TCET28B222P データシートの表示（PDF） - Token Electronics Industry Co., Ltd.

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Fixed Inductor Terminology Glossary

Matched Impedance

The condition that exists when two coupled circuits are adjusted so that the output impedance of one circuit

equals the input impedance of the other circuit connected to the first. There is a minimum power loss be-

tween two circuits when their connecting impedances are equal.

Multilayer Inductor

An inductor constructed by layering the coil between layers of core material. The coil typically consists

of a bare metal material (no insulation). This technology is sometimes referred to as “non-wirewound”.

The inductance value can be made larger by adding additional layers for a given spiral pattern.

Quality Factor Q

The Q value of an inductor is a measure of the relative losses in an inductor. The Q is also known as the

“quality factor” and is technically defined as the ratio of inductive reactance to effective resistance and is

represented by: Equation Q = XL / Re = 2πƒL / Re

Since XL and Re are functions of frequency, the test frequency must be given when specifying Q. XL

typically increases with frequency at a faster rate than Re at lower frequencies, and vice versa at higher

frequencies. This results in a bell shaped curve for Q vs frequency. Re is mainly comprised of the DC

resistance of the wire, the core losses and skin effect of the wire. Based on the above formula, it can be

shown that the Q is zero at the self resonant frequency since the inductance is zero at this point.

Rated Current

The level of continuous DC current that can be passed through the inductor. This DC current level is

based on a maximum temperature rise of the inductor at the maximum rated ambient temperature. The

rated current is related to the inductor’s ability to minimize the power losses in the winding by having a

low DC resistance. It is also related to the inductor’s ability to dissipate this power lost in the windings.

Thus, the rated current can be increased by reducing the DC resistance or increasing the inductor size.

For low frequency current waveforms, the RMS current can be substituted for the DC rated current.

The rated current is not related to the magnetic properties of the inductor.

Saturation Current

The DC bias current flowing through the inductor which causes the inductance to drop by a specified

amount from the initial zero DC bias inductance value. Common specified inductance drop percentages

include 10 % and 20 %. It is useful to use the 10 % inductance drop value for ferrite cores and 20 % for

powdered iron cores in energy storage applications.

The cause of the inductance to drop due to the DC bias current is related to the magnetic properties of the

core. The core, and some of the space around the core, can only store a given amount of magnetic flux

density. Beyond the maximum flux density point, the permeability of the core is reduced. Thus, the

inductance is caused to drop. Core saturation does not apply to “air-core” inductors.

Self-Resonant Frequency (SRF)

The frequency at which the inductor’s distributed capacitance resonates with the inductance. It is at this

frequency that the inductance is equal to the capacitance and they cancel each other. The inductor will

act purely resistive with a high impedance at the SRF point.

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