If you have a MOSFET in series with a thyristor, can turning the MOSFET off cause the thyristor to turn off?
If turning the mosfet off causesthe current through the scr to drop below its holding current, then yes, the scr will turn off. The mosfet could also be in parallel with the scr and when turning the mosfet on would cause the current through the scr to drop below the holding current.
How long would it take? Maybe a couple of microseconds. Depends on the specs of the scr.[edit] according to the Motorola datasheet for the C106 scr, turn off time is around 40us.