降压斩波电路 Stepdown Stepdown中英版

Item4Directcurrentchoppercircuit项目四直流斩波电路4.1.2Buckchoppercircuit4.1.2降压斩波电路TeachingResourcesDatabaseof

NationalVocationalEducationPowerSupplyTechnologyBilingualcourses.Powerelectronicstechnology电力电子技术

电路结构Circuitstructure

全控型器件若为晶闸管，须有辅助关断电路。FullcontroldeviceInthecaseofthyristor,auxiliaryshutoffcircuitisrequired.续流二极管Freewheelingdiode负载出现的反电动势Thebackelectromotiveforceoftheload典型用途之一是拖动直流电动机，也可带蓄电池负载。OneofthetypicalusesistodriveaDCmotor,butalsowithabatteryload.

降压斩波电路（BuckChopperCircuit)4.1.2Buckchoppercircuit降压斩波电路工作原理Workingprinciplec)电流断续时的波形WaveformwhencurrentisdiscontinuousEV+-MRLVDioEMuoiGtttOOOb)电流连续时的波形WaveformwhencurrentiscontinuousTEiGtontoffioi1i2I10I20t1uoOOOtttTEEiGiGtontoffiotxi1i2I20t1t2uoEMa)

电路图Circuitdiagram图1降压斩波电路得原理图及波形Figure1schematicdiagramandwaveformofstep-downchoppercircuitt=0时刻驱动V导通，电源E向负载供电，负载电压uo=E，负载电流io按指数曲线上升。Whent=0,Visdriventoturnon.ThepowersupplyEsuppliespowertotheload.TheloadvoltageUo=E,andtheloadcurrentIorisesaccordingtotheexponentialcurve.t=t1时控制V关断，二极管VD续流，负载电压uo近似为零，负载电流呈指数曲线下降。Whent=t1,thecontrolVisoff,thediodeVDcontinuesthecurrent,theloadvoltageUoisapproximatelyzero,andtheloadcurrentdecreasesexponentially.通常串接较大电感L使负载电流连续且脉动小。UsuallyalargeinductorLisconnectedinseriestomaketheloadcurrentcontinuouswithsmallpulsation.4.1.2Buckchoppercircuit降压斩波电路数量关系Quantitativerelations电流连续Currentcontinuity负载电压平均值：

Averageloadvoltageton——V通的时间timeofturningon

toff——V断的时间timeofturningoff

a--导通占空比dutycycleofconducting

电流断续，Uo被抬高，一般不希望出现。ThecurrentisintermittentandUoisincreased,whichisgenerallyundesirable.

负载电流平均值：

Averageloadcurrent4.1.2Buckchoppercircuit降压斩波电路斩波电路三种控制方式ThechoppercircuithasthreecontrolmodesT不变，变ton—脉冲宽度调制（PWM）。Tconstant,changeton--pulsewidthmodulation(PWM).ton不变，变T—频率调制。toninvariant,variableT-frequencymodulation.ton和T都可调，改变占空比—混合型。BothtonandTareadjustabletochangedutycycle-hybridtype.电力电子电路的实质上是分时段线性电路的思想。Theessenceofpowerelectroniccircuitistheideaoftime-dividedlinearcircuit.基于“分段线性”的思想，对降压斩波电路进行解析。Basedontheideaofpiecewiselinearity,thestep-downchoppercircuitisanalyzed.分V处于通态和处于断态VintheonstateandVintheoffstate初始条件分电流连续和断续Initialconditionsincludecontinuouscurrentanddiscontinuouscurrent此种方式应用最多Thisisthemostcommonlyusedmethod4.1.2Buckchoppercircuit降压斩波电路同样可以从能量传递关系出发进行的推导Wecanalsoderiveitfromtheenergytransferrelationship

由于L为无穷大，故负载电流维持为Io不变SinceLisinfinite,theloadcurrentismaintainedatIo

电源只在V处于通态时提供能量，为

ThepowersupplyonlyprovidesenergywhenVisintheonstate,whichis

在整个周期T中，负载消耗的能量为DuringthewholeperiodT,theenergyconsumedbytheloadis输出功率等于输入功率，可将降压斩波器看作直流降压变压器。Theoutputpowerisequaltotheinputpower,andthestep-downchoppercanberegardedasaDCstep-downtransformer.一周期中，忽略损耗，则电源提供的能量与负载消耗的能量相等。Inonecycle,ignoringtheloss,theenergyprovidedbythepowersupplyisequaltotheenergyconsumedbytheload.4.1.2Buckchoppercircuit降压斩波电路3-7

负载电流断续的情况：Theconditionofintermittentloadcurrent

I10=0，且andwhent=tx时，i2=0tx<toff电流断续的条件：

Conditionsfordiscontinuouscurrent负载电流平均值为：

Theaverageloadcurrentis输出电压平均值为：Th