Question
What is the purpose of C2 in the circuit shown in Figure E7-2?
Answer Options
- A) It bypasses rectifier output ripple around D1
- B) It is a brute force filter for the output
- C) To prevent self-oscillation
- D) To provide fixed DC bias for Q1
Correct Answer: C
Explanation
Figure E7-2 shows a linear voltage regulator where the pass transistor Q_1 acts as a high-gain amplifier in the feedback loop. High-gain amplifiers are susceptible to instability at high frequencies, which can cause the regulator circuit to break into unwanted oscillations.
Capacitor C2 is placed between the base of Q_1 and ground, serving as a bypass capacitor. Its primary purpose is to prevent self-oscillation of the regulator circuit. C2 acts as a compensation capacitor, ensuring that the high-frequency gain of Q_1 rolls off smoothly before the phase shift reaches 180^\circ, thereby stabilizing the entire feedback loop and preventing oscillation.
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