| 摘要 |
PURPOSE:To prevent the high voltage from being applied to a transistor and maintain good lighting by providing a control circuit turning off a switching element when the current from the switching element to a discharge lamp reaches a fixed level. CONSTITUTION:A control circuit 26 turning off a switching element 8 when the current from the switching element 8 to a discharge lamp 9 reaches a fixed level is provided, and the on-period of the element 8 at the time of preheating start is shortened. The current from the element 8 to the discharge lamp 9 at the time of preheating is larger then that at the time of lighting, thus the on-period of the element 8 at the time of preheating start can be made shorter than that at the time of lighting. The voltage of a preheating capacitor 10 is not increased, the voltage across a collector and an emitter when the element 8 is cut off is suppressed, the element 8 with the low withstand voltage can be used, and the occurrence of failures is prevented. The high voltage is thereby prevented from being applied to a transistor at the time of preheating, and good lighting is maintained. |
