Solid State Gap

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi All,

I did more testing with my solid state gap tonight.  I actually have it
hooked up to my small coil but was only running with a primary voltage of
50 volts so I could play with things :-))  Pictures of the setup are below.

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18/Setup.jpg

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18/SSgap.jpg

As this picture shows, it works (no load on top terminal, thus the very
long ringdown time) :-))

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18/Tek00007
.gif

The IGBT and the reverse diode seem to work perfectly well.  I looked at no
quench and first notch quenching:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18/NoQuench
.gif

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18/Quench.gif

I was originally thinking of just not worrying with quenching and shutting
the IGBT of after a few hundred microseconds.  However, unlike regular gaps
where getting first notch quenching is really hard, with this gap I just
set the pulse width trim pot :-))  I was using a 3pF probe (Tek 5100) in
series with a 220k Ohm resistor hooked to the coil's top terminal to
simulate a streamer load.  The RMS output was 78.72Vrms with no quenching
vs. 87.03Vrms with first notch quenching.  So that gives 10.6% more power.
That 10% power is also going into the streamer rather than heating the IGBT
which is a concern.  I was worried the cheap fiber optics may not run at
this high of speed but all seems well.  I was also worried that the soft
turn off of the IGBT would be a problem.  However, it seems that once the
IGBT begins to turn off, it looks like too high of a resistance for the
energy to swing back into the primary, so it's cutoff is actually quite
effective as shown:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18/Tek00004
.gif

Even though the IGBT's cutoff is very slow, almost perfect quenching is
still achieved.  That is an unexpected bonus!  Although, it makes perfect
sense once one see what is going on.  The turn on time is excellent so not
problems there.  One can even easily slow that down to help reduce that
nasty initial pulse that causes RFI if it is still there with this type of
gap. 

So It looks like the IGBT gap has the ability to transfer the primary
energy into the secondary and quench very easily.  Of course, this was only
about 50 volts with a little over 1 amp peak in the primary.  There is
still a little way to go before I get to 13kV and 400A peak the small coil
normally runs at...  Right now that would run about $650 but perhaps high
voltage/current IGBTs would be cheaper once all the bugs are worked out.

Cheers,

	Terry