Protection and input circuit for telecommunications line - has two stages of overload reduction to protect exchange from lighting or other abnormal signal

摘要

The protection circuit consists of a series/shunt circuit, a shunt/series circuit (PC2), and two integrated circuits which connect the line to the digital exchange circuits. The two wires of the transmission line are each connected to spark gaps which flash over to earth if the voltage on the lines exceeds 1,000 volts. The lines are then connected via positive temp. coefft. resistors to two semiconductor surge arresters. The resistors and surge arresters limit the voltage passed to 250 volts and the current to 150 mA. Further temp. correction is achieved by a third resistor connected to the second of the two integrated circuits. This unit is used to protect telephone or other telecommunication exchanges from damage caused by lightning or other abnormally high-amplitude signals occuring on a two-wire transmission line.