U.S. patent application number 13/159183 was filed with the patent office on 2012-06-14 for redundant backlight for liquid crystal displays.
This patent application is currently assigned to AMERCAN PANEL CORPORATION. Invention is credited to William Dunn.
Application Number | 20120147293 13/159183 |
Document ID | / |
Family ID | 46199053 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120147293 |
Kind Code |
A1 |
Dunn; William |
June 14, 2012 |
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.
Inventors: |
Dunn; William; (Alpharetta,
GA) |
Assignee: |
AMERCAN PANEL CORPORATION
Alpharetta
GA
|
Family ID: |
46199053 |
Appl. No.: |
13/159183 |
Filed: |
June 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61353986 |
Jun 11, 2010 |
|
|
|
Current U.S.
Class: |
349/65 ; 315/153;
349/61 |
Current CPC
Class: |
G02B 6/0068 20130101;
G02B 6/0061 20130101; G09G 2330/08 20130101; G09G 2320/0233
20130101; G09G 2320/0626 20130101; G02B 6/0073 20130101; G09G
3/3426 20130101; G02F 1/133603 20130101; G09G 3/3406 20130101; G09G
2360/16 20130101 |
Class at
Publication: |
349/65 ; 315/153;
349/61 |
International
Class: |
H05B 37/02 20060101
H05B037/02; G02F 1/13357 20060101 G02F001/13357 |
Claims
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application No.
61/353,986, filed Jun. 11, 2010, titled Redundant Backlight for
Liquid Crystal Displays, which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] Disclosed embodiments relate generally to an LED backlight
system for a liquid crystal display device.
BACKGROUND OF THE ART
[0003] Liquid Crystal Displays (LCDs) contain several layers which
work in combination to create a viewable image. A backlight is used
to generate the rays of light that pass through what is commonly
referred to as the LCD stack, which typically contains several
layers that perform either basic or enhanced functions. The most
fundamental layer within the LCD stack is the liquid crystal
material, which may be actively configured in response to an
applied voltage in order to pass or block a certain amount of light
which is originating from the backlight. The layer of liquid
crystal material is divided into many small regions which are
typically referred to as pixels. For full-color displays these
pixels are further divided into independently-controllable regions
of red, green and blue subpixels, where the red subpixel has a red
color filter, blue subpixel has a blue color filter, and green
subpixel has a green color filter.
[0004] The light which is passing through each subpixel typically
originates as "white" (or broadband) light from the backlight,
although in general this light is far from being uniform across the
visible spectrum. The subpixel color filters allow each subpixel to
transmit a certain amount of each color (red, green or blue). When
viewed from a distance, the three subpixels appear as one composite
pixel and by electrically controlling the amount of light which
passes through each subpixel, the composite pixel can produce a
very wide range of different colors due to the effective mixing of
light from the red, green, and blue subpixels.
[0005] Currently, the common illumination source for LCD backlight
assemblies or Back Light Unit (BLU) is fluorescent tubes, but the
industry is moving toward light emitting diodes (LEDs).
Environmental concerns, small space requirements, lower energy
consumption, and long lifetime are some of the reasons that the LCD
industry is beginning the widespread usage of LEDs for
backlights.
[0006] LCDs are becoming popular for not only home entertainment
purposes, but are now being used as informational/advertising
displays in both indoor and outdoor locations. When used for
information/advertising purposes, the displays may remain `on` for
extended periods of time and thus would see much more use than a
traditional home theatre use. Further, when displays are used in
areas where the ambient light level is fairly high (especially
outdoors or in aircraft cockpits) the displays must be very bright
in order to maintain adequate picture brightness. When used for
extended periods of time and/or outdoors, durability of the
components especially the illumination sources such as LEDs can
become an issue.
[0007] As is readily apparent, an LCD will not function
satisfactorily without an appropriate backlight system. The
backlight is essential for proper functioning as the image or data
displayed on the liquid crystal layer may only be viewed while the
backlight is providing proper illumination to the liquid crystal
stack. If the backlight system should fail completely or operate at
a less than optimal level, then the LCD will not perform
satisfactorily. While this may be a simple inconvenience when LCDs
are used for entertainment purposes, when used for information or
data displays this can be very costly. For example, LCDs are now
being used in cockpits of aircraft as well as the instrument panels
or display in ground vehicles and marine equipment. In these
applications, when there is a failure of the backlight, the LCD may
no longer display the important information for the
vehicle/aircraft and controls may cease to operate. These
situations can be undesirable not only to the passengers of the
vehicle/aircraft, but also other soldiers who are counting on this
part of the mission.
[0008] LEDs, however, have a limited life span, and eventually
their luminance will degrade until little or no luminance is
generated. Some LEDs may quickly fail simply due to a manufacturing
defect or may fail due to shock/forces applied to the aircraft or
ground vehicle. Currently when this occurs in an LED backlight, the
entire backlight assembly must be manually replaced (ie. the
element which every LED is mounted to is replaced with a new
element containing all new LEDs). This is expensive, and is often
time consuming. Alternatively, the LED backlight assembly could be
removed from the display housing, and the degraded or faulty LEDs
could be manually replaced. This is typically even more costly, and
involves extensive manual labor. In currently known units, this
also requires virtual complete disassembly of the LCD to gain
access to the backlight. This complete disassembly is not only
labor intensive, but must be performed in a clean room environment
and involves the handling of expensive, delicate, and fragile
components that can be easily damager or destroyed, even with the
use of expensive specialized tools, equipment, fixtures, and
facilities.
[0009] Thus, there exists a need for a more durable and dependable
backlight for a LCD so that failures can be accounted for and
vehicles/aircraft can complete a mission and/or return safely to
base.
SUMMARY
[0010] Exemplary embodiments provide a light source for a display
device having prominent color reproducibility. Exemplary
embodiments also provide a light source for a display device
enabling thin and compact display production continuously over
extended use periods. In order to ensure color reproducibility and
performance, the backlight of an electronic display should
preferably perform satisfactorily at all times.
[0011] Exemplary embodiments provide a backlight system for an
electronic display device, preferably an LCD device. The backlight
system includes a first backlight apparatus and at least one
additional backlight apparatus. The first backlight apparatus may
be capable of providing sufficient light to operate the display.
The second backlight apparatus may be operated in the event that a
portion of the first backlight apparatus falls below predetermined
operational standards.
[0012] In at least one embodiment, there may be a backlight
apparatus including a first array of LEDs mounted on a printed
circuit board (PCB). Additionally, there may be a second
(redundant) set of LEDs mounted adjacent to the first array of
LEDs. The redundant set of LEDs may be mounted on the same PCB as
the first array of LEDs. Alternatively if using an edge-lit design,
the first set of LEDs may be placed along a first edge of the
backlight while a second set of LEDs may be placed along another
edge of the backlight. A first control module may be associated
with the first array of LEDs while the redundant LEDs may be
controlled by a second control module. The two control modules may
be in a master/slave arrangement where the first control module is
the master while the second control module is the slave.
[0013] The system may include a device for monitoring the luminance
produced by the first and/or second array of LEDs. The monitoring
device may include predetermined operational standards for the
display. When the monitoring device detects that the display has
fallen below the predetermined standard for luminance, the
monitoring system may send a signal to one or both control modules.
If the first array of LEDs were the only source of illumination,
the control modules can then switch to the second array of LEDs as
there may have been a failure in the first array. The second or
redundant set of LEDs can be utilized seamlessly, thus ensuring
continuous operation of the LCD without the need for costly and
time consuming repairs of the backlight system.
[0014] Alternatively, the first and second array of LEDs may be
powered concurrently. Operating the LCD in this manner allows the
two LED arrays to operate at 1/2 the wattage while supplying the
same amount of illumination. This is noteworthy as LED efficiency
(sometimes measured as lumens per watt) is inversely related to
temperature and by powering each LED at a lower wattage less heat
is generated and the LEDs function at higher efficiency. If one
array were to fail, the other array could adequately illuminate the
LCD.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIG. 1 shows a front view of an embodiment for direct LED
backlighting an LCD.
[0016] FIGS. 2A and 2B show front views for alternative embodiments
of edge LED backlighting an LCD.
[0017] FIG. 3A shows a front view for an embodiment using edge LED
backlighting an LCD where the both opposing sides of the LCD are
illuminated.
[0018] FIG. 3B shows a front view for an embodiment using a
combination of edge LED backlighting and direct LED
backlighting.
[0019] FIG. 4 shows an electrical schematic for an exemplary
embodiment.
DETAILED DESCRIPTION
[0020] FIG. 1 provides one embodiment showing a direct backlight
assembly 100. A first plurality of LEDs 105 are mounted on a
mounting substrate 150. The mounting substrate 150 could be any
rigid or semi-rigid plate. An exemplary embodiment would use a
printed circuit board (PCB) as the mounting substrate 150. A second
(redundant) set of LEDs 120 are mounted adjacent to the first LEDs
105. The direct backlight assembly 100 preferably generates white
light. As shown in this embodiment, white LEDs are used to create
the white light. Therefore, in this embodiment, for every LED in
the first set 105, there is a corresponding LED for the second set
120 placed adjacent thereto.
[0021] Of course, there are many methods for generating white light
and any method could be used with the embodiments herein. Some
embodiments may use several colored LEDs in combination to create
the color white. Sometimes this is done with red, green, and blue
LEDs used in combination. Other times this may be done with a pair
of LEDs which contain a red-green and a red-blue LED that combine
to create white.
[0022] In one embodiment, the first plurality of LEDs 105 remain on
during normal operation while the second plurality of LEDs 120 are
off. If the system detects a failure in the first plurality of LEDs
105, the second plurality of LEDs 120 may be turned on while the
first plurality of LEDs 105 are now turned off. The changeover from
the first to second set of LEDs can happen very quickly, so that
there is no (or very minimal) interruption of the LCD operation
when there is a failure in the first plurality of LEDs 105. This
design has been found to provide many benefits. Notably, during
operation of an aircraft or ground vehicle, a failure in the first
plurality of LEDs 105 will not impact operation of the aircraft or
vehicle where before this could cause catastrophic events including
the loss of control of the aircraft or vehicle. Further, the
lifetime of the backlight device is effectively doubled without
having to manually repair or replace the backlight.
[0023] In another embodiment, both sets of LEDs may be operated
simultaneously. In this embodiment, each set of LEDs may be
operated at only 50% capacity. This may be very desirable for LED
operation as it can greatly increase the efficiency of the LED
backlight and thus reduce the overall energy consumption of the
device. Further, because the overall number of LEDs is effectively
doubled, the light density has increased and a more uniform level
of light may be produced. In the event that one of the sets of LEDs
may fail, the unit can be operated sufficiently by only the
remaining set of LEDs. This changeover can also happen very quickly
so that there would be no (or very minimal) interruption of the LCD
operation. One set of the LEDs may be powerful enough to operate
the LCD device at the desired brightness, color saturation,
contrast, and any other optical parameters set for the LCD device
operation. In other embodiments, one set of LEDs may be enough for
the device to be viewable by the pilot or vehicle operator but may
not be enough to operate at the desired levels for an extended
period of time. In this type of embodiment, the remaining LEDs
would allow the pilot or vehicle operator to complete the mission
and/or return to base but the LCD device may need manually serviced
before the next mission.
[0024] As an extension of this embodiment, three or four sets of
LEDs could be used to construct the backlight. Here, during normal
operation each set of LEDs could be driven at only 1/3 or 1/4 of
the normal capacity, resulting in high efficiency and light
uniformity. Upon failure of any one set of LEDs, the remaining sets
may be increased to provide the desired light levels. Again, this
changeover can happen very quickly so that there would be no (or
very minimal) interruption of the LCD operation.
[0025] FIG. 2A shows an alternative embodiment using an edge-lit
LED backlight 200. As known in the art, edge-lit LED backlights
place the LEDs along one of the edges of the backlight so that they
can provide illumination into the backlight cavity. This
illumination is typically directed out of the backlight cavity and
through the LCD stack as well as scattered and/or diffused to
provide a uniform light distribution. The scattering and directing
of the light can be accomplished in a number of different ways
(light guides, diffusing sheets, etc.) and the details of this will
not be discussed in detail as it is well known in the art. For the
edge-lit embodiment 200, the first plurality of LEDs 205 are placed
along a first edge while the second plurality of LEDs 220 are
placed along the opposing edge of the backlight. This design is
beneficial in an embodiment where both sets of LEDs are operated
simultaneously as they could combine evenly to create a uniform
distribution of light. Again, if the first set of LEDs 205 were to
fail, the second set of LEDs 220 could provide enough illumination
so that the LCD device could remain operational. The LCD device
could be adequately powered to the desired operation parameters
with the remaining set of LEDs or may simply be powered enough for
the image on the LCD to be viewable so that the aircraft or vehicle
could complete the mission and/or return to base.
[0026] FIG. 2B provides another embodiment using an edge-lit LED
backlight 300. Here, the first set of LEDs 305 is provided along
the vertical edge while the second set of LEDs 320 is provided
along the horizontal edge. Of course, there could be additional
sets of LEDs provided along the bottom horizontal edge and the left
vertical edge. In this type of arrangement, the additional LEDs
could correspond with the first or second LEDs 305 and 320 or may
be third and fourth sets of LEDs which are driven independently of
the first and second sets of LEDs 305 and 320.
[0027] FIG. 3A shows a front view for an embodiment 400 using edge
LED backlighting for an LCD where the both opposing sides of the
LCD are illuminated. Here, a first set of LEDs is comprised of two
arrays of LEDs 431 and 430 which are placed on opposing sides of
the LCD. Additionally, a second set of LEDs is comprised of two
arrays of LEDs 420 and 421 which are placed on opposing sides of
the LCD.
[0028] FIG. 3B shows a front view for an embodiment 450 using a
combination of edge LED backlighting and direct LED backlighting.
Here, a first set of LEDs may be provided in edge-lit fashion such
that LEDs 461 are along a first edge with LEDs 460 along an
opposing edge. Additionally, a second set of LEDs 480 is provided
in a direct lit fashion.
[0029] FIG. 4 provides an electrical schematic for an exemplary
embodiment. A first controller 515 is in electrical communication
with a first current source 510 which drives the first set of LEDs
505. A second controller 530 is in electrical communication with a
second current source 525 which drives the second set of LEDs 520.
The electrical connection 575 provides communication between the
first controller 515 and second controller 530. The first and
second controllers 515 and 530 may be any type of microprocessor,
application-specific integrated circuit, complex programmable logic
device, field-programmable gate array, or any other form of
electrical control. In some embodiments, the first and second
controllers 515 and 530 may be in a master/slave arrangement where
the first controller 515 is the master and the second controller
530 is the slave. In this arrangement, the first controller 515 may
provide adequate backlight luminance using just the first set of
LEDs 505. In the event that the master controller (first controller
515) detects a failure in the first set of LEDs 505, it may direct
the slave controller (second controller 530) to begin driving the
backlight with the second set of LEDs 520. A failure could be
detected by measuring the current draw of the LEDs and when the
measured amount falls outside of an acceptable threshold then a
failure may have occurred. A failure could also be detected by
measuring the luminance of the LEDs and indicating a failure when
the luminance levels fall below an acceptable amount.
[0030] Having shown and described preferred embodiments of the
invention, those skilled in the art will realize that many
variations and modifications may be made to affect the described
embodiments and still be within the scope of the claimed invention.
Additionally, many of the elements indicated above may be altered
or replaced by different elements which will provide the same
result and fall within the spirit of the exemplary embodiments. It
is the intention, therefore, to limit the invention only as
indicated by the scope of the claims.
* * * * *