Power Amplifiers: Class A, B, AB, and D Quiz Quiz

Explore the differences and characteristics of power amplifier classes A, B, AB, and D with this focused quiz covering operation, efficiency, linearity, and common applications. Designed for learners seeking to strengthen their understanding of analog and digital amplifier types in electronic circuits.

1. Class A Amplifier Operation

   Which statement best describes the operating point of a Class A power amplifier in a typical circuit?

   1. The output device conducts for only 90 degrees of the input waveform.
   2. The biasing is set so that conduction occurs only during positive input peaks.
   3. The transistor conducts for the complete 360 degrees of the input signal cycle.
   4. The amplifier operates without any quiescent current present at all times.

   Explanation: A Class A amplifier is characterized by its active device (such as a transistor) conducting for the entire 360 degrees of the input signal cycle, ensuring high linearity. This contrasts with conduction for only 90 degrees (option B) or only during positive peaks (option D), which matches Class C amplifiers. Option C is incorrect because Class A always operates with quiescent current, not without it.

2. Class B Amplifier Efficiency

   In audio amplification, what is the main advantage of a Class B power amplifier over a Class A design?

   1. It produces less crossover distortion at the output stage.
   2. It uses pulse-width modulation for signal amplification.
   3. It offers significantly higher power efficiency by conducting for half of the input cycle.
   4. It maintains the highest possible fidelity for all audio signals.

   Explanation: A Class B amplifier is known for better efficiency compared to Class A, as each device conducts for only 180 degrees of the signal. This efficiency comes at the cost of crossover distortion (contrary to option A), and lower fidelity (contradicting option C). Option D describes Class D operation, not Class B.

3. Crossover Distortion in Amplifiers

   When using a push-pull Class B amplifier to amplify a sine wave, which issue commonly appears near the zero-crossing point of the waveform?

   1. High-frequency oscillation increases signal power.
   2. Total harmonic distortion drops to zero.
   3. Crossover distortion is introduced due to non-linear switching.
   4. Thermal runaway occurs rapidly.

   Explanation: Crossover distortion happens in Class B amplifiers near the zero-crossing because each device turns on and off at this point, causing non-linearity. Thermal runaway (option A) is not primarily associated with this topology. Option C refers to unwanted oscillations, which are not inherent to Class B. Option D is incorrect, since distortion actually increases at the crossover point.

4. Class D Amplifiers and Signal Processing

   Which technique do Class D amplifiers mainly use to achieve high efficiency and reduced heat generation when driving speakers?

   1. Continuous conduction mode keeps output transistors always on.
   2. Direct analog amplification of input audio signals.
   3. Pulse-width modulation (PWM) switches output devices rapidly.
   4. Thermal feedback circuitry to manage device temperature.

   Explanation: Class D amplifiers utilize pulse-width modulation (PWM) to convert the analog input into switching signals, greatly improving efficiency and minimizing heat. Continuous conduction (option B) and direct analog amplification (option C) describe Class A or AB operations. Option D mentions thermal feedback, which manages temperature but is not the fundamental method behind Class D efficiency.

5. Application Suitability of Amplifier Classes

   For which of the following scenarios is a Class AB amplifier most commonly selected due to its balance between efficiency and linearity?

   1. Providing high-fidelity audio output in home stereo systems.
   2. Switching power supplies in industrial control panels.
   3. Driving high-frequency digital clock signals in microprocessors.
   4. Operating high-power RF transmitters with narrow bandwidth.

   Explanation: Class AB amplifiers are widely chosen for audio systems where good efficiency and low distortion (high linearity) are important, making them ideal for home stereos. Option A (digital clocks) relies more on digital circuits. RF transmitters (option C) often use Class C for high efficiency. Switching power supplies (option D) primarily use Class D or other switching topologies, not AB.