Abstract: In a power supply for an arc lamp in which a power source feeds an inverter consisting of a bridge network of field effect transistors, the current to the inverter is controlled by a switching transistor in accordance with the voltage applied bridge network in such a way as to maintain a constant power level over a specified operating range. A master oscillator and associated divider circuits provide a clock for controlling the switching transistor and pulses for driving the field effect transistors of the inverter at a frequency which is a submultiple of the clock frequency.