Redundant operation of a backlight unit of a display device under open circuit or short circuit LED string conditions

• US 9,271,379 B2
• Filed: 11/16/2012
• Issued: 02/23/2016
• Est. Priority Date: 11/16/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hussain, Asif, Pandya, Manisha P.
• Primary Examiner(s): Amadiz, Rodney
• Application Number:
  US13/679,728
• Publication Number:
  US 20140139498A1
• Time in Patent Office: 1,194 Days
• Field of Search: 345/102, 345/204
• US Class Current: 1/1
• 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 interleaved light-emitting diode (LED) strings of a backlight unit at a first luminance output when no open circuit conditions or short circuit string conditions are present in any of the interleaved LED strings, such that a target luminance output from the backlight unit is achieved;

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

controlling each remaining operational interleaved LED string independently 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 interleaved LED strings;

wherein at least two of the remaining operational interleaved LED strings are controlled to a second luminance output that is greater than the first luminance output, such that each LED of the at least two of the remaining operational interleaved LED strings outputs a second quantity of light;

wherein the at least two of the remaining operational interleaved LED strings each comprise functioning LEDs directly adjacent to non-functioning LEDs of the one of the plurality of interleaved LED strings comprising the open circuit condition or the short circuit string condition; and

wherein a remainder of the remaining operational interleaved LED strings are controlled to a third luminance output that is less than the second luminance output, such that each LED of the remainder of the remaining operational interleaved LED strings outputs a third quantity of light less than the second quantity of light.

2. The method of claim 1, wherein controlling each of the plurality of operational interleaved LED strings at a first luminance output comprises driving each of the plurality of operational interleaved LED strings using a first boost voltage generated by a first pulse-width modulation (PWM) signal having a first duty cycle, wherein controlling the at least two of the remaining operational interleaved LED strings at the second luminance output comprises driving the at least two of the remaining operational interleaved LED strings 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, and wherein controlling the remainder of the remaining operational interleaved LED strings at the third luminance output comprises driving the remainder of the remaining operational interleaved LED strings using a third boost voltage signal generated by a third PWM signal.

3. The method of claim 1, wherein the operational interleaved LED strings and the remaining operational interleaved LED strings are controlled using amplitude modulation, wherein controlling each of the plurality of operational interleaved LED strings comprises driving each of the plurality of operational interleaved LED strings using a first current, and wherein controlling the remaining operational interleaved LED strings to the second luminance output or the third luminance output comprises driving the remaining operational interleaved LED strings using a second current or a third current, respectively, wherein the second current is greater than the first current and the third current.

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

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 operational interleaved LED strings comprises a plurality of LEDs.

7. A display device comprising:

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

wherein at least two of the remaining independently controllable interleaved groups of LEDs are controlled to a second luminous flux output that is greater than a first luminous flux output of the independently controllable interleaved groups of LEDs controlled in the first manner, such that each LED of the at least two of the remaining independently controllable interleaved groups of LEDs outputs a second quantity of light;

wherein the at least two of the remaining independently controllable interleaved groups of LED strings each comprise functioning LEDs directly adjacent to non-functioning LEDs of the one of the independently controllable interleaved groups of LEDs comprising the open circuit condition; and

wherein a remainder of the remaining independently controllable interleaved groups of LEDs are controlled to a third luminous flux output that is different from the second luminous flux output, such that each LED of the remainder of the remaining independently controllable interleaved groups of LEDs outputs a third quantity of light less than the second quantity of light.

8. The display device of claim 7, wherein the backlight comprises an edge-lit backlight, and wherein the independently controllable interleaved groups of LEDs are arranged along an edge of the backlight.

9. The display device of claim 7, wherein the backlight driver comprises a pulse-width modulation (PWM) signal generator, and wherein controlling each of the independently controllable interleaved groups of LEDs in the first manner comprises using a PWM signal having a first duty cycle, and wherein controlling each of the remaining independently controllable interleaved groups of LEDs in the second manner comprises using PWM signals having a second duty cycle greater than the first duty cycle and a third duty cycle different from the second duty cycle.

10. The display device of claim 7, 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 interleaved groups of LEDs.

11. The display device of claim 10, 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 interleaved groups of LEDs.

12. The display device of claim 11, wherein the backlight driver is configured to detect an open circuit condition or short circuit string condition by monitoring a state of at least one of a set of the respective voltage feedback signals, the peak current feedback signals, and the current sink input signals.

13. The display device of claim 7, wherein the target luminous flux output corresponds to a maximum front-of-screen (FOS) brightness setting for the display device.

14. 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;

a 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 independently controllable interleaved light-emitting diode (LED) strings;

a backlight driver configured to control the independently controllable interleaved LED strings to provide an expected light output for the backlight unit, wherein the backlight driver controls each of the independently controllable interleaved LED strings to respectively provide a first amount of light, such that the first amount of light provided by each of the independently controllable interleaved LED strings collectively achieves the expected light output of the backlight unit, and wherein the backlight driver controls at least two remaining independently controllable interleaved LED strings when one of the independently controllable interleaved LED strings stops functioning due to an open circuit condition to respectively provide a second amount of light;

wherein a first LED string of the at least two remaining independently controllable interleaved LED strings and a second LED string of the at least two remaining independently controllable interleaved LED strings are controlled to a second driving strength, such that each LED of the first LED string and the second LED string outputs a second quantity of light;

wherein the first LED string and the second LED string comprise LEDs directly adjacent to non-functioning LEDs of the independently controllable interleaved LED string with the open circuit condition; and

wherein a remainder of the remaining independently controllable interleaved LED strings are controlled to a first driving strength, such that each LED of the remainder of the remaining LED strings outputs a first quantity of light less than the second quantity of light, and a combined light output from the remaining independently controllable interleaved LED strings achieves the expected light output of the backlight unit.

15. The electronic device of claim 14, wherein the second amount of light is greater than the first amount of light.

16. The electronic device of claim 15, wherein controlling the independently controllable interleaved LED strings to provide the expected light output comprises driving each of the independently controllable interleaved 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, wherein controlling the at least two remaining independently controllable interleaved LED strings to provide the second amount of light comprises driving each of the at least two remaining independently controllable interleaved LED strings with a second boost voltage generated by a second PWM signal having a second duty cycle, wherein the second duty cycle is greater than the first duty cycle.

17. The electronic device of claim 14, 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 of the independently controllable interleaved LED strings.

18. The electronic device of claim 14, 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.

19. The electronic device of claim 14, wherein the plurality of independently controllable interleaved LED strings comprises at least six LED strings.

20. A method of manufacturing a display device comprising:

providing a display panel;

providing an edge-lit backlight unit comprising a plurality of independently controllable light emitting diode (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 independently controllable LED strings in a first mode, wherein the independently controllable LED strings are controlled in a first manner to achieve a target light output, and to operate at least two remaining functional LED strings in a second mode, such that each LED of the at least two remaining functional LED strings outputs a second quantity of light, and a remainder of the remaining functional LED strings in a third mode, such that each LED of the remainder of the remaining functional LED strings outputs a third quantity of light less than the second quantity of light, when an open circuit condition is detected on one of the independently controllable LED strings, wherein the at least two remaining functional LED strings each comprise functioning LEDs directly adjacent to non-functioning LEDs of the one of the independently controllable LED strings comprising the open circuit condition, wherein the remaining functional LED strings are independently controlled in the second mode and the third mode to achieve the target light output by a combined output of the remaining functional LED strings, and wherein the second mode is different from the third mode.