A capacitor can be thought to be like a tank that stores electric charge inside it. The more the capacitance, the more charges a capacitor is capable to store. It comes in various shapes, sizes, and of course, different ratings. It is essentially made of two plates separated by an insulator or a dielectric and has an ample number of uses, and even in our daily life, we use it without even knowing it.
This article aims to give you some insights into the types and uses of one of the most used passive electrical components: the capacitor.
|Capacitors (Source: flickr by Eric Schrader)|
Before we delve into its applications, let us get familiar with the types of capacitors.
Types of capacitors
While designing a circuit for a specific use, the type of capacitor plays a key role in its proper functioning. Each capacitor has a particular set of specifications, like tolerance, voltage rating, etc.
Capacitors can be broadly classified into two categories: The variable and the fixed capacitors.
Variable capacitor, on the other hand, will have a capacitance value which can be changed. This capacitor has two plates, one of which is fixed and the other one connected to a movable shaft and the capacitance is varied by changing the movable plate.
Fixed capacitor, as the name suggests, this type of capacitor has a fixed capacitance value. Both the conducting plates are immobile and therefore its capacitance value cannot be altered.
Out of these, the fixed type is more commonly used. This article deals with some of the well-known fixed capacitor types.
Ceramic capacitors use ceramic material as a dielectric. You can identify it easily, as most of it comes in a disc shape. The disc is coated with ceramic material and is placed in between the two leads. When a higher capacitance value is needed, multiple layers of ceramic materials are fused together to form the dielectric.
The main advantage of this type of capacitor is that it is a nonpolarized capacitor. This means you can connect it in any direction in your circuit.
Based on their temperature ratings and tolerance, these are classified into three categories: Class 1, Class 2, and Class 3 ceramic capacitors.
Class 1 capacitors are the most stable one, with respect to its temperature tolerance and have good accuracy, while the Class 3 capacitors have relatively poor accuracy and least stability.
Aluminium Electrolytic Capacitors:
Aluminium Electrolytic capacitors have a wide tolerance capacity and hence are one of the most used capacitors. Here, a liquid or gel-type material filled with ions acts as the electrolyte. This electrolyte is responsible for the larger capacitance values of these capacitor types. These are polarized capacitors and hence have to be connected carefully on to a circuit board, keeping their positive/negative leads in mind. They come in a cylindrical shape with two leads of different lengths.
The shorter lead stands for the negative terminal while the longer one stands for its positive terminal. Therefore when you use it in your circuit, remember the golden rule: "The voltage on the positive side must be higher than that of the negative side."
The electrolyte may be either solid polymer or a wet electrolyte and consist of aluminum ions. With higher capacitance values, the electrolytic capacitor comes with drawbacks too. This includes large leakage currents, high-value tolerances and equivalent resistance.
Tantalum Electrolytic Capacitors:
Tantalum electrolytic capacitors are another type of electrolytic capacitor, where the anode is made of Tantalum. The use of Tantalum gives the capacitors higher tolerance value but lower maximum operating voltage than an aluminium electrolytic capacitor, it cannot be used as a direct replacement for the same.
Tantalum capacitors have a very thin dielectric layer and hence higher capacitance value per volume. It shows comparatively good stability and frequency characteristics than other capacitor types.
However, tantalum capacitors pose a risk of a potential failure mode, which may occur during voltage spikes when the anode comes in direct contact with the cathode. This may lead to a chemical reaction depending upon the strength of the energy produced during the process. Therefore while using this capacitor, you will have to use current limiters or thermal fuses as a preventive circuitry.
Film capacitors as the name suggests have dielectrics made of thin plastic film. This film is crafted out through a sophisticated film drawing process. The film can either be metalized or an untreated one, it depends upon the demand of the capacitor characteristics. This capacitor type has good stability with low inductance and is comparatively cheaper than its counterparts. Depending on the type of dielectric used, these film capacitors are classified into various categories like polyester film, plastic film, etc.
These are non-polarized capacitors with desirable characteristics. When compared to an electrolyte capacitor, it has a longer shelf and service life, making it more reliable.
Silver Mica Capacitors:
Silver Mica capacitors use mica, a group of natural minerals as dielectric which is sandwiched between two metal sheets. The specific crystalline binding of mica helps in manufacturing very thin layers of dielectric. This capacitor is popular for its reliability and stability for a small value of capacitances. These low loss capacitors are not polarized and can be made to many high tolerances.
Now that you have got an idea of some of the capacitors and their strengths, let us discuss the prominent areas of application for these capacitors.
Which capacitor can be used where?
These are probably the most widely produced capacitors, due to their infinite applications. The most prominent area where these capacitors are used is in the resonant circuit of a transmitter station, which requires high precision and high power capacitor. Owing to its non-polarity and availability in a wide range of capacitances, voltage ratings, and size, it is also popular as a general-purpose capacitor. In order to reduce the RF noise in a DC motor, ceramic capacitors can be used across the brushes of the motor.
For applications where high capacitances with no need of AC polarization(like a filtering circuit), electrolytic capacitors find their application. Other areas include switching mode power supply, smoothening of input and output in low pass filters. In circuits that have large amplitude and high-frequency signals, these cannot be used as these will have high ESR values.
These capacitors bear the advantage of having low leakage current along with high capacity and better stability and reliability. This makes them a good choice for sample and holds circuits, power supply filtering circuits of computers and cell phones. They are available in military versions that do not dry out with time and hence, act as a replacement for electrolytic capacitors in military applications.
These capacitors are popular among the power electronics enthusiast. They are used in almost all the power electronic devices, x-ray machines, phase shifters, and pulsed lasers. Even the switched power supply uses a film capacitor for power factor correction. The lower voltage variants find their roles as decoupling capacitors, filters, and A/D converters. They can be used as a part of conventional circuits as well to smooth out the voltage spikes.
Silver Mica Capacitors
In areas where low capacitance is required but with a need of high stability, such as in power RF circuits, silver Mica capacitors can be used. Its high breakdown voltage makes it suitable for high voltage applications. They exhibit low losses and therefore are popularly used in high frequency tuned circuits like oscillators.
This article has covered the most prominent types of capacitors. Apart from these, there are few other types like the trimmer capacitor, air capacitor, super capacitor, etc. Trimmer capacitor is a variable type and is not that commonly used. Supercapacitors are a combination of few electrolytic capacitors to form a capacitor of a higher value that exhibits the property of both capacitors and a battery bank.
With this, we have come to the end of the article. Hope you got a clear and crisp idea of the capacitor types and their various applications.
Thank you for reading!
Author: Cicy has a master's degree in electrical and electronics engineering with a specialization in Power Electronics. She is a freelance writer who writes to simplify complicated concepts in an understandable language.