Hi, I have a recurrent problem with a dimmer, triac moc circuit. There is too much noise on the AC when the light is set on a specific phase. I isolated the problem but I just can't resolve it !!

When I use one of the tri-phase AC alimentation with a 1000w bulb, there are some of the others (bulbs wich are powered with another phase) that light up. And it happens only when the first one is set on 1/3 of the phase… !

I saw a 3.5 volts noisy mini peak between the pin 1 of the triac (gate pin) and the pin 4 of the moc when the light is running on higher amplitude of other phase… just enough to trigger the triac gate pin.

I tried to use inductor choke on it (between triac and moc) and put RC filter…. No good news…

Have you any suggestion ? Thanks !

 

Wind a choke, 2 layers 12 awg. Haptz wire, on 2" x 1/4" dia ferrite, epoxy in place, should be about 10 micro-hys. Add snubber ; 0.22 mf + 470 ohms between Triac load side and choke line side. This should do the trick.

Cheers, DPW [ Spent years making heaters out of op-amps.]

 

Thanks Duane.

It's little bit weird project. We need to hear noise from bulb. So if we put snubber, I'll not hear the sound from phase cuting...! make music from independent > 45 bulbs 1K watt. Art project.

Other question. The MOC trig TRIAC at gate pin if the voltage is more than sensitive voltage gate trigger (something like +-1.5 volts) the triac will operated. If there is no signal from MOC = no output. There is no ground on triac so what's the reference? How the triac can compare the input phase amplitude for the sensitive voltage gate trigger ?

It's so mysterious for me. Thx