Abstract: An improved power supply is provided for circuit breaker applications and draws power from the power lines which the associated circuit breaker protects. The alternating current on the power lines is sensed by a current transformer and rectified by a full-wave rectifier. The full-wave rectified signal is alternately switched between a low impedance path, which does not provide power to the power supply, and a charging path, which does provide power to the power supply. During the major portion of the a.c. cycle, the full-wave rectified signal follows the low impedance path without loading the current transformer or distoring the current signal. However, near the zero crossings of the a.c. current signal, the low impedance path is opened so that the full-wave rectified signal charges a charging circuit. The charging circuit feeds a voltage regulator to provide output power from the power supply.