Efficiency calculation of class b amplifier
Facebook Twitter. Class-B Pushpull Amplifier Operation: Class - B operation is provided when the dc bias leaves the transistor biased just off, the transistor turning on when the ac signal is applied. This is essentially no bias, and the transistor conducts current for only one-half of the signal cycle. To obtain output for the full cycle of signal, it is necessary to use two transistors and have each conduct on opposite half-cycles, the combined operation providing a full cycle of output signal. 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.
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Content:
- How to calculate RF power amplifier efficiency
- Class D Audio Amplifiers: What, Why, and How
- Maximum Efficiency for Class B Power Amplifier
- Push-Pull Amplifiers Circuit Diagram, Working and Applications
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- Novel Wide Band High-Efficiency Active Harmonic Injection Power Amplifier Concept
How to calculate RF power amplifier efficiency
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. As the negative half cycle is completely absent, the signal distortion will be high. Also, when the applied signal increases, the power dissipation will be more.
But when compared to class A power amplifier, the output efficiency is increased. Well, in order to minimize the disadvantages and achieve low distortion, high efficiency and high output power, the push-pull configuration is used in this class B amplifier. Though the efficiency of class B power amplifier is higher than class A, as only one half cycle of the input is used, the distortion is high. Also, the input power is not completely utilized. In order to compensate these problems, the push-pull configuration is introduced in class B amplifier.
The circuit of a push-pull class B power amplifier consists of two identical transistors T 1 and T 2 whose bases are connected to the secondary of the center-tapped input transformer T r1. The emitters are shorted and the collectors are given the V CC supply through the primary of the output transformer T r2. The circuit arrangement of class B push-pull amplifier, is same as that of class A push-pull amplifier except that the transistors are biased at cut off, instead of using the biasing resistors.
The figure below gives the detailing of the construction of a push-pull class B power amplifier. The circuit of class B push-pull amplifier shown in the above figure clears that both the transformers are center-tapped. When no signal is applied at the input, the transistors T 1 and T 2 are in cut off condition and hence no collector currents flow. As no current is drawn from V CC , no power is wasted. When input signal is given, it is applied to the input transformer T r1 which splits the signal into two signals that are o out of phase with each other.
These two signals are given to the two identical transistors T 1 and T 2. For the positive half cycle, the base of the transistor T 1 becomes positive and collector current flows. At the same time, the transistor T 2 has negative half cycle, which throws the transistor T 2 into cutoff condition and hence no collector current flows.
The waveform is produced as shown in the following figure. For the next half cycle, the transistor T 1 gets into cut off condition and the transistor T 2 gets into conduction, to contribute the output. Hence for both the cycles, each transistor conducts alternately. The output transformer T r3 serves to join the two currents producing an almost undistorted output waveform. Hence the class B push-pull amplifier improves the efficiency than the class A push-pull amplifier. The push pull amplifier which was just discussed improves efficiency but the usage of center-tapped transformers makes the circuit bulky, heavy and costly.
To make the circuit simple and to improve the efficiency, the transistors used can be complemented, as shown in the following circuit diagram. When the input signal is applied, during the positive half cycle of the input signal, the NPN transistor conducts and the PNP transistor cuts off.
In this way, the NPN transistor amplifies during positive half cycle of the input, while PNP transistor amplifies during negative half cycle of the input. As the transistors are both complement to each other, yet act symmetrically while being connected in push pull configuration of class B, this circuit is termed as Complementary symmetry push pull class B amplifier.
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Class D Audio Amplifiers: What, Why, and How
Class B Amplifier — The inefficiency of Class-A amplifiers is largely due to the transistor bias conditions. In a Class-B amplifier, the transistors are biased to cutoff, so that there is no transistor power dissipation when there is no input signal. The output stage of a Class-B transformer-coupled amplifier is shown in Fig. Note that the supply is connected to the center-tap of the transformer primary, and that Q 2 and Q 3 have grounded emitters. The transistor bases are grounded via resistors R 1 and R 2 , so that both are biased off. The input signals applied to the transistor bases consist of two separate sine waves which are identical, except that they are in antiphase.
Maximum Efficiency for Class B Power Amplifier
This is a Most important question of gk exam. Buy Now! Managed Services By: www. Author: mympsc. What is the power gain? Online GK. Which of the push-pull amplifiers is presently the most popular form of the class B power amplifier?
Push-Pull Amplifiers Circuit Diagram, Working and Applications
Sign in Sign up. Thank you for your participation! Document related concepts. The Q-point is set near the middle of the load line. The Q-point is set at the cutoff point.
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Hello friends, I hope you all are doing great. Such amplifier which when biased at cutoff so it functions one eighty degrees in the linear region of input cycle and degree cutoff this amplifier known as class B amplifier. While the amplifier operates more than one-eighty degrees of input cycle called class AB amplifier. The main benefit of class B or class AB amplifier than class A amplifiers is that these are much efficient than class since from these amplifiers we can get more output power from the. With the advantage, the disadvantage of these two amplifiers is that it is difficult to implement their circuit to get linear regeneration of the input signal.
Novel Wide Band High-Efficiency Active Harmonic Injection Power Amplifier Concept
The Web This site. In amplifiers using class B bias, illustrated in Fig. This dramatically increases efficiency, compared with class A. The downside for this increased efficiency is that the transistor only amplifies half the waveform, therefore producing severe distortion. However, if the other half of the waveform can be obtained in some other way without too much distortion, then class B amplifiers can be used to drive most types of output device. The aim is to obtain a good power gain with as much of the energy consumed from the power supply going into the load as possible. This should be as consistent with reasonable linearity lack of distortion , as possible. Power output stages do however produce more distortion than do voltage or current amplifiers.
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We have already seen in our previous article about class B power amplifier that a push-pull circuit uses two transistors working in class B operation. For class B operation, the Q — point is located at cut-off on both d. For maximum signal operation, the two transistors in class B amplifier are alternately driven from cut-off to saturation. This is shown in fig.
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Questions Courses. Calculate the efficiency of a transformer-coupled Class A amplifier for a supply of 12 Volts and an. Show your calculations. With the help of sketches, explain the operation of a Class B amplifier.
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