JPH029522Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a ferrite magnetic core used, for example, in a power conversion transformer for a switching power supply, a chiyoke coil, or other transformers.

As a conventional ferrite magnetic core, an E-type ferrite magnetic core, which is constructed by structurally and magnetically connecting a center leg and a pair of outer legs outside the center leg through a plate-shaped connection part, is used for communication devices. It has been known. However, this E type ferrite magnetic core is
Because the width of the center leg and the outer leg are the same, partial saturation of the magnetic flux tends to occur, the shape becomes large, the magnetic shielding is insufficient, and the combination with the bobbin when mounted on a transformer is difficult. It had various problems such as not being very advantageous in terms of structure.

Therefore, in this invention, in a ferrite magnetic core consisting of a cylindrical center leg, a pair of outer legs, and a connection part that magnetically connects these legs, the plate-shaped connection part has a narrow width on the center leg side. A tapered portion is formed, and an exposed portion that is not connected to the connection portion is provided on the outer peripheral surface of the center leg at the connection portion between the center leg and the plate-shaped connection portion, and the outer circumference of the pair of outer legs is By forming the surface into a prismatic shape, partial saturation of the magnetic flux is eliminated and the distribution of magnetic flux density throughout the magnetic core is made uniform.The center leg is made small and the diameter of the inner peripheral surface of the outer leg is larger than the diameter of the cross section,
The purpose of the present invention is to provide a ferrite magnetic core whose winding is covered with the inner circumferential surface of the outer leg to increase the magnetic shielding effect and to facilitate mounting in a transformer.

Examples of this invention will be described below with reference to the drawings.

FIG. 1 is an overall perspective view of the ferrite magnetic core according to the invention, FIG. 2 is a front view thereof, FIG. 3 is a bottom view, and FIG. 4 is a plan view.

In Figures 1 to 4, the ferrite magnetic core has a central leg 1 and a pair of outer legs 2 and 3 on either side of the central leg 1.
and plate-shaped connecting parts 4 and 5 that connect them, and these are integrally molded from ferrite powder such as Mn-Zn through a manufacturing process of molding, firing, and processing.

The height H of the center leg 1 and the outer legs 2 and 3 are the same,
One end surface (flat surface) 1a of the center leg 1 and one end surface (flat surface) 2a, 3a of the outer legs 2, 3 are arranged on the same plane, and the connecting parts 4, 5 are arranged on the opposite side from these flat surfaces. The opposite end surfaces of the center leg 1, the opposite end surfaces of the outer legs 2 and 3, and the outer surfaces of the connecting portions 4 and 5 are aligned with the same plane P. In this way, an E-type ferrite magnetic core is formed, as shown in the longitudinal cross-sectional view of FIG.

When mounting this ferrite magnetic core in a transformer, two ferrite magnetic cores are attached via a bobbin (not shown) with their flat surfaces 1a, 2a, and 3a in contact with each other, and wound around the center leg 1. Place the line. The magnetic circuit branches from the center leg 1 of one ferrite magnetic core to connection parts 4 and 5, passes through each of the outer legs 2 and 3, passes through the outer leg and connection part of the other magnetic core, and joins the center leg. and close. In this magnetic circuit, if the material of the magnetic core is uniform, the magnetic flux density will be saturated at the part with the smallest cross-sectional area perpendicular to the magnetic flux, and there will be some margin in the magnetic flux density at the part where the cross-sectional area is larger than this minimum cross-sectional area. This results in wasted material, larger and heavier magnetic cores, and lower power per unit weight. Therefore, it is desirable to make the cross-sectional area of the entire magnetic circuit as uniform as possible.

Further, the outer legs 2 and 3 exhibit a magnetic shielding effect against the magnetic force generated by the winding wound around the center leg 1. Therefore, in order to increase this magnetic shielding effect, it is necessary to take structural considerations such that the outer legs 2 and 3 cover the windings as much as possible. It is desired that the magnetic core as a whole be small and have a compact outer shape, making it easy to mount and increasing the packaging density.

Accordingly, as shown in FIG. The cross-sectional diameter d ₁ of the outer legs 2, 3 is made considerably smaller than the width b of the outer legs 2, 3 (see FIG. 6). At this time, the diameter d ₁ of the central leg 1 is set to 15 to 70% of the inner diameter d ₂ formed by the inner peripheral surfaces 2b and 3b of the outer legs 2 and 3, preferably about 50%.
%. With this configuration, the windings are well covered by the outer legs 2 and 3, the magnetic shielding effect is increased, and the magnetic core can be easily attached to the winding bobbin.

Furthermore, the outer peripheral surfaces 2c, 2d, 3 of the outer legs 2, 3
c and 3d are flat, and the outer circumferential surface of the outer leg is shaped like a straight column. In this way, the outer shape of the magnetic core becomes small and simple, the mounting efficiency is improved, and the mounting density in a small space can be increased.

Further, the connecting portions 4 and 5 are formed with tapered portions 4a and 5a whose width decreases in the width direction from the connecting portion with the outer legs 2 and 3 toward the connecting portion with the center leg 1. Then, the area (that is, the cross-sectional area) of the flat surface 1a of the center leg 1 is S ₁ (=π/4d ₁ ² ), the area of the connection surface between the center leg 1 and the connecting parts 4 and 5 is S ₂ , S ₃ , and the outside legs 2,3
The area (i.e. cross-sectional area) of the flat surfaces 2a and 3a of
When S ₄ and S ₅ are set, the configuration is such that S ₁ ≒S ₂ +S ₃ ≒S ₄ +S ₅ . In this way, the magnetic flux density saturates almost simultaneously in these cross-sectional areas, so the magnetic flux is uniformly distributed throughout the magnetic core without local saturation, resulting in a good magnetic flux distribution and a uniform distribution of the material of the entire magnetic core. It eliminates waste, becomes smaller and lighter, and increases power per unit weight. Even more preferably, the above-mentioned tapered portions 4a,
5a, a tapered part is formed so that the thickness gradually becomes thinner from the center leg 1 side toward the outer legs 2 and 3, and the connection surface between the connecting parts 4 and 5 and the outer legs 2 and 3 is When the areas are S ₆ and S ₇ , S ₆ + S ₇ ≒ S ₁ ≒ S ₂ + S ₃ ≒ S ₄
If configured so that +S ₅ , the above-mentioned effect will further increase.

The two outer legs 2, 3 and the two connecting parts 4, 5 are symmetrical in shape, and have an area of S ₂ =S ₃ , S ₆ =S ₇ ,
Let S ₄ = S ₅ , so S ₁ = 2S ₂ (=2S ₃ ) = 2S ₆ (=2S ₇ )
=2S ₄ (=2S ₅ ), but as long as they satisfy the condition that the sum of the areas mentioned above is equal,
It is also possible to use an asymmetric type (therefore, S ₂ ≠ S ₃ , S ₄ ≠ S ₅ , S ₆ ≠ S ₇ ).

Tapered portions 4a, 5a in the width direction of the connecting portions 4, 5
is the center leg 1 while satisfying the condition S ₁ = S ₂ + S ₃
Second tapered portions 4b and 5b having larger slopes are formed near the connecting portions. Since the magnetic flux flows in a direction perpendicular to the circumferential surface of the center leg, the tapered portion 4
The flow of magnetic flux without b and 5b is as follows:
They are as shown in FIGS. 7A and 7B, respectively. It is assumed that the length B of the exposed portion of the center leg that is not connected to the connecting portion is equal in the cases of A and B in FIG. 7. The flow of magnetic flux curves along the contour of the connection part near the connection point A between the center leg and the connection part, and is likely to be saturated in this vicinity. The cross-sectional area of the connection part is the junction point A with the center leg.
Since the area near is the smallest, the above-mentioned saturation can be prevented by increasing the cross-sectional area in this area using the tapered portions 4b and 5b.

Furthermore, the existence of the tapered portions 4b and 5b can extend the life of the mold for manufacturing the core.

Since the middle cylinder, which has a shape corresponding to the cross section of the core connection part, comes into contact with the powder each time the powder is pressurized, the edges are likely to wear out, and especially when the edges are acute, the durability time will be shortened.

If the tapered portions 4b and 5b were not present, the middle tube would have sharp edges, but if the tapers were present, the angle of the edges would be large and the durability of the formwork would be prolonged. The tapered portion in the width direction of such a connecting portion can be formed by forming a plurality of tapered portions whose inclinations gradually increase from the outer legs 2 and 3 side to the center leg 1 side. increases.

Each ridge 2e of the prismatic portion on the outer periphery of the outer legs 2, 3,
3e may remain a right-angled sharp ridge, but
It is desirable to have an arc-shaped rounding or a chamfer, which will facilitate the manufacturing process of the ferrite magnetic core and make the magnetic flux distribution uniform.

Furthermore, the ridges 2f, 3f formed by the inner circumferential surfaces 2b, 3b and outer circumferential surfaces 2d, 3d of the outer legs 2, 3 are also preferably rounded or chamfered. In this way, a structure that does not damage the windings can be achieved.

In addition, the connecting part between the center leg 1 and the connecting parts 4 and 5 is
While satisfying the above-mentioned condition of S ₁ ≒ S ₂ + S ₃ , it is preferable to have an exposed portion 1b on the outer periphery of the center leg 1 that is not connected to the connecting portions 4 and 5 and leaves the outer periphery of the center leg 1 as it is. . This makes it easy to take out the winding lead wires from this part.

As explained above, according to the ferrite magnetic core of this invention, partial saturation of the magnetic flux is eliminated, the distribution of magnetic flux density throughout the ferrite magnetic core becomes uniform, and there is no excess portion from the viewpoint of magnetic flux density. As a result, the entire magnetic core becomes smaller and lighter, the electric power per unit weight becomes larger, and the magnetic shielding effect becomes larger. Furthermore, it exhibits various excellent effects such as easier mounting on a transformer, a simpler shape of the transformer after mounting, and higher mounting density in a smaller space. For example, as a ferrite magnetic core for a 50KHz forward converter method, 30~
An output of 400W can be obtained, and the practical benefits are significant when used as a ferrite magnetic core for power conversion transformers in switching power supplies, choke coils, and other transformers.

[Brief explanation of the drawing]

Figure 1 is an overall perspective view of the ferrite magnetic core according to this invention, Figure 2 is a front view, Figure 3 is a bottom view, and Figure 4 is a bottom view.
The figure is a plan view, FIG. 5 is a vertical sectional view taken along the line - in FIG. 4, and FIG. 6 is a cross sectional view taken along the line - in FIG. 2. FIGS. 7A and 7B are diagrams illustrating the effects of the present invention. 1... Center leg, 1a... Flat surface, 1b... Exposed part, 2, 3... Outer leg, 2a, 3a... Flat surface,
4, 5... Connection part, 4a, 5a, 4b, 5b...
Tapered part, d ₁ ... Diameter of the flat surface of the central leg, d ₂ ...
Diameter of the inner peripheral surface of the outer leg, S ₁ ... Area of the flat surface of the center leg, S ₂ , S ₃ ... Area of the connecting surface between the center leg and the connection part,
S ₄ , S ₅ ... Area of the flat surface of the outer leg, S ₆ , S ₇ ... Area of the connecting surface between the outer leg and the connection part.

Claims (1)

[Claims for Utility Model Registration] In a ferrite magnetic core consisting of a cylindrical center leg, a pair of outer legs, and a plate-shaped connection part that magnetically connects these legs, the plate-shaped connection part has the center Forming at least two tapered portions in which the inclination in the width direction gradually increases from the outer leg side toward the center leg side so that the width becomes narrower on the leg side, and the center leg and the plate-shaped connecting portion are connected to each other. At the connecting portion, an exposed portion not connected to the connecting portion is provided on the outer circumferential surface of the center leg, and the shape of the inner circumferential surface of the pair of outer legs is formed into a circumferential surface having the same central axis as the central axis of the center leg. A ferrite magnetic core characterized by having a prismatic outer peripheral surface.