Differentiate class A, class B and class C amplifiers.

Class A Amplifiers:

• Operating Principle: Class A amplifiers operate in a linear region, where the output current flows through the active device (typically a transistor) for the entire input cycle. This results in a faithful reproduction of the input signal with minimal distortion.
• Characteristics:
  • High-fidelity: Class A amplifiers offer excellent linearity and low distortion, making them suitable for high-quality audio applications.
  • Low efficiency: Due to the continuous flow of current through the active device, Class A amplifiers have low efficiency, typically ranging from 20% to 30%.
  • High power dissipation: The continuous current flow leads to high power dissipation, requiring large heat sinks to prevent overheating.
  • Simple design: Class A amplifiers have a relatively simple design, making them easy to implement.

Class B Amplifiers:

• Operating Principle: Class B amplifiers utilize two complementary transistors (one NPN and one PNP) that operate in a push-pull configuration. Each transistor conducts for half of the input cycle, allowing for higher efficiency compared to Class A amplifiers.
• Characteristics:
  • High efficiency: Class B amplifiers achieve higher efficiency, typically ranging from 60% to 70%, as each transistor conducts for only half of the input cycle.
  • Reduced power dissipation: Due to the reduced conduction time, Class B amplifiers have lower power dissipation compared to Class A amplifiers.
  • Crossover distortion: Class B amplifiers introduce crossover distortion at the zero-crossing point of the input signal, where both transistors are briefly turned off. This distortion can be minimized through careful design and circuit techniques.

Class C Amplifiers:

• Operating Principle: Class C amplifiers operate with the active device biased beyond cutoff, resulting in conduction for less than half of the input cycle. This allows for even higher efficiency than Class B amplifiers but introduces significant distortion.
• Characteristics:
  • Very high efficiency: Class C amplifiers achieve very high efficiency, typically exceeding 80%, due to the short conduction time of the active device.
  • High distortion: Class C amplifiers have significant distortion due to the nonlinear operation of the active device.
  • Limited applications: Class C amplifiers are typically used in high-power applications where efficiency is paramount and distortion is less critical.