Working of an Inductor

Working Of Inductors

I have explained many articles on various electronic circuits, which shows applications of Inductors. But I have not explained the proper working of inductor till now. Inductors are used in many analog circuits and are also used along with capacitors for forming filter circuits and thus signal processing. They are also used in Switched Mode Power Supplies (SMPS), oscillators, transmitters, receivers, voltage regulators and also for over voltage protection.

What is an Inductor?

An Inductor, also known as a reactor is simply a coil of wire, which has many electrical properties when subjected to a magnetic field. When an electric current is passed through it, a magnetic field is created. This magnetic field helps to store the electric current for a short time, even if the supply is removed. When the magnetic field around the coil collapses, the electric current also falls off. Actually, the inductor basics are based on the Faradays Laws of Induction.

The working of an inductor can be further explained with the help of an example.

Inductor Symbol

Simple Inductor Circuit

Consider a basic circuit consisting of a battery and a bulb. For this connection, there are only two outputs.  One is the bulb glow when the battery is connected and the other is the bulb off position when the connection is terminated. The circuit is shown below.

Now consider the same circuit with a coil of wire around the iron bar and the ends of the coil given across the bulb. Also connect a switch as shown in the diagram below.

When the switch is closed, instead of the bulb to glow as a normal dim light, it makes a transition from bright to dim. As soon as the switch is opened the bulb makes a transition from very bright to off. As you can see, this is very different from the earlier explained connection. This strange behaviour is because of the inductor. When the switch is closed, the current starts flowing from the battery to the coil. Thus the coil starts to make a magnetic field. During this time, the coil inhibits the flow of current. As soon as the magnetic field is built, there is only normal flow of current through the wire. That is why the bulb makes a transition from bright to dim. When the switch is opened, there will be a magnetic field around the coil for a short period, which  keeps the current in the coil steady. As soon as the field dies, the current also stops. That is why there is a sudden transition from bright light to off.

Thus the main two important notes of Inductors can be concluded as

• Inductors are used to store energy in its available magnetic field.

• An inductor resists any change in the amount of current flowing through it.

The value of an Inductor is called Inductance and is measured in Henries. It is actually the SI unit of Inductance.

1 Henry = 1 Weber/ 1 Ampere

Capacity of an Inductor

There are mainly four factors which depends on the capacity of an Inductor. They are

• Inductance increases with the increase in the number of coils and decreases with reduced number of coils.
• Inductance increases with more area in the cross-section of the coil and reduces with lesser area of cross-section.
• Inductance increases with the overlapping or narrowing of coils and decreases vice-versa.
• Inductance depends on the material that the coils are wrapped around (the core).

How to make an Inductor?

To make an inductor we mainly need

A coil of conducting material (mostly copper).

A core (air, ferromagnteic materials, ferrimagnetic materials)

The coil has to be wrapped around the core. The inductance highly depends on the core. When the magnetic field increases, the inductance also increases. For this to happen, the core material must have very high permeability than air. For transformers, low frequency inductors are used. For their construction, the cores are laminated with electrical steel so as to prevent eddy currents. Soft ferrites are widely used for cores above audio frequencies, since they don’t cause the large energy losses at high frequencies that ordinary iron alloys do. Inductances with small inductance can be easily etched on a PCB by laying out the trace in a spiral pattern. They can also be made on IC’s using the same process as that for transistors.

To know more about the making of an Inductor and to find the correct inductance value, please click at the link below.

TAKE A LOOK : HOW TO MAKE AN AIR-CORE INDUCTOR

Inductor Core Coils

There are many types of coils used in an Inductor. Some of them are

Air Core Coil

All coils that are wound in non-magnetic materials like plastic, ceramic and those coils that have air inside their windings are called Air core coils. Though they have very low inductance values they can be used for high frequency applications, because they do not possess any core losses because of the non-existence of ferromagnetic materials. For high frequencies they must be made on a single layer of winding. Air core coils are sometimes subjected to microphony, which causes a variation in the inductance value. This can be reduced if they are firmly supported on a plastic or ceramic base.

Ferromagnetic Core Coil

The core is made of ferromagnetic materials or ferrimagnetic materials. Though this greatly helps in increasing the inductance, there are also some losses that are associated with it. By using materials like iron as core, the magnetic permeability increases to a high extent, thus increasing the magnetic field.

The loss in this type of a material is

Core Losses

In a ferromagnetic inductor, when current is passed at a time, a time varying magnetic field is produced in its core causing energy loss in the form of heat. This is associated t0 three other parameters. They are eddy current loss, non-linearity and hysteresis loss.