Re: Recent s.s.t.c work

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Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>


An update for those interested...  Ref.

http://hot-streamer.com/temp/KCH_TCH1.jpg
 and
http://hot-streamer.com/temp/KCH_TCH2.jpg

I had started slowly to turn up the H.V. without taking sufficient 
precautions and blew both bricks.  With a tip from Steve Ward I've 
ordered some more--bigger ones--at a quite tolerable price.  In the 
interim, I'm finishing up some odds & ends and changing the circuits 
slightly.  One change is to incorporate a ferrite-cored feedback 
transformer rather than the Rogowski that I had before.  That, to 
minimize phase-shift of the feedback signal due to leakage 
inductance.  I've located the coil at the juncture of the primary's 
inductor and the capacitor-string--which (ideally) will remain at 
mains-common potential, the primary being driven by an H-bridge.  In 
order to keep it a bit nearer to that potential, I've included a 1 uF 
capacitor from that point to mains-common; there should be zero 
current in it with a perfect primary.

Another change has been to improve (I trust!) my 4 IGBT driver 
circuits, resultant from further simulation.  For now, I've gone back 
to the 12V l.v. supply rather than piggy-backing the 12V onto the 
5V.  If not enough, I can always re-do that.

I've added a 100 mV/50 A current shunt in the common bus connecting 
the two mains capacitors.  That, to monitor IGBT common-mode current, 
which I think is what shot me down initially.  I should be able to 
use that while the coil is operating, via a long twisted-pair to the 
differential scope inputs.

As soon as I receive the replacement bricks & install them, I'll be 
ready for the next anxiety moments.

Ken Herrick