One Passive component that always remains obscure is the inductors. These are the coil like structures that you find in most power electronic circuits and it is because of its properties your transformers work. The reason why many people do not understand Inductors is that they not only alter electric field but also the magnetic field around it. In this tutorial let us understand the basics of an Inductor and demystify it so that we will know how and when to use one in our applications.
What is an Inductor?
The inductor is perhaps the simplest of all electronic components, constructed much like a resistor – a simple length of wire that is coiled up. However, here, resistance is not the property we’re looking for. It is something that happens because of the shape of the wire – a coil – it creates a magnetic field when a current is passed through it. This induced magnetic field gives this bit of wire some interesting electrical properties, especially inductance – which gives these parts their name.
Working of an Inductor
An inductor, as already mentioned, is just a coil of wire.
Before we go into anything else, let’s ask the question, why a coil?
As we already know, any current carrying conductor generates a magnetic field in the following fashion:
However, if you plug in the value of the current into the formulas, then you’ll realize that the magnetic field produced is tiny – almost negligible, unless the currents are impossibly high, in the order of mega-amps.
So in order to increase the magnetic field created by a specific length of wire, we wrap it into the form of a coil. This increases the magnetic field, like so:
This shape is also called a solenoid.
When a voltage is applied across the terminals of an inductor, the current flowing creates a magnetic field. This magnetic field again creates an induced current in the inductor of opposite polarity, according to Lenz’s law. The currents do not cancel each other out – rather, the induced current actively tries to oppose the incoming current due to the voltage across the inductor. The overall result of this battle is that the current through an inductor cannot change rapidly – it is always a linear slope.
Different Types of Inductors
Now the µ in the above equation has some interesting implications. It suggests that the magnetic field inside the inductor can be manipulated. Like mentioned above, sometimes the magnetic field created even by a solenoid falls short of requirements sometimes. That is why in almost all cases you find inductors formed around a core material.
Cores are materials that support the creation of a magnetic field. They are generally made of iron and its compounds, such as ferrite (which is an oxide of iron). You can get a greater magnetic field using a core than without one.
1. AIR CORE INDUCTORS:
Like the name suggests, this kind of inductor has no core – the core material is air! Since air has a relatively low permeability, the inductance of air core inductors is quite low – rarely above 5uH. Since they have a low inductance, the rate of current rise is quite fast for an applied voltage and that makes them capable of handling high frequencies. They are mostly used in RF circuits.
2. IRON CORE INDUCTORS
Iron is perhaps the most recognizable magnetic material, which makes it an ideal choice for inductors. These take the form of iron-core inductors. They are usually used for low frequency line filtering, since they can be rather beefy and have large inductances. They are also used in audio equipment.
3. FERRITE CORE INDUCTORS
Ferrite is just a powder of oxides of iron. This powder is mixed with an epoxy resin and molded to form cores around which wires can be wound. Ferrite core inductors are easily the most recognizable because of their dull grey-black colour. They also are very brittle and break easily. They are the most widely used kinds of inductors, since the permeability can be finely controlled by controlling the ratio of ferrite to epoxy in the mix.
Symbols for Inductors
Like many other electronic components, the symbol for an inductor is a simplified pictogram of what it actually looks like:
The lines near the symbol represent the core material.
Inductors are primarily used in electrical power and electronic devices for these major purposes:
- Choking, blocking, attenuating, or filtering/smoothing high frequency noise in electrical circuits
- Storing and transferring energy in power converters (dc-dc or ac-dc)
- Creating tuned oscillators or LC (inductor / capacitor) “tank” circuits
- Impedance matching