| 摘要 |
A power source (4) supplies a constant voltage to a gate voltage input circuit (6,7) which applies that voltage to the gate terminal of the insulated gate bipolar transistor (1) according to a control signal. A circuit (41,42) detects a collector-emitter voltage of the transistor (1) and an adjusting circuit lowers the control signal voltage according to the detecting circuit output to reduce the gate voltage. The adjusting circuit includes an emitter follower (44) passing a collector current according to its emitter-base voltage. The voltage is obtained by a bleeder (41,42) dividing the emitter- collector voltage of the transistor (1). If the gate drop operation continues for more than a set period the transistor may be turned off.
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