| 摘要 |
PURPOSE:To improve the efficiency of telephone line of an exchange, by restoring a telephone line caught at a converter because of the power supply interruption of a PCM transmitter. CONSTITUTION:When the power supply of a PCM transmitter is interruted, it is detected at a power supply interruption detecting circuit 29 and a logical ''1'' level is inputted to a timer circuit 28 as the detecting signal. Then, logical levels ''0'', ''1'', ''0'' are outputted respectively to the outputs of inverters 30, 31, 32, resulting that a logical level ''1'' is outputted to an output of a driving circuit 19. Thus, the operation of a relay 18 is stopped with a time constant C1XR1 of the timer circuit 28. Thus, the connection of relay contacts 18-1, 18-2 is turned off, an earth line 21 is opened from ground 20 to restore the line. |
