| 摘要 |
PROBLEM TO BE SOLVED: To eliminate dying of a discharge lamp by irregularity in impedance, or stoppage of it by malfunction of a high frequency power source for the discharge lamp in high frequency lighting in a parallel lighting type. SOLUTION: A lamp current through each of plural discharge lamps is detected for every cyclic period T0. A detected value is compared with a predetermined backup threshold value I1 and a no-load detection threshold value I2, and when either lamp current is the threshold value or less, a cyclic period T2 is set of which detection timing is different from that of a predetermined cyclic period T1 to detect the lamp current. A lamp current value detected for each cyclic period T1 is compared with the threshold value I1, an output of a high frequency power source is increased for a predetermine timeαT1 in the cyclic period T1, a lamp current value detected for each cyclic period T2 is compared with the threshold value I2, the number of times of the cyclic period T2 in which the lamp current is the threshold value I2 or less is counted, and when the number exceeds a preset value, the high frequency power source is stopped. |
