| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem, where a short circuit current cannot be detected surely if the short circuit current is small when an IGBT device is short- circuited and hence an overcurrent cannot be cut off. SOLUTION: An inductance component of an inductance 70 of a main circuit including wirings from IGBT devices 1 and 2 to electrolytic capacitors 4 and 5 is increased. When the N-side IGBT device 2 is short-circuited while the P-side IGBT device 1 is in an ON-state, if the main circuit inductance 70 is increased, a voltage Ldi/dt is generated by the main circuit inductance 70 and the voltage VCE of the N-side IGBT device 2 is gradually lowered. As the voltages VCE of the P-side IGBT device 1 and the N-side IGBT device 2 are low, a feedback capacity is large and, if the saturation by a short circuit current is started, a displacement current is made to flow from a collector to a gate, a gate voltage is elevated, and the short circuit current is increased to reach a detection level of a CT 6. By the detection of the CT 6, an overcurrent can be cut off easily. |
