L6562+TSM1052

April2009DocID14425Rev21/33AN2711Applicationnote15WofflineTRIACdimmableLEDdriverIntroductionThecostofpowerLEDsisrapidlycomingdown,whileperformanceisimproving.Theirefficacy(lightoutperwattin)isnowcompetitivewithcompactfluorescentlamps,whiletheirlifeissignificantlylongerat100,000full-powerhours(11+years)tohalfbrightness.DimmingofLEDscanextendthelifetimefurtherandalsoreducespowerdrain.ByfarthemostcommondimmingmethodistheTRIACphase-controldimmer,whichreplacestheACon-offswitchdirectly,butcanbeusedonlyonincandescentlampsandspeciallydesignedfluorescentballasts.Thisapplicationnotepresentsalow-costdriverforLEDsthatiscompatiblewithTRIACphase-controldimmers.Thedesigngivesluminairemanufacturersalow-cost,commonlyavailabledimmingoptionforhomefixtures.Asidebenefitisthat,whennotwiredtoadimmer,theunit'spowerfactorisover0.9.ThedesignisbasedontheL6562Atransition-modePFCcontrollerdrivingasinglestagePFCflybackpowerconverter.AnSTMicroelectronicspatentapplicationispendingforthemethodfordimminganofflineLEDdriverbymeansofaTRIACbaseddimmerasdescribedinthisdocument.Figure1.15WofflineTRIACdimmableblockdiagram(STEVAL-ILL016V1)Figure2.15WevaluationboardtopsideFigure3.15Wevaluationboardbottomside=120Vac.....................................19Table3.Temperatureofmeasuredpointsat115Vac-fullload,25°Cambient...............20Table4.Windingcharacteristics....................................................21Table5.Documentrevisionhistory.................................................32AN2711ListoffiguresDocID14425Rev25/33ListoffiguresFigure1.15WofflineTRIACdimmableblockdiagram(STEVAL-ILL016V1)...................1Figure2.15Wevaluationboardtopside..............................................1Figure3.15Wevaluationboardbottomside...........................................1Figure4.Thyristor(TRIAC)dimmerwithlightbulb.......................................8Figure5.Non-dimmablepowerconverterLEDdriver.....................................8Figure6.Linecurrentwithoutdimming................................................9Figure7.Linecurrentwithdimming...................................................9Figure8.Linecurrentnearminimumconductionangle..................................10Figure9.LEDcurrentnearminimumconductionangle...................................10Figure10.Linecurrentat90°cond.angle..............................................11Figure11.LEDcurrentat90°cond.angle..............................................11Figure12.Linecurrentatmaxconductionangle.........................................11Figure13.LEDcurrentatmaxconductionangle.........................................11Figure14.Linecurrentwithnodimmer................................................12Figure15.LEDcurrentwithnodimmer...............