Circuit to maintain power to a 12volt fridge in a car from a permanent power outlet but to switch off if battery drops to 12.5 volts, so avoiding flattening the battery but still allowing the fridge to stay powered if the car's engine is stopped for a long time. Unit switches on at 13.5 volts and switches off at 12.5 volts. 5volt ref is a voltage reg and the supply can be adjusted from zero up to 15 volts (and beyond)
