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Abstract

An earth leakage breaker comprising a zero-phase-sequence current transformer for detecting a current difference on an AC line with respect to both positive (+) and negative (-) directions to sense an electric leakage of the AC line, a comparator for comparing an output voltage from the zero-phase-sequence current transformer with a trigger reference voltage, a delay for delaying the output voltage from the zero-phase-sequence current transformer by a desired period, a subtracter for subtracting an output voltage from the delay from the output voltage from the zero-phase-sequence current transformer, first and second level discriminators for discriminating levels of output signals from the comparator and the subtracter, respectively, first and second duration generators for generating durations in response to output signals from the first and second level discriminators, respectively, a first, pulse width generator for generating a pulse width corresponding to the duration from the first duration generator, a second pulse width generator for generating a pulse width corresponding to the duration from the second duration generator, an AND gate for ANDing the pulse widths from the first and second pulse width generators, and a trigger circuit for breaking the AC line by an output pulse width from the AND gate.

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