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IDescriptionTheswitchingpowersupplychipLM2596iscompact,low-cost,low-power,high-efficiencyandeasytousecomparedwithspecializedinstruments.ThepowersupplydescribedinthisblogisasteplessadjustableDCregulatedvoltagesupplybasedontheswitchingpowersupplychipLM2596.Figure1.LM2596CatalogIDescriptionIILM2596CircuitandDesignProcess2.1CircuitofSteplessAdjustableDCPowerSupply2.2DesignProcessofAdjustableDCVoltageSourceIIIHowtoApplyandUseLM2596SteplessAdjustableDCPowerSupply3.1HowtoApply?3.2HowtoUse?FAQOrdering&QuantityIILM2596CircuitandDesignProcess2.1CircuitofSteplessAdjustableDCPowerSupplyThispowersupplycircuitmainlyusesLM2596-ADJ.LM2596-ADJisastep-downswitchingpowersupplychip.Itsoutputvoltagerangeis1.2V-37V,anditsmaximumloadcurrentis3A,withexcellentlinearityandloadregulationcharacteristics.Only4externalcomponentsareneededinthemaincircuittoadjusttheoutputvoltage.TheLM2596-ADJchipintegratesfrequencycompensationandafixedfrequencygenerator,andtheswitchingfrequencyis150KHz,whichfacilitatestheuseofsmallerfiltercomponents,therebyreducingvolume,weight,lossandcost.Undercertaininputvoltageandoutputloadconditions,theoutputvoltageerroriswithin4%,theoscillationfrequencyerrorrangeiswithin15%,andthestandbycurrentcanbeonly80uA.Itcanrealizeexternalpower-offandhasaself-protectioncircuit(atwo-stagefrequencyreductioncurrent-limitingprotectioncircuitandanover-temperaturecompleteprotectioncircuitthatiscutoffinabnormalcases).TheLM2596-ADJpackageinthisarticleisTO220(T),whichrequiresanexternalheatsink.VOUT=1.23V*(1+R2/R1)WhendesigningthePCBboard,theexternalcomponentsshouldbeascloseaspossibletotheLM2596-ADJ,andusegroundwireshieldingorsingle-pointgrounding,andusemagneticshieldinginductors.Iftheinductorcoreusedisopen,andtheinductancefluxcrossesthesensitivefeedbackline,thegroundlineoftheintegratedchipandtheconnectionoftheoutputcapacitorCOUTmayhaveproblems.ThefeedbackresistorshouldbeclosetotheLM2596-ADJIC,andtherelatedwiringshouldbefarawayfromtheinductor.Figure2.AdjustableDCVoltageSourceCircuit2.2DesignProcessofAdjustableDCVoltageSourceVOUTistheadjustableoutputvoltageVIN(max)isthemaximumDCinputvoltage,ILOAD(max)isthemaximumloadcurrent,F=switchingfrequency(150KHz)1)OutputVoltageCalculationVOUT=VREF*(1+R2/R1)Amongthem,VREF=1.23V.Inthisblog,R1isa1Kmetalfilmresistorwithalowertemperaturecoefficientof1%accuracy;R2usesa30Kpotentiometer.2)InductorSelectionCalculatetheproductE*Toftheinductorvoltageandmicrosecondsbythefollowingformula:E*T=(VIN-VOUT-VSAT)*(VOUT+VD)/(VIN-VSAT+VD)*1000/150KHz(VuS)VSATistheinternalsaturationvoltageoftheswitch,VSAT=1.16VVDistheforwardvoltagedropofthediodeVD=0.5VUsetheE*TvalueintheformulatofindthematchinginductornumberfromtheordinateinFigure3,andselectthemaximumloadcurrentofthecircuitontheabscissa;determineaninductanceareabytheintersectionoftheE*Tvalue,andthemaximumloadcurrent,andeachareaiscorrespondingtoaninductancevalueandaninductanceserialnumber(LXX).SelecttheappropriateinductorfromthecomponentnumberofthemanufacturerlistedinTable1forLM2596-ADJcircuit,preferablyamagneticshieldinductor.Thisblogchooses68uHinductance.Figure3.LM2596-ADJApplicationInformation3)OutputCapacitorCOUTNumber/Inductance(H)/Current(A)SchottRencoPulseEngineeringCoilcraftIn-LineSurfaceMountIn-LineSurfaceMountIn-LineSurfaceMountSurfaceMountL15/22/0.996714835067148460RL-1284-22-43RL1500-22PE-53815PE-53815-SDO3308-223L21/68/0.996714407067144450RL-5417-5RL1500-68PE-53821PE-53821-SDO3316-683L22/47/1.176714408067144460RL-5417-6-PE-53822PE-53822-SDO3316-473L23/33/1.406714409067144470RL-5417-6-PE-53823PE-53823-SDO3316-333L24/22/1.706714837067148480RL-1283-22-43-PE-53824PE-53825-SDO3316-223L25/15/2.106714838067148490RL-1283-15-43-PE-53825PE-53824-SDO3316-153L26/330/0.806714410067144480RL-5471-1-PE-53826PE-53826-SDO5022P334L27/220/1.006714411067144490RL-5471-2-PE-53827PE-53827-SDO5022P224L28/150/1.206714412067144500RL-5471-3-PE-53828PE-53828-SDO5022P154L29/100/1.476714413067144510RL-5471-4-PE-53829PE-53829-SDO5022P104L30/68/1.786714414067144520RL-5471-5-PE-53830PE-53830-SDO5022P683L31/47/2.206714415067144530RL-5471-6-PE-53831PE-53831-SDO5022P473L32/33/2.506714416067144540RL-5471-7-PE-53932PE-53832-SDO5022P333L33/22/3.106714439067144500RL-1283-22-43-PE-53933PE-53833-SDO5022P223L34/15/3.406714440067144790RL-1283-15-43-PE-53934PE-53834-SDO5022P153L35/220/1.7067144170-RL-5473-1-PE-53935PE-53835-S-L36/150/2.1067144180-RL-5473-4-PE-54036PE-53836-S-L37/100/2.5067144190-RL-5472-1-PE-54037PE-53837-S-L38/68/3.1067144200-RL-5472-2-PE-54038PE-53838-S-L39/47/3.5067144210-RL-5472-3-PE-54039PE-53839-S-L40/33/3.506714422067148290RL-5472-4-PE-54040PE-53840-S-L41/22/3.506714423067148300RL-5472-5-PE-54041PE-53841-S-L42/150/2.7067144410-RL-5473-4-PE-54042PE-53842-S-L43/100/3.4067144240-RL-5473-2-PE-54043-L44/68/3.4067144250-RL-5473-3-PE-54044-Table1.ProductmodelofaninductormanufacturerInmostcases,wecanuselowequivalentresistanceelectrolyticcapacitorsorsolidtantalumcapacitorsbetween82uF~820uF.Wheninuse,thecapacitorshouldbeclosetotheforLM2596-ADJIC,andthepinsandconnectingcopperwiresshouldbeasshortaspossible.SeeTable2below.Inordertosimplifytheselectionofcapacitors,Table1containsthedifferentoutputvoltagesandoutputcapacitorsrequiredforthebestdesign.Thewithstandvoltageofthecapacitorisatleast5timestheoutputvoltage.Sometimes,inordertoobtainalowerrippleoutputvoltage,ahighercapacitorwithstandvoltagevalueisrequired.Thisblogchooses220uF/50Velectrolyticcapacitors.VOUTIn-LineCapacitorSurfaceMountCapacitorPANASONICHFQ(F/V)NICHICONPL(F/V)FeedforwardCapacitorAVXTPS(F/V)VISHAY595D(F/V)FeedforwardCapacitor2820/35820/3533nF330/6.3470/433nF4560/35470/3510nF330/6.3390/6.310nF6470/25470/253.3nF220/10330/1033nF9330/25330/251.5nF100/16180/161.5nF12330/25330/251nF100/16180/161nF15220/35220/35680pF68/20120/20680pF24220/35150/35560pF33/2533/25220pF28100/50100/50390pF10/3515/50220pFTable2.OutputCapacitorandFeedforwardCapacitorSelection4)FeedforwardCapacitorCFFWhentheoutputvoltageislarge,acompensationcapacitorwithatypicalvaluebetween100pFand33nFisrequired,whichisconnectedinparallelwiththeoutputvoltageadjustmentresistorR2.Itsfunctionistocompensatethefeedbackloopandincreasethephasemargintoimprovethestabilityoftheloop.Forhighoutputvoltage,lowinput-outputvoltageand/orlowequivalentresistanceoutputcapacitors,thiscapacitormakesthecircuitmorestable,suchassolidtantalumcapacitors.TheselectionstillreferstothecorrespondingfeedforwardcapacitorvalueinTable1.Thisblogchooses33nFceramiccapacitors.CFF=1/(31*1000*R2)Thiscapacitorcanbeaceramiccapacitor,plasticormicacapacitor.5)ZenerDiode(D1)SelectionThemaximumcurrentcapacityoftheZenerdiodeisatleast1.3timesthemaximumloadcurrent.Ifthedesignedpowersupplyistowithstandcontinuousshort-circuitoutput,themaximumcurrentcapacityoftheZenerdiodeisequaltothelimitoutputofLM2596Current.Itsfunctionistoprovideapathfortheinductorcurrentwhentheswitchisclosed.ThereversevoltageoftheZenerdiodeisatleast1.25timesthemaximumoutputvoltage;theZenerdiodemustbeafastrecoverydiodeandmustbeclosetotheLM2596-ADJIC.Atthesametime,thepinsandtheconnectedcopperwiresshouldbeshort.Therefore,weshouldfirstchooseSchottkydiodes.Thisblogchooses1N5825Schottkydiodehere.6)InputCapacitanceCINTheinputcapacitorisanelectrolyticcapacitorortantalumcapacitorwithalowequivalentresistance,whichisalsoclosetotheIC,andtheDCloadcurrentmustexceedtwicetherootmeansquareoftheinputcapacitorcurrent.Foraluminumelectrolyticcapacitors,themaximuminputvoltageis2/3ofthewithstandvoltage;fortantalumcapacitors,selectcapacitorsthatthemanufacturerhastestedforsurgecurrent.Wecanselecttheappropriateinputcapacitanceaccordingtothegraphshown.Thiscapacitorpreventsexcessivetransientvoltagefromappearingattheinput,andatthesametimeprovidestransientcurrentforLM2596-ADJeverytimeitswitches.Thisbloguses680uF/50Velectrolyticcapacitors.VROutputCurrent:3AOutputCurrent:4A~6ALnlineSurfaceMountLnlineSurfaceMountSchottkySuperFastRecoverySchottkySuperFastRecoverySchottkySuperFastRecoverySchottkySuperFastRecovery20VTheminimumwithstandvoltageofallsuchdiodesis50VMURS32030WF10IN5820Theminimumwithstandvoltageofallsuchdiodesis50VMURS320Theminimumwithstandvoltageofallsuchdiodesis50VMURS62050WF10SR502Theminimumwithstandvoltageofallsuchdiodesis50VMURS620HER601SK32SR302IN5823MBR320SB52030V30WQ03IN5821SK33MBR33050WQ03SR50331DQ03IN582440VIN5822SB530SK34SR30450WQ04SR504MBRS340MBR340IN582530WQ0431DQ04SB54050VorHigherSK35SR305MBRS360MBR35050WQ05SB55030WQ0531DQ0550SQ080Table3.ChoiceofDiodeFigure4.LM2596-ADJapplicationinformationIIIHowtoApplyandUseLM2596SteplessAdjustableDCPowerSupply3.1HowtoApply?ThedevicecanbeusedasapowersupplythatrequiresaDCvoltagesourcekit:radiopowersupplydoorbellpowersupplyalarmpowersupplypoweramplifierpowersupply51single-chippowersupply,etc.3.2HowtoUse?Theanodeoftheoutputend(redalligatorclip)isconnectedtotheanodeofthecircuit,andthecathodeoftheoutputend(blackalligatorclip)isconnectedtothecathodeofthecircuit.Plugthe220Vpowercordintothemainssocket.Turnonthepowerswitch,theDCvoltagesourceindicator(red)willlightup,adjusttheknobtooutputthevoltagechange,anditsvaluewillbedisplayedonthevoltmeterhead.FAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.Afterreadingtheblog,haveyoubetterunderstandLM2596?Finally,ifyouhaveanyquestionsaboutLM2596,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!

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IDescriptionTheswitchingpowersupplychipLM2596iscompact,low-cost,low-power,high-efficiencyandeasytous

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