平面变压器设计(design of planar transformer)0.pdf

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1、DesginofplanartransformerContents:InductionDesignprocedureDesignexamples–flybackFormualsLayerdesginIntroductionPlanartransformescanbeconstructedasstandalonecomponents,withastackedlayerdesginorasmallmultilayerPCB,orintegratedintoamultilaterboardofthepowersupply.Importantadvantag

2、esofplanarmagneticsare:---verylowprofile---excellentthermalcharacteristics---lowleakageinductance---excellentrepeatabilityofpropertiesDesignprocedure1)Calculationofmaximumfluxdensity:ThecoreandcopperlossinatransformerunderoperatingConditionswillinduceatemperaturerise!2)Intherma

3、lequilibriumthetotallossesinthetransformer(Ptrafo).Canberelatedtoatemperaturerise△TofthetransformerwithananalogousofOhm’slawby:Ptrafo=△T/RthNotes:inthisformulaRthrepresentsthethermalresistanceoftheTransformer.Ptrafo:caninfactinterpretedasthecoolingcapabilityofthetransformer.Des

4、ignprocedure(add---Pc)WiththeassumptionthathalfofthetotaltransformerlossiscoreLoss,itispossibletoexpressthemaximumcorelossdensityPcAsafunctionoftheallowedtemperaturerise△Tofthetransformeras;Pc=12*△T/√Ve(mW/cm*3)Previouswork,showedthatitispossibletoestablishanempiricalformulawhi

5、chrelatesthevalueofthermalresistanceofatransformerdirectlytothevalueoftheeffectivemagneticvolumeVeoftheferritecoreused.Designprocedure(add---Pcore)Powerlossesinourferriteshavebeenmeasuredasafunctionoffrequency(finHZ),peakfluxdensity(BinT)andtemperature(Tin℃).Corelossdensitycanb

6、eapproximatedbythefollowingformula:InthisformulaCm,x,y,ct0,ct1andct2areparameterswhichhavebeenfoundbycurvefittingofthemeasuredpowerlossdata.theyaredimensionedinsuchawaythatat100℃thevalueofCtisequaltoPtrafoformula.Designprocedure(add---Bpeak)MaximumallowedPcoreiscalculatedwitheq

7、uation.thisvalueisinsertedinequation.MaximumallowedfluxdensityBpeakcannowbecalculatedbyrewritingequation:WindingspaceForcostpricereasonsitisrecommendedtochooseastandardThicknessofthecopperlayers.Oftenathicknessof35umor70UmareusedbyPCBmanufacturers.Thechoic

8、eofthicknessoftThelayersplaysanimportantroleforthetemp