LED LightingSolutions Guide

Edition 1, July 2011

LED Lighting

1

LED Lighting

The Expanding Role for LED LightingLight-emittingdiodes(LEDs)arearapidlyevolvingtechnologyandarebecomingviableformanygenerallightingapplications,usuallyreferredtoassolid-statelighting(SSL).ThemostrelevantexamplesofLEDlightingapplicationsareindoorusesincommercial,industrial,andresidentialenvironments;outdoorapplicationslikestreetlightsandparkinglights;andarchitecturalanddecorativelightingwhereLEDswereinitiallyadoptedbecauseoftheirabilitytoemitthewholespectrumofcolors.

LEDshavebeenaneffectivesolutionforarchitecturallightingforsometime.TodayLEDsarepenetratingthemainstreamgenerallightingmarket,thankstotheirhigherperformancecomparedtootherlightingtechnologies:

They have a much longer lifetime than other lighting technologies.LEDscanoperatefor50,000hoursversus1,000to2,000hoursforincandescentlampsandabout5,000to10,000hoursforcompactfluorescentlights(CFLs).ThismarkedlylongerlifetimemakesLEDsidealformanycommercialandindustriallightingapplicationswherethelaborcosttoreplacealampishigh.

Their energy efficiency is superior to incandescent and halogen lamps, and often equivalent to fluorescent lamps.Additionally,theefficacyofLEDsiscontinuouslyimproving;theefficacyofwhiteLEDs(WLEDs)isnowforecastedtoimprovebyabout50%overthenextthreetofouryears.

They have a small form factor.LEDsfitinsomeformfactorslikeMR16andGU10lampswhereCFLsdonot.

They can be dimmed with the appropriate driver.Fluorescentlampsposetechnicallimitationswhentheapplicationrequiresdimming.AlthoughconventionalLEDdesignshaveencounteredsimilarissues,innovativeLEDdriversfromMaximarecompat-iblewithtriacandtrailing-edgedimmers.

They can provide focused light.Unlikeotherlightingtechnolo-gies,LEDsaremoreappropriateforapplicationslikenarrow-anglereflectorlampsthatrequireaverydirectionallight.

Their efficacy improves at lower temperatures.Theefficacyoffluorescentlampsdegradesatlowertemperatures.Incontrast,LEDsareidealforapplicationswithalowambienttemperaturelikerefrigeratorlighting.

It is very easy to change the color of their emitted light.ThismakesRGBLEDsidealforapplica-tionslikearchitecturalandmoodlightingwherethecolorofthelightmustchangeinrealtime.

Insummary,LEDsoffermanyadvan-tagesoverincandescent,halogen,andfluorescentlamps.Consequently,designerscontinuetofindmoreapplicationsforLEDlighting,butthatdiscussioncouldconsumeusforalongwhile.Thisreviewwillfocusononlytwo,butquitetimely,applications:LEDretrofitlampsandremote-controlledLEDlighting.

LEDretrofitlampsaremadetoreplaceincandescent,halogen,orfluorescentlampsinthesamesocket.TheseLEDlampsmustfitintheexistingformfactorandbecompat-iblewiththeexistinginfrastructure.

LEDsforremote-controlledlightingallowgreaterflexibilityindimmingandchangingthecolorofthelight.LEDlampsareinherentlydigitalsystems,makingitstraightforward

tointegratecommunicationsforlightingautomation.Theuseofwirelessorpowerline-communica-tion(PLC)remotecontrolreducespowerconsumption,lowersoperationandmaintenancecosts,andenablesnewLEDapplications.

LED Retrofit Lamps ManywouldarguethattheLEDretrofitlampmarketisthefastestgrowingapplicationforLEDlightingtoday.Thereasonforthisfastgrowthisactuallyquitestraightforward:theselampsdonotrequireanewelectricalinfrastructure(i.e.,cabling,transformers,dimmers,andsockets),asignificantadvantageforLEDtechnology.

FittinganLEDlampintotheexistinginfrastructurechallengesthedesignerintwoprincipalways:

1. The form factor.Retrofitlampsmustfitintheformfactorofthepreviouslightsource.

2. Electrical compatibility.Retrofitlampsmustworkcorrectlyandwithoutlightflickerintheexistingelectricalinfrastructure.

Weshalldiscusseachchallengeinturn.

Fitting the Existing Form Factor

Theexistingformfactorimposesbothaphysicallimitation(i.e.,thedriverboardhastobesmall

Maxim provides dimmable, flicker-free LED driver solutions for retrofit lamps.

www.maxim-ic.com/lighting 2

LED Lighting

enough)andathermallimitationonaretrofitlamp.Theselimitationsposechallengesforthedesignofareplacementlamp(e.g.,PAR,R,andAformfactors),challengesthatareparticularlyhardtoovercomeforsmallerformfactorslikeMR16andGU10.Forthisreason,MaximoffersadriverICwithintegratedMOSFET(MAX16840)forMR16applications.

Whilesizeisimportantforaretrofit,thermallimitationisoftenmorecritical.LEDsemitonlyvisiblelight;theydonotirradiateenergyatinfraredwavelengthslikeothertech-nologies.Thus,whileLEDsaremoreenergyefficientthanincandescentorhalogenlamps,theydissipatemuchmoreheatthroughthermalconductioninthelamp.

Thermaldissipationisalsothemainlimitingfactorfortheamountoflightthatalampcanproduce.TodaysLEDtechnologyinretrofitlampscanbarelyachievealevelofbrightnessthatisacceptableforthemainstream

market.Pushingthelimitsofbright-nessand,consequently,thermaldesignareessentialfordesigningacommerciallysuccessfulproduct.

Acorollaryissuetothethermaldissi-pationisthelifetimeofthedriverboard.Toemitmorelight,thelampmustworkatafairlyhightempera-ture(+80Cto+100C).Atthesetemperatures,thelifetimeofthedriverboardcanlimittheoperationofthewholelamp.Electrolyticcapac-itorsarethebiggestchallengesincetheyarethefirstcomponentthatfailsathightemperature.

Maximsdriversolutionsfor120VAC/230VACand12VACgivecustomerstheoptionofnothavingelectrolyticcapacitors,iftheycanaccepthigherLEDripplecurrent.Ifinsteadthecustomerdecidestouseelectrolyticcapacitors,Maximdriversolutionsarefaulttolerant:adeteri-orationoftheelectrolyticcapacitorscausestheLEDripplecurrenttoincrease,butthelampdoesnotfail.

Matching the Electrical Infrastructure

RetrofitLEDlampsmustworkcorrectlyininfrastructuresthatincludecut-angle(triacortrailing-edge)dimmersandelectronictransformers.

Workingoffthe120VAC/230VACline,thelampcanbeprecededbyatriacdimmer.Triacdimmersaredesignedtoworkwellwithincandescentandhalogenlamps,whichareperfectlyresistiveloads.WithLEDretrofitlamps,however,theLEDdriverisgenerallyaverynonlinearandnotpurelyresistiveload;itsinputbridgerectifiertypicallydrawsbrief,high-intensitypeaksofcurrentwhentheACinputvoltageisatitspositiveandnegativepeaks.ThisLEDbehaviordoesnotallowthetriacdimmertoworkproperly,becauseitprovidesneithertheneededstartcurrentnortheholdcurrent.Asaresult,thedimmerdoesnotstartproperlyorturnsoffwhileoperating,andtheLEDlampflickers.

12VAC

ELECTRONICTRANSFORMER

MR16

TRAILING-EDGE

DIMMER(OPTIONAL)

120VAC/230VAC

AC SUPPLY

LOW-VOLTAGE LED LIGHT BULB

LV LEDDRIVERS

90VAC TO 265VACLED DRIVERS

TRIACDIMMER

(OPTIONAL)

120VAC/230VAC

AC SUPPLY

A20

LINE-POWERED LED LIGHT BULB

Block diagrams for MR16 and offline lamps. For a list of Maxim's recommended solutions, please go to www.maxim-ic.com/lighting.

http://www.maxim-ic.com/MAX16840http://www.maxim-ic.com/lighting

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LED Lighting

SWITCHDEBOUNCER

POWER SUPPLY(DC-DC, LDO)

HIGH-BRIGHTNESSLED DRIVER

TEMPERATURESENSOR

WIRELESS Rx, Tx

OR

PROXIMITYDETECTOR

AMBIENT-LIGHTSENSOR

POWERMEASUREMENT

SoC

POWERLINE AFE POWERLINE MAC/PHY

H

N

AC LINE

LEDARRAY

FAULT REPORTING

PWM DIMMING

ANTENNA

SUPERVISOR

ISOLATED AC-DCPOWER SUPPLY

HPF ORLINE DRIVER

Theelectricalinfrastructureisevenmorecomplicatedfor12VACinputlamps,becauseanelectronictrans-formerandtrailing-edgedimmercanbeconnectedatthelampsinput.Again,a12VACinputlampdriverthatusesthetraditionalbridgerectifierandDC-DCconvertertopologyflickersbecauseofincompatibilitywiththetransformeranddimmer.

MaximsLEDsolutionsfor120VAC/230VACand12VACinputlampsuseasingle-stageconversion.Byshapingtheinputcurrentsothatthelightdoesnotflickerevenwhendimmed,thesesolutionsarecompatiblewithtriacandtrailing-edgedimmersandelectronictransformers.NoothersolutionsforMR16lightsofferthisfeature;fewsolutionsforPAR,R,andAlampsofferit.Inaddition,thesesolutionsprovidebetterthan0.9power-factorcorrectionandrequireaverylimitednumberofexternalcomponents.The120VAC/230VACinputsolutionusestheMAX16841,whilethe12VACsolutionemploystheMAX16840.Bothpartsareavailableforevaluationanduseinmassproduction.

Remote-Controlled Applications in Street, Parking, and Indoor Lights

Asstatedabove,LEDsoffermoredesignflexibilityfordimmingandchangingthelightcolor.Thisversatilitymakesthemidealforapplicationslikearchitecturallighting,indoorambientlighting,anddimmablestreetandoutdoorlighting.AlltheseapplicationsrequireatechnologytocontroltheLEDlightremotely.Fortheapplicationtobesuccessfulinthemarketplace,thecostofupgradingthelightinginfrastruc-turetonewLEDtechnologymustbeminimized.Notsurprising,solutionsthatcanreusethepresentinfrastruc-turewilllikelybethefirsttopenetratethemarket.

Whenconvertingtoremote-controlledLEDlighting,themostcostlyinfrastructureupgradetoantici-pateisthewiringtocontroltheLEDlights.Fortunately,LEDlampscanbecontrolledthroughexistingpowerlinesusingPLCtechnology.

PLCtechnologyallowscommu-nicationoveralongrange.NewOFDM-basedPLCtechnology,includingemergingstandardssuchasG3-PLC,issimplifyingintegra-tionoflightingcontrolapplicationsbyprovidingnoiseimmunityandinteroperability.

Themaindesignrequirementsforremote-controlledLEDlightingsolutionsare:

The communication range,whichisdictatedbytheapplication.Foranindoorresidentialapplication,somethingintherangeof30missufficient.Streetlightingcanrequirearangeofseveralkilometers.

Low power consumption.AnimportantsellingpointofLEDsistheirhighenergyefficiency.ItisimportantthatanLEDlamp

Block diagram of an LED lighting system controlled through PLC or wireless links. View recommended solutions at www.maxim-ic.com/lighting.

http://www.maxim-ic.com/MAX16841http://www.maxim-ic.com/MAX16840http://www.maxim-ic.com/lighting

www.maxim