Inductor Guide

Basic Facts about Inductors [Lesson 6] Why is there a direction mark on inductors?

We will follow up the previous lesson on inductor reliability with an introduction to inductors and the influence of magnetic fields.

<Why is there a direction mark on inductors?>

Sometimes there is a mark on inductors to distinguish direction.
Among Murata products, such marks can be found on the film-type LQP_T series, multilayer-type LQG series and some of the wire wound-type LQH inductors. If the inductor structure is not perfectly symmetric, properties will change with the mounting direction. We therefore leave a mark so that the user will know the inductor has directionality. That way, when they use the inductor, they can hope to make the fullest use of the intended properties.
Figure 1 shows examples of the rate of change in inductance value for different mounting directions.

Figure 1. Mounting direction and the rate of change of inductance value

<Inductors and the influence of magnetic fields>

Inductors fulfill their function by storing energy in the magnetic field. However, in addition to the magnetic energy they generate by themselves, inductors are also influenced by flux from the outside. The guaranteed inductance value of a component is the value in the absence of external flux. This means that, when you mount an inductor that is exposed to flux from its periphery, you may be unable to make full use of its intended function. A typical example of this is when two inductors are mounted extremely close together.
Figure 2 shows the change in inductance value when two inductors are mounted in parallel extremely close together.

Figure 2. Rate of change in mounting pitch and inductance value

Inductors generate flux. That flux is leaked outside (some products are made to prevent this flux from being emitted) and becomes energy loss. When two inductors are mounted extremely close together, the two fluxes leaked outside interfere with each other and the intended properties cannot be achieved.
In this way, the properties of inductors are influenced by flux leaked from outside, and may be affected by nearby components. It is therefore necessary to consider these points when selecting the components to be used and optimizing the layout.


Written by: S.T., Murata Manufacturing Co., Ltd.

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