Automatic protection circuit for switching system - includes discharge tubes and varistor elements providing protection against both voltage and current overload

摘要

The overvoltage and overcurrent protection circuit is connected between the lines of a communications switching circuit (T1, T2) and the subscriber lines (L1, L2). The four lines and an earth line (G) are formed on a printed circuit board (10) with a predetermined spacing. A gas discharge tube is connected between the subscriber lines (L1, L2) and earth. Varistors (11, 21) are connected in parallel with the gas discharge tube and coils of resistance wire (13, 23) are also connected, wound on reversible memory effect alloy carrying mobile connections (12a, 22a). Half of each resistance wire is wound in the opposite sense to the other half.