Finn Hammer wrote:
In my SISG scheme, where I bypass most of the SIDAC/SIDACtor's with a
SCR, the current can easily be supplied from the tank capacitor,
(When the SCR is trigged, the action is much like kicking the stool
away from under the feet of a poor sod with a rope around his neck)
and since the break over voltage rating of the one remaining SIDACtor
in each section is very low, a successfully triggered section cannot
be over volted.
Now that's an "analogy"! I like this triggering scheme Finn. It makes
sense to use a fractional sidac value on the top end keeping the
voltage across the IGBT string nearly identical.
But I am ultimately depending on the crowbar action of the
SIDAC/SIDACtor string: Some of the stacked sections are bound to get
triggered later than others, and these sections rely on the breakdown
of the full string of SIDACtor's to protest the IGBT from over
voltage. At least that is my cautious point of view.
This is what makes the SISG successful and why we can run several
IGBT's in series (24 in my case). The full string is required to fire
before the 25V TVS rings the doorbell. How close the TVS components
are to one another ultimately is the cause of why all the IGBT's fire
nearly at the same time (and turn off similarly). The SISG design is
really amazing when you compare schemes attempting dynamic gate
balance. From what I've read, there is the use of feedback charge
(similar to SISG, but still very different) and RC snubber passives
across CE to balance the rate of rise across the IGBT. None that I've
seen use the TVS scheme that Terry brilliantly conjured up. The 25V
TVS waits until the sidac string fires (bang), then it "quickly"
performs it's doorbell ring at the gate of the IGBT, and thus, they
all turn on nearly at the same time (Big Bang Theory). Turn off is
just as cool!
For my purposes, the Sidactor will not be used. I'll stay with the Sidac.
Take care,
Bart
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla