RE: SSTC problems1 (no its not a PlasmaSonic ;-))

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

Original poster: sebastian gaeta <sgtporky-at-prodigy-dot-net> 


Hi Malcolm,
Thanks for the info!
My coil blew up Friday night. I did some troubleshooting, and found out 
that two fets went CLOSOB (Conducts Like a Sonofagun). The 10 amp fuse of 
course remained intact even though one of the fets completely blew apart. I 
think a more appropriate use for MOSFETS is fast blow fuses >:(

Well anyway, the two mosfets that shorted were not supposed to be on at the 
same time. The two that were bad would have placed a short right across the 
DC buss. The other two tested good. It appears that the driver survived all 
this mayhem. It puts out a good waveform with only the good fets connected 
to it. So at 8:15 PM, the cause of death was determined to be shoot 
through. Now I had 10 ohm resistors in series with each gate with the 
schottky across each one. It did improve the waveform, so the only thing to 
do now is try and improve the layout of the GDT and MOSFETs.

I re-read the HV Guys instructions, and realised that I messed up big time 
with the antenna. They say to put it no closer than 20" from the secondary, 
and I had mine maybe 6" away, so maybe having it too close may have 
introduced parasitics, or some other bad noise into the system. I also used 
13 turns on my GDT instead of 10 like they suggested. With my resonant 
frequency being around 236 KHz, which is a little on the high side, I could 
probably do better with less turns on the GDT. I also noticed that they 
don't have a toroid in their photos. I used one because Dan's SSTC had one, 
but his circuit is also completely different than this one. I will do 
without the toroid in my next attempt.

If anyone can offer me any further insight, or suggestions, I would really 
appreciate it!

IGBTs sound nice, but I don't think I want to play with expensive IGBTs 
until I learn how to stop blowing P460s!

Sue

Tesla list <tesla-at-pupman-dot-com> wrote:
Original poster: "Malcolm Watts"

Hi Sue,
I did a switching device/diode product inventory of my bits
and pieces over the weekend and dug out some facts and figures on
power MOSFETs I have, some of which might assist: