A class-A power amplifier biased for sinusoidal output has maximum theoretical efficiency η_max equal to which?
A75% common-emitter standard
B100% (ideal lossless)
C12.5% always with no transformer
D25% (transformer-coupled goes to 50%)
Answer & Solution
Correct answer: D. 25% (transformer-coupled goes to 50%)
Class-A direct-coupled: η_max = P_AC/P_DC = (V²/8R)/(VCC²/R) → 25% peak. Transformer coupling doubles to 50%. Class-B push-pull reaches π/4 ≈ 78.5%.
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