An inductor is nothing but a coil of a wire wound around an iron or some kind of magnetic material. The function of the material in which the wire is wound around is to increase the magnitude of the magnetic field, thus increasing the storage capacity of the inductor. An inductor has a symbol of a coil of wire because it is really nothing but a coil.
Inductors are mostly used in Alternating current (AC) electronic equipment. Like a capacitor, the inductor dissipates negligible energy as heat.
Inductor symbols
Picture of a variety of inductors
Surface-mounted inductors(SMD) images
An inductor resists the change in alternating current flow. An inductor is a frequency sensitive component, if a DC source is applied to an inductor, the inductor will allow current to pass through it but when an Alternating current is applied, it will resist the current flow, the resistance is related to the frequency of the applied AC signal, if it is of high value the AC current would get completely blocked.
ω = 2πf. f is the frequency of the applied AC signal L = is the Inductance of the inductor.
Inductance is the characteristics of an inductor to generate a magnetic field for a given current. L is the symbol of an inductance it has a unit H, which is henry, inductors have values that typically range from 1 µH to 1H. Inductance can be defined mathematically as:
The relationship between the voltage across an inductor and the current flowing through it is given as:
This back EMF tends to oppose the increasing current in the coil of the inductor.
Effect of a DC to an inductor
When a DC is applied to an inductor, the current will pass through the inductor and the inductor will have a magnetic field around it. This is called the electromagnet. When the DC source is removed the magnetic field dies.
Effect of an AC to an inductor
When an AC is applied to an inductor, a voltage known as a back EMF will be developed by the inductor to resist the changing current, depending on the value of the inductor, small current pass through, if the varying AC signal has a very high frequency the inductor will block the current from passing through. The resistance of an inductor to the flow of AC signal is termed reactance.
Energy stored by an inductor
the energy stored by an inductor is given as:
In the figure below the inductor blocked AC but allows DC to pass-through.
Inductors come in many shapes. Some inductors are designed for a specific purpose, like Antenna coil which is used in a high-frequency application.
There are Air core inductors that have air as their core, these inductors have low inductance. There are Toroidal shaped inductors that have a donut shape, these inductors have a high value of inductance.
Inductors that are purposely used to limit AC but allows DC to pass are called chokes, some choke inductors look like a color-coded resistor.
The Transformer
When a coil of a wire is connected to an AC power and another coil of wire is brought near it, a voltage is induced in the second coil, the magnitude of the induced voltage depends on the number of turns of the coil in the second coil. This is called mutual inductance. This phenomenon (mutual inductance) is very important.
An alternating current of whatever value can be raised or lowered. DC voltage cannot be transformed by a transformer because mutual inductance doesn’t occur at 0 frequency.
A transformer is an electrical device that raises or lowers the voltage supplied to it.
The number of turns of coil of a transformer is proportional to the voltage induced in the coil. There is a very useful formula which is handy when winding a custom transformer. Conversely, the number of turns is inversely proportional to the current in the coil, the higher the turns(Voltage) the lower the current.
A transformer has an input terminal and an output terminal, the output terminal may contain many independent coils, that have different voltage. The input coil is called a primary coil and the output coil is called a secondary coil.
A transformer that transforms its input voltage to a higher voltage than the input is called a step-up transformer
A transformer that transforms its input voltage to a lower voltage than the input is called a step-down transformer.
A transformer that gives an output voltage of the same value as the input ( does not step-up or step-down ) is called an isolation transformer.
Transformer voltage, current, and the number of turns relationships.
There are many types of transformers, the most common ones are listed below:
Common transformers:
Center-tap transformer
This transformer has a tap in its primary or secondary coil, tapping on the secondary winding gives the transformer two or more output voltages.
Multiple winding transformer
This special transformer has multiple winding in its secondary coil which are electrically isolated from each other, each coil has its voltage based on its number of turns.
Auto-transformer
This transformer has a single coil with a tap at the center, that makes it primary and secondary.
Isolation transformer
This kind of transformer has an equal number of turns in both primary and secondary coils. It is used to isolate a circuit from another since the two circuits are only coupled magnetically not electrically and there is no way a DC can pass from one circuit to another.
A transformer can be used for impedance matching, to connected different devices that have entirely different impedance, eg high impedance amplifier and low impedance loudspeaker.
When two or more inductors are connected end to end their final inductance could b calculated as.
Inductors in parallel
When two or more inductors are connected side by side there final inductance could be calculated as
RL circuits
Current growth in an RL circuit
When a resistor and an inductor are connected in series and connected to a voltage source. The current in the inductor will not just rise to the final value, the current begins rising steadily based on the inductance of the inductor or the value of the resistor in series. The time that takes the current in the inductor to reach its final value depends on the inductor and the resistor.
Current decay in an RL circuit
From the above experiment when the voltage source is removed and the resistor and the inductor are connected as in the figure below. The current inside the inductor will not decay instantaneously but it decays smoothly to zero. The time that takes the current in the inductor to decay to zero depends on the value of the inductor and the resistor.
Mathematically
LC circuit
If a capacitor and an inductor are connected as in the figure below. There will be an energy transfer between the capacitor and the inductor. This arrangement creates an electrical oscillation.
Assume initially the capacitor is fully charged and the inductor is uncharged. When connected the capacitor starts discharging through the inductor smoothly until the capacitor becomes fully uncharged, at this moment the inductor becomes fully charged and the capacitor is uncharged, the moment the inductor becomes fully charged it starts discharging through the uncharged capacitor after a short while the inductor becomes fully uncharged while the capacitor becomes fully charged this whole process keeps repeating until the energy becomes damped.
The oscillation dies down over time due to energy lost as heat in the coil of the inductor and in the connecting wires.
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