Originally posted by yampa
Triacs allow RMS power and voltage control - you can mess with the waveform produced by the power supply. You can certainly apply PWM to a triac.
No, no, you can't. Once you switch it on, it's on. There's no turning it off. You can't PWM with one whatsoever, in the proper sense. The only "PWM" you can do is delay where in the incoming AC waveform you switch the triac on, and that's old fashioned phase control. You can't control voltage either. TRIACS can't be modulated like a transistor or FET, you fire them and they're on. That's it. No level control at all. And once on, the only way to turn it off is to wait for the current to fall to the critical level.
Who is to say that knowing the right way to switch the output doesn't facilitate a reaction? Perhaps he is switching to create some kind of harmonic? Or maybe wants a deliberately noisy signal, so switches it at random?
Me. I'm the one to say it. The output of a TRIAC is on, and once on, it's on until the current through it falls to near zero. There's no special way to do it. It's fired, or it isn't.
eta: and what you get out of it when you're phase controlling with AC isn't a sine wave - diddling the firing point in the phase gives you control over RMS power, but it's not a nice sine wave anymore, it's pretty nasty looking. Fine for a motor or an incandescent light, not so good for other things...
etaa: and the waveform you get is textbook typical for phase control using a TRIAC on AC. You can't make secret new waveforms with it.
edit on 22-5-2013 by Bedlam because: (no reason given)