Tried this circuit It does power the circuit if 12 volt is removed the 9v battery takes over, the only problem is that it resets the pic processor. The pic is running a countdown that I need to maintain. Steve -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Eoin Ross Sent: Wednesday, January 30, 2002 12:24 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]:Battery Backup? How about placing a diode in a trace from the 12V to the input of the regulator ... and another from the battery to the input of the reg. When the the 12V drops the power will be supplied by the battery. Does anyone see a problem with the reverse current through the battery diode damaging the battery? >>> kcer@COGECO.CA 01/30/02 11:48AM >>> Can anyone point me to any design notes on a regulator or circuit that will switch my 5volts to a 9v battery to power the 16f84 chip when the incoming 12v power is missing? Regards, Steve -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body