Power supply for circuit breaker static trip unit

Claim 1

In a circuit breaker electronic trip unit connected to receive rectified current inputs from individual phase current sensing transformers and including a burden resistor across which is developed a signal voltage proportional to the magnitude of the input current magnitude, a peak detector responsive to the signal voltage, at least one trip mode network processing the signal output of the peak detector pursuant to issuing a trip signal, and a driver circuit responsive to the trip signal for initiating energization of a trip coil operating no effect opening of breaker contacts, a power supply circuit for providing operating power for the peak detector, trip mode network, driver circuit and trip coil, said power supply circuit including, in combination: A. a power transistor connected between first and second regulated voltage buses; B. at least one storage capacitor connected between said first and second buses; C. a potential divider connected between said first and second buses for developing at a terminal thereof a monitoring voltage proportional to the regulated voltage across said buses; D. voltage threshold means responsive to said monitoring voltage; E. a regenerative trigger circuit operating under the control of said threshold means to maintain the voltage across said buses in regulation by switching said power transistor off when the regulated voltage falls below its regulated level to direct the input current flowing through the burden resistor into said storage capacitor to increase the charge thereon and by switching said power transistor on when the regulated voltage rises above its regulated level to shunt input current flowing through the burden resistor from said storage capacitor; and F. a diode serially connected in one of said first and second buses to prevent said storage capacitor from discharging through said power transistor while it is on.