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What Is an Inductor?

An inductor is one of the three fundamental passive electronic components, alongside resistors and capacitors. Unlike resistors, which dissipate energy as heat, or capacitors, which store energy in an electric field, inductors store energy in a magnetic field.

An inductor is typically constructed by winding a conductor around a magnetic core. When current flows through the winding, a magnetic field is created. Energy is stored within this magnetic field and can later be released back into the circuit.

Inductors are found in virtually every modern power electronics system, including:

• DC-DC converters
• AC-DC power supplies
• Battery chargers
• Electric vehicles
• Solar inverters
• Motor drives
• Telecommunications equipment
• Aerospace and defense electronics

Without inductors, modern power conversion would be significantly less efficient and often impossible.

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Definition of Inductance

This definition ties everything in this book together. It is the main unit of an inductor.

Main Formula:

Explanation

Where:

• L = Inductance (H)
• N = Number of turns
• Φ = Magnetic flux (Webers)
• I = Current (A)

This equation tells us that inductance is a measure of how effectively current produces magnetic flux.

Increasing:

• Number of turns
• Core permeability
• Core cross-sectional area

generally increases inductance.

Increasing air gap generally reduces inductance.

This relationship forms the foundation of magnetic component design and is the reason that core geometry, materials, and winding arrangements have such a large impact on performance.

Why Inductors Matter

Modern electronic systems require power to be converted, filtered, and regulated.

Inductors perform several critical functions:

Energy Storage

Switching power supplies transfer energy through magnetic fields. The inductor acts as a temporary energy reservoir, smoothing the flow of power between the source and the load.

The most important equation is:

Explanation

Where:

• E = Stored energy (Joules)
• L = Inductance (Henrys)
• I = Current (Amperes)

This equation explains why inductors are used in switching power supplies. As current increases, energy is stored in the magnetic field surrounding the winding. When the current decreases, that stored energy is released back into the circuit.

Notice that energy increases with the square of current. Doubling the current stores four times as much energy.

Current Smoothing

Current flowing through an inductor cannot change instantaneously. This property makes inductors ideal for reducing ripple current and creating stable power rails.

The key relationship is:

Explanation

Where:

• V = Voltage across the inductor
• L = Inductance
• dI/dt = Rate of current change

This is arguably the most important equation in all of magnetic design.

It tells us that an inductor resists changes in current.

A large inductance requires a larger voltage to rapidly change current.

This property is what allows inductors to smooth ripple current in buck converters, boost converters, and filters.

Noise Reduction

Inductors can block high-frequency noise while allowing DC current to pass. This characteristic is widely used in EMI filters and signal conditioning circuits.

The most useful equation here is the inductive reactance equation:

Explanation

Where:

• XL = Inductive reactance (Ohms)
• f = Frequency (Hz)
• L = Inductance (H)

This equation explains why inductors block high-frequency noise.

As frequency increases:

• Reactance increases
• Impedance increases
• Noise current decreases

For DC:

f = 0

so:

XL = 0

which means the inductor passes DC current while impeding high-frequency signals.

This behavior makes inductors useful in:

• EMI filters
• Input filters
• Output filters
• Common-mode chokes

Energy Transfer

In transformers and coupled inductors, magnetic fields transfer energy between isolated circuits.

For transformers and coupled inductors, I’d introduce the classic transformer relationship:

Explanation

Where:

• Vp = Primary voltage
• Vs = Secondary voltage
• Np = Primary turns
• Ns = Secondary turns

This equation shows how energy can be transferred from one winding to another through a magnetic field.

The magnetic core guides flux generated by the primary winding, which induces voltage in the secondary winding.

This principle is used in:

• Flyback transformers
• Forward transformers
• Push-pull converters
• Full-bridge converters
• Grid power transformers

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Where You Encounter Inductors

Many engineers use inductors every day without realizing it.

Examples include:

Laptop Power Supplies

Every laptop charger contains magnetic components that convert high-voltage AC power into low-voltage DC power.

Electric Vehicles

Modern EVs contain dozens of magnetic components responsible for charging, propulsion, and auxiliary systems.

Smartphones

Compact high-frequency inductors regulate battery voltage and support wireless charging systems.

Industrial Automation

Motor drives and power conversion systems rely heavily on magnetic energy storage.

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The Basic Structure of an Inductor

Most inductors consist of two primary elements:

Winding

The winding is the conductor carrying current.

Common winding materials include:

• Copper
• Silver-plated copper
• Litz wire
• Copper foil

Magnetic Core

The core guides magnetic flux and improves energy storage capability.

Common core materials include:

• Ferrite
• Powdered Iron
• Sendust
• Nanocrystalline
• Amorphous alloys

Core material selection significantly influences performance, losses, temperature rise, and cost.

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The Role of Magnetism

Whenever electrical current flows through a conductor, a magnetic field is generated.

By wrapping the conductor into a coil, these magnetic fields reinforce one another, creating a stronger overall magnetic field.

This magnetic field stores energy according to the amount of current flowing through the winding.

The ability of a component to store magnetic energy is measured as inductance.

Inductance is measured in:

• Henrys (H)
• Millihenrys (mH)
• Microhenrys (µH)
• Nanohenrys (nH)

Most power electronics inductors operate within the microhenry range.

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Why Inductor Design Is Difficult

Many beginners assume that designing an inductor simply means selecting a core and winding wire around it.

In reality, successful designs require balancing numerous competing requirements:

• Inductance
• Saturation current
• Temperature rise
• Copper loss
• Core loss
• Cost
• Size
• Manufacturability
• Reliability

Improving one parameter often worsens another.

A smaller design may run hotter.

A cooler design may cost more.

A lower-loss design may require a larger core.

Engineering is ultimately the process of making informed tradeoffs.

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How This Guide Is Organized

This guide walks through the complete design process used by practicing engineers.

Topics include:

Fundamentals

• Inductance
• Magnetic fields
• Energy storage

Core Selection

• Core materials
• Core families
• Air gaps
• Saturation

Winding Design

• Wire selection
• Current density
• Fill factor

Performance Optimization

• Loss calculations
• Thermal analysis
• Efficiency improvements

Practical Design

• Real-world examples
• Manufacturing considerations
• Automated design tools

By the end of this guide, readers will understand not only how inductors work, but how professional engineers design magnetic components for production applications.

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What You’ve Learned

In this chapter you learned:

• What an inductor is
• How inductors store energy
• Why inductors are important
• Where inductors are used
• The basic structure of magnetic components
• Why magnetic design requires engineering tradeoffs

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Continue Reading

➡ Chapter 02: Understanding Inductance

In the next chapter we will examine inductance itself, how it is measured, what factors influence it, and why it forms the foundation of all magnetic component design

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