On 9/27/06, Alan B. Pearce wrote: > >1. I've never done PWM on 120V before. Can anyone recommend > >what type/value of semiconductor to use? I'd assume that a > >bipolar or darlington transistor won't be the best choice. > >A reference circuit would be awesome if someone can point > >me to something. > > I would think you will need a transistor suitable for the output stage of an > off-line switch mode power supply, seeing the string will be operating at > line voltages. Could be bi-polar or FET. An FET will probably require 10-15V > gate drive rather than be 5V driveable, and will probably require some form > of protection to stop drain-gate miller effect feeding undesirable spikes > back into the micro circuitry, while a bi-polar will require lower voltage, > but higher current drive, and again some form of protection against miller > feedback of spikes. Hmm....this is starting to get too far out of my comfortable area. Perhaps I'm looking at this problem the wrong way? I wanted to stay away from phase control on the LEDs as it didn't seem like a great choice, and it's not as easy as PWM for me to code. That said, TRIACs are easy for me to obtain and drive. So can anyone else offer any advice on PWM on 120VDC before I just abandon the idea? I really really don't want to give up on it... Thanks! Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist