DEVICE FOR PROTECTION OF TELEPHONE LINE AGAINST SHORT CIRCUITS Russian patent published in 1999 - IPC

FIELD: telephone equipment. SUBSTANCE: short circuits in telephone line may occur in cases of line break, fault telephone set, and after prolonged pickup of telephone hand set. Delay gate outputs signal after given delay in order to release relay contacts and to switch user off communication line. Power supply of delay gate is provided by voltage generator, which is connected to telephone line in series through controlled thyristor gate. Power supply of relay windings which control release of relay contacts is provided by line wires through transistor gate, which is triggered by signal from delay line. Voltage to delay gate, and respectively to winding of polarized relay is supplied only in case of short circuit in telephone line. EFFECT: simplified design, decreased weight and size. 14 cl, 2 dwg