A primary winding of a transformer is coupled to a source of input voltage and to a controllable switch. The switch is responsive to a first control signal for generating output pulses in the transformer secondary windings. A supply circuit is responsive to the output pusles and generates a first supply voltage. A capacitor charging circuit includes a thyristor that is coupled to one of the transformer secondary windings. The thyristor receives the output pulses for providing charging pulses to the capacitor for generating a second supply voltage. A control circuit is coupled to the thyristor for varying the number of output pulses occurring relative to a given number of charging pulses to regulate the second supply voltage.