| 摘要 |
PURPOSE:To prevent deterioration of the service life of a discharge lamp by connecting a series circuit of diodes and a D.C. voltage source higher than the lighting-up voltage while lower than the start voltage of a discharge lamp to a switching element parallely, and clamping both end voltage. CONSTITUTION:A series circuit of a switching element SW1 and an impedance element Z2 is connected is parallel to a discharge lamp 1. A diode D is provided in series at a D.C. power supply 6 generating a D.C. voltage V lower than a start voltage Vst while higher than a lighting voltage Vla of a discharge lamp 1, and the series circuit of the power supply 6 and the diode D is connected in parallel to the switching element SW1. With the constitution, when the voltage Vst is applied to the discharge lamp 1, the diode D has continuity and the potential of the element SW on the discharge lamp 1 side is made lower V than the voltage Vst, thereby reducing stress. After lighting-up of the discharge lamp 1, the diode D has non-continuity to be equivalent to a value in the case where there is no series circuit of the power supply 6 as well as the diode D. It is thus possible to prevent deterioration in the service life of the discharge lamp through prevention of generation of asymmetrical current therein. |
