Re: A s.s. head-scratcher

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Original poster: Ken or Doris Herrick <kchdlh@xxxxxxxxx>

Awaiting replacement IGBT bricks (used, of course, and perhaps 
already no-good as were some of the others, I'm sure), I've simulated 
something interesting.  See Single res..._p-p4c.pdf in 
http://www.pupman.com/current/kcherrick --giving Chip a bit of time to post it.

Q1 & Q4 are driven out of phase by +/- 25 V square waves at the 
secondary's Fr.  They're in push-pull with the two main, untuned, 
primaries of TX1.  D6/C3 and D9/C5 conventionally snub the 
collectors' overshoots--and at the same time slow the collectors' 
voltage rises during turn-off.  The "snub" primaries act to discharge 
the snubbing capacitors on alternate half-cycles.  Notice that each 
of them is returned to the opposite transistor's collector.

The V4 & V5 circuits simulate MOVs, added as insurance to clip any 
overshoots exceeding ~900 V.

I haven't fully doped it out, but I found it a little startling that 
in this simulation I realize half-again the voltage rise at the 
output--and that, occurring in half the time--as I had obtained with 
my prior simulation of the push-pull "snub-primary" idea.  Of course, 
the mains current is too much--for my mains, at the 1% 
duty-cycle--but the scheme does seem worth pursuing.  I'll try 
another turn on each of the primaries, to cut down that current.

The waveforms are of the 4 primary currents plus the C4 mains-current.
I manually added up the amplitudes of the primary currents and found 
that the sum did, indeed, match the shape and amplitude of the C4 
current, as I think one should expect.  So all that wiggle-waggle 
produces some 800 A p-p of net primary current.

Any comments on this will be most welcome; and I repeat: if anyone 
has SiMetrix and would like to play with this, I'll send along the 
file.  I intend to re-connect my hardware to try this out within the 
next few days--assuming the "new" bricks work.

Ken Herrick