LED LIGHT FLUX CONTROL DEVICE, AND ROAD ILLUMINATING DEVICE

摘要

PROBLEM TO BE SOLVED: To provide an LED light flux control device capable of constantly controlling a light flux of an LED with a high accuracy without using a sensor such as an optical sensor and a temperature sensor.SOLUTION: An LED light flux control device comprises: a constant current power supply part 11 performing constant current drive of an LED 5; a switching transistor 12 connected in series to the LED 5; voltage dividing resistors 13 and 14 dividing a both-end voltage (a forward voltage Vf) of the LED 5; a differential amplifier circuit 15 amplifying a difference between the divided voltage and a reference voltage Vf; an A/D converter 16 performing A/D conversion of output voltage &Dgr;Vf; and a CPU 17 turning on and off the switching transistor 12 to control the LED 5 in a PWM system. The CPU 17 calculates a light flux corresponding to an actual forward voltage calculated from an output of the A/D converter 16 by using known characteristics of the forward voltage and a light flux, and controls a PWM duty ratio so that the light flux of the LED 5 becomes a target value.