(8.1.4)--Chapter 12 Power Amplifier模拟电子技术基础.ppt

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1、Chapter 12 Power AmplifierOutlineIntroduction-definitions Amplifier Types Class B Amplifier OperationClassAB Amplifier Circuits IntroductionSmall-signal approximation and models either are not applicable or must be used with care.Deliver the power to the load in efficient manner.Power dissipation is

2、 as low as possible.12.1 Introduction-definitions Amplifier Types Power amplifiers are classified according to the collector current waveform that results when an input signal is applied.Conducting angle.Classification of Power AmplifierCollector current waveforms for transistors operating in(a)clas

3、s A,(b)class BClassification of Power Amplifier class AB class C12.2 Class B Amplifier Operation A class B output stage.Complementary circuits.Push-pull operationMaximum power-conversion efficiency is 78.5%Transfer CharacteristicCrossover DistortionPower DissipationThe load powerMaximum load powerPo

4、wer DissipationTotal supply powerMaximum total supply powerPower DissipationPower-conversion efficiencyMaximum power-conversion efficiencyPower DissipationPower dissipationMaximum Power dissipation12.3 Class AB Amplifier Circuits A bias voltage VBB is applied between the bases of QN and QP,giving rise to a bias current IQ.Thus,for small vI,both transistors conduct and crossover distortion is almost completely eliminated.A Class AB Output Stage Utilizing Diodes for BiasingA Class AB Output Stage Utilizing A VBE Multiplier for Biasing