Re: DRSSTC - I think I heard Cross Conduction...

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Original poster: Sue Gaeta <sgsparky@xxxxxxxxxxx>

Get used it! It always happens that way. I have blown many 20A MOSFETs to 
bits, but I still have the original 10 amp fast blow fuse that I started 
out with!

And everyone thought I was crazy when I said we should be using MOSFETs as 
drop in replacement for fuses :-)

I have replaced all my MOSFETs with IGBTs now. Not that I thought I would 
get better performance, but I just wanted to see if burning IGBTs smelled 
any different >:]

I started playing around with my coil again last week, and I added a 
0.186uF cap in series with the primary. It is now officially a DRSSTC. My 
tuning was way too high from where I predicted it should have been when I 
swept the primary tank arrangement with the signal generator, which was 
odd. The interesting thing that I noticed was that a dip in average H 
bridge supply current, and an increase in spark length (obvious) coincided 
with resonance. Just like a real transmitter! People don't usually talk 
about tuning for a dip in supply current in this arena, but I just found 
out that it does apply here. Yes, I am pulsing the driver at 100 Hz, but I 
am talking about average current.

When I build the bigger H bridge, I have to look into why I can't use as 
much top loading as Steve W. uses. I have enough extra turns available to 
get it in tune, but I get smaller sparks, and it draws much more current :-(.
Sue

I am beefing up the traces, but I don't think anything could stop it once
it lets go. But the breakers and fuses did not trip so the IGBTs blew
themselves out of the circuit very quickly. Good since that really helps
limit damage. I am using the little IGBT as fuses in that case and they
almost worked. Maybe I need smaller IGBTs ;-))

Cheers,

Terry