Module 3 − Inductors

Introduction

Inductors are components that are simple in their construction, consisting of coils of insulated copper wire wound around a former that will have some type of core at its centre. This core might be a metal such as iron that can be easily magnetised; or in high frequency inductors, it will more likely to be just air.

Inductors depend for their action on the magnetic field that is present around any conductor when it is carrying a current. If the wire coil is wound around a core made of a material that is easily magnetised, such as iron, then the magnetic field around the coil is concentrated within the core; this greatly increases the efficiency of the inductor.

 

Inductors in AC Circuits.

Inductors are extensively used in alternating current (AC) applications such as radio, TV and communications equipment, and in these systems, how inductors react to AC signals of different frequencies is very useful.

Chokes.

Another name used for an inductor is a "Choke". Inductors, being just coils of copper wire, will allow DC to pass easily, but when AC is applied, inductors create an opposition to current flow that increases, as the frequency of the alternating current increases. Therefore AC is prevented from flowing or is "Choked off" while DC is allowed to pass. This effect is used in power supply circuits where the public AC mains (line) supply has to be converted to a DC supply suitable for powering electronic circuits.

Energy Storage.

The magnetic field around an inductor is a store of energy (from the current that caused the field). When the current is turned off, the energy stored in the magnetic field is returned to the inductor, causing a current to flow in the opposite direction. This can produce a pulse of high voltage across the coil. The pulse of energy can be a problem in some electronic circuits and can easily destroy other components if not properly controlled, but it can also be extremely useful; such high voltage pulses produced by an inductor are used to create the spark that ignites the petrol in automobile engines.

Inductors of many types.

The physical size of inductors varies greatly, depending on the power being handled, and on the frequency of the AC being used; from huge power transformers in power stations and the electricity supply grid, to tiny inductors in radio equipment consisting of a few turns of wire and only a few millimetres across.