I've been coming up to speed on thyristors, and triacs in particular. I've found detailed material on them a little hard to find, in particular on the device physics. Horowitz & Hill is silent on them, Sedra & Smith as well, not even a mention.
I suppose I get a vague idea that thyristors belong a bit to a past era, but they're still a key component in solid state relays (SSR) for example, so I thought I'd be able to dig up more.
Anyway, one of the questions that's still open for me is why a triac triggers with gate current in either direction (in/out). That seems a bit odd so definitely aroused my curiosity.
Does anyone understand how that bit works?