How many microseconds does it take for a mains triac to turn fully ON?

[treez]

How many microseconds does it take for a mains triac to turn fully ON?
-Speaking of a mains triac dimmer...I presume there is a transistion period, where the triac goes through its linear region?

 

[Dan Mills]

Check the data sheet, they usually specify a di/dt limit which effectively tells you about the switching time of the thing.

Note that a properly designed phase angle dimmer has a series choke for interference suppression which serves as the actual limit on di/dt.
Good dimmers designed for TV studio use have rise times measured in hundreds of microseconds (almost all of it limited by that choke).

Regards, Dan.

 

[FvM]

Turn on time of triacs is usually specified in a few µs range. I agree with Dan Mills that critical dI/dt is the important parameter to determine usable switching speed in triac applications.

The reason for rating dI/dt isn't that the triac goes through a linear region. The positive feedback of the four-layer structure causes fast transition to full conduction, but not for the full chip area immediately. Conduction starts in a smaller zone around the gate electrode and the potentially too high current density during the first microseconds can kill a triac or thyristor,