| 摘要 |
PROBLEM TO BE SOLVED: To improve life characteristics of a discharge lamp and provide a double countermeasure against low temperature, by setting up an applied voltage to rather low to such a degree to enable start-up at ordinary temperatures. SOLUTION: This device is provided with a resonance circuit 30 including a ballast inductor 32 connected in series, and a pre-heating capacitor 33 connected in parallel, with a discharge lamp 31. An inverter 20 energized by a direct-current power supply 10 and loaded with the resonance lighting circuit 30, and a control circuit 40 for changing the oscillation frequency of the inverter are provided. A first timer circuit 61 is provided for setting up a first oscillation- frequency changing period during which the oscillation frequency is changed in the forward direction that heightens a voltage applied to the discharge lamp after the power supply 10 is turned on. A discharge-lamp lighting detection circuit 80 is provided. A second timer circuit 62 is provided for setting up a second oscillation-frequency changing period during which the oscillation frequency is further changed in the forward direction, if lighting of the lamp is not determined by the circuit 80 after the first oscillation-frequency changing period has ended. Forward changes of the oscillation frequency is limited during the first and second oscillation-frequency changing periods. |
