| 摘要 |
PROBLEM TO BE SOLVED: To provide a power supply switching system capable of accurately judging whether to perform remote power supply or local power supply to an NT(network terminator) corresponding to the state of a remote power supply current. SOLUTION: In the case that a detection circuit detects a sufficient current from a subscriber's line 4, a switch 21 is turned OFF and the remote power supply is performed. When the sufficient current from the subscriber's line 4 can not be detected, the switch 21 is turned ON and the local power supply is performed. Thus, corresponding to the state of the remote power supply current, whether to perform the remote power supply or the local power supply to the NT is accurately judged. In this case, as the detection circuit, a phototransistor constituted by a photodiode serially connected to a power feeding line and a transistor to be turned ON/OFF by receiving the emitted light of the photodiode is used and the phototransistor is also used for the changeover of a power source. |
