Fixed Inductors

An inductor—also referred to as a coil, choke, or reactor—is a passive, two-terminal electrical component that stores energy in a magnetic field when current flows through it. As the current changes, the magnetic field also changes, inducing a voltage that opposes the change in current. This phenomenon is described by Lenz’s Law. The unit of inductance is the henry (H), named after American scientist Joseph Henry.

Inductors come in various mounting styles, including surface mount, through-hole, and chassis-mounted configurations, depending on the application’s size, current, and mechanical requirements.

Construction and Operation
An inductor typically consists of an insulated wire wound into a coil around a core material, such as air, iron, or ferrite. The core enhances the magnetic field and, in turn, increases inductance. The inductance value determines how much energy the inductor can store for a given current.

Types of Inductors
Fixed Inductors
Fixed inductors have a constant inductance value that cannot be adjusted. They come in several core types, including:

Air-core: Lightweight and free of core losses, suitable for high-frequency applications.

Iron-core: Offers higher inductance but is bulkier and more lossy at high frequencies.

Ferrite-core: Provides a good balance of size, cost, and performance for many general-purpose applications.

Fixed inductors are compact, reliable, and ideal for circuits requiring consistent inductance, such as power supplies, filters, and RF applications.

Variable Inductors
Variable inductors allow manual adjustment of inductance, typically by moving a ferrite core in and out of the coil. Inserting the core increases permeability and inductance; withdrawing it decreases both.

Variable inductors are commonly used in tuned circuits, such as radios and oscillators, where precise frequency control is essential. They are also useful in applications requiring fine calibration where fixed inductors may not offer sufficient precision.