Placing the SCR in a FW rectifier seems to be a worse solution (to me) than using a triac. You'll get two diode drops plus the SCR drop, which I believe would be considerably higher than the drop on a triac. Also, the drive circuit floats a bit wildly since the negative side of the bridge is now alternately connected to each of the AC terminals of the bridge, depending on line polarity. With a triac, you need to pull the gate towards MT2 to turn it on, and towards MT1 to turn it off. In the light dimmers I design, we typically have a "pull down resistor" between the gate and MT1. We then have an opto triac with a resistor (and a few other parts) to pull the gate up. Works well and is pretty cheap... Harold Harold Hallikainen harold@hallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm On Fri, 14 May 1999 11:38:07 -0500 Lawrence Lile writes: >The solution proposed in this is really interesting for a project I'm >on. >Placing the SCR inside a full wave bridge is a neat trick. > >In this arrangement, the full wave bridge obviously has to handle the >dfull >load current of the load. What about the load on the SCR? Is it also >the >full load current, or something larger? > > > > > >-----Original Message----- >From: Peter van Hoof >To: PICLIST@MITVMA.MIT.EDU >Date: Thursday, May 13, 1999 6:14 PM >Subject: Re: Driving Back to Back SCR's from PIC or Where do I Find a >Cheap >Triac > > >>-----Original Message----- >>From: Jim Ruxton >>To: PICLIST@MITVMA.MIT.EDU >>Date: Thursday, May 13, 1999 12:20 PM >>Subject: Driving Back to Back SCR's from PIC or Where do I Find a >Cheap >>Triac >> >> >>>Hi Everyone, >>> >>> I'm trying to figure out how to drive 2 inverse parallel SCRs. >From a >>>PIC to control a full wave AC load. I am using a cheap and dirty non >>>isolated power supply so my pic ground is sitting at neutral. >Driving >>>the one SCR that has its Cathode on the neutral line is no problem >but >>>driving the one that has its' Anode attached to neutral is the >problem. >>>I would use a triac but can't find one as cheap as the two SCRs. If >any >>>one knows where to get a cheap sensitive gate triac in a TO92 >package >>>for about 8 cents in quantity of 250K I'd love to hear about it or >knows >>>how to drive a full wave AC. load with one SCR from a PIC using a >>>nonisolated supply , even better. >>>Thanks >>>Jim >>> >>>------| |--- >> >> >>how about this solution >>http://www.vertonet.com/members/pvh/scr.pdf i'm also ascii art >impaired but >>can use drawing software >> >>basicaly a scr in a full wave bridge in series with the load >>get power for the pic from the other side of the load with diode, cap >and >>resistor in series. >> >> >>Peter > ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]