the present invention features a voltage - limiting regulator for use with an ac generator having dc - excited fields . the ac output voltage from the generator is sensed and compared to a fixed reference voltage . an algebraic difference voltage representative of the sensed difference is amplified and applied to the dc field excitation input of the ac generator . as the dc voltage supplied to the field varies , the ac output voltage from the generator may be held constant under varying load conditions . the voltage - limiting regulator is particularly useful for vehicle - mounted , high power , single phase ac generators .