Back light and liquid crystal display
View Patent ↗A back light is provided with light sources, lighting control circuits for lighting the light sources, respectively, and a brightness control circuit for outputting light volume adjusting signals to the lighting control circuits, respectively. The brightness control circuit receives a luminance adjusting signal, adjusts only a part of the light volume adjusting signals, and fixes output of the rest of the light volume adjusting signals. The lighting control circuits apply voltages corresponding to the light volume adjusting signals to the light sources, thereby adjusting the light sources in luminance. The light volume adjusting signals can be adjusted one by one, which facilitates luminance adjustment. Thus, by lighting only one light source at the minimum luminance, the screen brightness of the liquid crystal display having this back light can be lowered to an appropriate level when it is used in dark places.
1. A back light comprising:
a plurality of light sources;
a brightness control circuit for selecting and adjusting at least one of a plurality of light volume adjusting signals, and fixing output of the rest of said light volume adjusting signals according to a luminance adjusting signal when said luminance adjusting signal changes, said light volume adjusting signals being for adjusting said light sources in luminance, respectively, said luminance adjusting signal being for adjusting a total luminance of said light sources; and
a plurality of lighting control circuits corresponding to said plurality of light sources, respectively, for receiving said light volume adjusting signals and adjusting voltage waveforms to be applied to said light sources according to the received light volume adjusting signals, respectively,
wherein said brightness control circuit comprises:
a detecting part for outputting a detecting signal when a luminance of one of said light sources corresponding to a selected light volume adjusting signal reaches a minimum luminance; and
an adjusting part for successively performing a luminance-down operation, a turn-off operation, and a selecting operation while a luminance indicated by said luminance adjusting signal is smaller than an actual total luminance of said light sources, said luminance-down operation being for changing said selected light volume adjusting signal to lower luminances of the respective light sources, said turn-off operation being for fixing said selected light volume adjusting signal to a turn-off level of said light sources in response to said detecting signal, said selecting operation being for selecting anew, in response to said detecting signal, another one of said light volume adjusting signals corresponding to a light source which is lit.
2. The back light according to claim 1 , wherein
said adjusting part changes, in synchronization with said turn-off operation, one of said light volume adjusting signals corresponding to at least one of said light sources in which are lit so as to enhance at least one of said light sources in luminance temporarily.
3. The back light according to claim 1 , wherein
said detecting part includes a monitoring circuit for detecting that the luminance of each of said light sources reaches the minimum luminance by detecting a current supplied to each of said light sources.
4. The back light according to claim 1 , wherein
when said luminance adjusting signal indicates a minimum luminance, said brightness control circuit selects and adjusts only one of said light volume adjusting signals to turn on its corresponding light source at the minimum luminance, and fixes the rest of said light volume adjusting signals to a turn-off level at which their corresponding light sources are turned off.
5. A back light comprising:
a plurality of light sources;
a brightness control circuit for selecting and adjusting at least one of a plurality of light volume adjusting signals, and fixing output of the rest of said light volume adjusting signals according to a luminance adjusting signal when said luminance adjusting signal changes, said light volume adjusting signals being for adjusting said light sources in luminance, respectively, said luminance adjusting signal being for adjusting a total luminance of said light sources; and
a plurality of lighting control circuits corresponding to said plurality of light sources, respectively, for receiving said light volume adjusting signals and adjusting voltage waveforms to be applied to said light sources according to the received light volume adjusting signals, respectively; and
a reflector containing said light sources, said reflector having a reflecting part for reflecting light emitted from said light sources, wherein:
said light sources are fluorescent tubes;
different parasitic capacitances occur between said fluorescent tubes and said reflecting part according to positions of said fluorescent tubes relative to said reflecting part; and
said lighting control circuits set an effective voltage applied to one of said fluorescent tubes having a relatively small parasitic capacitance to be lower than an effective voltage applied to another one of said fluorescent tubes having a relatively large parasitic capacitance.
6. A back light comprising:
a plurality of light sources;
a brightness control circuit for selecting and adjusting at least one of a plurality of light volume adjusting signals, and fixing output of the rest of said light volume adjusting signals according to a luminance adjusting signal when said luminance adjusting signal changes, said light volume adjusting signals being for adjusting said light sources in luminance, respectively, said luminance adjusting signal being for adjusting a total luminance of said light sources;
a plurality of lighting control circuits corresponding to said plurality of light sources, respectively, for receiving said light volume adjusting signals and adjusting voltage waveforms to be applied to said light sources according to the received light volume adjusting signals, respectively; and
a reflector containing said light sources, said reflector having a reflecting part for reflecting light emitted from said light sources, wherein:
said light sources are fluorescent tubes; and
different parasitic capacitances occur between said fluorescent tubes and said reflecting part according to positions of said fluorescent tubes relative to said reflecting part; and
a diameter of one of said fluorescent tubes having a relatively small parasitic capacitance is smaller than a diameter of another one of said fluorescent tubes having a relatively large parasitic capacitance.
7. A back light comprising:
a plurality of light sources;
a brightness control circuit for selecting and adjusting at least one of a plurality of light volume adjusting signals, and fixing output of the rest of said light volume adjusting signals according to a luminance adjusting signal when said luminance adjusting signal changes, said light volume adjusting signals being for adjusting said light sources in luminance, respectively, said luminance adjusting signal being for adjusting a total luminance of said light sources; and
a plurality of lighting control circuits corresponding to said plurality of light sources, respectively, for receiving said light volume adjusting signals and adjusting voltage waveforms to be applied to said light sources according to the received light volume adjusting signals, respectively; and
a reflector containing said light sources, said reflector having a reflecting part for reflecting light emitted from said light sources, wherein:
said light sources are fluorescent tubes;
different parasitic capacitances occur between said fluorescent tubes and said reflecting part according to positions of said fluorescent tubes relative to said reflecting part; and
a pressure of internal gas contained in one of said fluorescent tubes disposed in a position in which a relatively small parasitic capacitance occurs is higher than a pressure of internal gas contained in another one of said fluorescent tubes disposed in a position in which a relatively large parasitic capacitance occurs.
8. The back light according to claim 1 , comprising a plurality of reflectors containing said light sources, respectively, said reflectors having reflecting parts for reflecting light emitted from said light sources, respectively.
9. A back light comprising:
a plurality of fluorescent tubes;
a reflector containing said plurality of fluorescent tubes, said reflector having a reflecting part for reflecting light emitted from said fluorescent tubes; and
a plurality of lighting control circuits for adjusting voltage waveforms to be applied to said fluorescent tubes, wherein
different parasitic capacitances occur between said fluorescent tubes and said reflecting part according to positions of said fluorescent tubes relative to said reflecting part; and
said lighting control circuits set an effective voltage applied to one of said fluorescent tubes having a relatively small parasitic capacitance to be lower than an effective voltage applied to another one of said fluorescent tubes having a relatively large parasitic capacitance.
10. A back light comprising:
a plurality of fluorescent tubes; and
a reflector containing said plurality of fluorescent tubes, said reflector having a reflecting part for reflecting light emitted from said fluorescent tubes, wherein:
different parasitic capacitances occur between said fluorescent tubes and said reflecting part according to positions of said fluorescent tubes relative to said reflecting part; and
a diameter of one of said fluorescent tubes having a relatively small parasitic capacitance is smaller than a diameter of another one of said fluorescent tubes having a relatively large parasitic capacitance.
11. A back light comprising:
a plurality of fluorescent tubes; and
a reflector containing said plurality of fluorescent tubes, said reflector having a reflecting part for reflecting light emitted from said fluorescent tubes, wherein
different parasitic capacitances occur between said fluorescent tubes and said reflecting part according to positions of said fluorescent tubes relative to said reflecting part; and
a pressure of internal gas contained in one of said fluorescent tubes disposed in a position in which a relatively small parasitic capacitance occurs is higher than a pressure of internal gas contained in another one of said fluorescent tubes disposed in a position in which a relatively large parasitic capacitance occurs.
12. A liquid crystal display comprising:
a liquid crystal panel;
a plurality of light sources arranged in rear of said liquid crystal panel;
a brightness control circuit for selecting and adjusting at least one of a plurality of light volume adjusting signals, and fixing output of the rest of said light volume adjusting signals according to a luminance adjusting signal when said luminance adjusting signal changes, said light volume adjusting signals being for adjusting said light sources in luminance, respectively, said luminance adjusting signal being for adjusting a total luminance of said light sources; and
a plurality of lighting control circuits corresponding to said light sources, respectively, for receiving said light volume adjusting signals and adjusting voltage waveforms to be applied to said light sources according to the received light volume adjusting signals, respectively, wherein said brightness control circuit comprises:
a detecting part for outputting a detecting signal when a luminance of one of said light sources corresponding to a selected light volume adjusting signal reaches a minimum luminance; and
an adjusting part for successively performing a luminance-down operation, a turn-off operation, and a selecting operation while a luminance indicated by said luminance adjusting signal is smaller than an actual total luminance of said light sources, said luminance-down operation being for changing said selected light volume adjusting signal to lower luminances of the respective light sources, said turn-off operation being for fixing said selected light volume adjusting signal to a turn-off level of said light sources in response to said detecting signal, said selecting operation being for selecting anew, in response to said detecting signal, another one of said light volume adjusting signals corresponding to a light source which is lit.
13. The liquid crystal display according to claim 12 , comprising
a light guide plate placed in the rear of said liquid crystal panel, wherein
said light sources are placed on one side of said light guide plate.
14. The liquid crystal display according to claim 12 , comprising
a light guide plate placed in the rear of said liquid crystal panel, wherein
said light sources are placed on both sides of said light guide plate.