Backlight and display device provided with same
A liquid crystal driving frequency detection unit that determines a liquid crystal driving frequency based on a vertical synchronization signal is provided in an LED drive circuit. In addition, a look-up table that holds a correspondence relationship between the liquid crystal driving frequency and the lighting frequency of the LEDs is provided in a control unit in the LED drive circuit. The correspondence relationship is held in the look-up table such that, for example, when the liquid crystal driving frequency becomes one-nth of that before change, the lighting frequency of the LEDs becomes n times of that before change. The LED drive circuit determines the lighting frequency of the LEDs by referring to the look-up table when the liquid crystal driving frequency changes.
1. A backlight for a display panel, the backlight including a plurality of LEDs as light sources, and the backlight comprising:
a plurality of LED units divided into a plurality of blocks, each of the plurality of LED units including one or more LEDs, and
a turn-on control circuit configured to turn on the plurality of LEDs in a time-sharing manner and on a block-by-block basis, wherein
in regard to a first frequency and a second frequency which are two frequencies satisfying a following expression, when a driving frequency of the display panel changes from the first frequency to the second frequency, the turn-on control circuit increases a lighting frequency of the plurality of LEDs:
the first frequency>the second frequency, wherein
the turn-on control circuit includes a table that holds a correspondence relationship between the driving frequency of the display panel and the lighting frequency of the plurality of LEDs, and
the turn-on control circuit determines the lighting frequency of the plurality of LEDs by referring to the table when the driving frequency of the display panel changes, and
correspondence relationship is held in the table such that when the driving frequency of the display panel becomes 1/n, the lighting frequency of the plurality of LEDs is multiplied by n.
2. The backlight according to claim 1 , wherein
the turn-on control circuit includes a driving frequency detection unit configured to determine the driving frequency of the display panel based on a synchronization signal that are supplied from outside, and
the driving frequency detection unit includes a timer, measures a length of one frame period based on the synchronization signal by using the timer, and determines the driving frequency of the display panel based on the length of one frame period that is a measurement result.
3. The backlight according to claim 1 , wherein information on the lighting frequency of the plurality of LEDs is supplied from outside, and the turn-on control circuit turns on the plurality of LEDs based on the information.
4. The backlight according to claim 1 , wherein
the turn-on control circuit includes
a power supply switching circuit configured to switch a supply destination of a power source voltage for LED driving among the plurality of blocks, and
an LED drive circuit configured to control a time length for supplying an LED that is a lighting target with a current, by using a PWM signal,
the LED drive circuit transmits a switching control signal to the power supply switching circuit based on the lighting frequency of the plurality of LEDs and a number of the plurality of blocks, and
the power supply switching circuit switches the supply destination of the power source voltage among the plurality of blocks based on the switching control signal.
5. A display device comprising:
a display panel including a display portion configured to display an image, and
a backlight configured to irradiate the display portion with light, the backlight including a plurality of LEDs as light sources, wherein
the backlight includes
a plurality of LED units divided into a plurality of blocks, each of the plurality of LED units including one or more LEDs, and
a turn-on control circuit configured to turn on the plurality of LEDs in a time-sharing manner and on a block-by-block basis, and
in regard to a first frequency and a second frequency which are two frequencies satisfying a following expression, when a driving frequency of the display panel changes from the first frequency to the second frequency, the turn-on control circuit increases a lighting frequency of the plurality of LEDs:
the first frequency>the second frequency, wherein
the turn-on control circuit includes a table that holds a correspondence relationship between the driving frequency of the display panel and the lighting frequency of the plurality of LEDs, and
the turn-on control circuit determines the lighting frequency of the plurality of LEDs by referring to the table when the driving frequency of the display panel changes, and
correspondence relationship is held in the table such that when the driving frequency of the display panel becomes 1/n, the lighting frequency of the plurality of LEDs is multiplied by n.