| 摘要 |
PURPOSE:To automatically control brightness according to the state of a picture and to constantly and easily see the picture of a liquid crystal television by comparing a reference voltage relating to a white level of a video signal with the video signal and controlling the brightness of a picture display part by a comparison output. CONSTITUTION:The video signal Sv inputted from a video signal input terminal 1 is inputted to a negative input terminal of a comparator 2. To the positive input terminal of the comparator 2, the reference voltage E is inputted from a direct current power source 3 selected to a required value for obtaining the picture of the easily seeing brightness. From an output terminal 2a of the comparator 2, an output signal Sc of a pulse corresponding to a time length of the video signal of the white level exceeding the reference voltage is outputted and a voltage elevated according to a white level time is outputted from an integration circuit 4. The voltage outputted from a terminal 5 is inputted to an alternating current driving waveform generating circuit as a luminance signal to maintain a constant brightness.
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