| 摘要 |
PROBLEM TO BE SOLVED: To keep lighting of a lamp by discriminating earth fault from a state even if an arc discharge length is elongated due to vibration to a discharge lamp and a lamp voltage thereby temporarily rises. SOLUTION: A discharge lamp lighting device is equipped with a DC-DC converting circuit, a DC-AC converting circuit and an igniter circuit, and additionally a voltage detecting section to detect an output voltage of the DC-DC converting circuit and a controlling section. The controlling section detects a time during which a detected voltage detected by the voltage detecting section is not more than a first threshold value set at a lower limit value or a less value in the normal lighting voltage range, and, if the time continues for not less than a first threshold time shorter than a half cycle of the DC-AC converting circuit output, detects an earth fault and suspends the DC-DC converting circuit; and the controlling section detects a time during which a detected voltage is not less than a second threshold value set at an upper limit value or a higher value in the normal lighting voltage range, and, if the time continues for not more than a second threshold time longer than a half cycle thereof, keeps the operation of the DC-DC converting circuit. COPYRIGHT: (C)2009,JPO&INPIT |
