| 摘要 |
PURPOSE:To eliminate mutual interference even if plural telephone sets are connected to one line and to attain release of privacy call by providing a rectifier circuit, a DC closing circuit, a control circuit controlling a current of the DC closing circuit and a stabilizing circuit operating stably it. CONSTITUTION:The side tone from a transmission circuit 23 to a reception circuit 24 at talking is reduced to some degree by a balancing circuit 25. In releasing the privacy call of line in this state, a DC flowing to a DC closing circuit 20 is halved and a terminal voltage of the line is decreased and when the line terminal voltage in the control circuit 21 starts decreasing, a transistor (Tr)36 is turned OFF, a Tr37 is turned ON and an emitter-collector voltage of a Tr38 is increased, then the line terminal voltage is not decreased. Since the stabilizing circuit 22 changes gradually the Tr36 from ON to OFF, the line voltage is not decreased, the reception circuit 24 and the transmission circuit 23 keep stably operating and the release of privacy call is attained. |
