Inductance and its classification
    Inductance is a property of a circuit element that reflects the ability of a conductor or coil to block changes in current. Inductance exists because a magnetic field is generated around the conductor when the current changes, and when the current changes, this magnetic field also changes, resulting in a reverse electromotive force (EMF) that impedes the change in the current.

‌I、The basic concept of inductance
    1,Definition: Inductance is a measure of the ability of a circuit element (usually a coil) to resist a change in current, measured in Henry (H). It represents the proportional relationship between the induced voltage generated by the element and the rate of current change when the current changes.
    2,Formula: The definition of inductance L can be expressed by Faraday's law of electromagnetic induction:
       VL=?LdtdI
       Among them:
          •VL is the induced voltage on the inductor
          •L is for inductance
          •dtdI is the rate of change of current
    The unit of inductance is Henry (H), 1 Henry indicates that when the current change rate is 1 ampere per second, the inductor generates 1 volt of induced voltage.
    3,How it works: When an electric current passes through a conductor, it creates a magnetic field. If the current changes, so does the magnetic field. According to Faraday's law of electromagnetic induction, when the magnetic field changes, a voltage is induced in the conductor, and this induced voltage will resist the current change, thus achieving the "inertia" effect of the current.

II、Classification of inductors
    Inductors can be divided into different types according to different standards, and common classification methods include:
      1,Classification by structure:
          •Air inductance: The air inductance is the part of the coil without magnetic materials, and the magnetic field is completely provided by the air. The inductance value of air inductors is relatively small, but it has high stability and less loss, which is suitable for high frequency circuits.
          •Iron core inductors: Iron core inductors use iron or other magnetic materials inside the coil to enhance the strength of the magnetic field, usually a higher inductance value, suitable for low-frequency circuit applications, such as power filters and transformers.
          •Iron powder inductors: Iron powder inductors use iron powder as a magnetic core material, this inductor has better saturation resistance and small temperature coefficient. It is often used in medium-frequency circuits, especially in power supplies and high-frequency circuits.
          •Aluminum inductors: Aluminum inductors are often used where lighter inductors are required. The aluminum material is lighter than the iron core, but the inductance value is correspondingly lower.
    2,Classification by use: 
          •Conventional inductors: This type of inductor is commonly found in power supply circuits, filters, oscillators and other applications, and is usually used in low-frequency circuits.
          •High frequency inductors: Used in radio frequency (RF) circuits, high frequency filtering, wireless communication and other high frequency applications. They usually have low resistance and low loss.
          •Inductor: This inductor is wound by a coil and is suitable for high current applications, such as motors, transformers and electromagnetic relays.
          •Adjustable inductance: The inductance value can be adjusted by adjusting the position of the iron core or the number of turns of the coil, commonly found in some tuned circuits.
    3,Classification by inductance value:
          •Low inductance: Usually the inductance value is small, used for high-frequency signal filtering, noise suppression, etc.
          •High inductance: The inductance value is large, usually used in lower frequency circuits, such as power filter, transformer, etc.
    4,Classification by package type:
          •Surface Mount inductors (SMD inductors) : These inductors are small and suitable for use on the circuit boards of modern small electronic devices.
          •Socket inductor: This inductor is large, usually need to be inserted into the hole of the circuit board, suitable for large power circuit.

III、Application of inductance
    Filters: Inductors are often used in filtering circuits, especially in power supply circuits, using inductors to prevent high-frequency noise signals from passing through, allowing only low-frequency signals to pass through.
    Power management: In switching power supplies, converters, and power adapters, inductors are used for energy storage and conversion.
    Signal processing: In wireless communication, inductors are used to filter out unwanted high-frequency noise and maintain the quality of the signal.
    Oscillators and tuning circuits: Inductors are used together with capacitors to form LC oscillators and tuning circuits.
    Electric motors and transformers: In electric motors and transformers, inductors are used to convert electrical energy.

IV、Inductance selection
    When choosing an inductor, there are several key factors to consider:
    Inductance value: Inductance value needs to be selected according to the requirements of the circuit, usually the larger the inductance, the stronger the resistance of current change.
    Current capacity: When selecting an inductor, it is necessary to consider the current it can withstand to avoid damage to the inductor due to overload.
    Frequency response: High-frequency circuits require the inductor to have smaller resistance and lower loss.
    Size and package: The size and package of the inductor need to match the space and installation in the actual application.