In the fascinating world of electronic circuits, capacitors are an extremely important component—acting like tiny "reservoirs" that silently store and release electrical energy. Whether on complex computer motherboards or in simple doorbell circuits, capacitors are everywhere. Today, I will introduce this component to you.

1. Basic Concepts of Capacitors

Simply put, a capacitor is a component that stores electric charge. Its basic structure consists of two conductive plates separated by an insulating dielectric material.

When voltage is applied across the two plates, charge accumulates on them—much like filling a reservoir with water. A capacitor’s ability to store charge is measured in farads (F). However, since a farad is impractically large, we commonly use microfarads (μF), nanofarads (nF), and picofarads (pF). The conversion between them is: 1F = 1000000μF，1μF = 1000nF，1nF = 1000pF.

2. Types of Capacitors

The capacitor family is vast, with different types offering distinct performance characteristics based on their dielectric materials and structures.

Ceramic Capacitors

It uses ceramic material as the dielectric medium, offering advantages such as compact size, high stability, and excellent high-frequency performance. It excels in various everyday applications—for instance, ceramic capacitors are widely used in the RF circuits of smartphones to process high-frequency signals.

Electrolytic Capacitors

These capacitors use a metal oxide film as the dielectric and are prized for their high capacitance values at relatively low voltages—like a large-capacity "water bucket." They are commonly used in power filtering and audio coupling circuits. However, they are polarized, meaning they must be connected correctly to avoid damage or even explosions. You’ll find them in computer power supplies, where they smooth out unstable voltage outputs.

Film Capacitors

These use plastic films (such as polyester or polypropylene) as the dielectric. They offer good insulation and stability, making them suitable for high-frequency and high-voltage circuits. For instance, they play a crucial role in inverter circuits, handling high voltages and frequencies.

Mica Capacitors

With mica as the dielectric, these capacitors are known for their high precision, stability, and low losses—earning them the title of "aristocrats" among capacitors. However, due to their high cost and larger size, they are typically used only in high-end measuring instruments where performance is critical.

3. The Role of Capacitors in Circuits

Filtering

In power supply circuits, capacitors are responsible for filtering out the AC components from the output, ensuring a more stable DC voltage. A common practice is to use a large electrolytic capacitor in parallel with a small ceramic capacitor—the electrolytic capacitor handles low-frequency ripple, while the ceramic capacitor suppresses high-frequency noise. Working together, they provide clean and reliable power to the circuit.

Coupling

Capacitors serve as bridges between circuit stages, allowing AC signals to pass while blocking DC interference. In audio amplifiers, coupling capacitors transfer signals between amplification stages without disrupting DC bias.

Bypassing

They act as "shortcuts," diverting high-frequency noise to ground. For example, a small ceramic capacitor near an IC’s power pin provides a low-impedance path for high-frequency interference, ensuring stable operation.

Energy Storage

In circuits requiring sudden energy bursts (e.g.camera flashes), capacitors store and rapidly release energy.

4. Usage Precautions

Polarized Capacitors Must Be Connected with Correct Polarity

For electrolytic and other polarized capacitors, strict adherence to proper polarity is mandatory during installation. Reverse polarity can trigger abnormal internal chemical reactions, leading to overheating, bulging, or even explosions, posing serious risks to circuit safety. PCB layouts typically include clear polarity markings—always double-check during installation.

Control Soldering Temperature and Time

Excessive heat or prolonged soldering can permanently damage capacitors. Use appropriate soldering tools and precisely regulate temperature (300–350°C) and time (3–5 seconds max) to prevent thermal degradation.

Avoid Mechanical Stress

During handling and installation, protect capacitors from mechanical stress (e.g., crushing, bending), which may compromise internal integrity. Ensure secure, properly aligned mounting on PCBs to prevent accidental damage in subsequent operations.

Learning Capacitor Usage from Scratch: An Essential Skill in the Electronics World