At 07:37 AM 9/7/2005, Russell McMahon wrote: >This design works superbly in practice. I haven't quite finalised >it. Said reverse protection diodes may yet appear, but probably not. >Oscilloscope will tell. Circuit is drawn "strangely" to meet >certain drawing constraints caused by a hobbled antiquated PCB >package. After next week my circuits may never look like this ever again :-). I have some minor suggestions that might reduce component count slightly: Approach #1: Eliminate D31, D32. Move lower ends of R41, R46 to bases of Q12, Q22 and reduce to 10K or lower. Disconnect lower end of R34 from D41, D42 and move it to incoming Vbatt. Move D41, D42: anodes are tied to emitters of Q32, Q33 and R33. Connect cathodes to collectors of Q11, Q21. Idea is that the voltage regulator is enabled by Q11 or Q21. Advantage of this is there is no leakage path to gnd - quiescent current should approach 0. Approach #2: Your circuit as posted: use a resistive sum to turn on the voltage regulator instead of D41, D42. In other words, replace D41 & D42 with two resistors, R34 is now a short. This depends on the micro having enough sink capability to ensure the side that is off remains off. 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