JP2000323333A - Magnetic core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic core which has synthetically low loss as an inductance component little heat generation caused by a high frequency current, by considering hysteresis loss and conduction loss of winding. SOLUTION: This magnetic core is provided with a bottom plate 13 of a rectangular paralleopiped, outer legs 12 which are formed integrally with the bottom plate on both end portions of a long side on one surface of the bottom plate and a center leg 11 which is formed integrally with the bottom plate, in the central part of the bottom plate in such a manner that the long axis direction coincides with the direction of the long side of the bottom plate, and makes a pillar having a rectangular section. The distance between the side surface of the center leg and the inner side surface of the outer leg is constant. The length of the long side of the bottom plate part is at least 1.0 time and at most 1.5 times the length of the short side of the bottom plate and at least 1.2 times and at most 2 times the long axis of the center leg.

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 an inductance component such as a switching transformer or a choke coil in a switching power supply or the like.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for downsizing, thinning, and high output of switching power supplies used in electric equipment. In order to meet the demands for downsizing, thinning, and high output of switching power supplies, it is necessary to downsize inductance components such as switching transformers and choke coils that are used components and to improve characteristics. Usually, an inductance component has a structure in which a conductor is wound around a magnetic core mainly made of a ferrite material.

FIGS. 7 and 8 show a conventional magnetic core.
This will be described with reference to FIG. FIG. 7A is a front view of a conventional choke coil using a magnetic core, and FIG.
It is bb sectional drawing of. 7A and 7B, the magnetic core half 91 is composed of a bottom plate portion 94, a middle foot portion 92, and an outer foot portion 93 made of a material such as ferrite having a high magnetic permeability and a low core loss. You. The midfoot portion 92 is cylindrical.
The outer foot portion 93 is a rectangular parallelepiped. The bottom plate portion 94 is rectangular. The winding 95 is wound around the midfoot 92.
When a transformer or a choke coil is formed using the magnetic core halves 91, as shown in FIG. 7A, the two magnetic core halves 91 are connected to the end faces of both outer foot portions 93 and the middle foot portion 92, respectively. Are combined so that they face each other. FIGS. 8A and 8B are a plan view and a front view, respectively, showing another conventional magnetic core half described in Japanese Utility Model Laid-Open No. 5-87918. 8A and 8B, the magnetic core half 100
Is an oval pillar-shaped middle foot 101 and a rectangular outer foot 10
2. It is composed of a bottom plate 103. The bottom plate 103 has a width L3 of the attachment portion 103A of the middle foot portion 101 and the width L3 of the outer foot portion 1.
02 is smaller than the width L1 of the mounting portion. The major axis direction of the cross section of the middle foot portion 101 is oriented in the longitudinal direction of the outer foot portion 102.

[0004]

In the conventional example shown in FIG. 7, since the magnetic flux inside the magnetic core 91 passes through the shortest path, the inside of the connecting portion between the middle foot portion 92 and the outer foot portion 93 and the bottom plate portion 94 is formed. It is known that magnetic flux concentrates on the regions 92A and 93A of the section. When a high-frequency alternating current flows through the winding 95, a hysteresis loss occurs due to a magnetic hysteresis characteristic inherent in the magnetic core material, and the magnetic core 91 itself generates heat. In the example of FIG. 7, since the cross section of the middle foot portion 92 is circular, the degree of concentration of the magnetic flux is larger at the root 92A of the middle foot portion 92 than near the root 93A of the outer foot portion 93. Hysteresis loss generally increases in proportion to the square of the magnetic flux density or more.
When the magnetic flux is concentrated on a specific area of the magnetic core, the hysteresis loss increases and the heat generation also increases.

On the other hand, in the conventional magnetic core shown in FIG. 8, the cross-sectional shape of the middle foot portion 101 is oval and the major axis direction is the width direction of the bottom plate portion 103. The cross-sectional area of the inner root portion of the connection portion with 103 increases, and the magnetic flux concentration is reduced. However, such a simple oval of the middle foot part, although reducing the loss of the magnetic core, makes the length of the winding longer than in the case of a circle having the same cross-sectional area,
The problem is that the winding resistance increases and the loss due to the resistance of the winding due to the current flowing increases.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a magnetic core which has low loss and low heat generation as an inductance component in consideration of conductor loss.

[0007]

In order to solve this problem, a magnetic core according to the present invention comprises a bottom plate having a substantially rectangular parallelepiped shape, and the bottom plate being provided at both ends on one long side of one surface of the bottom plate. A pair of outer legs formed integrally with the pair of outer legs, and a substantial axis direction is disposed between the pair of outer legs in a substantially central portion of the bottom plate portion so that a major axis direction coincides with a direction of a long side of the bottom plate portion. A bottom plate having a substantially rectangular cross section formed integrally with the bottom plate, wherein a distance between a side surface of the middle foot and an inner surface of the outer foot is constant; The length of the long side of the portion is 1.0 times or more and 1.5 times or less the length of the short side of the bottom plate portion,
The length of the long axis of the middle foot portion is 1.2 times or more and 2 times or less. With this configuration, the distribution of magnetic flux inside the magnetic core becomes more uniform, so that a hysteresis loss is reduced and a low-loss, low-heat-generating core is provided as an overall inductance component including the conductor loss of the winding. It becomes possible.

According to another aspect of the present invention, there is provided a magnetic core having a substantially elliptical plate-like bottom plate and one end of the bottom plate on the short-axis side of the bottom plate. A pair of outer foot portions, substantially at the center of the bottom plate portion, a major axis direction coinciding with a major axis direction of the bottom plate portion is disposed between the pair of outer foot portions and integrally with the bottom plate portion. A middle foot portion, which is a pillar having a substantially elliptical cross section, is formed, and a distance between a side surface of the middle foot portion and an inner side surface of the outer foot portion is constant, and a long axis of the bottom plate portion is formed. The length is 1.1 of the length of the short axis of the bottom plate.
It is not less than 0 times and not more than 1.5 times, and not less than 1.2 times and not more than 2 times the major axis of the midfoot. By providing such a configuration, the distribution of magnetic flux inside the magnetic core becomes more uniform, so that the hysteresis loss is reduced, and a low-loss, low-heat-generating core is provided overall as an inductance component including the conductor loss of the winding. Becomes possible.

A magnetic core according to the present invention according to another aspect is characterized in that both ends of the bottom plate in the long axis direction are formed in a straight line parallel to the short axis and coincident with the end face of the outer foot. I do. By providing such a configuration, the distribution of magnetic flux inside the magnetic core becomes more uniform, so that the hysteresis loss is reduced, and a low-loss, low-heat-generating core is provided overall as an inductance component including the conductor loss of the winding. Becomes possible.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments showing a magnetic core of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 FIGS. 1A and 1B are a plan view and a front view, respectively, showing the configuration of a magnetic core according to Embodiment 1 of the present invention. 1A and 1B, the magnetic core half 1 is composed of a middle foot portion 11, an outer foot portion 12, and a bottom plate portion 13 formed of a material such as ferrite having a high magnetic susceptibility and a low core loss. ing. The bottom plate 13 has a short side length W
1. It is a rectangular parallelepiped having a rectangular shape having a long side length L1 as an upper surface and a bottom surface. The midfoot portion 11 is oval, and the length of its long axis is L2. The middle foot portion 11 has a columnar structure of an oval cross section integrally formed with the bottom plate portion 13 so that the major axis direction thereof coincides with the long side direction of the bottom plate portion 13. The outer foot portions 12 are formed integrally with the bottom plate portion 13 at both ends on the long side of one surface of the bottom plate portion 13, respectively. In addition, the outer foot 12
Is formed such that the distance W3 to the side surface of the middle foot portion 11 is constant.

When a choke coil or a transformer is formed by using the above-described magnetic core halves 1, two magnetic core halves 1 having the same shape are used.
Are combined such that the end faces of the middle foot 11 and the outer feet 12 face each other, and an electric wire is wound around the middle foot 11 to form the coil 10 (FIG. 2). When the two magnetic core halves 1 are combined, an opening is formed on the front and the back, and the terminal of the coil 10 wound around the middle foot 11 is pulled out from the opening. The advantages of such a structure will be described below. The distribution of magnetic flux of a transformer or a choke coil using the magnetic core of the present embodiment will be described with reference to FIGS. FIG. 2 is a vertical sectional view showing a magnetic flux distribution of a magnetic core obtained by combining two magnetic core halves 1 of the present embodiment.
FIG. 2 is a horizontal sectional view showing the distribution of the magnetic flux of the magnetic core half 1. 3, illustration of the coil 10 is omitted.

The base of the midfoot 11 has an oval horizontal cross section. For this reason, the area of the base of the middle foot 11 is increased, the concentration of magnetic flux on the base of the middle foot 11 is reduced, and the hysteresis loss in the same region is reduced. FIG.
As shown in (1), the magnetic flux is concentrated near the center of the core half 1 and the inner base of the outer foot 12 by the current flowing through the winding 10. Further, as shown in FIG. 3, the magnetic flux in the middle foot portion 11 extends from the near side to the back side perpendicularly to the paper surface, and passes through the bottom plate portion 13 toward the outer foot portion 12 as indicated by a dotted line with an arrow. It is toward you by the outer foot part 12. These lines of magnetic force pass the shortest distance in the magnetic core 1.

In the conventional magnetic cores of FIGS. 7 and 8 and the magnetic core of the present embodiment, the cross-sectional area of the magnetic core at an arbitrary position on the path of the magnetic flux is at least equal to or larger than the cross-sectional area of the middle foot portion 11. When the cross-sectional area, the height, the distance W3, the gap distance g, the number of turns of the winding, and the magnitude of the current of the middle foot portion 11 are the same, the total magnetic flux in the magnetic core is the same as that of the conventional example. Is almost the same as However, since the peripheral length of the middle foot portion 11 and the outer foot portion 12 in the magnetic core 1 of this embodiment is longer, the magnetic flux is more dispersed at the base of the middle foot portion 11 and the outer foot portion 12.

As shown in FIG. 1A, the distance W3 between the outer side surface of the middle foot portion 11 and the inner side surface of the outer foot portion 12 is formed to be substantially constant. Bottom plate 13
, The magnetic resistance on the shortest path of the line of magnetic force reaching the outer leg 12 becomes substantially constant. Therefore, it is possible to prevent the magnetic flux from concentrating on a specific path. Therefore, the distribution of the magnetic flux from the middle foot portion 11 to the outer foot portion 12 through the bottom plate portion 13 becomes more uniform, and the hysteresis loss in the bottom plate portion 13 is reduced.

In the outer foot portion 12, the length L1 of the long side of the bottom plate portion 13 is longer than the length L2 of the long axis of the middle foot portion 11, and particularly the length L1 is 1.2 times or more and 2 times or less of L2. Then, the magnetic flux is further dispersed in the bottom plate portion 13 and the outer foot portion 12 than at the base portion of the middle foot portion 11. Therefore, the distribution of the magnetic flux inside the outer leg 12 becomes more uniform, and the hysteresis loss in the outer leg 12 is reduced. If the length L1 is more than twice as large as L2, the portion of the outer foot portion that is too far from the middle foot portion increases, and the line of magnetic force does not pass through this portion, and does not contribute to the reduction of the hysteresis loss. In general, when the length of the long side of the bottom plate portion 13 is smaller than 1.0 times the length of the short side or 1.2 times of the long side of the midfoot portion, the magnetic core is more reduced than the conductor loss of the winding is reduced. The increase in the hysteresis loss exceeds that, and the loss of the entire inductance component increases. on the other hand,
When the length of the long side of the bottom plate portion 13 is larger than 2.0 times the length of the short side or 2.0 times of the long axis of the midfoot portion, the conductor loss of the winding is smaller than the reduction of the hysteresis loss of the magnetic core. And the loss of the entire inductance component increases. 4 (a) and 4 (b) respectively show the dimensional ratios L1 / W1, L1 / L2 of the core half 1 and various losses (hysteresis loss of the core, winding conduction) of the transformer using the core half 1. FIG. 4 is a graph showing the relationship between the loss and the total loss that is the sum of the losses. The dimensional ratios L1 / L2 and L1 /
W1 is fixed at 1.5 times. FIG. 4 (a), FIG.
As is clear from (b), L1 is at least 1 time and 1.5 times W1.
If L1 is less than or equal to L2, and if L1 is greater than or equal to 1.2 and less than or equal to L2, the total loss of the transformer is reduced.

The conditions at this time are shown in FIGS. 4 (a) and 4 (b).
W1 = 24 mm, L2 = 18 mm, the core material is ML-24D manufactured by Hitachi Metals, Ltd., and the primary winding is a 2-turn, stamped copper plate with a thickness of 0.5 mm, and the secondary winding is One turn of a punched copper plate having a thickness of 0.5 mm. The self-inductance of the primary winding was 17 μH (adjusted with a gap in the middle foot), and the applied primary current was 23 Ap-
o The secondary winding is -40Ap-o (opposite phase to the primary winding) 13
A 0 kHz sine wave alternating current was used.

In the above description, the horizontal cross-sectional shape of the middle foot portion 11 is an ellipse. However, a rectangular shape or a flat shape obtained by rounding four corners of a rectangle with an appropriate radius may be used. The same effect can be obtained if they coincide with the side direction. Further, with the above configuration, the same effect can be obtained even if there are deformations such as rounding of the four corners of the bottom plate portion and the outer leg portions associated therewith.

Embodiment 2 FIGS. 5A and 5B are a plan view and a front view showing the structure of a magnetic core in Embodiment 2 of the present invention, respectively. In FIG. 5, the magnetic core half 20 includes a middle foot portion 21, an outer foot portion 22, and a bottom plate portion 23 formed of a material such as ferrite having a high magnetic susceptibility and a low core loss. The bottom plate portion 23 is an elliptical plate having a minor axis length W10 and a major axis length L10. The middle foot portion 21 is a column having an elliptical cross section whose major axis direction coincides with the major axis direction of the bottom plate portion 23, provided at the center of the bottom plate portion 23. The middle foot portion 23 has a horizontal section having a major axis length of L20 and a minor axis length of W20. Outer foot 22
Are formed integrally with the bottom plate 23 at both ends on the short axis side of the upper surface of the bottom plate 23. The outer foot portion 22 is provided such that the distance W3 between the inner side surface 22A and the outer side surface 21A of the middle foot portion 21 is constant. When a choke coil or a transformer is configured by using the magnetic core halves 20, the two magnetic core halves 20 are respectively connected to the middle foot 21 and the both outer feet 22.
The electric wire is wound around the combined midfoot portion 21 such that the end faces of the electric wire face each other.

With such a structure, the following effects are obtained. The horizontal cross-sectional shape of the middle foot part 21 is made elliptical,
By increasing the area of the base portion with respect to the horizontal cross-sectional area of the middle foot portion 21, the concentration of magnetic flux at the base portion of the middle foot portion 21 is reduced. Further, by keeping the distance W3 constant, concentration of magnetic flux on a specific path is prevented. Further, the length L10 of the bottom plate portion 23 in the long side direction is longer than the length L20 of the middle foot portion 21 in the long axis direction, and in particular, the length L10 is L20.
By setting the length L10 to be 1.0 to 1.5 times W10, the distribution of the magnetic flux is made uniform, and the hysteresis loss of the magnetic core and the conduction loss of the winding are added. Is minimized.

Further, since the thickness of the outer leg portion 22 is more uniform than in the first embodiment, the magnetic flux passing through the outer leg portion 22 is more evenly distributed throughout the outer leg portion. Thereby, the core material required for forming the magnetic core is reduced. Also, by diverting the surplus material to the other part of the magnetic core, the concentration of the magnetic flux viewed from the entire magnetic core can be prevented, and the loss of the magnetic core can be reduced. Also, by making the shape of the magnetic core half 20 elliptical, the installation area of the magnetic core can be reduced as compared with that of the first embodiment having the same specification. Further, since both end portions of the bottom plate portion 23 without the outer foot portion 22 are protruded, the middle foot portion 21 is formed.
This also has the effect of suppressing the radiation of the leakage magnetic flux from the winding wound around and the lead-out portion.

<< Embodiment 3 >> FIGS. 6A and 6B show the configuration of a magnetic core according to Embodiment 3 of the present invention.
It is a front view. In FIG. 6, the magnetic core half 30 includes a middle foot portion 31, an outer foot portion 32, and a bottom plate portion 33 formed of a material such as ferrite having a high magnetic susceptibility and a low core loss. Midfoot 3
1 is an elliptical shape having a major axis length L25 and a minor axis length W25 in a horizontal section. The bottom plate 33 has both ends in the major axis direction of the bottom plate portion formed in a straight line parallel to the short axis and coinciding with the end face of the outer foot portion 32. In other words, the bottom plate portion 33 has a structure in which both ends in the major axis direction of the elliptical plate are formed in a straight line parallel to the short axis and coincident with the end surface of the outer leg portion. The outer foot portion 32 is formed integrally with the bottom plate portion at both ends on the short axis side of the upper surface of the bottom plate portion 33, and the distance W3 between the inner surface of the outer foot portion 32 and the outer surface of the middle foot portion 31 becomes constant. It has been made like that. The other configuration except for the above structure is the same as that of the second embodiment. Such a shape has the following effects. By making the horizontal cross-sectional shape of the middle foot portion 31 elliptical and increasing the area of the base portion with respect to the horizontal cross-sectional area of the middle foot portion 31, the concentration of magnetic flux at the base portion of the middle foot portion 31 is reduced. You. By keeping the distance W3 constant, the concentration of magnetic flux on a specific path is prevented. The length L1 of the bottom plate 33 in the long side direction is longer than the length L25 of the middle foot portion 31 in the long axis direction.
In particular, when the length L1 is 1.2 to 2 times L25 and the length L1 is 1.0 to 1.5 times W1, the distribution of magnetic flux is made uniform and the loss is minimized. Become. In the present embodiment, not only the effect of saving the core material compared to the second embodiment, but also the installation area of the magnetic core can be reduced more than in the second embodiment.

[0023]

As described above, according to the present invention, the horizontal cross-sectional shape of the middle foot portion of the magnetic core is flattened, the distance between the side surface of the middle foot portion and the side surface of the outer foot portion facing the middle foot portion is made constant. By making the foot longer than the middle foot, limiting the aspect ratio in the bottom plate bottom shape, etc., the hysteresis loss of the magnetic core and the conduction loss of the winding are reduced overall, and heat generation is reduced. The effect is obtained.

[Brief description of the drawings]

FIG. 1A is a plan view and FIG. 1B is a front view showing a magnetic core according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a core showing a magnetic flux distribution of a magnetic core according to the first embodiment of the present invention.

FIG. 3 is a sectional view taken along the line III-III of FIG. 2;

FIGS. 4A and 4B are graphs showing a relationship between L1 / W1 and L1 / L2 and loss due to the magnetic core according to the first embodiment of the present invention.

5A is a plan view and FIG. 5B is a front view showing a magnetic core according to a second embodiment of the present invention.

6A is a plan view and FIG. 6B is a front view showing a magnetic core according to a third embodiment of the present invention.

7A is a plan view showing a conventional magnetic core, and FIG.
Is a front view

8A is a plan view showing a conventional magnetic core, and FIG.
Is a front view

[Explanation of symbols]

 1, 20, 30, 91, 100 Half core 10 Coil 11, 21, 31 Middle foot 12, 22, 32 Outer foot 13, 23, 33 Bottom plate

Claims (3)

[Claims] 1. A bottom plate having a substantially rectangular parallelepiped shape, a pair of outer legs formed integrally with the bottom plate at both ends on one long side of one surface of the bottom plate, respectively, Substantially in a central portion, a substantially rectangular direction in which a major axis direction is substantially coincident with a direction of a long side of the bottom plate portion is disposed between the pair of outer foot portions and integrally formed with the bottom plate portion. It has a middle foot portion that is a pillar in cross section, the distance between each side surface of the middle foot portion and the inside surface of the outer foot portion is substantially constant, and the length of the long side of the bottom plate portion is 1.0 times or more of the length of the short side of the bottom plate.
A magnetic core, wherein the length is not more than 5 times and not less than 1.2 times and not more than 2 times the length of the major axis of the midfoot portion. 2. A bottom plate portion having a substantially elliptical plate shape, a pair of outer foot portions integrally formed with the bottom plate portion at both short-axis side ends of one surface of the bottom plate portion, A substantially central portion of the bottom plate portion has a major axis direction substantially coincident with a major axis direction of the bottom plate portion, is disposed between the pair of outer feet, and is substantially formed integrally with the bottom plate portion. A middle foot portion, which is a column having an oval cross section, wherein a distance between a side surface of the middle foot portion and an inner side surface of the outer foot portion is substantially constant, and a length of a long axis of the bottom plate portion; Is 1.0 or more times the length of the minor axis of the bottom plate.
A magnetic core, wherein the core is not more than 5 times and not less than 1.2 times and not more than 2 times the major axis of the midfoot portion. 3. The magnetic core according to claim 2, wherein both ends of the bottom plate in the long axis direction are formed in a straight line parallel to the short axis and coincident with the end face of the outer foot. .