Light source unit, liquid crystal display having the same, and method thereof

• US 7,868,972 B2
• Filed: 02/05/2008
• Issued: 01/11/2011
• Est. Priority Date: 02/15/2007
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Um, Jae-eun, Han, Song-yi, Choi, Min-soo
• Primary Examiner(s): Pak; Sung H
• Application Number:
  US12/025,847
• Publication Number:
  US 20080198299A1
• Time in Patent Office: 1,071 Days
• Field of Search: 349/69
• US Class Current: 349/68
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133612 Electrical details
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/35 Balancing circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A light source unit which can minimize current differences between a plurality of light emitting diodes (“LEDs”) includes a printed circuit board (“PCB”) which includes an active region that emits light and an inactive region that accounts for a remainder of the PCB, an LED array which includes a plurality of LEDs that are arranged at regular intervals, and a current balancing circuit which is disposed in the inactive region, generates a plurality of current balancing voltages by uniformly adjusting current differences between the LEDs, and outputs the current balancing voltages. A liquid crystal display (“LCD”) including the light source unit, and a method of minimizing current differences between a plurality of LEDs are further provided.

Claims

1. A light source unit, comprising:

a printed circuit board which comprises an active region that emits light and an inactive region that accounts for a remainder of the printed circuit board;

a light emitting diode array which comprises a plurality of light emitting diodes that are arranged at regular intervals; and

a current balancing circuit which is disposed in the inactive region of the printed circuit board along a transverse direction, generates a plurality of current balancing voltages by uniformly adjusting current differences between the light emitting diodes, and outputs the current balancing voltages.

2. The light source unit of claim 1, wherein the light emitting diode array comprises a plurality of channels, each of the channels comprising a plurality of light emitting diodes that are connected in series.

3. The light source unit of claim 2, wherein each of the light emitting diodes comprises red, green, and blue sub-light emitting diodes.

4. The light source unit of claim 1, wherein:

a channel of light emitting diodes is provided with first through third forwarding voltages by an external source and outputs first through third light emitting diode voltages;

a plurality of red sub-light emitting diodes which are connected in series to one another in the channel emit light by being provided with the first forwarding voltage and output the first light emitting diode voltages;

a plurality of green sub-light emitting diodes which are connected in series to one another in the channel emit light by being provided with the second forwarding voltage and output the second light emitting diode voltages; and

a plurality of blue sub-light emitting diodes which are connected in series to one another in the channel emit light by being provided with the third forwarding voltage and output the third light emitting diode voltages.

5. The light source unit of claim 1, wherein the current balancing circuit generates first through third current balancing voltages by being provided with first through third light emitting diode voltages and uniformly adjusts current differences between the light emitting diodes, and outputs the first through third current balancing voltages.

6. The light source unit of claim 5, further comprising a light emitting diode driving circuit which compares the first through third current balancing voltages with a reference voltage, adjusts first through third forwarding voltages according to a comparison result, and feeds adjusted first through third forwarding voltages back to each of a plurality of channels of light emitting diodes.

7. The light source unit of claim 5, wherein the current balancing circuit comprises:

a first current balancing circuit which generates the first current balancing voltage by being provided with a plurality of the first light emitting diode voltages and uniformly adjusting current differences between a plurality of red sub-light emitting diodes;

a second current balancing circuit which generates the second current balancing voltage by being provided with a plurality of the second light emitting diode voltages and uniformly adjusting current differences between a plurality of green sub-light emitting diodes; and

a third current balancing circuit which generates the third current balancing voltage by being provided with a plurality of the third light emitting diode voltages and uniformly adjusting current differences between a plurality of blue sub-light emitting diodes.

8. The light source unit of claim 1, wherein the current balancing circuit comprises:

a first switching device, a base of which is provided with a first light emitting diode voltage via a first resistor and a collector of which is provided with a power supply voltage via a second resistor, the first switching device being turned on in response to the first light emitting diode voltage;

a plurality of second switching devices, bases of which are provided with a voltage of an emitter of the first switching device via third resistors, collectors of which are provided with one of the first light emitting diode voltage, a second light emitting diode voltage, and a third light emitting diode voltage, and emitters of which are respectively connected to first ends of a plurality of fourth resistors, the second switching devices being turned on in response to the voltage of the emitter of the first switching device; and

fifth and sixth resistors, first ends of which are connected to the emitter of the first switching device, the fifth and sixth resistors being connected in parallel to each other.

9. The light source unit of claim 8, wherein second ends of the fourth resistors are connected to a same node.

10. The light source unit of claim 8, wherein second ends of the fifth and sixth resistors are grounded.

11. The light source unit of claim 1, wherein the current balancing circuit comprises:

a first stage current mirror which comprises a plurality of first switching devices, first sources of which are provided with one of first, second, and third light emitting diode voltages and first gates of which are provided with whichever of the first, second, and third light emitting diode voltages is supplied to the first sources; and

a second stage current mirror which comprises a plurality of second switching devices, second sources of which are connected to first drains of the first switching devices and second gates of which are provided with a same voltage supplied to the second sources.

12. The light source unit of claim 1, wherein the current balancing circuit comprises:

a plurality of diodes, anodes of which are provided with one of first, second, and third light emitting diode voltages and cathodes of which are connected to a same node;

a plurality of first resistors, first ends of which are respectively connected to the anodes of the diodes and second ends of which are connected to a same node;

a second resistor, a first end of which is connected to the first resistors in series and a second end of which is grounded;

an operational amplifier, an inverting terminal of which is connected to the cathodes of the diodes and a non-inverting terminal of which is provided with a reference voltage, the operational amplifier comparing a voltage applied to the inverting terminal and the non inverting terminal and outputting a comparison result; and

a ripple remover, a first end of which is connected to the inverting terminal of the operational amplifier and a second end of which is connected to an output terminal of the operational amplifier.

13. The light source unit of claim 12, wherein the ripple remover comprises:

first and second capacitors which are connected in parallel; and

a third resistor which is connected to the first capacitor in series, first ends of the first and second capacitors being connected to each other and second ends of the first and second capacitors being connected to a first end of the third resistor.

14. The light source unit of claim 1, wherein the light emitting diode array is disposed on at least one side of the printed circuit board.

15. The light source unit of claim 1, wherein the light emitting diode array is disposed in the active region of the printed circuit board.

16. A liquid crystal display, comprising:

a liquid crystal panel assembly which comprises a liquid crystal panel that displays images and a first printed circuit board that generates a plurality of driving signals driving the liquid crystal panel and that provides the driving signals to the liquid crystal panel; and

a backlight unit which comprises a light source unit, the light source unit comprising a second printed circuit board which comprises an active region that emits light and an inactive region that accounts for a remainder of the second printed circuit board, a light emitting diode array which comprises a plurality of light emitting diodes that are arranged at regular intervals, and a current balancing circuit which is disposed in the inactive region of the second printed circuit board along a transverse direction, generates a plurality of current balancing voltages by uniformly adjusting current differences between the light emitting diodes, and outputs the current balancing voltages.

17. The liquid crystal display of claim 16, wherein the light emitting diode array comprises a plurality of channels, each of the channels comprising a plurality of light emitting diodes that are connected in series.

18. The liquid crystal display of claim 17, wherein each of the light emitting diodes comprises red, green, and blue sub-light emitting diodes.

19. The liquid crystal display of claim 16, wherein:

a channel of light emitting diodes is provided with first through third forwarding voltages by an external source and outputs first through third light emitting diode voltages;

a plurality of red sub-light emitting diodes which are connected in series to one another in the channel emit light by being provided with the first forwarding voltage and output the first light emitting diode voltages;

a plurality of green sub-light emitting diodes which are connected in series to one another in the channel emit light by being provided with the second forwarding voltage and output the second light emitting diode voltages; and

a plurality of blue sub-light emitting diodes which are connected in series to one another in the channel emit light by being provided with the third forwarding voltage and output the third light emitting diode voltages.

20. The liquid crystal display of claim 16, wherein the current balancing circuit generates first through third current balancing voltages by being provided with first through third light emitting diode voltages and uniformly adjusting current differences between the light emitting diodes, and outputs the first through third current balancing voltages.

21. The liquid crystal display of claim 20, further comprising a light emitting diode driving circuit which compares the first through third current balancing voltages with a reference voltage, adjusts first through third forwarding voltages according to a comparison result, and feeds adjusted first through third forwarding voltages back to each of a plurality of channels of light emitting diodes.

22. The liquid crystal display of claim 20, wherein the current balancing circuit comprises:

a first current balancing circuit which generates the first current balancing voltage by being provided with a plurality of the first light emitting diode voltages and uniformly adjusting current differences between a plurality of red sub-light emitting diodes;

a second current balancing circuit which generates the second current balancing voltage by being provided with a plurality of the second light emitting diode voltages and uniformly adjusting current differences between a plurality of green sub-light emitting diodes; and

a third current balancing circuit which generates the third current balancing voltage by being provided with a plurality of the third light emitting diode voltages and uniformly adjusting current differences between a plurality of blue sub-light emitting diodes.

23. The liquid crystal display of claim 16, wherein the current balancing circuit is disposed at an upper portion or a lower portion of the inactive region of the second printed circuit board along the transverse direction.

24. The liquid crystal display of claim 16, wherein the current balancing circuit is disposed at both an upper portion and a lower portion of the inactive region of the second printed circuit board unit along the transverse direction.

25. The liquid crystal display of claim 16, wherein the light emitting diode array is disposed on at least one side of the second printed circuit board.

26. The liquid crystal display of claim 16, wherein the light emitting diode array is disposed in the active region of the second printed circuit board.

27. A method of minimizing current differences between a plurality of light emitting diodes in a light source unit, the light source unit including a printed circuit board having an active region, upon which the light emitting diodes are disposed in channels, and an inactive region, upon which a current balancing circuit is disposed along a transverse direction, the method comprising:

providing forwarding voltages from a light emitting diode driving circuit to each channel of light emitting diodes;

sending light emitting diode voltages from each channel of light emitting diodes to a current balancing circuit disposed on the inactive region of the printed circuit board;

uniformly adjusting current differences between the light emitting diodes in the current balancing circuit;

outputting current balancing voltages from the current balancing circuit to the light emitting diode driving circuit;

comparing the current balancing voltages to a reference voltage in the light emitting diode driving circuit; and

,

controlling the forwarding voltages based on comparison of the current balancing voltages to the reference voltage in the light emitting diode driving circuit.