Retriggerable monostable multivibrator quickly discharges power-supply capacitor

摘要

Universal power supplies must work from mains power lines ranging from 90 to 264V ac at 50 or 60 Hz. Directly rectifying the input voltage charges the filter capacitor to 120 to 370V dc. Such voltages present a serious threat to personnel who are prototyping or repairing the power supply. It is desirable to discharge the filter capacitor when mains power is off so workers can safely deal with the power supply.