At 07:14 AM 6/1/2005, Wouter van Ooijen wrote: >A customer let the smoke out of a H-bride motor driver I made for him, >so now I want to add reverse-power protection. My standard anti-parallel >1N4004 won't do much good when connected to a lead accu, so I am >considering a series diode (1N4004, or a schottky). But now the back-emf >from the motor, which is fed to the power rail by the 4 diodes, has >nowhere to go. What is the solution to this? A big zener on the power >rail, for let's say 150% of the maximum power supply? If so, which >wattage would be needed? Or maybe a consensator? If you, what capcity >and what type? Or are there other solutions, maybe with a polyfuse? How much current does it have to handle? The two solutions that come to mind are: 1) reverse-connected MOSFET in series with battery, biased so that correct battery polarity biases it full on. (Bob Pease from National Semiconductor is the first person I saw mention this - he says that he should have taken a patent out on the concept!) 2) relay with NO contacts connected in series with battery. Coil fed with blocking diode from battery. Both techniques work very well - its a matter of cost, available space, battery consumption. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 21 years of Engineering Innovation (1984 - 2005) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist