| 摘要 |
PURPOSE: To improve the short circuit withstanding capacity of an IGBT by providing an MOSFET for reducing a short circuit current flowing through the IGBT by decreasing the voltage being applied to the gate thereof. CONSTITUTION: The circuit 10 comprises an MOSFET 14 connected with the gate G of an IGBT 12 through Zener diodes 13, 15 facing each other wherein the gate of the MOSFET 14 is connected with the gate of the IGBT 12 through a voltage divider comprising resistors 16, 18 and 20 having resistance of R1 , R2 and R3 . Point (a) between the resistors 16 and 18 is connected through a diode 22 with the collector C of the IGBT 12. If a trouble occurs when the IGBT 12 is conducting, a voltage to be applied thereto increases abruptly in the direction of DC line voltage and the diode 22 is biased reversely. Consequently, a gate drive begins to charge the input capacity of the MOSFET 14 at a rate dependent on the time constant and the voltage driver drives the MOSFET 14 into conducting state. |
