Backlight unit and display device

[0001] 1. Field of the Invention

[0002] The present invention relates to a backlight unit, and in particular to a backlight unit for a display device having a main screen and a sub screen. The backlight unit drives light-emitting diodes corresponding to the sub screen utilizing an independent circuit, thereby reducing current consumption.

[0003] 2. Description of the Related Art

[0004] Liquid crystal displays (LCDs) are employed applied in variety of electronic devices, such as mobile phones, digital cameras, personal digital assistants, and other devices used in environments providing varying degrees of brightness. In order to provide adequate display brightness, backlight sources are provided located in an rear of the LCD panel.

[0005] Currently, many mobile phones have hinged displays with a main screen and a sub screen disposed on eacg side thereof. The main screen is disposed on the inner side of the hinged display and displays a main menu and related information. The sub-screen is disposed on the outer side of the hinged display and displays general information, such as data, time and so on. Generally, the main screen and the sub screen respectively have a light source and a light guide configured in a backlight unit within a liquid crystal module of the mobile phone. The described mobile phone suffer from the disadvantages of large volume and excessive power consumption.

[0006] To solve the described problems, light-emitting diodes (LEDs) coupled in series and one light guide are employed in a backlight unit for displaying images in the main screen and the sub screen. FIG. 1 shows a schematic diagram of the backlight unit with serial light-emitting diodes. A main screen MD1 and a sub screen SD1 are relatively disposed. LEDs 1A to 1D correspond to the main screen MD1 and LEDs 1B and 1C further correspond to the sub screen SD1. When the main screen MD1 or the sub screen SD1 is used, all LEDs 1A to 1D are driven to emit light. That is, the LEDs corresponding to the main screen MD1 and the LEDs corresponding to the sub screen SD1 are all lit.

[0007] Practically, when the mobile phone is in standby mode, the hinged cover is closed such that the sub screen SD1 on the outer side of the flip cover can be viewed. Meanwhile, the LEDs 1B and 1C corresponding to both screens MD1 and SD1, and LEDs 1A and 1D corresponding to the main screen MD1 are all driven to emit light. The lit LEDs 1A and 1D cause unnecessary power consumption and reduced battery life.

[0008] Additionally, LEDs 2A to 2D coupled in parallel are applied in a backlight unit, as shown in FIG. 2. Because the impedances of LEDs 2A to 2D are different, brightness thereof is unequal, resulting in uneven brightness of the backlight unit and poor display quality.

[0009] Accordingly, one object, of the present invention is to provide a backlight unit for application in a display device comprising a main screen and a sub screen. The backlight unit respectively drives LEDs corresponding to the main screen and LEDs corresponding to the sub screen via two independent circuits.

[0010] According to the object described above, an embodiment of the present invention provides a backlight unit for a display device having a main screen and a sub screen. The backlight unit comprises a first light-emitting unit and a second light-emitting unit. When the display device uses the sub screen, the first light-emitting unit provides a first light to the sub screen. When the display device uses the main screen, the first and the second light-emitting units respectively emit a second light and a third light, and a first aggregate light including the second light and the third light is provided to the main screen.

[0011] The present invention further provides a display device. The display device comprises a main screen, a sub screen, a first light-emitting unit, a second light-emitting unit, and a control unit. The sub screen is disposed opposite to the main screen. When the display device uses the sub screen, the control unit drives the first light-emitting unit to provide a first light to the sub screen. When the display device uses the main screen, the control unit drives the first and second light-emitting units to respectively emit a second light and a third light, and a first aggregate light comprising the second light with the third light is provided to the main screen.

[0012] A detailed description is given in the following embodiments with reference to the accompanying drawings.

[0018] FIG. 3 shows a schematic diagram of a LCD of the present invention. The LCD D3 has a single light guide and two screens comprising, a main screen MD3 and a sub screen SD3. Referring to FIGS. 4a and 4b, the main screen MD3 and the sub screen SD3 are disposed respectively on the inner side 40 and the outer side 41 of the LCD D3. In FIG. 3, the sub screen SD3, disposed opposite to the main screen SD3, is represented by dotted lines. A backlight unit U3 comprises a first light-emitting unit T1 and a second light-emitting unit T2. The first light-emitting unit T1 has two LEDs 3B and 3C coupled in series, wherein a cathode of the LED 3B is coupled to the anode of the LED 3C, and a cathode of the LED 3C is coupled to a ground. Similarly, the second light-emitting unit T2 has two LEDs 3A and 3D coupled in series, wherein a cathode of the LED 3A is coupled to the anode of the LED 3D, and a cathode of the LED 3D is coupled to the ground. The LEDs 3A to 3D correspond to the main screen MD3, wherein the LEDs 3B and 3C also correspond to the sub screen SD3. Two output terminals of a control unit C3 are respectively coupled to the cathodes of the LEDs 3A and 3B to control the first and the second light-emitting units T1 and T2.

[0019] When receiving a first signal indicating that the sub screen SD3 is assigned to display images, the control unit C3 provides a first voltage to the anode of the LED 3B, such that the first light-emitting unit T1 emits light to the sub screen SD3. When receiving a second signal indicating that the main screen MD3 is assigned to display images, the control unit C3 provides the first voltage and a second voltage respectively to the anodes of the LEDs 3B and 3A, such that the first and second light-emitting units T1 and T2 emit light to the main screen MD3 simultaneously.

[0020] Moreover, when receiving the first signal, the control unit C3 further provides the first voltage and a third voltage respectively to the anodes of the LEDs 3B and 3A. The third voltage is less than the first voltage, so brightness of the first light-emitting unit T2 is lower than that of the second light-emitting unit T1.

[0021] In the present invention, the LED circuit corresponding to the sub screen SD3 and other LED circuits are controlled independently. When only the sub screen SD3 is assigned to display images, the corresponding LEDs 3B and 3C are lit while the other LEDs either remain unlit or emit light with low brightness. Therefore, less voltage is provided to the LEDs unrelated to the sub screen SD3, reducing power consumption and prolonging standby duration.

[0022] In the present invention, the number of serial LEDs of the first and second light-emitting units T1 and T2 can be determined according to system requirements, without limitation.

[0023] While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.