| 摘要 |
PURPOSE:To reduce the power for telephone input and the total power consumption per subscriber, by adjusting a DC resistor in a current supply circuit of an exchanger in response to a resistance of a subscriber line. CONSTITUTION:When a hook switch 4 is closed with off-hook and a DC loop between an exchanger and a telephone set is formed, a channel current determined with a voltage of a constant voltage power supply 1, resistance of resistors 2 and 3 and a variable resistor 6 and a DC resistance of a telephone set power supply circuit 11 flows to a subscriber line. A control circuit 10 compares a terminal voltage of the resistor 2 with a reference voltage of a reference voltage generating circuit 9 and when both the voltages are not equal, a trigger signal is outputted. Further, the variable resistor circuit 6 is operated with a trigger signal from the control circuit 10 so that a switch 7 in the variable resistor selects a plurality of resistors, and when the terminal voltage at the resistor 2 and the reference voltage are equal, the circuit 10 stops the transmission of the trigger signal and the switch stops the selection for steady state. |
