Sounds like you're using a transistor in an AC circuit, so half the time the transistor has reverse polarity on it. I just did a triac drive circuit using the MOC3023 opto coupler. For noninductive loads, it's real simple. See Motorola Ap Note AN780A, if you can find it... Harold On Tue, 7 Nov 2000 14:35:27 -0000 "John Walshe @Inpact" writes: > Hi guys, > I'm having a bit of a problem driving a triac from a pic. > The electrical main is 220Vac 50Hz. > I have the Vdd of the pic connected to the live and Vss is 5v less > than > live. > I have a PNP transistor: emitter to live, collector to triac > trigger,base > via resistor (1k) to the pic i/o pin. The base is also connected to > the live > via 10k resistor (to prevent false trigger at powerup). > > My theory is that with the pic i/o pin high the transistor is off > and > therfore high z to the trigger so no leakage current can trigger > it.Thus the > triac doesn't conduct. > With the pic i/o pin low the transistor is switched on and the > trigger gets > all the current it needs and the Triac conducts. > > The triac I'm using is a BTA12 from Philips (logic level driven > device). > > My target use is for a small motor but I'm using a lightbulb for > testing. > > The Problem: The bulb is always on! > > I thought I had all the bases covered but obviously I'm missing > something. > > Has anyone got an idea what this 'something' is. > > Thanks in advance > John > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ YOU'RE PAYING TOO MUCH FOR THE INTERNET! Juno now offers FREE Internet Access! Try it today - there's no risk! For your FREE software, visit: http://dl.www.juno.com/get/tagj. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu