Patent ID: 7646989

Claim:
A light emitting element driving device comprising: at least one light emitting element; and a power supply device for generating a driving current of said light emitting element, said power supply device comprising a step-up type DC-DC converter circuit having a soft-start function for gradually increasing said driving current at a rise of said driving current in generation of said driving current, wherein said step-up type DC-DC converter circuit comprises a capacitor, one electrode of the capacitor is connected to a fixed electrode and the other electrode of the capacitor is connected to said light emitting element, further comprising a first switch element for turning said driving current on and off, wherein said first switch element is controlled to be turned on and off by a dimmer pulse having a relatively long cycle, said dimmer pulse started a predetermined time after a startup time, wherein said step-up type DC-DC converter circuit comprises a second switch element, and said soft-start function is performed by gradually lengthening an ON period of said second switch element, and wherein said second switch element is controlled to intermittently repeat ON and OFF in a relatively short cycle, and the relatively short cycle being less than the relatively long cycle.