JPH0587918U - Ferrite core - Google Patents

Abstract

(57) [Abstract] [Purpose] It is difficult to magnetically saturate even if the bottom plate is made thin, so it is suitable for thinning and large capacity, and has a uniform cross-sectional area over the entire magnetic path to reduce the space factor during vertical mounting it can. [Structure] Outer legs 14, 1 are provided at both ends of the bottom plate 12, respectively.
6 has an integral structure in which a middle foot portion 18 is arranged in the center. The bottom plate portion 12 has a planar shape in which the center of the side surface of the rectangle is narrowed, and the two side surfaces at both ends of the bottom plate portion are continuous without a step toward the center. The two outer legs 14 and 16 have a rectangular planar shape, and the outer three surfaces thereof and one end surface and two side surfaces of both ends of the bottom plate portion 12 form one surface. The middle foot portion 18 has a planar shape in which two semicircles each having a diameter of two opposite sides of a rectangle are combined, and is provided such that its major axis direction coincides with the width direction of the bottom plate portion. The short axis side surface of the middle foot portion 18 faces the narrowed side surface of the bottom plate portion.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a ferrite magnetic core having an integral structure in which an outer foot portion is arranged at each end of a planar bottom plate portion having a rectangular side surface with a narrowed center, and a middle foot portion is arranged at the center. More specifically, the present invention relates to a ferrite magnetic core having a magnetic core height dimension of 1/2 or less of a magnetic core length dimension or a magnetic core width dimension, which is particularly suitable for vertical surface mounting on a circuit board.

[0002]

[Prior Art]

 With the progress of thinner and larger capacity of switching power supplies, similar demands are being made for transformers and choke coils that are used parts. The ferrite magnetic core suitable for such thinning and large capacity is a type (vertical mounting type) in which each foot is surface-mounted in a direction extending in the direction perpendicular to the circuit board surface.

As a ferrite core of this kind, for example, as shown in FIG. 4, outer legs 44 and 46 are provided at both ends of the bottom plate 42, and a cylindrical middle leg 48 is provided at the center thereof in the same direction. There is a structure in which they are integrally projected, and the height of the magnetic core is 1/2 or less of the magnetic core length (the length of the bottom plate portion 42) or the magnetic core width (the width of the bottom plate portion 42). The bottom plate portion 42 has a planar shape in which both ends of the rectangular side surface are widened and have a step 50 toward the center, and the center of the side surface is narrowed by a notch portion 49. The two outer legs 44, 46 have a planar shape in which the outer three faces thereof, one end face of both ends of the bottom plate and two side faces form one face, and the side faces of the middle leg 48 face the narrowed side faces of the bottom plate 42. There is.

[0004]

[Problems to be solved by the device]

 In order to reduce the thickness of the ferrite core, it is necessary to lower the outer and middle legs first and at the same time make the bottom plate as thin as possible. However, the heights of the outer and middle feet are limited by the space of the windings housed inside. If the bottom plate can be made thinner, it will lead to weight reduction of the magnetic core, which is preferable. However, in the ferrite core having the above-described shape, the magnetic path cross-sectional area at the root of the middle foot is originally small, so if the bottom plate becomes thinner, the magnetic flux density at that part increases and becomes saturated. Then, for example, when it is used for a transformer or the like, desired characteristics cannot be obtained, and significant waveform distortion and temperature rise are caused. If the bottom plate is made thinner to reduce the thickness of the ferrite core as described above, magnetic saturation occurs at the root of the middle foot, and the capacity cannot be increased.

Further, in the outer root portion, since the bottom plate has a step, the magnetic path cross-sectional area is sharply reduced. Therefore, if the bottom plate portion becomes thinner, the wide outer foot portion cannot be effectively used in the magnetic path. Therefore, such a magnetic core shape has a problem that it is difficult to reduce the space factor at the time of mounting.

The object of the present invention is to prevent magnetic saturation even when the bottom plate is thinned, and therefore suitable for thinning and large capacity, and as a substantially uniform cross-sectional area over the entire magnetic path, a space factor in vertical mounting. It is to provide a ferrite magnetic core that can reduce

[0007]

[Means for Solving the Problems]

 The present invention has an integrated structure in which outer legs are arranged at both ends of the bottom plate and a middle leg is arranged in the center, and the height of the core is a ferrite core having a length less than 1/2 of the length or width of the core. is there. In order to achieve the above object, in the present invention, the bottom plate has a planar shape in which the center of the side surface of the rectangle is narrowed, and the two side faces at both ends of the bottom plate are connected to each other without a step toward the center. The foot portion has a planar shape in which the outer three surfaces thereof, one end surface at both ends of the bottom plate portion, and two side surfaces form one surface. However, the short-axis side surface of the midfoot faces the narrowed side surface of the bottom plate. The planar shape of the middle foot portion is a shape obtained by combining two semicircles each having a diameter of two opposite sides of a rectangle, or an elliptical shape.

[0008]

[Action]

 According to the present invention, the planar shape of the middle foot portion is an elliptical shape, and the long axis direction thereof coincides with the width direction of the bottom plate portion, so that the cross-sectional area at the middle foot root portion increases. For example, if the midfoot has a planar shape that combines two semicircles with two opposite sides each having a rectangular shape, the cross-sectional area at the midfoot root is only rectangular compared to the conventional circular shape. Will increase. Therefore, assuming that the thickness of the bottom plate is the same as that of the conventional product, the magnetic flux density is reduced by the increase of the cross-sectional area, magnetic saturation becomes difficult, and the capacity can be increased. If the same capacity as the conventional product is required, the bottom plate can be made thinner.

Since the bottom plate portion is continuous from the two side faces at both ends toward the center without a step, the magnetic path cross-sectional area of the outer foot portion is substantially equal to the magnetic path cross-sectional area of the bottom plate portion. However, compared to the conventional product, there is no extra protrusion in the width direction, each magnetic path can be effectively utilized, and the space factor at the time of mounting becomes smaller.

[0010]

【Example】

 FIG. 1 is a plan view showing an embodiment of a ferrite core according to the present invention. The ferrite magnetic core has an integral structure in which outer foot portions 14 and 16 are arranged at both ends of the bottom plate portion 12 and a middle foot portion 18 is arranged at the center. The bottom plate portion 12 has a narrowed planar shape by forming a cutout portion 19 at the center of a rectangular side surface, and the two side surfaces at both ends of the bottom plate portion are continuous without a step toward the center. The two outer legs 14 and 16 have a rectangular planar shape, and the outer three faces thereof and one end face and two side faces of both ends of the bottom plate 12 are flush with each other. The middle foot portion 18 has a planar shape in which two semicircles each having a diameter of two opposite sides of a rectangle are combined, and is provided so that its major axis direction coincides with the width direction of the bottom plate portion. The short axis side surface of the middle foot portion 18 faces the narrowed side surface (notched surface) of the bottom plate portion.

When constructing a transformer or a choke coil, as shown in FIG. 2, two such ferrite magnetic cores are combined so that the end faces of their respective foot portions face each other. Although not shown, a bobbin wound with a coil is mounted in the space between them.

Here, the height H _{1 obtained} by combining the two ferrite magnetic cores is 1/2 or less of the magnetic core length (the length of the bottom plate portion 12) L ₁ . The length L ₂ of the middle leg 18 in the major axis direction is calculated from the magnetic core width (width of the bottom plate 12) L ₃ by the amount corresponding to the coil winding width minus the terminal lead-out amount of the bobbin wound with the coil. Is also small. The thickness H ₃ of the bottom plate portion 12 is almost the same as the height H ₂ of each foot portion.

In this combined ferrite core, the magnetic path passes through the middle foot portion 18, the bottom plate portion 12, and the outer foot portions 14 and 16 of one ferrite magnetic core, and the outer foot portions 14 and 16 and the bottom plate of the other ferrite magnetic core. It is formed so as to pass through the portion 12 and the midfoot portion 18. In this ferrite core, since the middle leg 18 has a shape combining a rectangle and a semicircle, and the long axis direction thereof coincides with the width direction of the bottom plate 12, the length of the middle leg is equal to the length of one side of the rectangle. The magnetic path cross-sectional area in the area increases. Therefore, magnetic saturation is less likely to occur, and the capacity can be increased. On the contrary, when the capacity is not required to be so large, the bottom plate portion can be thinned, and the ferrite magnetic core can be thinned.

Further, in the present invention, at both end portions of the bottom plate portion 12, the two side surfaces thereof have a continuous shape without a step toward the center. In other words, the outer legs do not project in the width direction of the magnetic core, unlike the conventional products. Therefore, the outer foot root does not have an excessively large cross-sectional area, and the cross-section is almost the same as the middle foot root. As a result, there is no waste in the magnetic path cross-sectional area, and there is no protrusion in the width direction of the magnetic core.

Another embodiment of the present invention is shown in FIG. In FIG. 3A, the central constriction portion of the bottom plate portion 22 has a rounded shape, and the inner surfaces of the outer leg portions 24 and 26 are formed as concave curved surfaces. With this arrangement, it becomes easy to mount the bobbin wound with the coil on the middle foot portion 28, and the coupling state between the coil and the ferrite core becomes good. In FIG. 3B, the planar shape of the middle foot portion 38 is an ellipse, and the inner surfaces of the outer foot portions 34, 36 are also curved (corresponding to the outer surface shape of the middle foot portion 38). With this configuration, the cross-sectional area at the base of the middle foot is increased, so that favorable characteristics are obtained.

[0016]

[Effect of the device]

 According to the present invention, since the plane shape of the middle foot is made elliptical and the long axis direction is arranged in the width direction of the bottom plate as described above, the length of the root portion of the middle foot is increased, and accordingly The increase in the cross-sectional area at that portion makes it difficult for magnetic saturation to occur, thereby achieving a large capacity. Further, when the same capacity as the conventional one is sufficient, the bottom plate portion can be thinned, and the ferrite magnetic core can be thinned.

Further, in the present invention, since the two side surfaces at both ends of the bottom plate are continuous toward the center without a step, the cross-sectional area of the outer foot base portion does not become excessively large, and is substantially uniform over the entire magnetic path. The cross-sectional area can be made different, and the ferrite material can be effectively used, resulting in an optimum shape. As a result, the widthwise spread at both ends of the bottom plate portion is eliminated, the size can be reduced, and the space factor at the time of vertical mounting on the circuit board can be reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a ferrite core according to the present invention.

FIG. 2 is a side view showing a state where two ferrite magnetic cores of FIG. 1 are combined.

FIG. 3 is a plan view showing another embodiment of the ferrite core according to the present invention.

FIG. 4 is a plan view showing an example of a conventional ferrite magnetic core.

[Explanation of symbols]

 12 Bottom plate part 14 Outer foot part 16 Outer foot part 18 Middle foot part

Claims (2)

[Scope of utility model registration request] 1. A ferrite magnetic core having an integral structure in which outer legs are arranged at both ends of the bottom plate and a middle leg is arranged in the center, and the height of the magnetic core is 1/2 or less of the length or width of the magnetic core. The bottom plate has a rectangular planar shape with a narrowed center, and the two side faces at both ends of the bottom plate are continuous without a step toward the center. One end surface and two side surfaces of the middle foot portion are in a plane shape, and the middle foot portion has an elliptical shape in plan view, and the long axis direction thereof coincides with the bottom plate width direction, and the short foot side surface of the middle foot portion. A ferrite magnetic core characterized in that it faces the narrowed side surface of the bottom plate. 2. The ferrite core according to claim 1, wherein the planar shape of the middle foot portion is a shape obtained by combining two semicircles each having a diameter of two opposite sides of a rectangle, or an elliptical shape.