Patent ID: 8111236

Claim:
A backlight driving device for driving a backlight that illuminates a display panel, the backlight driving device comprising: a luminance data input device into which luminance data indicated by a video signal is entered; a duty cycle setting device configured to create a duty cycle setting signal based on values of the luminance data entered into the luminance data input device, in which the duty cycle setting signal indicates a duty cycle set between a minimum value and a maximum value in which both the minimum value and the maximum value are nonzero values; a drive signal-generating device configured to create a drive signal made of a signal which is pulse width-modulated so as to have the duty cycle according to the duty cycle setting signal such that the duty cycle is associated with a whole period, a driving circuit configured to supply power to the backlight according to the drive signal created by the drive signal-generating device so as to drive the backlight; a video signal decision device configured to make a decision as to whether each value of the luminance data entered into the luminance data input device is smaller than a given value to determine if the video signal is not an effective signal or higher than the given value to determine if the video signal is an effective signal; and a thinning-out device configured to (i) thin out components of the drive signal created by the drive signal- generating device when the video signal decision device has determined that the video signal is not an effective signal and when the duty cycle setting signal created by the duty cycle setting device indicates that the duty cycle has a low value and supply the thinned drive signal to the driving circuit, (ii) not thin out components of the drive signal created by the drive signal-generating device so as to maintain the created duty cycle when the video signal decision device has determined that the video signal is an effective signal and when the duty cycle setting signal created by the duty cycle setting device indicates that the duty cycle has a low value and supply the drive signal to the driving circuit, and (iii) not thin out components of the drive signal created by the drive signal-generating device so as to maintain the created duty cycle when the video signal decision device has determined that the video signal is an effective signal and when the duty cycle setting signal created by the duty cycle setting device indicates that the duty cycle has a high value and supply the drive signal to the driving circuit.