| 摘要 |
PURPOSE:To surely light a discharge lamp when the lighting voltage of the discharge lamp is reduced with the elapse of the operating time by providing a voltage superimposition circuit control means increasing the output voltage of a voltage superimposition circuit in steps in response to the change of the cumulative operating time. CONSTITUTION:The magnitude of the output voltage of a voltage superimposition circuit 7 is controlled in response to the cumulative operating time of a discharge lamp 5, or the output voltage is controlled in response to the number of lighting occasions (number of high-voltage pulse application occasions) to prevent the defective lighting from occurring when the voltage change of the discharge lamp 5 is increased. When a new discharge lamp 5 is to be turned on, for example, a cumulative time detection section 9 is reset to the initial state by a reset means 10. The cumulative operating time is reset to 0 by this resetting, and a voltage superimposition circuit control section 11 controls the voltage superimposition circuit 7 to obtain the rated superimposed voltage. The discharge lamp can be stably kept on for a long time. |
