Capacitors are among the most essential electronic components found in every circuit, from simple hobbyist projects to advanced digital devices. In this guide, we explain what a capacitor is, how it works, how to identify different types, and how to use them correctly. Whether you’re building a basic LED circuit or exploring complex power supply designs, understanding capacitors is foundational to success in electronics.
Table of Contents
- What Is a Capacitor?
- Common Types of Capacitors
- Capacitor Symbol in Circuit Diagrams
- Understanding Capacitance and How to Calculate It
- Using a Capacitance Meter
- Tips for Capacitors
- Did You Know?
- Frequently Asked Questions (FAQ)
- Conclusion
What Is a Capacitor?
A capacitor is a passive electronic component that stores energy in the form of an electric field. It consists of two conductive plates separated by an insulating material called the dielectric. When voltage is applied across the plates, electric charge accumulates and can later be released.
Capacitors are used in a wide range of applications, including:
- Filtering and smoothing voltage
- Timing circuits
- Signal coupling and decoupling
- Power conditioning
- RF tuning
The ability of a capacitor to store charge is called capacitance, measured in Farads (F). However, in electronics, most capacitors are rated in microfarads (µF), nanofarads (nF), or picofarads (pF).
Common Types of Capacitors
There are several types of capacitors, each with specific characteristics and applications. Here’s a breakdown:
| Type | Description | Typical Range |
|---|---|---|
| Electrolytic Capacitor | Polarized, used in power filtering | 1µF – 4700µF |
| Tantalum Capacitor | Stable, compact, polarized | 0.1µF – 470µF |
| Ceramic Capacitor | Non-polarized, used for decoupling caps | 1pF – 100nF |
| Film Capacitor | High stability, non-polarized | 1nF – 1µF |
| Super Capacitors | Very high capacitance for energy storage | 1F – 1000F |
| Variable Capacitor | Tunable, used in RF circuits | 10pF – 500pF |
| Trimmer Capacitor | Small adjustable capacitor for fine tuning | 1pF – 100pF |
| Multilayer Ceramic Capacitor (MLCC) | Surface mount version with high reliability | 1nF – 100µF |
Polarized Electrolytic Capacitors
The following image shows some examples of electrolytic capacitors commonly used in hobby electronics. Electrolytic capacitors are a type of polarized capacitor. This means that they have a positive (+) terminal and a negative (-) terminal. The longer lead or leg of an electrolytic capacitor is the positive terminal.
In addition to the longer capacitor lead being the positive terminal, the negative terminal of an electrolytic capacitor is marked with a minus sign or negative symbol. The following image shows this marking. Capacitance value and maximum voltage rating is usually also printed on the body of the capacitor.
Non-polarized Capacitors
Non-polarized capacitors can be connected to a circuit either way around, as there is no positive or negative terminals. The following image shows examples of non-polarized capacitors.
Surface Mount Capacitors
Surface mount capacitors are compact components designed for automatic placement on printed circuit boards (PCBs). These capacitors are widely used in modern electronics due to their small size and suitability for high-density circuit layouts.
The two main types of surface mount capacitors are:
- Non-polarized surface mount capacitors, such as ceramic chip capacitors, which are shown in the image below labeled Surface Mount Non-Polarized Capacitors. These are commonly used for decoupling and filtering in digital circuits. A common example is the 104 capacitor, which represents 100nF.
- Polarized surface mount capacitors, like surface mount electrolytic capacitors, are shown in the image labeled Surface Mount Polarized Capacitors. These are used in applications where higher capacitance is required, such as power supply filtering. Polarity must be observed when placing these components, as incorrect orientation can cause failure.
Surface mount versions of many capacitor types exist, including tantalum capacitors and multilayer ceramic capacitors (MLCCs). These are available in various standard package sizes (e.g., 0805, 0603) and can be tested using a capacitance meter for verification during prototyping or repair.
When working with SMD capacitors, always check markings and datasheets, as many small packages lack clear value codes.
Capacitor Symbol in Circuit Diagrams
Recognizing the capacitor symbol is essential for reading electronic schematics. There are two main symbols used to represent capacitors in circuit diagrams, depending on whether the component is polarized or non-polarized. The following image shows the non-polarized symbol on the left and the polarized symbol on the right.
- Non-polarized Capacitor Symbol:
This symbol features two parallel lines of equal length. It represents capacitors like ceramic capacitors, film capacitors, or multilayer ceramic capacitors that can be connected in either direction. - Polarized Capacitor Symbol:
One line is straight, and the other is curved. This symbol is used for capacitors with polarity, such as electrolytic capacitors and tantalum capacitors. The straight line marks the positive terminal.
Summary Table of Capacitor Symbols
| Capacitor Type | Symbol | Symbol Description | Examples |
|---|---|---|---|
| Non-polarized |  | Two equal parallel lines | Ceramic, film, MLCC |
| Polarized |  | One straight, one curved line | Electrolytic, tantalum |
| Variable Capacitor |  | Arrow through one plate | Tuning circuits, radios |
| Trimmer Capacitor |  | Diagonal arrow and adjustment mark | PCB fine-tuning applications |
Always pay attention to polarity when working with polarized capacitors, especially when placing them in capacitor in parallel and series configurations. Incorrect polarity can lead to capacitor failure.
Regional Differences in Capacitor Symbols
The capacitor symbol featuring one straight line and one curved line is the American standard for a polarized capacitor, commonly used in U.S. schematics to indicate the positive and negative terminals—typically for components like electrolytic capacitors.
In European circuit diagrams, capacitor symbols may differ slightly. Both plates are often shown as boxes, and polarity is indicated with a plus sign (+) near the positive terminal rather than using a curved line. The empty box is the positive plate and the filled box is the negative plate. It’s important to be familiar with both standards when reading international datasheets or circuit diagrams.
The following image shows a European symbol for a polarized capacitor on the right. The non-polarized capacitor on the left is used in both European and American circuit diagrams.
Example Circuit Diagram
Below is part of the Arduino Uno R4 circuit diagram. It is the power regulator section of the circuit. This diagram shows a number of capacitors in the circuit. They are all of the non-polarized type.
Understanding Capacitance and How to Calculate It
Capacitance depends on the surface area of the plates, the distance between them, and the dielectric material. The larger the area and the closer the plates, the higher the capacitance.
Calculating Capacitance in Circuits
Capacitance is calculated differently for capacitors in parallel to each other, compared to capacitors in series with each other. This is explained in the following two sub-sections.
Capacitors in Parallel
The following image shows capacitors connected in parallel.
Total capacitance adds up for capacitors in parallel.C_total = C1 + C2 + C3 + …
In the above circuit example, the total parallel capacitance is:
100µF + 100µF + 100µF = 300µF
Capacitors in Series
Total capacitance for capacitors in series use the following formula.
Use the reciprocal formula.1/C_total = 1/C1 + 1/C2 + 1/C3 + …
The following image shows capacitors connected in series.
The total capacitance in the above circuit is calculated as follows:
Using a Capacitance Meter
A capacitance meter is a helpful tool for identifying unknown capacitors or confirming their actual values. This is especially useful for unmarked or old components, or when troubleshooting faulty capacitors.
Tips for Capacitors
- Always check polarity: Electrolytic and tantalum capacitors are polarized; reverse connections can destroy them.
- Mind the voltage rating: Use a capacitor rated at least 25–50% higher than your circuit voltage.
- Use decoupling caps: Place ceramic capacitors (e.g., 100nF) near power pins of ICs to reduce voltage spikes.
- Label your components: Keep types of capacitors organized by value and voltage to avoid mix-ups.
- Test before use: Use a capacitance meter to verify component values when in doubt.
Did You Know?
- The earliest capacitor was the Leyden jar, developed in the 18th century for static electricity experiments.
- A super capacitor can power small devices or provide short-term backup power during outages.
- Many capacitors are coded using a three-digit marking system, like the 104 capacitor, which equals 100nF.
- Variable capacitors were once key components in analog radio tuners.
- Trimmer capacitors are typically adjusted once during manufacture or servicing and then left untouched.
Frequently Asked Questions (FAQ)
What is the function of a capacitor in electronics?
Capacitors store and release electrical energy, filter out voltage noise, and manage timing and frequency behavior in circuits.
How do I know which type of capacitor to use?
Choose based on your circuit needs. Use electrolytic capacitors for power filtering, ceramic capacitors for decoupling, and film capacitors for audio or precision applications.
What happens if I reverse the polarity of a polarized capacitor?
Reversing polarity on a tantalum or electrolytic capacitor may cause it to leak, overheat, or explode. Always double-check orientation.
Can I use a multimeter to test a capacitor?
Some multimeters include a capacitance mode, but a dedicated capacitance meter offers more accurate readings.
What does a “104 capacitor” mean?
The marking “104” means 100,000 picofarads or 100nF. It’s a standard ceramic capacitor code.
Conclusion
The capacitor is a versatile and indispensable component in electronic circuits. By understanding the various types of capacitors, from electrolytic to ceramic, and knowing how to use tools like a capacitance meter, you’ll be better equipped to build, troubleshoot, and improve your projects. Whether you’re working with a surface mount capacitor or selecting a decoupling cap, having a solid grasp of capacitor fundamentals is a key skill for every electronics enthusiast.
To continue learning about electronic components, explore more guides in our Components & Tools section.