Patent ID: 7986294

Claim:
A method for driving a planar light source device, the planar light source device including a plurality of planar light source units to light a color LCD device from the back, each planar light source unit including a red LED, a green LED, and a blue LED; and a driving circuit to perform ON/OFF control of the red LED, the green LED, and the blue LED included in each planar light source unit on the basis of pulse-width modulation, and wherein, when pulse-width modulation unit clocks in the pulse-width modulation for ON/OFF control of the red, green, and blue LEDs included in each planar light source unit are CL R-unit , CL G-unit , and CL B-unit ; when ON time of the red LED in each planar light source unit is t R-ON ; when OFF time of the red LED is t R-OFF ; when a value of a pulse-width modulation output signal to control light emission time of the red LED is S R ; when ON time of the green LED is t G-ON ; when OFF time of the green LED is t G-OFF ; when a value of a pulse-width modulation output signal to control light emission time of the green LED is S G ; when ON time of the blue LED is t B-ON ; when OFF time of the blue LED is t B-OFF ; and when a value of a pulse-width modulation output signal to control light emission time of the blue LED is S B , equations t R-ON +t R-OFF =t G-ON -t G-OFF =t B-ON-OFF =constant value t Const ; t R-ON =CL R-unit ×S R ; t G-ON =CL G-unit ×S G ; and t B-ON =CL B-unit ×S B are satisfied, the method comprising the step of: adjusting a pulse duration of each of the pulse-width modulation unit clock CL R-unit , the pulse-width modulation unit clock CL G-unit , and the pulse-width modulation unit clock CL B-unit by adjusting a number of frequency division cycles of a system clock in the driving circuit that corresponds to the pulse duration of the respective pulse-width modulation unit clocks CL R-unit , CL G-unit , and CL B-unit in each planar light source unit, wherein the adjusting comprises increasing or decreasing the number of the frequency division cycles by at least one unit clock, based on a difference between luminance of each of the red LED, the green LED and the blue LED measured in a previous frame and respective estimated luminance of each of the red LED, the green LED and the blue LED calculated based on respective values of S R , S G and S B in the previous frame.