Capacitors can be seen in most of the electronic circuits. Basically, they are used for storing charges, signal smoothing purposes. In this tutorial, I am going to unlock the details of the capacitors. Here you will learn -

1. Capacitor definition.
2. Capacitor types.
3. Capacitor capacitance
4. Capacitor charging and discharging.
5. Capacitor working.
6. Capacitor formulas.
7. Capacitor application.
8. How to choose capacitors for circuits.

## What is Capacitor?

Capacitors are passive electronic components, that can store electric charges and used as a small battery in the circuits. In the form of a capacitor, it consists of two conducting parallel metal plates separated by an insulating material called the dielectric.

When the power source connected to the plates of the capacitor then one plate of the capacitor accumulates positive charges and another plate accumulates negative charges. As a result, a potential difference is produced in the system. So it acts like an energy source in the circuits.

The conductive metal plates of the capacitor can be either square, circular, rectangular, cylindrical and spherical shape depending on its application and voltage rating.

 Parallel metal plates, dielectric mediums, and two terminals of the capacitor

Symbol of the capacitor in the electronic circuits

To design an electronic circuit the symbol of the capacitor is used. In the electronic circuit different type of symbol is used to show the polarized, non-polarized and variable capacitor.

In the polarized capacitor, the positive and negative sign is used to show the polarity of the capacitor and in the non-polarized capacitor, there is no polarity to show in the symbol. In the variable capacitor, an arrow is shown in the symbol.

 Capacitor symbols

### Types of Capacitor

There are many types of capacitors used in electronic circuits. Mainly capacitors are divided into two common groups called the fixed capacitor and the variable capacitor.

In the fixed capacitor, the value of capacitance can not be changed. But in the variable capacitor, you can change the value of capacitance. In this tutorial, we will discuss some major types of capacitor

1. Electrolytic capacitor.
2. Ceramic capacitor.
3. Film capacitor.
4. Variable capacitor.

1. Electrolytic capacitor

Electrolytic capacitors are a type of capacitor that is polarized. They can only be placed one way round in the circuit. This type of capacitor is most popular for they are able to the high capacitance values typically above 1µF.

They do not operate well at high frequency and are typically not used for frequencies above 50 - 100 kHz. This type of capacitor is used for making the power supplies, decoupling, filtering, and audio coupling applications. There are many different types of electrolytic capacitors like aluminum, tantalum, niobium electrolytic capacitor.

 Electrolytic capacitor

2. Ceramic capacitor

In this capacitor, the ceramic dielectric is used, for using this ceramic dielectric the capacitor is said to the ceramic capacitor. In this capacitor, there is no polarity. This type of capacitor gives the many properties including a low loss factor and a reasonable level of stability.

Ceramic dielectrics do not give as high a level of capacitance per unit volume. the capacitance value range of ceramic capacitor from a few picofarads to 0.1µF. This type of capacitor is used for decoupling and in many applications from audio to RF.

 Ceramic capacitors

3. Film capacitor

The film capacitor additionally arrives in a combination of shapes and case styles. They are available in almost any value and voltages as high as 1500 volts.

The electrodes of the film capacitor may be metalized aluminum or zinc, applied on one or both sides of the plastic film. For this reason, the capacitor is called the film capacitor.

There are different types of film capacitor are used in electronic circuits like polystyrene film capacitor, polyester film capacitor, and metalized polyester film capacitor.

 Film capacitors

Polystyrene film capacitor

This type of capacitor is tubular in shape. The frequency range of this type of capacitor is to a few hundred kHz. This type of capacitor is used in high voltage.

 Polystyrene film capacitor

Polyester film capacitor

The polyester capacitor is based around the polyester dielectric like polyethylene terephthalate, PET. Polyester has a high dielectric constant and it is able to deliver a low-cost product and it is able to operate at high temperatures up to 125°c.

This type of capacitor is used for general coupling, decoupling application, dc blocking, filtering, and audio applications.

 Polyester film capacitor

4. Variable capacitor

A variable capacitor is made like the capacitance of this capacitor very either electrically or mechanically. There are many uses of these variable resistors such as for tuning in LC circuits of radio receivers, for many impedance matching in antennas, etc.

The main types of variable capacitors are Tuning capacitors and Trimmer capacitors.

 Variable capacitor

Tuning capacitor

Tuning capacitors are a popular type of variable capacitor. They contain a stator, a rotor, a frame of support the stator and a mica capacitor. The tuning capacitor is mostly used in LC circuits in radio receivers.

 Tuning capacitor

Trimmer capacitor

The trimmer capacitors are varied using a screwdriver. There are three leads of a trimmer capacitor, one connected to the stationary plate, one to rotary and the other one is common. The movable disc is a semi-circular shaped one.

 Trimmer capacitor

The capacitance of the capacitor

If we applied a voltage V across the two terminal of the capacitor then the amount of stored charge Q is directly proportional to the applied voltage i.e.

Q ∝ V or Q = CV

Where C is the capacitance of the capacitor.

Capacitance:

The capacitance of the capacitor is defined as if a capacitor has the capacitance of 1F then it stores 1C charge on the plates by applying 1V of voltage.

The capacitance of the capacitor is measured in the unit of coulomb/volt is called farad(F).

The other units to measure capacitance are statfarad, microfarad, picofarad, etc. The relation of these units are given below

1F = 9✕1011 statF, 1µF = 10-6F, 1nF = 10-9F, and 1pF = 10-12F

Measurement of the capacitance by using a multimeter

To measuring the capacitance of the capacitor at first to ensure that the capacitor is fully discharged. If the capacitor is chared then it may cause shock in your hand.

You can use a resistor (2kΩ) or screwdriver to discharge the capacitor. After discharging the capacitor you can measure it safely. Here we discuss how to measure polar and non-polar capacitors using the multimeter.

Measurement of the polar capacitor

At first set the meter on continuity mode or ohm range(Set it at lease1000ohm = 1kΩ). After setting the meter, connect the meter leads to the capacitor terminal. The red lead of the multimeter is connected to the big electrode and the black lead connected to the small electrode.

After connecting the leads of the multimeter it will show some number for a second(note the number) and then immediately it will return to the OL(Open Line) which means the capacitor is good condition. If there is no change, then the capacitor is dead.

Measurement of the non-polar capacitor

In the non-polar capacitor, there is no polarity so you can connect the leads of the multimeter to any electrodes of the capacitor. But in this capacitor, if there is no reading in the multimeter so the capacitor is in good condition and if the multimeter is showing some values then the capacitor is dead.

### Capacitor charging and discharging

Charging of the capacitor

Initially charge on the plates of the capacitor is zero. When the capacitor is connected to a DC voltage source then current flows through the capacitor and charge being accumulated on the plates of the capacitor. This accumulation of charge is called the charging of the capacitor.

Discharging of the capacitor

After charging the capacitor when removed the power supply from the capacitor and connect an external device like a led bulb in series with the charged capacitor.

Then the capacitor acts as a voltage source and current flows through the device or in the circuits until the voltage on the capacitor becomes zero again. This is called the discharging of the capacitor.

 Charging and discharging graph

### Capacitor working

If we connect a power source or a battery to the metal plates of the capacitor, a current will flows or the electrons from the plate connected to the positive lead of the battery will start moving to the plate connected to the negative lead of the battery.

However, because of the dielectric between the plates, the electrons won't be able to pass through the capacitor so they will start accumulating on the plates.

The first plate has developed a net negative charge, and the second plate has developed an equal net positive charge, creating an electric field with an attractive force between them which holds the charge of the capacitor. In the capacitor, the dielectric can increase the capacitance of the capacitor.

A dielectric contains molecules that are polar which means that they can change their orientation based on the charges on the two plates. So the molecules align themselves with the electric field in such a way enabling more electrons to be attracted to the negative plate, while repelling more electron out of the positive plate.

So once the capacitor is fully charged, if we remove the battery, it will hold the electric charge for a long time, acting as an energy source.

### Capacitor formulas

To design circuits by capacitor some formulas are used. These formulas are given below

1. The basic capacitance formula

The basic formula of the capacitor is

Where C = Capacitance of the capacitor in farad.
Q = Charge of the capacitor in coulomb.
V = Applied voltage in volt.

2. The capacitance of the capacitor in the series combination

If N number of capacitors is connected in series then the formula for the equivalent capacitance is

3. The capacitance of the capacitor in the parallel combination

If N number of capacitors is connected in parallel then the formula for the equivalent capacitor is

4. The formula for capacitive reactance

The capacitive reactance(Xc) of the capacitor changes with respect to the applied frequency(f) and the formula used for it is

Where f = frequency in Hertz.

5. The formula for the energy stored in a capacitor

The energy stored in a capacitor can be calculated from the formula

Where V = voltage in volt.

6. The formula for the self-resonant frequency

The formula for the self-resonant frequency is

Where L = Inductance in Henry

Some other formulas used for making the capacitor. These formulae are given below

7. The capacitance of a parallel plate capacitor

The formula for the capacitance of a parallel plate capacitor is

Where A = Area of each plate.
d = Separation between the two plates.
𝜖 = Permittivity of the medium.

8. The capacitance of a spherical capacitor

The formula for the capacitance of a spherical capacitor is

Where a = Radius of the inner sphere.
b = Radius of the outer sphere.
𝜖 = Permittivity of the medium.

9. The capacitance of a cylindrical capacitor

The formula for the capacitance of a cylindrical capacitor is

Where a = Radius of the inner sphere.
b = Radius of the outer sphere.
𝜖 = Permittivity of the medium.

### Application of the capacitor

In the electronic circuits, the capacitor is used in many different ways. Capacitors used for coupling, decoupling or smoothing or filtering and as an energy-storing component.

1. Use of the capacitor as coupling

In electronics circuits, the capacitor is used for AC coupling.

AC coupling

The AC coupling consists of using a capacitor to filter out the DC signal from a signal with both AC and DC. In the amplifier when we amplify some signal like audio then we just want a pure AC signal to amplify it.

But in a signal with both AC and DC may cause distortion in the output signal so we need AC coupling. In the arrangement of the capacitor, the capacitor must be in series with the signal. For this reason, the capacitor is used in RC coupled amplifier.

 AC coupling

2. Use of the capacitor as decoupling

A decoupling capacitor acts as a local electrical energy reservoir. Capacitors, like batteries, need time to charge and discharge. When used as decoupling capacitors, they oppose quick changes of voltage.

If the input voltage suddenly drops, the capacitor provides sufficient energy to keep the voltage stable.

 Capacitor as filter

Similarly, if there is a voltage spike, the capacitor absorbs the excess energy. For this reason, the capacitor is used as a voltage smoothing component. In the arrangement of the capacitor, the capacitor must be in parallel with the signal.

In the making of variable power supply after rectification, some AC component is coming with the signal, to removing this AC component from the signal we needed the capacitor. In this process, we use L-section, T-section and ℼ-section filters.

How to choose capacitors for circuits

When you design circuits using capacitor then mainly you need to look at two values of the capacitor that is the voltage rating and the capacitance( Both are written on the most capacitor).

For example, if you are going to charge a capacitor with 24V, you need to make sure your capacitor will support that voltage; so you will need a capacitor for at least  25V( Plus error margin).

The capacity will depend on how much you need in each instance, how much time it will take the capacitor to charge/discharge, etc. When you need different values you can combine two of those.

For example, two 100µF capacitors in series make a 50µF capacitor and two 100µF capacitors in parallel make a 200µF capacitor. This way you can make any value you need.

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