Redundant backlight for liquid crystal displays

Abstract

A redundant LED backlight and method for controlling the same. At least two plurality of LEDs are used to create a backlight where any individual set of LEDs may be driven at power level P to provide the desired overall luminance for the backlight. If two plurality of LEDs are used, then the LEDs may be driven simultaneously at one-half P during normal operations until a failure has been detected in one of the plurality of LEDs. In alternate embodiments, four plurality of LEDs may be used and driven simultaneously at one-fourth P during normal operations until a failure has been detected in one of the plurality of LEDs. The LEDs may be in edge-lit, direct-lit, or any combination of these two orientations. Upon failures, only one plurality of LEDs may be used to provide operation of the LED backlight and any associated LCD device.

1 . A method for driving a redundant LED backlight having a desired overall luminance output, the method comprising the steps of:
 providing a first and second plurality of LEDs where the application of power level P to either the first or second plurality of LEDs will produce the desired overall luminance output for the backlight;   driving the first and second plurality of LEDs simultaneously at approximately one-half of P; and   monitoring the luminance generated by the first and second plurality of LEDs and comparing this value to the desired overall luminance output and increasing the power level to the first, second, or first and second plurality of LEDs when the generated luminance falls below the desired overall luminance.   
     
     
         2 . The method of  claim 1  wherein:
 the driving step is performed by a current source. 
 
     
     
         3 . The method of  claim 1  wherein:
 the monitoring step is performed by a first controller in electrical communication with the first plurality of LEDs and a second controller in electrical communication with the second plurality of LEDs. 
 
     
     
         4 . The method of  claim 3  wherein:
 the first and second controllers are in a master/slave arrangement. 
 
     
     
         5 . The method of  claim 1  wherein:
 the first and second plurality of LEDs are in a direct-lit arrangement. 
 
     
     
         6 . The method of  claim 1  wherein:
 the first and second plurality of LEDs are in an edge-lit arrangement. 
 
     
     
         7 . The method of  claim 1  wherein:
 the first plurality of LEDs are in a direct-lit arrangement and 
 the second plurality of LEDs are in an edge-lit arrangement. 
 
     
     
         8 . A method for driving a redundant LED backlight having a desired overall luminance output, the method comprising the steps of:
 providing a first, second, third, and fourth plurality of LEDs where the application of power level P to any one of the plurality of LEDs will produce the desired overall luminance output for the backlight;   driving the first, second, third, and fourth plurality of LEDs at approximately one-fourth of P; and   monitoring the luminance generated by the first, second, third, and fourth plurality of LEDs and comparing this value to the desired overall luminance output and increasing the power level to the first, second, third, or fourth plurality of LEDs when the generated luminance falls below the desired overall luminance.   
     
     
         9 . The method of  claim 8  further comprising the step of:
 monitoring the luminance generated by the first, second, third, and fourth plurality of LEDs and comparing this value to the desired overall luminance output and driving the first plurality of LEDs at P while turning off the second, third, and fourth plurality of LEDs when the generated luminance falls below the desired overall luminance. 
 
     
     
         10 . The method of  claim 8  further comprising the step of:
 monitoring the luminance generated by the first, second, third, and fourth plurality of LEDs and comparing this value to the desired overall luminance output and driving the first plurality of LEDs at one-half P and the second plurality of LEDs at one-half P while turning off the third, and fourth plurality of LEDs when the generated luminance falls below the desired overall luminance. 
 
     
     
         11 . The method of  claim 8  wherein:
 the driving step is performed by first, second, third, and fourth current sources. 
 
     
     
         12 . The method of  claim 8  wherein:
 the first and second plurality of LEDs are in a direct-lit arrangement and 
 the third and fourth plurality of LEDs are in an edge-lit arrangement. 
 
     
     
         13 . The method of  claim 8  wherein:
 the first, second, third, and fourth plurality of LEDs are in an edge-lit arrangement. 
 
     
     
         14 . The method of  claim 8  wherein:
 the first, second, third, and fourth plurality of LEDs are in a direct-lit arrangement. 
 
     
     
         15 . A liquid crystal display (LCD) comprising:
 a LCD stack;   an LED backlight placed behind the LCD stack and comprising a first and second plurality of LEDs where the application of power level P to either the first or second plurality of LEDs will produce the desired overall luminance output for the backlight;   wherein the first and second plurality of LEDs are adapted to be driven simultaneously at one-half P until the first or second plurality of LEDs fails.   
     
     
         16 . The LCD of  claim 15  wherein:
 the first and second plurality of LEDs are in a direct-lit arrangement. 
 
     
     
         17 . The method of  claim 15  wherein:
 the first and second plurality of LEDs are in an edge-lit arrangement. 
 
     
     
         18 . The method of  claim 15  wherein:
 the first plurality of LEDs are in a direct-lit arrangement and 
 the second plurality of LEDs are in an edge-lit arrangement.