Method and system for controlling an LED backlight in flat panel displays wherein illumination monitoring is done outside the viewing area

• US 6,521,879 B1
• Filed: 04/20/2001
• Issued: 02/18/2003
• Est. Priority Date: 04/20/2001
• Status: Expired due to Term

• Current Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rockwell Collins, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Bishop, Gary D., Rand, Ryan J.
• Primary Examiner(s): Allen, Stephone B.
• Assistant Examiner(s): Glass, Christopher W.
• Application Number:
  US09/839,008
• Time in Patent Office: 669 Days
• Field of Search: 250/205, 250/204, 345/102, 345/5, 349/116, 349/61-71, 315/155-159, 315/151, 362/800, 362/31, 362/561, 362/252, 362/249, 362/236, 362/276
• US Class Current: 250/205
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• 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 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/54 in a series array of LEDs

Abstract

A system and method for controlling light emitted by a group of independent strings of LEDs in an LED backlight for a flat panel LCD display, in which optical feedback is used to increase a light output of remaining strings of LEDs when a string fails.

Claims

1. An apparatus comprising:

a driven array of LEDs adapted and configured as a backlight for a flat panel display;

said driven array of LEDs comprising

a first LED string, having a first LED driver, a first string sensor LED and a plurality of first string viewing area component LEDs disposed therebetween,

a second LED string, having a second LED driver, a second string sensor LED and a plurality of second string viewing area component LEDs disposed therebetween, and

a third LED string, having a third LED driver, a third string sensor LED and a plurality of third string viewing area component LEDs disposed therebetween, wherein said pluralities of first, second and third string viewing area component LEDs are disposed within a viewing area that is substantially aligned with a display viewing window of a flat panel display, said pluralities of first, second, and third string viewing area component LEDs arranged and collectively configured to emit light to provide backlighting for the flat panel display, and wherein said first, second and third string sensor LEDs are positioned outside of the viewing area such that light emitted therefrom does not substantially contribute to the backlighting of the flat panel display;

a light sensing assembly, having therein a photodetector positioned outside of the viewing area and adjacent the first, second and third string sensor LEDs, said photodetector adapted and configured for detecting light emitted, from outside said viewing area, by said first string sensor LED, said second string sensor LED, and said third string sensor LED;

an optical feedback control which is adapted and configured to receive a detected light level signal from said photodetector and generate a commanded output signal in response thereto; and

,

an optical feedback line adapted and configured to carry said commanded output signal to said first LED driver, said second LED driver, and said third LED driver.

2. An apparatus of claim 1 wherein said photodetector is disposed centrally among said first string sensor LED, said second string sensor LED and said third string sensor LED.

3. An apparatus of claim 2 wherein said photodetector is disposed under a reflective dome that reflects light emitted by the first, second and third string sensor LEDs toward the photodetector.

4. An apparatus of claim 3 further comprising a failure mode indicator LED disposed outside said viewing area which is adapted and configured to display a variable indication of a number of failed strings of LEDs in said driven array based on a measurement of light detected by the photodetector.

5. An apparatus comprising:

first means for emitting light, from a plurality of discrete locations, in response to a first driving means, said first means for emitting light including a first plurality of LEDs positioned in a viewing area and a first sensor LED positioned outside of the viewing area;

second means for emitting light, from a plurality of discrete locations, in response to a second driving means, said second means for emitting light including a second plurality of LEDs positioned in the viewing area and a second sensor LED positioned outside of the viewing area;

third means for emitting light, from a plurality of discrete locations, in response to a third driving means, said third means for emitting light including a third plurality of LEDs positioned in the viewing area and a third sensor LED positioned outside of the viewing area;

means for detecting light output from outside of the viewing area, from at least one of the first, second, and third sensor LEDs, wherein said means for detecting light is a photodetector disposed centrally among the first, second and third sensor LEDs; and

,

means for generating and delivering, to said first driving means, an increased brightness command signal which is responsive to said means for detecting light.

6. An apparatus of claim 5 further comprising:

means for shuttering light in response to an input electrical signal.

7. An apparatus of claim 6 wherein said means for shuttering is an LCD having a viewing window.

8. An apparatus of claim 7 wherein said means for generating and delivering is responsive to a failure in at least one of the first, second and third means for emitting light.

9. An apparatus of claim 8 wherein said first plurality of LEDs contains a non-linear arrangement of LEDs.

10. An apparatus of claim 9 wherein said means for detecting light receives reflected light from a reflector disposed between said means for detecting and a viewer location for said LCD, said reflector directing light away from the viewer location.

11. An apparatus of claim 10 further comprising a means, based upon a measurement of the photodetector, for variably visually indicating how many of the first, second, and third plurality of LEDs have failed.

12. A method of controlling an LCD backlight, said backlight including a plurality of strings of LEDs, wherein each of the plurality of strings of LEDs has at least one sensor LED positioned to emit light substantially outside an LCD viewing area, the method comprising the steps of:

monitoring, at a location other than within the LCD viewing area, light emitted by the at least one sensor LED from each of the plurality of strings of LEDs; and

,

generating a signal commanding each of said plurality of strings of LEDs to produce an increased level of light, in response to a reduction in light level determined through said step of monitoring light level.

13. A method of claim 12 wherein said step of generating a signal is repeated in response to a failure of at least one of the strings of LEDs.

14. A method of claim 13 wherein said step of monitoring includes monitoring only a single LED from each of said plurality of strings of LEDs.

15. A method of claim 14 further comprising the step of generating a variable visible indication which depicts a variable number of failures among said plurality of strings of LEDs.