On Sun, 18 Jan 2026 00:48:06 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 1/18/26 00:33, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Wallikerdissipation
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid >>>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
I need something like 1.5K resistance across a 750 volt pulse. >>>>>> Pulse
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power
across theper resistor will be 125 watts at 250 volts. I think that's OK >>>>>> but I
want to test it.
Here's the tester. The DUT (device under torture) will go
enough? Yougap on the left.f
I have both regular thickfilm resistors and some thinfilms to >>>>>> test. I
theorize that the thinfilms will hold up better.
Would a non-inductively-wound wirewound resistor work well
gives youwould have plenty of mass to average-out the pulse energy. >>>>>>>>>>>WWs are great for pulse overload, not so great for PCB density. The >>>>>>>>>>> best would be to use three (or two, or one) surface-mount 1206 >>>>>>>>>>> thickfilm that we have in stock.
I could stand a micohenry or so parasitic inductance. The 1.5K >>>>>> will in
fact be in series with a small inductor.
There's your answer; make the resistor and the inductor one and >>>>>> the same
component. For a small investment in suitable machinery this
supply thetotal security of supply, quality control and an edge over any >>>>>>>>>> competitor who can't make things but just buys them in (or tries >>>>>> to copy
your design without realising what that component really does). >>>>>>>>>>
Vertical integration was the cornerstone of nearly all the successful
electronics firms. (Philips even owned the sand quarries to
direction. Thesand to make the glass to make the valves and light bulbs.) >>>>>>>>>>
Experiment with winding a number of turns of resistance wire on a >>>>>> former
in one direction, then winding some more in the opposite
ratio between the two sets of turns can be adjusted to give the >>>>>> required
inductance and the total number of turns gives the resistance. The >>>>>>>>>> former could be a small piece of heatproof material shaped like a >>>>>> dog's
bone to retain the wire, with a notch to catch the wire and prevent it
from unwinding at the reversal point.
Yikes. That would be a huge diversion from getting a product done. >>>>>>>>>
I found one paper that shows that thinfilms are tougher than >>>>>>>>> thickfilms, but thinfilm MELFs are even better. That makes sense. >>>>>>>>>
When I visited the factory of a smart meter manufacturer I noticed that
they used melf surface mount resistors for mains voltage sensing. There
were several in series.
John
Makes sense. For a given pcb footprint, they have about pi times the >>>>>>> surface area to work with, for a correspondingly bigger conductor >>>>>>> area. The cooling might be even better.
This misses the point. The Vishay resistor data showed that - at least >>>>>> for their surface mount thin film resistors - the heat doesn't get >>>>>> beyond the resistive track itself for about 300usec.
If you get the track too hot for any time shorter than that it can melt >>>>>> (or at least get hot enough to let the atoms move around). For their >>>>>> resistors, nothing lower than 10k can take 1kV, which equates to a peak >>>>>> current of 100mA.
Once you've work out how much resistive area you need to use to work >>>>>> with any pulse shorter than 300usec, you then need to work out the duty >>>>>> cycle of your short pulses and make sure that you can dissipate the >>>>>> average power to ambient without getting the average temperature too high.
I don't expect to have much average power dissipation. The resistor on >>>>> my prototype is rising about 15c at 180 watts and 1 us/1KHz pulses,
according to my thermal imager. Do the math on that.
You'd need to identify the resistor so that I could get the thermal
resistance of the resistor to ambient before I could do that. If you
knew what you were talking about you'd know that
I'll reveal the secret mathematics:
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Degrees per watt.
Jeroen Belleman
Oops. You knew what I meant.
The 83 K/W is reasonable, considering that measuring a 1206 temp with
a cheap thermal imager isn't an exact science.
After several days pulsing at 300 volts, 180 watts, the thickfilm
resistance was bobbling around in the 5th decimal place. Boring.
I stepped it up to 350v, about 250 watts. That's 1000x the part's DC
power rating. I'll check that now and then.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On 1/18/26 16:55, john larkin wrote:
On Sun, 18 Jan 2026 00:48:06 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 1/18/26 00:33, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>> wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Wallikerdirection. The
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid >>>>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:WWs are great for pulse overload, not so great for PCB density. The
I need something like 1.5K resistance across a 750 volt pulse. >>>>>>> Pulsef
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power >>>>>>> dissipation
per resistor will be 125 watts at 250 volts. I think that's OK >>>>>>> but I
want to test it.
Here's the tester. The DUT (device under torture) will go >>>>>>> across the
gap on the left.
I have both regular thickfilm resistors and some thinfilms to >>>>>>> test. I
theorize that the thinfilms will hold up better.
Would a non-inductively-wound wirewound resistor work well >>>>>>> enough? You
would have plenty of mass to average-out the pulse energy. >>>>>>>>>>>>
best would be to use three (or two, or one) surface-mount 1206 >>>>>>>>>>>> thickfilm that we have in stock.
I could stand a micohenry or so parasitic inductance. The 1.5K >>>>>>> will in
fact be in series with a small inductor.
There's your answer; make the resistor and the inductor one and >>>>>>> the same
component. For a small investment in suitable machinery this >>>>>>> gives you
total security of supply, quality control and an edge over any >>>>>>>>>>> competitor who can't make things but just buys them in (or tries >>>>>>> to copy
your design without realising what that component really does). >>>>>>>>>>>
Vertical integration was the cornerstone of nearly all the successful
electronics firms. (Philips even owned the sand quarries to >>>>>>> supply the
sand to make the glass to make the valves and light bulbs.) >>>>>>>>>>>
Experiment with winding a number of turns of resistance wire on a >>>>>>> former
in one direction, then winding some more in the opposite
ratio between the two sets of turns can be adjusted to give the >>>>>>> required
inductance and the total number of turns gives the resistance. The >>>>>>>>>>> former could be a small piece of heatproof material shaped like a >>>>>>> dog's
bone to retain the wire, with a notch to catch the wire and prevent it
from unwinding at the reversal point.
Yikes. That would be a huge diversion from getting a product done. >>>>>>>>>>
I found one paper that shows that thinfilms are tougher than >>>>>>>>>> thickfilms, but thinfilm MELFs are even better. That makes sense. >>>>>>>>>>
When I visited the factory of a smart meter manufacturer I noticed that
they used melf surface mount resistors for mains voltage sensing. There
were several in series.
John
Makes sense. For a given pcb footprint, they have about pi times the >>>>>>>> surface area to work with, for a correspondingly bigger conductor >>>>>>>> area. The cooling might be even better.
This misses the point. The Vishay resistor data showed that - at least >>>>>>> for their surface mount thin film resistors - the heat doesn't get >>>>>>> beyond the resistive track itself for about 300usec.
If you get the track too hot for any time shorter than that it can melt >>>>>>> (or at least get hot enough to let the atoms move around). For their >>>>>>> resistors, nothing lower than 10k can take 1kV, which equates to a peak >>>>>>> current of 100mA.
Once you've work out how much resistive area you need to use to work >>>>>>> with any pulse shorter than 300usec, you then need to work out the duty >>>>>>> cycle of your short pulses and make sure that you can dissipate the >>>>>>> average power to ambient without getting the average temperature too high.
I don't expect to have much average power dissipation. The resistor on >>>>>> my prototype is rising about 15c at 180 watts and 1 us/1KHz pulses, >>>>>> according to my thermal imager. Do the math on that.
You'd need to identify the resistor so that I could get the thermal
resistance of the resistor to ambient before I could do that. If you >>>>> knew what you were talking about you'd know that
I'll reveal the secret mathematics:
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Degrees per watt.
Jeroen Belleman
Oops. You knew what I meant.
The 83 K/W is reasonable, considering that measuring a 1206 temp with
a cheap thermal imager isn't an exact science.
After several days pulsing at 300 volts, 180 watts, the thickfilm
resistance was bobbling around in the 5th decimal place. Boring.
I stepped it up to 350v, about 250 watts. That's 1000x the part's DC
power rating. I'll check that now and then.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
I've been abusing Welwyn SMD resistors in a similar manner. Never a
problem. Good to know.
On the other hand, I've tried to use 10W Radiall SMA attenuators
with ns kW-level pulsed power, and they'd die, even though the
average power was very much below 10W. 15W attenuators held up
fine, fortunately. I never tried to find out why that was. Maybe
the geometry of the 10W attenuators was small enough to cause a
spark discharge.
Jeroen Belleman
On Sun, 18 Jan 2026 19:43:30 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 1/18/26 16:55, john larkin wrote:
On Sun, 18 Jan 2026 00:48:06 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 1/18/26 00:33, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Wallikerdirection. The
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:WWs are great for pulse overload, not so great for PCB density. The
I need something like 1.5K resistance across a 750 volt pulse. >>>>>>>> Pulsef
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power >>>>>>>> dissipation
per resistor will be 125 watts at 250 volts. I think that's OK >>>>>>>> but I
want to test it.
Here's the tester. The DUT (device under torture) will go >>>>>>>> across the
gap on the left.
I have both regular thickfilm resistors and some thinfilms to >>>>>>>> test. I
theorize that the thinfilms will hold up better.
Would a non-inductively-wound wirewound resistor work well >>>>>>>> enough? You
would have plenty of mass to average-out the pulse energy. >>>>>>>>>>>>>
best would be to use three (or two, or one) surface-mount 1206 >>>>>>>>>>>>> thickfilm that we have in stock.
I could stand a micohenry or so parasitic inductance. The 1.5K >>>>>>>> will in
fact be in series with a small inductor.
There's your answer; make the resistor and the inductor one and >>>>>>>> the same
component. For a small investment in suitable machinery this >>>>>>>> gives you
total security of supply, quality control and an edge over any >>>>>>>>>>>> competitor who can't make things but just buys them in (or tries >>>>>>>> to copy
your design without realising what that component really does). >>>>>>>>>>>>
Vertical integration was the cornerstone of nearly all the successful
electronics firms. (Philips even owned the sand quarries to >>>>>>>> supply the
sand to make the glass to make the valves and light bulbs.) >>>>>>>>>>>>
Experiment with winding a number of turns of resistance wire on a >>>>>>>> former
in one direction, then winding some more in the opposite
ratio between the two sets of turns can be adjusted to give the >>>>>>>> required
inductance and the total number of turns gives the resistance. The
former could be a small piece of heatproof material shaped like a >>>>>>>> dog's
bone to retain the wire, with a notch to catch the wire and prevent it
from unwinding at the reversal point.
Yikes. That would be a huge diversion from getting a product done. >>>>>>>>>>>
I found one paper that shows that thinfilms are tougher than >>>>>>>>>>> thickfilms, but thinfilm MELFs are even better. That makes sense. >>>>>>>>>>>
When I visited the factory of a smart meter manufacturer I noticed that
they used melf surface mount resistors for mains voltage sensing. There
were several in series.
John
Makes sense. For a given pcb footprint, they have about pi times the >>>>>>>>> surface area to work with, for a correspondingly bigger conductor >>>>>>>>> area. The cooling might be even better.
This misses the point. The Vishay resistor data showed that - at least >>>>>>>> for their surface mount thin film resistors - the heat doesn't get >>>>>>>> beyond the resistive track itself for about 300usec.
If you get the track too hot for any time shorter than that it can melt
(or at least get hot enough to let the atoms move around). For their >>>>>>>> resistors, nothing lower than 10k can take 1kV, which equates to a peak
current of 100mA.
Once you've work out how much resistive area you need to use to work >>>>>>>> with any pulse shorter than 300usec, you then need to work out the duty
cycle of your short pulses and make sure that you can dissipate the >>>>>>>> average power to ambient without getting the average temperature too high.
I don't expect to have much average power dissipation. The resistor on >>>>>>> my prototype is rising about 15c at 180 watts and 1 us/1KHz pulses, >>>>>>> according to my thermal imager. Do the math on that.
You'd need to identify the resistor so that I could get the thermal >>>>>> resistance of the resistor to ambient before I could do that. If you >>>>>> knew what you were talking about you'd know that
I'll reveal the secret mathematics:
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Degrees per watt.
Jeroen Belleman
Oops. You knew what I meant.
The 83 K/W is reasonable, considering that measuring a 1206 temp with
a cheap thermal imager isn't an exact science.
After several days pulsing at 300 volts, 180 watts, the thickfilm
resistance was bobbling around in the 5th decimal place. Boring.
I stepped it up to 350v, about 250 watts. That's 1000x the part's DC
power rating. I'll check that now and then.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
I've been abusing Welwyn SMD resistors in a similar manner. Never a
problem. Good to know.
On the other hand, I've tried to use 10W Radiall SMA attenuators
with ns kW-level pulsed power, and they'd die, even though the
average power was very much below 10W. 15W attenuators held up
fine, fortunately. I never tried to find out why that was. Maybe
the geometry of the 10W attenuators was small enough to cause a
spark discharge.
Jeroen Belleman
It was hard to find attenuators that would survive 700v sub-usec
pulses, with low average power dissipation.
We blew out a bunch of the MIniCircuits VAT parts.
https://www.dropbox.com/scl/fi/jsk5os0hurourqd60myv0/VAT-20.JPG?rlkey=bh6idhj33xfe98sdmtgumbfri&raw=1
They seem to fail near the laser trims where current concentrates.
I made one atten using the Caddock dpak resistors. It wasn't beautiful
for step response but did survive.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Sun, 18 Jan 2026 00:48:06 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 1/18/26 00:33, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Wallikerdissipation
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid >>>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
I need something like 1.5K resistance across a 750 volt pulse. >>>>>> Pulse
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power
across theper resistor will be 125 watts at 250 volts. I think that's OK >>>>>> but I
want to test it.
Here's the tester. The DUT (device under torture) will go
enough? Yougap on the left.f
I have both regular thickfilm resistors and some thinfilms to >>>>>> test. I
theorize that the thinfilms will hold up better.
Would a non-inductively-wound wirewound resistor work well
gives youwould have plenty of mass to average-out the pulse energy. >>>>>>>>>>>WWs are great for pulse overload, not so great for PCB density. The >>>>>>>>>>> best would be to use three (or two, or one) surface-mount 1206 >>>>>>>>>>> thickfilm that we have in stock.
I could stand a micohenry or so parasitic inductance. The 1.5K >>>>>> will in
fact be in series with a small inductor.
There's your answer; make the resistor and the inductor one and >>>>>> the same
component. For a small investment in suitable machinery this
supply thetotal security of supply, quality control and an edge over any >>>>>>>>>> competitor who can't make things but just buys them in (or tries >>>>>> to copy
your design without realising what that component really does). >>>>>>>>>>
Vertical integration was the cornerstone of nearly all the successful
electronics firms. (Philips even owned the sand quarries to
direction. Thesand to make the glass to make the valves and light bulbs.) >>>>>>>>>>
Experiment with winding a number of turns of resistance wire on a >>>>>> former
in one direction, then winding some more in the opposite
ratio between the two sets of turns can be adjusted to give the >>>>>> required
inductance and the total number of turns gives the resistance. The >>>>>>>>>> former could be a small piece of heatproof material shaped like a >>>>>> dog's
bone to retain the wire, with a notch to catch the wire and prevent it
from unwinding at the reversal point.
Yikes. That would be a huge diversion from getting a product done. >>>>>>>>>
I found one paper that shows that thinfilms are tougher than >>>>>>>>> thickfilms, but thinfilm MELFs are even better. That makes sense. >>>>>>>>>
When I visited the factory of a smart meter manufacturer I noticed that
they used melf surface mount resistors for mains voltage sensing. There
were several in series.
John
Makes sense. For a given pcb footprint, they have about pi times the >>>>>>> surface area to work with, for a correspondingly bigger conductor >>>>>>> area. The cooling might be even better.
This misses the point. The Vishay resistor data showed that - at least >>>>>> for their surface mount thin film resistors - the heat doesn't get >>>>>> beyond the resistive track itself for about 300usec.
If you get the track too hot for any time shorter than that it can melt >>>>>> (or at least get hot enough to let the atoms move around). For their >>>>>> resistors, nothing lower than 10k can take 1kV, which equates to a peak >>>>>> current of 100mA.
Once you've work out how much resistive area you need to use to work >>>>>> with any pulse shorter than 300usec, you then need to work out the duty >>>>>> cycle of your short pulses and make sure that you can dissipate the >>>>>> average power to ambient without getting the average temperature too high.
I don't expect to have much average power dissipation. The resistor on >>>>> my prototype is rising about 15c at 180 watts and 1 us/1KHz pulses,
according to my thermal imager. Do the math on that.
You'd need to identify the resistor so that I could get the thermal
resistance of the resistor to ambient before I could do that. If you
knew what you were talking about you'd know that
I'll reveal the secret mathematics:
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
Degrees per watt.
Jeroen Belleman
Oops. You knew what I meant.
The 83 K/W is reasonable, considering that measuring a 1206 temp with
a cheap thermal imager isn't an exact science.
After several days pulsing at 300 volts, 180 watts, the thickfilm
resistance was bobbling around in the 5th decimal place. Boring.
I stepped it up to 350v, about 250 watts. That's 1000x the part's DC
power rating. I'll check that now and then.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On 18/01/2026 10:33 am, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Walliker
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid >>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid >>>>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
<snip>
I'll reveal the secret mathematics:
The secret you reveal isn't in the mathematics. It's the thermal
resistance from the dissipating element to ambient
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
Why? It's on the data sheet of whatever resistor you happen to be using, >which you haven't specified. You may not realise this.
4 days at 350 volts, still no resistance change.
I guess I'll try 500. That will be 500 watts peak.
On 2026-01-21 13:42, john larkin wrote:
<snip>
4 days at 350 volts, still no resistance change.
I guess I'll try 500. That will be 500 watts peak.
Moughghghgahahaaa!
Cheers
Phil Hobbs
On Sun, 18 Jan 2026 15:29:11 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 18/01/2026 10:33 am, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Walliker
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid >>>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
<snip>
I'll reveal the secret mathematics:
The secret you reveal isn't in the mathematics. It's the thermal
resistance from the dissipating element to ambient
No; average power is low.
What matters is microsecond-range heat capacity in the resistive
element. The ceramic substrate may help a little.
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
Why? It's on the data sheet of whatever resistor you happen to be using,
which you haven't specified. You may not realise this.
The data sheet of a cheap thickfilm resistor does not characterize it
for pulsing at 1000x rated power.
Or 2000x, which I'm running now.
On 22/01/2026 5:48 am, john larkin wrote:
On Sun, 18 Jan 2026 15:29:11 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 18/01/2026 10:33 am, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>> wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Walliker
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid >>>>>>>>>> (Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
<snip>
I'll reveal the secret mathematics:
The secret you reveal isn't in the mathematics. It's the thermal
resistance from the dissipating element to ambient
No; average power is low.
What matters is microsecond-range heat capacity in the resistive
element. The ceramic substrate may help a little.
The impulse load ratings for the Vishay thin films that I posted
suggested that for them the thermal mass of the substrate stops
mattering below about 300usec.
You may have to worry about the skin effect as well, which restricts
very high frequency components to the edge of any track. For higher >resistance metal film resistors the tracks tend to be pretty narrow anyway.
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
Why? It's on the data sheet of whatever resistor you happen to be using, >>> which you haven't specified. You may not realise this.
The data sheet of a cheap thickfilm resistor does not characterize it
for pulsing at 1000x rated power.
So you probably shouldn't use them for that job.
Or 2000x, which I'm running now.
And where you are starting to see changes in resistance with time.
On Thu, 22 Jan 2026 22:45:56 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 22/01/2026 5:48 am, john larkin wrote:
On Sun, 18 Jan 2026 15:29:11 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 18/01/2026 10:33 am, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Walliker
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
<snip>
I'll reveal the secret mathematics:
The secret you reveal isn't in the mathematics. It's the thermal
resistance from the dissipating element to ambient
No; average power is low.
What matters is microsecond-range heat capacity in the resistive
element. The ceramic substrate may help a little.
The impulse load ratings for the Vishay thin films that I posted
suggested that for them the thermal mass of the substrate stops
mattering below about 300usec.
You may have to worry about the skin effect as well, which restricts
very high frequency components to the edge of any track. For higher
resistance metal film resistors the tracks tend to be pretty narrow anyway. >>
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
Why? It's on the data sheet of whatever resistor you happen to be using, >>>> which you haven't specified. You may not realise this.
The data sheet of a cheap thickfilm resistor does not characterize it
for pulsing at 1000x rated power.
So you probably shouldn't use them for that job.
Should be fine at 250 volts per resistor.
Or 2000x, which I'm running now.
And where you are starting to see changes in resistance with time.
After a day of pulsing at 500v, 500 watts, the resistance has dropped
about 0.1%.
It takes me about a minute a day to run this experiment, so I'll let
it run some more.
I might try the thinfilm 1206 just for fun.
I should have bought a higher voltage version of this power supply.
The mosfet is good for 1500 volts.
On 23/01/2026 6:44 am, john larkin wrote:
On Thu, 22 Jan 2026 22:45:56 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 22/01/2026 5:48 am, john larkin wrote:
On Sun, 18 Jan 2026 15:29:11 +1100, Bill Sloman <bill.sloman@ieee.org> >>>> wrote:
On 18/01/2026 10:33 am, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>> wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>>>> wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Walliker
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
<snip>
I'll reveal the secret mathematics:
The secret you reveal isn't in the mathematics. It's the thermal
resistance from the dissipating element to ambient
No; average power is low.
What matters is microsecond-range heat capacity in the resistive
element. The ceramic substrate may help a little.
The impulse load ratings for the Vishay thin films that I posted
suggested that for them the thermal mass of the substrate stops
mattering below about 300usec.
You may have to worry about the skin effect as well, which restricts
very high frequency components to the edge of any track. For higher
resistance metal film resistors the tracks tend to be pretty narrow anyway. >>>
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
Why? It's on the data sheet of whatever resistor you happen to be using, >>>>> which you haven't specified. You may not realise this.
The data sheet of a cheap thickfilm resistor does not characterize it
for pulsing at 1000x rated power.
So you probably shouldn't use them for that job.
Should be fine at 250 volts per resistor.
Or 2000x, which I'm running now.
And where you are starting to see changes in resistance with time.
After a day of pulsing at 500v, 500 watts, the resistance has dropped
about 0.1%.
It takes me about a minute a day to run this experiment, so I'll let
it run some more.
0.1% in a day is worryingly high.
I might try the thinfilm 1206 just for fun.
A prudent engineer would try a part that was specified for some kind of >short pulse use, rather than one which wasn't at all.
I should have bought a higher voltage version of this power supply.
The mosfet is good for 1500 volts.
All sorts of nasty stuff starts happening at high voltages. Cambridge >Instruments didn't like photomultipliers where the photocathode was more >that 1kV away from ground. The glass widow of the photomultiplier tube
and the glass window of the sample chamber both started conducting
current by ion migration at that sort of voltage, with a little >electroluminescence, which was an inconvenient source of noise.
On Sat, 24 Jan 2026 01:56:46 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 23/01/2026 6:44 am, john larkin wrote:
On Thu, 22 Jan 2026 22:45:56 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 22/01/2026 5:48 am, john larkin wrote:
On Sun, 18 Jan 2026 15:29:11 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>> wrote:
On 18/01/2026 10:33 am, john larkin wrote:
On Sat, 17 Jan 2026 15:58:01 +1100, Bill Sloman <bill.sloman@ieee.org> >>>>>>> wrote:
On 17/01/2026 4:19 am, john larkin wrote:
On Sat, 17 Jan 2026 03:59:00 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 16/01/2026 11:01 am, john larkin wrote:
On Thu, 15 Jan 2026 23:01:38 +0000, John R Walliker
<jrwalliker@gmail.com> wrote:
On 15/01/2026 18:15, john larkin wrote:
On Thu, 15 Jan 2026 17:51:59 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid
(Liz Tuddenham) wrote:
john larkin <jl@glen--canyon.com> wrote:
<snip>
I'll reveal the secret mathematics:
The secret you reveal isn't in the mathematics. It's the thermal
resistance from the dissipating element to ambient
No; average power is low.
What matters is microsecond-range heat capacity in the resistive
element. The ceramic substrate may help a little.
The impulse load ratings for the Vishay thin films that I posted
suggested that for them the thermal mass of the substrate stops
mattering below about 300usec.
You may have to worry about the skin effect as well, which restricts
very high frequency components to the edge of any track. For higher
resistance metal film resistors the tracks tend to be pretty narrow anyway.
180 watts at 0.1% duty cycle is 0.180 watts.
15c divided by 0.18 is 83 watts per degree C.
Please keep this confidential.
Why? It's on the data sheet of whatever resistor you happen to be using, >>>>>> which you haven't specified. You may not realise this.
The data sheet of a cheap thickfilm resistor does not characterize it >>>>> for pulsing at 1000x rated power.
So you probably shouldn't use them for that job.
Should be fine at 250 volts per resistor.
Or 2000x, which I'm running now.
And where you are starting to see changes in resistance with time.
After a day of pulsing at 500v, 500 watts, the resistance has dropped
about 0.1%.
It takes me about a minute a day to run this experiment, so I'll let
it run some more.
0.1% in a day is worryingly high.
It's within the tempco range of a cheap thickfilm.
If the resistor is being damaged, we may have fused a few weak spots,
and things may stabilize. So I'll let it keep running.
I might try the thinfilm 1206 just for fun.
A prudent engineer would try a part that was specified for some kind of
short pulse use, rather than one which wasn't at all.
A sensible engineer will test parts that are available. Maybe you can
find a small surface-mount 499 ohm resistor that is specified to
tolerate kilowatt pulses.
Being prudent isn't fun, or a good way to invent things.
It's good to get crazy and reckless once in a while, destroy things.A lunatic might think that.
The final design stages of a sellable product should be very prudent
and reviewed by careful and prissy people.
I should have bought a higher voltage version of this power supply.
The mosfet is good for 1500 volts.
All sorts of nasty stuff starts happening at high voltages. Cambridge
Instruments didn't like photomultipliers where the photocathode was more
that 1kV away from ground. The glass widow of the photomultiplier tube
and the glass window of the sample chamber both started conducting
current by ion migration at that sort of voltage, with a little
electroluminescence, which was an inconvenient source of noise.
Numbers under a kv or so aren't too scary on a surface-mount PCB. Much
higher ones are.
I need something like 1.5K resistance across a 750 volt pulse. Pulse
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power dissipation
per resistor will be 125 watts at 250 volts. I think that's OK but I
want to test it.
Here's the tester. The DUT (device under torture) will go across the
gap on the left.
https://www.dropbox.com/scl/fi/2z1g2hlz9tjpkrtpaf4l0/X124_WB_1.jpg?rlkey=nj4qnztwzfmjobobdgti9vf6k&raw=1
https://www.dropbox.com/scl/fi/8j18qqnk1e4kjslkrb4v0/X124_Dremel.jpg?rlkey=j2ck2tyg2wy76jgyzfimdd3u5&raw=1
I have a 500 volt supply so I'll run that up and see what happens.
500v will be 500 watts into 500 ohms.
I have both regular thickfilm resistors and some thinfilms to test. I >theorize that the thinfilms will hold up better.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
On Wed, 14 Jan 2026 17:07:45 -0800, john larkin <jl@glen--canyon.com>
wrote:
I need something like 1.5K resistance across a 750 volt pulse. Pulse
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power dissipation
per resistor will be 125 watts at 250 volts. I think that's OK but I
want to test it.
Here's the tester. The DUT (device under torture) will go across the
gap on the left.
https://www.dropbox.com/scl/fi/2z1g2hlz9tjpkrtpaf4l0/X124_WB_1.jpg?rlkey=nj4qnztwzfmjobobdgti9vf6k&raw=1
https://www.dropbox.com/scl/fi/8j18qqnk1e4kjslkrb4v0/X124_Dremel.jpg?rlkey=j2ck2tyg2wy76jgyzfimdd3u5&raw=1
I have a 500 volt supply so I'll run that up and see what happens.
500v will be 500 watts into 500 ohms.
I have both regular thickfilm resistors and some thinfilms to test. I
theorize that the thinfilms will hold up better.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
I ran the cheap thickfilm 1206 at 250v, then 350v, and then at 500
volts, days at each voltage. Resistance value changes were down at the 5-digit measurement noise level. Boring.
So I tried a Panasonic ERA-series thinfilm. I figured I could start at
350 v. It died instantly.
Another is running OK at 100 volts.
So much for theory.
john larkin <jl@glen--canyon.com> wrote:
On Wed, 14 Jan 2026 17:07:45 -0800, john larkin <jl@glen--canyon.com>
wrote:
I need something like 1.5K resistance across a 750 volt pulse. Pulse
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power dissipation
per resistor will be 125 watts at 250 volts. I think that's OK but I
want to test it.
Here's the tester. The DUT (device under torture) will go across the
gap on the left.
https://www.dropbox.com/scl/fi/2z1g2hlz9tjpkrtpaf4l0/X124_WB_1.jpg?rlkey=nj4qnztwzfmjobobdgti9vf6k&raw=1
https://www.dropbox.com/scl/fi/8j18qqnk1e4kjslkrb4v0/X124_Dremel.jpg?rlkey=j2ck2tyg2wy76jgyzfimdd3u5&raw=1
I have a 500 volt supply so I'll run that up and see what happens.
500v will be 500 watts into 500 ohms.
I have both regular thickfilm resistors and some thinfilms to test. I
theorize that the thinfilms will hold up better.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
I ran the cheap thickfilm 1206 at 250v, then 350v, and then at 500
volts, days at each voltage. Resistance value changes were down at the
5-digit measurement noise level. Boring.
So I tried a Panasonic ERA-series thinfilm. I figured I could start at
350 v. It died instantly.
Another is running OK at 100 volts.
So much for theory.
How do you figure?
Thick films dissipate the power throughout a thicker layer, which has much >higher heat capacity than a very thin metal film.
Cheers
Phil Hobbs
On Tue, 27 Jan 2026 02:32:07 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
john larkin <jl@glen--canyon.com> wrote:
On Wed, 14 Jan 2026 17:07:45 -0800, john larkin <jl@glen--canyon.com>
wrote:
I need something like 1.5K resistance across a 750 volt pulse. Pulse
widths will be below 1 us.
Three 1206's in series, 499r each, would work. Peak power dissipation
per resistor will be 125 watts at 250 volts. I think that's OK but I
want to test it.
Here's the tester. The DUT (device under torture) will go across the
gap on the left.
https://www.dropbox.com/scl/fi/2z1g2hlz9tjpkrtpaf4l0/X124_WB_1.jpg?rlkey=nj4qnztwzfmjobobdgti9vf6k&raw=1
https://www.dropbox.com/scl/fi/8j18qqnk1e4kjslkrb4v0/X124_Dremel.jpg?rlkey=j2ck2tyg2wy76jgyzfimdd3u5&raw=1
I have a 500 volt supply so I'll run that up and see what happens.
500v will be 500 watts into 500 ohms.
I have both regular thickfilm resistors and some thinfilms to test. I
theorize that the thinfilms will hold up better.
John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics
I ran the cheap thickfilm 1206 at 250v, then 350v, and then at 500
volts, days at each voltage. Resistance value changes were down at the
5-digit measurement noise level. Boring.
So I tried a Panasonic ERA-series thinfilm. I figured I could start at
350 v. It died instantly.
Another is running OK at 100 volts.
So much for theory.
How do you figure?
Thick films dissipate the power throughout a thicker layer, which has much >> higher heat capacity than a very thin metal film.
Cheers
Phil Hobbs
Apparently so. But a link I posted above says that thinfilms are about
twice as tough as thicks for short pulses.
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