Efficiency of class a amplifier

The Web This site. The Class A Common Emitter Amplifier described in Amplifier Module 1 , Module 2 and Module 3 has some excellent properties that make it useful for many amplification tasks, however its use as a power amplifier is limited by its poor efficiency. Although Class A may be used for power output stages usually low to medium power , it is less used for higher power output stages, as more efficient classes of amplifier such as Classes B, AB or even classes D, E, F, G and H are available. The classes A, B, AB and C refer to the way the amplifiers are biased, although class C is mainly used in oscillator circuits.

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Content:

• Select any 5 courses for free
• Power amplifier classes
• Class A Power Amplifiers
• Series fed Class-A Amplifier Operation
• Maximum Collector Efficiency of Class A Amplifier
• Class A Power Amplifier – Tutorial with Design and Theory
• Transformer Coupled Class A Power Amplifier
• Series fed Class-A Amplifier Operation
• Analyse A Meter
• Amplifier Classes: A, B, AB, C, D, etc

WATCH RELATED VIDEO: 33. Class A Amplifier Efficiency

Select any 5 courses for free

Class A power amplifier is a type of power amplifier where the output transistor is ON full time and the output current flows for the entire cycle of the input wave form. Class A power amplifier is the simplest of all power amplifier configurations.

They have high fidelity and are totally immune to crossover distortion. Even though the class A power amplifier have a handful of good feature, they are not the prime choice because of their poor efficiency. Since the active elements transistors are forward biased full time, some current will flow through them even though there is no input signal and this is the main reason for the inefficiency.

Output characteristics of a Class A power amplifier is shown in the figure below. From the above figure its is clear that the Q-point is placed exactly at the center of the DC load line and the transistor conducts for every point in the input waveform.

Majority of the power wasted is lost as heat on the active elements transistor. As a result, even a moderately powered Class A power amplifier require a large power supply and a large heatsink. The circuit diagram of a two stage single ended Class A power amplifier is shown above.

R1 and R2 are the biasing resistors. They form a voltage divider network which supplies the base of the transistor with a voltage 0. This is the reason behind the transistor being ON irrespective of the input signal amplitude. Capacitor Cin is the input decoupling capacitor which removes the DC components present in the input signal.

If Cin is not there, and there are DC components in the input signal, these DC components will be directly coupled to the base of the transistor and will surely alter the biasing conditions. Rc is the collector resistor and Re is the emitter resistance. Their value is so selected that the collector current is in the desired level and the operating point is placed at the center of the load line under zero signal condition. Placing operating point as close as possible to the center of load line is very essential for the distortion free operation of the amplifier.

Cc is the coupling capacitor which connects the two stages together. Its function is to block passage of DC components from first stage to the second stage. Ce is the emitter by-pass capacitor whose function is to by-pass the AC components in the emitter current while amplifier is operating. If Ce is not there, the AC components will drop across the emitter resistor resulting in reduced gain degenerative feedback.

The most simple explanation is that, the additional voltage drop across Re will get added to the base-emitter voltage and this means additional forward voltage is required to forward bias the transistor. Cout is the output coupling capacitor which couples the output to the load loud speaker.

Cout blocks the DC components of the second stage from entering the load loud speaker. The Coupling capacitor Cout, Cin and Cc all degrades the low frequency response of the amplifier. This is because these capacitors form high pass filters in conjunction with the input impedance of succeeding stages resulting in the attenuation of low frequency components. Input and output waveforms of a two stage RC couple amplifier is shown in the figure below.

An amplifier where the load is coupled to the output using a transformer is called a transformer coupled amplifier. Using transformer coupling the efficiency of the amplifier can be improved to a great extend.

The coupling transformer provides good impedance matching between the output and load and it is the main reason behind the improved efficiency. Impedance matching means making the output impedance of the amplifier equal to the input impedance of the load and this is an important criteria for the transfer of maximum power. Circuit diagram of typical single stage Class A amplifier is shown in the circuit diagram below. Impedance matching can be attained by selecting the number of turns of the primary so that its net impedance is equal to the transistors output impedance and selecting the number of turns of the secondary so that its net impedance is equal to the loudspeakers input impedance.

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Power amplifier classes

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Class A Power Amplifiers

The class A power amplifier as discussed in the previous chapter, is the circuit in which the output current flows for the entire cycle of the AC input supply. We also have learnt about the disadvantages it has such as low output power and efficiency. In order to minimize those effects, the transformer coupled class A power amplifier has been introduced. The construction of class A power amplifier can be understood with the help of below figure. This is similar to the normal amplifier circuit but connected with a transformer in the collector load. Here R 1 and R 2 provide potential divider arrangement. The resistor Re provides stabilization, C e is the bypass capacitor and R e to prevent a. The transformer used here is a step-down transformer. The high impedance primary of the transformer is connected to the high impedance collector circuit.

Series fed Class-A Amplifier Operation

In this work, a new approach of analysis is developed by suggesting some modified drain current waveforms and comparing the resulting theoretical performance characteristics such as drain efficiency and output RF power with the conventional type. Besides, a simple analytic technique for extracting the device harmonic load impedances for the desired band is also presented. Based on the theoretical analysis, a 6 W power amplifier circuit was designed and simulated to operate within the frequency band — MHz. RF power amplifiers are key elements in modern mobile radio systems.

Maximum Collector Efficiency of Class A Amplifier

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Class A Power Amplifier – Tutorial with Design and Theory

Facebook Twitter. Series fed Class-A Amplifier: The simple fixed-bias circuit connection shown in the figure below can be used to discuss the main features of a series fed class A amplifier. The only differences between this circuit and the small-signal version considered previously are that the signals handled by the large-signal circuit are in the range of volts and the transistor used is a power transistor that is capable of operating in the range of a few to tens of watts. As will be shown in this section, this circuit is not the best to use as a large-signal amplifier because of its poor power efficiency. The beta of a power transistor is generally less than , the overall amplifier circuit using power transistors that are capable of handling large power or current while not providing much voltage gain.

Transformer Coupled Class A Power Amplifier

Class A power amplifier is a type of power amplifier where the output transistor is ON full time and the output current flows for the entire cycle of the input wave form. Class A power amplifier is the simplest of all power amplifier configurations. They have high fidelity and are totally immune to crossover distortion.

Series fed Class-A Amplifier Operation

Common emitter voltage amplifiers are the most commonly used type of amplifier as they have a large voltage gain. They are designed to produce a large output voltage swing from a relatively small input signal voltage of only a few millivolt's and are used mainly as "Small Signal Amplifiers" as we saw in the previous tutorials. However, sometimes an amplifier is required to drive large resistive loads such as a loudspeaker and for these types of applications where high switching currents are needed Power Amplifiers are required. The main function of the Power amplifier, which are also known as a "Large Signal Amplifier" is to deliver power, which is the product of voltage and current to the load. Basically a power amplifier is also a voltage amplifier the difference being that the load resistance connected to the output is relatively low, for example a loudspeaker of 4 or 8Os resulting in high currents flowing through the Collector of the transistor.

Analyse A Meter

This paper presents a novel amplifier that satisfies both low distortion and high efficiency for high-frequency wireless ultrasound systems with limited battery life and size. While increasing the amplifier efficiency helps to address the problems for wireless ultrasound systems, it can cause signal distortion owing to harmonic components. Therefore, a new type of class F amplifier is designed to achieve high efficiency and low distortion. In the amplifier, the resonant circuit at each stage controls the harmonic components to reduce distortion and improve efficiency. Transformers with a large shunt resistor are also helpful to reduce the remaining noise in the input signal. The proposed class F amplifier is tested using simulations, and the voltage and current waveforms are analyzed to achieve correct operation with adequate efficiency and distortion. The measured performance of the class F amplifier has a gain of

Amplifier Classes: A, B, AB, C, D, etc

The Application Activity in this is a public address system. Recall that the complete system includes the preamplifier, a power amplifier, and a dc power supply. You will focus on the power amplifier in this section and complete the total system by combining the three component parts. Power amplifiers are large-signal amplifiers.