| 摘要 |
PURPOSE:To foresee the breakdown of a gate turn-OFF thyristor by detecting the decreased voltage initially of a voltage between the anode and the cathode of the thyristor at the gate turning OFF time. CONSTITUTION:A voltage Va between the anode and the cathode of a gate turn- OFF thyristor 13 is detected at the gate turning OFF time, and after the voltage Va is risen, the difference voltage DELTAVa between the voltage Va(t1) when the rising rate initially becomes zero and the voltage Va(t2)emerging immediately after the time t1 is detected. When the ratio of the Va(t1) and the DELTAa falls within a predetermined range, an output signal Z is outputted from a discriminating circuit 17 to a gate current supply circuit 15, the gate current supply is stopped, and it can prevent the breakdown of the thyristor, thereby preventing the breakdown of the gate turning-OFF thyristor. |
