On Sep 10, 8:05*pm, Grumpy The Mule wrote:
my guess is the quasi-push pull output is due to the leakage energy
recovery circuit. *HV flyback transformers usually have very high
leakage inductance (the part of the magnetizng inductance not coupled
to the secondary is leakage inductance) because distance between
windings is a major cause of poor coupling and you need distance for
isolation. *

Exactly right I was in a hurry to get off to work and cut out the part
about the Damper diode and hold down capacitor. So yeah the diode
which looks like a varistor and may very well be a varistor, is the
push pull switch shorting out the induced trailing edge energy of the
IGBT. They use a .032 mfd across the primary along with the damper.
So the damper is switching on after the IGBT turned is off.

At least that's how I think it works... Please let me know when you've
scoped the waveforms.

Hopefully on the day 911, I get this powered up with low voltage. .
VK3HZ waveforms were at 50 hz trace sweep frequency so you couldn't
see the 30khz waveform.

73 OM
n8zu