Triac Trouble

Hi, I have followed the diagram on for an Arduino controlled triac. However, even with the optoisolator out of the circuit the triac is on. (the light comes on that the triac should be switching.) I have tried with several triacs and keep having the same problem. What am I doing wrong?

I guess it would be helpful to know what hardware I'm using.... The trac is a bta41-600 and the opto-isolator is a m0c3041

Check that the light and AC are hooked to A1 and A2. Doublecheck the pinout from the TRIAC datasheet, it doesn't match the layout of the circuit diagram.

Unless you give us more information about what wires are hooked to which pins, we can't help you.

Right.. Sorry. Im really bad at posting all the info. The gate goes to the opto-coupler with a 330 ohm resister inline then from the opt-isolator to M2. Nuetral ties to M2 and the load is on M1 with the hot wire going to the other side of the load. Also, there is a snubber across M1 and M2.

The load connects to A1? That could be your problem. Switch the load to the A2 side and see if that changes anything. I'm not intimately familiar with TRIACs, but the one thing I remember from using one once in class is that A1 and A2 are NOT interchangeable. It didn't work until the right things where hooked up to the right places.

Match the wiring diagram EXACTLY, and then see if there's still a problem.

I double checked everything... again.. and tried your suggestion. I still get the same problem. However, if I use a 24 volt AC power supply I don't have any trouble turning on and off a LED.

Hi, I looked up the data for the opto and the triac.
The opto will be okay if all you want to do is switch the lamp on and off as it is a zero crossing type.
If you want to change the lamp brightness then you will have to use a different opto.
Try this circuit, also check your triac by assembling the triac load and supply with the 330R Gate to M1 (T1) terminal and see if it stays OFF. Leave the opto out of circuit.

Hope it helps, Tom… :slight_smile:



The thing with triacs is that there is a leakage current. With a mains input if the load is not high enough it will look like the light is on. What power light bulb are you using? Try a 100W bulb.

TomGeorge, Thanks! I will try that when I get home this evening.

Grumpy_Mike, I have 2 100Watt light bulbs.

have 2 100Watt light bulbs.

That should be fine then.