At 03:52 PM 3/9/2010, Xiaofan Chen wrote: >On Wed, Mar 10, 2010 at 1:23 AM, Dwayne Reid wrote: > > > I'm currently doing something similar with a 12f675 running directly > > from a 120Vac power-line input. > > >Just wondering how you power up the 12F675? Since it is pure AC, >there are different ways to do that. > >In my past job, I developed two universal power supply sensors, >one level sensor and one photoelectric sensor. Both run >from 20...250 VAC and 12...60V DC (actually 12...250V DC). >I have to use a full bridge rectifier and DC/DC converters >made of transistors. The two design are different, but >both use buck converter. The current requirement is not high >though (a PIC running slow and a relay). This version uses a standard capacitive-type power supply. However, the circuit topology is quite different in that the relay portion of the circuit has one power supply and the rest of the electronics has a separate supply. The two supplies are in series - I have lots of voltage available but limited current. Operating range for this particular product is 90 through 150Vac but there is no reason that the power supply wouldn't do 90 through 240Vac. It works rather well and I hope to publish the details in EDN or Electronic Design sometime soon. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist