What is magnetism, What is an Inductor?

This article explains the basic definition of What is magnetism, What an inductor is? as a passive electronic component, and its main application and technologies.

Inductors, also called coils or sometimes choke, are important passive components along with resistors (R) and capacitors (C). Coils usually refer to wound conductive wires, and among them, those with a single wound wire have, in recent years, mainly been referred to as inductors. If it is intended for low-frequency applications, it usually has a core with a closed magnetic circuit that consists of laminated iron (power frequency) or a ferrite toroid (above 1kHz).

Inductance is usually represented by the symbol “L.” Although this L is said to come from Lenz of “Lenz’s Law” related to electromagnetic induction, there also appear to be various theories.

The basic structure of an inductor consists of a conductive wire wound in a coil shape and can convert electric energy to magnetic energy and store it inside the inductor. The inductor’s inductance determines the storable amount of magnetic energy and is measured in Henry (H).

Inductors slow down current surges or spikes by temporarily storing energy in an electromagnetic field and then releasing it back into the circuit. In hydrodynamic analogy (Fig.1.) inductor works as a large flywheel that offers resistance to every change in the flow/current. Anyone who has turned a bike upside down and turned the wheel up to speed knows there is a certain resistance to start. But, as soon as you have gained speed on the wheel, it requires very little force to maintain its velocity. If you then want to brake, it requires considerable force.

Figure 1. inductor as “flywheel” in hydrodynamic analogy

Inductor Applications

Inductors are primarily used in electrical power and electronic devices for these major purposes:

1. Choking, blocking, attenuating, or filtering/smoothing high-frequency noise in electrical circuits
2. Storing and transferring energy in power converters (dc-dc or ac-dc)
3. Creating tuned oscillators or LC (inductor/capacitor) “tank” circuits
4. Impedance matching
5. Inductors are also employed in electrical circuits to reduce EMI by attenuating high-frequency noise to meet EMC emission and immunity requirements.

What is a choke?

Primarily inductors consist of a coil. If we insert a core of magnetic material the inductive properties of the coil will increase. Such coils are then called chokes. When we draw current through a choke, electric currents are induced in the magnetic material that tries to create a counteracting magnetic field. These currents are undesired both for that reason and because they create heat losses.

Homogeneous magnetic bodies are excluded; the induced current would be too high. Instead, mutually isolated ribbons are used or a powder technology where the binder material between the magnetic granules limits the induced current by their resistivity.

Connection

Inductors may be connected in series or in parallel; inductance then complies with the same laws as resistors.

Connection in series

series inductance connection equation [1]

Connection in parallel
For loss-free coils and coils with the same angle of phase, applies

parallel inductance equation [2]

Inductive Reactance

Just like a capacitor, the inductor presses a reactance on an AC circuit. To divide this reactance from that of a capacitor, it is called inductive reactance, XL. The quantity is expressed in ohms and complies with the formula:

Basic Structure of Inductors and Inductance

The most basic inductors consist of a conductive wire wound in a coil shape, with both ends of the conductive wire as external terminals. In recent years, most inductors include a core, around which a conductive wire is a wound.

Figure 2. basic structure of an inductor (left) and its practical examples (right)

Figure 3. Equivalent circuit of the inductor.

At lower frequencies the capacitance plays a minor part, but as frequency rises we reach the self resonant frequency, fr, (sometimes abbreviated SRF) where the impedance curve arrives at a peak and then turns downwards and becomes capacitive.

inductor self-resonance frequency equation [4]

The measurement frequency (test frequency) is at a sufficient distance from fr and always is stated for a respective inductor.

Electric vs Magnetic Field

Comparing magnetic fields with electrical fields, analogies emerge between certain parameters. These are summarized in Table 1.:

Tab. 1. Analogies between magnetic and electric fields

Resources: EPCI Blog