Logic Level Triac

[skimask]

I've played about with "disco light controllers" based around PICs around this time last year. Rather than use triacs or thyristors to drive the mains lamps I used solid state relays. These work in exactly the same way as a normal relay, but have no mechanical parts, all the switching is done optically. This has the advantage of keeping the 240v mains AC isolated from the 5v DC side of the board. The ones I used operated from 5v DC and has such a low draw current could be driven direct from the PIC without the need for a driver transistor. Do a search on e-bay or some of the surplus electronic sites, I picked up 8 for around £1 each.

Triacs are triggered by current rather than voltage, and as most PICs can sink / sorce 25mA you should be able to drive them direct from the PIC. However, have a look at http://ww1.microchip.com/downloads/e...tes/00958A.pdf which shows a triac used in a thermostat based around a PIC - the driver circuit (transistor) may be adapted to suit your needs.

I think I already know the answer to this one...but....
You can't do dimming with an SSR and PWM at the input, or can you?

My answer: The line frequency isn't high enough and it'll cause flickering as you lower the pulse width going into the SSR.

Correct? Worth a try? Might work if you're only using incandescent (resistive type) lights/loads, but LEDs and flourescent lights won't work.

JDG

[malc-c]

This is my understanding, but then I'm no expert. The problem you may have is that most thyristors and triacs use the "zero" switching method, ie in an AC environment they change state as the mains crosses from negative to positive phase (and vice-verce), so you have a 50 / 60 hz pulse to start with, and if you have a small PPm signal on the gate this may cause the flashing / pulsing often seen.