Inductor is an element that can convert electrical energy into magnetic energy and store it. The structure of the Inductor is similar to that of a transformer, but it has only one winding. The inductor has a certain inductance, it only hinders the change of current. If the inductor is in a state where no current is flowing, it will try to block the current from flowing through it when the circuit is on; if the inductor is in a state where current is flowing, it will try to maintain the current when the circuit is off. Inductors are also called chokes, reactors, and dynamic reactors.


Inductors are generally composed of skeletons, windings, shields, packaging materials, magnetic cores or iron cores.

  1. Skeleton The skeleton generally refers to the bracket on which the coil is wound. Some large fixed inductors or adjustable inductors (such as oscillating coils, choke coils, etc.), most of which are enameled wires (or yarn-covered wires) around the skeleton, and then magnetic cores or copper cores, iron cores, etc. Put it into the inner cavity of the skeleton to increase its inductance. The skeleton is usually made of plastic, bakelite, ceramic, and can be made into different shapes according to actual needs. Small inductors (such as color code inductors) generally do not use a skeleton, but directly wind the enameled wire on the core. Air-core inductors (also called out-of-body coils or air-core coils, mostly used in high-frequency circuits) do not use magnetic cores, skeletons and shielding covers, etc., but are wound on the mold and then removed from the mold, and the coils are pulled between the turns Drive a certain distance.
  2. Winding Winding refers to a set of coils with specified functions, which are the basic components of inductors. There are single-layer and multi-layer windings. There are two types of single-layer windings: close winding (the wires are wound next to each other when winding) and indirect winding (the wires are separated by a certain distance when winding); the multilayer winding has layered flat winding and random winding. Winding, honeycomb winding and many other methods.
  3. Magnetic cores and magnetic rods Magnetic cores and magnetic rods generally use nickel-zinc ferrite (NX series) or manganese-zinc ferrite (MX series) and other materials, which have “I” shape, cylindrical shape, cap shape, and “E”. Various shapes such as shape and pot shape.
  4. Iron core The iron core material mainly includes silicon steel sheet, permalloy, etc., and its shape is mostly “E” type.
  5. Shielding cover In order to prevent the magnetic field generated by some inductors from affecting the normal operation of other circuits and components, a metal screen cover (such as the oscillation coil of a Semiconductor radio, etc.) is added for it. The inductor with a shielding case will increase the loss of the coil and reduce the Q value.
  6. Packaging materials After some inductors (such as color code inductors, color ring inductors, etc.) are wound, the coils and magnetic cores are sealed with packaging materials. The packaging material is plastic or epoxy resin.

Copper coil
Inductance is the ratio of the magnetic flux of the wire to the current that produces this magnetic flux when an alternating current is passed through the wire, which generates an alternating magnetic flux around the inside of the wire. When a direct current flows through the inductor, only fixed magnetic lines of force appear around it, which does not change with time;

However, when an alternating current is passed through the coil, the magnetic field lines that change with time will appear around it. According to Faraday’s law of electromagnetic induction—magnetism generates electricity, the changing magnetic field lines will generate an induced electric potential at both ends of the coil. This induced electric potential is equivalent to a “new power source”. When a closed loop is formed, this induced potential will produce induced current. It is known from Lenz’s law that the total amount of magnetic field lines produced by the induced current is to try to prevent the change of magnetic field lines. The change of the magnetic field line comes from the change of the external alternating power source, so from the objective effect, the inductance coil has the characteristic of preventing the current change in the alternating current circuit. Inductance coils have characteristics similar to inertia in mechanics. They are named “self-induction” in electricity. Usually, sparks will occur at the moment when the knife switch is opened or the knife switch is turned on. This self-inductance phenomenon produces a lot of Caused by high induced potential.
In short, when the inductance coil is connected to the AC power supply, the magnetic lines of force inside the coil will always change with the alternating current, causing the coil to produce electromagnetic induction. This kind of electromotive force generated by the change of the current of the coil itself is called “self-induced electromotive force”. It can be seen that the inductance is only a parameter related to the number of turns, size and shape of the coil and the medium. It is a measure of the inertia of the inductance coil and has nothing to do with the applied current.
Substitution principle: 1. The inductance coil must be replaced with the original value (the number of turns is the same, the size is the same). 2. The chip inductors only need to be the same size, and can also be replaced with 0 ohm resistors or wires.

The characteristics of an inductor are exactly the opposite of those of a capacitor. It has the characteristic of preventing the passage of alternating current and allowing direct current to pass smoothly. The resistance when a DC signal passes through the coil is that the resistance voltage drop of the wire itself is very small; when an AC signal passes through the coil, self-induced electromotive force will be generated at both ends of the coil, and the direction of the self-induced electromotive force is opposite to the direction of the applied voltage, which hinders the passage of AC Therefore, the characteristic of the inductor is to pass direct current and resist alternating current. The higher the frequency, the greater the impedance of the coil. Inductors often work with capacitors in circuits to form LC filters and LC oscillators. In addition, people also use the characteristics of inductance to manufacture choke coils, transformers, relays, etc.
Direct current: means that the inductor is closed to the DC. If the resistance of the inductor coil is not taken into account, then the DC current can pass through the inductor “unimpededly”. For DC, the resistance of the coil itself has little hindrance to the DC, so It is often ignored in circuit analysis.
Resistance to alternating current: when alternating current passes through the inductor coil, the inductor has an obstructive effect on the alternating current. What hinders the alternating current is the inductive reactance of the inductor coil.

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