I wonder if that's hot.

AFAIR, yes. I had a quick squiz, but I havent got any references handy.

OK, thats not strictly true, but all the good ones do (I forget if there is a fancy name for them). the trick is mounting the FETs in the press-pack, to minimise inductance, then using carefully designed transmission-line structures for the FET supply.

the turn-off current gain is extremely low, so FET current is enormous. Mohan et al give Boff = a2/(a1+a2-1) where a = current gain (slightly less than 1), so 1 < Boff < 2 (ish).

for a 9,000A GTO, you need to suck a good 5,000A out its gate. Given Vg = say 2.5V, and say 1us, the required inductance is tiny - 1/2nH. (numbers plucked from thin air)

In practice a negative voltage is used, increasing this to a somewhat less ridiculous, but still bloody tricky, amount - the magnitude of the

-ve bias is constrained by the required Rdson of the FET(s).

I read an interesting paper a few years back, that pointed out the highly interdigitated structure of GTOs makes it quite straightforward for high-energy cosmic particles to turn them on, regardless of gate potential. so GTO drive designers must ensure their products can cope with dead shorts across the DC bus :)

Cheers Terry

there are some interesting things in that datasheet, eg peak snubber inductance < 200nH, turn-off gate current = 950A, peak reverse gate power = 24kW :)

Cheers Terry

Keith wrote in news: snipped-for-privacy@att.bizzzz:

I've found my finger nails work decently for avoiding burns and telling if something's really hot. I usually don't get too close to super hot stuff, so I haven't taken the risk of burning my finger nails off...

Puckdropper

they are called gate-turn-off SCR (thyristors (tm) GE) when this property is specifically improved. The turn off is slower than using a commutating SCR but not much.