国家半导体的LED照明解决方案图文精Word文档下载推荐.docx

国家半导体的LED照明解决方案图文精Word文档下载推荐.docx

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ithhigherefficienciesthanincandescentbulbsandwithoutthehazardouschemicalsfoundinColdCathodeFluorescentLamps（CCFL,LEDlightingisgainingpopularityasanenvironmentallyfriendlylightingsolution.TheabilitytocontrolbrightnessandcolortemperaturebyelectronicdimmingmakesLEDlightinganappealingsolutionformanyilluminationapplicationsrangingfrommoodlightingtovideoprojection.

LEDDriverDesignConsiderations

Nationalhasadiverseportfolioofconstant-currentregulatorsfordrivingLEDs.Regardlessoftype,size,orpower,allLEDsworkbestwhendrivenwithaconstantcurrentsincetheLEDcolorchangeswithsmallvariationstodrivingcurrent.Therefore,LEDmanufacturersspecifycharacteristicssuchasthelumens,beampattern,andcoloroftheirdevicesataspecificforwardcurrent（IF,notataspecificforwardvoltage（VF.MostpowersupplyICsaredesignedtoprovideconstantvoltageoutputsoverarangeofcurrents,nottoprovideaconstantcurrentasneededfordrivingLEDs.Usingaconstant-currentregulatorisalsobetterthanusingaresistorasacurrentsourcebecause,witharesistor,thecurrentaccuracyisdirectlyimpactedbytheaccuracyoftheinputvoltage,thetoleranceoftheresistor,andvariationstothenumberor

OtherchallengeswithdrivingLEDsdependontheLEDconfiguration.PlacingalltheLEDsinaseriesstringensurestheexactsamecurrentflowsthrougheachLED.Thedrivingcircuitryfortheseriesconfigurationissimpli-fiedduetoguaranteedcurrentmatching,butthenumberofLEDsthatcanbedrivenoffanoutputrailislimited.WithanarrayofLEDs,everyparallelLEDstringmustbedrivenwiththesamecurrenttoobtainevenbrightnessandcolor.ThisconfigurationallowsmanymoreLEDstobedrivenoffanoutputrailbutalsoincreasesthedrivingcircuitrycomplexity.ChoosefromNational’sLEDdriversforbothparallelandseriesconfigurationswithfeaturessuchasbuilt-incurrentmatching,higheffi

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ForacompletelistofLEDDrivers,visit

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High-BrightnessLEDDrivers

LightingManagementUnits

LEDDrivers

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Overview

Low-powerLEDsareidealforbacklightingapplications,especiallyinsmall-tomedium-scaledisplays,becausetheyareefficientandeasytodrive.Formanyportableapplications,eachlow-powerLEDrequiresupto4Vat30mAfromalithium-ionbatterythattypicallysupplies3.6V.TooperatemorethanoneLEDforalightingsolution,aboostLEDdriverisrequiredtosupplyenoughvoltagetoforward-biastheLEDsandprovideregulatedcurrent.

Inmedium-scaledisplayssuchaslaptopsandGPSnavi-gationdevices,aboostregulatormayalsobeneededtodrivelong,parallelstringsoflow-powerLEDs.National’sinductive-boostregulatorsprovideLEDdriversolutionsthatarehighlyefficientandcapableofdrivinghighcur-rents.Inthissection,you’llfindvarioustypesofboostLEDdriverswithdifferentdimminginterfacestoaccommodatemultipleLEDbacklightingapplications.

Switchingregulatorsthatarecurrent-modeboostcon-vertersoperatingatfixedfrequenciesof1.6MHz（“X”optionand600kHz（“Y”option.

TheSOT-23packaginganduseofsmallinductorsandcapacitorsresultintheindustry’shighestpowerdensity.The22Vinternalswitchmakesthesedevicesperfectforboostingtovoltagesupto20V.

Protectionisprovidedthroughcycle-by-cyclecurrentlimitingandthermalshutdown.Internalcompensationsimplifiesdesignandreducescomponentcount.Package:

5-LeadSOT-23

WhiteLEDFlashApplication

LM2731–0.6/1.6MHzBoostConverterwith22VInternalFETSwitchCurrentmodestep-upDC-DCconverterwitha1.2AinternalNMOSswitch,designedtodeliverupto120mAat16Vfromalithium-ionbattery.Thedevice’ssynchro-nousswitchingoperation（noexternalSchottkydiodeatheavy-load,andnon-synchronousswitchingoperationatlight-load,maximizespowerefficiency.Trueshut-downfunctionbysynchronousFETandrelatedcircuitryensuresinputandoutputisolation.Aprogrammablesoft-startcircuitallowstheusertolimittheamountofinrushcurrentduringstartup.Theoutputvoltagecanbeadjustedbyexternalresistors.

Package:

Lowprofile10-pinLLP（3mmx3mmx0.8mm

LM4510TypicalApplicationCircuit

LM4510–SynchronousStep-UpDC-DCConverterforWhiteLEDsand/orOLEDDisplays

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boostconverterofferstwoseparateoutputs:

（MAINisaconstant-currentsinkfordrivingserieswhiteLEDs,and（S