| 摘要 |
PROBLEM TO BE SOLVED: To prevent useless power from being consumed by starting a power supply of an energy-saving interphone system after a call button of a doorphone slave set is depressed and stopping the power supply when a call time expires or at the end of a speech. SOLUTION: The energy-saving interphone system where an interphone master set 1 having an interphone control section 2 and a switching power supply 4 and the doorphone slave set 3 having the call button 13 are interconnected and the interphone master set can make a speech with the doorphone slave set in response to the call from the doorphone slave set. The switching power supply is connected to an AC power supply 15 and the call button. The interphone control section is provided with a light emitting diode 14 that outputs a power supply start signal to start the switching power supply when the call button of the doorphone slave set is operated and the interphone control section is called and that outputs a power supply stop signal to stop the switching power supply when the call time expires or the speech is finished. The switching power supply is provided with a photo transistor 12 that starts the switching power supply by the power supply start signal and stops the switching power supply by the power supply stop signal.
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