BJT current relationships: In normal forward-active operation, is the collector current approximately equal to the base current?

Introduction / Context:
Understanding the relative magnitudes of base current (I_B) and collector current (I_C) is essential when biasing BJTs. In forward-active operation, the collector current is controlled by the base–emitter junction but is typically much larger than the base current, with the ratio defined by current gain β (also written h_FE).

Given Data / Assumptions:

• Forward-active region (not cutoff or deep saturation).
• β is significantly greater than 1 for a typical small-signal BJT.
• Steady quiescent bias with small-signal excursions.

Concept / Approach:
By definition, β = I_C / I_B. For common BJTs, β may range from tens to hundreds depending on device and operating point. Therefore, I_C ≈ β * I_B, making I_C much larger than I_B. Saying they are “approximately equal” is incorrect except in contrived cases where β ≈ 1, which is not representative of normal BJT behavior. Design equations and bias networks always account for a small I_B compared with I_C (and with emitter current I_E ≈ I_C + I_B).

Step-by-Step Solution:

Verification / Alternative check:
Datasheets list h_FE values; bench measurements with a simple CE stage confirm that a milliamp of I_C requires only microamps of I_B for β ~ 100.

Why Other Options Are Wrong:
Deep saturation changes relationships but the prompt says “in a BJT” generally; using β = 1 is atypical; feedback does not force equality of I_B and I_C.

Common Pitfalls:
Confusing current gain with voltage gain; forgetting that I_E ≈ I_C + I_B is the only near-equality, not I_C ≈ I_B.

Final Answer:
Incorrect