分立元件数字功放设计

 UM10155DiscreteClassDHighPowerAudioAmplifierUM10155：分立元件D类大功率音频功放Keywords：ClassDAudioAmplifier,UniversalClassD,UcD,PWMAudioAmplifier,HighPowerAudio.关键词：D类音频放大器，全D类（UcD）,PWM功放，大功率功放Abstract：ThisusermanualdescribestheoperatinginstructionsandthemostimportantbackgroundinformationofthePhilipsSemiconductorDiscreteClassDHighPowerAudioAmplifierDemonstratorBoard.WithproperheatsinkingofthePowerMOSFETsandawelldimensionedpowersupply,thePWMamplifieriscapableofsupplying200Wofhighqualityaudiopowerintoa4Ωloudspeaker.内容摘要：本用户手册描述了飞利浦半导体分立D类高功率音频放大器演示板的操作方法和最重要的背景资料。在适当的功率管散热器的和很好的供电情况下，这台PWM放大器能提供200 W高质量音频输出给一个4Ω的扬声器。 1.Introduction简介TheUniversalClassD(UcD)version1.00demonstratorboardimplementsa200WtrueRMS(intoa4Ωload)highqualityaudiopoweramplifieronaverycompactprinted-circuitboard.Theamplifierisbuilt-upofdiscretecomponentsonly,andmakesuseofPhilipspatentWO03/090343.这个1.0版本的全D类功放(UcD)示范板是一个在非常紧凑的PCB板上输出200 W真有效功率(4Ω负载)的高质量音频功放。 Fig1.Generalview001aaf1482.Circuitdiagram电路原理图ThedemonstratorboardisintendedtoillustratethecapabilityofPhilipsPowerMOSFETsindiscretehigh-endPWMaudioamplifierapplications.Theboardisself-containedandonlyrequiresasimple(non-stabilized)dualpowersupply,anaudiosource(e.g.functiongenerator,CDplayer)andaloudspeakertodemonstrateitscapabilities.ForevaluationathighoutputpoweraprovisionismadetoattachanappropriateheatsinktotheMOSFETsontheboard.本演示板意欲图解说明飞利浦功率MOSFET在分立高档PWM音频放大器上的应用能力。本板自我包含了齐全的功能，只需要简单的正负电源（非稳压），加上音源和扬声器即可示范其性能。为评价在大功率下的性能，需要附上一个适当的散热片到MOSFET上。  Table1.Connections表一：连接器ConnectorFunctionRemarksJ1audioin-signalusetogetherwithJ2J2audioin-groundusetogetherwithJ1J3amplifierenabletheamplifierisenabledwhenconnectedtoground(J4)J4groundusetogetherwithJ3J5positivesupplyvoltage30Vto45V(noneedforastabilizedpowersupply)J6positivecurrentsensecanoptionallybeusedinanovercurrentprotectionschemeJ7powersupplyground0VJ8negativecurrentsensecanoptionallybeusedinanovercurrentprotectionschemeJ9negativesupplyvoltage−30Vto−45V(noneedforastabilizedpowersupply)J10loudspeakeroutputusetogetherwithJ11J11loudspeakergroundusetogetherwithJ10J1和J2用于音频输入；J3和J4用于控制功放是否启用；J5和J9是30V至45V正负供电，不需稳压；J6和J8是电流感应端，用于设计功放保护；J7是电源的地；J10和J11是输出端，用于接扬声器。译者为了说明电路工作原理，作了一个示意原理图，参见左图：运放输出的信号经28uH电感和680nF电容后有延迟，对某些频率来讲，延迟的时间正好使信号反相，这个信号反馈到运放的负输入端，与其它元件配合，即形成一个400kHz的方波振荡器，且运放正输入端的音频能调制这个振荡器，从运放输出输出一个PWM信号，经28uH电感和680nF电容滤波后送给扬声器放大了的模拟音频功率信号。译者认为，原作者的这个电路的确非常巧妙。  001aaf150001aaf151Fig3.TopcopperlayoutFig4.Bottomcopperlayout  001aaf152001aaf153Fig5.ComponentlayoutFig6.Topsilk-screen         Table2.SpecificationsSymbolParameterConditionsValueVPsupplyvoltageequalpositiveandnegativesupplyvoltages±30Vto±45VPLoutputpowerVP=±45V;RL=4Ω;appropriateheatsinkneeded200W(RMS)ηefficiencyPL=100W;RL=4Ω>92%THD+Ntotalharmonicdistortion-plus-noisePL=10W;frequencyrangefrom20Hzto20kHz<0.03%S/Nsignal-to-noiseratio>120dBfPWMPWMfrequencyidle~400kHzVoffsetoffsetvoltageDCvalue<50mV 4.1Pop-less/click-lessstartupandshutdown功放上电和关机时防止“噗、噗”声和“喀、喀”声Aprovisionhasbeenaddedtothecircuittoprovidepop-less/click-lessstartupandshutdown.Tomakeuseofthestartupfacility,makesurethatthesupplypower(pinsJ5andJ9)isappliedpriortoenablingtheamplifier(connectingJ3toJ4).Tobenefitfromthepop-lessshutdownfeature,disabletheamplifier(disconnectJ3andJ4)priortoremovingthesupplypower.电路预备了一个在功放上电和关机时防止出现“噗、噗”声和“喀、喀”声的功能。开机上电时，令电源（J5和J9）提前于功放控制信号（J3和J4）；关机时则先断开J3、J4，后切断电源J5和J9。4.2Overcurrentprotection过流保护AprovisionhasbeenaddedtothecircuittomonitorthecurrentflowingthroughthePowerMOSFETs(Q13andQ14).ThevoltageappearingbetweenpinsJ5andJ6isproportionaltothecurrentinMOSFETQ14(ratio:50mV/A)andthevoltagebetweenJ8andJ9isproportionaltothecurrentinMOSFETQ13(ratio:50mV/A).Withtheuseofanexternalcircuitthesetwosignalsmaybeusedtodisabletheamplifier(disconnectJ3andJ4)incaseofanovercurrentsituation.SimilarlytheJ3-J4pincombinationcanbeusedtodisabletheamplifierincaseofotherfaultconditions.电路预备了一个监视功率管(Q13和Q14)电流的功能。在J5和J6之间会出现一个正比于流过功率管Q14电流的电压（比率为：50mV/A）；同理，在J8和J9之间会出现一个正比于流过功率管Q13电流的电压。当出现过流时，使用一个外接电路，利用这两个电压信号能禁止功放工作（利用这两个电压切断J3与J4）。在其它故障条件下，同样可利用J3与J4禁止功放工作。4.3Importantnotice重要 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The‘HighPowerClassDAudioAmplifierDemonstratorBoard’ismeanttodemonstratethecapabilitiesofthespecificClassDAmplifierdesignanditssemiconductorcomponents.Noprovisionsforshort-circuitandovercurrentprotectionweremadeonthedemonstratorboarditself.Neitherwasanoperatingtemperaturecompensationfeatureimplementedontheboard.Thecircuitontheboardisreducedtoitsessentials.本电路板是示范一个特殊的D类功放电路设计及其半导体器件，板子本身没有过流保护和短路保护功能，也没有温度补偿功能，板上的电路尽量只做出核心部分，能反映电路本质。Inthisimplementationthe‘HighPowerClassDAudioAmplifierDemonstratorBoard’isnotintendedtobeusedforlongtermoperationorunderextremetemperatureconditionswhendeliveringsubstantialoutputpower.本电路板未设计成在满功率输出时能长期工作或在极端温度条件下工作。 5.Wiringdiagramandpowering-up接线图和上电Audioinput:J1issignal;J2isground音频输入：J1是信号；J2是地线Initially,leaveJ6andJ8unconnected;J7andJ11areatthesame(ground)potential开始时，J6和J8不用接，J7和J11是等电位的（地线）。Fig7.Wiringdiagram 6.Addingexternalfeatures添加外接功能6.1Electronicenabling/disablingoftheamplifier电子激活/禁止功放 Enablesignal:激活信号：（或称“使能信号”）(HIGH=enable)高电平=激活(LOW=disable)低电平=禁止Fig8.Enabling/disablingoftheamplifierElectronicenabling/disablingcanbeusedfor:电子激活/禁止的功能可用于： •Implementingpop-lessandclick-lessstart-upandshut-down功放上电和关机时防止“噗、噗”声和“喀、喀”声•Shuttingdowntheamplifierincaseofafailurecondition(short-circuit/overcurrent/over-temperature)在短路、过流、超温等破坏条件下半闭功放Thetransistorintheenabling/disablingcircuitmustbelowcurrent,60Vtype(suchasBC846)andtheresistormustlimitthebasecurrentofthetransistortoapproximately1mA(incaseoflogicleveldriving,thatwouldmeanR=4.7kΩ).用于电子激活/禁止的三极管需要小电流、60V耐压的，电阻令三极管的基极电流约1毫安（使用TTL逻辑电平时R=4.7kΩ）。  6.2Short-circuitandovercurrentprotection短路和过流保护 Fig9.Short-circuitandovercurrentprotection  The‘Short-circuitandovercurrentprotection’circuitmustbeusedtogetherwiththe‘Electronicenabling/disabling’circuit.�短路和过流保护�电路须配合�电子激活/禁止”电路使用。TheoutputpinsofIC1andIC2produceaHIGHlogiclevelpulsewhenovercurrentisdetectedineitherthelowsideMOSFET(Q13ontheDemonstratorBoard)andhighsideMOSFET(Q14ontheDemonstratorBoard)respectively.ThetwosignalsarecombinedthroughtheIC3or-gate.Theresultingsignalmustbeprocessedinthe‘µPorotherlogic’block.Oneofthesimplestsolutionswouldbealatchcircuit,whichonahighpulseforcestheoutputgolow.Thiscausesthe‘Electronicenabling/disablingcircuit’todisabletheamplifier.Throughmanualinterventionand/orafteracertainwhile,thelatchshouldberesettoaHIGHlogiclevel,whichinturnre-enablestheamplifier.当分别在Q13和Q14上检测到过流时，IC1和IC2的输出脚分别产生一个高逻辑脉冲。这两个信号通过IC3“或门”组合。由此产生的信号须经“微处理器或其它逻辑”模块进行处理。最简单的办法是做一个闩锁电路，一个高逻辑脉冲将使输出变低。这将令�电子激活/禁止”电路禁止功放工作。确定问题后通过人工干预，闩锁电路可复位到高逻辑电平，激活功放工作。 Table3.Components元件清单（外接的）ComponentValueR1,R4270ΩR2,R34.7kΩR5,R6,R7,R8,R9,R10,R11,R1210kΩC1,C24.7nF D1,D5PhilipsPDZ10BD2,D3,D4,D6PhilipsPDZ5.1BQ1PhilipsBC846Q2PhilipsBC856IC1,IC2Fastoperationalamplifier;feedwith+12Vand−12Vsupplies快速运放，使用正负12V供电IC3PhilipsHEF4071;feedwith5V  6.3SonicperformanceversusEfficiencytrade-off音质与效率的权衡Thedead-timethatisallowedbetweenQ13andQ14conductiondeterminestheefficiencyoftheDemonstratorBoardforagreatdeal;alongdead-timeleadstobetterefficiency.Ontheotherside,longdead-timealsoleadstoworsesonicperformance;ithasimportantadverseconsequencesfore.g.THD.在测量示范板的效率时，很大程度上取决于允许Q13和Q14之间有多少“死区”。长时间的死区将带来高效率，但同时令音质变坏。死区令效率与失真等指标产生矛盾。Shortdead-timecausesquiescentcurrenttogoup,thusreducingefficiencyandimprovingsonicperformance.Thehigherquiescentcurrentistheresultofmorecross-conductionofQ13andQ14.So,mostofthepowerthatislostinthiswayisdissipatedinQ13andQ14,whichmayheat-upexcessively.ThismaycausethermallyinstablebehavioroftheMOSFETs.Forthatreason,theDemonstratorBoardisshippedinlowquiescentcurrentmode–duringinitialevaluationtheriskofdamagingtheMOSFETsthroughthermalrunawayisthusreduced.短时间的死区将令静态电流增加，如此会降低效率和改善音质。高的静态电流是Q13和Q14两只管同时导通的结果，故而许多能量在Q13和Q14上损耗掉了，而且可能过度发热。这可能是引起MOSFET不稳定的原因之一。因上述原因，示范板设定在低静态电流模式，降低了MOSFET通过热途径损坏的风险。Nevertheless,bymodifyingoneresistorvalue,thedead-timecanbeshortenedandevaluationinenhancedsonicperformancemodecantakeplace.ChangingR9toalowervaluedecreasesdead-time.Itislefttheresponsibilityoftheexperimentertopreventthermalrunaway,butassistancefromPhilipswillbeavailablethroughthelocalsalesrepresentatives.不过，修改一个电阻值即可缩短死区时间，增强音质。将R9减小就能缩短死区时间。它让实验者有了防止热失控的责任，可通过Philips就近的销售代表获得协助。Toreducetheriskofthermalrunawayintheenhancedsonicperformancemode,athermalfeedbackloopcanbeimplemented:theoperatingtemperatureoftheMOSFETscanbefed-backtothedead-timecontrolbychangingthefixedR9value,mountingaPTCresistorontheheatsinkoftheMOSFETsandconnectingthePTCinparallelwithR9.Again,anychangesarelefttheresponsibilityoftheexperimenter,butassistancefromPhilipswillbeavailablethroughthelocalsalesrepresentatives.为防止在增强音质模式产生的热失控，可实现一个热反馈环路：在MOSFET上安装个PTC电阻，将其并联在R9上。重申：如有问题，可从Philips各地经销商获得帮助。   翻译：广州市迪士普音响技术有限公司  王齐祥 2008年4月20日星期日