How to trigger triac gate with optocoupler


Joined Aug 21, 2008
You will notice that in both this thread and your previous thread that we think the MOC3043 is a much better couple for your purpose than the PC817. Turning on traics handling any real power well is a little more complicated than you seem to imagine and the MOC3043 give you a solution with all the hard work (extra circuitry) already inside.


Joined Aug 27, 2022
Might someone at any point if it's not too much trouble, let me know what i'm fouling up here and furnish me with a more exact clarification on the setting off of an entryway on a triac? All I comprehend is that you want some ongoing streaming among Gate and MT1 (Some say MT2!), and that implies that you put the entryway on 5V, MT2 on GND (or the other way around) and you'll set off the TRIAC and short MT1 and MT2 permitting AC conductivity between them.


Joined Aug 7, 2020
If you put a current that is greater than the trigger current into the gate (in either direction*) the triac will turn on and AC current can flow between MT2 and MT1.
The triac will turn off when the current between MT2 and MT1 falls below the holding current or when the trigger current is removed.
That's all there is to it.

It looks very much like an AC version of a transistor with MT1=emitter, MT2=collector and gate=base

*trigger current may be different values for positive and negative, and some triacs will only trigger with negative voltage on the gate.
[and you might be in trouble for hijacking an old thread - if you want to ask a question start a new thread]


Joined Aug 27, 2022
Many thanks for the clarification, Now I get it! So essntially the opto triac will give setting off to the TRIAC in every one of the 4 cases (quadrants). My inquiry is, the reason is it when I apply a GND to MT2 and a 5V to Gate, the triac is turned on (light is ON without any issues , implying that AC current/voltage is exchanging however the light is still on) , shouldn't the shortfall of an optotriac upset this? Additionally how can it be that after I put the MT2 to GND, Gate to 5VCC, after the triac is ON, what at any point esteem I put Gate to (GND or 5V) , it stays on.

Kodi nox