Shutdown Protection Circuit for Peripheral Equipment
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
This article describes a shutdown circuit that senses a fault condition (overvoltage, overcurrent, etc.) and sinks a start current that is used to activate an "on/off" circuit. This circuit can be used to turn off a power supply. The supply remains off until the fault is corrected and the external start current is reset. In the figure, the shutdown circuit is identified by numeral 10. The occurrence of any fault condition causes the emitter-base junction of Q6 to be forward biased. Therefore, Q6 turns on and current flows into the gate of SCR Q7. This causes Q7 to turn on and sinks all of the current provided by the start signal. Under normal conditions the output of the comparator is high. This means the output stage of the comparator is an open circuit, and it cannot sink any current.