Preface: I am designing a UPS such that if the AC main fail the device can continue to run for at least 10 days. My goal here is to make a design that can last years off a non-rechargeable battery. When starting this I originally thought to use a comparator, but after looking/googling I found that the diode approach was superior.
Design: What: A 3.3 Volt .5 Amp UPS(Uninterrupted Power Supply)//I know you guys like numbers :)
1) Use a diode or schottky diode?
schottky diode pros - I will enjoy the efficiency on the low voltage drop when operating from the battery
schottky diode cons - The higher reverse leakage current will decrease the lifespan of the battery which is my biggest design constraint.
2)Is this sufficient with regard to the battery not supplying current back towards the mains? Should I include a diode from the mains towards the load?
3) Would it make more sense for the back up power to come after a voltage regulator? I know that AC mains can fluctuate quiet a bit so this could remove any instance were the battery may engage when its not needed.
4) Are there cheap/simple alternatives to the diode approach that could provide superior results to my proposed method?