| 摘要 |
PURPOSE:To reduce power consumption at the time of trouble and to prevent reliability decline of parts due to abnormal heat generation, by reducing talking current at the time of ground fault or battery trouble, in talking current supplying circuits. CONSTITUTION:At a talking current supplying circuit connected to a subscriber's circuit, etc., of an exchange device, talking current detecting circuit 21A and 21B having a fixed threshold level are installed to both the ends of both talking lines A and B, and a coincidence detecting circuit 28 which detects coincidence of detecting information of A and B lines, and a talking current limiting circuit are installed. Since outputs of the detecting circuit 21A and 21B become O level and 1 level, respectively, when a ground fault occurs, only a logical operation circuit 28-3 of the coincidence detecting circuit 28 becomes 1 level, and, by driving a photocoupler 26A-2, the electric current flowing through another photocoupler 26A-1 is set to a value between the threshold level S of the detection circuit 21A and the electric current In at the normal time. In this way, the electric current is reduced during the course of ground fault. When the battery is in trouble, a logical operation circuit 28-2 works and the talking current is reduced. |
