Abstract: An off-power line switching mode power supply which employs current and voltage feedback and sensing converts primary rectified, unregulated high voltage to a number of regulated d.c. secondary voltages and a low frequency, high voltage output suitable for enabling ringing of standard telephones. Two high voltage field effect transistors connected in the half-bridge configuration power multiple output circuits via a capacitively coupled transformer. A pulse width modulator controls the high frequency switching times of the field effect transistors via a transformer-coupled drive circuit.