Conduction angle identification: In a class A power amplifier, for how much of the input signal cycle does the collector (or drain) current flow?

Introduction / Context:
Amplifier “class” describes the bias point and conduction angle, which in turn affects linearity and efficiency. Class A operation is the benchmark for linearity in many small-signal applications, though it sacrifices efficiency.

Given Data / Assumptions:

• Sine-wave input signal.
• Proper bias so the active device never cuts off during the cycle.
• Focus is on classic class A (not special topologies like push-pull class A/B hybrids).

Concept / Approach:
In class A, the transistor is biased in the middle of its active region so that current flows continuously. The conduction angle is therefore the entire 360° of the input cycle. This maximizes linearity and minimizes crossover distortion but results in low efficiency because current still flows at zero signal.

Step-by-Step Solution:

Verification / Alternative check:
Compare with class B (conduction 180°) and class AB (between 180° and 360°). These reference points confirm the definition for class A.

Why Other Options Are Wrong:

• Less than or equal to 180° describes class B or class C, not class A.
• “Less than 360° but more than 180°” is class AB, not class A.

Common Pitfalls:
Confusing classes due to push-pull implementations; even with two devices in push-pull, each class A device conducts for the full cycle.

Final Answer:
Full 360° of the cycle.