| 摘要 |
PURPOSE:To reduce a surge voltage by decreasing the current of a GTO as a self-extinguishing type semiconductor element to an overcurrent defect and turning it OFF, thereby reducing the load of the GTO. CONSTITUTION:When a main circuit current abruptly increased due to a malfunction of a load 9, a control signal is outputted from a level detector 21 to a drive circuit 22, which applies a firing pulse to a thyristor 12. Thus, the thyristor 12 is conducted, and the charge stored in a capacitor 26 is discharged. This discharging current flowed in the discharging circuit of the capacitor 16, a reactor 22, the thyristor 12, an inverter bridge 8 and the capacitor 26 in reverse direction to the main circuit current. Then, the output from the detector 21 due to the detection of the overcurrent is applied to an OFF drive circuit 20, and the GTOs start turning OFF. At this time the main circuit current is already decreasing. |
