DC-DC Power Supply 介绍与主要元件参数选择.ppt

Classification of Power Supply Linear : Regulator or LDO ( Low drop out ) Switching : Buck conversion Boost conversion Buck-Boost conversion(SEPIC,Cuk…) How to separate Linear or Switching ? Linear : 將一 DC 電壓經由電路元件,直接線性轉換為另一DC 電壓. For example: How to separate Linear or Switching ? Switching : 電源電路中使用一個或多個開關元件,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. Advantage and Disadvantage Advantage of Linear Cost lower Low output noise and ripple Good output regulation Disadvantage of Linear Efficiency lower Need bigger transformer and heat sink Narrow input voltage range Low hold up time (~1ms) Advantage and Disadvantage Advantage of switching High frequency operating to reduce size of inductor and capacitor Light weight and Small total size High efficiency and power density High input voltage range and hold up time(~25ms) Disadvantage of switching High ripple voltage Circuit design complicated Higher EMI interference Switching circuit DC-DC circuit Buck converter Switching circuit Buck converter function description Q?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Q off) Switching circuit Buck converter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RL Switching circuit Buck converter 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由D,L釋放至負載,L上的電流呈線性衰退 Design Buck converter How to select inductor ?L=[Vin(min)-Vsat-Vout]*Ton(max) 2Io(min) Vo/Vi=D=ton/Ts Design Buck converter How to select Cin? ?Cin電壓rating至少為 Vin 1.5倍 Iin的計算方式如下表所示: Design Buck converter How to select Cout? Esr=Vripple/2Io(min) Cout=△ IL/8*fs* △Vo How to select Diode? Vrrm=1.25Vin(max) Ipk=Io(max)-Io(min) Switching circuit DC-DC circuit Boost converter Switching circuit Boost converter 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 Switching circuit Boost converter工作原理: