Now I know what you mean. A future design will use these.
A digitally-made picket fence made lots of improvement.
This one has been licked!
I recalculated and re-located my RC snubber, and now the original
short-pulse gating scheme works flawlessly. (I finally came up with a simple
little formula for snubbers that seems to work)
My next board will either use pulse transformers, or if I still need the
simplicity of the optical isolation, I'll go for greater dv/dt on the
opto-isolators, even if I have to use several in series- because this is
what I think the snubber benefitted most. I found the SCR's had dv/dt
ratings in the kV, but the opto's only hundreds. I'll also do something so
the gate pulse shape and duration will be user-selectable. All these
combined will let this thing gate many different thyristors in almost any
circumstance.

Many thanks for all the help, folks....
Chris

> >        I'm curious as to how you're driving the thyristor
> gate with the
> >"picket fence." Getting drive near zero cross without a separate gate
> >drive power supply sounds like a good reason to use a pulse
> transformer
> >to drive the gate. You could even drive it with a PIC!
>
> If the picket fence is powered by AK voltage and the
> thyristor fires then
> the remaining pulses of the picket fence are not interesting.
> But a pulse
> transformer is better, I aggree.
>
> Peter

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