What is the frequency characteristic of an inductor?

First of all, inductors (coils) have the following basic characteristics, which are called "inductive reactance of inductance"

① DC basically flows directly.

②For AC, it acts like a resistance.

③The higher the frequency, the more difficult it is to pass.

The following is a schematic diagram showing the frequency and impedance characteristics of the inductor.

In an ideal inductor, the impedance increases linearly with the increase in frequency, but in an actual inductor, as shown in the equivalent circuit, there is a parasitic capacitance EPC in parallel, which will cause self-resonance.

Therefore, before the resonance frequency, the inductance is inherently inductive (impedance increases with increasing frequency), but after the resonance frequency, the influence of parasitic capacitance is dominant, showing capacitive characteristics (impedance decreases with increasing frequency) ). That is, in the frequency range higher than the resonance frequency, it does not function as an inductance.

The resonant frequency of the inductor can be obtained by the above formula. Except for the difference between the main body is the capacitance or the inductance, the formula is basically the same as the formula for the resonance frequency of the capacitor. It can be seen from the formula that the resonance frequency will increase when the inductance value L becomes smaller.

In the parasitic component of the inductor, in addition to the parasitic capacitance EPC, there are the resistance component ESR (Equivalent Series Resistance) of the inductor winding, and the EPR (Equivalent Parallel Resistance) that exists in parallel with the capacitor. The resistance component limits the impedance at the resonance point.

Key points:

The inductance presents an inductive characteristic before the resonance frequency (impedance increases with increasing frequency).

The inductance exhibits capacitive characteristics after the resonance frequency (impedance decreases with increasing frequency).

In the frequency band higher than the resonance frequency, the inductance does not function as an inductance.

When the inductance value L becomes smaller, the resonance frequency of the inductance will increase.

The impedance at the resonance point of the inductor is limited by the parasitic resistance component.

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