| 摘要 |
PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device capable of dimming or turning off a discharge lamp at the end of its life without using a complex protective circuit even in the case of a discharge lamp with a slender bulb. SOLUTION: While a discharge lamp 3a is fully on, a high frequency sufficiently lower than the natural resonant frequency of a load circuit including the discharge lamp 3a, an inductance 3b, and a capacitance 3d is output from a high frequency generation means 2; while the discharge lamp 3a is dimmed, a high frequency higher than the natural resonant frequency is produced. During the full on state, the load circuit does not resonate and therefore an open voltage is low while a short-circuit current is relatively large. In contrast, during the dimmed state, the open voltage is high while the short-circuit current is relatively low. Hence, when the discharge lamp 3a comes to the end of its life, the lamp voltage is higher than the open voltage and the discharge lamp 3a cannot be kept turned on but is turned off, but since it is turned on in the region of load characteristics where output current is small, it is greatly dimmed. Therefore, since no abnormal temperature rise occurs near electrodes, the glass bulb, the base, the socket, and the like are not melted. |
