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Inductor Symbols, What Inductors Do And What Is An Inductor

Inductor Symbols, What Inductors Do And What Is An Inductor

September 06 , 2023 0

Inductance is a property of a closed loop and is a physical quantity. When a current passes through a coil, a magnetic field is induced in the coil, and the induced magnetic field in turn produces an induced current to counteract the current passing through the coil. It is a circuit parameter that describes the effect of induced electromotive force in this coil or in another coil due to a change in coil current. Inductance is a general term for self-inductance and mutual inductance.

Basic Principles of Inductance

Inductors, along with capacitors and resistors, are the three basic passive devices of electronics; the function of an inductor is to store electrical energy in the form of magnetic field energy.
When a constant current flows through a coil, a static magnetic field in the direction shown is formed according to the right-hand spiral rule. The magnetic field produced by an alternating current flowing through an inductor is an alternating magnetic field. The changing magnetic field produces an electric field and an induced electromotive force on the coil, which produces an induced current:

When the current becomes large, the magnetic field becomes stronger, the direction of the magnetic field changes in the same direction as the original magnetic field, according to the left-handed helix rule, the induced current generated is in the opposite direction of the original current, and the inductor current decreases;
When the current becomes small, the magnetic field becomes weak, the direction of the magnetic field changes in the opposite direction to the original magnetic field, according to the left-handed helix rule, the induced current generated is in the same direction as the original current, and the inductance current becomes larger.
Although using the left hand and the direction of magnetic field change to determine the direction of the induced current is correct in the result, there is no such thing as the left hand spiral law. According to the corrugated law, the direction of the induced magnetic field is opposite to the direction of the magnetic field change. Then according to the right hand spiral law to determine the direction of the induced current.

The above is the corrugated law, and the ultimate effect is that the inductor will prevent the current flowing through it from producing a change, that is, the inductor has a high impedance to the alternating current. The same inductor, the higher the rate of change of current, the greater the induced current, the higher the impedance of the inductor; if the same rate of change of current, different inductors, if the induced current is greater, the higher the impedance of the inductor.

Therefore, the impedance of an inductor is related to two factors: one is the frequency; the other is the intrinsic property of the inductor, which is the value of the inductor, also known as inductance. According to the theoretical derivation, the formula for the inductance of a cylindrical coil is as follows:

You can see that the size of the inductance is related to the size of the coil and the material of the core.

The characteristics of the actual inductance are not only a function of inductance, but also other factors such as:

The wire used to wind the coil is not an ideal conductor and has a certain resistance;
There is a certain amount of heat loss in the core of the inductor;
The presence of distributed capacitance between the conductors inside the inductor.
Therefore, it is necessary to use a more complex model to represent the actual inductance, the commonly used equivalent model is as follows

The form of the equivalent model may be different, but it should be able to reflect the losses and the distributed capacitance. Based on the equivalent model, two important parameters of the actual inductor can be defined.
Self-Resonance Frequency (SRF)
Due to the presence of Cp, which together with L forms a resonant circuit, the resonant frequency is the self-resonance frequency of the inductor. Before the self-resonance frequency, the impedance of the inductor increases with frequency; after the self-resonance frequency, the impedance of the inductor increases with frequency and becomes smaller, which is capacitive.