| 摘要 |
PURPOSE:To surely turn off a gate turn-off thyristor GTO provided with an inductive load in the cathode side by providing a transistor TR between the gate and the cathode of the GTO and selectively turning on this TR by a turning-off pulse in accordance with the potential of the cathode of the GTO at the time of turning-off. CONSTITUTION:The second TR Q70 for turning-off is provided besides the first TR Q40 for turning-off. In case a pulse is applied from a power source 82 for turning-off is applied to switch a GTO 2 from the turning-on state to the turning-off state, the cathode potential of the GTO 2 is reduced from a value approximately equal to a voltage Vcc of a power source 70 for load. The turning-off pulse has two kinds of supply path, namely the first path passing a diode 64 and the TR Q from the power source to the earth potential and the second path passing a diode 65, the TR Q70, and a cathode potential VK applying part of the GTO 2 from the power source 82 to the earth potential. the TR Q70 is turned off and the turning-off pulse flows to the first path if the cathode potential VK of the GTO 2 is higher than the value according with an equation I, but the TR Q70 is turned on and the pulse flows to the second path if the potential VK is lower than the value according with the equation I. |
