Telephone subset line switch or line interface circuit

摘要

The apparatus has a serial conductive path of a transistor (TR1) forming the line switch path. The base of the transistor is coupled to a control device (RD) associated with a telephone subset circuit for controllably switching the loop current when the transistor is serially connected in the loop current circuit in response to a hook-switch signal and at least one other subset function signal coupled to the control device input. - A further transistor (TRS) is coupled between the control device output and the initial transistor (TR1). An overcurrent protection circuit consisting of a resistor (R1) and two diodes (D1,D2) couples across the initial transistor so as to turn if off when the current rises.