Abstract: To reduce the cost of insulation in a high-voltage power supply capable of constant current or constant power operation, the power supply includes an optical self-powered feedback circuit from its high-voltage section to the low-voltage section to control the output of the power supply. The feedback circuit includes within the high-voltage section of the power supply: (1) a sensing circuit for obtaining an amplitude modulated signal related to current flowing through at least certain output terminals; (2) a voltage-to-frequency converter for converting the amplitude modulated signal to a frequency modulated signal; (3) a pulse shaper for generating pulses having a duration of less than 3 microseconds to reduce power consumption; and (4) a light emitting diode. Light from the diode is transmitted to a low-voltage section where it is utilized in the feedback network. The high-voltage feedback circuitry utilizes less than 75 microamps.

Abstract: To detect a ground fault, the alternating current leakage current to common AC electrical ground is sensed across a resistor and applied to one input of an analog gate. The analog gate is opened by the positive going voltage from the high-voltage secondary of the power supply transformers between 7 degrees from the crossover point and 103 degrees to pass only that portion of the potential representing the alternating current leakage current which is in phase with the potential on the secondary windings of the power supply transformer and thus provide a signal representing the real component of the AC impedance to ground. A reference preset level of impedance and the signal from the analog gate are compared to provide a signal whenever the real component of the AC leakage current exceeds the preset value.