ADDITIONAL LINE COUPLING CIRCUIT TO AN INTERCOM TELEPHONE SET

摘要

An additional signalling line coupling circuit for an intercom station has a DC/DC decoupling converter and opto-electronic signal couplers. The circuit comprises the additional line(LC), the intercom telephone set(PI), a d.c. line uncoupling circuit (CC), a transmitter(OC1) and a receiver (OC2). The uncoupling circuit is a d.c.-d.c. current inverter. The transmitter is composed of an optocoupler comprising a phototransistor(PL1) which controls a transistor(T1) connected in series with one wire(L3). The receiver is composed of an optocoupler(OC2) comprising a lightemitting diode(D2) connected in series with another wire(L4).