H.R. Hertz of Germany in 1887 and N. Tesla of the United States in 1890 are very famous inductors used in experiments, called Hertz coil and Tesla coil respectively.

II. Functional Uses

In the circuit, the inductor mainly plays the role of filtering, oscillation, delay, notch, etc., as well as filtering signals, filtering noise, stabilizing current and suppressing electromagnetic interference. The most common function of the inductor in the circuit is to form the LC filter circuit together with the capacitor.

The capacitor has the characteristics of "blocking DC, passing AC", while the inductor has the function of "passing DC, blocking AC.

If the direct current accompanied by many interference signals passes through the LC filter circuit, then the AC interference signal will be consumed by the inductor into heat energy. When the relatively pure DC current passes through the inductor, the AC interference signal is also changed into magnetic induction and heat energy, and the higher frequency is most likely to be impedance by the inductor, which can suppress the higher frequency interference signal.

Inductors have the characteristics of preventing the passage of alternating current and allowing direct current to pass smoothly. The higher the frequency, the greater the coil impedance. Therefore, the main function of the inductor is to isolate the AC signal, filter or form a resonant circuit with capacitors, resistors, etc.

Structure of 3. inductor

Inductors are generally composed of a skeleton, a winding, a shielding case, a packaging material, a magnetic core or an iron core, etc.

1. Skeleton

The skeleton generally refers to the stent on which the coil is wound. Some of the larger fixed inductor or adjustable inductor (such as oscillation coil, choke coil, etc.), most of the enameled wire (or yarn) around the skeleton, and then the magnetic core or copper core, iron core, etc. into the inner cavity of the skeleton, in order to improve its inductance.

The skeleton is usually made of plastic, bakelite and ceramic, and can be made into different shapes according to actual needs. Small inductors (such as color code inductors) generally do not use the skeleton, but directly around the core of the enameled wire. Air-core inductors (also known as tufted coils or air-core coils, mostly used in high-frequency circuits) do not use magnetic cores, skeletons, shielding covers, etc., but are wound on the mold before taking off the mold, and pull a certain distance between the coils.

2. Winding

Winding refers to a set of coils with a specified function, which is the basic component of an inductor. There are single-layer and multi-layer windings. Single-layer winding also has two forms: close winding (when winding, the wires are wound one by one) and inter-winding (when winding, each turn of the wires is separated by a certain distance). Multi-layer winding includes layered flat winding, random winding, honeycomb winding, etc.

3. Magnetic core and magnetic bar

The magnetic core and the magnetic rod are generally made of nickel zinc ferrite (NX series) or manganese zinc ferrite (MX series) and other materials, which have "I" shape, column, hat, "E" shape, tank shape and other shapes.

4. Iron core

Core materials are mainly silicon steel sheet, permalloy, etc., 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 oscillating coil of a semiconductor radio) is added. The inductor using the shield 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 coil and magnetic core are sealed with packaging materials. The packaging material is plastic or epoxy resin.

4. copper coil

Inductance is the ratio of the magnetic flux of the wire to the current that produces an alternating magnetic flux around the inside of the wire when an alternating current passes through the wire. When a direct current passes through the inductor, only a fixed magnetic field line appears around it, which does not change with time;

However, when an alternating current passes through the coil, magnetic lines of force that change with time will appear around it. According to Faraday's law of electromagnetic induction-magnetic electricity to analyze, the change of magnetic field lines at both ends of the coil will produce an induced potential, which is equivalent to a "new power supply". When a closed loop is formed, this induced potential generates an induced current.

According to Lenz's law, the total amount of magnetic lines of force generated by induced current should be tried to prevent the change of magnetic lines of force. The change of magnetic field line comes from the change of external alternating power supply, so from the objective effect, the inductance coil has the characteristic of preventing the current change in the AC circuit. Inductive coils have similar characteristics to the inertia in mechanics, and are electrically named "self-induction". Sparks will occur at the moment when the knife switch is pulled open or the knife switch is turned on. This self-induction phenomenon is caused by high induced potential.

In short, when the inductance coil is connected to the AC power supply, the magnetic field lines inside the coil will change with the alternating current, causing the coil to produce electromagnetic induction.

The 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, shape and medium of the coil. It is a measure of the inertia of the inductor coil and has nothing to do with the applied current.

The principle of substitution:

1. The inductance coil must be replaced by the original value (the number of turns is equal and the size is the same).

2. The patch inductor only needs to be the same size, and can also be replaced by 0 ohm resistor or wire.

Classification of 5. inductors

Self-sensor:

When there is a current through the coil, a magnetic field is generated around the coil. When the current in the coil changes, the magnetic field around it also produces corresponding changes. This changing magnetic field can cause the coil itself to generate induced electromotive force (induced electromotive force) (electromotive force is used to represent the terminal voltage of the ideal power supply of the active element), which is self-inductance.

Made of wire wound, with a certain number of turns, can produce a certain amount of self-inductance or mutual inductance of electronic components, often called inductance coil. In order to increase the inductance value, improve the quality factor and reduce the volume, iron core or magnetic core made of ferromagnetic material is often added. The basic parameters of the inductor are inductance, quality factor, inherent capacitance, stability, through the current and frequency of use. An inductor composed of a single coil is called a self-inductor, and its self-inductance is also called a self-inductance coefficient.

Transformer:

When two inductance coils are close to each other, the magnetic field change of one inductance coil will affect the other inductance coil, and this effect is mutual inductance. The size of the mutual inductance depends on the degree of coupling between the self-inductance of the inductance coil and the two inductance coils. Components made by this principle are called transformers.

VI. Characteristics of Inductors

The characteristics of an inductor are the opposite of the characteristics of a capacitor. It has the characteristic of preventing alternating current from passing through and allowing direct current to pass smoothly. The resistance when the DC signal passes through the coil is that the resistance voltage drop of the wire itself is very small. When the AC signal passes through the coil, self-induced electromotive force will be generated at both ends of the coil. The direction of self-induced electromotive force is opposite to the direction of the applied voltage, which hinders the passage of AC. Therefore, the characteristics of the inductor are to pass DC and block AC. The higher the frequency, the greater the coil impedance. Inductors often work with capacitors in circuits to form LC filters, LC oscillators, etc. In addition, people also use the characteristics of the inductance, manufacturing a choke coil, transformer, relay and so on.

Through DC:It means that the inductor is in a through-circuit off state to DC. If the resistance of the inductor coil is not counted, then the DC can pass through the inductor "unimpeded". For DC, the resistance of the coil itself is very small to hinder the DC, so it is often ignored in circuit analysis.

AC blocking:When the alternating current through the inductor coil, the inductor has a blocking effect on the alternating current, and it is the inductive reactance of the inductor coil that hinders the alternating current.