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
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