*Question G7B02:
Which of these classes of amplifiers has the highest efficiency?*  

*Correct Answer is  D: Class C*  

### AI Response: (may contain errors)  

To determine which class of amplifiers has the highest efficiency, let's look at each class:

### Correct Answer: Class C

- **Efficiency**: Class C amplifiers are designed to operate with a conduction angle of less than 180 degrees. This means they are on for a shorter period during each cycle of the input signal, which allows them to achieve efficiencies of up to 80% or more.
- **Usage**: They are typically used in RF (radio frequency) applications where high efficiency is crucial.

### Why the Other Choices are Incorrect:

- **Class A**:
  - **Efficiency**: Class A amplifiers have a conduction angle of 360 degrees, meaning they are always on. This results in low efficiency, typically around 20-30%.
  - **Usage**: They provide excellent linearity and are often used in audio applications.

- **Class B**:
  - **Efficiency**: Class B amplifiers have a conduction angle of 180 degrees, which allows for better efficiency than Class A, typically around 50-70%. However, they can introduce distortion at low signal levels.
  - **Usage**: Commonly used in push-pull configurations for audio and RF applications.

- **Class AB**:
  - **Efficiency**: Class AB amplifiers combine features of Class A and Class B, with a conduction angle greater than 180 degrees but less than 360 degrees. Their efficiency typically ranges from 50-70%, making them more efficient than Class A but less than Class C.
  - **Usage**: They are widely used in audio applications where a balance between efficiency and linearity is needed.

### Summary of Efficiencies:
- Class A: 20-30%
- Class B: 50-70%
- Class AB: 50-70%
- Class C: Up to 80% or more

### Conclusion:
Class C amplifiers are the most efficient due to their design, which minimizes the time the amplifier is active during each cycle. Understanding these differences is crucial for selecting the appropriate amplifier class for specific applications.