A radiation generating system for treating a coating on a substrate. A high voltage circuit provides power to a microwave generator that, in turn, supplies microwave radiation to drive a lamp. A current limiting device is connected between the high voltage circuit and the microwave generator, and a fault detector is connected to the high voltage circuit for providing an error signal in response to excess current being supplied to the microwave generator. A control is operative to interrupt a supply of AC power to the high voltage circuit in response to the error signal.