At 09:20 PM 2/27/2005, Russell McMahon wrote: >>>Wouldn't it be better to eliminate R4 altogether and put the zener >>>at the base of Q8? > >NO! >The zener is not principally to limit the drive voltage level - its job is >to clamp transisents on the gate coupled in by eg the Miller capacitance >from the Drain. Placing it elsewhere removes this protection and FET death >has been know to follow. I understand your reasoning but offer the following for consideration: Placing the zener at the base of Q6 still allows it to clamp those gate transients via D1. Admittedly, R4 limits the zener's effectiveness but using low values of R4 (or replacing R4 with a ferrite bead) should minimize the problem. FWIW, I'm using a 1n5819 schottky diode for D1 - I've had problems with 1n4148 as suggested by many of the app-notes using this circuit. You bring up good points, Russell. I'll spend some time with the DSO and see what I can see on those gates when the high-side switches operate. 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