From: jrwalliker@gmail.com   
      
   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  wrote:   
   >>   
   >>> On Thu, 15 Jan 2026 15:18:31 +0000, liz@poppyrecords.invalid.invalid   
   >>> (Liz Tuddenham) wrote:   
   >>>   
   >>>> john larkin  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.   
   >>>> 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 enough?  You   
   >>>> would 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 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 direction.  The   
   >> 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   
      
   > I'm not a fan of MELFs - they roll off ones bench onto the floor - but   
   > a boy has to do what he has to do.   
   >   
   > https://www.vishay.com/docs/28870/pulseloadsmdlimit.pdf   
   >   
   >   
   > John Larkin   
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