Control TRIAC with DC

[axro]

Is it possible to control a TRIAC with DC?

 

[Gary B]

It is possible indirectly. Pass your DC pulses through a transformer to the control gate. The TRIAC sees AC but your circuitry is strictly DC.

 

[Boncuk]

Yes and No.

Use an opto-triac to be controlled by the primary control circuit (MCU, etc.).

The opto-triac should be controlled synchronously with mains frequency to prevent main triac (BTA41 in the schematic) misfires, which are desastreous connecting inductive loads.

Boncuk

 

[MrAl]

Hello,

Actually, some triacs can be controlled with a DC gate provided you dont go over the maximum gate input current, and that gets a little tricky sometimes.
If you look closely at triac data sheets you'll see that if you use the triac in a certain set of two modes (out of three or four) you can get the triac to work with less DC current than the two other modes. Unfortunately, some triacs only have three modes of operation so you may not be able to trigger the triac in the best possible set of two modes. The ones with four modes however i believe you can get to work with DC by using the correct set of two modes. The idea with DC is to be able to energize the gate without overpowering it, and that may or may not be possible depending on the triac spec's. You have to check the data sheet for the exact part number you are working with.
Normally in triac applications there is a gate pulse, and that pulse is enough to trigger the triac but when it ends the power ends and so the gate is not overpowered. The gate pulse is designed to be just the right width and with just enough current to energize the gate (with some error margin in mind too) but not burn it out. That means energizing it with pure DC isnt as simple as connecting a DC source to the gate, at least without checking over the spec's carefully first
If i remember right, a negative gate signal (instead of positive with respect to MT1) requires the least amount of current which results in the least amount of energy to turn the triac on, but that only works with triacs that can operate in all four conduction modes..
I think the sensitive gate triacs would be best for DC but i'd still check over the spec's first.