国家半导体的LED照明解决方案-图文(精)

2WithhigherefficienciesthanincandescentbulbsandwithoutthehazardouschemicalsfoundinColdCathodeFluorescentLamps(CCFL,LEDlightingisgainingpopularityasanenvironmentallyfriendlylightingsolution.TheabilitytocontrolbrightnessandcolortemperaturebyelectronicdimmingmakesLEDlightinganappealingsolutionformanyilluminationapplicationsrangingfrommoodlightingtovideoprojection.LEDDriverDesignConsiderationsNationalhasadiverseportfolioofconstant-currentregulatorsfordrivingLEDs.Regardlessoftype,size,orpower,allLEDsworkbestwhendrivenwithaconstantcurrentsincetheLEDcolorchangeswithsmallvariationstodrivingcurrent.Therefore,LEDmanufacturersspecifycharacteristicssuchasthelumens,beampattern,andcoloroftheirdevicesataspecificforwardcurrent(IF,notataspecificforwardvoltage(VF.MostpowersupplyICsaredesignedtoprovideconstantvoltageoutputsoverarangeofcurrents,nottoprovideaconstantcurrentasneededfordrivingLEDs.Usingaconstant-currentregulatorisalsobetterthanusingaresistorasacurrentsourcebecause,witharesistor,thecurrentaccuracyisdirectlyimpactedbytheaccuracyoftheinputvoltage,thetoleranceoftheresistor,andvariationstothenumberorOtherchallengeswithdrivingLEDsdependontheLEDconfiguration.PlacingalltheLEDsinaseriesstringensurestheexactsamecurrentflowsthrougheachLED.Thedrivingcircuitryfortheseriesconfigurationissimpli-fiedduetoguaranteedcurrentmatching,butthenumberofLEDsthatcanbedrivenoffanoutputrailislimited.WithanarrayofLEDs,everyparallelLEDstringmustbedrivenwiththesamecurrenttoobtainevenbrightnessandcolor.ThisconfigurationallowsmanymoreLEDstobedrivenoffanoutputrailbutalsoincreasesthedrivingcircuitrycomplexity.ChoosefromNational’sLEDdriversforbothparallelandseriesconfigurationswithfeaturessuchasbuilt-incurrentmatching,higheffiSeriesTopologiespositive(+tonegative(-.Advantage:ParallelTopologiesLpositive(+tonegative(-.Advantage:visit:=FormoreinformationaboutNational’sPowerWiseproducts,visitficientandeasytodrive.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-23WhiteLEDFlashApplicationLM2731–0.6/1.6MHzBoostConverterwith22VInternalFETSwitchCurrentmodestep-upDC-DCconverterwitha1.2AinternalNMOSswitch,designedtodeliverupto120mAat16Vfromalithium-ionbattery.Thedevice’ssynchro-nousswitchingoperation(noexternalSchottkydiodeatheavy-load,andnon-synchronousswitchingoperationatlight-load,maximizespowerefficiency.Trueshut-downfunctionbysynchronousFETandrelatedcircuitryensuresinputandoutputisolation.Aprogrammablesoft-startcircuitallowstheusertolimittheamountofinrushcurrentduringstartup.Theoutputvoltagecanbeadjustedbyexternalresistors.Package:Lowprofile10-pinLLP(3mmx3mmx0.8mmLM4510TypicalApplicationCircuitLM4510–SynchronousStep-UpDC-DCConverterforWhiteLEDsand/orOLEDDisplays7national.com/LEDCurrent-modeboostconverterofferstwoseparateoutputs:(MAINisaconstant-currentsinkfordrivingserieswhiteLEDs,and(SUB/FBisconfigurableasaconstant-currentsinkforserieswhiteLEDbias,orasafeedbackpintosetaconstantoutputvoltageforpower-ingOLEDpanels.Whenconfiguredasadual-output,whiteLEDbiassup-ply,theLM3509adaptivelyregulatesthesupplyvoltageoftheLEDstringstomaximizeefficiencyandensurethecurrentsinksremaininregulation.Themaximumcurrent-per-outputissetviaasingleexternallow-powerresistor.AnI2C-compatibleinterfaceallowsforindepen-dentadjustmentoftheLEDcurrentineitheroutputfrom0tomaxcurrentin32exponentialsteps.WhenconfiguredasawhiteLED+OLEDbiassupply,theLM3509canindependently,andsimultaneously,driveastringofupto5whiteLEDswhiledeliveringaconstantoutputvoltageofupto21VforOLEDpanels.Package:Lowprofile10-pinLLP(3mmx3mmx0.8mmDualWhiteLEDBiasSupplyVIN=LM3509TypicalApplicationCircuitLM3509–High-EfficiencyBoostforWhiteLEDsand/orOLEDDisplaysTheLM3430isarobustboostcontrollercapableofveryhighdutycycl