Power amplifier classes: For a given supply and proper loading, which amplifier class can deliver the maximum average load power under linear operation—Class A, Class AB, Class B, or Class C?

Introduction / Context:
Power amplifier classes (A, AB, B, C) are defined by the conduction angle of the output device and strongly influence efficiency and the maximum undistorted power delivered to the load. This question checks recognition of which conventional linear class (excluding switching Class D) can deliver the most average load power for a given supply voltage and load.

Given Data / Assumptions:

• Amplifier operates in its intended linear region (not clipping).
• Supply voltage and load impedance are fixed and identical for each class.
• Comparison among traditional linear classes A, AB, B, C.

Concept / Approach:

Class A conducts 360°, is very linear but wastes headroom; its theoretical efficiency is 25% to 50% depending on configuration, so the maximum deliverable power is limited. Class B conducts 180° per device in a push-pull stage, allowing the output to swing nearly the full supply across the load with no standing current, achieving a theoretical efficiency of ~78.5% and the largest undistorted output swing among the linear classes. Class AB is a compromise between A and B with some conduction overlap; its maximum power is close to but slightly less than ideal Class B. Class C conducts less than 180°, is non-linear and intended for tuned RF loads; average power at audio/untuned loads is not maximized.

Step-by-Step Solution:

Verification / Alternative check:

Textbook results show Pout,max ∝ V²/R with the largest coefficient for Class B due to near-rail voltage swing and zero quiescent loss at ideal conditions, confirming the selection.

Why Other Options Are Wrong:

• Class A: limited by large quiescent dissipation.
• Class AB: improved over A but not as high as ideal B.
• Class C: suited to resonant RF; not a general maximum-power linear stage.
• Class D: a switching class not listed in the original comparison; excluded by the linear-operation context.

Common Pitfalls:

• Confusing highest efficiency with highest fidelity—Class B is efficient but requires crossover-distortion management.

Final Answer:

Class B