| 摘要 |
PROBLEM TO BE SOLVED: To detect the short-circuit current in a household electric appliance so as to discriminate it from the load current thereof, by processing adequately through an operating circuit the digital voltage values outputted from an A/D converter circuit to output plural deciding values, and by comparing the summed value of the plural deciding values with the threshold. SOLUTION: A microcomputer 11 has an A/D converter circuit 4, an operation circuit 12, a register circuit 13, and a circuit-break output circuit 6. After the division of the output voltage of a rectifier circuit 3, the A/D converter circuit 4 converts it into a digital voltage. The operation circuit 12 processes the digital voltage generated correspondingly to the half period of a commercial frequency voltage to add to the resultant a deciding value stored in the operation circuit 12. The register circuit 13 discards in every unit time its oldest decided value and reads in it its latest deciding value outputted from the operation circuit 12 to store always in it its plural new deciding values. The circuit-break output circuit 6 reads from the register circuit 13 the plural new deciding values to sum them, and when the summed value exceeds a threshold, the circuit-break output circuit 6 decides it as the occurrence of a short-circuit to output a sensing signal. Thereby, the fault current in a household electric appliance can be discriminated from its load current.
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