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Re: RE: Sold state IGBT disruptive coil spark gap idea

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Greg,

At 10:32 PM 5/4/2006, you wrote:
Nice work over the last few days Terry. How long till we can see this
actually running on a coil and making sparks?


Greg Peters

This all grew out of a completely different project sort of by accident. I now find that I really don't have a good coil on hand just to throw it into so I will have to whip another coil up or something. There is no planning here :o))

I still need to do some higher current testing and such... I hope I still have my big HV bridge rectifier around since it is a DC coil thing....

I probably also want to have boards made to get rid of some inductance and resistance that messes with the hand wired version...

I have not really though much about the next step ;-)

Bert wrote:


This is truly breakthrough work - excellent stuff!

BTW, it looks like the "direct short" you applied through the wire is actually a small spark gap (at least for the first ~60 usec). You can see the characteristic linear decrement in the yellow trace.

It makes a nice flash and pop.

The exponential decrement from the saturated IGBT shows that it is acting more like a (lower equivalent) resistor. In any event, a stack of saturated IGBT's should have considerably lower voltage drop than even a single spark gap.

Yes. I did not expect that it would do "that" well so it was quite a surprise! The "hand shorting" probably would do a lot better with a relay with proper fast contacts and all.

I recorded the voltage across and current through the IGBT gap here:


The raw data file is here but I have not had time to calculate anything with it yet:


With MathCad, excel, staroffice, etc. one should be able to find dynamic resistance, power dissipation, etc. It is nice that the blocks are still low enough voltage that conventional test equipment can measure them.

By using a directly driven IGBT at the base of the stack, you may be able to emulate a triggered/sync gap. And by reducing the gate RC time constant (or perhaps by only removing the triggering signal!), you may then be able to emulate first or second notch "quenching".

I have the voltage on the cap to run say a 555 timer and a drain transistor (just a little TO-92) to pull the gate down. I am not sure a 555 could setup fast enough though. But there are many hooks and possibilities for other circuits to be added.

You would only need to fire a few of the sections early to trigger the thing. You might be able to do that just be fiddling with a few of the SIDAC parallel resistors. Maybe you could set it to fire early in that case or something.

Triggering and quenching are probably not hard circuit additions. But it would require much more thought *;-))



Best wishes,