Class A And Class B Amplifiers Pdf

class a and class b amplifiers pdf

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In this new tutorial, we will present in detail another class of amplifiers known as Class B that have been developed as an answer to the low efficiency of the Class A.

Facebook Twitter. Since one part of the circuit pushes the signal high during one half-cycle and the other part pulls the signal low during the other half-cycle, the circuit is referred to as a push-pull circuit. Figure shows a diagram for push-pull operation. An ac input signal is applied to the push-pull circuit, with each half operating on alternate half-cycles, the load then receiving a signal for the full ac cycle.

Class-B Pushpull Amplifier Operation

The class of an amplifier is selected to meet the overall requirements. Different amplifier classes provide different characteristics, enabling the amplifier to perform in a particular way and also with a level of efficiency. The different amplifier classes provide different performance characteristics. These make the different types of amplifier class suitable for different situations. A tabular summary of their different characteristics is given below. A class A amplifier is biassed so that it conducts over the whole of the cycle of the waveform.

When the collector current flows only during the positive half cycle of the input signal, the power amplifier is known as class B power amplifier. The biasing of the transistor in class B operation is in such a way that at zero signal condition, there will be no collector current. The operating point is selected to be at collector cut off voltage. So, when the signal is applied, only the positive half cycle is amplified at the output. When the signal is applied, the circuit is forward biased for the positive half cycle of the input and hence the collector current flows. But during the negative half cycle of the input, the circuit is reverse biased and the collector current will be absent. Hence only the positive half cycle is amplified at the output.

Class-B Pushpull Amplifier Operation

In earlier days, before the invention of electronic amplifiers , the coupled carbon microphones are used as crude amplifiers in telephone repeaters. The first electronic device that practically amplifies was the Audion vacuum tube, invented by the Lee De Forest in the year The term amplifier and amplification are from Latin word amplificare to expand or enlarge. The vacuum tube is the only simplifying device for 40 years and dominated electronics up to When the first BJT was in the market it has created another revolution in the electronics and it is a first portable electronic device like transistor radio developed in the year


Class B: provides an output signal varying over one-half the input signal cycle, or for ° of signal. •. Bias at the zero level. Page 6. Amplifier Efficiency. 6.


The Classes and Classification of Amplifiers With Their Applications

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In electronics , power amplifier classes are letter symbols applied to different power amplifier types. The class gives a broad indication of an amplifier 's characteristics and performance. The classes are related to the time period that the active amplifier device is passing current, expressed as a fraction of the period of a signal waveform applied to the input. A class A amplifier is conducting through all the period of the signal; Class B only for one-half the input period, class C for much less than half the input period.

In this new tutorial, we will present in detail another class of amplifiers known as Class B that have been developed as an answer to the low efficiency of the Class A. In the first section, we will present what a Class B amplification consists of and an overview of its characteristics. We will see in a later section, however, that in order to work properly, two complementary transistors are needed in order to ensure the reproduction of the input signal, in what is commonly known as a push-pull configuration. Moreover, we will highlight an undesired distortion happening in Class B amplifiers and some possible solutions to limit it. At the last section of this tutorial, we will give a step by step method on how to calculate the theoretical maximum efficiency of Class B amplifiers.

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Namo G.

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A push pull amplifier is an amplifier which has an output stage that can drive a current in either direction through through the load.

Charles H.

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