| 摘要 |
PURPOSE:To prevent trouble such as the waste of a power source if a thyrister is unnecessarily turned on by providing a control means which is operated on receiving output supply from a voltage monitoring means and controls a switching circuit to be turned off at the time of inverting actions. CONSTITUTION:In case the thyrister 12 serially connected to a flashing discharge tube 4 malfunctions owing to noise, etc., and maintains its on state, the voltage monitoring means 22 beings to monitor a voltage impressed on resistances 7 and 8 for charging a commutation capacitor 6 serially connected to a main thyrister 5. On the other hand, when the thyrister 12 continues its on state, it is maintained at high voltage. Consequently, after a prescribed time has passed since malfunction started, the voltage monitoring means 22 carries out an inverting action, whereby the control means 29 controls the switching circuit to be turned off. As a result, a current loop through the thyrister 12 and the resistances 7 and 8 for charging the commutation capacitor 6 is cut off to return the thyrister 12 to a turned-off state. Thus, trouble such as the waste of the power source can be prevented surely. |
