In transistor amplifiers, we generally use _______ capacitors

Question

Examoogle · Accepted Answer

Electrolytic

Explanation: Electrolytic capacitors are primarily used in transistor amplifiers, particularly for coupling and decoupling stages, because they provide high capacitance values in a relatively small physical size. This allows for effective filtering of low-frequency signals and bypassing of power supply noise in compact electronic circuits.

Working Principle: In amplifier circuits, coupling capacitors are essential for passing AC signals while blocking the DC biasing voltage between stages. To maintain a low reactance ($X_c = \frac{1}{2\pi fC}$) at low signal frequencies, a large capacitance ($C$) is required. Electrolytic capacitors achieve these large values by using an oxide layer as the dielectric, which is extremely thin, maximizing the capacitance-to-volume ratio.

Key Formulas: $X_c = \frac{1}{2\pi fC}$ — The capacitive reactance formula showing the inverse relationship between capacitance and frequency-dependent resistance.

Key Points: Electrolytic capacitors are polarized and must be connected with the correct DC bias polarity.; They are widely used in power supply filtering and audio frequency coupling.; For high-frequency applications, non-polarized capacitors like ceramic or mica are preferred over electrolytic types due to lower Equivalent Series Inductance (ESL).; They have higher leakage currents compared to other capacitor types.

Advantages: High capacitance density (compact size); Cost-effective for large capacitance values; Available in wide range of voltage ratings

Disadvantages: Polarized (cannot be used in pure AC circuits); Higher leakage current; Limited operating lifespan due to electrolyte drying

Applications: Audio amplifier coupling stages; Power supply decoupling; DC blocking in signal paths

Additional Info: The use of large capacitance ensures that the corner frequency ($f = \frac{1}{2\pi RC}$) is well below the audio bandwidth.. Option B (Mica) and D (Air) are typically used in high-frequency tuned circuits where high stability and low loss (high Q-factor) are required.

Answer: A is correct — Electrolytic capacitors provide the large capacitance required for low-frequency AC signal coupling in transistor amplifier circuits.

Exam Tip: Always ensure the electrolytic capacitor is connected with the positive terminal towards the higher potential point to prevent device failure or explosion.

Related Questions

Discussion (0)