REDUNDANT OPERATION OF A BACKLIGHT UNIT OF A DISPLAY DEVICE UNDER OPEN CIRCUIT OR SHORT CIRCUIT LED STRING CONDITIONS

• US 20140139498A1
• Filed: 11/16/2012
• Published: 05/22/2014
• Est. Priority Date: 11/16/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hussain, Asif, Pandya, Manisha P.
• Granted Patent: US 9,271,379 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2330/08 Fault-tolerant or redundant circuits, or circuits in which repair of defects is prepared
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• 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 5/00 Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators image data processing or generation, in general G06T
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 47/23 of two or more light sources connected in series

Abstract

Disclosed embodiments relate to techniques for operating a backlight unit of a display device in a redundant mode and a non-redundant mode in the event of an open circuit condition or short string condition. For instance, in a redundant mode, multiple LED strings are driven to provide a first quantity of light, such that the combined output from all LED strings is capable of providing a total light output corresponding to a maximum brightness setting for the display device. In the case that one of the LED strings fails due to an open circuit condition or short string condition, the remaining LED strings may be driven to provide a second quantity of light that is greater than the first, such that the combined light output from the remaining LED strings provides the same total light output for achieving the maximum brightness setting.

Claims

1. A method comprising:

controlling each of a plurality of operational light-emitting diode (LED) strings of a backlight unit in a redundant mode when no open circuit conditions or short circuit string condition are present in any of the LED strings, such that a target luminance output from the backlight unit is achieved when each of the plurality of LED strings are controlled in the redundant mode;

determining whether an open circuit condition or short circuit string condition occurs for any of the LED strings; and

controlling each of the remaining operational LED strings in a non-redundant mode to achieve the target luminance output from the backlight unit in response to detecting an open circuit condition or short circuit string condition in one of the plurality of LED strings.

2. The method of claim 1, wherein controlling each of the plurality of LED strings in the redundant mode comprises driving each of the plurality of LED strings using a first boost voltage generated by a first pulse-width modulation (PWM) signal having a first duty cycle, and wherein controlling each of the remaining LED strings in the non-redundant mode comprises driving each of the remaining LEDs using a second boost voltage signal generated by a second PWM signal having a second duty cycle, wherein the second duty cycle is greater than the first duty cycle.

3. The method of claim 1, wherein the LED strings are controlled using amplitude modulation, wherein controlling each of the plurality of LED strings in the redundant mode comprises driving each of the plurality of LED strings using a first current, and wherein controlling each of the remaining LED strings in the non-redundant mode comprises driving each of the remaining LEDs using a second current, wherein the second current is greater than the first current.

4. The method of claim 1, comprising receiving at least one feedback signal from each LED string, wherein determining whether an open circuit condition or short LED string condition occurs in any of the LED strings comprises monitoring the respective feedback signals from each LED string.

5. The method of claim 4, wherein the at least one feedback signal comprises at least one of a peak current feedback signal, a voltage feedback signal, or a current sink feedback signal, or any combination thereof.

6. The method of claim 1, wherein each of the plurality of LED strings comprises a plurality of LEDs, wherein the plurality of LED strings are configured in an interleaved arrangement.

7. The method of claim 1, wherein switching control of the LED strings to non-redundant mode comprises setting a value to a register in response to detecting the open circuit condition.

8. A display device comprising:

an liquid crystal display (LCD) panel;

a backlight configured to provide light to the LCD panel, wherein the backlight comprises a plurality of light-emitting diodes (LEDs) arranged in independently controllable groups; and

a display controller comprising;

display driving circuitry configured to provide image signals and scanning signals to the LCD panel; and

a backlight driver configured to control each independently controllable group of LEDs in a first manner to provide a target luminous flux output from the backlight when all of the independently controllable groups of LEDs are functional, and to control each of the remaining independently controllable groups of LEDs in a second manner to provide the same target luminous flux output when one of the independently controllable groups of LEDs becomes nonoperational due to an open circuit condition.

9. The display device of claim 8, wherein the backlight comprises an edge-lit backlight, and wherein the independently controllable groups of LEDs are arranged along an edge of the backlight.

10. The display device of claim 9, wherein the independently controllable groups of LEDs are arranged in an interleaved manner along the edge of the backlight.

11. The display device of claim 8, wherein the backlight driver comprises a pulse-width modulation (PWM) signal generator, and wherein controlling each independently controllable group of LEDs in the first manner comprises using a PWM signal having a first duty cycle, and wherein controlling each independently controllable group of LEDs in the second manner comprises using a PWM signal having a second greater duty cycle.

12. The display device of claim 8, wherein the backlight driver comprises boost converter circuitry, wherein the boost converter circuitry is configured to receive a respective voltage feedback signal and a respective peak current feedback signal from each of the independently controllable groups of LEDs.

13. The display device of claim 12, wherein the backlight driver comprises current sink circuitry, wherein the current sink circuitry is configured to receive a respective current sink input signal from each of the independently controllable groups of LEDs.

14. The display device of claim 13, wherein the backlight driver is configured to detect an open circuit condition or short string condition by monitoring the state of at least one of the set of respective voltage feedback signals, peak current feedback signals, and current sink input signals.

15. The display device of claim 8, wherein the total luminous flux output corresponds to a maximum front-of-screen (FOS) brightness setting for the display device.

16. An electronic device comprising:

a processor;

a memory configured to store instructions executable by the processor, wherein at least a portion of the instructions defines an application;

a display configured to generate images associated with the execution of the application, wherein the display comprises;

an liquid crystal display (LCD) panel comprising an array of image pixels arranged in rows and columns;

a display controller comprising source driving circuitry configured to provide image signals to the array of image pixels and gate driving circuitry configured to provide scanning signals to the array of image pixels;

a backlight unit having a light source comprising a plurality of interleaved light-emitting diode (LED) strings;

a backlight driver configured to control the LED strings in a redundant mode and a non-redundant mode of operation to provide an expected light output for the backlight unit, wherein the backlight driver controls each of the redundant mode LED strings to respectively provide a first amount of light, such that the first amount of light provided by each LED string collectively achieves the expected light output of the backlight unit, and wherein the backlight driver controls each of the remaining LED strings in the non-redundant mode when one of the LED strings stops functioning due to an open circuit to respectively provide a second amount of light, such that the second amount of light provided by each of the remaining LED strings collectively achieves the expected light output of the backlight unit.

17. The electronic device of claim 16, wherein the second amount of light is greater than the first amount of light.

18. The electronic device of claim 17, wherein controlling the LED strings in the redundant mode comprises driving each of the LED strings with a first boost voltage generated by a first pulse-width modulation (PWM) signal having a first duty cycle to provide the first amount of light, and wherein controlling the remaining LED strings in the non-redundant mode comprises driving each of the remaining LED strings with a second boost voltage generated by a second PWM signal having a second duty cycle to provide the second amount of light, wherein the second duty cycle is greater than the first duty cycle.

19. The electronic device of claim 16, wherein the backlight driver is configured to detect an open circuit condition by monitoring at least one of a voltage feedback signal, a current feedback signal, or a current sink signal provided by each LED string.

20. The electronic device of claim 16, comprising at least one of a desktop computer, notebook computer, a tablet computer, a cellular telephone, a portable media player, a personal digital assistant, an internet communications device, or any combination thereof.

21. The electronic device of claim 16, wherein the plurality of LED strings comprises at least six LED strings.

22. A method of manufacturing a display device comprising:

providing a display panel;

providing a edge-lit backlight unit comprising a plurality of LED strings arranged along an edge of the backlight in an interleaved manner, wherein the backlight unit is disposed behind a viewable area of the display panel;

providing a backlight driver configured to operate the LED strings in a redundant mode, wherein the LED strings are controlled in a first manner to achieve a target light output in the redundant mode, and to operate the LED strings in a non-redundant mode when an open circuit condition is detected on one of the LED strings, wherein the remaining functional LED strings are controlled in a second manner to achieve the target light output in the non-redundant mode.