| 摘要 |
PROBLEM TO BE SOLVED: To ensure the safety and to supply desired power by supplying power of a low voltage to digital subscriber lines and selecting a high voltage power supply when a DC loop formed is detected by local power supply stop of a network terminator connecting to subscriber terminal equipments. SOLUTION: When a network terminator 2 connecting to a subscriber terminal equipment 3 stops local power feeding, a power failure detection section 10 closes a contact 8 to allow a feeding circuit 1 to form a DC loop via a phantom feeding section 9. A loop detection section 4 of the feeding circuit 1 detects the DC loop based on a current flowing to a constant current circuit and a voltage across the constant current circuit or a line voltage of a digital subscriber line, a feeding voltage changeover section 5 applies a low voltage V2 to the digital subscriber line 12 in the case of local feeding of the network terminator 2 and when the section 5 detects the DC loop formed by stop of local feeding, a high voltage V, is selected and a high voltage power supply is fed to the digital subscriber line 12. |
