Capacitors: Types, Function, Characteristics, Applications and Circuits

If you have researched about electronics, it is possible you have encountered capacitors. These are key electronic devices vital for many applications today. However, do you know what a capacitor is and how it works?

What is a Capacitor?

A capacitor is an electrical device that stores energy in an electric charge form. Capacitors are made by having two conductors separated by a distance or space. This space can be filled with an insulating material or a vacuum.
Because they can store energy, capacitors have many applications in modern electronics. Expect to see them in almost all electronics, where they do much more than energy storage. They can also be used for power conditioning, filtering, tuning, etc.

How Do Capacitors Work?

Capacitors store electrical energy through charge accumulation between two conductive plates separated by a dielectric, thus creating an electric field. How does this happen?

During the charging phase, a voltage source, such as a battery, is connected to the capacitor. In this case, electrons flow from the negative terminal to one of the capacitor plates and accumulate there, leaving it negatively charged. The other capacitor plate also loses electrons to the negative side, meaning it is now positively charged.

The act of accumulating charges on the capacitor plates creates an electric field, which is vital for storing electrical energy.

The discharging part happens when the voltage source is disconnected, and the capacitor is connected to a load such as a bulb. In this case, the stored charges flow through the load, creating a current until the capacitor fully discharges.

Types of Capacitors

Capacitors are often classified based on structure. There are three main types of capacitors: fixed capacitors, variable capacitors, and trimmer capacitors.

Fixed capacitors have a fixed capacitance value, compared to variable capacitors, whose capacitance can be varied. Let us look at the different types of capacitors in detail below.

Fixed Capacitors

• Ceramic Capacitors

This is the most common capacitor you will get in the market. It comes with a dielectric material, and it is a nonpolar device. It can work in any direction, making it suitable for many circuits.

These capacitors are further classified into three classes. Class 1 ceramic capacitors offer the best stability, while class 2 are best for volumetric efficiency but lack accuracy and stability. Class 3 offers high volumetric efficiency but a low dissipation factor and accuracy. They are often used for decoupling applications.

• Film Capacitors

In this case, these capacitors come with a film dielectric. The use of such a dielectric leaves you with a highly durable capacitor. Even with good durability, they are still inexpensive.

The application where the capacitor would be used determines its construction. If it has to be used with high voltage, expect it to have more thin films. Depending on the construction, film capacitors can handle from 50V to 2KV.

• Power Film Capacitors

This one has the same construction such as the film dielectric. The only difference is that polypropylene film is used in this case to make it suitable for specialized applications.

• Electrolytic Capacitors

This type of capacitor comes with a metallic anode that has been oxidized using a specific dielectric. For example, you can get an aluminum electrolytic capacitor, meaning it has an aluminum oxide dielectric. So, it depends on the dielectric to determine the type of electrolytic capacitor.

These capacitors are also polarized. That is how you end up with a cathode and anode.

• Paper Capacitors

The dielectric for these capacitors is a paper. The amount of charge that can be stored is fixed compared to other capacitors whose values vary. Because of their design, they will work well for noise filtering and coupling systems. Expect to come across them in audio systems meant for cars.

Variable Capacitors

Tuning capacitors are examples of variable capacitors. They are common in radio circuits and are used to tune the frequency by simply adjusting the capacitance.

Trimmer capacitors also come with adjustable capacitance, vital for fine-tuning circuits.

Characteristics of Capacitors

Whether you choose an HVAC capacitor or an AC capacitor, the characteristics are often the same. Below are some of the notable characteristics of capacitors you should know.

Capacitance (C)

Capacitance is the ability of a capacitor to store electrical energy. It is measured in Farads (F), with the commonly used units being nanofarads, picofarads, and microfarads.

The dimensions of the capacitor and dielectric materials affect the overall capacitance of a capacitor.

Working Voltage (WV)

This is the maximum amount of voltage that can be applied to a capacitor without breaking it down or damaging it. It is vital to know the working voltage as it leads to a reliable operation and prevents potential capacitor failure.

Tolerance

The tolerance of a capacitor is the permissible variation in terms of capacitance value compared to its stated value. Capacitors usually have a tolerance of ±5%, ±10%, or ±20%. This will be clearly indicated so that you know what you are working with.

Leakage Current

There is no perfect dielectric material. This means a small amount of current can sometimes flow through the capacitor when voltage is still applied. This is called leakage current.

This current is largely influenced by the dielectric material, voltage, and operating temperature of the capacitor.

Polarization

This simply means buying capacitors that have specific polarity, such as positive and negative terminals. Because of their polarity, they have to be connected to the circuit correctly for it to work correctly.

When you connect the capacitor incorrectly, it might damage the capacitor.

Applications of Capacitors

Capacitors have plenty of applications, the most notable being energy storage. Expect to find them in power supplies. Their job is to smooth out the pulsating DC output of rectifiers, resulting in a more stable power supply.

Camera flashes also use capacitors, which provide a quick burst of energy for the flash units.

Backup power could also use capacitors to maintain power in case of an outage or while making battery changes. This helps prevent data loss.

Filtering is another big use of capacitors. For example, a car audio capacitor can remove unwanted frequencies from the signals. This includes the removal of noise in audio equipment.

AC/DC signal separation process also uses capacitors to block the DC signals while allowing the AC signals to pass through.

Pros and Cons of Capacitors

Capacitors can have pros and cons too. It all depends on how you use them. Here is what to expect.

Pros

• They offer fast charging and discharging
• Impressive lifespan with minimal maintenance
• They exhibit low energy loss compared to other energy storage mediums
• Capacitors are highly versatile as they come in various sizes and types
• They are quite cost-effective. It all depends on the dielectric material.
• Can be suitable for high-frequency applications
• The capacitors are highly stable and are made to maintain capacitance over time

Cons

• Capacitors have a limited energy storage capability
• The energy can still be depleted even when not used
• Expect variations in the storage voltage in capacitors
• Some materials, such as polyester dielectric, have a higher absorption affecting precision circuits.

How Capacitors Behave in Circuits

Like other electronic devices, capacitors have different characteristics depending on the circuit connection. Here is what to expect for various circuits.

• Parallel

In this case, the capacitance in the circuit will be the sum of individual capacitances. For example:

All the capacitors being in parallel means they share the same voltage across their plates.

• Series

Capacitance for capacitors in series will be calculated using the reciprocal formula to get the total capacitance in the circuit. The formula is

In a series connection, each capacitor in the circuit will have a different voltage amount, depending on its position in the circuit.

Common Issues with Capacitors

Capacitors may also have some issues, even if they seem to always work great. Some of them include;

• Excessive heat can cause overheating, which can damage the dielectric material and lead to short circuits or leaks.
• Overvoltage is not recommended. Applying more voltage than the capacitor’s rated voltage can damage it.
• Dielectric breakdown is possible. For example, excessive voltage can lead to dielectric breakdown. This means current can easily flow when it is not supposed to.
• Electrolyte leakage can happen in electrolytic capacitors. This is where the electrolyte can lead or dry out over time. This is possible with age or when exposed to excessive heat.
• Physical damage can also occur. It can be due to physical stress, such as shock, vibration, or improper handling. This damage can also lead to internal shorts or opens.

How to Choose the Right Capacitor

Choosing an AC start capacitor or any other type depends on your needs and application. Below, we discuss in more detail how you can select the right multilayer ceramic capacitor and other types.

1. Capacitance

Before you buy an ASUS P4PE capacitor, look at its capacitance. It depends on the application. Some applications require higher capacitance, while others do not. For example, higher-frequency applications need small capacitance values, while the opposite is true for energy and filtering applications.

2. Voltage Rating

Choose a capacitor that is within the voltage rating of your application. Choosing one with a higher voltage rating is even better. The failure rate will be higher when you use a capacitor with a lower rating than needed.

3. Dielectric Type

The dielectric material affects the capacitor’s frequency response, physical size, and temperature stability. Ceramic capacitors are an example. Their dielectric makes them suitable for high-temperature and frequency applications. Electrolytic capacitors are suitable for low-frequency and high-capacitance applications.

4. Tolerance

Tolerance is how much the actual capacitance varies from the nominal value. When handling sensitive circuits, the tolerance should be really low to work with a figure close to the rated value.

5. Size and Package

The capacitor size should be within the space available to install it. There are different sizes of capacitors in the market. Look at your design constraints and pick a capacitor that will fit your project.

6. Temperature Range

Capacitors are designed to operate within certain temperature ranges. So, choose a capacitor that can handle the temperature extremes of an application. This rating will be indicated by the manufacturer to help you choose better.

How to Test a Capacitor

Testing a capacitor can be done in so many ways. However, we will consider how to check a capacitor with a multimeter. This is because multimeters are readily available and should be easy to use.

Follow these steps to test the capacitor.

• Discharge the capacitor

Make sure the capacitor is discharged before testing it. This ensures that you prevent shocks or damage to the multimeter. Connecting a resistor across the capacitor or using a capacitor discharge tool will do the job.

• Setup the multimeter

Make sure the multimeter is in the capacitance mode so that you can test the capacitor. Look for symbols such as F or Farad to show capacitance.

• Connect the multimeter

Connect the red probe to the positive terminal and the black probe to the negative terminal. This is for polarized capacitors. If it is non-polarized, the probes can connect in any manner, and they will still work.

• Read the capacitance

Read the value shown on the multimeter. That is the capacitance value in farads or microfarads, depending on the multimeter scale. Now, compare this value with the rated value on the capacitor. If it is significantly different, the capacitor may be faulty.

Conclusion

Capacitors remain essential for many circuits. It is hard to miss them in various electronics. It is all about their importance in ensuring electronics run smoothly. If you are designing a circuit, it is best to choose capacitors based on their usability and performance so that you realize the circuit’s functionality. If things are not working as expected, always troubleshoot the capacitor to see if this improves the functionality of a circuit.