| 摘要 |
PROBLEM TO BE SOLVED: To avoid a sound resonance phenomenon certainly and to make it control illumination continuously on the occasion of the high frequency lighting of a high pressure electric discharge lamp. SOLUTION: It consists of the high pressure electric discharge lamp, a high frequency electric power supply circuit which supplies alternate current electric power of 1 kHz or more to the high pressure electric discharge lamp, a driver which drives the high frequency electric power supply circuit, a frequency change circuit which switches the output frequency of the driver to a 1st and a 2nd frequencies, and a dimmer signal generating circuit which determines the duty ratio of the 1st and 2nd frequencies. It is made to have a composition, in which the 1st and the 2nd frequency belong to the different frequency bands, which do not contain sound resonance frequencies respectively peculiar to the high pressure electric discharge lamp, and at the same time, the dimmer signal generating circuit makes the duty ratio of the frequency of the lower one of the 1st and the 2nd frequencies the maximum in all light instruction states. COPYRIGHT: (C)2003,JPO |
