Hi! http://www.phys.ualberta.ca/~gingrich/phys395/notes/node71.html" [Broken]'s an electrical network for a diode OR gate. It says there that "[t]he 12 V battery does nothing until the power fails; then it takes over without interruption." I just wonder what eletrical circuits (closed loops) are there. I attached an image of how I think the loop looks when the 15V power supply works. But what about the battery loop in this case?