| 摘要 |
PROBLEM TO BE SOLVED: To suppress wasteful power by connecting a commercial AC power source to a charging power circuit, when potential lowering of a power circuit is detected, and cutting the charging power circuit off from the commercial AC power source when restoration of the potential is detected. SOLUTION: The power circuit 10 of a parent apparatus 2 is charged by direct current beforehand for using it as an operating power source, when the apparatus is in a state of standing-by for a call from an entrance child apparatus 1, or in an operating state, and a DC voltage is fed to a main circuit 11 and a detector 12. The detector 12 monitors a state of power feeding to the main circuit 11, and detects a charged quantity of the power circuit. If the potential of the power circuit 10 to be detected by the detector 12 is a specified threshold level or higher, caused by the matter that consumption of DC current fed from the power circuit 10 is small, like the parent apparatus 2 in a standby state in which operation of the main circuit 11 is unnecessary, a switch 13 is opened by the control of the detector 12, and a power feeding line from a commercial AC power source 3 to a charging power circuit 14 is cut off. Consequently, generation of reactive power is prevented, and wasteful power is suppressed.
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