Triacs are bi-lateral devices, thus can be turned on in all 4 quadrants.
While the Igt & Vgt requirements are different in each quadrant, they will
typically turn on in a few microseconds if they are gated properly. It is
most common to gate them in quadrants 1 & 3 where the gate supply is is
synchronized with the main terminal supply, meaning the gate is positive
when the MT2 is positive, and likewise for negative.
Here's what your counterpart may be talking about: It is difficult to get
riacs to latch on in quadrant 2 when the MT current is low, - this might be
interpreted as reason for delaying turn on in practice, so as to avoid
uncertain turn-on in that quadrant. You can only determine this period by
examining the specific device's data sheet.


BTW, what forum is discussing this topic?

Chris

> How fast are generic Radio Shack triacs for switching 110v
> 60Hz current to...say...a 150Watt incandecsent light bulb.
>
> When the triac is enabled, where on the AC wave form will it
> turn on? Anywhere?
>
> How about turning off, as I recall, the AC needs to cross
> zero for a triac to turn off?
>
> Thanks for any help. I am in a real pickle here. Got caught
> BSing  on a forum and need to do some damage control. ; )
>
> John

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