Patent ID: 8860321

Claim:
An LED control device turning on and off a plurality of LEDs for each of LED groups connected to a plurality of constant-current output circuits, comprising: an LED driving portion that individually controls whether to supply currents to the LED groups by the constant-current output circuits, in accordance with PWM signals input corresponding respectively to the LED groups; a power-supply control portion that, when at least one of the LED groups is turned on, controls a power supplied from a power-supply device to which the LED groups are connected in parallel by a first voltage control mode in which a voltage at a cathode end of the lighting LED group is kept at a predetermined first voltage value, and, when all the LED groups are turned off, controls the power by a second voltage control mode in which a voltage at an anode end of the LED group is kept at a predetermined second voltage value; and a phase difference control portion that produces a phase difference of 2π/n (n: the number of LED groups) to the PWM signals corresponding respectively to the LED groups input to the LED driving portion, a dimming portion that controls luminance of the LED by a duty ratio of the PWM signal input to the LED driving portion, wherein the phase difference control portion produces a phase difference of 2π/n to the PWM signals if the duty ratio of a lighting period set by the dimming portion is not less than a first predetermined value that is 100/n % or more and produces a phase difference not less than 3.6 times the value of the duty ratio and not more than 2π/n to the PWM signals if the duty ratio is less than a second predetermined value that is not more than 100/n %, and the first predetermined value and the second predetermined value are set with hysteresis.