Triac Dimmer: transformer making noise

Troubleshooting
1

I have 220V. I’m trying to make a dimmer and using the following code.
I use a triac dimmer like this.

void zero_cross_int()  //function to be fired at the zero crossing to dim the light
{
// Firing angle calculation : 1 full 50Hz wave =1/50=20ms 
// Every zerocrossing : (50Hz)-> 10ms (1/2 Cycle) For 60Hz: (1/2 Cycle) => 8.33ms 
// 10ms=10000us 
// 10000 10 / 128 = 78 For 60Hz: (8333us - 8.33us) / 128 = 65 

int dimtime = (78*dimming);    // For 60Hz =>65    
delayMicroseconds(dimtime);    // Wait till firing the TRIAC
digitalWrite(AC_LOAD, HIGH);   // Fire the TRIAC
delayMicroseconds(10);         // triac On propogation delay (for 60Hz use 8.33)
digitalWrite(AC_LOAD, LOW);    // No longer trigger the TRIAC (the next zero crossing will swith it off) TRIAC
}

and attachInterrupt(D4, zero_cross_int, RISING); in setup().
When I connect directly to a halogen lamp everything is working as expected. When I connect to a lamp with this transformer, the transformer is making a buzzing noise except for when the brightness is high. Flickers for some values.

What could be the problem? Feels like some frequency mismatch.

Here is the Full Code

2

What Triac are you using?
With inductive loads at low dimming levels you may need to hard-fire the triac as the “lagging” current might not reliably reach the threshold level in time.

3

Hi, Thanks for your reply.I use this. What do you mean by “hard-fire” I’m not an electronics person. How do I do that?

4

Since I can’t find any schematics it’s hard to say, but looking at the images there is a TRIAC DRIVER marked on the board which will probably do the hard-firing already.

But the buzzing noises might also come from resonances in your hardware setup which are hard to control/get rid of - for that reason I prefer electronic “transformers” (which require trailing edge dimming tho’).

5

Thanks. I can get this electronic transformer How do I do trailing edge dimming?

Also the one in the picture (the one I am using) says it’s an electronic one. I did not connect ground in the power supply. Could that be a problem?

6

Trailing edge dimming would be that the triac opens on zero-cross and your code switches it off after the desired time according to dimming level, while leading edge means that your code gets a sync on zero-cross, waits a while and then fires the triac which will then open till next zero-cross and shut after that till you fire it again.

Your dimmer is a leading-edge dimmer and I’m pretty sure this won’t let you do the trailing-edge dimming.

But for the unit to work at all, you should definetly have the signal GND lines connected (DC power supply, dimmer and µC) - but keep away from the AC side!!!

7

Thank you so much. I get the idea. I was talking about the ac ground.
Also, what would happen if electronic transformer is used with leading edge dimmer? Looks like that is happening.

8

This might provide some extra info
http://lightingmatters.com.au/lighting-guide-lighting-techniques-learn-about-led-lighting/15--dimming-led-lights.html

and reads for your question

9

Thanks. I get the idea. It looks like it is hard to find a trailing edge dimmer for my purpose. I’m going to remove the transformer and going to have 220V G4 dimmable bulbs instead of 12V G4’s. It Should work.

220v dimmable G4