穩(wěn)壓電源中英文翻譯

英文原文PAGE1NCswitchingpowersupplyAbstractThissystembasedon51SCMcontrolunit,usedforLM2576-wildnumericalcontrolaswitchingpowersupplyoffuzzydigitalcontroltechnology,adjustloadR1,R2proportiontochangeoccupiesemptiescomparedtomaketheoutputstability,andcanbethroughthebuttons,digitaldisplaytorealizeoutputvoltagenumericalcontrol.Inaddition,thesystemtoinputpressure,flow,inputoutputflow,switchtubeoverheataswellastheprotectioncircuit,ensurethatthesystemisstableandreliable.Keywords:thenumericalcontrolswitchpowersupply，LM2576-wildmicrocontrollerThefirstchaptertasksandrequirements(a)ThetaskDesignandconstructionofaswitchingpowersupply,itsstructurediagramshownasshowninfigure1(b)Requirements1,basicrequirements(1)Basicspecifications:inputvoltage:+10V/DC(fluctuatingrange8to12V)Outputvoltage:+2.5V/DC~+6.5V/DC(2)Thebasictechnicalindex:Theoutputofsubsectionpowershift,and8from+2.5Vto6.5V+,andevery0.5Vincrease.Namely(2.5,3,3.5,4,4.5,5,5.5,6)Efficiency:70%(p<+2.5V/DC,1Atestingaccurate)Maximumoutputcurrent:2A;Voltageadjustmentrate:2%orless;Currentadjustrate:2%orless(3)Canbearbitrarytunedtotherequirementsoftheoutputvoltage,andwithacertainwayofthedisplay.(4)canbearbitrarythroughthekeyboardcontrolopen/closetheoutputvoltage.2.Playapart(1)Haveover-voltageprotection,inputvoltageprotectionmovement,thereare15Vovercurrentprotection,morethan3Aoutputcurrentprotectionmovement(2)Improveefficiency:80%(p<circuitto+2.5V/DC,2Atestingaccurate)(3)Theripple:1%orless(+2.5V/DC,2A20MHzoscilloscopetestingaccurate)(4)Pressfromlowtohighorfromhightoloworderautomaticallychangetheoutputvoltage,eachfile2~3seconds,betweentimeandspaceinthetest.ThesecondchapterschemecomparisonandselectionPlan1:thedivisioncomponents,suchasSelf-excitationswitchingpowersupply,thecircuitprinciplediagramisasfollows:TheinputvoltageforAC220v,50Hzacalternatingcurrent,afterfiltering,againbyrectifierbridgeafterrectifyingintoadc,throughthecontrolcircuitswitchtubeconductionandglobemakehighfrequencytransformerofalowvoltagemeasurementproducehigh-frequencyvoltage,smallpowerbyhigh-frequencytransformercouplingtosecondtest,thenthroughrectifierfilter,getdcvoltageoutput.Inordertomaketheoutputvoltagestability,withtheTL431samplingerror,theopticalcouplingamplifier,throughthePWMtocontrolswitchtubeconductionanddeadline(i.e.occupiesemptiescompared),makestheoutputvoltageremainstable.Fromtheforegoing,thisschemecircuitismorecomplex,difficult,sodon'tdebuggingfeasible.Plan2：DC-DCtransformtheBUCKtypewithA/Dconverter,andconstantlytestingpoweroutputvoltage,dependingonthepowersupplyoutputvoltageandofthedifferenceofthesetvalue,useofPWMmodulePWMwavesinoutput,directcontrolofthepowersupply.ARMextendedbuttons,digitaldisplaytorealizethenumericalcontroloutputvoltage.Thisschemeissimple,butallthecircuitbydivisioncomponents,interference;AndPWMmodulesingle-chipmicrocomputercontrolprogramiscomplicated,consider52andA/Dprogrambetweenfactors,willcausetheoutputofthePWMdelay,distortion,sothattheoutputvoltageisnotquitestable,andsoon.Plan3:thespecialchippowerLM2576-suchaswild,itstypicalcircuitareasfollows:LM2576seriesofstabilizerwhicharemonolithicintegratedcircuit,canprovidethebuckswitchingvoltageregulators(buck)allsortsoffunctions,candrive3Aload,haveexcellentlinearandloadadjustmentability,andLM2576stabilizerinteriorcontainsfrequencycompensationdeviceandAfixedfrequencyasits,thenumberoftheexternalcomponentscanbeminimized,andeasytouse.Thisscheme,220V/50HzacvoltageafterrectifyingcircuitandDC/DCvoltagechipLM2576wildtransformationforstable-DCvoltage,andthenthroughtheadjustmentoftherelationshipofscaleandR2R1toadjustLM2576chipoftheinputoutputvoltagestabilitythanempty.Anexternalcircuitcomponentsnumberless,andtheprogramissimple,andtheoutputvoltagestabilityisgood.Throughvariousprogram,feasibility,complexity,systemindexcomparativeadvantagesanddisadvantagesofeachscheme,comprehensive,weusethethirdplan.Inthethirdchapterofthesystemhardwaredesign(a)Thedesignofthewholesystem1.ThedesignthoughtSystemtomonolithicintegratedcircuitAT89S52,LM2576-forthecorepart,andthewildthroughthemonolithicintegratedcircuittooutputvoltagegather,comparison,operations,andtheoutputvoltagecontrol,automaticregulationsystemstructurediagramshownasshowninfigure1.220V/50HzacvoltageafterrectifyingcircuitandDC/DCvoltagechipLM2576wildtransformationforstable-5~12VDCvoltageoutput,theoutputvoltagethroughsamplingcircuitbysampling,A/DconversionchipADC0804afterconvertingto52afterprocessing,controlsimulationelectronswitchtochoose4051respectivelytheninepotentiometerR2,changeR1andR2ratiovalues,whichchangeLM2576-ofthewildchipPWMpulseofempty,MOStubesworkthantoswitchstatein,theinputof15VDCvoltage"chopped"fortheandofthesamefrequencyPWMwavespulsewave,pulsewavethroughtherectifierfiltercircuitoutputfor5~12VDCvoltage.Becauseofthisthetopicrequesthavenineoutputsteppingdemand,socantuneinadvanceeachvoltageresistance,throughthecorrespondingkeychoiceoutputvoltage,directlytotheanalogswitch4067chooseresistance,theycangettooutputvoltage.Atthesametime,todetectthevoltage,currentvaluethroughthedisplayLCD1062real-timedisplay.Ifworkingcurrentistoobig,theflowdetectioncircuitwillbesenttothetestingresultsofsingle-chipmicrocomputer,SCMcontrolrelaythroughtheacbranchrealizeover-currentprotectionsysteminfault,aftertheoperationissetbytheresetbuttontomaycausethesystemtoresumenormalwork.2.Theblockdiagramofthewholesystem(b)Unitcircuitfunctionandtheanalysisoftheoperation1.MinimumAT89S52SCMsystemMinimumsystemincludingcrystaloscillatorcircuitandresetswitchandpowersupplyparts.Figure2fortheminimumAT89S52SCMsystem.2.Rectifiercircuit.Thewaverectifiercircuitismadeupoftwohalfwaveofrectifiercircuit.Becauseinthenexttwo,addonmiensinputvoltageoftheoppositepolarity,therefore,toadynamicbalance,ineverysignalcycle,theC1andC2experience2timescharger,dischargeprocess,currentwillappeartwocurrentpulsewithpolarity.SoinadditiontotheVosawtoothwaveonthewavyfrequency,improvetheabilityofdoublefiltering,thusreduceripplevoltage.3.PowersupplycircuitThedcpowerbypowersupply,filtering,protection,suchasvoltage,fourbasicmodules.(1)ThepowertransformerUSESastep-downtransformer,thepowergridvoltage220Vtransformintoneedacvoltage.TheacvoltageAfterrectifying,mayobtainelectronicequipmentneeddcvoltage.(2)Userectifiercircuitbridgerectifiercircuitsingle-phase,50HzacalternatingcurrenttransformationfordirectioninvariablebutstillhasthepulsesizestraightFlowelectricity.Itsadvantageishighvoltageripplevoltage,small,theutilizationrateoftransformerhigh.ThisdesignbyAbridgepileofbridgerectifier,RS808domaximumcurrentcanreach8A,cooperatewiththedesignofthelargefiltercapacitance,sothepoweroftheinstantaneouslargecurrentpowersupplycharacteristics,lownoise,goodreactionspeed,outputripplesmall.（3）Filtercircuitusingcapacitancefiltercircuit,willthepulsationoftherectifiercircuitoutputfilter,getmostofthecomponentsissmoothdctheelectricity.Thiscircuitadopts4700uF/50VlargecapacitanceC3,C4tomaketheoutputvoltagemoresmooth,thepowersupplycharacteristicsmoment,suitablefortaketheperceptualload,suchasmotorstart-up.C3,C4everyparallelconnectiona0.1uF/63VCBBcapacitance,filtertohighfrequencyinterference,makeinputtointegratedcircuitsL11,L12ofdcasfaraspossiblethesmoothandpure.（4）ByLM317outputvoltagecircuitispower,LM337outputnegativesupply.LM317andLM337areusedinternalheatLoad,containsovercurrentprotection,hotoffandsafetyworkingareaforperfectprotectioncircuit,thatpowercansavethefuse,andsoeasylossdevice.Regulatingcircuit:tomeettheneedsofthedifferentapplicationsituationandthevoltageissettocanbeadjusted.ThecalculationoftheoutputvoltageVo=1.25x(1+Rf/R),adjustableresistanceinuseprecisioncanberesistorandguaranteethepreciseoutputvoltagecanbeadjusted.Ifthisarticlechoosesfor5kofRfΩ,Rfor270Ωcombination,canrespectivelyon1.25V~24V1.25V~24Vachievecontinuousadjustablebetween.（5）Protectioncircuitforlinearpowersupplyheat,sothepowerlargeraddenoughradiator.Duetothehighperformanceintegratedcircuit,whichcansimplifythecircuitstructure,highlightingtheimportantpartinthepowertransformation.Throughthecommissioningandtesting,goodperformance.ThewholecircuitThepowernotonlycanbeusedalone,alsocanbeinotherelectronicequipmentusedinvoltageorcurrentstabilizationsourceuse.4.LM2576-voltagecircuitwildWorkingprinciple:Assumethattheswitchtransistors,diodesareidealcomponents,inductanceandcapacitanceisidealcomponents,theoutputvoltageripplevoltageoutputvoltageandtheratioofthesmalltoallowoversight.AccordingtothecurrentcycletobegininILinductanceisstartingfromscratch,canbedividedintocurrentcontinuousworkingmodeandinductanceinductivecurrentisdiscontinuousworkpatterns.Duetothecontinuousworkmodeinductancecurrentconverter,haveverygoodcontrolcharacteristic;Inductivecurrentisdiscontinuousworkmode,puttheelectric,inductanceandcapacitanceeasytoproducetheoscillation,thusaffectingtheoutputvoltageripple;Andthesameoccupiesemptiescompared,outputvoltageindiscretemodelunderthemodeofworkthanthebig,highefficiency.Tosumup,themostidealsituationisincriticalcondition,stabilizerwhichworksoweusetwokindsofmethods:(1)Theincreaseoftheinductanceinductiveenergystorage,increase,andextendthedischargeoftime(2)ImprovetheworkandreducethefrequencyswitchtimeMaketransistorincurrentcontinuousstate.5.ThewholewaveoutputrectifiercircuitparameteranalysisOutputfilterbyfree-wheelingdioderectifiercircuit,inductanceandcapacitancecomposition.Considerfree-wheelingdiodeintubebyPMOStransistorconduction,whenenergyconsumption,andworkinthestate,soweusedthelowpowerconsumption,highcurrent,high-speedScottydiodesIN5817,thecharacteristicsasfollows:Maximumpeakreversevoltage:40VThebiggestreverseRMSvoltage:28VThebiggestdcvoltage:40VblockThebiggestpositiveaveragerectifiercurrent:1AThebiggestpositivepressuredrop:0.6V(1A)BUCKconverterprinciplebyanalysisshowsthatinordertomakeworkininductivecurrentcircuitcontinuousmode,andtheripplevoltageSoasfaraspossible,shouldbemadegreatinductancewechoosefor8mHinductanceCapacitorsmainlyisthe"absorb"ripplewithasmooth,theroleofthevoltagewaveform.Capacitanceandinductanceisequivalenttoalowpassfilteringfilter,thecut-offfrequencydefinedasConsideringthecapacitanceequivalentseriesresistancelosses,wechoosethecapacitancefor1000uF.Atthistimethecut-offfrequencyofabout562Hzac,visibletodozensofkHzPWMwaveshaveverygoodfilteringeffect.6.Inputover-voltageprotectionWhentheinputvoltageinthenormalrange,theinputsamplingvoltagecomparator,lessthanthebenchmarkvoltageoutputlowlevel;Whentheinputpressure,inputvoltageisgreaterthanthebenchmarksamplingcomparisonoutputvoltage,highlevel,ARMproduceexternalinterruption,warning,blockade,makePMOStransistortubePWMsignal,inordertoprotectthecircuitdamage.7.Over-currentprotectionUsuallywithhallcurrentsensordetectionofcurrentdirectlyPMOStransistor,andthenwithsettingtheIdthresholdvalue,comparedwithcomparisontocontroltheoutputofthedriversignalshutoff;Orbyindirectmethod,theflowtestvoltagewhenthevoltagedroptheVsdPMOStransistor,becausethepressuredropcontainsshort-circuitcurrentinformationflow,whentheVsdincreasing,andbasicallyforlinearrelationshipbetweentheflowoftesting,whentheVsdandwithsettingthethresholdvalueisusedinthecomparison,thecomparatoroutputcontrolpowercircuitoftheshutoff.8.LCDdisplaycircuitChapter5systemcommissioning1.ThesoftwaredebuggingThedesignofthesoftwareismoresimple,onlythekeysandLCDdisplaytwomodules.Throughthekeycontroloutputvoltageandthechangeofthecommissioning,abegantodiscoverthatstepissometimes0.5v,sometimesbecome1v,thenaddthedelay,eliminatebuttonsditherprogramcan.2.HardwaredebuggingFirstofall,pointsmoduledebugging.First,thendebuggingpowermoduleLM2576-and4067wildvoltageanalogswitchmodule,firstwithhighandlowleveldirectlyelected4067,usingamillimeterstomeasuretheoutputvoltageiscorrect,afterrightinwith4067single-chipmicrocomputercontrol,observationoutputvoltage,withascrewdriverfine-tuningnineR2resistance,changeandanumberofR2R1toadjustoutputvoltage.Throughthesepreliminarycommissioning,theoutputvoltagetendtobenormal.3.Themachinecommissioning1)theoutputvoltagecanonlyto5.62v,highestcan'tcarryitupagain.Reason:analogswitchofthe4067workingvoltageandchoosetoosmall.Thesolution:themicrocontrolleroutputand4067atransistor,indirecttransistorisinstate,whentransistorswitchwhenclosed,4067thevoltagebylargevoltagechoose,sothat,oncethesingle-chipmicrocomputerchoosethe4067,theworkingvoltageincrease.2)Keyspressed,foundthestepvoltageissometimes0.5v,sometimesis1v.Reason:usuallywekeyspressed,therewillbedelayjittereffect.Solution:intheprogramandbuttonincasetimedelayjitterprogram.3)whentheSCMP1mouthdirectlyelectedin4067theoutput,measuredusingamultimediaP1mouthoutputlevel,foundthattotalforthelowlevel,willsingle-chipmicrocomputerand4067connectionsdisconnected,usingamultimediaafterinthemouthoutputlevel,foundtheP1normal.Reason:52chipiswithaeraseprogramafterboardofthesmallestsystemdirectlyintothegeneraleffect,choose4067outputlevelwillbedown.Thesolution:thepresstheresetbutton52singlechipcan.PAGE14Chapter6systemtests1.Thetestprojectcircuit2.TestinginstrumentsThreeandahalfdigitalmultimedia(MASTECHmy61)Dcpowersupply(MOTECHLPS-305)Digitaloscilloscopes(TektronixTDS1002)3.Testresults1)intheinputvoltagefor15V,respectivelyfor200ohmload,150ohm,100ohm,outputvoltageaccuracyofthetest2)intheinputvoltagefor15V,loadresistancefornominalresistance(i.e.currentfor500mA),outputripplevoltageandefficiencytest3)theinputvoltagechangecircumstances,outputvoltagerippleandefficiency,precisiontestingFromthetablethreecansee,calibrationconstantinputvoltage,thehigherthevoltage,theripplevoltage,thegreatertheinputcurrentissmaller,thelowertheefficiency.

【reference】[1]GaoJiXiang.Analogelectroniccircuitdesign[M].Beijingelectronicindustrypress,2007[2]ZhouZhiGuang.Microcontrollertechnologyandapplication[M].Hunanzhongnanuniversitypress,2005[3]YanShi.Digitalelectronictechnologybase【M】highereducationpress.Beijing.2004[4]PengJieHua.The"curriculumdesignofelectronictechnology[M].Beijingguidanceofhighereducationpress,1999[5]HuangYouQuan.LiGuiPing.BasedonthedesignofmanyChinesecharactersAT89S52display【J】.Electronicdesignengineering,2008中文譯文PAGE30數(shù)控開關(guān)穩(wěn)壓電源摘要 本系統(tǒng)基于51單片機(jī)為控制單元，采用LM2576-ADJ數(shù)控開關(guān)穩(wěn)壓電源中的模糊數(shù)字控制技術(shù)，調(diào)整負(fù)載R1,R2比例來改變占空比使輸出穩(wěn)定，并且可通過按鍵、數(shù)碼顯示實現(xiàn)輸出電壓數(shù)控。此外，系統(tǒng)加以輸入過壓、輸入過流、輸出過流、開關(guān)管過熱等保護(hù)電路，保證系統(tǒng)穩(wěn)定可靠地工作。關(guān)鍵字：數(shù)控開關(guān)電源LM2576-ADJ單片機(jī)第一章任務(wù)與要求（一）任務(wù)設(shè)計并制作一個開關(guān)電源，其結(jié)構(gòu)框圖如圖1所示圖1

電路框圖

（二）要求1、基本要求(1)基本規(guī)格：輸入電壓：+10V/DC

(波動范圍8~12V)輸出電壓：+2.5V/DC~+6.5V/DC(2)基本技術(shù)指標(biāo)：輸出電壓分8檔，從+2.5V到+6.5V，每0.5V遞增。即(2.5,3,3.5,4,4.5,5，5.5,6)效率：≥70%

(以+2.5V/DC,1A測試為準(zhǔn))最大輸出電流：2A；

電壓調(diào)整率：≤2%；

電流調(diào)整率：≤2%(3)可任意調(diào)到要求的一檔輸出電壓，并用一定的方式顯示出來。(4)可任意通過鍵盤控制打開/關(guān)閉輸出電壓。2、發(fā)揮部分(1)有過壓保護(hù)，輸入電壓15V保護(hù)動作，有過流保護(hù)，輸出電流大于3A保護(hù)動作(2)提高電路效率：≥80%

(以+2.5V/DC,2A測試為準(zhǔn))

(3)紋波：≤1%

(以+2.5V/DC,2A，20MHz示波器測試為準(zhǔn))(4)按從低到高或從高到低順序自動改變輸出電壓，每檔間隔2~3秒，測試時空載。第二章方案比較與選擇方案1：采用分立元件，例如自激式開關(guān)穩(wěn)壓電源，電路原理圖如下：輸入電壓為AC220v，50Hz的交流電，經(jīng)過濾波，再由整流橋整流后變?yōu)橹绷?，通過控制電路中開關(guān)管的導(dǎo)通和截止使高頻變壓器的一次測產(chǎn)生低壓高頻電壓，經(jīng)由小功率高頻變壓器藕合到二次測，再經(jīng)整流濾波，得到直流電壓輸出。為了使輸出電壓穩(wěn)定，用了TL431取樣，將誤差經(jīng)光耦合放大，通過PWM來控制開關(guān)管的導(dǎo)通與截止時間（即占空比），使得輸出電壓保持穩(wěn)定。 由上可見，這種方案電路比較復(fù)雜，調(diào)試難度大，所以不可行。方案2：開關(guān)變換電路開關(guān)變換電路輸出濾波整流電路采樣電路AT89S52A/D處理PWM按鍵顯示PMOS驅(qū)動電路20V輸入5～12V輸出過壓、過流、短路、過熱外部中斷A/D轉(zhuǎn)換DC-DC變換采用BUCK型變換器，用A/D不斷檢測電源的輸出電壓，根據(jù)電源輸出電壓與設(shè)定值之差，利用片內(nèi)PWM模塊輸出PWM波，直接控制電源的工作。ARM擴(kuò)展按鍵、數(shù)碼顯示功能實現(xiàn)數(shù)控輸出電壓。 此方案電路雖簡單，但均由分立元件組成，受干擾大；并且PWM模塊中單片機(jī)52控制程序復(fù)雜，考慮與A/D程序切換等因素，會造成輸出的PWM波形延遲、失真，這樣致使輸出電壓不夠穩(wěn)定等等。方案3：采用電源專用芯片如LM2576-ADJ，其典型電路如下：LM2576系列的穩(wěn)壓器是單片集成電路，能提供降壓開關(guān)穩(wěn)壓器（buck）的各種功能，能驅(qū)動3A的負(fù)載，有優(yōu)異的線性和負(fù)載調(diào)整能力，并且LM2576穩(wěn)壓器內(nèi)部含有頻率補(bǔ)償器和一個固定頻率正當(dāng)其，能將外部元件的數(shù)目減到最少，使用簡便。本方案中，220V/50Hz交流電壓經(jīng)過整流電路和DC/DC穩(wěn)壓芯片LM2576-ADJ變換為穩(wěn)定的直流電壓，然后通過調(diào)整R1和R2的比例關(guān)系來調(diào)整LM2576芯片的輸入占空比來穩(wěn)定輸出電壓。外部電路元件數(shù)量較少，程序也比較簡單，并且輸出電壓穩(wěn)定性也比較好。通過對各種方案可行性、復(fù)雜程度、系統(tǒng)指標(biāo)等方面的比較，綜合各方案的優(yōu)缺點(diǎn)，我們采用第三種方案。第三章系統(tǒng)硬件設(shè)計（一）系統(tǒng)的總體設(shè)計1. 設(shè)計思想系統(tǒng)以單片機(jī)AT89S52、LM2576-ADJ為核心部件，通過單片機(jī)對輸出電壓進(jìn)行采集、比較、運(yùn)算，從而對輸出電壓進(jìn)行自動調(diào)節(jié)控制，系統(tǒng)結(jié)構(gòu)框圖如圖1所示。220V/50Hz交流電壓經(jīng)過整流電路和DC/DC穩(wěn)壓芯片LM2576-ADJ變換為穩(wěn)定的直流電壓5～12V輸出，輸出電壓通過取樣電路采樣，經(jīng)A/D轉(zhuǎn)換芯片ADC0804轉(zhuǎn)換后送給52處理后，控制模擬電子開關(guān)4051來分別選通9個電位器R2，改變R1和R2比例值，從而改變LM2576-ADJ芯片的PWM脈沖的占空比，使MOS管工作于開關(guān)狀態(tài)，將輸入的15V直流電壓“斬波”為與PWM波頻率相同的脈沖波，脈沖波通過整流濾波電路輸出為5～12V的直流電壓。因為此題目要求有9個輸出步進(jìn)需求，所以可以事先調(diào)好每個電壓對應(yīng)的電阻值，通過按鍵選擇輸出電壓，直接送給模擬開關(guān)4067選通電阻，就可以得到要輸出的電壓。同時將檢測到的電壓、電流值通過顯示器LCD1062實時顯示。若工作電流太大時,過流檢測電路將檢測結(jié)果送至單片機(jī),單片機(jī)通過控制繼電器切斷交流支路實現(xiàn)過流保護(hù),系統(tǒng)在故障后通過操作設(shè)置的復(fù)位鍵可以使系統(tǒng)恢復(fù)正常工作。2. 系統(tǒng)總體框圖LM2576-ADJ穩(wěn)壓電路LM2576-ADJ穩(wěn)壓電路輸出濾波整流電路LCD顯示電路AT89S52LCD控制PWM按鍵顯示選通模擬電子開關(guān)4052，控制電位器R2220V/50Hz交流電壓輸入5～12V輸出過壓、過流、短路外部中斷整流電路圖1系統(tǒng)總體框圖（二）單元電路功能以及工作原理的分析AT89S52單片機(jī)最小系統(tǒng)最小系統(tǒng)包括晶體振蕩電路、復(fù)位開關(guān)和電源部分。圖2為AT89S52單片機(jī)的最小系統(tǒng)。圖2AT89S52最小系統(tǒng)圖整流電路圖3整流橋電路全波整流電路是由兩個半波整流電路組成。由于加在上、下兩整流管的輸入交流電壓極性相反，因此，達(dá)到動態(tài)平衡后，在每一個信號周期內(nèi)，C1和C2經(jīng)歷2次充、放電過程，電流會出現(xiàn)兩個同極性電流脈沖。因此疊加在Vo上的鋸齒波狀波動頻率加倍，提高了濾波能力，從而減小紋波電壓。電源電路圖4電源電路本直流電源由電源、濾波、保護(hù)、穩(wěn)壓等四個基本模塊組成。（1）電源變壓器采用降壓變壓器，將電網(wǎng)交流電壓220V變換成需要的交流電壓。此交流電壓經(jīng)過整流后,可獲得電子設(shè)備所需要的直流電壓。（2）整流電路利用單相橋式整流電路,把50Hz的交流電變換為方向不變但大小仍有脈動的直流電。其優(yōu)點(diǎn)是電壓較高、紋波電壓較小,變壓器的利用率高。本設(shè)計用橋堆RS808做全橋整流,最大電流可達(dá)8A,配合本設(shè)計的大濾波電容,使得本電源的瞬時大電流的供電特性好、噪聲小、反應(yīng)速度快、輸出紋波小。（3）濾波電路采用電容濾波電路,將整流電路輸出的脈動成分大部分濾除,得到比較平滑的直流電。本電路采用4700μF/50V的大電容C3、C4使輸出電壓更加平滑,電源瞬間特性好,適合帶感性負(fù)載，如電機(jī)的啟動。C3、C4各并聯(lián)了一只0.1μF/63V的CBB電容，濾去高頻干擾,使輸入到集成電路L11、L12的直流電盡可能的平滑和純凈。（4）穩(wěn)壓電路由LM317輸出正電源,LM337輸出負(fù)電源。LM317和LM337均使用了內(nèi)部熱過載,包含過流保護(hù)、熱關(guān)斷和安全工作區(qū)補(bǔ)償?shù)韧晟频谋Ｗo(hù)電路,使得電源可以省去保險絲等易損耗器件。調(diào)節(jié)電路:為適應(yīng)不同應(yīng)用場合的需要而將電壓設(shè)置為可調(diào)。輸出電壓的計算Uo=1.25×(1+Rf/R),可調(diào)電阻選用精密可調(diào)電阻,保證輸出電壓的精確可調(diào)。如本文選用的Rf為5kΩ、R為270Ω的組合,可以分別對1.25V～24V-1.25V～-24V之間實現(xiàn)連續(xù)可調(diào)。（5）保護(hù)電路因為線性電源發(fā)熱量較大，所以本電源中加了足夠的散熱器。由于采用高性能的集成電路,從而簡化了電路的結(jié)構(gòu),突出了電源變換問題中的關(guān)鍵部分。通過調(diào)試與檢測,電路整體性能良好。本電源不僅可以單獨(dú)使用,還可以置于其他電子設(shè)備中用作穩(wěn)壓或穩(wěn)流源使用。LM2576-ADJ穩(wěn)壓電路原理框圖如下：圖5LM2576-ADJ構(gòu)成的DC/DC轉(zhuǎn)換電路工作原理：假定開關(guān)晶體管、二極管均是理想元件，電感、電容是理想元件，輸出電壓中的紋波電壓與輸出電壓的比值小到允許忽略。三極管工作在開關(guān)狀態(tài)，如下：圖6想情況下變化器原理導(dǎo)通（開關(guān)S位置在A）電流is流過電感線圈，在電感線圈未飽和前，電流線性增加，在負(fù)載R上流過電流Io,兩端輸出電壓Vo，極性上正下負(fù)。當(dāng)is>Io時，電容在充電。這時續(xù)流二極管承受反向電壓截止（開關(guān)S位置在B）由導(dǎo)通到截止，線圈L中的磁場改變線圈L兩端的電壓極性，以保持其電流iL不變。負(fù)載R兩端電壓仍是上正下負(fù)。iL<Io時，電壓處在放電狀態(tài)，有利于維持Io、Vo不變。這時二極管D1，承受正向偏壓為電流iL構(gòu)成通路。按電感電流IL在周期開始時是否從零開始，可分為電感電流連續(xù)工作模式和電感電流不連續(xù)工作模式。由于電感電流連續(xù)工作模式下，變換器有很好的控制特性；電感電流不連續(xù)工作模式下，電感放完電，電感與電容容易產(chǎn)生振蕩，從而影響輸出電壓的紋波；又相同的占空比，輸出電壓在不連續(xù)模式工作模式下比大，效率高。綜上所述，最理想的情況是穩(wěn)壓器工作于臨界狀態(tài)，所以我們采用兩種方法：①增大電感值，增加電感儲能，延長放電時間 ②提高開關(guān)工作頻率，減小開關(guān)斷開的時間使三極管工作在電流連續(xù)狀態(tài)。 輸出整波整流電路參數(shù)分析輸出濾波整流電路由續(xù)流二極管、電感和電容組成。考慮續(xù)流二極管在PMOS管截止時導(dǎo)通，消耗能量，又工作于高速狀態(tài)，所以我們采用了低功耗、大電流、超高速的肖特基二極管IN5817，其特性如下：最大峰值反向電壓：40V最大反向有效值電壓：28V最大直流阻斷電壓：40V最大正向平均整流電流：1A最大正向壓降：0.6V（1A）由BUCK變換器原理分析可知，為了使電路工作在電感電流連續(xù)模式下，又紋波電壓所以電感應(yīng)該盡可能取得大，我們選擇的電感為8mH 電容主要是“吸收”紋波，具有平滑電壓波形的作用。電容與電感相當(dāng)于一個低通濾波濾器，其截止頻率定義為考慮到電容上等效串聯(lián)電阻的損耗，我們選擇的電容為1000uF。此時截止頻率約為562Hz，可見對于幾十kHz的PWM波有很好的濾波效果。輸入過壓保護(hù) 當(dāng)輸入電壓在正常范圍，輸入采樣電壓小于基準(zhǔn)電壓，比較器輸出低電平；當(dāng)輸入過壓，輸入采樣電壓大于基準(zhǔn)電壓，比較器輸出高電平，ARM產(chǎn)生外部中斷，發(fā)出警報，封鎖PWM信號，使PMOS管截止，從而保護(hù)電路損壞。圖7輸入過壓保護(hù)電路過流