Basically, a capacitor is formed from two conducting plates separated by a thin insulating layer.
There are different types of capacitors that are manufactured in many forms, styles, and materials. Understanding the basics of them help you to choose the capacitor for your application.
Before going to each of them, let us understand the basic uses of a capacitor in a circuit.
Capacitors are widely used in electrical and electronic circuits.
In electronic circuits, small value capacitors are used,
- to couple signals between stages of amplifiers.
- as components of electric filters and tuned circuits.
- as parts of power supply systems to smooth rectified current.
- for energy storage in such applications as strobe lights.
- as parts of some types of electric motors.
- for power factor correction in AC power distribution systems
Standard capacitors have a fixed value of capacitance, but adjustable capacitors are frequently used in tuned circuits.
Types of Capacitors
Now we will learn different types of capacitors and how they are classified. Also in this section, you can find out how these capacitors got their name we call them now.
Generally, capacitors are divided into two common groups:
- Fixed Capacitors
- Variable Capacitors
Fixed Capacitors are those capacitors with fixed capacitance values. While Variable Capacitors have the variable (trimmer) or adjustable (tunable) capacitance values. Out of these the most important group is fixed capacitors.
Fixed capacitors include polarized and non-polarized.
Ceramic and Film capacitors are examples of non-polarized capacitors. Electrolytic and Super Capacitors are included in the group of polarized capacitors.
The classification of fixed capacitors is shown in the figure below.
Some of the important capacitors are listed here:
- Ceramic capacitors
- Film and paper capacitors
- Aluminum, tantalum and niobium electrolytic capacitors
- Polymer capacitors
- Silver mica, glass, silicon, air-gap and vacuum capacitors
In addition to the above-shown capacitor types, which derived their name from historical development, there are many individual capacitors that have been named based on their application.
The capacitors that derived their name based on their application include the following:
- Power capacitors, motor capacitors, DC-link capacitors, suppression capacitors, audio crossover capacitors, lighting ballast capacitors, snubber capacitors, coupling, decoupling or bypassing capacitors.
Often, more than one capacitor family is employed for these applications, e.g. interference suppression can use ceramic capacitors or film capacitors.
Overview of Different Types of Capacitors
As we explained above, there are many different types of capacitor that can be used. Some of the major types are outlined below:
The ceramic capacitor is a type of capacitor that is used in many applications from audio to RF.
Values range from a few picofarads to around 0.1 microfarads. Ceramic capacitor types are by far the most commonly used type of capacitor being cheap and reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use.
In view of their constructional properties, these capacitors are widely used both in leaded and surface mount formats.
Electrolytic capacitors are a type of capacitor that is polarised.
They are able to offer high capacitance values – typically above 1μF. These capacitors are most widely used for low-frequency applications – power supplies, decoupling and audio coupling applications as they have a frequency limit if around 100 kHz.
Like electrolytic capacitors, tantalum capacitors are also polarised and offer a very high capacitance level for their volume.
However, this type of capacitor is very intolerant of being reversely biased, often exploding when placed under stress.
This type of capacitor must also not be subject to high ripple currents or voltages above their working voltage.
They are available in both leaded and surface mount formats.
Silver Mica Capacitor:
Silver mica capacitors are not as widely used these days, but they still offer very high levels of stability, low loss and accuracy where space is not an issue.
They are primarily used for RF applications and they are limited to maximum values of 1000 pF or so.
Polystyrene Film Capacitor
Polystyrene capacitors are a relatively cheap capacitor but offer a close tolerance capacitor where needed.
They are tubular in shape resulting from the fact that the plate / dielectric sandwich is rolled together, but this adds inductance limiting their frequency response to a few hundred kHz.
They are generally only available as leaded electronics components.
Polyester Film Capacitor
Polyester film capacitors are used where cost is a consideration as they do not offer a high tolerance.
Many polyester film capacitors have a tolerance of 5% or 10%, which is adequate for many applications. They are generally only available as leaded electronics components.
Metallised Polyester Film Capacitor
This type of capacitor is essentially a form of polyester film capacitor where the polyester films themselves are metallised.
The advantage of using this process is that because their electrodes are thin, the overall capacitor can be contained within a relatively small package.
The metallised polyester film capacitors are generally only available as leaded electronics components.
The polycarbonate capacitors have been used in applications where reliability and performance are critical.
The polycarbonate film is very stable and enables high tolerance capacitors to be made which will hold their capacitance value over time.
In addition, they have a low dissipation factor, and they remain stable over a wide temperature range, many being specified from -55°C to +125°C.
However, the manufacture of polycarbonate dielectric has ceased and their production is now very limited.
The polypropylene capacitor is sometimes used when a higher tolerance type of capacitor is necessary than polyester capacitors offer.
As the name implies, this capacitor uses a polypropylene film for the dielectric. One of the advantages of the capacitor is that there is very little change of capacitance with time and voltage applied.
This type of capacitor is also used for low frequencies, with 100 kHz or so being the upper limit. They are generally only available as leaded electronics components.
As the name implies, this capacitor type uses glass as the dielectric. Glass capacitors are generally expensive.
Although expensive, these capacitors offer very high levels of performance in terms of extremely low loss, high RF current capability, no piezo-electric noise, and other features.
These features make them ideal for many performance RF applications.
SuperCap is also known as a supercapacitor or ultracapacitor.
As the name implies these capacitors have very large values of capacitance, of up to several thousand Farads.
SuperCap find uses for providing a memory hold-up supply and also within automotive applications.