| 摘要 |
PURPOSE: An apparatus is provided to operate as a direct current power supply having a function which transmits output voltage change request data to a direct current power supply device while maintaining a two wire direct current power input line. CONSTITUTION: A control microcomputer(U2) controls a voltage applied to a thermoelement based on an inner temperature of a storage room sensed by a temperature sensor(TH). When a high level signal is outputted to a first output terminal of the control microcomputer(U2), a transistor(TR) and an FET are turned on and off so that a voltage is not applied to a thermoelement. When a low level signal is outputted to a first output terminal of the control microcomputer(U2), a transistor(TR) and an FET are turned off and on so that a full voltage is applied to an input terminal of the thermoelement. When a normal current flows through a load of a power supply device, an output of a comparator(U4) is low. When a load current does not flow, since a positive input terminal voltage of the comparator(U4) becomes greater than a negative input terminal voltage, the output of a comparator(U4) is high.
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