Inductance is the ratio of alternating magnetic flux generated around the inside of the conductor to the magnetic flux of the conductor and the current that generates this magnetic flux when alternating current passes through the conductor. When DC current passes through the inductor, only a fixed magnetic field line appears around it, which does not change with time; However, when alternating current passes through the coil, the magnetic field lines around the coil will change with time.

According to Faraday's law of electromagnetic induction-magnetic induction, the changing magnetic field lines will produce an induced potential at both ends of the coil, which is equivalent to a "new power supply". When a closed loop is formed, this induced potential will generate an induced current. According to Lenz's law, the total amount of magnetic field lines generated by induced current should be prevented from changing as much as possible.

The change of magnetic field lines comes from the change of external AC power supply, so from the objective effect, the inductance coil has the characteristic of preventing the current change in AC circuit. Induction coil has similar inertia characteristics in mechanics and is named "self-inductance" in electricity. Sparks usually occur at the moment when the knife switch is turned on or off, which is caused by the high induced potential.

Inductor has the characteristics of preventing alternating current from passing and allowing direct current to pass smoothly. The higher the frequency, the greater the coil impedance. Therefore, the main function of inductance is to isolate and filter AC signals or form a resonant circuit with capacitors and resistors.

Second, the use of inductors.

Inductance mainly plays the roles of filtering, oscillation, delay, notch and so on, as well as shielding signals, filtering noise, stabilizing current and suppressing electromagnetic interference. The most common function of inductance in circuit is to form LC filter circuit with capacitance. Capacitors have the characteristics of "DC resistance and AC resistance", while inductors have the functions of "DC resistance and AC resistance".

If DC with more interference signals passes through LC filter circuit, AC interference signals will be converted into heat energy by inductance and consumed; When pure DC current passes through the inductor, the AC interference signal in it is also converted into magnetic induction and heat energy, and the higher frequency is most easily impedance by the inductor, which can suppress the interference signal with higher frequency.

Inductor has the characteristics of preventing alternating current from passing and allowing direct current to pass smoothly. The higher the frequency, the greater the coil impedance. Therefore, the main function of inductance is to isolate and filter AC signals or form a resonant circuit with capacitors and resistors.

Extended data:

Classification of inductance

1, self-inductance coil

When current passes through the coil, a magnetic field will be generated around the coil. When the current in the coil changes, the magnetic field around it changes accordingly. This changing magnetic field can make the coil itself produce induced electromotive force (electromotive force is used to represent the terminal voltage of the ideal power supply of active components), which is self-induction.

An electronic component with a certain number of turns and a certain self-inductance or mutual inductance, which is formed by winding wires, is usually called an inductance coil. In order to increase inductance, improve quality factor and reduce volume, iron cores or iron cores made of ferromagnetic materials are often added. The basic parameters of inductor include inductance, quality factor, inherent capacitance, stability, passing current and working frequency. The inductance composed of a single coil is called self-inductor, and its self-inductance is also called self-inductance coefficient.

2. Transformer

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

References:

Baidu encyclopedia-inductance