Electronic switch for selection pulse circuit in telephone - has thyristor turned on by resistor and off by transistor driven from RE circuit

摘要

The electronic switch consists of a thyristor (1) with its gate/anode path shunted by a turn-on resistor (3) and its gate/cathode path shunted by a controlled semiconductor (4). An auxiliary voltage source (2) is connected between the thyristor cathode and the controlled semicondcutor. The switch main current flows via the thyristor and the auxiliary voltage source. The controlled semiconductor turns the switch off and may be a transistor receiving the turn-off signal at its base. The turn-off transistor is turned on by a signal larger than the one needed to keep it on. An RC circuit (5) is used to produce this instantaneous larger signal.