LED驱动需要不需要电容

《LED驱动需要不需要电容》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、LED驱动需不需要电容林伟涛信息工程学院DrivingLEDs:ToCaporNottoCapIntroductionHigh-brightnessLEDsareavailabletodaywithforwardcurrentsmorethan100timesgreaterthantheirpredecessors.Thesenewdevicesarenotjusthighbrightness,butarehighpoweraswell.Singlediewithdissipationsof5Wandmulti-diemoduleswithpowerinexc

2、essof25Warenowavailable.TherequirementsofhighefficiencyandlowdissipationdictateaswitchingpowersupplyforthisnewgenerationofHigh-Brightness(HB),High-Power(HP)LEDs,asavoltageregulatorandacurrentlimitingresistorarenolongerappropriate.High-brightness,high-powerLEDsrequireaconstant-curren

3、tsourcetotakefulladvantageoftheirever-increasingluminousefficiencyandvibrant,purecolor.Thetopologyofchoiceforthisnewbreedofswitchingconstantcurrentsourcesisthebasicbuckconverter.ThemostconvincingargumentforusingabuckconverteristheeasewithwhichthissimpleDC-DCconvertercanbeturnedintoa

4、constant-currentsource.Thisarticlewillexplaintheselectionof,orpossibleexclusionof,anoutputcapacitorwhendesigningabuckregulatorforconstant-currentdriveofHBLEDs.ControlledCurrentThebuckregulatorisuniquelysuitedtobeaconstantcurrentdriverbecausetheoutputinductorisinserieswiththeload.Reg

5、ardlessofwhetherabuckregulatorisusedasavoltagesourceoracurrentsource,selectionoftheinductorformsthecornerstoneofthesystemdesign.Withaninductorinserieswiththeoutput,theaverageinductorcurrentisalwaysequaltotheaverageoutputcurrent,andthebuckconverternaturallymaintainscontroloftheAC-cur

6、rentripple.Bydefinition,theLEDdriveisaconstantloadsystem;hencealargeamountofoutputcapacitanceisnotnecessarytomaintainVOduringloadtransients.NoOutputCapYieldsHighOutputImpedanceIntheory,aperfectcurrentsourcehasinfiniteoutputimpedance,allowingthevoltagetoslewinfinitelyfastinordertomai

7、ntainaconstantcurrent.Forswitchingregulatordesignerswhohaveconcentratedonvoltageregulators,thisconceptmaytakeamomenttosinkin.Completelyremovingtheoutputcapacitorfromabuckregulatorforcestheoutputimpedancetodependontheinductor.WithoutanycapacitancetoopposechangesinVO,theoutputcurrent(

8、referredtoasforward