gate-drivingtriactrigger
I am trying to understand the parameter Vgt (max) for a triac (or any semiconductor with a gate threshold parameter), mainly the max. part of it. For example, on page 2 of the following datasheet:
VGT (VD = 12V RL = 60 Ω) MAX. 1.3 V
Could anyone please help me understand how to interpret max. here? Does it mean gate threshold can be 1.3V at max. and that we need at least 1.3V to trigger it and allow the current flow?
A triac is used to control an AC load, just like a transistor can be used to control a DC load. It is drawn like a couple of diodes in each direction which are then triggered to turn on. They will turn off when the current drops below a certain threshold. So if you just want it on or off you leave the signal on or off and at the next zero-crossing of the AC it will be in that state.
You can also get fancy and turn it on only sometimes, which is where the microprocessor programming comes in. Once you have a zero cross detector you can then turn it on in a "gentle" manner as well as keeping trac of percentages on/off if you are trying to reduce the power or control a speed by leaving it off for some cycles.
I think no capacitor at all is appropriate. The graph indicates it's stable at any anode current with no capacitor.
If you did put a capacitor on there, for your stated reason, I would definitely not put it where it is shown, I'd put it across the gate-MT1, and no more than a few nF.
In the shown position, if the power is applied suddenly, the triac may trigger via the cap, causing the crowbar to short the supply.
Best Answer
It's not an absolute max rating so, it can be assumed the supplier is saying that to guarantee switching you must exceed 1.3 volts. However, you must protect this part by limiting current to no more than 1.2 amps (see AMR table for \$I_{GTM}\$).