Driving Triac With MOC3021 for 12 v ac

Question

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

https://i.stack.imgur.com/OaRTr.png

It's because the BT136 is probably too powerful. – Marko Buršič Mar 19 '19 at 08:36 — Marko Buršič, Mar 19 '19 at 08:36

score 1 · Answer 1 · answered Mar 19 '19 at 07:58

1

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:

Source of picture: this question.

answered Mar 19 '19 at 07:58

Bimpelrekkie

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but i am giving proper current. at the output i am getting only positive cycle – RIMPY JAIN Mar 19 '19 at 09:18
And what is the current when it is flowing ? Is it close to the **holding current**? – Bimpelrekkie Mar 19 '19 at 09:23
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Do you mean 0.2 mA ( = 200 uA) ? Compare that to the **holding current** in the datasheet. Learn here what holding current means: https://electronics.stackexchange.com/questions/188492/thyristor-latching-and-holding-current-confusion It is a **miracle** that you even get that positive current. – Bimpelrekkie Mar 19 '19 at 09:46
bcoz i am using 12v 1amp transformer – RIMPY JAIN Mar 19 '19 at 09:55
so tell me how can i solve this – RIMPY JAIN Mar 19 '19 at 10:00
OK, so you do **not** understand the concept of holding current. Fine, your choice. No, not going to tell you if you don't want to understand what the actual problem is. – Bimpelrekkie Mar 19 '19 at 10:01
i understand that holding current is that which stay on the triac – RIMPY JAIN Mar 19 '19 at 10:20

Driving Triac With MOC3021 for 12 v ac

1 Answers1