开关电源forward converter动作原理_rev4

1、1Copyright HIPRO Co. All Rights Reserved Forward Power Converter 動作原 Reporter：Sean Hsia(夏存孝) Date：2009 / 04 /03 2Copyright HIPRO Co. All Rights Reserved Outlines Forward Converter Introduction Operation of Forward Converter Dual-Forward Converter Introduction 3Copyright HIPRO Co. All Rights Reserved Forward Converter Introduction (1) 優點優點： (1) 銅損(Copper loss)比較小，變壓器溫升可以減少一些，鐵心之大 小在選擇上也可以小一些 (2) 輸出電感器儲存能提供負載使用，輸出電容器在值大小可 減少許多，電容對波電額定值之大小要求也會小些 (3) 經功開關峰值電較小 (4) 經輸出電感器之電並非脈動電，在輸出端之波電壓之 大小比返馳式小 缺點缺

2、點： (1) 與返馳式轉換器比較起，成本較高，這是因為增加輸出電感 器與輸出二極體 (2)在輕載情況下，轉換器進入DCM操作模式，則在其他無回授 之輸出端上，其輸出電壓可能會過大，一般在輸出端加入 Dummy Resistor解決。順向式轉換器一般是設計工作在CCM 之情況操作 4Copyright HIPRO Co. All Rights Reserved Operation of Forward Converter (1) S Vds Ids Vlm Ilm Vlo Ilo Idr 0 t 1 t 2 t 3 t 5Copyright HIPRO Co. All Rights Reserved Operation of Forward Converter - CCM (1) S Vds Ids Vlm Ilm Vlo Ilo Idr 0 t 1 t 2 t 3 t 等效電 in p s V N N 6Copyright HIPRO Co. All Rights Reserved Operation of Forward Converter - CCM (2) in r p V N

3、N 0 t 1 t 2 t 3 t 等效電 CoRo Lo Vo Ilo 7Copyright HIPRO Co. All Rights Reserved 0 t 1 t 2 t 3 t Operation of Forward Converter - CCM (3) 等效電 CoRo Lo Vo Ilo 8Copyright HIPRO Co. All Rights Reserved Function of Forward Converter for CCM () sw swMAX f D TDt = 1 1 prr p swswr p NN D D D N N f D f D N N + 1 1 1 1 直電壓轉換方程式： 轉換器最大責任週期： pr NN D + 1 1 p s in o N N D V V = swr p swm in sw m in m in r p f D t N N f D L V TD L V t L V N N = 9Copyright HIPRO Co. All Rights Reserved Min. Output Inductance for C

4、CM s oP inS s o o LoB TD LN VND TD L V II = = )1 ( 2 )1 ( 22 1 要使轉換器操作在CCM模式則 )1 ( 2 )1 ( 2 D I TV LL DD LN TVN III LoB so oBo oP sinS oBLoBo = =或 10Copyright HIPRO Co. All Rights Reserved MOSFET的選擇 功開關 耐壓值 耐值 平均電值 m ins o P S Lmo P S ds L VTDI I N N I I I N N I + +=+ +=) 2 () 2 ( max, += r p inds N N VV1 max, oo P S avgds IDID N N I= , 11Copyright HIPRO Co. All Rights Reserved DIODE的選擇(1) 二極體D1 耐壓值 耐值 平均電值 D V V N N V o in P S D = max, 1 += += oin P S swo o Lo oD VV N N fL D I I II 22 max, 1 oa

5、vgD IDI= , 1 12Copyright HIPRO Co. All Rights Reserved DIODE的選擇(2) 二極體D2 耐壓值 耐值 平均電值 D V V N N V o in P S D = max, 2 += += oin P S swo o Lo oD VV N N fL D I I II 22 max, 2 () oavgD IDI= 1 , 2 13Copyright HIPRO Co. All Rights Reserved 輸出電容的選擇 )1 ( 88 8 2 1 2 1 2 1 2 D VL VT V TI C C TI C TI C Q V oo os o s o o s o s o o = = = = = s o o rmsCo o TD L VI I I V ESR = = )1 ( 32 1 32 )( max, 14Copyright HIPRO Co. All Rights Reserved S Vds Ids Vlo Ilo Ico 0 t 1 t 2 t 3 t 4 t Operation of Forward Convert

6、er - DCM (1) Lm Lo Ilo Ilm Vo in p s V N N Vin 等效電 15Copyright HIPRO Co. All Rights Reserved Operation of Forward Converter - DCM (2) Lm Ilm in r p V N N S Vds Ids Vlo Ilo Ico 0 t 1 t 2 t 3 t 4 t 等效電 CoRo Lo Vo Ilo 16Copyright HIPRO Co. All Rights Reserved Operation of Forward Converter - DCM (3) S Vds Ids Vlo Ilo Ico 0 t 1 t 2 t 3 t 4 t 等效電 CoRo Lo Vo Ilo 17Copyright HIPRO Co. All Rights Reserved Operation of Forward Converter - DCM (4) S Vds Ids Vlo Ilo Ico 0 t 1 t 2 t 3 t 4 t CoRo Vo 等效電 18Co

7、pyright HIPRO Co. All Rights Reserved 雜散元件的影響 Vin Ds CoRo Lm S Coss Llk Np ： Ns D1 D2 Lo RESR Vo Cd1 Cd2 Rlo Nr Dr Vds Ilo 1. 雜散元件效應 (a) 增加半導體元件電壓及電應 (b) 振現象(ringing)導致能損失加大 2. 需增加減震電(Snubber)及箝制電(Clamp) 3. 功密無法大幅提升 MOSFET Diode Layout Transformer LrpLrs Lm 19Copyright HIPRO Co. All Rights Reserved Forward Converter with Parasitical Components Vin CoRo Lm S Np ： Ns D1 D2 Lo Vo Dsn Csn Rsn Ilo 20Copyright HIPRO Co. All Rights Reserved Dual Forward Power Converter 動作原 21Copyright HIPRO Co. All Rig

8、hts Reserved Dual Forward Converter Introduction (1) 22Copyright HIPRO Co. All Rights Reserved Dual Forward Converter Introduction (2) 等效電 S1&S2 Turn-on 23Copyright HIPRO Co. All Rights Reserved Dual Forward Converter Introduction (3) 等效電 S1&S2 Turn-off 24Copyright HIPRO Co. All Rights Reserved Min. Output Inductance for CCM s oP inS s o o LoB TD LN VND TD L V II = = )1 ( 2 )1 ( 22 1 要使轉換器操作在CCM模式則 )1 ( 2 )1 ( 2 D I TV LL DD LN TVN III LoB so oBo oP sinS oBLoBo = =或 25Copyright HIPRO Co. All Rights Reserved

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