TRIAC as AC regulator?

[Wahid_pk]

Salam: According to the data sheet of TRIAC (BT136-800) it can handle input voltage upto 800V. Can we use it to get fix output 100V from input 100V-500V. 10V up or down is not a problem for my project load of circuit is 300mA.

My actual problem is to derive 12v dc from AC 200V to 500V. My plan is first to regulate it at 100V through triac and than using transformer. If transformer can be eliminated that will be the best.

 

[edeca]

You could, that's how a light dimmer works. But reading a few topics from Google (e.g. this one) suggests it might not be the best idea if you are going to turn it into DC afterwards.

Also, my limited understanding suggests this solution would require a fixed input voltage. You'd be better off with a small PCB mount transformer, which can supply 300mA easily.

 

[BrownOut]

Better I think to put the transformer ahead of the triac. That's the way HP did it in my power supply.

 

[dougy83]

You can regulate it straight to 12V with just the triac. Just make sure you turn it on when the AC voltage wave is 12V approaching 0V (e.g. approaching pi and/or 2pi radians for a sine wave), otherwise you'll get the full 500V into your circuit if the triac latches on for more of the cycle. You could alternately use a transistor (FET or BJT is OK), which doesn't have the latching characteristic.

Disclaimer: Personally, I wouldn't recommend you doing this as it is potentially lethal. The output voltage will also not be isolated.