| 摘要 |
PURPOSE:To simplify system constitution by adding a maens giving directivity to a DC current to a talking line or a control information line on which the power in a terminal device is superimposed to protect damage to be caused to a transformer if mis-connection occurs in the line. CONSTITUTION:DC reverse flow preventing diodes 23-26 are inserted respectively to a transmission circuit 3 and a reception circuit 7 in a terminal device 1 of a terminal device connecting system. An exchange 2 having a reception circuit 4, transmission circuit 8, and a feeding line 6 is connected to the terminal device via talking lines 21, 22. Further, the polarity of the diodes 23, 24 is arranged in the direction from the device 2 to the terminal device 1, and the polarity of the diodes 25, 26 is directed from the terminal device 1 to the device 2 and each diode is made coincident with the current direction of the feeding circuit 6. If there exists mis-connection in terminals 13-20 of the talking lines 21, 22, the damages of transformers 9-12 are protected and the system constitution is simplified. |
