Patent ID: 6949893

Claim:
A television receiver comprising: a cold-cathode tube which constitutes a light source for backlight of a liquid crystal panel; a lighting driving means for lighting the cold-cathode tube using a lighting/driving signal at a first frequency; a current detecting means for detecting a current flowing through the cold-cathode tube; and a luminance control means for stabilizing the luminance of the cold-cathode tube at a target luminance in such a manner that the ratio of the interval during which the lighting/driving of the cold-cathode tube is done by the lighting driving means to the interval during which the lighting/driving of the cold-cathode tube is stopped is set at a value corresponding to the result of detection by a duty ratio of an intermittent control signal at a second frequency lower than the first frequency; wherein the second frequency is set at a frequency lower than 1/10 of the first frequency; the lighting driving means comprises: a driving transistor for driving, by self-oscillation, a primary coil of a transformer around which a secondary coil to send out a lighting/driving signal is wound, and a control transistor for changing the base potential of the driving transistor between a potential where a base current flows through the driving transistor and another potential where the base current ceases to flow; the current detecting means comprises: a current detecting resistor inserted in a current path to the cold-cathode tube, a diode for rectifying a voltage generated across the current detecting resistor, and a π-type filter which is a low-pass filter for removing a first frequency component from the output of the diode and passing a second frequency component; and the luminance control means comprises: a current value computing means for producing, as a current average value, a multiplied result of a ratio of an interval during which the output level of the π-type filter is higher than a prescribed level to a period with which the output level of the π-type filter changes and the output level of the π-type filter during the interval during which the output level of the π-type filter is higher than the prescribed level, and a duty control means for stabilizing the luminance of the cold-cathode tube at the target luminance in such a manner that the duty ratio of the intermittent control signal is set at a value corresponding to a difference between the current average value outputted from the current value computing means and a target value thereof.