| 摘要 |
PROBLEM TO BE SOLVED: To surely protect a circuit, while preventing generation of cataphoresis phenomenon, by detecting a life end of a discharge lamp even if the circumambient temperature is high or low. SOLUTION: Generation of abnormality like no-emission is decided by inserting impedance elements Z1, Z1 between one end of filament of two discharge lamps La1, La2 and a potential point (ground) which does not have high frequency-like amplitude, and detecting the difference of alternating current component of lamp voltages Vla1, Vla2 of each discharge lamps La1, La2, in the closed loop including the impedance element Z1, Z1, and discharge lamps La1, La2. Owing to the above, the generation of abnormality can be decided stably and surely, even if absolute value of amplitude of lamp voltages Vla1, Vla2 changes, which happens when circumambient temperature is high or low. Further, it is unnecessary to install a direct current cutting capacitor at the secondary winding N2 of a leakage transformer LT1, and as direct current component becomes is not impressed to the discharge lamps La1, La2, generation of cataphoresis phenomenon can be prevented. |
