1. Field of the Invention
The present invention relates in general to the field of information handling system displays, and more particularly to a system and method for managing LED backlight performance in a display.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
One goal of information handling systems is to present visual images from visual information generated by the information handling system. Liquid Crystal Displays (LCDs) offer a number of advantages that have made them a popular choice for the presentation of visual information as visual images. LCDs generate images with pixels disposed in a panel that vary the color of a white backlight that passes through the panel. One advantage of an LCD is that high quality resolution visual images are presentable from a relatively thin panel. Another advantage of an LCD is that the backlight typically uses reduced amounts of power relative to other types of illumination in other types of displays, such as plasma and rear projection displays. These advantages and others have made LCDs a natural choice for presenting images from portable information handling systems since portable information handling systems have small profiles and depend on internal battery power. However, LCDs are often also selected for use as external peripherals for desktop information handling systems as well as for use as televisions.
Typically, LCDs have used Cold Cathode Florescent Lamps (CCFL) to provide white backlight to a panel. Although CCFLs have relatively small power demands and provide reliable backlight, they generally use relatively high alternating voltages that require conversion by an inverter associated with the panel. One attractive alternative to CCFLs are light emitting diodes (LEDs) that use direct current voltage applied to semiconductor material to produce light. LEDs do not require conversion of direct current power to alternating current power and use even less power than CCFLs. To provide backlight to a typical LCD, four to six strings of LEDs are distributed across the back of the panel with each string having ten or so LEDs. Two types of LEDs are available to provide backlight: white LEDs (WLEDs) that produce white light with a blue LED having a phosphor coating; and Red Green and Blue LEDs (RGB LEDs) that use separate red, green and blue LEDs that illuminated together provide white backlight. One difficulty with LEDs as compared to CCFLs is that the use of plural LEDs instead of a single light source can make the generation of an evenly-distributed backlight more difficult. Further, failure analysis in the event of poor backlight performance tends to present increased complexity with LEDs as compared to CCFLs since failure of a CCFL typically results in no illumination while partial failure of LEDs can still produce illumination that may appear to an end user as having poor quality.
Therefore a need has arisen for a system and method which manages LED backlight performance in a display.
In accordance with the present invention, a system and method are provided which substantially reduce the disadvantages and problems associated with previous methods and systems for managing display backlight performance. LEDs of a display backlight are automatically monitored for failures by monitoring voltage at termination of the LED power circuit. Failure of one or more LEDs is automatically compensated by altering illumination from other LEDs of the backlight system.
More specifically, an information handling system has plural processing components that generate visual information for presentation as visual images at a display, such as an LCD. Pixels of the display present the visual image with backlight illuminated from the rear of the display. An LED backlight system has plural LED strings to provide illumination with each LED string having plural LEDs. An LED monitor detects the voltage and current levels at the termination of the LED strings. A balancing circuit interfaced with the LED monitor adjusts the power provided to the LED strings based upon the detected current and voltage. The balancing circuit analyzes the voltage drop across the LED strings to determine LED failures. A reduced voltage drop indicated by an increased terminating voltage indicates a short at an LED. A voltage drop to zero indicates an open circuit at the LED string and failure of all LEDs in the string. The LED balancing circuit compensates for failed LEDs by increasing illumination from non-failed LEDs, or, alternatively, provides failure information to the information handling system so that processing components or the operating system can compensate with additional illumination. In addition, the LED balancing circuit provides LED failure information to other processing components so that the identity of the failed LEDs and types of failures is available to the end user for fault analysis and physical correction of the failures.
The present invention provides a number of important technical advantages. One example of an important technical advantage is that LED backlight failures are automatically detected, analyzed and identified for corrective action. Corrective actions include improved response by technicians to correct failures by providing accurate on-board diagnostics information presented at the display or through a network connection. Corrective actions also include automated alterations to properly-operating LEDs to minimize the impact of failed LEDs on backlight illumination. Overall end user satisfaction with visual images presented by an LCD remains high despite partial failures, and correction of failures has reduced complexity for technicians with detailed information as to the types and numbers of failures.
The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.
Information handling system displays having LED backlights provide automated LED fault detection and compensation to maintain desired display illumination. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components.
Referring now to
The amount and balance of illumination provided by LEDs 24 is managed by an LED controller 28, located on display 20 or the motherboard of information handling system 10, that controls electrical power provided from an LED power regulator 30. Current levels measured at the termination of each LED string 26 by an LED monitor 32 are balanced by an LED balancing circuit 34 to provide desired illumination at each LED string 26 through a control unit 36, which controls the current levels provided from LED power regulator 30. In addition, LED monitor 32 measures the voltage at the termination of each LED string 26 so that LED balancing circuit 34 can analyze, identify and take corrective action for faults in one or more of the LEDs 24. For example, if a short occurs in an LED 24, voltage at the string termination 27 of LED string 26 will increase more than normal. An increased voltage level at the termination 27 of a string 26 is analyzed by LED balancing circuit 34 as a short and compensated for by having control unit 34 increase illumination from non-shorted LEDs 24 by an amount that offsets the number of shorted LEDs 24. If an open circuit occurs in an LED string 26, the voltage measured by LED monitor 32 for that string is zero. LED balancing circuit 34 analyzes zero voltage at termination of an LED string 26 as an open circuit and compensates for the open circuit by increasing illumination from non-open LED strings 26. In the event that a failed LED 24 is a particular color, such as red, green or blue, LED balancing circuit 34 compensates for the loss of the identified color by increasing illumination from similarly-colored LEDs. In addition to compensating for detected faults, LED balancing circuit 34 can initiate an alert of the fault, such as through presentation of a fault message at display 20 or communication of fault information to a network location. Alternatively, as part of a built-in self-test or system start-up, processing components of information handling system 10 inquire of LED controller 28 to retrieve the status of LEDs 24 so the processing components can adjust brightness settings to compensate for LED failures and issue fault messages.
Referring now to
Compensation commands by balancing circuit 34 attempt to provide improved backlight illumination quality in light of identified failures by adjusting the illumination of non-failed LEDs 24. For example, if 4 of 40 LEDs have failed to reduce illumination by 10%, then the remaining LEDs have their illumination increased to provide an illumination level requested by an end user. If an end user requests illumination at a 20% brightness level, then balancing circuit 34 illuminates the operational LEDs at a 22.2% brightness level to achieve desired brightness. An SMBus interface 42 or similar management bus interface allows communication of LED fault information to information handling system processing components in support of fault alerts and built-in self-tests of the display backlight system. Precise information about LED failures provides a basis for definitive corrective action. For example, a threshold level of allowed LED failures might be set which, if exceeded, will result in replacement of the display due to excessive degradation of display quality.
Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.