System and Method for Managing Backlight Luminance Variations

• US 20110163691A1
• Filed: 11/24/2010
• Published: 07/07/2011
• Est. Priority Date: 05/21/2008
• Status: Active Grant

• Current Assignee: Manufacturing Resources International, Inc.
• Original Assignee: Manufacturing Resources International, Inc.
• Inventors: Dunn, William
• Granted Patent: US 8,988,011 B2
• Time in Patent Office: Days
• US Class Current: 315/297
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs

Abstract

An LED assembly containing separately-controllable regions of LEDs with temperature sensing devices placed to measure the temperature within each region of LEDs. When the temperature difference between two regions becomes higher than an acceptable maximum, the system may adjust the power to one or more LED regions to maintain luminance uniformity. The regions can be arranged vertically or horizontally or both. A software processor may be used to interpret the data from the temperature sensing devices and control the power sent to the various LED regions. Embodiments can be used at least in LED backlights for LCD displays or for LED displays.

Claims

1. A method for controlling luminance variations in LED assemblies having a plurality of LEDs divided into two or more controllable regions, the method comprising:

driving a first and second LED region at preferred power levels;

measuring the temperature at the first and second LED regions;

calculating the temperature difference (Δ

T_1-2) between the first and second LED regions;

comparing Δ

T_1-2 with a predetermined temperature difference Δ

T; and

increasing power to the LED region having the higher temperature measurement if Δ

T_1-2 is greater than Δ

T or

continuing with preferred power levels if Δ

T_1-2 is less than Δ

T.

2. The method of claim 1 wherein:

the first and second LED regions are arranged vertically.

3. The method of claim 1 wherein:

the steps are performed by a microprocessor.

4. The method of claim 1 wherein:

the steps are performed by a CPU.

5. The method of claim 1 further comprising the steps of:

driving a third LED region at a preferred power level;

measuring the temperature at the third LED region;

calculating Δ

T_1-3 between the first and third LED regions and Δ

T_2-3 between the second and third LED regions;

comparing Δ

T_1-3 and Δ

T_2-3 with a predetermined temperature difference Δ

T; and

increasing power to the LED region having the highest temperature measurement if either Δ

T_1-3 or Δ

T_2-3 is greater than Δ

T or

continuing with preferred power levels if Δ

T_1-3 and Δ

T_2-3 are less than Δ

T.

6. The method of claim 5 wherein:

the first, second, and third LED regions are arranged vertically.

7. A method for controlling luminance variations in LED assemblies having a plurality of LEDs divided into two or more controllable regions, the method comprising:

driving a first and second LED region at preferred power levels;

measuring the temperature at the first and second LED regions;

calculating the temperature difference (Δ

T_1-2) between the first and second LED regions;

comparing Δ

T_1-2 with a predetermined temperature difference Δ

T; and

decrease power to the LED region having the lower temperature measurement if Δ

T_1-2 is greater than Δ

T or

continue with preferred power levels if Δ

T_1-2 is less than Δ

T.

8. The method of claim 7 wherein:

the first and second LED regions are arranged vertically.

9. The method of claim 7 wherein:

the steps are performed by a microprocessor.

10. The method of claim 7 wherein:

the steps are performed by a CPU.

11. The method of claim 7 further comprising the steps of:

driving a third LED region at a preferred power level;

measuring the temperature at the third LED region;

calculating Δ

T_1-3 between the first and third LED regions and Δ

T_2-3 between the second and third LED regions;

comparing Δ

T_1-3 and Δ

T_2-3 with a predetermined temperature difference Δ

T; and

decreasing power to all LED regions except for the region having the lowest temperature measurement if either Δ

T_1-3 or Δ

T_2-3 is greater than Δ

T or

continuing with preferred power levels if Δ

T_1-3 and Δ

T_2-3 are less than Δ

T.

12. The method of claim 11 wherein:

the first, second, and third LED regions are arranged vertically.

13. A system for controlling luminance variations across an LED assembly comprising:

a first plurality of LEDs in electronic communication with a first power source;

a first temperature sensing device placed to measure the temperature (T1) of the first plurality of LEDs;

a second plurality of LEDs in electronic communication with a second power source;

a second temperature sensing device placed to measure the temperature (T2) of the second plurality of LEDs;

a processor in electrical communication with the power sources and temperature sensing devices, and adapted to;

drive the first and second plurality of LEDs at preferred power levels;

calculate the difference (Δ

T_1-2) between T1 and T2;

compare Δ

T_1-2 with a predetermined temperature difference Δ

T; and

increase power to the plurality of LEDs having the higher temperature measurement if Δ

T_1-2 is greater than Δ

T or

continue with preferred power levels if Δ

T_1-2 is less than Δ

T.

14. The system of claim 13 wherein:

the first and second LED regions are arranged vertically.

15. The system of claim 13 further comprising:

a third plurality of LEDs in electronic communication with a third power source;

a third temperature sensing device placed to measure the temperature (T3) of the third plurality of LEDs;

wherein the processor in electrical communication with the third power source and third temperature sensing device, and further adapted to;

drive the third plurality of LEDs at a preferred power level;

calculate the difference Δ

T_1-3 between T1 and T3 and Δ

T_2-3 between T2 and T3;

compare Δ

T_1-3 and Δ

T_2-3 with a predetermined temperature difference Δ

T; and

increase power to the plurality of LEDs having the highest temperature measurement if either Δ

T_1-3 or Δ

T_2-3 is greater than Δ

T or

continue with preferred power levels if Δ

T_1-3 and Δ

T_2-3 are less than Δ

T.

16. The system of claim 15 wherein:

the first, second, and third LED regions are arranged vertically.

17. An LED assembly comprising:

a first plurality of LEDs in electronic communication with a first power source;

a first temperature sensing device placed to measure the temperature (T1) of the first plurality of LEDs;

a second plurality of LEDs in electronic communication with a second power source, the LEDs placed above the first plurality of LEDs;

a second temperature sensing device placed to measure the temperature (T2) of the second plurality of LEDs;

a third plurality of LEDs in electronic communication with a third power source, the LEDs placed above the second plurality of LEDs;

a third temperature sensing device placed to measure the temperature (T3) of the third plurality of LEDs;

a processor in electrical communication with the power sources and temperature sensing devices, and adapted to;

drive the first, second, and third plurality of LEDs at preferred power levels;

calculate the difference (Δ

T_1-2) between T1 and T2, Δ

T_1-3 between T1 and T3, and Δ

T_2-3 between T2 and T3;

compare Δ

T_1-2, Δ

T_1-3, and Δ

T_2-3 with a predetermined temperature difference Δ

T; and

increase power to the plurality of LEDs having the highest temperature measurement if either Δ

T_1-3, Δ

T_2-3, or Δ

T_1-2 is greater than Δ

T or

continue with preferred power levels if Δ

T_1-3, Δ

T_2-3, and Δ

T_1-2 are less than Δ

T.

18. The system of claim 17 further comprising:

a printed circuit board having a front and back surface where the LEDs and temperature sensing devices are mounted on the front surface.

19. The system of claim 17 further comprising:

a metal core printed circuit board having a front and back surface where the LEDs are mounted on the front surface and the temperature sensing devices are mounted on the back surface.