Electrical – Driving Triac With MOC3021 for 12 v ac


enter image description here

i am using triac bt136 with moc3021 to drive 12vac but i found the problem
is it possible to drive the triac on 12vac
i made the circuit as shown in link on 12 vac
but i didn't get any exact sine wave at the output


Best Answer

The TRIAC needs a certain current to flow into the gate (I'm assuming we're on the positive part of the sinewave of the AC supply). According to the datasheet of the BT136 that current is typically between 2.5 mA and 11 mA. Before that current can flow there needs to be enough voltage across the 100 ohm and 330 ohm resistors, the opto-TRIAC and the TRIAC's gate to T1/T2. So only when the AC voltage is large enough to trigger the TRIAC will the TRIAC be triggered.

So there will be a short period of time, between the zero-crossing of the AC voltage and the point where the TRIAC triggers, where the TRIAC does not conduct and the voltage across the load will be almost zero. The voltage across the load will look something like:

enter image description here

Source of picture: this question.