FERNSPRECHSCHUTZSCHALTUNG

A circuit for protecting sensitive telephone equipment from voltage or current overloads on the TIP or RING line includes a resistor (R3) serially positioned in the line and a triac (THY1) triggered by a voltage differential across the resistor (R3). A pair of fast diodes (D1,D2) is positioned on the line adjacent to the telephone equipment for momentarily clamping the voltage on the line at that point between ground and the voltage supply of the equipment. The momentary clamping of the voltage creates the voltage differential across the resistor (R3) which triggers the triac. The fast diodes (D1,D2) are capable of passing current for a time sufficient to allow the triac (THY1) to begin shunting current to ground. An enhanced form of the protection circuit includes a second pair of diodes (D6,D7) extending in parallel with the fast pair of diodes (D1,D2) and positioned on the line between the pair of fast diodes (D1,D2) and the triac (THY1). Inclusion of the second pair of diodes (D6,D7) allows the circuit to utilize a triac (THY1) with a slower turn-on time and a higher on-state voltage.