| 摘要 |
PROBLEM TO BE SOLVED: To exclude unnecessary consumption of a commercial power source by discriminating presence of phantom power feeding from the side of a line terminating device and switching whether or not the phantom power feeding is to be performed to the output of a constant voltage power source. SOLUTION: When a terminal device is connected, a power feeding presence/ absence discriminating part 17 discriminates whether power is supplied from a line terminating device (DSU) 2 to the terminal device and displays the discriminated result on a power feeding presence/absence display part 18. Therefore, from display on the power feeding presence/absence display part 18, a user can recognize whether a power supplying device 1 is required for this terminal device. When the power supplying device 1 is not required, this power supplying device 1 is detached, and the terminal device is directly connected to a bus 3 or a DC constant voltage generated from a commercial power source 5 is prevented from being supplied to the side of the terminal device by a constant voltage power source part 13 through turning off of a power supply changeover switch 14. When the power supplying device 1 is required, a DC constant voltage is supplied by turning on the power supply changeover switch 14.
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