Abstract: The DC secondary output voltage of a high voltage switched-type power supply is regulated by automatically increasing or decreasing the amplitude of the primary circuit retrace pulse to compensate for variations in loading imposed on the secondary or output circuit. The automatic regulation is accomplished by the use of a passive saturable reactor coupled in a series with the primary winding of the step-up transformer. The saturable reactor has a saturation characteristic with a relatively low saturation level. Within the saturation limits, the saturable reactor provides a reservoir of energy which can be used to buck the peak voltage pulse applied across the primary, thus controlling the output voltage. The apparatus provides good regulation with minimum number of additional components.