On 9/11/06, David VanHorn wrote: > On 9/11/06, Lee McLaren wrote: > > > > I remember once seeing a circuit for a triac or SCR preregulator for a > > DC power supply but can no longer find the circuit. It was in the form > > of the bridge rectifier and used and error feedback from the output of > > the final regulator so that the final regulator had a pre-set voltage > > drop to keep power dissipation down. > > > I did that in a printer design, wasn't hard. Basically, take a "light > dimmer" sort of circuit, and apply the output of a voltage comparator, so > that if your voltage is high enough, you skip the next half-cycle. Bridge > rectifier on the front end, and SCR between that and the filter cap. Maybe the SCR in front of the bridge on the AC path, or two thyristors as half bridge and two diodes as other half bridge. Else how you fired off the SCR as long there is no zero cross (or lower than sustaining current of the SCR) current on the filter capacitor ? Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist