| 摘要 |
PURPOSE:To detect a response by a circuit simply convertible to IC without using a detecting circuit of high accuracy by detecting a response of an incoming subscriber by supervising both DC component value of a subscriber's line and current value of a current supply circuit. CONSTITUTION:A series circuit of electronic switches 1, 2, a resistance 7 and a call signal source 13 is connected to a subscriber's line 15 connected to a telephone set 12, and a response of an incoming subscriber is detected by a DC detecting circuit 18, and outputted as a response detecting output 26 through an OR circuit 25. Also, a line ground-fault protecting circuit 21 of a subscriber is connected to the subscriber's line 15 through a current supply circuit 9. By this circuit 9 and the circuit 21, an inflow of a call signal current to an equalizing resistance 10 to a subscriber of a short distance is increased, an electronic switch 6 is opened, and the call signal current is detected by a subscriber's line ground-fault detecting circuit 22. When it exceeds a prescribed value, a ground- fault detecting output 24 is generated, also provided to the circuit 25, and a response of an incoming subscriber is detected exactly by a simple circuit. |
