资源描述:
《DC-DC Power Supply 介绍与主要元件参数选择.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、ClassificationofPowerSupplyLinear:RegulatororLDO(Lowdropout)Switching:BuckconversionBoostconversionBuck-Boostconversion(SEPIC,Cuk…)HowtoseparateLinearorSwitching?Linear:將一DC電壓經由電路元件,直接線性轉換為另一DC電壓.Forexample:3.3V5VCin10uFAP1117312INADJOUTCout100uFHowtoseparateLinearorSwitching?Switching:電源電路中使用一個或多
2、個開關元件,來切換能量之儲存或轉移,同時可利用各種電路架構來達到升壓.降壓.極性反轉或直流電壓轉交流電壓,交流電壓轉直流電壓…等要求.AdvantageandDisadvantageAdvantageofLinearCostlowerLowoutputnoiseandrippleGoodoutputregulationDisadvantageofLinearEfficiencylowerNeedbiggertransformerandheatsinkNarrowinputvoltagerangeLowholduptime(~1ms)AdvantageandDisadvantageAdvan
3、tageofswitchingHighfrequencyoperatingtoreducesizeofinductorandcapacitorLightweightandSmalltotalsizeHighefficiencyandpowerdensityHighinputvoltagerangeandholduptime(~25ms)DisadvantageofswitchingHighripplevoltageCircuitdesigncomplicatedHigherEMIinterferenceSwitchingcircuitDC-DCcircuitBuckconverterSwi
4、tchingcircuitBuckconverterfunctiondescriptionQ控制能量儲存與傳送方向L傳送與儲存能量及濾除電流雜訊C傳送與儲存能量及濾除電壓雜訊D提供放電迴路(當Qoff)SwitchingcircuitBuckconverter工作原理說明:Q導通,D截止,電感器之電壓為VL=Vi-Vo故電感器iL會開始持續線性上升,其交流成分iL(ac)流經電容器C產生漣波,直流成分會供應至負載RLSwitchingcircuitBuckconverter工作原理說明:Q截止,電感器瞬間電流不變,故為感一反電動勢VL=-Vo而促使D導通,此時C原來所儲存的能量可經
5、由D,L釋放至負載,L上的電流呈線性衰退DesignBuckconverterHowtoselectinductorL>=[Vin(min)-Vsat-Vout]*Ton(max)2Io(min)Vo/Vi=D=ton/TsDesignBuckconverterHowtoselectCin?Cin電壓rating至少為Vin1.5倍Iin的計算方式如下表所示:DesignBuckconverterHowtoselectCout?Esr=Vripple/2Io(min)Cout>=△IL/8*fs*△VoHowtoselectDiode?Vrrm>=1.25Vin(max)Ipk=Io(
6、max)-Io(min)SwitchingcircuitDC-DCcircuitBoostconverterSwitchingcircuitBoostconverter工作原理:Q導通,D截止,電感器之電壓為一固定値VL=Vi,故電感器電流iL會開始持續線性上升補充能量,此時電容器瞬間電壓不變開始釋放能量致負載SwitchingcircuitBoostconverter工作原理:Q截止,D導通,電感器瞬間電流不變,故會感應一反電動勢-VL=Vi-Vo,此時輸出電壓將會備昇壓,電感與電源同時釋放能量至負載及電容器C上,電感之電流iL開始持續線性下降釋放能量至一定値Boostconverter
7、DesignHowtoselectinductor?L=[Vin(min)-Vds(sat)]*Dmax△IL*fsVo/Vi=1/1-DD=ton/TsThermalConsiderationSwitchingICThermalconsiderationPloss=PQ+Psat+PswherePQ:quiescentlossPsat:saturationlossPs:switchinglossThermalConsi