Basic Concepts

An inductor is an electronic component that converts electrical energy into magnetic energy and stores it. The main characteristic of an inductor is its resistance to changes in current, i.e., when the current through the inductor changes, the inductor generates an induced electromotive force to impede the change in current. This resistance is expressed in terms of the inductance L in Henrys (H). Its basic structure is similar to that of a transformer, but with only one winding. The main function of an inductor is to impede changes in current; as current passes through the inductor, it tries to maintain current stability and stop sudden changes in current.

An inductor (coil) is one of the three major passive components in electronics, along with resistors and capacitors. They utilize the coil's unique response to electric current, and play an indispensable role in a variety of fields such as power supply circuits, signal circuits, and high-frequency circuits.

Basic Composition of Inductors

Inductors are mainly composed of the following parts:

Coils: As the core of the inductor, the coils are wound from copper or aluminum wires, and their turns, diameter and length have a direct impact on the performance of the inductor.

Core: Used to enhance the magnetic field strength of the inductor, it is usually made of magnetic materials such as ferrite, iron powder or nickel-zinc alloy. It enhances the inductance value of the inductor and helps to reduce energy loss.

Skeleton: Made of non-magnetic materials such as plastic or ceramic, the main function is to support the coils and maintain their shape, as well as provide insulation to prevent short circuits between coils.

Shielding: Some high-performance inductors employ a shield to minimize the effects of external electromagnetic interference and to prevent their own magnetic field from interfering with surrounding electronic equipment.

Termination: Responsible for connecting the inductor to the circuit, common forms include pins and pads.

Encapsulation: Inductors are sometimes encapsulated in plastic housings designed to provide physical protection, minimize electromagnetic radiation, and enhance mechanical strength.

Key Characteristics of Inductors

The core characteristic of an inductor is undoubtedly its inductance, measured in Henrys. In addition, there are a number of other key characteristics of interest, such as DC resistance and saturation current. Together, these characteristics determine an inductor's performance in a circuit and its range of applications.

Quality Factor (Q)

Quality factor is a measure of the energy loss of an inductor at a given frequency. Inductors with a high Q have a lower energy loss at that frequency, which is especially important in high frequency applications.

Self-Resonant Frequency (SRF)

SRF is the frequency at which an inductor's inductance resonates with its distributed capacitance in series. The SRF is a critical parameter for high frequency applications because it limits the effective operating frequency range of the inductor.

Rated Current

This is the maximum value of current that an inductor can carry continuously without significant temperature rise.

Operating Temperature Range

The temperature range in which an inductor can operate normally is known as the operating temperature range. The performance of different types of inductors may vary under temperature changes.

Core Material

Core materials have a significant impact on the performance of an inductor because different materials have different permeability, loss characteristics, and temperature stability. Common core materials include ferrite, iron powder and air.

Packaging

The packaging form of an inductor affects its physical size, mounting method, and heat dissipation characteristics. For example, surface mount technology (SMT) inductors are suitable for high-density circuit boards, while through-hole mount inductors are suitable for applications requiring higher mechanical strength.

Shielding

Some inductors are designed with a shielding layer designed to minimize the effects of electromagnetic interference (EMI).

Basic Principles of Inductor Operation

A) When a current is passed through a coil, a magnetic field is generated around the coil. When the current in the coil changes, the magnetic field around it changes accordingly.

B)Electrical energy is converted into magnetic energy and stored up.

C) DC will flow through it, but AC is less likely to flow through it, and the higher the frequency, the less likely it is to flow through it.

A and B are based on the characteristics of electromagnetic induction in inductors.

C is the characteristic of an inductor that “blocks AC and passes DC”. Here are some specific examples of how to utilize these characteristics.

When a current is passed through a coil, a magnetic field is generated around the coil. When the current in the coil changes, the magnetic field around the coil changes accordingly. ⇒ Principle of Transformer

Types of Inductors

Inductors can be classified into various types according to different classification criteria. According to the winding method, they can be classified as single-layer coils, multi-layer coils, honeycomb coils, etc.; according to the nature of the magnet conductor, they can be classified as air-core coils, ferrite coils, iron-core coils, copper-core coils, etc.; according to the nature of the work, they can be classified as antenna coils, oscillating coils, choke coils, filtering coils, trapping coils, deflection coils, etc.

Classification of Inductors

According to the structure, inductors can be classified into the following categories:

Air Core Inductors

: This type of inductor has no magnetic core, and is only wound by wire, and is suitable for high-frequency applications.

Iron Core Inductors

: These inductors use ferromagnetic materials such as ferrite and iron powder as the core and are suitable for low to medium frequency applications.

Air Core Inductors

: Air core inductors have excellent temperature stability and are suitable for high frequency applications.

Ferrite Core Inductors: Inductors with ferrite cores are particularly suitable for high-frequency applications, such as radio frequency and communications, due to their high saturation flux density.

Integrated Inductors

: Miniature inductors manufactured through integrated circuit technology, ideal for high density circuit boards.

Further categorized by application, we have:

Power Inductors

: They are mainly used in power conversion circuits, such as switching power supplies and inverters, and are capable of handling high currents.

Signal Inductors

: These inductors are used in signal processing circuits, such as filters and oscillators, and are ideally suited for high frequency signal processing.

Chokes

: Chokes are used in RF circuits to suppress high frequency noise or prevent high frequency signals from passing through.

Coupling Inductors

: They are used for coupling between circuits, such as connecting the primary and secondary coils of a transformer.

Common-mode inductors

: Common-mode inductors are used to suppress common-mode noise and are often used to protect power and data lines.

In addition, inductors can be categorized into surface mount inductors, through-hole mount inductors, wirewound inductors and printed circuit board inductors according to the different package forms.

Application Areas

Inductors have a wide range of applications in many fields:

Power supply circuits: used for filtering, voltage stabilization and electromagnetic interference suppression.

Signal circuits: used for signal processing and filtering to reduce noise interference.

High-frequency circuits: used in oscillators, filters and antennas, etc., to realize the transmission and conversion of signals.

The role of inductors

Inductors mainly play the following roles in circuits:

Filtering: Inductors can prevent high-frequency currents from passing through and have less effect on low-frequency currents, so they are commonly used in filtering circuits to filter out high-frequency noise.

Oscillation: Inductors and capacitors can be combined to form an oscillating circuit, generating oscillating signals of a specific frequency.

Delay: The resistance of inductors to changes in current makes it impossible for the current to change abruptly, thus producing a delaying effect.

Energy storage: Inductors store electrical energy and release it to maintain the current when the circuit is de-energized.

How to choose inductors and considerations

Select the right type of inductor and inductance according to the circuit requirements. Consider the operating current and voltage of the inductor to ensure that it is within the rated range. Pay attention to the inductor's quality factor Q. The higher the Q, the better the performance of the inductor. Consider the size and mounting of the inductor to fit the board layout.

An inductor, a type of electronic component, is designed to store magnetic field energy. It usually presents itself in the form of a winding of one or more turns of wire, known as a coil. When current flows through an inductor, a magnetic field is excited, thus accomplishing the storage of energy. The core characteristic of an inductor is its inductance, which is measured in Henrys, but is more commonly measured in millihenries and microhenries.