DV/DT Protection circuit device for gate turn-off thyristor

Claim 1

A dv/dt protection circuit device for a gate turn-off (GTO) thyristor which has a gate, an anode and a cathode and which is turned on in response to a gate turn-on signal and turned off in response to a gate turn-off signal from a gate turn-off (GTO) signal source, said circuit device comprising: a snubber circuit connected in parallel with said GTO thyristor; a saturable reactor connected in series with said GTO thyristor and saturated by a load current flowing through said gate turn-off (GTO) thyristor and said saturable reactor; and means for restoring said saturable reactor to a nonsaturated condition; wherein said saturable reactor is constituted by a ring core, a first conductor coupled to said anode of said GTO thyristor passing through said ring core, said load current flowing through said first conductor; wherein said restoring means includes a second conductor passing through said ring core, said second conductor coupling said gate of said GTO thyristor to said gate turn-off signal source; and wherein a gate turn-off current from said gate turn-off signal source flowing in said second conductor produces a magnetic flux in said ring core which opposes the magnetic flux produced in said ring core by said load current flowing said first conductor; whereby said circuit device controls the dv/dt applied to said GTO thyristor at the time of turn-off.