Question 3-51G4

Class C amplifiers provide the highest efficiency because they are biased well below cutoff. This means the amplifier conducts current for significantly less than 180 degrees of the input signal cycle. By being "on" for such a short duration, the transistor spends minimal time dissipating power, leading to theoretical efficiencies that can exceed 90%. The brief conduction period effectively "kicks" an output resonant tank circuit, which then "rings" to reconstruct the full sine wave. This makes Class C ideal for constant amplitude signals like FM or CW, where linearity isn't as critical as for AM signals. In contrast: * **Class A** amplifiers conduct for 360 degrees, always "on," offering high linearity but low efficiency (25-50%). * **Class B** amplifiers conduct for 180 degrees, improving efficiency (50-78.5%) but introducing crossover distortion. * **Class AB** is a compromise, conducting slightly more than 180 degrees to reduce distortion, with efficiency between Class A and B.