Buck变换器的损耗分析及轻载高效原理.ppt
Monolithic Power Systems,Buck变换器的损耗分析及轻载高效原理2011-12-15,刘少纯 15813848835,Buck变换器损耗分析,轻载高效原理,MPS 轻载高效Buck变换器,内容,（常数值，基本不变）（强非线性，是Vds的函数）（强非线性，是Vds的函数）,简化的MOSFET等效电路,导通后等效为电阻,MOSFET损耗,Crss=Cgd,MOSFET开通（turn on）过程,SW,SW,SW,SW,t1，驱动电压到Vth,t2，电流建立,t3，Vds电压下降,T4-5，完全导通,MOSFET损耗,MOSFET损耗Rds和Rg电阻损耗,开/关损耗,导通损耗,Coss损耗,驱动损耗,自身损耗,MOSFET损耗,Diode损耗肖特基不计反向恢复损耗,Diode损耗,L/C损耗,1、电感会产生磁芯损耗和绕组铜损；2、纹波电流会在电容ESR上产生损耗；3、适当增加电感值，可以降低电流纹波，减小有效值电流，改善效率。,L/C损耗,IC损耗,IC损耗,综合上述分析可知，影响效率的因素主要有Rds（on），开关频率，有效值电流。,Buck变换器损耗分析,Buck变换器损耗分析,轻载高效原理,MPS 轻载高效Buck变换器,内容,负载电流从2A下降到0A时，电感纹波电流不变，影响导通损耗；开关频率不变，影响开关损耗，驱动损耗。,轻载高效原理,不具备轻载高效的同步整流IC,Pulse Skip Mode（PSM）,轻载高效原理,经典峰值电流模式（PCM）IC,增加轻载管理功能,PFM/PWM IC,轻载高效原理,PSM模式框图,-,VIN,R1,R2,VREF,VOUT,+,-,+,vC,iHS,Conventional Peak Current Mode Control,When load current reduces,VC reduces,IL reduces,When load current further reduces,VC further reduces,IL further reduces,Fixed frequency DCM,轻载高效原理,经典峰值电流模式,-,VIN,R1,R2,VREF,VOUT,+,-,+,vC,iHS,AAM,When load current reduces,VC reduces,IL reduces,When load current further reduces,VC clamps AAM voltage,IL peak forces to be constant,Frequency Extended,How AAM works,轻载高效原理,PSM模式,轻载高效原理,PSM模式脉冲,Up to 16V,3.3V,Small Amount of EVB could be Sampled!,5.6uH,轻载高效原理,(VOUT=3.3V),Unbeatable 92%Efficiency 3A 82%Light Load Efficiency 12V,CCM Mode,W/Light load Mode(AAM),Light Load Mode+Low Rdson=High Efficiency,轻载高效原理,COT控制Constant On Time（恒定导通时间）,轻载高效原理,轻载高效原理,Ton and SW frequency fairly constantFast transient responseEasy loop stabilizationSW frequency automatically reduced light load,轻载高效原理,工作波形,交流等效电路 关键波形,注,滤波电容短路滤波电感开路SW电压-57V，D=5/12,轻载高效原理,FB 电压的直流分量,叠加原理,轻载高效原理,In discontinues mode,when the inductor current is zero,the output capacitor support current to the load,and the FB voltage down with slope du/dt=Iload/Cout,断续模式波形,ref,轻载高效原理,Buck变换器损耗分析,轻载高效原理,MPS 轻载高效Buck变换器,内容,Brief Introduction,AAM:Advanced asynchronous mode,MPS 轻载高效Buck变换器（PSM）,MPS 轻载高效Buck变换器（COT）,Monolithic Power Systems,Q&A,Monolithic Power Systems,Inc.US Headquarters6409 Guadalupe Mines RoadSan Jose,CA 95120Tel:(408)826-0600,
