| 摘要 |
PURPOSE:To limit power consumption in a two-wire power receiving channel board only to the one caused by a loop current by performing power supply by separating the loop current from a telephone exchange by using a DC-DC converter. CONSTITUTION:When the two-wire power receiving channel board 6 is being used, a closed loop state is set between a chip wire 9 and a ring wire 8 by a DC loop signal sending circuit 1, then, the loop current flows. The current is separated from a loop by a DC-DC switching circuit 2, and a voltage of positive side is applied on the anode terminal of a first diode 4. By setting the output voltage of the circuit 2 higher than that of the power source 7 of a local station de vice, the power source of the internal circuit 3 of the two-wire power receiving channel board is supplied from the circuit 2 via the diode 4 at the closed loop state. When an open loop state is set by the DC loop signal sending circuit 1, no loop current flows between the chip wire 9 and the ring wire 8, and the output voltage of the circuit 2 goes less than that of the power source 7. |
