| 摘要 |
PROBLEM TO BE SOLVED: To lower a spike voltage at turning off, and to shorten the operation starting time by clamping a gate voltage at turning off to a voltage between a reverse bias voltage and a threshold voltage only for a constant time, and returning it to the reverse bias voltage after that. SOLUTION: If a signal changes from an on-signal to an off-signal, a transistor TR4 is turned on instantly, and a current flows between the base and the emitter of a transistor TR3 and turns it on. Following this, charging of the capacitor (input capacity) between the gate and the emitter of an insulated gate bipolar transistor IGBT is started toward a reverse bias voltage, and the insulated gate bipolar transistor IGBT starts its turn-on operation. Then when it reaches the zener voltage VZD1 of a zener diode ZD1, the transistor TR3 is turned off, and the charging into the input capacity of the insulated gate bipolar transistor IGBT is stopped and the voltage between the gate and the emitter is clamped. Here, the value of the zener voltage VZD1 is set to a value, which makes the gate voltage a value between a threshold voltage and the reverse bias voltage. If the transistor TR4 is turned off, if time set by a timer passes after inputting of an off-signal, a gate voltage clamping circuit GC is cut off, and the insulated gate bipolar transistor IGBT is turned off by the reverse bias voltage. |
