Using PWM to drive DC with Triacs

[avatar-it]

Guys,

after reading the wiki about why to run the PWM firmware on the renard.

I have a questions.

My understanding is that the standard firmware uses the ZC pulse to time when to pulse the triac to turn it on and have it latch on will the end of the AC cycle.

The PWM firmware is different in that it drives the Traic all the time allowing the system to turn on the triac and keep it on while there is not enough current to make the triac latch.

My question is this.

if we could change the triac to a different model that had a latching current fairly high but we were still able to turn it on with the standard output we have atm. could we run a DC or AC signal though the triac and allow it to be turned off and on at will?

This would then allow us to run almost any light off the one SSR type.

I guess im wondering if my thoughts are right and if such triacs exist.

anyway its just me thinkiing out loud.

Peter Rogers

[NogginBoink]

Your proposal is to take a part (a TRIAC) and use it for a purpose for which it really isn't well suited. A TRIAC just isn't supposed to behave the way you're proposing.

A better solution would be to find a switching device with the same footprint as the TRIAC that would be able to switch DC currents. I'm an idiot when it comes to analog stuff, and I don't know transistors from a hole in the ground, so I'll leave it to the more experienced folks to determine if such a part exists.

A third option would be to create a circuit board that has pads for both a TRIAC and a DC switching device, and the end user could install one or the other depending on his application.

[avatar-it]

Yes i understand im suggesting something that there not designed to do.
The main problem i see with switching components is that this year you might want standard AC on those point then next year you get a great deal on 10000 LED strings that run off DC and then you want to run DC though them all, are you gonna resolder them all?

if the same board could be used for both it would be a better solution overall.

looks its probably not practical to do. as i said just thinking out loud. but hey isnt that what this place is for :D

Peter

[P. Short]

The dropout current is not a parameter that is very well controlled. In addition, the opto also latches, usually at a much lower current level than the triac. Better to use a SSR that is intended for DC use.

Also, it's my understanding that the scheme used in the Lynx (full-wave rectifiers on the incoming power, MOSFETS driven on a PWM basis are used for switching the power) works the way that you want.

--

Phil

[Trepidati0n]

There is a way to get around the SCR or rectify and use a single FET method...and that involves back to back FET's. We do this quite often to select a certain source without the diode losses.