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1、DC-DCconverterElectronicpowerconversiondevicesTheAC/DCpowersupply(Adapter,SPS...)DC/DCconverterTheDC/ACinverter(forlamp…)LinearRegulatorIin=IoutVo/Vi<1LinearRegulatorFeature:FastSourceResponseNoSwitchingNoiseCostEffectiveDesignformAClassVoltageSourceSmallerrip
2、pleSimpleandEasyUseLowEMIDrawback:LowefficiencyHeavyandbigSwitchingRegulator原理:開關(guān)穩(wěn)壓器利用無(wú)源磁性元件和電容電路元件的能量存儲(chǔ)特性,從輸入電壓源獲取分離的能量,暫時(shí)地把能量以磁場(chǎng)形式存儲(chǔ)在電感器中,或以電場(chǎng)形式存儲(chǔ)在電容器中,然後將能量轉(zhuǎn)換到負(fù)載,實(shí)現(xiàn)DC/DC變換。Buck:usedtoreduceaDCvoltagetoalowerDCvoltage.Boost:providesanoutputvoltagethatishighe
3、rthantheinput.Buck-Boost:producesaDCoutputvoltagethatisoppositeinpolaritytotheinput.Thenegativeoutputvoltagecanbeeitherlargerorsmallerinmagnitudethantheinputvoltage.SwitchingRegulatorSwitchingRegulatorFeature:SmallLightHighEfficiencyLargearrangeofinputvoltageD
4、rawback:BigrippleandnoiseHighEMISwitchingRegulator分析升壓電路的工作原理時(shí),首先假定電路中電感L很大,電容C也很大。當(dāng)晶閘管處?kù)秾?dǎo)通狀態(tài)時(shí),電源E向電感L充電,充電電流基本恒定位I1,同時(shí)電容C上的電壓向負(fù)載R供電。因電容C值很大,基本保持輸出電壓u0為恒定值,即為U0。設(shè)T處?kù)锻☉B(tài)的時(shí)間為ton,此階段電感上積蓄的能量為EI1ton。當(dāng)T斷態(tài)時(shí)E和L共同向電容C充電,並向負(fù)載R提供能量。設(shè)T處?kù)稊鄳B(tài)的時(shí)間為toff,則在此期間電感L釋放的能量為(U0-E)I1to
5、ff。當(dāng)電路工作于穩(wěn)態(tài)時(shí),一個(gè)週期T中電感L積蓄的能量與釋放的能量相等,即:EI1ton=(U0-E)I1toff上式中的T/toff≥1,輸出電壓高於電源電壓,故稱該電路為升壓電路。也有的文獻(xiàn)中直接採(cǎi)用其英文名稱,稱為Boost變換器。令T/toff為升壓比,調(diào)節(jié)其大小,即可改變輸出電壓U0的大小。若令升壓比的倒數(shù)為b,即b=toff/T,則它與導(dǎo)通占空比的關(guān)係有:a+b=1化簡(jiǎn)後可得:U0=[(ton+toff)/toff]E=(T/toff)E因此,輸出電壓可表示為:SwitchingRegulatorPWM
6、:thefeedbackloopadjuststheoutputvoltagebychangingtheONtimeoftheswitchingelementintheconverter.Example:LCfilterTheoutputvoltagecanbedirectlycontrolledbychangingtheONtimeoftheswitchPulsewidthmodulation(PWM)BasicPrincipleofBoost-1BasicPrincipleofBoost-2Theinducto
7、rcurrentdecreaseduringtheQ1OFFtimeisgivenby:Insteadystate,△IL(+)=△IL(-),→IgnoreRL,VQVd:TheoutputvoltageiscontrolledbysettingtheONtimeofQ1.TheinductorcurrentincreaseduringtheQ1ONtimeisgivenby:EFFICIENCY=EFFICIENCY=6.6W(0.61A)(12V)X100=90%6.6W(2A)(12V)X100=28%Pd
8、=(12-3.3)*2A=17.4W!!Pd=12*0.61*10%=0.73WLinearRegulators與SwitchingRegulators比較Veryhot!ComparisonChargepumpVinVoutChargepump半波雙倍壓電路原理圖PrincipleofChargePumpQ2onChargingphase:Q2ONVcch