| 摘要 |
PROBLEM TO BE SOLVED: To control backlight according to ambient luminance by generating a lighting control signal according to an output voltage level of a photo- detecting part. SOLUTION: A photo-detecting part 22 detects ambient light by a photodiode 26, and an operational amplifier 27 operates current-voltage conversion of the photo detection current according to the light intensity, and outputs the voltage to a voltage comparison circuit 23. The voltage comparison circuit 23 compares the voltage outputted from the photo detecting part 22 with a preset reference voltage by a comparator 28, and outputs a logic signal to a lighting control signal generation circuit part 24. The lighting control signal generation circuit 24 makes use of operation of a one-shot multi-vibrator 29, to convert several or more frequent short-time variations of the voltage comparison circuit 23 into a specified single pulse. A backlight control circuit 25 is provided with a switch 31, which is to be closed (lighted) when the output from the lighting control signal generation circuit part 24 is at the level L, and is to be opened (unlighted) when it is at the level H.
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