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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®drivers | BACKLIGHTINGMatching driver design with LED backlightscheme optimizes energy savingsLED backlighting is a requisite for TVs to meet more demanding Energy Star requirements, explainsGYAN TIWARY, and matching the driver design to the backlight implementation delivers maximumenergy savings.GYAN TIWARY (gtiwary@iWatt.com) is thesenior vice president and general manager ofthe DC/DC Business Unit at iWatt, Inc. (www. ___iwatt.com).______Direct dimming*TABLE 1. Characteristics of LED backlight types.Energy Star requirements for flat-paneltelevisions have become more stringentin recent years. If the Energy Star6.0 proposal is accepted, it mandates that allTVs larger than 50 inches must consume nomore than 85W of power by the fall of 2012.Two years ago, such TVs consumed close to200W. These strict standards that attemptto curb power consumption worldwide haveled to significant innovations in LCD TVs,especially in the backlight unit (BLU) whichis a major source of power consumption.LED-based BLU can offer significant powerreduction although the driver design mustbe optimized for the different direct- andedge-backlit schemes.Active power consumption in an LCD TVconsists of two main components: displaypower and baseline power. Baseline powerencompasses the video-processing aspectsof the TV and the main power supply, andtypically accounts for about a third of thetotal power. Various components and scenarioswill impact baseline power consumption,such as frame rate and power supplyefficiency. In a 3D TV scenario, for example,additional image processing, a faster refreshrate and increased brightness can increasebaseline power by 50-100% relative to standardTVs. Similarly, smart Internet-connectedTVs require a higher performanceprocessor, additional memory, and otherelements adding a few watts of power. Still,the baseline power adders are a small fractionof the overall TV power consumption.Display power refers to the power consumedby the LCD screen, BLU, and associatedcircuitry, and accounts for about two thirds ofthe total power consumed by a TV. Therefore,it would be logical for the industry to focus onreducing power consumption in this area.Display power usage is high largelybecause the luminous efficiency of LCD TVsis very poor. An LCD panel has an extremelylow transmittance level, in the 4-6% range,as the light travels from the BLU throughthe light guide, diffuser, optical film, andcolor filter. For example, if the BLU generates8000-10000 cd/m² of luminance, thenthe final, visible-to-the-eye output mighttypically be between 380-450 cd/m².The BLU must therefore generate considerablelight and consumes the largestamount of power inside an LCD TV. Anyimprovement in BLU efficacy will lead todramatic power savings for the TV.Not too many years ago, cold cathode fluorescentlight (CCFL)-backlit LCD displayswere the biggest power guzzlers inside LCDSegment-edge/hybrid dimming*Edgedimming**Picture quality Best Medium WorseEnergy consumption Lowest Medium HighestForm factor Thicker (by