JPH04241406A - Magnetic core - Google Patents

Abstract

PURPOSE:To miniaturize and lighten a magnetic core by preventing the heat generation of the magnetic core caused by the magnetic saturation accompanying the excessiveness of the magnetic density in the connection between the center foot and the bottom face of the crucible type magnetic core used for a transformer and the drop of the inductance value of a coil being set. CONSTITUTION:In a magnetic core, which has a center foot, a bottom being made in the shape of a cavity around it, and a contour being made around the bottom, the sectional area of the connection between the center foot with minimum sectional area where the magnetic density becomes maximum and the bottom is made larger than the sectional area of the center foot. By enlarging the sectional area of the connection, the magnetic density therein becomes low, and the magnetism saturating point can be elevated without enlarging the dimension of the magnetic core. Accordingly, the temperature rise of the magnetic core and the drop of the inductance value do not occur. Moreover, as compared with the conventional magnetic core, the magnetic core can be miniaturized and lightened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic core used for forming an inductance element such as a transformer, and more particularly to a small pot-shaped magnetic core.

0002

2. Description of the Related Art Examples of inductance elements include transformers for switching power supplies. BACKGROUND OF THE INVENTION As electronic devices, such as personal computers, become smaller, switching power supplies used as power supplies installed in these electronic devices are also required to be smaller and lighter. therefore,
The magnetic cores that make up the transformers used in switching power supplies are also required to be smaller and lighter.

[0003] FIG. 7 shows a conventional magnetic core called a ``pot-shaped'' magnetic core as such a small-sized magnetic core. 7(a) is a plan view of the magnetic core, and FIG. 7(b) is a sectional view of the magnetic core taken along line XX' in FIG. 7(a). The magnetic core 10 is composed of a middle part 11, a bottom part 14, and an outer part 15, which are integrally formed of a magnetic material. Pre-wound coil 1
7 is fitted into an annular hole defined by the midfoot portion 11, the outer shell portion 15, and the bottom portion 14 formed in a concave shape between them. A magnetic core 20 having the same shape as the magnetic core 10 or a flat magnetic core (not shown) is connected oppositely to the top of the middle leg 11 and the top of the outer shell 15 of the magnetic core 10, and is connected via the middle leg 11 and the outer shell 15. Form a magnetic path. As a result, the middle leg portion 11, bottom portion 14, outer shell portion 15, and magnetic core 20 of the magnetic core 10
A transformer having one round magnetic path formed by the outer part, bottom part, and midfoot part is formed. The magnetic flux distribution is as follows:
Magnetic flux is distributed radially with 1 as the center. Arrows in FIG. 7 indicate the flow of magnetic flux.

0004

[Problem to be solved by the invention] Magnetic core 10 shown in FIG.
, 20, the magnetic flux density is highest at the connection portion 18, which has the smallest cross-sectional area, and as the magnetic field is increased, magnetic saturation occurs first at the connection portion 18, causing a temperature rise in the magnetic core 10 and a rise in the coil 17. A decrease in the inductance value occurs. In order to suppress the temperature rise of the magnetic core 10 due to magnetic saturation and prevent a decrease in the inductance value of the coil 17, it is necessary to make the entire magnetic core 10 large in order to increase the cross-sectional area of the connecting portion 18 in order to reduce the magnetic flux density there. This poses a problem that hinders the miniaturization and weight reduction of the magnetic core and, by extension, the transformer.

[0005] Although the pot-shaped magnetic core used in a transformer for a switching power supply has been exemplified, the above-mentioned problems also occur in other inductance elements using magnetic cores similar to those described above. Therefore, an object of the present invention is to solve the problems caused by the high magnetic flux density at the connection portions described above, and to provide a magnetic core that has high magnetic performance and can be made smaller and lighter.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention aims to increase the cross-sectional area of the connection between the midfoot and the bottom part, where the magnetic flux density of the magnetic core is highest, without increasing the size of the magnetic core. Enlarge. That is, the magnetic core of the present invention has a central mid-foot portion formed to fit a coil, a bottom surface portion formed on a recess around this mid-foot portion, and an outer shell formed around this bottom surface portion. The cross-sectional area of the connection between the midfoot and the bottom surface is larger than the cross-sectional area of the midfoot.

[0007]

[Effect] By making the connection between the midfoot and the bottom surface larger than the cross-sectional area of the midfoot, the magnetic flux density at the critical connection is reduced, and the magnetic flux density distribution throughout the magnetic core is reduced. It becomes uniform. Therefore, magnetic saturation at the connection portion is alleviated, and heat generation of the magnetic core and reduction in the inductance value of the coil inserted into the magnetic core due to magnetic saturation at the connection portion can be prevented.

[0008]

Embodiment FIG. 1 shows a magnetic core 1 according to a first embodiment of the present invention. Figure 1(a) is a plan view of the magnetic core 1, and Figure 1(b) is Figure 1(a).
It is a sectional view taken along line XX' of This magnetic core 1, like the magnetic core 10 in FIG.
In addition to having a bottom part 14 formed in an annular concave shape around the periphery of the foot and an outer part 15 formed on the outside of the bottom part 14, the part connecting the midfoot part 11 and the bottom part 14 is tilted. It has a tapered portion 12. The magnetic core 1 is integrally formed of a magnetic material. A coil (not shown) is fitted into the annular hole defined by the midfoot section 11, the bottom section 14 and the shell section 15. However, since the magnetic core 1 shown in FIG. 1 is formed with a tapered portion 12, its coil is slightly different from the coil 17 shown in FIG. 7, and only the portion of the tapered portion 12 is recessed. As illustrated in FIG. 7, magnetic cores (not shown) having the same shape as the magnetic core 1 are combined to face the magnetic core 1 to form a transformer.

The magnetic characteristics of the magnetic core 1 will be described. Fig. 2 shows a partial view of the magnetic core 1 shown in Fig. 1 divided into four using symmetry, and Fig. 2(a) shows the left half of the cross-sectional view of Fig. 1(b). 2(b) shows the upper left quarter of the plan view of the magnetic core 1 of FIG. 1(a). Figure 3 is Figure 2
This is a graph of the magnetic properties of the magnetic core, showing the results of simulating the magnetic flux density distribution with the Z-axis as the origin and distances taken in the direction of the arrow A along the Y-axis direction. The horizontal axis shows the distance (m) in the Y-axis direction, and the vertical axis shows the magnetic flux density (Tesla). The physical property values used in the simulation are as follows. B-H curve data of magnetic core 1, BMAX: approximately 0.4
Magnetic potential value of T magnetic potential value of midfoot part 11: ni = 1.313 outer part 15
Value of magnetic potential: ni = 0.0 Shape and dimensions Radius of midfoot portion 11 = 3.5 mm Outer radius of bottom portion 14 = 7.3 mm In order to compare with the characteristics of the magnetic core 1 shown in FIG. FIG. 4 shows a four-part magnetic core of the magnetic core 10 shown in FIG. 7, which corresponds to FIG. 2, and FIG. 5 shows the magnetic characteristics of the magnetic core of FIG. 4, which corresponds to FIG. The size of the magnetic core 10 in Fig. 4 and the magnetic core material are the magnetic core 1 in Fig. 2.
The size and material are the same.

Comparing the characteristic curve in FIG. 3 with the characteristic curve in FIG. 5, firstly, both show the maximum magnetic flux density at the midfoot portion 11, the bottom surface portion 14, and the connection region, but the magnetic flux density in FIG. The maximum of the magnetic flux density in FIG. 5 is approximately 27x10-2 (Tesla), whereas the maximum of the magnetic flux density in FIG. 5 is as large as approximately 39x10-2 (Tesla). That is, the magnetic core 1 of the first embodiment of the present invention
Since the tapered portion 12 is formed in the connecting portion to increase the cross-sectional area and reduce the magnetic flux density, the maximum magnetic flux density is lower than the maximum magnetic flux density of the magnetic core 10 shown in FIG. Next, the magnetic flux density of the magnetic core 1 of this embodiment is distributed almost uniformly in the bottom surface portion 14 in the Y direction. On the other hand, the magnetic flux density of the magnetic core 10 in FIG. 4 lacks uniformity because the maximum magnetic flux density is high.

When the magnetic core 1 and the magnetic core 10 are manufactured under the same conditions, the magnetic core 1 of this embodiment in which the tapered portion 12 is formed at the connecting portion between the midfoot portion 11 and the bottom portion 14 has a lower maximum magnetic flux density. This makes it possible to make the magnetic flux density distribution uniform. Therefore, when the magnetic cores are manufactured using the same magnetic material and the same dimensions, the magnetic saturation of the magnetic core 1 shown in FIG. 1 is relaxed, and the inductance value of the coil does not decrease. In other words,
Since the magnetic resistance of the magnetic core 1 has decreased and the inductance value has increased, when manufacturing a magnetic core under the same conditions where magnetic saturation occurs, the shape of the magnetic core according to the present invention can be downsized,
It can be made lighter.

[0012] When the cross-sectional area of the midfoot part 11 is S, the circumference length around the midfoot part 11 is L, and the thickness of the bottom part 14 is t, when (S/L) is greater than or equal to t. In particular, the above-mentioned effects of the present invention are significant.

FIG. 6 shows the structure of a magnetic core 1A according to a second embodiment of the present invention. This magnetic core 1A has a stepped portion 13 in place of the tapered portion 12 in the magnetic core 1 shown in FIG. Similar to the purpose of forming the tapered part 12, the purpose of forming the stepped part 13 is to increase the cross-sectional area in order to limit the magnitude of magnetic flux density at the connection part between the midfoot part 11 and the bottom part 14. The magnetic property simulation results of the magnetic core 1A in FIG. 6 also obtained results similar to those shown in FIG. 3. Further, similarly to the above, when (S/L) is greater than or equal to t, the above-mentioned effects of the present invention are large.

When the magnetic core 1 in FIG. 1 and the magnetic core 1A in FIG.
In order to form a magnetic circuit, magnetic cores having the same shape as magnetic core 1 and magnetic core 1A each fitted with a coil are connected to face each other. However, the magnetic bodies mounted facing each other to form a magnetic path need not have the same shape as the magnetic cores 1 and 1A, and may be flat plates or the like.

In carrying out the present invention, various modifications can be made in addition to the embodiments described above. For example, as shown in FIGS. 1 and 6, in addition to forming the bottom part 14 and the tapered part 12 or the stepped part 13 in a rectangular shape, the corners of the outer part 15 are formed parallel to the outer circle of the bottom part 14. You can also cut off parts other than the parts. Further, although the bottom surface portion 14 is formed in the form of notches at the top and bottom in the drawing, it may be formed into a completely annular hole. Moreover, although the midfoot portion 11 is formed in a cylindrical shape, it may be formed in a rectangular column shape.

[0016]

[Effects of the Invention] As described above, according to the magnetic core of the present invention, the cross-sectional area of the connecting portion between the midfoot portion and the bottom portion is increased to reduce the maximum magnetic flux density there, and the magnetic core as a whole Since the magnetic flux density is made uniform, the magnetic flux distribution is well-balanced, and problems such as temperature rise in the magnetic core caused by local magnetic saturation problems and a decrease in the inductance value of the fitted coil are eliminated. Ru. Moreover, according to the magnetic core of the present invention, when manufacturing a magnetic core with the same performance, the size of the magnetic core can be reduced, and the size and weight of the magnetic core can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram showing a magnetic core according to a first embodiment of the present invention.

2 is a partial diagram of the magnetic core of FIG. 1 used to simulate the characteristics of the magnetic core of FIG. 1; FIG.

FIG. 3 is a graph showing simulation results of the characteristics of the magnetic core in FIG. 2;

FIG. 4 is a partial diagram of the magnetic core of FIG. 7 used to simulate the characteristics of a conventional magnetic core.

FIG. 5 is a graph showing simulation results of the characteristics of the magnetic core in FIG. 4;

FIG. 6 is a structural diagram showing a magnetic core according to a second embodiment of the present invention.

FIG. 7 is a structural diagram showing a conventional magnetic core.

[Explanation of symbols]

1, 1A...Magnetic core, 11...Middle leg 11, 12...
Tapered parts 12, 13...Stepped part, 14...Bottom part, 1
5. Outer part.

Claims (1)

[Claims] [Claim 1] It has a central midfoot portion formed to fit a coil, a bottom portion formed in a concave shape around the midfoot portion, and an outer shell portion formed around the bottom portion. and a magnetic core characterized in that the cross-sectional area of the connecting portion between the midfoot and the bottom surface is wider than the cross-sectional area of the midfoot.