Patent ID: 7291989

Claim:
A lighting control circuit for a vehicle lighting device, comprising: a switching regulator for converting an input voltage from a power supply into an electromagnetic energy by an ON/OFF operation of a switching element connected to a transformer or a coil, and discharging the electromagnetic energy; an energy propagating means for propagating the electromagnetic energy discharged from the switching regulator to a semiconductor light source as luminous energy; a controlling means for generating a switching signal based on an arithmetic process, and controlling the ON/OFF operation of the switching element in accordance with the switching signal; and an input voltage sensing means for providing an input-voltage sudden-change sense signal to the controlling means when the input voltage sensing means senses that the input voltage of the switching regulator is out of a set voltage; wherein the controlling means is adapted to reduce an ON duty of the switching signal smaller than a preceding ON duty in response to the input-voltage sudden-change sense signal.