What Is a Capacitor?
A capacitor is a basic passive component that stores electric charge. It's made by placing an insulator (dielectric) between two conducting plates; when voltage is applied it accumulates energy and releases it when needed.
How Does It Work?
When voltage is applied to a capacitor, opposite charges collect on the plates; the dielectric between them holds that charge. This charge-storing ability is called capacitance.
Capacitance and Its Unit
The unit of capacitance is the farad (F); but since 1 F is very large, in practice µF, nF, pF are used (SI prefixes). For example, 1 µF = 1,000 nF = 1,000,000 pF.
Capacitor Types
| Type | Standout | Polarity |
|---|---|---|
| Ceramic (MLCC) | Small, cheap, common | None |
| Electrolytic | High capacitance | Yes |
| Film | Stable, low loss | None |
| Tantalum | Compact, stable | Yes |
Each type has its own detailed article: ceramic (MLCC), film, tantalum, polymer and mica capacitors, and the very high-capacity supercapacitors.
Where Is It Used?
In power-line filtering, noise suppression (decoupling), signal coupling, energy storage and timing (RC) circuits.
How to Choose a Capacitor
Look at three things: the required capacitance (µF/nF/pF), a working voltage higher than the voltage applied, and a type suited to the application. Electrolytic for high capacitance, ceramic for high frequency/decoupling, film for stability. On polarized types, direction matters as much as the value.
Common Mistakes
- Ignoring polarity: electrolytic and tantalum are polarized; installing them backwards leads to bursting.
- Exceeding the voltage rating: using it above the capacitor's rated voltage destroys it.
- Forgetting DC bias: on some ceramics the capacitance drops under the applied voltage.
Frequently Asked Questions
What's the difference between a capacitor and a battery?+
Does a capacitor have a direction?+
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