Overvoltage protection circuit for telephone exchange - has zener diode and triac circuits controlled by overvoltage detector

摘要

The overvoltage protection circuit includes line protection devices (PR1,PR2) for each wire of the telephone line (1,2). Each circuit includes a positive temp. coefficient of resistance element (CTP1, and 2) placed in series in the line. A zener diode (D21 and 2) is connected between the line and a potential (V) with a triac (TR1,2) in parallel with the diode. A fault detection circuit (DFP) detects any voltage surge on the line and controls the two protection devices (PR1 and 2). The fault detection circuit has inputs (E1,E2) connected to the gates of the two triacs. The inputs are connected to the lines before the protection devices which in turn are before the terminal circuit (CY) of the line. The overvoltage detection circuit includes two correcting cells (R5C1 and R13C2).