Patent ID: 7031131

Claim:
An over-current protection device for shutting off power to a load when an overloaded current flows, comprising: a switching element for switching a current from a power-supply source to the load, a current detector for detecting a current supplied from the power-supply source to the load, and a controlling power-supply source for supplying power to each of the switching element and current detector, wherein said current detector includes magnetism detection elements having a magnetic impedance effect and corresponding to phases of the power-supply source; AC-current supply means for applying an AC current to each magnetism detection element through one oscillating means and a first switch corresponding to each magnetism detection element; bias-current supply means formed of bias coils wound on the respective magnetism detection elements, bias-current applying means, and frequency-dividing means connected to the oscillating means via a third switch and dividing a frequency output from the oscillating means for supplying a current having different polarities to the bias coils based on first and second timings; wave detection means corresponding to the magnetism detection elements for converting an impedance variation into a voltage and for passing a peak of the voltage; second switches corresponding to the wave detection means for selecting an output of the wave detection means; first holding means for holding an output of the selected voltage of the wave detection means; two fourth switches for selecting the held voltage based on the first and second timings; two second holding means for holding the two selected voltages; and amplifying means for amplifying a difference in outputs of the two second holding means, and the current for each phase is detected based on selective operations of the first, second, third, and fourth switches.