JPH0631697Y2 - Ferrite core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a ferrite core used in a noise filter.

[Conventional technology]

When electric wires are placed outside, noise enters directly or indirectly through various routes. For this reason, it is necessary to take noise countermeasures in advance in a place where noise is likely to be mixed in, and the noise filter is used in such a case.

This noise filter not only improves the noise resistance of the circuit, but also suppresses its own radiation noise.

There is a ferrite core as one of the above noise filters.

There are various types of ferrite cores, such as toroidal cores, ferrite beads and split cores for cables.

In such a ferrite core, an electric wire or the like that generates and transmits noise or emits noise and serves as an antenna is inserted into the ferrite core, or the inserted electric wire is wound several times.

Since the ferrite core used in this way is made of a ferromagnetic material, it captures the magnetic flux created by the current flowing through the wire, and at that time, due to the inductance created by the magnetic flux and the current and the loss generated in the ferrite core, The noise component of the current is reduced.

[Problems to be solved by the device]

By the way, in the above ferrite core, if an attempt is made to reduce the size by reducing the outer die, the magnetic flux passing through the ferrite core is reduced due to the reduction in the cross-sectional area of the ferrite core, so the impedance is reduced, the noise reduction effect is reduced, and the size is reduced. There are issues that cannot be solved.

Then, this invention aims at solving the above-mentioned subject by adding a device to the shape of the ferrite core.

[Means for Solving the Problems]

In order to solve the above problems, in the present invention, an electric wire material is inserted into an air core, and in a ferrite core for removing noise of the electric wire material, the ferrite core is cut along a plane parallel to the axis of the air core. , The centroids of the ferrite core cross sections obtained on both sides of the air core are
The configuration is on the air core side from 1/2.

[Action]

In the ferrite core configured as described above, the centroid is set for each cross section obtained on both sides of the air core when the ferrite core is cut along a plane parallel to the air core.

Further, since the centroid is set to be closer to the air core than half the sectional thickness, the centroid of each cross section is located on the air core side.

Therefore, the cross-sectional shape is large on the air-core side close to the centroid and small on the outside far from the centroid.

Further, here, the magnetic field H generated by the electric wire material inserted through the air core
Is r, the distance from the center of the conductor is Indicated by.

That is, the magnetic field H decreases with increasing distance from the conductor center.

For this reason, as described above, the centroid of each cross section is on the air core side with respect to half the cross-sectional thickness, and in the ferrite core with a large cross-sectional area on the air core side, disconnection of the part approaching the wire material Since the area is formed large, a large magnetic field generated by the electric wire material can be received in a large cross section, and a large noise reduction effect can be enhanced.

〔Example〕

The present invention will be described below with reference to FIGS.

As shown in FIGS. 1 to 3, the ferrite core 1 is
When cut by a plane parallel to the axis of the air core 2, the centroid of the cross section 5 obtained on both sides of the air core 2 is set to 1/2 of the thickness h of the cross section.
By being located on the side, for example, the area increases as it approaches the air core 2 side, as in the case where the center of gravity of the solid body is lowered.

Therefore, the ferrite core 1 thus formed effectively captures the magnetic flux φ generated outside the conductor by the current I passing through the conductor of the electric wire material 3 inserted into the air core 2 and obtains a large noise reduction effect. You can

This is because when the electric wire material 3 is inserted into the air core 2 of the ferrite core 1 and a current I is caused to flow through the electric current I, a magnetic field H is generated outside the conductor inside the electric wire material 3.

This magnetic field H becomes ∫c (H · ds) = ∫cHds = 2πrH, where r is the distance from the center of the conductor.

Also, it is the current I that passes through this integration path, so this value is 2πrH = I, and the magnetic field H is Indicated by.

When the above equation is illustrated, as shown in FIG.
Decreases as the distance from the surface of the radius a of the conductor increases.

At this time, the magnetic flux φ generated inside the ferrite core 1 per unit of the electric wire material 3 is r ₁ from the center of the conductor to the ferrite core surface and r ₂ from the ferrite core surface outer periphery to Becomes

Therefore, the ferrite core 1 formed so as to increase the cross-sectional area on the side of the air core 2 as described above is caused by the current I passing through the conductor of the electric wire material 3 just inserted into the air core 2.
The cross section of the ferrite core 1 at the distance r _{1 in which} the large magnetic field H generated outside the conductor is distributed as shown in FIG. 5 is enlarged, and the magnetic flux φ can be effectively captured.

Therefore, it has a larger impedance than the conventional ferrite core 1 having a rectangular cross section shown in FIG.

Therefore, in order to obtain the same noise reduction effect as the conventional one, it is possible to manufacture with a small amount of ferrite material, and it is possible to reduce the size.

This embodiment is configured as described above. Next, the ferrite core 1 having a triangular cross section shown in FIG.
(Inner diameter 6 mm, outer diameter 18 mm, length 20 mm, weight 10 g)
And a conventional annular ferrite core 1 (inner diameter 6 mm, outer diameter 18 mm, length 10 mm, weight 12 g) shown in FIG. 4, each having a vinyl flat cord 6 (0.75 mm ² , long diameter 5.6 mm, short diameter 2.8 m).
m) was inserted, a current I was passed, and the impedance against common mode noise at 10 MHz was measured.

As a result, the impedance of the ferrite core 1 of this embodiment shown in FIG. 1 was 54Ω.

On the other hand, the impedance of the conventional ferrite core 1 shown in FIG. 4 was 40Ω.

From this result, the ferrite core 1 of this embodiment is
With a lighter weight than the annular ferrite core 1 in the figure, it has a large impedance of 1.35 times, showing a high noise reduction effect.

The ferrite core 1 can be used not only for the flat cord 6 but also for various wire materials such as a single core wire and an interface cable.

At this time, when the outer peripheral surface of the ferrite core 1 is formed into a shape having a good conformability suitable for winding with a gentle inclination as shown in FIGS. 2 and 3, the wire material 3 or each insulated wire is used. 8 as shown by the chain lines in FIGS. 2 and 3,
Can be wound closely.

That is, the wire material 3, 8 wound around the ferrite core 1
The magnetic flux generated by the largest magnetic field generated by the current flowing through the ferrite core 1 can be captured, and the ferrite core 1 can exhibit a large impedance.

For this reason, it is possible to significantly improve noise, and it is possible to obtain a relatively large noise reduction effect even if the number of windings is reduced.

Therefore, for example, the number of windings can be reduced, the number of processing steps required for winding can be reduced, and the manufacturing cost can be reduced.

〔effect〕

According to this invention, a large noise reduction effect can be obtained by arranging the ferrite core so that the centroid of the cross section is closer to the air core than half the thickness of the cross section.

Therefore, the size can be reduced without impairing the reduction effect.

Further, therefore, it is possible to reduce the cost because less ferrite material is used.

[Brief description of drawings]

1 to 3 are sectional views of the embodiment, FIG. 4 is a sectional view of a conventional example, and FIG. 5 is an operation explanatory view. 1 ... Ferrite core, 2 ... Air core, 3 ... Electric wire material, 5 ... Ferrite cross section, 6 ... Flat two-core wire, 8 ... Insulated wire, I ... Current, H ... Magnetic field, h ... …thickness.

Claims (1)

[Scope of utility model registration request] 1. A ferrite core 1 in which electric wire members 3, 6, 8 are inserted through an air core 2 to remove noise from the electric wire members 3, 6, 8; When cut on a plane parallel to the axis, each centroid of the cross section 5 of the ferrite core 1 obtained on both sides of the air core 2 is 1/2 of the thickness of the cross section 5.
A ferrite core 1 which is located closer to the air core 2.