Modeling and Simulation of Non-ideal Buck Converter in DCM

ISSN 2249-6343International Journal of Computer Technology and Electronics Engineering (IJCTEE)Volume 2, Issue 2d ( D dˆ)( I iˆ)i d( D dˆ ) ( D v dˆ iˆ)1 1 1 L LL1dD22D2 D2ˆ112g1LVgD1ILD D D I 2D I ˆ D ˆD D D D V D D D Dd1d d21 1 2 L2 L1I ˆLv2 gd2 1i2 L12(12) g(12) (12)1 2( D ˆ ˆ1d1)( Vgvg)vg( ˆ D D) ( ˆ ˆ DD d D v d iˆ)2 2 21 1 2 g 1 LVgD1ILD D ( D 2 D ) 2D VˆˆD D V V v d iˆD D D D D D D D I1 1 1 22 g1 2 gg 2 g 2 12 L12(12) (12) (12)L(16)(17)Neglecting the small signal perturbations, DC equivalentcircuit model of non-ideal Buck converter in DCM as shownin Fig.5:I I RLE V ESV gD1D D12I LD1D DFig.5 DC equivalent circuit model of Non-ideal Buck converterin DCMVODD1Vg VE1D2RE1RE. Small-signal Equivalent Circuit Model12V gR(18)Removed the DC component in the equation (16) & (17),the small-signal equivalent circuit model of non-ideal Buckconverter in DCM as shown in Fig.6:vˆgî Savˆga ˆd 21 1a iˆ3 LîLb vˆ1 gb 2 ˆd 1b iˆ3 LFig.6 Small-signal equivalent circuit model of Non-ideal Buckconverter in DCMFrom Fig.6, the open loop transfer function of Buckconverter from duty cycle to output voltage in DCM can beobtained:LR ECR CRV ovˆoovˆ () sG () s vd odˆ 1 () svˆ g ( s) 0b2R(1 sRCC)2E 3(C(C)(E 3) ) (C)R R b s RR C R R R b C L s R R LCs1bR2z1 (19)2R REb3s s 1 QooWhere,R REb3( R R ) LCC,( R RE b3)( R RC)LCQ R ( RE b3) C RRC C ( RE b3)RC C ,L1z1 .RCCIV. SIMULATIONIn this paper, a Buck converter with the followingparameters is assumed:V 10V, V 5V, R 25 , L 2 ,goR 3.5m , C 3mF, R 20m , R 10m ,RfLDS1m , V 0.4V 200kHZDC, the switching frequency. The simulation result as follows:Fig.7 The simulation results (the solid line is for considering theparasitic components, dash line is for without considering theparasitic components)Compared with the ideal model, there is a zero in thetransfer function of non-ideal model. So in theamplitude-frequency curve, the solid line declines at the slope6of 20 dB / dec after 10 H z , while the dash line dose atthe slope of 40 dB / dec .S74