Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In str uction For technicalinformation,[email protected] RESOURCES Inductor Applications Electrical Relationships Factors Affecting Performance Inductor Technologies Electrical Specifications Core Materials Magnetic Core Types Introduction TABLE CONTENTS OF al Gu i d e INDUCTORS 1/ 8 Discrete Semiconductors and Passive Components Instructional Guide 101 Vish INDUCTORS One oftheWorld’s LargestManufacturers of a y In tertec VM N -SG2139-1203 l hno
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L Y O G . Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In metal combinationsare manganeseandzinc(MnZn),nickel(NiZn).Thesemetalscanbeeasilymagnetized. by thecore. ThecostofMPPissignificantlyhigherthan KoolMu,powdered irons, andmostferritecores withsimilarsizes. The core characteristicsallowinductorstoperformvery wellinswitchingpowerapplications.Sincehigherenergy canbestored materials are nickel,iron, andmolybdenum.MPPstores higheramountsofenergy and hasahigherpermeabilitythanKoolMu. This characteristicallowsahigher DCcurrent leveltoflowthrough theinductorbefore theinductorsaturates.Thebasicraw air gapallowsthecore tostore higherlevelsofmagneticfluxwhencompared toothermagneticmaterials, suchasferrites. MPP isanacronym formolypermalloypowder. Itisamagneticmaterialthathasaninherent distributedairgap.The MPP Core Kool Mu Kool Mu amount oftimeandprofile. ThegeneralcompositionofferritesisxxFe molecular structure. Thecrystalline structure iscreated byfiringtheferrite material ataveryhightemperature foraspecified Ferrite isamagneticmaterialwhichconsistsofmixedoxideiron andotherelementsthatare madetohavecrystalline Ferrite Core values, verylowcore losses, andhighQvaluesare required. as “aircore” inductors.Ceramic core inductorsare mostoftenusedinhigh-frequency applicationswhere lowinductance properties. Thus,there isnoincrease inpermeabilityduetothecore material.Ceramiccore inductorsare oftenreferred to This allowsforrelatively high inductancestabilityovertheoperatingtemperature ranges.Ceramichasnomagnetic designs italsoprovides the structure toholdtheterminalsinplace.Ceramichasaverylowthermalcoefficient ofexpansion. Ceramic isoneofthecommonmaterialsusedforinductorcores. Itsmainpurposeistoprovide aformforthecoil.Insome Ceramic Cores Core Materials inductance valuesbefore reaching saturation. gapped “E”cores havea partially openmagneticpath.Theadvantageofgappingan“E”core isthatyoucanobtainhigher “E” cores are shapedlikean“E”andhaveaclosedmagneticpathtoroidal core whenconfigured asungapped.The “E” Core between windingsandearlysaturation. Characteristics oftoroidal inductorsinclude:selfshielding(closedmagneticpath),efficient energy transfer, highcoupling in manymagneticcore materialswithinthefourbasictypes:ferrite,powdered iron, alloyandhighflux,tapewound. An inductorconstructedbyplacingawinding(s)oncore thathasadonutshapedsurface.Toroidal cores are available Toroidal Core Magnetic Core Types Thus, theinducedvoltageisproportional totheinductancevalueandrateofcurrent change. V =Ldi/dt induced across aninductorbyachangeofcurrent isdefinedas: opposes thefield-producing current. Thisproperty ofimpedingchangescurrent isknownasinductance.Thevoltage Current passingthrough aninductorwillproduce amagneticfield.Achangingfieldinducesvoltagewhich to resist changesincurrent andstore energy initsmagneticfieldaccountforthebulkofusefulproperties ofinductors. A passivecomponentdesignedtoresist changesincurrent. Inductorsare oftenreferred toas“ACresistors”. Theability Inductors significantly higherthanpowdered iron. than powdered iron andlowercore losses.KoolMuperformswellinpowerswitchingapplications.Therelative costis up ofnickelandiron powder(approx. 50%ofeach)andisavailableinseveralpermeabilities.Ithasahigher permeability higher DCcurrent leveltoflowthrough theinductorbefore theinductorsaturates.KoolMumaterialisanalloythatmade higher levelsofmagneticfluxwhencompared toothermagneticmaterials,suchas ferrites.Thischaracteristicallowsa str uction ® isamagneticmaterialthathasaninherent distributedairgap.Thegap allowsthecore tostore ® Core al Gu i d e 2/ 8 2 Instructional Guide O 4 where xxrepresents severalmetals.Themostpopular Vish INDUCTORS a y In tertec l hno VM N -SG2139-1203
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L Y O G . Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In current isnotrelated to themagneticproperties oftheinductor. (AlsoseeIncremental Current andSaturation Current) the inductorsize.Forlowfrequency current waveforms,theRMScurrent canbesubstitutedfortheDCratedcurrent. Therated dissipate thispowerlostinthe windings.Thus,theratedcurrent canbeincreased byreducing theDCresistance orincreasing ability tominimizethepowerlosses inthewindingbyhavingalowDCresistance. Itisalsorelated totheinductor'sability temperature riseoftheinductoratmaximumrated ambienttemperature. The ratedcurrent isrelated totheinductor's The levelofcontinuousDCcurrent thatcanbepassedthrough theinductor. ThisDCcurrent levelisbasedonamaximum Rated Current The rateatwhichtheinductancewilldrop isalsoafunctionofthecore shape.(AlsoseeSaturationCurrent) saturation characteristics.Thismeanstheirinductancedrop from higherDClevelsismuchmore gradualthanferritecores. current isincreased further. Thisappliesmostlytoferritecores inlieuofpowdered iron. Powdered iron cores exhibit“soft” inductance value.Thiscurrent levelindicateswhere theinductancecanbeexpectedtodrop significantlyiftheDCbias The DCbiascurrent flowingthrough theinductorwhichcausesaninductancedrop of5%from theinitialzero DCbias Incremental Current inductors. (AlsoseeIncremental Current andPermeability) the permeabilityofcore isreduced. Thus,theinductanceiscausedtodrop. Core saturationdoesnotapplyto“air-core” the spacearound thecore, canonlystore agivenamountofmagneticflux density. Beyondthemaximumfluxdensitypoint, of theinductancetodrop duetotheDCbiascurrent isrelated tothemagneticproperties ofthecore. Thecore, andsomeof the 10%inductancedrop valueforferritecores and20%forpowdered iron cores inenergy storageapplications.Thecause zero DCbiasinductancevalue.Commonspecified drop percentages include10%and20%.Itisusefultouse The DCbiascurrent flowingthrough theinductorwhichcausesinductancetodrop byaspecifiedamount from theinitial Saturation Current of aninductor. Theunitofmeasure isohms,anditusuallyspecifiedasamaximumrating. The resistance oftheinductor windingmeasuredcurrent. withnoalternating TheDCRismostoftenminimizedinthedesign Dcr (cResistance) 1 henry(H)=10 inductance tomicrohenries. Thus,47mHwouldequal47,000μ. most oftenhavetheirinductancesexpressed inmicrohenries (μH).Thefollowingtablecanbeusedtoconvertunitsof given inductorisinfluencedbythecore material,corecount,andtheshapeofcoil.Inductors shapeandsize,theturns That property ofacircuit elementwhichtendstoopposeanychangeinthecurrent flowingthrough it.Theinductancefora Inductance Electrical Specifications some inductordesignsbutare more commonina wide varietyoftransformerapplications. permeabilities. Eachlaminationhasaninsulatedsurfacewhichis commonlyanoxidefinish.Laminatedcores are usedin and thicknesses.Somelaminationsare madetohavethegrainsorientedminimizecore lossesandgivehigher Cores constructedbystackingmultiplelaminationsontopofeach other. Thelaminationsare offered inavarietyofmaterials Laminated Cores a more stabletemperature coefficient thanferrites. into thefinalcore shape.Powdered iron cores areandtheirpermeabilitiestypicallyhave typicallythelowestcostalternative 100 %iron. Theiron particlesare insulatedfrom eachother, mixedwithabinder(suchasphenolicorepoxy)andpressed higher DCcurrent leveltoflowthrough theinductorbefore theinductorsaturates.Powdered iron cores are madeofnearly higher levelsofmagneticfluxwhencompared toothermagneticmaterials,suchasferrites.Thischaracteristicallowsa Powdered iron isamagneticmaterialthathasaninherent distributedairgap.Thegapallowsthecore tostore Powdered Iron Core 1 nanohenry(nH)=10 1 microhenry (μH)=1μ 1 millihenry(mH)=10 str uction al 6 μH Gu 3 -3 μH i d μH e 3/ 8 Instructional Guide Vish INDUCTORS a y In tertec l hno VM N -SG2139-1203
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L Y O G . Inductors - Primer this point. Based ontheaboveformula,itcanbeshownthatQiszero attheself-resonant frequency sincetheinductanceiszero at curve forQvsfrequency. ReismainlycomprisedoftheDCresistance ofthewire, thecore lossesandskineffect ofthewire. frequency atafasterrate thanReatlowerfrequencies, andviceversaathigherfrequencies. Thisresults isabell-shaped Power Loss=(DCR)(I given DCbiascurrent. Thispowerlossisreferred toas the“copper”lossandisequalto: the storagetemperature inthatitaccountsforthecomponent’s selftemperature risecausedby the windinglossfrom a Range ofambienttemperatures overwhichacomponentcanbeoperatedsafely. Theoperatingtemperature isdifferent from Operating Temperature Range and Core Losses) values orathigherfrequencies. Skineffect andcore lossesalsoaddtotheimpedanceofaninductor. (AlsoseeSkinEffect L isinhenriesandfhertz.Thisequationindicatesthat higher impedancelevelsare achievedbyhigherinductance Z =XL2πfL sinusoidal ACsignal: inductor reactance. Thefollowingformulacalculatestheinductivereactance ofanidealinductor(i.e.,onewith nolosses)toa component oftheimpedanceissimplyDCresistance ofthewinding.TheACcomponentimpedanceincludes The impedanceofaninductoristhetotalresistance totheflowofcurrent, includingtheACandDCcomponent.The Impedance Since X is technicallydefinedastheratioofinductive reactance toeffective resistance, andis represented by: The Qvalueofaninductorisameasure oftherelative lossesinaninductor. TheQisalsoknownasthe“qualityfactor”and Q (Also seeSRF) Lower distributedcapacitancesforagiveninductancevaluewill result inahigherSRF valuefortheinductorandviceversa. the inductor. Thisparallelcombinationwillresonate atsomefrequency whichiscalledtheself-resonant frequency (SRF). canberepresentedturn as asinglecapacitanceknownasthedistributedcapacitance.Thisisinparallelwith In theconstructionofaninductor, ofwire eachturn orconductoractsasacapacitorplate.Thecombinedeffects ofeach Distributed Capacitance (Also seeDistributedCapacitance) since theinductivereactance iszero. TheSRFisspecified inMHzandislistedasaminimumvalueonproduct datasheets. the parallelcombinationwillbecomedominantcomponent.Also, theQofinductorisequaltozero attheSRFpoint around thecore. Thiscapacitanceisinparalleltothe inductance.Atfrequencies abovetheSRF, thecapacitivereactance of ofwireimpedance attheSRFpoint.Thedistributedcapacitanceiscaused bytheturns layered ontopofeachotherand the inductanceisequaltocapacitanceandtheycanceleach other. Theinductorwillactpurely resistive, withahigh The frequency atwhichtheinductor’s distributedcapacitanceresonates withtheinductance.Itisatthisfrequency that Srf (Self-ResonantFrequency) permeability materials. material, andagivenwinding,higherpermeabilitymagneticmaterials result inhigherinductancevaluesasopposedtolower The core material,aswellthecore geometry, affect thecore’s “effective permeability”.Foragivencore shape,sizeand The permeabilityofamagneticcore isthecharacteristicthatgivescore theabilitytoconcentratelinesofmagneticflux. Permeability (Core) SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In Q str = uction L andReare functionsoffrequency, thetestfrequency mustbe givenwhenspecifyingQ.X Re X L al = Gu 2πfL Re i d 2 dc e ) 4/ 8 Instructional Guide Vish INDUCTORS a y In tertec L typicallyincreases with l hno VM N -SG2139-1203
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L Y O G . Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In tends totakeallpossiblepositions inthecross section ofthewire asawhole.The current through eachindividualstrand Wire consistingofanumberseparatelyinsulatedstrands that are wovenorbunched togethersuchthateachstrand Litz Wire further tothesurfaceasfrequencycurrent ofthealternating increases. (AlsoseeLitzWire) conductor whichopposestheflowofmaincurrent nearthecenterofconductor. Themain current flowisforced to increase. Themagneticfieldassociatedwiththecurrent intheconductorcauseseddycurrents nearthecenterof that utilizestheentire cross-sectional area oftheconductor. Thisphenomenoncausestheresistance oftheconductor Skin effectcurrent isthetendencyforalternating toflownearsurfaceofconductor inlieuofflowingamanner Skin Effect since theeddycurrents flowinaplanethatisperpendiculartothemagneticfluxlines. This willresult ineddycurrents ifthemagneticcore materialhaselectricalconductivity. Lossesresult from thisphenomenon As forthecore losses,anelectricfieldaround magneticflux. thefluxlinesinmagneticfieldisgeneratedbyalternating conductor) contributetotwomaintypesoflosses: Eddy current lossesare present inboththemagneticcore andwindingofaninductor. Eddycurrents inthewinding(or Eddy Current Losses inductor performancebykeepingthecore lossestoaminimum. higher powerandfrequency switchingregulators andRFdesignsrequire careful core selectiontoyieldthehighest current andresidual losses.Theselossesvaryconsiderablyfrom onemagnetic materialtoanother. Applicationssuchas frequency andthetotalmagnetic fluxswing.Thetotalcore lossesare made upofthree maincomponents:hysteresis, eddy Core lossesare magneticfieldinthecore causedbyanalternating material.Thelossesare afunctionoftheoperating Core Losses resistance ofthewire (I The powerlostbycurrent flowingthrough thewinding.Thepowerlossisequaltosquare ofthecurrent multipliedbythe Copper Loss Factors Affecting Performance Laser cut Film Multilayer ceramic Multilayer ferrite Wirewound Inductor Technologies str • Skin effects. effects. • Skin effects to proximity due • Losses • Inductor • Bead • Toroidal • Bobbin uction al Gu i d 2 Bobbins R). Thispowerlossistransferred intoheat. e Radial Leaded Axial Leaded Single layer Leadless 5/ 8 Instructional Guide Vish To Multilayer r oidal Inductors INDUCTORS Surface Mount a y In tertec Thr ough Hole l hno VM N -SG2139-1203
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L Y O G . Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In *Increased permeabilitycanresult intheReincreasing atcertainfrequencies resulting inalowerQ. considered abroadband filter. A lowerQgenerallyindicatesanattenuationoverabroader rangeoffrequencies. AferritebeadhasalowQ andisthus so theycanbemore frequency selective. A higherQgenerallyindicatesaninductorthatisamore selectivefilter. InductorsusedinRFcircuits usuallyhavehigh Q’s decrease.* If thepermeabilityofcore isincreased, thenumberofwindingscanbereduced andincremental current mayincrease or ofwire)On agivendesign,asinductance(turns goesup,theQdown. “Q” capacitance). If thepermeabilityofcore isincreased, thenumberofwindingscanbereduced, andSRFwillincrease (lessdistributed down. ofwire)On agivendesign,asinductance(turns goesup,thedistributedcapacitancewillalsogoandSRF go SRF *If theincreased permeability decreases thepointatwhichcore saturates, theactualincremental current cangodown. decrease.* If thepermeabilityofcore isincreased, thenumberofwindingscanbereduced andincremental current mayincrease or ofwire)On agivendesign,asinductance(turns goesup,theincremental current goesdown. Incremental Current If thepermeabilityofcore isincreased, thenumberofwindingscanbereduced andratedcurrent willgoup. ofwire)On agivendesign,asinductance(turns goesuptheratedcurrent goesdown. Rated Current If thepermeabilityofcore isincreased, thenumberofwindingscanbereduced, andDCRwillgodown. ofwire)On agivendesign,asinductance(turns goesup,sodoestheDCR. DCR Electrical Relationships is thetemperature atwhichtheinitialpermeabilityhasdropped to10%ofitsoriginalvalueatroom temperature. permeability drops tonearunityatthecurietemperature, whichcausestheinductancetodrop dramatically. Thecuriepoint dramatically asthecore temperature approaches thecurietemperature, whichcausestheinductancetoincrease. The The temperature abovewhichaferritecore losesits magneticproperties. Thecore’s permeability typicallyincreases Curie Temperature frequency increases. (SeealsoSkinEffect) a LitzconductorhaslowerAClossesthancomparablesolid-wire conductors,whichbecomesimportantastheoperating is dividedequallysincethiswire designequalizesthefluxlinkagesand reactance oftheindividualstrands.Inotherwords, str uction al Gu i d e 6/ 8 Instructional Guide Vish INDUCTORS a y In tertec l hno VM N -SG2139-1203
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L Y O G . Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In digital circuits. by sometypeofswitchingcircuit. Commonsources includeswitchingvoltageregulators andclockedsignals,suchas Unwanted electricalenergy inacircuit thatisunrelated tothedesired signal.Sources ofnoiseare mostoften generated Noise interchangeably with“noise”.Ferritebeadsare themostcommondeviceusedforEMIattenuation. EMI isanacronym forelectromagnetic interference. Itisunwantedelectricalenergy inanyform.EMIisoftenused EMI impedances are equal. the inputimpedanceofothercircuit. There isaminimumpowerlossbetweentwocircuits whentheirconnecting The conditionthatexistswhentwocoupledcircuits are adjustedsothattheoutputimpedanceofonecircuit equals Matched Impedance mainly ofnoise.Bandpass,orlowpassfilters,are commonlymadeupofinductorandcapacitorcombinations. meaning theypasslowfrequency signalssuchastheDCpower, and attenuatehigherfrequency signalswhichconsist from thepowerbus.The filter isdesignedto reject noisewithinafrequency band. Typically, thesefilters are low-passfilters, A powerfilterplacedontheinputtoacircuit orassemblythatattenuatesnoiseintroduced Input LineFilter are commonlyfoundnear dc-to-dcconverterstofilterripplecurrent andvoltage. A filterconsistingoftwocapacitorsconnectedinparallelwithaseries inductor. Thesefilters PI-Filter types offilters.Thesepassivecomponentsinclude resistors, capacitorsandinductors. range offrequencies. Groups ofpassivecomponentsare commonlyusedto constructmany A circuit ordevicewhose purposeistocontrol electricalenergy atagivenfrequency orovera Filter configured tohavethecommon noisecancelitselfinthetransformer. electrical linesinrelation to earthground. Acommonmodechokeisactuallyatransformer Used toattenuatecommonmodenoiseorelectricalinterference thatiscommontoboth Common-Mode Choke switch (transistor)onandoff. energy inaninputinductorandthentransferring theenergy ashunt totheoutputbyturning produces ahigher, regulated outputvoltage.Thishighervoltageisachievedbystoring A basicdc-to-dcswitchingconvertertopologythattakesanunregulated inputvoltage,and Boost Regulator(DC-DC) inductor andcapacitorcircuit. input voltagewithaseriesofconnectedswitches(transistor)that applypulsestoanaveraging produces alower, regulated outputvoltage.Thisvoltageisachievedbychoppingthe A basicdc-to-dcswitchingconvertertopologythattakesanunregulated inputvoltage,and Buck Regulator(DC-DC) Inductor Applications str
uction al Gu i d e 7/ 8 Instructional Guide Vish INDUCTORS a y In tertec V in + V in - - + V in - + Signal Input Simplified BoostRegulator Simplified BuckRegulator C 1 Basic Pi-Filter L Q l hno Use CommonModeChoke Between SignalLines VM L Q N D C 2 -SG2139-1203
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L Y O G . Inductors - Primer SPECIFIC DISCLAIMERS, SETF ORTH ATwww.vishay.com/doc?91000 This do cument issubj ect tochange withoutnotice . THEPRODU CTS DESCRIBE HEREINANDT IS DOCUMENTARES UBJECT TO In str uction FAX: +86-21-52587979 PH: +86-21-52585000 P.R. China Shanghai 200030 55 HuaiHaiWestRoad 15D, SunTongInfoprt Plaza Visha p F Ph: +65-6788-6668 Singapore 528886 37A T Visha singapore Asia F Ph: +1-402-563-6866 United States Shelton, CT06484 One GreenwichPlace Visha United states The Americas W fax: +81-3-5466-7160 Ph: +81-3-5466-7150 Japan Tokyo 150-0002 Shibuy 3-12-22, Shibuy Shibuy VISHA japan ax: +65-6788-0988 ax: +1-402-563-6296 .r China o ampines Street92#07-00 rl y ChinaCo.,L y intertechnology AsiaPteL y Americas Y JAPAN CO.,LT D. a-ku a PrestigeBldg.4F al dw Gu i d a i d e e Sales td. Con td. tacts F Ph: +33-4-9337-2727 France 06003 nice,cedex1 199, bddelamaelEin Visha france F Ph: +49-9287-71-0 Germany 95100 Selb Dr.-Felix-Zandman-Platz 1 Visha Germany EUROPE F Ph: +44-191-516-8584 UNITED KINGDOM Sunderland SR53XJ Sunderland EnterpriseP St Suite 6C,TowerHouse Visha united kingdom ax: +33-4-9337-2726 ax: +49-9287-70435 ax: +44-191-549-9556 . Catherine’s Court 8/ y S.A. y ElectronicGmbH y L 8 td. Instructional Guide Vish INDUCTORS a ark y In tertec l hno VM N -SG2139-1203
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