有关LED照明电源设计难题的探讨.docx

有关LED照明电源设计难题的探讨.docx

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有关LED照明电源设计难题的探讨

英文

有关LED照明电源设计难题的探讨TheLEDlightingpowersupplydesign

Problemsofdesign：

1.ElectrolyticcapacitorsandLEDlifeissuesdonotmatch

2.LED灯闪烁的常见原因与处理办法CommoncauseofLEDlightsflashingandapproach

3.PWM调光对LED的寿命有何影响利用TRIAC调光调控LED亮度的潜PWMdimmingtheimpactonthelifeofLEDdimmingcontrol

4.UsingRIACLEDbrightnessofthepotentialproblems

在LED照明电源设计中，存在以下几个设计难题：

电解电容寿命与LED不相匹配、LED灯闪烁的常见原因与处理办法、PWM调光对LED的寿命有何影响、利用TRIAC调光调控LED亮度的潜在问题。

IntheLEDlightingpowersupplydesign,thereareseveraldesignchallenges:

lifeelectrolyticcapacitorsdonotmatchwiththeLED,LEDlightsflashingcommoncausesandsolutions,PWMdimmingoftheLED'slifeimpactoftheuseofTRIACLEDdimmingcontrolbrightnessofthepotentialproblems.ONSemiconductorSeniorApplicationEngineeringManagerChengwereinthetextbeforetheoccurrenceoftheseproblemscausesandsolutiontostarton.

1.电解电容寿命与LED不相匹配的问题ElectrolyticcapacitorsandLEDlifeissuesdonotmatch

LED照明的一个重要的考虑因素，就是LED驱动电路与LED本身的工作寿命应该能够相提并论。

LEDlightingisanimportantconsiderationistheLEDdrivecircuitandtheLEDitselfshouldbeabletocomparetheworkoflife.虽然影响驱动电路可靠性的因素有很多，但其中电解电容对总体可靠性有至关重要的影响。

Althoughthereliabilityofthefactorsaffectingdrivercircuitalot,buttheoverallreliabilityofelectrolyticcapacitorshaveacriticalinfluence.为了延长系统工作寿命，需要有针对性地分析应用中的电容，并选择恰当的电解电容。

Inordertoextendtheservicelifeofthesystem,whichrequiresfocusedanalyticalapplicationsincapacitors,andselecttheappropriateelectrolyticcapacitors.

实际上，电解电容的有效工作寿命在很大程度上受环境温度及由作用在内部阻抗上的纹波电流导致的内部温升影响。

Infact,theeffectiveworkinglifeofelectrolyticcapacitorsinlargepartbyenvironmentaltemperatureandtheroleoftheinternalimpedanceoftheripplecurrentcausedbyimpactoftheinternaltemperaturerise.电解电容制造商提供的电解电容额定寿命是根据暴露在最高额定温度环境及施加最大额定纹波电流条件下得出的。

Electrolyticcapacitorelectrolyticcapacitormanufacturer'sratedlifeisbasedonthemaximumratedtemperature,exposuretotheenvironmentandtoexertmaximumratedripplecurrentconditionsobtained.在105°C时典型电容额定寿命可能是5,000小时，电容所实际遭受的工作应力相比额定电平越低，有效工At105°Cratedlifeoftypicalcapacitancemaybe5,000hours,capacitancecomparedtotheactualworkingstresssufferedbythelowerratinglevel,themoreeffectivelongworkinglife.因此，一方面，选择额定工作寿命长及能够承受高额定工作温度的电解电容当然能够延长工作寿命。

Therefore,ontheonehand,chooseratedlonglifeandcanwithstandhighoperatingtemperaturesofelectrolyticcapacitorsratedtoextendtheworkinglifeofcourse.另一方面，根据实际的应力和工作温度，仍然可以选择较低额定工作温度和额定寿命的电容，从而提供更低成本的解决方案；换个角度说，在设计中考虑保持适当的应力和工作温度，可以有效地延长电解电容的工作寿命，使其更能与LED寿命相匹配Ontheotherhand,accordingtotheactualstressandtemperature,youcanstillchoosealowertemperatureratingandratinglifeofthecapacitor,therebyprovidingamorecost-effectivesolutions;anotherpointofview,aproperconsiderationinthedesignofthestressandtemperature,caneffectivelyextendtheservicelifeofelectrolyticcapacitors,tobettermatchwiththeLEDlifetime.

举例来说，安森美半导体符合“能源之星”固态照明标准的离线型LED驱动器GreenPoint®参考设计选择了松下的ECA-1EM102铝电解电容，其额定值为1000µF、25V、850mA、2,000小时及85°C。

Forexample,ONSemiconductormeet"EnergyStar"standardsforoff-line-basedsolidstatelightingLEDdriverGreenPoint®referencedesignchosenPanasonicECA-1EM102aluminumelectrolyticcapacitor,itsratingof1000μF,25V,850mA,2,000hoursand85°C.在假定50°C环境温度条件下，这电容的可用寿命超过12万小时Assuming50°Cambienttemperatureconditions,thecapacitanceoftheusefullifeover120,000hours.因此，尽力使LED驱动电路工作在适宜的温度条件并妥善处理散热问题，就能实现LED驱动电路与LED工作寿命的匹配问题。

Therefore,strivetomakeLEDdrivercircuitintheappropriatetemperatureconditionsandproperlyhandletheheatdissipation,LEDdrivercircuitcanbeachievedwithLEDworkinglifeofthematchingproblem.

总的来看，如果LED驱动电路中必须使用电解电容，那就必须努力控制电容所受的应用力及工作温度，从而最大程度延长电容工作寿命，以期与LED寿命匹配；另一方面，设计人员也应该尽可能地避免使用电解电容。

Ingeneral,iftheLEDdrivecircuitmustusetheelectrolyticcapacitor,itmuststrivetocontroltheapplicationofpowercapacitorsandsufferedoperatingtemperature,thusextendingthemaximumcapacitanceofworkinglifeinordertomatchwithLEDlife;theotherhand,designersshouldalsobepossibletoavoidtheuseofelectrolyticcapacitors.

2.LED灯闪烁的常见原因与处理办3.CommoncauseofLEDlightsflashingandapproach

通常人眼能够感知到频率达70Hz的光闪烁，高于这个频率则不会Usuallythehumaneyecanperceivefrequenciesupto70Hzflickeroflight,abovethisfrequencywillnotbeperceived.故在LED照明应用中，如果脉冲信号出现频率低于70Hz的低频分量，人眼就会感受到闪烁Therefore,inLEDlightingapplications,ifthepulsesignalsfrequencybelow70Hzlow-frequencycomponents,thehumaneyewillfeeltheflicker.当然，在具体应用中，有多种因素可能导致LED灯闪烁Ofcourse,inspecificapplications,thereareseveralfactorsthatmaycauseLEDlightflashes.例如，在离线式低功率LED照明应用中，一种常见的电源拓扑结构是隔离型反激拓扑结构Forexample,inofflineLEDlightinglow-powerapplications,acommonpowersupplytopologyisisolatedflybacktopology.以安森美半导体符合“能源之星”固态照明标准的8W离线型LED驱动器GreenPoint®参考设计为例，由于反激稳压器的正弦方波功率转换并未给初级偏置提供恒定能量，动态自供电（DSS）电路可能会激活并引发光闪烁。

ONSemiconductortomeetthe"EnergyStar"8Wsolid-statelightingstandards-basedoff-lineLEDdriverGreenPoint®referencedesign,forexample,becausetheflybackvoltageregulatorsinesquarewavepowerconversionbiasisnottoprovideaconstantprimaryenergy,DynamicSelf-Supply（DSS）circuitmaybeactivatedandtriggeraflashinglight.Toavoidthisproblem,mustbemadetotheinitialbiasineachhalfcyclepartofthedischarge,thecorrespondingneedtoproperlyselectthebiascircuitconstitutethecapacitanceandresistancevalue.

另外，即使是在使用提供极佳功率因数校正、支持TRIAC调光的LED驱动应用中，也要求电磁干扰（EMI）滤波器。

Inaddition,evenintheuseofpowerfactorcorrectiontoprovideexcellentsupportofTRIACdimmingLEDdriverapplications,alsocalledelectromagneticinterference（EMI）filter.由TRIAC阶跃（step）引起的瞬态电流会激发EMI滤波器中电感和电容的BytheTRIACstep（step）inducedtransientcurrentEMIfilterwillstimulatethenaturalresonantinductorandcapacitor.如果这谐振特性导致输入电流降至TRIAC维持电流之下，TRIAC将会关闭IfthisresonancecharacteristicsleadtoreducedinputcurrentbelowtheholdingcurrentTRIAC,TRIACwillbeclosed.Afterashortdelay,TRIACwillturnoftentostimulatethesameresonance.在输入电源波形的一个半周期内，这系列事件可能会重复多次，从而形成可见的LED闪烁。

Inasemi-inputpowerwaveformcycle,thisseriesofeventsmayberepeatedseveraltimestoformthevisibleLEDblinks.Toaddressthisproblem,TRIACdimmerisakeyrequirementisverylowinputcapacitanceEMIfilterandthecapacitortobeabletothroughtheTRIACandthewindingimpedancedecoupling.根据 公式，调光模块中电容减小的话，就能够增大谐振电路的电阻，原理上就抑制振荡，恢复想要的电路工作Accordingtotheformula,dimmingmodulecapacitancedecreases,thenitcanincreasetheresonantcircuitofresistance,ontheprincipleofvibrationsuppression,restorationofthedesiredcircuit.

3.PWM调光对LED的寿命有3PWMdimmingoftheLED'slifeimpact

LED本身的寿命很长，PWM调光并不会损及LED的预期寿命；甚至由于PWM调光帮助减小LED发热量，实际上还能帮助延长LED预期寿命。

ItsverylonglifeLED,PWMdimmingLEDwillnothurtthelifeexpectancy;evenasPWMdimmingLEDtohelpreducetheheat,infact,alsohelptoextendtheLEDlifeexpectancy.当然，在系统设计中，需要有效地检测及控制LED温度，保证LED可靠工作，体现其长寿命和低维护成本的优势Ofcourse,inthesystemdesign,theneedforeffectivedetectionandcontrolofLEDtemperature,toensurereliableoperationLED，reflectingitslonglifeandlowmaintenancecostadvantages.

4.利用TRIAC调光调控LED亮度的潜4LEDdimmingcontrolusingTRIACbrightnessofthepotentialproblems

CurrentTRIACdimmingisfairlypopularwiththemarketwelcomedthedimmingmode.TRIACdimmeroriginallydesignedforincandescentlamps,butsuchasONSemiconductorhasintroducedaleadingproviderofsupportTRIACdimmingoftheLEDdriverisidealforLEDlightingisprovidedintheTRIACdimmer.However,thisapproachhasitslimitationslie,suchasincreasedcircuitcomplexity,affectthepowerfactor;dimminglevelisrelativelylimitedandsoon.ONSemiconductor,asappliedtothefirstgreenhigh-performanceelectronicproducts,energyefficientsiliconsolutionsproviderrecentlyintroducedforresidentialandcommercialLEDlightingapplications.Thisdeviceisusingthecriticalconductionmode（CrM）anti-shockstructureofasingle-stagetopologytoprovidepowerfactorhigherthan0.95,sotheysaveDC-DC（DC-DC）conversionsection,simplifyingthecircuit.Thisislowevenwhenthedevicealsooffershighenergyefficiency;complywithallregulatoryrequirementsandoverallsystemopticalefficiencyrequirements.Inaddition,thisdeviceiscompatiblewiththefrontendofTRIACdimmeranddimmeralongthetransistor,dependingontheuseofdimmers,LEDlightoutputcanbeadjustedtolessthan2%,providingexcellentdimmingperformance.

5.ONSemiconductor'sLEDdriverpushingtherecenthotprogram

安森美半导体近期推出了几款重要的高能效GreenPoint®LED驱动器参考设计，分别是Semiconductorrecentlyintroducedseveralimportantenergy-efficientGreenPoint®LEDdriverreferencedesignis:

1）3W至5WLED驱动器参考设计方案。

1）3Wto5WLEDdriverreferencedesign.ThisreferencedesignforMR16LEDreplacementwiththesizeandcharacteristicsofconfiguration,havebeencarefullyconstructedandtestedfordrivinghigh-brightnessLED.这参考设计基于降压-升压型拓扑结构，使用安森美半导体的非隔离型恒流配置、工作在约150千赫兹（kHz）频率的NCP3065开关稳压器。

Thisreferencedesignisbasedonbuck-boosttopology,usingONSemiconductor'snon-isolatedconstantcurrentconfiguration,theworkofabout150kHz（kHz）frequencyNCP3065switchingregulator.这参考设计电路适合轨道照明、汽车照明及景观照明等12Vac或12Vdc应用，不论输入线路及输出LED电压如何变化，均提供平坦的电流稳流。

Thisreferencedesigncircuitfortracklighting,automotivelightingandlandscapelighting,12Vacor12Vdcapplications,regardlessofinputandoutputLEDlinevoltagetochange,provideasmoothsteadyflowofcurrent.这参考设计还提供独特的自动检测电路，支持12Vdc或12Vac电源输入，同时维持目标输出电流。

Thisreferencedesignalsoprovidesauniqueauto-detectioncircuit,supporting12Vdcor12Vacpowerinput，whilemaintaining