Patent ID: 7764474

Claim:
An Earth Leakage Circuit Breaker (ELCB) having a switching unit ( 10 ) for automatically cutting off supply of power from an electrical circuit under control of a control unit ( 50 ); a zero-phase current transformer ( 20 ) for detecting leakage current of an electrical circuit; an amplifier for amplifying voltage of the leakage current received from the zero-phase current transformer ( 20 ); a detector ( 40 ) for rectifying and smoothing the leakage current received from the amplifier ( 30 ) and generating leakage voltage; the control unit ( 50 ) for determining whether leakage occurs by comparing the leakage voltage from the detector ( 40 ) with reference voltage and automatically controlling operation of the switching unit ( 10 ); and a power supply controller ( 60 ) for controlling supply of power from the electrical circuit to the respective elements, comprising: a voltage divider ( 70 ) for dividing and detecting voltage of the electrical circuit; a synchronization signal generator ( 80 ) for converting the detected voltage from the voltage divider ( 70 ) into a square wave synchronization signal; and a synchronous detector ( 90 ) for synchronously detecting, rectifying and smoothing the leakage current received from the amplifier in synchronization with the synchronization signal from the synchronization signal generator ( 80 ) and then generating net leakage voltage; wherein the control unit ( 50 ) determines whether leakage occurs by comparing the leakage voltage from the detector ( 40 ) with the reference voltage and automatically controls the operation of the switching unit ( 10 ), and determines whether leakage occurs by comparing the net leakage voltage from the synchronous detector ( 90 ) with net reference voltage and automatically controls the operation of the switching unit ( 10 ).