Patent ID: 7505291

Claim:
An AC/DC converter comprising: a rectifier circuit for converting an input alternating current (AC) power source to a direct current (DC) power source; at least one restraining unit coupled to the DC power source of the rectifier circuit, the restraining unit comprising a resistor and a switch connected in parallel; and a power interruption detection circuit for detecting whether or not the input AC power source is regular, the power interruption detection circuit comprising: an AC synchronous signal detection circuit connected between the input AC power source and the rectifier circuit to provide a full-wave voltage signal; an integrating circuit connected to the AC synchronous signal detection circuit to receive the full-wave voltage signal and to charge or discharge a capacitor based on the full-wave voltage signal; and a comparison circuit having a first input terminal connected to the capacitor of the integrating circuit to obtain a voltage level of the capacitor; and a second input terminal receiving a default reference value so that the comparator compares the voltage of the capacitor with the default reference value the switch of the restraining unit should be turned on or turned off; wherein when the input AC power source is interruptive, the comparison circuit outputs a signal to change a state of the switch in the restraining unit to make the resistor of the restraining unit to restrain current; and wherein the integrating circuit comprises a transistor having a base connected to the AC synchronous signal detection circuit to receive the full-wave voltage signal and having an emitter and a collector; the capacitor connected to a power source through a resistor, and connected in parallel to the collector and the emitter of the transistor.