This article describes what a power amplifier is and its requirements, different types and categories of power amplifiers, and several applications of power amplifiers.
At the end of the article, we will show you 250 design drawings of power amplifiers for your reference. If you like, please bookmark this article and share it with more people.
Power amplifier definition
A power amplifier is an electronic amplifier designed to increase the power amplitude of a given input signal. The power of the input signal is increased to a level sufficient to drive the load of output devices such as speakers, headphones, and RF transmitters.
Unlike voltage/current amplifiers, power amplifiers are designed to directly drive the load and serve as the final module in the amplification chain. The input signal of the power amplifier must be higher than a certain threshold.
Therefore, instead of passing the original audio/RF signal directly to the power amplifier, it is pre-amplified with a current/voltage amplifier and sent to the power amplifier as input after making the necessary modifications.
You can observe the block diagram of the audio amplifier and the usage of the power amplifier below.
In this case, the microphone is used as the input source. The signal strength from the microphone is not strong enough for the power amplifier.
First pre-amplify it, and then slightly increase its voltage and current. Then, the signal passes through the tone and volume control circuit to make aesthetic adjustments to the audio waveform. Finally, the signal passes through the power amplifier, and the power amplifier’s output is fed to the speaker.
Types of power amplifier
According to the type of output device connected, the power amplifier is divided into the following three types:
Audio power amplifier
RF power amplifier
DC power amplifier
Audio power amplifier
This type of power amplifier is used to increase the power level of weaker audio signals. Amplifiers used in speaker drive circuits of TVs, mobile phones, etc. fall into this category.
The output range of audio power amplifiers ranges from a few milliwatts (such as headphone amplifiers) to several kilowatts (such as power amplifiers in Hi-Fi/home theater systems).
Wireless transmission requires modulated waves to be sent over long distances through the air. The antenna is used to transmit the signal, and the transmission range depends on the power of the signal fed to the antenna.
For wireless transmissions such as FM broadcasting, the antenna needs to input signals with a power of several thousand kilowatts. Here, the RF power amplifier is used to increase the power amplitude of the modulated wave to a level sufficient to achieve the required transmission distance.
DC power amplifier
The DC power amplifier is used to amplify the power of the PWM (Pulse Width Modulation) signal. They are used in electronic control systems that require high-power signals to drive motors or actuators.
They take input from the microcontroller system, increase its power, and feed the amplified signal to the DC motor or actuator.
PA class
There are many ways to design power amplifier circuits. The operation and output characteristics of each circuit configuration are different from each other. To distinguish the characteristics and performance of different PA circuits are used, in which letter symbols are assigned to identify operation methods.
They are roughly divided into two categories. Power amplifiers designed to amplify analog signals belong to Class A, B, AB, or C.
Power amplifiers designed to amplify pulse width modulated (PWM) digital signals are located under D, E, F, etc.
The most commonly used power amplifiers are those used in audio amplifier circuits. They belong to Class A, B, AB, or C. So let us understand them in detail.
Class A power amplifier
The analog waveform is composed of positive high points and negative low points. In this type of amplifier, the entire input waveform is used in the amplification process. A single transistor is used to amplify the positive and negative half of the waveform.
This makes their design simple and makes Class A amplifiers the most commonly used type of PA. Although such PAs have been replaced by better designs, they are still very popular among hobbyists.
In this type of amplifier, even if there is no input signal, the active components (electronic components used for amplification, in this case, transistors) are always in use.
In the case of a normal configuration, this will generate a lot of heat and reduce the efficiency of the Class A amplifier to 25%. In the case of a transformer-coupled configuration, the efficiency will be reduced to 50%.
The conduction angle of the Class A amplifier (the part of the waveform used for amplification in 360 degrees) is 360°. Therefore, the signal distortion level is very small, which can provide better high-frequency performance.
Class B amplifier
Class B amplifiers are designed to reduce the efficiency and heating problems that exist in Class A amplifiers. This type of amplifier uses two complementary transistors instead of a single transistor to amplify the entire waveform.
One transistor amplifies the positive half of the waveform, and the other amplifies the negative half of the waveform. Each active device conducts half of the waveform (180°), and two of them will amplify the entire signal when they are turned on.
Due to the two-transistor design, the efficiency of the Class B amplifier has been greatly improved compared with the Class A amplifier. They can reach about 75% of the theoretical efficiency.
This type of power amplifier is used in battery-powered equipment, such as FM radios and transistor radios. Since the two halves of the waveform overlap, there is little distortion in the intersection area. To reduce this signal distortion, a class AB amplifier is designed.
Class AB amplifier
Class AB amplifier is a combination of Class A and Class B amplifiers. This type of amplifier is designed to reduce the inefficiency of Class A amplifiers and the signal distortion in the crossover area of Class B amplifiers.
It can maintain high-frequency response like a class A amplifier and maintain good efficiency like a class B amplifier. The combination of diode and resistor is used to provide a very small bias voltage, thereby reducing waveform distortion near the crossover area. Therefore, the efficiency drops slightly (60%).
Class C amplifier
Class C amplifier design can achieve higher efficiency and reduce linearity/conduction angle (below 90°).
To improve efficiency, the quality of amplification is sacrificed. A smaller conduction angle means greater distortion, so this type of amplifier is not suitable for audio amplification. They are used for the amplification of high-frequency oscillators and radio frequency signals.
Class C amplifiers usually contain a tuned load that filters and amplifies the input signal at a specific frequency, while waveforms at other frequencies are suppressed.
In this type of PA, the active element only turns on when the input voltage is higher than a certain threshold, thereby reducing power consumption and improving efficiency.
Other PAs
Power D amplifiers, E, F, G, etc. are used to amplify PWM modulated digital signals. They belong to the category of switching power amplifiers, which can continuously turn the output on or off without any other level in between. Due to this simplicity, PAs belonging to the above categories can achieve theoretical efficiencies as high as (90-100)%.
Applications
The following are the applications of PAs in different fields.
Consumer electronics products
Audio power amplifiers are used in almost all consumer electronic devices, from microwave ovens, headphone drivers, TVs, mobile phones, and home theater systems to theater and concert enhancement systems.
Industry
Switching power amplifiers are used to control most industrial actuator systems, such as servos and DC motors.
Wireless communication
High-power amplifiers are very important for transmitting cellular or FM broadcast signals to users. Thanks to the PA higher power levels are possible, thereby increasing the data transmission rate and availability. They are also used in satellite communication equipment.
Below are the more than 250 PA design circuit diagrams for your reference. Besides this, the PA supplier C&T RF Antennas Inc also provides the existing RF PAs and RF PA design services.
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