Abstract: An electric current sensor, including a circular magnetic material core, an excitation coil wound around the magnetic material core, a supplemental excitation coil wound around the magnetic material core, a first excitation circuit that applies an alternating excitation voltage to the excitation coil, a second excitation circuit that applies pulsed voltages synchronized with rising edges and lowering edges of the excitation voltage, the pulsed voltages causing the supplemental coil generate magnetic fields having the same directions as that of the magnetic fields generated by the excitation coil, a current-to-voltage converter that converts a current flows through the excitation coil into a voltage, and a detection unit that detects respective timings when the alternating magnetic field in the magnetic material core is saturated in a positive direction and in a negative direction.

Abstract: A flux-gate leakage current sensor includes: an annular core; a coil wound around the core; a driving circuit which applies to the coil a voltage with a positive/negative symmetric rectangular wave so as to saturate a density of a magnetic flux of the coil while reversing a direction of the magnetic flux; a comparator circuit which compares a measured voltage changing according to a coil current flowing in the coil with a positive-side reference voltage and a negative-side reference voltage that are positive/negative symmetric to each other, and outputs a positive-side electric signal corresponding to a period in which the measured voltage is higher than the positive-side reference voltage and a negative-side electric signal corresponding to a period in which the measured voltage is lower than the negative-side reference voltage; and a determination circuit which compares the positive-side electric signal and the negative-side electric signal output from the comparator circuit.