Control circuit for a gate turn-off thyristor

摘要

To ensure higher operational reliability particularly for high-power gate-turn-off thyristors (20), a resistor (R5) is connected between gate electrode (G) and cathode (K) of the gate turn-off thyristor (20) and is monitored by means of an impedance detector (36) connected thereto. If the detector impedance drops below a predeterminable impedance limit value during the turn-off phase of the gate turn-off thyristor (20), an error signal is generated by an optocoupler (42) and a transistor (Tr1) located in its circuit and a light-emitting diode (D1) does not generate a no-error signal (76). This monitoring circuit also includes a direct-voltage source (6) from which the control voltages (7-9) for the gate turn-off thyristor (20) are taken. A switched current source (11-13, Tr2, D3) in the feed line to a turn-on thyristor (Tr2) for the firing pulse of the gate turn-off thyristor (20) can be used for improving the efficiency and the life of the control circuit. <IMAGE>