Over 10 years we help companies reach their financial and branding goals. Engitech is a values-driven technology agency dedicated.



411 University St, Seattle, USA


+1 -800-456-478-23


In this blog, we will learn about Power Amplifiers, their types, their classes, and the benefits and drawbacks of those classes, among other things. Power amplifiers are primarily used to boost the power level of an input signal. Power amplifiers are also known as large-signal amplifiers because, to produce a large amount of power at the output, the input signal voltage must be large as well. They are used in audio applications, radio communication equipment, and medical equipment (MRI) properties of a power amplifier the performance of a power amplifier is measured using parameters such as collector efficiency, power dissipation capability, and distortion. We will go over each of these properties one by one. Continue reading to find out more.

More Interested: L-Band Power Amplifier

Features of Power Amplifiers


Distortion is defined as a change in the shape of an amplifier’s output waveform from its input waveform. When the output wave shape differs from the input wave shape, the amplifier is said to be distorted. Power amplifiers handle larger signals than voltage amplifiers. As a result, distortion occurs immediately in these amplifiers. As a result, in this type of amplifier, we must pay close attention to this factor.

Collector Efficiency 

The collector efficiency, or efficiency of the collector of an amplifier, is defined as the ratio of a power amplifier’s AC output power to its DC input power or zero signal power. The percentage of DC power converted into AC power by the amplifier is indicated by collector efficiency. For example, if the source supplies 10W of DC power and the AC output power is 4W, the collector efficiency is 40%, implying that the higher the collector efficiency, the better the amplifier.

Power Dissipation Capability

Power dissipation capability refers to a power transistor’s ability to dissipate heat generated during operation. Power transistors in a power amplifier, as we know, carry a large current during operation. This causes the collector junction to heat up. The operating conditions of the transistor are influenced by the increase in temperature. As a result, the transistor used must be capable of dissipating this heat into the surrounding environment.

Types of Power Amplifiers

Power amplifiers are classified into three types based on the type of output device to which they are connected or the range of signals they amplify.

  • Power Amplifiers for Audio
  • Power Amplifiers for RF
  • Power Amplifiers for Direct Current
  • Audio Power Amplifiers

This type of power amplifier is used to boost the magnitude of a weaker audio signal. This category includes amplifiers used in speaker driving circuitries of televisions, mobile phones, and other electronic devices. An audio power amplifier’s output can range from a few milliwatts (as in headphone amplifiers) to thousands of watts (as in power amplifiers in Hi-Fi/Home theater systems).

More Interested:RF Signal Distribution

Radio Frequency Power Amplifiers

Wireless transmissions necessitate the transmission of modulated waves over long distances through the air. Signals are transmitted via antennas, and the range of transmission is determined by the magnitude of power fed to the antenna.

Antennas require input signals with thousands of kilowatts of power for wireless transmissions such as FM broadcasting. Radio Frequency Power Amplifiers are used in this case to boost the magnitude of power of modulated waves to a level sufficient for reaching the required transmission distance.

DC Power Amplifiers

PWM (Pulse Width Modulated) signals are amplified using DC power amplifiers. They are employed in electronic control systems that require high-power signals to drive motors or actuators. They take input from microcontroller systems, amplify it, and feed it to DC motors or Actuators.

However, it is classified into four classes based on its mode of operation, i.e. the portion of the input cycle during which the collector current flows through the circuit:

Class A

The output current flows for the entire input cycle in this class of power amplifiers. It only operates on the linear region of the load because the operating point is chosen in such a way that the output is exactly the same as the input.

In this case, the maximum possible efficiency is 50%. When we simply want a distortion-free output, we use this class.

The transistor remains in forward bias mode throughout the input signal. In this class, the transistor is always in active mode, resulting in excessive heat generation and a reduction in efficiency.

When an input voltage is applied to the base terminal of a transistor in CE mode, the base current varies; this variation in IB causes a similar variation in collector current, and the output is taken across the load.

The applied input causes the collector current to fluctuate from maximum to minimum, causing the Q point to move along the load line.


It offers distortion-free amplification.

Even a weak signal can be amplified.


The efficiency of collectors is low.

The output power is insufficient.

Heat sinks are required due to excessive heat generation, which makes them expensive and bulky.

Class B

The transistor in this type is biased so that current flows only during the positive half of the input cycle. Two complementary transistors are used in this circuit to receive an input signal of equal magnitude but opposite in phase.

When the input is applied to the transformer’s center-tapped secondary, it generates two identical signals of opposite phase, which drive the two transistors.

When V1 becomes positive, V2 becomes negative, causing Q1 to conduct while Q2 remains inactive. The positive half of the input signal is produced as the collector current in Q1 increases.

When V1 becomes negative and V2 becomes positive, Q2 automatically begins conducting and Q1 becomes inactive. As the collector current in Q2 increases, another half of the voltage signal is generated. As a result of the two transistors’ operation, the output is a complete sine wave.

When no input signal is present, both transistors turn off and no current is drawn. This prevents the transistor from working inefficiently, lowering the device’s chances of overheating.

Working with class B causes crossover distortion because, as we know, the transistor requires 0.7v to begin conduction, so the transistor will not be active below 0.7v. This means that the wave portion will not be reproduced at the output, resulting in distorted output. This type of zero-crossing distortion is known as crossover distortion.


It is more efficient than the class A power amplifier.

Because of the push-pull mechanism, even harmonics are avoided.


It causes crossover distortion.

The cost and size of coupling transformers are increased.

Class AB

It is a hybrid of class A and class B power amplifiers. This class was created primarily to eliminate the crossover distortion that occurs in class B.

The angle of conduction, in this case, ranges from 180 to 360 degrees. The transistor biasing is done in this case in such a way that the operating point Q is close to the cut-off voltage.

The collector current flows for more than half of the input cycle, implying that it operates during the positive half of the input cycle. The input circuit becomes forward biased for a small portion of the negative half cycle.

However, as the transistor becomes reverse biased, conduction ceases for a brief period of the negative half cycle.Its efficiency ranges from 50 to 60 percent.


It removes crossover distortion.

It is less expensive than class B.


Efficacy is low.

There is a possibility that DC components will be present at the output.

Class C

This type of power amplifier is intended to have the highest efficiency of around 80%. In the case of resonant frequency tuned circuits, these are biased in such a way that it operates for less than 180 of the input signal but provides the full output signal. The collector current flows for less than half of the time that the input signal is active. For more than half of the input cycle, the transistor remains idle and does not conduct.


The power amplifier increases efficiency, and the system is physically small.


  • It is not suitable for audio applications.
  • A power amplifier’s linearity is low.
  • Popular Applications of Power Amplifiers

High power amplifiers are used in the transmission of cellular or FM broadcasting signals to users, in the control of most industrial actuator systems such as servos and DC motors, and in almost all consumer electronic devices such as microwave ovens, televisions, mobile phones, headphone drivers, home theater systems, and also in  theatrical and concert reinforcement systems.

Leave a comment

Your email address will not be published.