| 摘要 |
PROBLEM TO BE SOLVED: To provide a discharge lamp lighting circuit capable of avoiding occurrence of abnormal high voltage caused by wiring state of the secondary side when the secondary side of a transformer is in non-load state. SOLUTION: The discharge lamp 19 is made to be lighted by gradually changing the oscillation frequency of an inverter circuit 14 from the oscillation frequency of 200 kHz shifted from the resonance frequency of the secondary side of a transformer 15 to the oscillation frequency of 50 kHz at the time of regular lighting of the discharge lamp 19. When a prescribed high voltage can be generated in the secondary side such as no-load or overload, the oscillation circuit 13 is operated at 200 kHz. Thereby, a so-called secondary side resonance state in which the inverter circuit 14 and the secondary side resonance frequency of the transformer 15 coincide is not brought about. As a result, an abnormal high voltage is not generated at the secondary side of the transformer 15. Further, when a prescribed over-voltage exceeding an over-voltage judgement threshold established beforehand is generated, oscillation action of the oscillation circuit 13 is made to be stopped by detecting this. COPYRIGHT: (C)2007,JPO&INPIT |
