| 摘要 |
PROBLEM TO BE SOLVED: To dispense with an expensive CPU or a memory and to stably correct luminance in spite of fluctuation of a peripheral temperature or a change along with the lapse of time of a fluorescent tube by comparing a target luminance set value with an actual luminance detection value, using the result as a luminance control signal, and correcting power to be fed to a backlight light source. SOLUTION: A tube current flowing through a fluorescent tube 2 is converted into a voltage by a resistor 8 so as to undergo alternating-direct current conversion by means of a diode 9 and a capacitor 10. A tube current controller 5 compares the voltage with a luminance control voltage 4 so as to turn on/off a power source voltage to be inputted to an inverter circuit 1 for controlling luminance. An optical sensor 6 installed to the vicinity of a backlight light source takes out backlight luminance as a luminance detection voltage. A comparator 7 compares the voltage with a voltage set in a luminance setting volume 3 setting a target luminance so as to determine the result as a luminance control voltage 4. In this way, luminance is always set to be that set in the luminance set volume 3. |
