Exchange station transmitter for communication with terminal, e.g. telephone, modem

摘要

The transmitter includes control electronics responsive to a loop closing pulse of the terminal. A bridge rectifier (11) is provided between the terminal leads of the exchange station. An electronic relay (14) is provided parallel to the ac side of the bridge rectifier (11). The switch (13) of the relay is connected in series with a current-limiting resistance (12). The relay switch is closed by the loop closing pulse from the terminal. When the loop current reaches a threshold value, the control electronics re-open the relay contact. The relay (14) is pref. an optoelectronic relay. A switching transistor (18) and a further transistor (17) may be connected in-series with the relay (14,15). The loop pulse then makes the transistors conduct. The transistor (17) is blocked when the loop current threshold value is reached.