| 摘要 |
PURPOSE:To foresee the breakdown of a gate turn-OFF thyristor by detecting the increased current emerging after the lapse of the anode current drop time of the thyristor at the gate turning OFF time. CONSTITUTION:The anode current ia of a gate turn-OFF thyristor 13 is detected at the gate turning OFF time, and the difference current DELTAia between the current ia(t1) when the decreasing rate becomes initially zero at t1 and the current ia (t2) emerging immediately after the time t1 after the current decreases, is detected. When the ratio of the ia(t1) and DELTAi1 falls within a predetermined range, an output signal Z is outputted from a discriminating circuit 17 to a current supply circuit 15, the gate current supply is stopped, thereby preventing the breakdown of the gate turning-OFF thyristor. |
