/diy/ - Do It Yourself

>>1433675
try this. it conducts the higher of the two voltages to the load and prevents the higher voltage supply back-feeding into the lower
caveat: you need the main supply to be a bit higher in voltage than the backup supply, half a volt should be enough
caveat2: the Schottky diodes will drop a little bit of voltage. regular silicon diodes e.g. 1N400x will drop about twice as much for the same current, but you could use them in a pinch