JPH0456303A - High-frequency inductor - Google Patents

Abstract

PURPOSE:To reduce an AC loss by a method wherein a conductor foil is radially installed on the seating faces of laminated perforated cores, the section of the conductor foil is installed zigzag and the thickness of the conductor foil is specified conforming to the frequency of a current made to flow. CONSTITUTION:A perforated core 10 consists of a multitude of laminated torus-shaped troidal cores, an inner side surface 12 positioned on a hollow window, seating faces (laminated faces) 14 and 18 having a torus-shaped flat surface and an outer side surface 16. A conductor foil (a copper foil winding) 20 is provided between the layers of the laminated cores 10 and is provided with a first surface 22 which is positioned on the sides of the inner side surfaces 12, second surfaces 24, which have the same width as that of the surface 22, are divided in a prescribed width W. and are installed radially on the seating faces 14, a third surface 26, which is installed on the outer side surfaces 16 and is connected with the second surfaces 24 at the end parts of the surfaces 24 and fourth surfaces 28, which are mounted on the seating faces 18 on the opposite side to the seating faces 14 and are radially mounted at positions where the surfaces 28 coincide roughly with the surfaces 24 and moreover, the foil 20 is similarly continued also to the lower layers of the cores. The thickness (delta) of this conductor foil is set at a range that delta<3xK/sq. rt. f (f: the frequency of a current which is made to flow through an inductor, K: the skin effect constant of the material for the conductor foil) is valid.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a high frequency inductor suitable for use in electronic devices that handle high frequencies of approximately several MHz, and particularly relates to improvements in lower loss and thinner inductor.

<Conventional technology> Inductors usually use windings to pass current.
In the low frequency region, it flows uniformly across the cross section of the conductor. However, there is a problem in that copper loss increases due to skin effect and proximity effect in a high frequency range of about several MHz. Hereinafter, these relationships will be explained using the drawings.

■ Skin effect Figure 8 is an explanatory diagram of the skin effect, where (A) is a conductor cross section, (B
) represents the current distribution in the diameter direction.

The skin effect refers to the fact that as the frequency increases, current flows concentrated on the surface of the conductor.The skin thickness δ, which occurs when leakage magnetic flux around the conductor enters the inside of the conductor, is the constant of the surface effect. Letting K, it is given by the following equation.

δ=to/√f[mml (1) where f is the frequency. When / is IMHz and the conductor is copper, K is 66.1, so δ is 66.1 μm. Therefore, in the case of a single wire, the internal AC resistance can be reduced by making the wire diameter as thick as the skin. However, there is a certain limit to the current density that can be passed through the conductor, so the inductor needs to be shaped like a foil to ensure a sufficient cross-sectional area.

■ Proximity Effect Figure 9 is an explanatory diagram of the proximity effect, where (A) shows the case where current flows in the same direction in two lined up conductors, and (B) shows the case where the current flows in the opposite direction. Proximity effect refers to the fact that when there is a current-carrying conductor in close proximity, the magnetic field created by this conductor is not uniform across the conductor's cross section, so the magnetic field inside the conductor is not completely canceled out and losses increase. When flowing in the same direction, the current is distributed on the outside, and when flowing in the opposite direction, the current is distributed on the inside. To alleviate this problem, adjacent conductors may be spaced apart by approximately the thickness of the skin.

In FIG. 10, the conductor is made of copper foil, and these two copper foils are located in parallel with a distance d between them. Figure 11 is the 10th
FIG. 3 is an explanatory diagram of AC resistance Rac in the arrangement shown in the figure. The vertical axis shows AC resistance Rac based on DC resistance Rdc,
The horizontal axis shows the distance lad. The width W of the copper foil is 5.
This is an example of calculation when the thickness is 100 μm and the frequency I is IMHz. @Rac/Rd for foil alone
c is 1.5, but increases to 2.2 in the same direction (e.g. in an inductor with coiled windings), and increases to 2.2 in the opposite direction (e.g. - in an inductor with alternating primary and secondary windings). transformer), it has decreased to 1.3.

<Problems to be Solved by the Invention> As described above, there is a problem in that when a conductor wire that allows current to flow in the same direction, such as a coiled inductor, is used, AC resistance increases and loss increases.

The present invention solves these problems and aims to provide a high frequency inductor with low AC resistance.

Means for Solving the Problems> The high-frequency inductor of the present invention that achieves the above object includes a perforated core made of a magnetic material and arranged in layers, and a first core located on the inner side of the perforated core. a second surface that has the same width as the first surface and is divided into predetermined widths and is attached radially to the seating surface of the perforated core; and this second surface that is attached radially. a third surface that is connected at each end and is attached to the outer surface of the perforated core; and a fourth surface that is radially attached at a position that substantially coincides with the second surface.

Then, the thickness (δ) of this conductor foil is δ<3xK/√f /: Frequency of current flowing through the inductor K: skin effect constant of conductor foil material It is characterized by the fact that it is set within the range in which it holds true.

Functions Each component of the present invention has the following functions. The conductor foil is attached to the laminated perforated core in a meandering cross-section.

As a result, in each core cross section, current flows in opposite directions above and below the seat surface, reducing AC loss. Furthermore, since the thickness of the conductor foil is matched to the frequency of the flow, the influence of eddy currents is reduced and AC loss is reduced. Large inductance can be obtained by increasing the number of core layers.

<Example> The present invention will be explained below using the drawings.

Fig. 1 is a configuration diagram showing an embodiment of the present invention, (A) is a top view, (B) is a side view, and Fig. 2 is a cross-sectional view taken along line 2-2 of Fig. 1A. Here, the perforated core 10 is made by laminating a large number of annular toroidal cores, has a substantially rectangular cross section, and has an inner surface 12 located at the hollow window.
, seat surfaces 14 and 18 having annular flat surfaces, and a concave side surface 16. Seat surface 14.18 is another perforated core IO
When stacked, the bearing surfaces 14 and 1g face each other. The inner diameter of this core is dl, and the outer diameter is dl. The conductor foil 20 is provided between each layer of the laminated perforated core 10, and is made of copper foil, for example. The conductor foil 20 includes
A first surface 22 located on the inner surface 12 side of the perforated core 10
and has the same width as this first surface and a predetermined width (In
1) and has a second surface 24 attached radially to the seat surface 14.18. For example, if it is separated into 8 lines as shown in the figure, the following relationship is satisfied: 2, 8υ) 1 in π・d 1 (2
) The third surface 26 is attached to the outer surface 16 of the perforated core 10 and is connected to the second surface 24 at each end.

Therefore, the width W2 of the core exposed surface appearing on the outer surface satisfies the following relationship.

W2-π・d2/8-1p1 (3)
The fourth surface 28 is attached to the seat surface opposite to the seat surface to which the second surface 26 is attached, with respect to the perforated core 10 having the third surface attached to the outer surface 26. and is attached radially at a position that roughly coincides with the second surface.

If the perforated core 10 is also present in a lower layer, this fourth layer 28 may be followed by a first surface 22 that is attached to the inner surface 12 of the lower core. In addition, the conductor foil 2
0 is preferably covered with an insulator on both sides to prevent short circuits.

The operation of the device configured in this way will be described next. Third
The figure is a 3-3 sectional view of FIG. The copper foil windings 20 flow in the same direction in each layer sandwiched by the perforated core 10, but flow in the opposite direction for the copper foil windings 20 in adjacent layers. As for the copper foil winding 20 separated by the perforated core 10, the alternating current resistance is reduced as explained in FIG. 11. On the other hand, since the distance L7 between the same layers is considerably smaller than the thickness δ or the interval thereof, the influence can be ignored except in the region close to the inner surface. Note that the shaded area inside the copper foil winding 20 indicates the area through which current flows.

Generally, the magnetic resistance RC of one 1-roidal core is given by the following equation.

Re =2yr/1μm1-1nfd2/d1))(
4) Here, μ represents magnetic permeability and j represents thickness. Therefore, the inductance LC is given by the following equation.

L,,c=1/Rc=μm1-In(d2/d1)/2yr (5)
If it is configured with n cores, it will be n times the number of - cores. Therefore, in order to have a thin shape while having the same inductance, the following points should be taken into consideration.

(1) The core shape should have a small inner diameter and a large outer diameter.

(11) Select a core material with high magnetic permeability and reduce the number of six-sided cores.

FIG. 4 is an explanatory diagram of the copper foil thickness δ. With respect to the skin thickness of 66 μm shown in the first equation, if the thickness is approximately three times the thickness, the AC resistance will be less than twice the DC resistance, which is preferable.
If the thickness is greater than that, the AC resistance will increase significantly.

The eddy current induced by the magnetic field distributed in the width direction of the copper foil increases the thickness of the copper foil to a thickness similar to that of the skin effect. If the foil has
This is thought to be because the eddy current generated on the opposite surface is canceled out. On the other hand, making the copper foil thinner has no problem in terms of AC resistance, but the limits are determined by the amount of current to flow or mechanical strength.

Therefore, it is preferable that the thickness δ of the conductor foil 20 satisfies the following formula.

δ＜3K/J/
(6) Fig. 5 is an explanatory diagram when the conductor foil 20 is used w: (A) is a side view, (B) is a front view after bending, (C
) is a front view after making the cut. The length 11 of the first surface 22 and the length 13 of the third surface 26 are the same as those of the perforated core 1.
It is made to match the thickness of 0. In addition, the second surface 24
The length 12 of and the length 14 of the fourth surface 28 match the width (d2-a!1)/2 of the seat surface of the perforated core 10. A predetermined length of 11~
Make creases in units of 14. Next, the second to fourth
A cut with a predetermined width W1 is provided between the surfaces.

FIGS. 6 and 7 are explanatory diagrams of the process of attaching the conductor foil 20 to the perforated core 10, in which (A) is a top view and (B) is a side view. The conductor foil 20 is bent and attached to the perforated core 10 so as to cover the outer surface thereof (Fig. 6).
. Next, a C-shaped core (combining the two pieces will make 10 perforated cores)
) is installed between this perforated core 10 @L
5 (FIG. 7), attach the first surface 22 of the conductor foil to the surface corresponding to the inner surface. After this, you can easily assemble it by gluing it together. Then, by connecting a conductive wire that carries a current to the conductor foil 20, it functions as a high frequency inductor.

In the above embodiment, the shape of the perforated core 10 is described as a toroidal core, but the present invention is not limited to this, and the inner and outer surfaces may be polygonal. The conductor foil 20 may be attached by bonding the conductor foils together using an adhesive or by soldering.

<Effects of the Invention> As explained above, the present invention has the following effects.

■ A perforated core 10 is provided in multiple layers, and a conductor foil 2 is placed between each layer.
0 and alternated the connections between the inner and outer surfaces, so the current flowing through the conductor foil across the core is in the opposite direction.
AC resistance decreases and copper loss decreases.

■ The thickness of the conductor foil is about the same as that of the skin effect, so AC resistance is reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
2-2 sectional view of Figure A, Figure 3 is 3-3 sectional view of Figure 2,
Fig. 4 is an explanatory diagram of the copper foil thickness δ, Fig. 5 is an explanatory diagram when manufacturing the conductor foil 20, and Figs. 6 and 7 are the perforated core 1.
FIG. Fig. 8 is an explanatory diagram of the skin effect, Fig. 9 is an explanatory diagram of the proximity effect, Fig. 10 is an explanatory diagram of the conductor using copper foil, and Fig. 11 is an illustration of the AC resistance RaC in the arrangement shown in Fig. 10. It is an explanatory diagram. 10... Perforated core, 20... Conductor foil (#l foil),
5th ward

Claims (1)

[Scope of Claims] A perforated core made of a magnetic material and having a hollow window arranged in layers, a first surface located on the inner side of the perforated core, and having the same width as the first surface. a second surface divided into predetermined widths and attached radially to the seating surface of the perforated core, and connected to the radially attached second surface at each end and an outer surface of the perforated core; a third surface of the perforated core that is attached to the second surface of the perforated core, and a third surface of the perforated core that is radially attached to a seat surface on the side opposite to the seat surface on which the second surface of the perforated core is attached at a position that approximately coincides with the second surface of the perforated core. 4, and the thickness (δ) of the conductor foil is δ<3xK/√f f: Frequency of current flowing through the inductor K: Skin effect constant of the conductor foil material holds. A high frequency inductor characterized by a specified range.