| 摘要 |
PROBLEM TO BE SOLVED: To prevent circuit damage caused by a continuous heater current resulting from the failure of discharge lamp lighting. SOLUTION: Current is caused to flow in a resonance circuit 5 so as to light a discharge lamp 1 by turning off MOSFETs 21, 22 constituting an inverter bridge through drive signals D1, D2 from a drive circuit 23 receiving the oscillation outputs I1, I2 of an oscillation circuit 20. A current limit circuit 6 is for controlling the oscillation frequency of the oscillation circuit 20 so as to control flowing current in the resonance circuit 5. When such a situation occurs as a heater current flows continuously resulting from the failure of discharge lamp lighting, the current flowing in the resonance circuit 5 is detected and converted into a voltage by a current detection circuit portion 71, and a frequency control circuit portion 72 responds to output voltage increase so as to increase the oscillation frequency of the oscillation circuit 20. |
