搜索
2016年全国大学生电子设计竞赛降压型直流开关稳压电源(A题)【本科组】2016年7月28日摘要本系统介绍了一种DC-DCBuck同步整流变换器的基本原理和实现方法。通过LM5117芯片产生PWM信号驱动MOS管；利用反馈网络控制PWM的占空比，对输出电压进行调整；反馈网络及斜波补偿，使系统实现稳压输出。同时该系统具有过流保护功能，通过电流检测芯片ACS712，将电流信号转化为电压信号，由单片机TM4C123G通过AD采样并对系统加以控制。当电流超过3.2A时，单片机输出信号给LM5117，使其启动保护机制关闭输出，从而实现过流保护。通过按键开关实现恒压模式与负载识别模式的切换，在恒压模式下输出稳定的5V电压，最大电流大于3A，负载调整率为1.2%，电压调整率为0.02%，满载下效率高达91%。而负载识别模式下，根据所接入的元件阻值调整系统的输出电压。此外单片机还负责电流电压显示。最后通过改进测试方法、增大输出电容等方法，纹波得到了有效的控制，峰峰值主体在50mv以内。本系统的全部指标均达到题目要求，具有高性能、高效率、小质量的特点。关键词：LM5117；同步整流；低压大电流；负载识别ABSTRACTThissystemintroducesaDC-DCBucksynchronousrectifierconverterbasicprincipleandimplementationmethod.ThroughLM5117chipproducesPWMsignalstodrivetheMOStube;UsingfeedbacknetworkcontrolPWMdutyratio,toadjustoutputvoltage.Feedbacknetworkandobliquewavecompensation,makethesystemtorealizethevoltageoutput.Thesystemhasthefunctionofover-currentprotectionatthesametime,throughthecurrentchipACS712,convertcurrentsignaltovoltagesignal,bythesinglechipmicrocomputerTM4C123GthroughADsamplingandtocontrolsystem.Whenthecurrentexceeds3.2AmicrocontrolleroutputsignaltoLM5117,makeitstarttoclosetheoutputprotectionmechanism,soastorealizetheover-currentprotection.Bykey-pressswitchswitching,constantpressureandloadidentificationmodelinconstantvoltagemodestableoutput5vvoltage,maximumcurrentisgreaterthan3a,theloadadjustmentratewas1.2%,thevoltageregulationratewas0.02%,theefficiencyisashighas91%underload.Andloadidentificationmode,dependingontheaccesselementresistanceadjustingtheoutputvoltageofthesystem.Singlechipmicrocomputerisalsoresponsibleforcurrentvoltagealsorevealed.Finallythroughimprovedtestingmethod,themethodsofincreasingtheoutputcapacitance,ripplehasbeeneffectivelycontrolled,Vppwithin50mv.lindexesmeetthesubjectrequirementsofthissystem,hasthecharacteristicsofhighperformance,highefficiency,smallquality.Keyword:DC-DCtransform;LM5117;Modeswitch;Overcurrentprotection目录一方案论证......................................................................................................-1-1.1论证比较.............................................................................................-1-1.1.1DCDC降压模块的论证与选择................................................-1-1.1.2PWM调制模块的选择............................................................-3-1.1.3恒压输出与负载识别功能的切换..........................................-4-1.1.4过流保护的实现......................................................................-5-1.2方案描述.............................................................................................-5-二理论分析与计算........................................................................................-6-2.1参数的计算..........................................................................................-6-2.1.1开关频率的计算.......................................................................-6-2.1.2电感的计算...............................................................................-6-2.1.3LM5117外围参数选择............................................................-6-2.1.4其他外围参数选择...................................................................-9-2.2稳定控制方法.....................................................................................-9-2.2.1稳压指标..................................................................................-9-2.2.2稳压电路的设计...................................................................-10-2.3降低纹波的方法..............................................................................-11-2.3.1纹波产生的原因...................................................................-11-2.4.2降低纹波的方法...................................................................-11-三电路与程序设计.....................................................................................-13-3.1系统结构框图...................................................................................-13-3.1.1主系统框图...........................................................................-13-3.1.2主控芯片设计........................................................................-13-3.1.3自举电路及斜波补偿...........................................................-14-3.1.4MOS管驱动电路...................................................................-15-3.1.5电流检测电路.......................................................................-15-3.1.6负载识别电路……......…...….………………….…………………………...-16-3.2器件选择...........................................................................................-16-四测试方案与测试结果.............................................................................-19-4.1测试方案及测试条件.......................................................................-19-4.1.1测试方案...............................................................................-19-4.1.2测试条件...............................................................................-19-4.2测试结果及其分析...........................................................................-20-4.2.1测试结果...............................................................................-20-4.2.2测试分析...............................................................................-21-五总结..............................................