Protective circuit utilizing multilevel power supply output

Abstract

A power supply has both high and low voltage power sources connected to a common output terminal. A switching circuit is connected between the high voltage source and this terminal, the switching circuit being controlled by a control circuit. The control circuit operates in response to malfunction and temperature sensors when these sensors have outputs indicative of equipment operating conditions outside of predetermined ranges for each of the sensed parameters. When the control circuit is not being actuated by an output from one of the sensors, the switching circuit is actuated to connect the high voltage output to the output terminal. In the event, however, that one of the temperature or malfunction sensors senses a condition outside of range, the control circuit is actuated, thereby deactuating the switching circuit to remove the high voltage output from the output terminal, leaving low voltage output. The control circuit operates in conjunction with a timer-reset circuit which resets the control circuit cyclically after a predetermined timing cycle. With each resetting, the control circuit will be reactuated by one of the sensors only if an out-of-range condition still exists. However, if after any resetting of the control circuit, there no longer is an out-of-range parameter being sensed, the control circuit will remain deactuated so as to restore high voltage output.