| 摘要 |
PURPOSE: To prevent an allowable anode-to-cathode voltage from being dropped without making a device large-sized by a method wherein a GTO thyristor is turned off by using the electric discharge of a backup capacitor in the service interruption of an external controlled power supply and a low-resistance short circuit part is formed across a gate and a cathode for the GTO thyristor. CONSTITUTION: The loss of the supply of electric power from an external controlled power supply 19 is detected by a service-interruption detection part 21. A signal VOFF which instructs the output of a turn-off gate signal is output to an ON/OFF-signal composition part 13. A backup capacitor 22 backs up a reverse bias voltage required until a GTO thyristor is turned off due to the discharge of its changed electric charge. As a result, the GTO thyristor can be turned off surely. In addition, by the stop of the output of a reverse-bias-drop detection part 24, a make and break contact 25b for a contact operating-type switching circuit 25 is closed, and a low-resistance short circuit part is formed. As a result, it is possible to prevent an allowable anode-to-cathode voltage from being dropped. |
