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Transistor Audio Power Amplifier: Voltage vs. Power Amplification in Electronics-II

This submission discusses transistor audio power amplifiers, voltage vs. power amplification, key terms, power amplifier classification, heatsink importance, tuned voltage amplifier, feedback in amplifiers, and sinusoidal oscillators in Electronics-II.

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Transistor Audio Power Amplifier: Voltage vs. Power Amplification in Electronics-II

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  1. ELECTRONIC-II • Submitted To:- Submitted by Mr. Manish Aggarwal Ms. Annu Lamba • H.O.D Electrical Engg

  2. Chapter–1.TransistorAudioPowerAmplifier • Atransistoramplifierwhichraisesthepowerlevelofthesignalsthathaveaudiofrequencyrangeisknownastransistoraudiopoweramplifier.

  3. Differencebetweenvoltageandpoweramplifier. VoltageamplifierPoweramplifier • Voltageamplifierisusedtoraisevoltagelevelofweaksignal. • Noneedofheatsinkinvoltageamplifier. • Distortioninoutputwillbeminimum. • Sizeoftransistorusedissmall. • RCcouplingiswidelyused. • Usedasfirststageofamplifier. • Outputimpedanceishigh. • Poweramplifierisusedtoraisepowerlevelofweaksignal. • Heatsinkareusedinpower • amplifier. • Distortioninoutputwillbeminimum. • Sizeofpowertransistorislarge. • Transformercouplingiswidelyused. • Usedaslaststageofamplifier. • Outputimpedanceislow.

  4. ImportanttermsofPowerAamplifier • Collectorefficiency:Theratioofacoutputpowertothedcinputpowerorzerosignalpowerofapoweramplifierisknownascollectorefficiency. • Distortion:Thechangeofoutputwaveshapefromthe • inputwaveshapeofanamplifierisknownasdistortion. • Powerdissipationcapability:Theabilityofapowertransistortodissipateheatdevelopedinitduringoperationis • knownasdissipationcapability.

  5. Classificationofpoweramplifiers ClassApoweramplifier ClassBpoweramplifier ClassCpoweramplifier ClassABpoweramplifier Ifthecollectorcurrentflowsatalltimeduringthefullcycleof signal,thepoweramplifieriscalledclassApoweramplifier. IfthecollectorcurrentflowsduringthepositivehalfcycleofinputsupplyiscalledclassBpoweramplifier. IfthecollectorcurrentflowsforlessthanhalfcycleofinputsupplyiscalledclassCpoweramplifier. IfthecollectorcurrentflowsformorethanhalfcycleiscalledclassABpoweramplifier.

  6. Heatsinkinpoweramplifiers • Poweramplifierhandlelargeamountofcurrent.Becauseofheavycurrent,transformersareheatedupduringoperation.Soexcessiveheatistobedissipated.Thedeviceusedforthispurposeiscalledheatsink. • Heatsinkisjustasheetofmetalwhichimprovetheheatdissipationofpowertransistor.

  7. Chapter– 2 Tuned VoltageAmplifier • TunedVoltageAmplifier • Tunedvoltageamplifierisusedtoamplifytheweaksignaltoaparticulartunedfreq.Itusesatunedparallelcircuiti.e.aparallelresonancecircuitisemployedasaloadinthecollector.Wheninputsignalofdifferentfrequenciesareusedorappliedatinputterminal,theamplifierselectssinglefrequencytowhichitistunedandamplifiesit.Itrejectsallotherfrequencyandhenceamplifiestheweaksignalselected.

  8. Advantagesoftunedvoltageamplifier • Smallerpowerloss:Tunedvoltageamplifieremploys • smallerpowerloss. • HighSelectivity:Tunedamplifierselectshighselectivity. • Smallercollectorsupplyvoltage:Itrequiressmall • Vcc.

  9. Applicationsoftunedamplifier • Duetohighselectivity,highgainandrequired • bandwidth. • EmployedinTVreceiver. • Radioreceiver. • Portablesystem.

  10. DoubleTunedVoltageamplifier • Toobtainhighselectivity,highgainandrequiredbandwidth,double-tunedvoltageamplifiersareused.Themaindisadvantageofsingletunedvoltageamplifieri.e.lowbandwidthandundesirableattenuationareovercomebyusingdoubletunedvoltageamplifier.

  11. ELECTRONICS - II • Submitted To:- Submitted by Mr. Manish Aggarwal Ms. Annu Lmba • H.O.D Electrical Engg

  12. Chapter– 3 FeedbackinAmplifiers • Feedback:Theprocessinwhichapartofoutputenergyisfeedingbacktoinputiscalledfeedback. • Typesoffeedback. • 1.+vefeedback • 2.-vefeedback • Whenfeedbackenergyisinphasewiththeinputsignalisknownas+vefeedback.Itisalsoknownasdirectorregenerativefeedback. • Whenfeedbackenergyisoutofphaseor180phaseshiftwiththeinputsignalisknownas-vefeedback.Itisalsoknownasindirectorreversefeedback.

  13. AdvantagesandDisadvantagesof–vefeedback • Advantages • Highlystabilizedgain • ReducedDistortion • ReducedNoise • IncreasedBandwidth • IncreasedInputimpedance • Reducedoutputimpedance • Disadvantages • When–vefeedbacksignalisused,gainreducedbyafactor • 1/1+AB

  14. EmitterFollowerAmplifier • Emitterfollowerisalsocalledcommoncollectoramplifierbecausecollectoriscommonbetweeninputandoutputofcircuit.Ascircuitinputresistanceishigh,therefore.Itavoidsloadingofpreviousstageofamplifier.

  15. ApplicationsofEmitterfollower • Itisusedasbufferamplifierinbetweentwo • stagesforimpedancematchingpurpose. • Itisusedforthepurposeofreductioninnoise • atthereceiverkit. • Itisusedasisolatorinelectroniccircuit.

  16. Chapter– 4SinusoidalOscillator • Oscillator:Oscillatorisanelectronicdevicewhichgeneratesoscillationsofdesiredfrequencyiscalledoscillator.ThesecangeneratesignaloffrequencyfromfewHztoMHz. • Essentialsofanoscillator • Anoscillatorcircuitmustcontain; • Frequencydeterminingnetwork • Properlybiasedamplifiertoboosttheoscillator • Feedbacknetwork.

  17. Differencebetweenoscillatorandalternator. OscillatorAlternator • Anoscillatorisannonrotatingdevicehaveverylittlewear&tear • Ithaslongerlifeandhighefficiency. • Inoperationanoscillatorisquitesilent. • Oscillatorsaresmallerinsizeandlowerincost. • Ithasbetterfrequencystability. • Theoperationofanoscillatorisveryeasyportable. • Analternatorisarotatingdevice. • Ithasshorterlifeandpoorefficiency. • Inoperationofanalternatorisnoisy. • Alternatorsarehigherincost. • Ithaspoorfrequencystability. • Theoperationofanalternatorisdifficultanddifficulttoport.

  18. Barkhausencriterionforoscillations Theoscillatorwillprovideundampedoscillationsatfrequencyforwhichloopgainisequaltounity. <AB=0or2n(pi)wherenisinteger Theoscillatorwillproduceundampedoscillationsatfrequencyforwhichloopgainisequaltounity. IAbI>=1

  19. Typesofsinusoidaloscillations 1.DampedOscillations: Iftheamplitudeofoscillationsdecreaseswithtimethenitisknownasdampedoscillations. 2.UndampedOscillations Iftheamplitudeofoscillationsdoesnotchangewithtimeitisknownasundampedoscillations.

  20. Chapter–5WaveShapingandSwitchingCircuits • Waveshapescircuitisusedtochangeshapeofwaveformtothedesiredshape.Theyareoftwotypes. • LinearWaveshaper:ThesewaveshapershavepositivecomponentssuchasR,L&C.Thebasicpropertyofcircuitisthat they don’t change the shape of waveform. Ex. are LPF, HPF,attenuator. • Non-LinearWaveshaper:ThecircuitconsistofR,L,Cdiodeandzenerdiode,.Thebasicpropertyofcircuitisthattheoutputwillnotbeofsameshape.Ex.are:clippercircuit,clampercircuitandcomparatorcircuit.

  21. ClipperandClampercircuit • Clippercircuit:Ithelpsinremovingeitherpositiveornegativepartsofwaveformsothatthevoltageleveliskeptbelowthethresholdlimit.Therearetwotypesofclippercircuits.Positiveclipperremovesthepositivepartofthewaveformandnegativeclipperremovesthenegativepart. • Clampercircuit:Thesecircuitsaddsdcleveltoacsignal.Itshiftseithertheentirewaveinpositivesideorinnegativeside.Twotypesofclampersarethere.Positiveclampershiftsthewaveformtowardspositivesideandnegativeclampershiftsthewaveformtowardsnegativeside.

  22. TransistorasaSwitch • Transistorcanbeemployedasanelectronicswitch.To understand it’s working, considered a npntransistor.Whentransistorisusedasaswitch,itisoperatorincutoffandsaturationregion. • Cutoffregion:-Whentheinputbasevoltageiszeroornegative,thetransistorissaidtobeintheOFFcondition.Inthiscondition,basecurrentIb=0andcollectorcurrentisequaltoICEO. • Saturationregion:-Whentheinputbasevoltageis • positive,thetransistorissaidtobeintheONcondition.

  23. Multivibratorand it’s applications • Anelectroniccircuitthatgeneratessquarewavesiscalledamultivibrators. • Applications • Itisusedtogeneratesquarewaveandpulse • generate. • Itisusedasfrequencydividers. • Itisusedasstandardfrequencysource. • Itcanbeusedasgenerationoftimedelays. • ItisusedinradarandTVcircuits. • Itisalsousedasmemoryelementsincomputer.

  24. Chapter– 6PowerSupplies • RegulatedPowerSupply • Adcpowersupplythatmaintainstheoutputvoltageconstantirrespectiveofthefluctuationsinacmainsorvariationsinloadisknownasaregulatedpowersupply.

  25. DistinctionbetweenCVTandStabilizer CVT Itsinputvoltageis170-270Vat50Hzandoutputvoltageis230V+2V. At1000V,insulationismorethan500megaohmsinCVT. Itsefficiencyismorethan85percent. ItisusedmostlywithPCs. CVThavemoreweight,largesizeandmorecost. MorelifeasnomaintenanceisrequiredinCVT. Itsinputvoltageliesbetween140-270Vandoutputvoltageliesbetween195-235V. Noisolationatall,Verylittleprotectionisprovided. Itsefficiencyis70-75percent. Itisusedinhouseappliancesuchasrefrigerator,TVetc. Stabilizerhavelowerweight,smallersizeandlesscost. Instabilizer,verylesslifeasmovingpartsaredeterioratequ Stabilizer

  26. SMPSSwitchedModePowerSupply • SMPSsupplyprovidesconstantdcvoltage.Itiswidelyusedincomputersystem,television,receivers,VCRetc.SMPSsuppliesaresmallerandlightinweightascomparedtootherregulatedpowersupplies.Thepowerdissipationisminimumascomparedofothersupplies.Thereforeefficiencyisquitehigh.

  27. AdvantagesandDisadvantages • Advantages • Switchingdeviceareelectronicswitchessuchastransistor,MOSFET,thereareONOFFdevices.Powerdissipationisminimum. • EfficiencyofSMPSishigher. • SMPScanevenoperateunderlowasvoltage. • Disadvantages • InSMPS,electromagneticinterferenceisproducedfromON/OFFofelectronicswitches. • SMPSpowersuppliesarecomplex. • Thecontrolcircuitisexpensiveandlessrelisble

  28. Chapter– 7OperationAmplifier • Operationalamplifierisdirect-coupledhighgainamplifier.Asshowninblockdiagram,itconsistsoffollowingstages: • Twostagedifferentialamplifier. • Leveltranslator. • Pushpullamplifier.

  29. IdealOperationalAmplifier • Idealoperationalamplifierhasfollowingcharacteristics: • Infiniteopenloopgain. • Infiniteinputimpedance. • Zerooutputresistance. • InfinitecommonmoderejectionRatio(CMRR). • Infinitebandwidth. • Infiniteslewratei.e.outputshouldrespondsimultaneouslytovariationininput. • Zerooffsetvoltage.8

  30. Applications SummingandSubtractorop–Amp Differentiatorandintegrator Analogtodigitalconverter Digitaltoanalogconverter Voltageclamper.

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