or a depletion fet?
That circuit may be very inefficient, depending on the LEDs and the
input voItage range, and could fry those dinky little transistors. It >>>>> should be a switcher. That could be done with 4 or 5 parts for about >>>>> 35 cents.
EDN doesn't specify the transistors at all.
??????
It sure does, in plain sight. Silly little TO-92s.
Oops. My mistake. Also EDNs. They didn't specify the LEDs to be driven, or with what current so specifying specific transistors
was a mistake.
They don't have to be dinky.
No, but they are.
A practical design couldn't start until the nature and number of LEDs
being driven had been specified. If the designer was remarkably
incompetent they could put together something that might fry the
transistors. Since John Larkin may select his staff on their willingness >>>> to flatter him it might happen. None of the people I've worked with have >>>> ever been that silly - they made less obvious mistakes.
Conservation of energy requires that the circuit dissipate
I*(Vsupply-Vled)... unless you use a switcher.
So what?
It wouldn't be a constant-current block of course; constant-power.
Why? You could do either. What you want from LEDs is constant
brightness, which equates to constant current. The voltage drop across a >>>> LED isn't linearly dependent on the current through them, so that does >>>> come pretty close to constant power.
A switcher would be constant power in and constant current out. And
very efficient.
It might be. Switching losses are real, and inept design can make them quite large.
Give it a try.
Specify the LEDs you want to drive, and the current you want to drive them at, and I might. Without that information the problem
is undefined and perfectly insoluble. Since you wouldn't build the device, it would a waste of effort even if you produced a
specification of what you wanted.
--
Bill Sloman, Sydney
Ok please make an equivalent of this but to your design standards and low cost.
Note that I'm not asking for criticism of this circuit. There are many reasons why
reality may not be the same as its simulation but I had fun doing it.
If it doesn't give a constant current of 500mA, open it in Notepad++
Under Encoding, convert to ANSI and save it.
Version 4.1
SHEET 1 2820 680
WIRE 976 -128 272 -128
WIRE 1072 -128 1040 -128
WIRE 16 -48 -16 -48
WIRE 96 -48 16 -48
WIRE 240 -48 96 -48
WIRE 336 -48 240 -48
WIRE 448 -48 336 -48
WIRE 464 -48 448 -48
WIRE 528 -48 464 -48
WIRE 608 -48 528 -48
WIRE 672 -48 608 -48
WIRE 784 -48 768 -48
WIRE 816 -48 784 -48
WIRE 864 -48 816 -48
WIRE 992 -48 944 -48
WIRE 1024 -48 992 -48
WIRE 1072 -48 1072 -128
WIRE 1072 -48 1024 -48
WIRE 1264 -48 1072 -48
WIRE 1360 -48 1264 -48
WIRE 240 -16 240 -48
WIRE 336 -16 336 -48
WIRE 1264 0 1264 -48
WIRE 1360 0 1360 -48
WIRE -16 32 -16 -48
WIRE 608 32 608 -48
WIRE 1168 32 608 32
WIRE 448 64 448 -48
WIRE 464 64 464 -48
WIRE 96 80 96 -48
WIRE 240 80 240 64
WIRE 272 80 272 -128
WIRE 272 80 240 80
WIRE 336 80 336 64
WIRE 384 80 336 80
WIRE 416 80 384 80
WIRE 816 80 816 -48
WIRE 992 80 992 -48
WIRE 1168 80 1168 32
WIRE 336 96 336 80
WIRE 336 96 304 96
WIRE 656 96 480 96
WIRE 688 96 688 0
WIRE 688 96 656 96
WIRE 1232 96 1200 96
WIRE 1264 96 1264 64
WIRE 1264 96 1232 96
WIRE 240 112 240 80
WIRE 384 112 240 112
WIRE 416 112 384 112
WIRE 528 112 528 -48
WIRE 608 112 608 32
WIRE 1104 112 1088 112
WIRE 1136 112 1104 112
WIRE 240 128 240 112
WIRE 336 128 336 96
WIRE 1312 128 1200 128
WIRE 1360 128 1360 80
WIRE 1360 128 1312 128
WIRE 1360 160 1360 128
WIRE -16 176 -16 112
WIRE 240 240 240 208
WIRE 336 240 336 208
WIRE 336 240 240 240
WIRE 384 240 336 240
WIRE 432 240 432 128
WIRE 432 240 384 240
WIRE 448 240 448 128
WIRE 448 240 432 240
WIRE 464 240 464 128
WIRE 464 240 448 240
WIRE 528 240 528 176
WIRE 528 240 464 240
WIRE 544 240 528 240
WIRE 608 240 608 176
WIRE 608 240 544 240
WIRE 1360 240 1360 224
WIRE 1424 240 1360 240
WIRE 1536 240 1424 240
WIRE 1696 240 1600 240
WIRE 1872 240 1760 240
WIRE 544 272 544 240
WIRE 1264 272 1264 96
WIRE 1360 272 1360 240
WIRE -16 368 -16 256
WIRE 96 368 96 144
WIRE 96 368 -16 368
WIRE 544 368 544 352
WIRE 544 368 96 368
WIRE 816 368 816 144
WIRE 816 368 544 368
WIRE 992 368 992 144
WIRE 992 368 816 368
WIRE 1168 368 1168 144
WIRE 1168 368 992 368
WIRE 1264 368 1264 352
WIRE 1264 368 1168 368
WIRE 1360 368 1360 336
WIRE 1360 368 1264 368
WIRE 1872 368 1872 240
WIRE 1872 368 1360 368
WIRE -16 384 -16 368
WIRE 304 448 304 96
WIRE 992 448 304 448
WIRE 1088 448 1088 112
WIRE 1088 448 1072 448
FLAG -16 384 0
FLAG 16 -48 in
FLAG 784 -48 sw
FLAG 1024 -48 out
FLAG 1312 128 isense
FLAG 1232 96 iref
FLAG 1104 112 ifb
FLAG 384 80 cmp-
FLAG 384 112 cmp+
FLAG 656 96 gate
FLAG 384 240 cmpv-
FLAG 1424 240 led
SYMBOL Comparators\\LT1719 448 32 R0
WINDOW 0 27 27 Left 2
WINDOW 3 -92 6 Left 2
SYMATTR InstName U1
SYMBOL res 320 112 R0
WINDOW 0 41 34 Left 2
WINDOW 3 35 64 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL ind 960 -64 R90
WINDOW 0 63 51 VBottom 2
WINDOW 3 -27 53 VTop 2
SYMATTR InstName L1
SYMATTR Value 0.068m
SYMATTR SpiceLine Ipk=0.85 Rser=0.21 Rpar=0 Cpar=0
SYMBOL res 1376 -16 M0
WINDOW 0 -37 34 Left 2
WINDOW 3 -57 63 Left 2
SYMATTR InstName R8
SYMATTR Value 0.68
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL res 224 -32 R0
WINDOW 0 -35 19 Left 2
WINDOW 3 -49 48 Left 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL schottky 832 144 R180
WINDOW 0 -42 30 Left 2
WINDOW 3 -119 -3 Left 2
SYMATTR InstName D2
SYMATTR Value MBRS130L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL pmos 768 0 M270
WINDOW 0 10 129 VLeft 2
WINDOW 3 -10 67 VLeft 2
SYMATTR InstName M1
SYMATTR Value AO6407
SYMBOL voltage -16 160 R0
WINDOW 0 -75 16 Left 2
WINDOW 3 -71 54 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 -185 81 Left 2
SYMATTR InstName V3
SYMATTR Value 12
SYMBOL res -32 16 R0
WINDOW 0 -39 29 Left 2
WINDOW 3 -63 65 Left 2
SYMATTR InstName R9
SYMATTR Value 0.001
SYMBOL zener 544 176 R180
WINDOW 0 37 29 Left 2
WINDOW 3 78 -5 Right 2
SYMATTR InstName D1
SYMATTR Value BZX84C6V2L
SYMBOL res 320 -32 R0
WINDOW 0 40 7 Left 2
WINDOW 3 37 33 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL res 528 368 M180
WINDOW 0 39 76 Left 2
WINDOW 3 38 42 Left 2
SYMATTR InstName R5
SYMATTR Value 220
SYMATTR SpiceLine tol=1 pwr=0.25
SYMBOL cap 592 176 M180
WINDOW 0 29 52 Left 2
WINDOW 3 30 13 Left 2
SYMATTR InstName C3
SYMATTR Value 100n
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.0337 Lser=180p mfg="W?rth Elektronik" pn="885012104009 WCAP-CSGP 0201" type="X5R"
SYMBOL polcap 976 80 R0
WINDOW 3 -11 59 Left 2
WINDOW 0 27 9 Left 2
SYMATTR Value 100000n
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.9 Lser=0 mfg="AVX" pn="TAJD107M006" type="Tantalum"
SYMBOL res 224 112 R0
WINDOW 0 -40 33 Left 2
WINDOW 3 -52 57 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL polcap 80 80 R0
WINDOW 3 -27 60 Left 2
WINDOW 0 -39 4 Left 2
SYMATTR Value 100000n
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.9 Lser=0 mfg="AVX" pn="TAJD107M006" type="Tantalum"
SYMBOL LED 1536 256 R270
WINDOW 0 72 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName LED1
SYMATTR Value LXZ1-PB01
SYMBOL res 976 432 M90
WINDOW 0 -2 59 VBottom 2
WINDOW 3 35 64 VTop 2
SYMATTR InstName R6
SYMATTR Value 22K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL cap 976 -144 M90
WINDOW 0 -3 31 VBottom 2
WINDOW 3 36 35 VTop 2
SYMATTR InstName C5
SYMATTR Value 10n
SYMATTR SpiceLine V=16 Irms=0 Rser=0.0747 Lser=525p mfg="W?rth Elektronik" pn="885012210001 WCAP-CSGP 1812" type="X7R"
SYMBOL OpAmps\\OP07 1168 48 M0
WINDOW 0 12 22 Left 2
WINDOW 3 9 103 Left 2
SYMATTR InstName U2
SYMBOL res 1248 368 M180
WINDOW 0 -40 81 Left 2
WINDOW 3 -51 46 Left 2
SYMATTR InstName R7
SYMATTR Value 470
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL schottky 1280 0 M0
WINDOW 0 43 24 Left 2
WINDOW 3 40 -8 Left 2
SYMATTR InstName D3
SYMATTR Value BAT54AHY
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL FerriteBead 1360 192 R0
SYMATTR InstName L2
SYMATTR Value 6?
SYMATTR SpiceLine Ipk=3 Rser=0.0102 Rpar=1220 Cpar=1.9p
SYMBOL cap 1344 272 R0
SYMATTR InstName C4
SYMATTR Value 1n
SYMATTR SpiceLine V=10 Irms=0 Rser=0.1909 Lser=177p mfg="W?rth Elektronik" pn="885012205006 WCAP-CSGP 0402" type="X7R"
SYMBOL LED 1696 256 R270
WINDOW 0 72 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName LED2
SYMATTR Value LXZ1-PB01
TEXT -24 440 Left 2 !.tran 0 0.001 0 1u startup
TEXT -24 480 Left 2 !.options plotwinsize=0
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>>> wrote:
Let's see Bill's circuit next.
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>>>> wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>>>>> wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>>>>>> wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of >point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could
mock you about that, but you do a pretty good job of sending yourself up
all on your own.
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>>>>>> wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
--
Bill Sloman, Sydney
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>> Edward Rawde is apparently willing to play with you. I'm happy to leave >>>> you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>> wrote:
https://www.edn.com/a-fully-floating-bjt-based-led-current-driver/ >>>>>>
Why does it even start?
Why not use a cc diode or a depletion fet?
That circuit may be very inefficient, depending on the LEDs and the
input voItage range, and could fry those dinky little transistors. It >>>>> should be a switcher. That could be done with 4 or 5 parts for about >>>>> 35 cents.
EDN doesn't specify the transistors at all.
??????
It sure does, in plain sight. Silly little TO-92s.
Oops. My mistake. Also EDNs. They didn't specify the LEDs to be driven, or with what current so specifying specific transistors
was a mistake.
They don't have to be dinky.
No, but they are.
A practical design couldn't start until the nature and number of LEDs
being driven had been specified. If the designer was remarkably
incompetent they could put together something that might fry the
transistors. Since John Larkin may select his staff on their willingness >>>> to flatter him it might happen. None of the people I've worked with have >>>> ever been that silly - they made less obvious mistakes.
Conservation of energy requires that the circuit dissipate
I*(Vsupply-Vled)... unless you use a switcher.
So what?
It wouldn't be a constant-current block of course; constant-power.
Why? You could do either. What you want from LEDs is constant
brightness, which equates to constant current. The voltage drop across a >>>> LED isn't linearly dependent on the current through them, so that does >>>> come pretty close to constant power.
A switcher would be constant power in and constant current out. And
very efficient.
It might be. Switching losses are real, and inept design can make them quite large.
Give it a try.
Specify the LEDs you want to drive, and the current you want to drive them at, and I might. Without that information the problem
is undefined and perfectly insoluble. Since you wouldn't build the device, it would a waste of effort even if you produced a
specification of what you wanted.
--
Bill Sloman, Sydney
Ok please make an equivalent of this but to your design standards and low cost.
Note that I'm not asking for criticism of this circuit. There are many reasons why
reality may not be the same as its simulation but I had fun doing it.
If it doesn't give a constant current of 500mA, open it in Notepad++
Under Encoding, convert to ANSI and save it.
Version 4.1
SHEET 1 2820 680
WIRE 976 -128 272 -128
WIRE 1072 -128 1040 -128
WIRE 16 -48 -16 -48
WIRE 96 -48 16 -48
WIRE 240 -48 96 -48
WIRE 336 -48 240 -48
WIRE 448 -48 336 -48
WIRE 464 -48 448 -48
WIRE 528 -48 464 -48
WIRE 608 -48 528 -48
WIRE 672 -48 608 -48
WIRE 784 -48 768 -48
WIRE 816 -48 784 -48
WIRE 864 -48 816 -48
WIRE 992 -48 944 -48
WIRE 1024 -48 992 -48
WIRE 1072 -48 1072 -128
WIRE 1072 -48 1024 -48
WIRE 1264 -48 1072 -48
WIRE 1360 -48 1264 -48
WIRE 240 -16 240 -48
WIRE 336 -16 336 -48
WIRE 1264 0 1264 -48
WIRE 1360 0 1360 -48
WIRE -16 32 -16 -48
WIRE 608 32 608 -48
WIRE 1168 32 608 32
WIRE 448 64 448 -48
WIRE 464 64 464 -48
WIRE 96 80 96 -48
WIRE 240 80 240 64
WIRE 272 80 272 -128
WIRE 272 80 240 80
WIRE 336 80 336 64
WIRE 384 80 336 80
WIRE 416 80 384 80
WIRE 816 80 816 -48
WIRE 992 80 992 -48
WIRE 1168 80 1168 32
WIRE 336 96 336 80
WIRE 336 96 304 96
WIRE 656 96 480 96
WIRE 688 96 688 0
WIRE 688 96 656 96
WIRE 1232 96 1200 96
WIRE 1264 96 1264 64
WIRE 1264 96 1232 96
WIRE 240 112 240 80
WIRE 384 112 240 112
WIRE 416 112 384 112
WIRE 528 112 528 -48
WIRE 608 112 608 32
WIRE 1104 112 1088 112
WIRE 1136 112 1104 112
WIRE 240 128 240 112
WIRE 336 128 336 96
WIRE 1312 128 1200 128
WIRE 1360 128 1360 80
WIRE 1360 128 1312 128
WIRE 1360 160 1360 128
WIRE -16 176 -16 112
WIRE 240 240 240 208
WIRE 336 240 336 208
WIRE 336 240 240 240
WIRE 384 240 336 240
WIRE 432 240 432 128
WIRE 432 240 384 240
WIRE 448 240 448 128
WIRE 448 240 432 240
WIRE 464 240 464 128
WIRE 464 240 448 240
WIRE 528 240 528 176
WIRE 528 240 464 240
WIRE 544 240 528 240
WIRE 608 240 608 176
WIRE 608 240 544 240
WIRE 1360 240 1360 224
WIRE 1424 240 1360 240
WIRE 1536 240 1424 240
WIRE 1696 240 1600 240
WIRE 1872 240 1760 240
WIRE 544 272 544 240
WIRE 1264 272 1264 96
WIRE 1360 272 1360 240
WIRE -16 368 -16 256
WIRE 96 368 96 144
WIRE 96 368 -16 368
WIRE 544 368 544 352
WIRE 544 368 96 368
WIRE 816 368 816 144
WIRE 816 368 544 368
WIRE 992 368 992 144
WIRE 992 368 816 368
WIRE 1168 368 1168 144
WIRE 1168 368 992 368
WIRE 1264 368 1264 352
WIRE 1264 368 1168 368
WIRE 1360 368 1360 336
WIRE 1360 368 1264 368
WIRE 1872 368 1872 240
WIRE 1872 368 1360 368
WIRE -16 384 -16 368
WIRE 304 448 304 96
WIRE 992 448 304 448
WIRE 1088 448 1088 112
WIRE 1088 448 1072 448
FLAG -16 384 0
FLAG 16 -48 in
FLAG 784 -48 sw
FLAG 1024 -48 out
FLAG 1312 128 isense
FLAG 1232 96 iref
FLAG 1104 112 ifb
FLAG 384 80 cmp-
FLAG 384 112 cmp+
FLAG 656 96 gate
FLAG 384 240 cmpv-
FLAG 1424 240 led
SYMBOL Comparators\\LT1719 448 32 R0
WINDOW 0 27 27 Left 2
WINDOW 3 -92 6 Left 2
SYMATTR InstName U1
SYMBOL res 320 112 R0
WINDOW 0 41 34 Left 2
WINDOW 3 35 64 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL ind 960 -64 R90
WINDOW 0 63 51 VBottom 2
WINDOW 3 -27 53 VTop 2
SYMATTR InstName L1
SYMATTR Value 0.068m
SYMATTR SpiceLine Ipk=0.85 Rser=0.21 Rpar=0 Cpar=0
SYMBOL res 1376 -16 M0
WINDOW 0 -37 34 Left 2
WINDOW 3 -57 63 Left 2
SYMATTR InstName R8
SYMATTR Value 0.68
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL res 224 -32 R0
WINDOW 0 -35 19 Left 2
WINDOW 3 -49 48 Left 2
SYMATTR InstName R1
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL schottky 832 144 R180
WINDOW 0 -42 30 Left 2
WINDOW 3 -119 -3 Left 2
SYMATTR InstName D2
SYMATTR Value MBRS130L
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL pmos 768 0 M270
WINDOW 0 10 129 VLeft 2
WINDOW 3 -10 67 VLeft 2
SYMATTR InstName M1
SYMATTR Value AO6407
SYMBOL voltage -16 160 R0
WINDOW 0 -75 16 Left 2
WINDOW 3 -71 54 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 -185 81 Left 2
SYMATTR InstName V3
SYMATTR Value 12
SYMBOL res -32 16 R0
WINDOW 0 -39 29 Left 2
WINDOW 3 -63 65 Left 2
SYMATTR InstName R9
SYMATTR Value 0.001
SYMBOL zener 544 176 R180
WINDOW 0 37 29 Left 2
WINDOW 3 78 -5 Right 2
SYMATTR InstName D1
SYMATTR Value BZX84C6V2L
SYMBOL res 320 -32 R0
WINDOW 0 40 7 Left 2
WINDOW 3 37 33 Left 2
SYMATTR InstName R3
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL res 528 368 M180
WINDOW 0 39 76 Left 2
WINDOW 3 38 42 Left 2
SYMATTR InstName R5
SYMATTR Value 220
SYMATTR SpiceLine tol=1 pwr=0.25
SYMBOL cap 592 176 M180
WINDOW 0 29 52 Left 2
WINDOW 3 30 13 Left 2
SYMATTR InstName C3
SYMATTR Value 100n
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.0337 Lser=180p mfg="Wrth Elektronik" pn="885012104009 WCAP-CSGP 0201" type="X5R"
SYMBOL polcap 976 80 R0
WINDOW 3 -11 59 Left 2
WINDOW 0 27 9 Left 2
SYMATTR Value 100000n
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.9 Lser=0 mfg="AVX" pn="TAJD107M006" type="Tantalum"
SYMBOL res 224 112 R0
WINDOW 0 -40 33 Left 2
WINDOW 3 -52 57 Left 2
SYMATTR InstName R2
SYMATTR Value 10K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL polcap 80 80 R0
WINDOW 3 -27 60 Left 2
WINDOW 0 -39 4 Left 2
SYMATTR Value 100000n
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=6.3 Irms=0 Rser=0.9 Lser=0 mfg="AVX" pn="TAJD107M006" type="Tantalum"
SYMBOL LED 1536 256 R270
WINDOW 0 72 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName LED1
SYMATTR Value LXZ1-PB01
SYMBOL res 976 432 M90
WINDOW 0 -2 59 VBottom 2
WINDOW 3 35 64 VTop 2
SYMATTR InstName R6
SYMATTR Value 22K
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL cap 976 -144 M90
WINDOW 0 -3 31 VBottom 2
WINDOW 3 36 35 VTop 2
SYMATTR InstName C5
SYMATTR Value 10n
SYMATTR SpiceLine V=16 Irms=0 Rser=0.0747 Lser=525p mfg="Wrth Elektronik" pn="885012210001 WCAP-CSGP 1812" type="X7R"
SYMBOL OpAmps\\OP07 1168 48 M0
WINDOW 0 12 22 Left 2
WINDOW 3 9 103 Left 2
SYMATTR InstName U2
SYMBOL res 1248 368 M180
WINDOW 0 -40 81 Left 2
WINDOW 3 -51 46 Left 2
SYMATTR InstName R7
SYMATTR Value 470
SYMATTR SpiceLine tol=1 pwr=0.1
SYMBOL schottky 1280 0 M0
WINDOW 0 43 24 Left 2
WINDOW 3 40 -8 Left 2
SYMATTR InstName D3
SYMATTR Value BAT54AHY
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL FerriteBead 1360 192 R0
SYMATTR InstName L2
SYMATTR Value 6æ
SYMATTR SpiceLine Ipk=3 Rser=0.0102 Rpar=1220 Cpar=1.9p
SYMBOL cap 1344 272 R0
SYMATTR InstName C4
SYMATTR Value 1n
SYMATTR SpiceLine V=10 Irms=0 Rser=0.1909 Lser=177p mfg="Wrth Elektronik" pn="885012205006 WCAP-CSGP 0402" type="X7R"
SYMBOL LED 1696 256 R270
WINDOW 0 72 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName LED2
SYMATTR Value LXZ1-PB01
TEXT -24 440 Left 2 !.tran 0 0.001 0 1u startup
TEXT -24 480 Left 2 !.options plotwinsize=0
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com> >>>>>>> wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. Edward Rawde is apparently willing to play with you. I'm
happy to leave you in his capable hands.
--
Bill Sloman, Sydney
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>> Edward Rawde is apparently willing to play with you. I'm happy to leave >>>> you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>>> Edward Rawde is apparently willing to play with you. I'm happy to leave >>>>> you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place. >>> It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or
more LXZ1-PB01 LEDs".
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he
asked how it would start up.
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>>> wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>>> Edward Rawde is apparently willing to play with you. I'm happy to leave >>>>> you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place. >>> It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
John Larkin wants to see it as some kind of teaching exercise, not realising that he'd failed the course when he asked how it
would start up. Instructing people who don't know how to learn - and don't seem to want to - is a pointless exercise.
--
Bill Sloman, Sydney
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>>>> Edward Rawde is apparently willing to play with you. I'm happy to leave >>>>>> you in his capable hands.
Please don't think that I am mocking you for being unable to design
simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place. >>>> It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or
more LXZ1-PB01 LEDs".
Why not?
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he
asked how it would start up.
How would it start up?
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be
entered.
Because sometimes they do.
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally?
John Larkin wants to see it as some kind of teaching exercise, not realising that he'd failed the course when he asked how it
would start up. Instructing people who don't know how to learn - and don't seem to want to - is a pointless exercise.
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally?
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
John Larkin wants to see it as some kind of teaching exercise, not realising that he'd failed the course when he asked how it
would start up. Instructing people who don't know how to learn - and don't seem to want to - is a pointless exercise.
--
Bill Sloman, Sydney
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>>>>> Edward Rawde is apparently willing to play with you. I'm happy to leave >>>>>>> you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place. >>>>> It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or
more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your
mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he
asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar >transistor junction.
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be
entered.
Even when the "failure state" is entirely imaginary?
Because sometimes they do.
Because you left out a connection?
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally?
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
Thank you for your input, I will modify the specification as follows:
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved, so there is currently no exact target for efficiency or cost.
Let me know when you have met this specification.
Your design need not, of course, be anything like the design I posted.
John Larkin wants to see it as some kind of teaching exercise, not realising that he'd failed the course when he asked how it
would start up. Instructing people who don't know how to learn - and don't seem to want to - is a pointless exercise.
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>>>>>> Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place. >>>>>> It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or >>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your
mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he
asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
I've measured collector leakage currents as low as 10 fA in cheap transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors
would need >1 beta at the pA or fA currents.
Even a dirty PCB could kill beta enough to prevent startup.
Q1 and Q4 don't help a bit.
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be
entered.
Even when the "failure state" is entirely imaginary?
Not starting up would not be an imaginary failure.
But a state-free design will always have few hangup states.
Because sometimes they do.
Because you left out a connection?
Because something unexpected happens. In a current case, a new digital
delay generator design, interesting things can happen if it's being
triggered with one set of delays and widths, and the user reprograms
them on-the-fly.
What's a boy to do?
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally?
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
Thank you for your input, I will modify the specification as follows:
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved, >> so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted.
If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
John Larkin wants to see it as some kind of teaching exercise, not realising that he'd failed the course when he asked how it
would start up. Instructing people who don't know how to learn - and don't seem to want to - is a pointless exercise.
--
Bill Sloman, Sydney
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously. >>>>>>>> Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place. >>>>>> It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or >>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your
mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he
asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
I've measured collector leakage currents as low as 10 fA in cheap transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors
would need >1 beta at the pA or fA currents.
Even a dirty PCB could kill beta enough to prevent startup.
Q1 and Q4 don't help a bit.
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be
entered.
Even when the "failure state" is entirely imaginary?
Not starting up would not be an imaginary failure.
But a state-free design will always have few hangup states.
Because sometimes they do.
Because you left out a connection?
Because something unexpected happens. In a current case, a new digital
delay generator design, interesting things can happen if it's being
triggered with one set of delays and widths, and the user reprograms
them on-the-fly.
What's a boy to do?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally?
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
Thank you for your input, I will modify the specification as follows:
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted.
If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
John Larkin wants to see it as some kind of teaching exercise, not realising that he'd failed the course when he asked how it
would start up. Instructing people who don't know how to learn - and don't seem to want to - is a pointless exercise.
On 06/04/2026 20:08, john larkin wrote:
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or >>>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your
mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he >>>>> asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
I've measured collector leakage currents as low as 10 fA in cheap
transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors
would need >1 beta at the pA or fA currents.
Even a dirty PCB could kill beta enough to prevent startup.
Q1 and Q4 don't help a bit.
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be
entered.
Even when the "failure state" is entirely imaginary?
Not starting up would not be an imaginary failure.
But a state-free design will always have few hangup states.
Because sometimes they do.
Because you left out a connection?
Because something unexpected happens. In a current case, a new digital
delay generator design, interesting things can happen if it's being
triggered with one set of delays and widths, and the user reprograms
them on-the-fly.
What's a boy to do?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Yep, I built the circuit using R1=33ohm and R2,3=22ohm and BC557 and
BC548 (closest I had) and it worked as advertised at approx 45mA limit.
It would startup even if I cranked the bench PSU up very slowly. I guess
C-B mirror leakage was enough to overcome B-E leakage to allow that, at >least at room temp. However 47megohm B-E mirror leakage was enough to >completely stop it starting unless the power was rapidly applied,
presumably C-B capacitance allowing startup. Conclusion: this is not
really a practical design!
piglet
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally?
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
Thank you for your input, I will modify the specification as follows:
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted.
If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
On Tue, 7 Apr 2026 09:27:18 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver toWhat's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally? >>>>>
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
Thank you for your input, I will modify the specification as follows:
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted.
If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
Take a look at the cute little TI switchers, like TPS562208. Simple, spread-spectrum, cheap. We pay 21 cents for that one. There are higher voltage parts in the family.
I think one could design a switchmode 500 mA LED current limiter with
that chip and maybe 5 cheap passives.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On 7/04/2026 5:08 am, john larkin wrote:
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
500mA is lot to get from 100mA parts like the BC550 and BC557.
Nobody who actually wanted to use the circuit would talk about "two or >>>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your
mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he >>>>> asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
You first.
I've measured collector leakage currents as low as 10 fA in cheap
transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
Your capacity to make bad measurements is well known.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors
would need >1 beta at the pA or fA currents.
Which they've got.
Even a dirty PCB could kill beta enough to prevent startup.
It never seems to.
Q1 and Q4 don't help a bit.
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be
entered.
Even when the "failure state" is entirely imaginary?
Not starting up would not be an imaginary failure.
If it happened.
But a state-free design will always have few hangup states.
Really? Bad designers can make remarkably silly mistakes, but my thirty >years in industry did suggest that those errors usually got caught
before the design made it to production. There was one project where >experienced engineers had to spend six months cleaning up after less >experienced engineers, but that didn't happen again.
Because sometimes they do.
Because you left out a connection?
Because something unexpected happens. In a current case, a new digital
delay generator design, interesting things can happen if it's being
triggered with one set of delays and widths, and the user reprograms
them on-the-fly.
What's a boy to do?
Learn to be a better designer? When you couldn't recognise a classic two >transistor emitter-coupled monostable as a viable circuit you did make
it plain that you still have quite a lot to learn.
"john larkin" <jl@glen--canyon.com> wrote in message news:hjaatk1mged6g36r5r9iej70btidivgq0t@4ax.com...
On Tue, 7 Apr 2026 09:27:18 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driver toWhat's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally? >>>>>>
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other LEDs
failed.
Thank you for your input, I will modify the specification as follows: >>>>>
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted. >>>>If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
Take a look at the cute little TI switchers, like TPS562208. Simple,
spread-spectrum, cheap. We pay 21 cents for that one. There are higher
voltage parts in the family.
I think one could design a switchmode 500 mA LED current limiter with
that chip and maybe 5 cheap passives.
Do any similar parts exist which have LTSpice models?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Tue, 7 Apr 2026 12:46:49 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"john larkin" <jl@glen--canyon.com> wrote in message news:hjaatk1mged6g36r5r9iej70btidivgq0t@4ax.com...
On Tue, 7 Apr 2026 09:27:18 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote: >>>>>>>>>>>>>>>>>>> On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driverWhat's hard to understand about two or more LXZ1-PB01 LEDs? >>>>>>>>>> 12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally? >>>>>>>
to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other
LEDs
failed.
Thank you for your input, I will modify the specification as follows: >>>>>>
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted. >>>>>If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
Take a look at the cute little TI switchers, like TPS562208. Simple,
spread-spectrum, cheap. We pay 21 cents for that one. There are higher
voltage parts in the family.
I think one could design a switchmode 500 mA LED current limiter with
that chip and maybe 5 cheap passives.
Do any similar parts exist which have LTSpice models?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
TI has Pspice models of many of their parts. I don't have much luck
importing them into LT Spice, but I know that it can be done.
I'd like to find someone to do that for me now and then, pick up
something like the TPS chip and deliver a working LT sim.
https://www.electronics-related.com/showthread/sci.electronics.design/892705-1.php
It wouldn't be hard to breadboard the circuit.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
"john larkin" <jl@glen--canyon.com> wrote in message news:jviatklk108hs6oad36v8hdlpg90u5irl2@4ax.com...
On Tue, 7 Apr 2026 12:46:49 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"john larkin" <jl@glen--canyon.com> wrote in message news:hjaatk1mged6g36r5r9iej70btidivgq0t@4ax.com...
On Tue, 7 Apr 2026 09:27:18 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde" >>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote: >>>>>>>>>>>>>>>>>>>> On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driverWhat's hard to understand about two or more LXZ1-PB01 LEDs? >>>>>>>>>>> 12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally? >>>>>>>>
to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other
LEDs
failed.
Thank you for your input, I will modify the specification as follows: >>>>>>>
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted. >>>>>>If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
Take a look at the cute little TI switchers, like TPS562208. Simple,
spread-spectrum, cheap. We pay 21 cents for that one. There are higher >>>> voltage parts in the family.
I think one could design a switchmode 500 mA LED current limiter with
that chip and maybe 5 cheap passives.
Do any similar parts exist which have LTSpice models?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
TI has Pspice models of many of their parts. I don't have much luck
importing them into LT Spice, but I know that it can be done.
I'd like to find someone to do that for me now and then, pick up
something like the TPS chip and deliver a working LT sim.
I got TPS54302.LIB and made a symbol. The pin names don't match but presumably PH is SW
and VSENSE is FB.
I then tried to make Fig 7-1 in the data sheet but although it runs it does not so far do anything useful.
https://www.electronics-related.com/showthread/sci.electronics.design/892705-1.php
It wouldn't be hard to breadboard the circuit.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
"Edward Rawde" <invalid@invalid.invalid> wrote in message news:10r3o3u$vq7$1@nnrp.usenet.blueworldhosting.com...
"john larkin" <jl@glen--canyon.com> wrote in message news:jviatklk108hs6oad36v8hdlpg90u5irl2@4ax.com...
On Tue, 7 Apr 2026 12:46:49 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"john larkin" <jl@glen--canyon.com> wrote in message news:hjaatk1mged6g36r5r9iej70btidivgq0t@4ax.com...
On Tue, 7 Apr 2026 09:27:18 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde" >>>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote: >>>>>>>>>>>>>>>>>>> On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote: >>>>>>>>>>>>>>>>>>>>> On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in the driverWhat's hard to understand about two or more LXZ1-PB01 LEDs? >>>>>>>>>>>> 12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally? >>>>>>>>>
to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other
LEDs
failed.
Thank you for your input, I will modify the specification as follows: >>>>>>>>
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost.
The EDN circuit specified BC557B and BC550B transistors
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted. >>>>>>>If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
Take a look at the cute little TI switchers, like TPS562208. Simple, >>>>> spread-spectrum, cheap. We pay 21 cents for that one. There are higher >>>>> voltage parts in the family.
I think one could design a switchmode 500 mA LED current limiter with >>>>> that chip and maybe 5 cheap passives.
Do any similar parts exist which have LTSpice models?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
TI has Pspice models of many of their parts. I don't have much luck
importing them into LT Spice, but I know that it can be done.
I'd like to find someone to do that for me now and then, pick up
something like the TPS chip and deliver a working LT sim.
I got TPS54302.LIB and made a symbol. The pin names don't match but presumably PH is SW
and VSENSE is FB.
I then tried to make Fig 7-1 in the data sheet but although it runs it does not so far do anything useful.
News just in. The alternate solver produces 5V at 3A into 1.7 ohm. Switching looks fine.
On Tue, 7 Apr 2026 16:12:15 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Edward Rawde" <invalid@invalid.invalid> wrote in message news:10r3o3u$vq7$1@nnrp.usenet.blueworldhosting.com...
"john larkin" <jl@glen--canyon.com> wrote in message news:jviatklk108hs6oad36v8hdlpg90u5irl2@4ax.com...
On Tue, 7 Apr 2026 12:46:49 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"john larkin" <jl@glen--canyon.com> wrote in message news:hjaatk1mged6g36r5r9iej70btidivgq0t@4ax.com...
On Tue, 7 Apr 2026 09:27:18 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r26qm$2k1q7$2@dont-email.me...
On 7/04/2026 4:12 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10r0s20$28hv3$4@dont-email.me...The EDN circuit specified BC557B and BC550B transistors
On 7/04/2026 1:56 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qveo5$1sobp$1@dont-email.me...
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde" >>>>>>>>>>>>>>>>> <invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote: >>>>>>>>>>>>>>>>>>>> On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote: >>>>>>>>>>>>>>>>>>>>>> On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
The circuit is a constant current driver. If enough LEDS fail short you might end up dissipating enough power in theWhat's hard to understand about two or more LXZ1-PB01 LEDs? >>>>>>>>>>>>> 12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or more LXZ1-PB01 LEDs".
Diodes tend to fail short. I have no information on the extent to which these LEDs fail short but
do you want the others to die quicker or continue working normally? >>>>>>>>>>
driver
to
blow it up too, but until that happened the surviving LEDs will see exactly the same current as they did before the other
LEDs
failed.
Thank you for your input, I will modify the specification as follows: >>>>>>>>>
Drive 500 mA +/- 50mA constant current though a string of 1,2,3 or 4 LXZ1-PB01 LEDs
In the case of 0 LEDs (short circuit) no damage should occur and the current may be 500mA or lower.
Cathode connection to LEDs should be grounded.
Anode connection should be filtered as necessary so as to comply with CISPR 22 Class B.
Input 12 - 15 V DC.
High efficiency and low cost is required, depending on what can be achieved,
so there is currently no exact target for efficiency or cost. >>>>>>>>
https://www.onsemi.com/download/data-sheet/pdf/bc556b-d.pdf
specifies an maximum continous current of 100mA, peak 200m
https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
specifies an maximum current of 100mA.
They won't meet your specification.
Let me know when you have met this specification.
Since the specification is nonsense in the context of this thread, I'm obviously not going to take it seriously.
Your design need not, of course, be anything like the design I posted.
If you can't get the current levels right there's not a lot of point in looking at your "design'. I haven't done so because
I
don't take you all that seriously.
In other words you're not able to meet my specification which clearly requires more
current than the EDN circuit.
Take a look at the cute little TI switchers, like TPS562208. Simple, >>>>>> spread-spectrum, cheap. We pay 21 cents for that one. There are higher >>>>>> voltage parts in the family.
I think one could design a switchmode 500 mA LED current limiter with >>>>>> that chip and maybe 5 cheap passives.
Do any similar parts exist which have LTSpice models?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
TI has Pspice models of many of their parts. I don't have much luck
importing them into LT Spice, but I know that it can be done.
I'd like to find someone to do that for me now and then, pick up
something like the TPS chip and deliver a working LT sim.
I got TPS54302.LIB and made a symbol. The pin names don't match but presumably PH is SW
and VSENSE is FB.
I then tried to make Fig 7-1 in the data sheet but although it runs it does not so far do anything useful.
News just in. The alternate solver produces 5V at 3A into 1.7 ohm. Switching looks fine.
Be careful - LTSpice can have lots of problems with pspice syntax
which are not always apparent. Simulations can appear to run but in
fact generate bollocks. LTSpice 26 is a great improvment over earlier versions in this regard. Attached is a TPS562208 sim - it looks OK in
26, but will run incorrectly in 25.
https://mega.nz/file/g8EVHD7Z#4MDojAygdgfvhsauUKhFyutfCrkK3Q-_EHpxWMNtT2o
--
This email has been checked for viruses by Avast antivirus software. www.avast.com
On Tue, 7 Apr 2026 16:34:07 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 5:08 am, john larkin wrote:
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
500mA is lot to get from 100mA parts like the BC550 and BC557.
Nobody who actually wanted to use the circuit would talk about "two or >>>>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your >>>> mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he >>>>>> asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
You first.
I've measured collector leakage currents as low as 10 fA in cheap
transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
Your capacity to make bad measurements is well known.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors
would need >1 beta at the pA or fA currents.
Which they've got.
What transistors do you know of that have useful betas at picoamp or
femtoamp currents? That would be good to know.
There is basically no data on super-low-current bipolar transistor
behavior.
On Tue, 7 Apr 2026 15:58:13 +0100, piglet <erichpwagner@hotmail.com>
wrote:
On 06/04/2026 20:08, john larkin wrote:
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>>>>> wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or >>>>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your >>>> mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he >>>>>> asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
I've measured collector leakage currents as low as 10 fA in cheap
transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors
would need >1 beta at the pA or fA currents.
Even a dirty PCB could kill beta enough to prevent startup.
Q1 and Q4 don't help a bit.
I have a policy against designing things that have failure states,
even when the creators of those states claim that they will never be >>>>> entered.
Even when the "failure state" is entirely imaginary?
Not starting up would not be an imaginary failure.
But a state-free design will always have few hangup states.
Because sometimes they do.
Because you left out a connection?
Because something unexpected happens. In a current case, a new digital
delay generator design, interesting things can happen if it's being
triggered with one set of delays and widths, and the user reprograms
them on-the-fly.
What's a boy to do?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Yep, I built the circuit using R1=33ohm and R2,3=22ohm and BC557 and
BC548 (closest I had) and it worked as advertised at approx 45mA limit.
It would startup even if I cranked the bench PSU up very slowly. I guess
C-B mirror leakage was enough to overcome B-E leakage to allow that, at
least at room temp. However 47megohm B-E mirror leakage was enough to
completely stop it starting unless the power was rapidly applied,
presumably C-B capacitance allowing startup. Conclusion: this is not
really a practical design!
Applying power to a breadboard with a wire will generate the
capacitive spikes to start it up.
But transistors aren't specified for beta at femtoamp currents.
It's really a dumb circuit for several reasons. An LM317 and one
resistor would work fine. It always starts and one can use a dpak or
TO-220 and get good thermals.
LM317s thermal limit too. Those dinky TO-92 things will smoke.
To light LEDs you can probably do without ICs or even capacitors, here
is an almost-two-terminal very cheap and dirty switcher idea ...
<https://www.dropbox.com/scl/fi/4w3k0rvr5g7up8occfsjj/Buck_Hysteretic.jpeg?rlkey=bb2nlbzyzprxrzegb9wfddem4&st=n3btk1il&raw=1>
On 8/04/2026 4:02 am, john larkin wrote:
On Tue, 7 Apr 2026 16:34:07 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 5:08 am, john larkin wrote:
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message
news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message >>>>>>>>>>>>> news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a >>>>>>>>> lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I >>>>>>>>> could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
500mA is lot to get from 100mA parts like the BC550 and BC557.
Nobody who actually wanted to use the circuit would talk about "two or >>>>>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your >>>>> mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he >>>>>>> asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
You first.
I've measured collector leakage currents as low as 10 fA in cheap
transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
Your capacity to make bad measurements is well known.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors >>>> would need >1 beta at the pA or fA currents.
Which they've got.
What transistors do you know of that have useful betas at picoamp or
femtoamp currents? That would be good to know.
Piglet's evidence shows that the BC557 and BC548 have enough to let the circuit work. I've no idea what he means by "47megohm B-E mirror
leakage" - it's not clear to me where he put the 47megohm resistor.
There is basically no data on super-low-current bipolar transistor
behavior.
So generate some, rather than posting guesswork.
The LM108 used a specialised input transistor which had a current gain
of 5000 at 1uA.
R. J. Widlar, ??Super Gain Transistors for IC,??
IEEE Journal of Solid-State Circuits , Vol. SC-4, No. 4, August, 1969
It was probably still pretty respectable at 1nA.
On 8/04/2026 2:00 am, john larkin wrote:
On Tue, 7 Apr 2026 15:58:13 +0100, piglet <erichpwagner@hotmail.com>
wrote:
On 06/04/2026 20:08, john larkin wrote:
On Tue, 7 Apr 2026 03:47:49 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 7/04/2026 12:25 am, john larkin wrote:
On Mon, 6 Apr 2026 15:01:57 +1000, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 6/04/2026 4:07 am, Edward Rawde wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qu787$1ije3$1@dont-email.me...
On 6/04/2026 3:10 am, john larkin wrote:
On Mon, 6 Apr 2026 02:59:12 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 6:57 pm, john larkin wrote:
On Sun, 5 Apr 2026 01:10:08 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:10qsnim$15pr5$1@dont-email.me...
On 5/04/2026 12:37 pm, john larkin wrote:
On Sun, 5 Apr 2026 12:24:42 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 5/04/2026 11:07 am, john larkin wrote:
On Thu, 02 Apr 2026 13:56:47 -0700, john larkin <jl@glen--canyon.com>
wrote:
<snip>
Let's see Bill's circuit next.
You needed find somebody silly enough to take this nonsense seriously.
Edward Rawde is apparently willing to play with you. I'm happy to leave
you in his capable hands.
Please don't think that I am mocking you for being unable to design >>>>>>>>>> simple circuits. That would be unkind.
I can't see why you bothered to post the EDN circuit in the first place.
It's obvious how it works. Without a specific load there's not a lot of point in discussing it and plausible alternatives.
You don't seem to have enough sense to realise this. I suppose I could mock you about that, but you do a pretty good job of
sending yourself up all on your own.
What's hard to understand about two or more LXZ1-PB01 LEDs?
12V isn't hard to find.
Nobody who actually wanted to use the circuit would talk about "two or >>>>>>> more LXZ1-PB01 LEDs".
Why not?
Because if you are going to build the circuit you have to make up your >>>>> mind before you build it.
But at 500 mA and 3 volts or so per LED, they will be
blinding and need some serious heat sinking.
John Larkin wants to see it as some kind of
teaching exercise, not realising that he'd failed the course when he >>>>>>> asked how it would start up.
How would it start up?
Think about it. Think - for instance - about transistor leakage
currents, which flow whenever you put a voltage across and bipolar
transistor junction.
YOU think about it. Quantitatively.
I've measured collector leakage currents as low as 10 fA in cheap
transistors, 10 fA being my resolution limit. I could measure much
less, with a bit of effort.
For that circuit to start up, the current gain around the loop would
have to be above one for, likely, sub pA leakages, and the transistors >>>> would need >1 beta at the pA or fA currents.
Even a dirty PCB could kill beta enough to prevent startup.
Q1 and Q4 don't help a bit.
I have a policy against designing things that have failure states, >>>>>> even when the creators of those states claim that they will never be >>>>>> entered.
Even when the "failure state" is entirely imaginary?
Not starting up would not be an imaginary failure.
But a state-free design will always have few hangup states.
Because sometimes they do.
Because you left out a connection?
Because something unexpected happens. In a current case, a new digital >>>> delay generator design, interesting things can happen if it's being
triggered with one set of delays and widths, and the user reprograms
them on-the-fly.
What's a boy to do?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Yep, I built the circuit using R1=33ohm and R2,3=22ohm and BC557 and
BC548 (closest I had) and it worked as advertised at approx 45mA limit.
It would startup even if I cranked the bench PSU up very slowly. I guess >>> C-B mirror leakage was enough to overcome B-E leakage to allow that, at
least at room temp. However 47megohm B-E mirror leakage was enough to
completely stop it starting unless the power was rapidly applied,
presumably C-B capacitance allowing startup. Conclusion: this is not
really a practical design!
Applying power to a breadboard with a wire will generate the
capacitive spikes to start it up.
That isn't what piglet did. "It would startup even if I cranked the
bench PSU up very slowly."
But transistors aren't specified for beta at femtoamp currents.
This isn't a femtoamp circuit. Transistors aren't specified for current
gain at low currents because it would take too long to measure it, but
some parts are known to have current gains of about 10 to 50 at 1nA.
If you stand back from the microscopic current mirror circuit
interpretation, the transistor equivalent of the DIAC using Q2,4,3,
with a threshold of 2.5V or so, comes into focus. Then add in some
current limiting/ regulating resistors here and there, and you end
up with the floating current source. The BC557C has an absurdly
small Early voltage and RCE, combined with the 'C' version beta in
the range of 200-800, and start-up is a done deal. Voltage compliance
shouldn't be a serious issue for driving LEDs, but it would be nice
to see an analytic to that effect. AI hasn't penetrated deeply enough
into our freebie CADs to give us that capabilty, so we're stuck with
looking at graphs.
Allow me to transition this topic to 120 VAC LED COB filaments. This
picture shows such specimens, with the topmost powered-on and the
bottommost powered-off:
<https://crcomp.net/led/accob.png>
The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.
On Thu, 9 Apr 2026 09:17:04 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Allow me to transition this topic to 120 VAC LED COB filaments. This >>picture shows such specimens, with the topmost powered-on and the >>bottommost powered-off:
<https://crcomp.net/led/accob.png>
The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.
Look up NUD4011 and it's alternatives, it'll be something that
operates in a similar fashion.
On Thu, 9 Apr 2026 09:17:04 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Allow me to transition this topic to 120 VAC LED COB filaments. This >>picture shows such specimens, with the topmost powered-on and the >>bottommost powered-off:
<https://crcomp.net/led/accob.png>
The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.
Look up NUD4011 and it's alternatives, it'll be something that
operates in a similar fashion.
On Thu, 09 Apr 2026 16:16:34 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Thu, 9 Apr 2026 09:17:04 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Allow me to transition this topic to 120 VAC LED COB filaments. This >>>picture shows such specimens, with the topmost powered-on and the >>>bottommost powered-off:
<https://crcomp.net/led/accob.png>
The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.
Look up NUD4011 and it's alternatives, it'll be something that
operates in a similar fashion.
That would need the NUD chip and a bridge rectifier and maybe a
resistor and a varistor.
I'd expect simpler and cheaper in that tiny gadget.
What do you call that axial lead LED thing?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Thu, 09 Apr 2026 16:16:34 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Thu, 9 Apr 2026 09:17:04 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Allow me to transition this topic to 120 VAC LED COB filaments. This >>>picture shows such specimens, with the topmost powered-on and the >>>bottommost powered-off:
<https://crcomp.net/led/accob.png>
The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.
Look up NUD4011 and it's alternatives, it'll be something that
operates in a similar fashion.
That would need the NUD chip and a bridge rectifier and maybe a
resistor and a varistor.
I'd expect simpler and cheaper in that tiny gadget.
What do you call that axial lead LED thing?
On Thu, 09 Apr 2026 16:16:34 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
On Thu, 9 Apr 2026 09:17:04 -0000 (UTC), "Don" <g@crcomp.net> wrote:
Allow me to transition this topic to 120 VAC LED COB filaments. This >>>picture shows such specimens, with the topmost powered-on and the >>>bottommost powered-off:
<https://crcomp.net/led/accob.png>
The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.
Look up NUD4011 and it's alternatives, it'll be something that
operates in a similar fashion.
That would need the NUD chip and a bridge rectifier and maybe a
resistor and a varistor.
I'd expect simpler and cheaper in that tiny gadget.
What do you call that axial lead LED thing?
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
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