At 05:17 AM 1/24/2015, Isaac Marino Bavaresco wrote: >I studied your suggestion and improved the design. The circuit is >attached as a PDF. I can't help thinking that is has gotten way complicated. Maybe I'm=20 just not seeing some of your constraints. Question: why can't you just use a diode from CN1 to feed the=20 midpoint between T1 & T2? If you do your switching right, T2 is OFF=20 whenever you have input voltage to IC1. That is: a diode from CN1 to=20 the gate of T2. Add appropriate transient suppression. Same with monitoring the input voltage for dropout - simply look at=20 the voltage across IC1. Use a voltage divider from B-E of that=20 transistor to IC1 out to set the dropout voltage if 1 Vbe is too=20 low. The collector of that transistor also connects to the gate of=20 T2 to turn it OFF whenever there is sufficient voltage across IC1. I haven't checked boundary conditions when the input voltage is near=20 dropout. You will have to check those to ensure that your desired=20 switching occurs cleanly. dwayne --=20 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 --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .