What is a Power Amplifier?

The power amplifier is an electronic amplifier designed to maximize the signal strength of a given input. The input signal strength is enhanced to a high enough level to drive output devices such as speakers, headphones, RF (Radio frequency) transmitters, etc. Unlike voltage / current amplifiers, the power amplifier is designed to drive core loads directly and is used as a storage block in the amplifier series.

How does a power amplifier work?

The amplifier picks up the input signal from a source, such as a laptop, turntable, or CD player, and creates a large copy of the original signal before sending it to the speakers.

It gets the power to do this from the main power supply, which is sent directly to the the pre-amplfier. It is converted from the current switch to the direct, flowing only in one direction, and sent to the transistor.

The transistor acts as a valve and determines the amount of current flowing in the circuit at any time, supports that decision in input signal size from the source. That means a larger signal will cause the transistor to allow more current flow, which in turn will create greater magnification.

Types of power amplifier

There are many types of power amplifiers such as:

Audio power amplifier

This form of the power amplifier is used for growing the magnitude of the power of a weaker audio signal. The amplifiers are utilized in speaker driving circuitry of televisions, mobile phones, etc. The input signal for the amplifier, as well as the signal from the electric guitar, can also measure only a hundred microwaves, the output may be some watts for small consumer equipment, as well as clocks, tens or hundreds of watts for home stereo system, a few thousand watts in a nightclub sound system (speaker xls1002, stereo) or tens of thousands of watts for music shows. At the same time as pre-amplifiers are available in independent units, usually targeted at the hello-fi audiophile market project (marketplace) for audio lovers and sound system technicians, consumers, speakers, and digital clocks, boomboxes, stereo, televisions, etc, have relatively small amplifiers that can be integrated into the product.

Different audio power amplifier working stages are shown in the block diagram.
Audio power amplifier

The output of an audio power amplifier stages from some milliwatts (like in headphone amplifiers, speakers, subwoofers) to thousands of watts (like power amplifiers in hi-fi/home stereo systems).

There are various uses of audio amplifiers or speakers. Some of these are listed as follows:

  • In sound/stereo systems.
  • In various musical-related instruments (like speakers, sound system, guitar, all audio system type components).
  • In radio broadcasts.
  • Long-distance signal transmission.
  • To transmit wireless signals, stereo, sound application components are required.

DC power amplifiers

The Direct coupled amplifier is one in which multiple stages are cascaded to form a single amplifier, the coupling in done in such a way that only amplified DC part of the output of one stage is given as the input to the next stage. The direct couple amplifier is not specifically named as a direct current amplifier as it can be operated with both the AC and the DC supply.

Classes of power amplifier

There are many ways to design a power amplifier circuit. The performance and output characteristics of each circuit configuration differ from each other.

Characteristics and behavior of different circuits of power amplifiers can be done by the power training where character symbols are assigned to select the operating mode.

They are broadly divided into two categories. Amplifiers designed to amplify analog signals that fall under category A, B, AB, or C. Power amplifiers designed to amplify digital pulse width modulated (PWM) signals under D, E, F, and more.

The most widely used power amplifiers are those used in audio amp and come under training A, B, AB, or C. So, let's take a closer look:

Class A power amplifier

The class A amplifier condusct current for both positive and negative half of a waveform (360°). It gives a better high frequency, stability loop reaction and is easy to construct. Apart from these advantages and the top line of the path, there are many limitations. Due to its continuous nature, the class A amplifier introduces a higher power loss. Also, because of the high line, the class amplifier offers unwanted distortion and noise. Energy delivery and bias production require careful choice of coponents to keep away from unwanted noise and minimize distortion.

Because of the high power loss within the class, an amplifier emits heat and calls for a high-temperature immersion. The performance may be very low for the class A amplifiers. In theory, the performance varies among 25 and 30% whilst used with popular configurations. Performance may be improved by the use of inductively well-matched configurations, but efficiency in any such situation is not more than 45-50%, so it is suitable for low signal or low power booster purposes.

The Class A amplifier is a high-performance amplifier with a high line. In the case of a Class A amplifier, the driving angle is 360 degrees. As mentioned above, a 360-degree conduction angle means that the amplifier device stays active all the time and uses a complete input signal.
Class A power amplifier

Class B power amplifier

Class B amplifiers are designed to reduce the efficiency and temperature problems that exist within the class A. One transistor increases the positive half waveform, and the other increases the negative half waveform. Thus, each active device forms one (180°) waveform and two-channel of them, when combined, amplify the entire signal.

The Class B amplifier is slightly different from the Class A. It is designed using two active devices that run half a real cycle, i.e. 180 degrees of a cycle. Two devices provide an integrated current drive.
Class B power amplifier

Class AB power amplifier

Class AB amplifiers are a combination of class A and class B amplifiers. This class of amplifiers is designed to reduce the problem of efficiency of class A amplifiers and signal distortion in crossover of class B amplifiers.

Other power amplifier classes

Power amplifier class-D, class-E, class-F, class-G, etc. are used to amplify modified PWM signals. They fall under the amp switch feature and open or close output at all times without any other levels in between.

Applications of a power amplifier

Below are the uses of energy boosters in various fields:

  • Consumer electronics: audio amplifiers are used in almost every consumer electronics item, from microwave ovens, drivers for headphones, speakers, televisions, cell phones, and home stereo systems to concert and concert booster programs.
  • Industry: switch-type amplifiers are used to control most industrial actuator systems such as servos and dc motors.
  • Wireless communications: high power amplifiers are essential for transmitting mobile or FM broadcast signals to users. High-end levels of power are possible due to power amplifiers that increase data transfer and usability. They are also used in satellite communications.

Common Mistakes

Students may be confused and make some mistake in:

  • Not calculating the error in the amplifier gain correctly.
  • Not considering the bandwidth limit of the amplifier.
  • Adding noise in the error amplifier input.

Context and Applications

In each of the expert exams for undergraduate and graduate publications, this topic is huge and is mainly used for:

  • Bachelor of technology in the electrical and electronic department
  • Bachelor of science in physics
  • Master of science in physics
  • Current amplifier
  • Voltage amplifier
  • Transconductance amplifier
  • Operational amplifier
  • Marantz amplifier

Practice Problems

Question 1- The maximum collector efficiency of class B operation___________

  1. 78.50%
  2. 56.90%
  3. 79.56%
  4. 50.78%

Correct option- (a)

Explanation- The maximum collector efficiency of class B operation is 78.50%. Since the active device is turned off part of the input cycle, the active device consumes less energy and that is why efficiency is improved.

Question 2- The maximum collector efficiency of class A operation___________

  1. 78.50%
  2. 50.00%
  3. 25.56%
  4. 25.78%

Correct option- (b)

Explanation-  The maximum collector efficiency of class A operation is 50.00% with capacitive coupling and inductive loads.

Question 3- The maximum collector efficiency of class C operation___________

  1. 90.50%
  2. 56.90%
  3. 90.56%
  4. 90.00%

Correct option- (d)

Explanation-  The maximum collector efficiency of class C operation is 90.00%. This type of amplifier is not used in audio amplifiers due to a large amount of distortion.

Question 4- The Class A power amplifier uses ___________.

  1. one transistor
  2. two transistor
  3. three transistor
  4. four transistor

Correct option- (b)

Explanation- The Class A power amplifier uses two transistor.

Question 5- Power amplifier result in low efficiency is due to ________.

  1. low forward bias
  2. more battery consumption
  3. low battery consumption
  4. none of these

Correct option- (b)

Explanation- The low-efficiency result of the power amplifier is more battery consumption.

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