| 摘要 |
PROBLEM TO BE SOLVED: To detect removal of a discharge lamp (filament) with a detecting circuit by stopping the output of an inverter circuit at the time of lighting a lamp in the end of the lifetime thereof and when a filament is removed during lighting. SOLUTION: In the end of lifetime of a discharge lamp, a discharging phenomenon called as a half-wave discharge that discharge is performed from the only one of a pair of electrodes and that discharge from the other electrode is hardly performed is generated in a discharge lamp. In this case, a threshold value V is set between the voltage V (normal) to be generated in a capacitor at the time of normal lighting and the voltage V (lifetime) to be generated in the capacitor 11 at the time of half-wave discharge in the end of the lifetime, and when the voltage, which exceeds the threshold value V, is generated, a control circuit 4 stops the oscillation of the inverter circuit, and removal of a discharge lamp and the end of the lifetime of the discharge lamp are detected so as to protect the inverter circuit at the time of lighting the lamp. |
