JPH0521244A - Thin transformer - Google Patents

Abstract

PURPOSE:To reduce loss of a plane coil caused by skin effect in use at high frequency in a thin transformer which is formed by laminating a plane coil. CONSTITUTION:A coil part of a thin transformer is constituted of at least three plane coils 2a, 2b, 3. The plane coil 3 is held between two plane coils 2a, 2b, the plane coils 2a, 2b are made one coil and the plane coil 3 is made the other coil. Here, magnetmotive force by a current flowing to one coil is reduced by connecting the plane coils 2a, 2b in parallel. Influence of skin effect is reduced by reduction of the magnetmotive force, and loss caused thereby is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a thin transformer used for power conversion, insulation, etc. in a switching power supply and the like, and more particularly to a thin transformer for reducing loss of a coil portion.

[0002]

2. Description of the Related Art The structure of a conventional thin transformer is shown in FIGS. 6 (a) and 6 (b). In FIG. 6, (a)
Is a partially broken perspective view, (b) is a sectional view of the broken portion A, and θ, Z, and r are coordinate axes of the space. In the structure of this conventional example, 101 is a ring-shaped space S inside.
A pair of ferrite magnetic cores having recesses for forming
102 is one coil composed of a planar coil, 103
Is the other coil which is also composed of a planar coil. Although the winding ratio of the coil 102 and the coil 103 can be designed freely, the case of 4: 1 is shown in the illustrated example. The coil 102 and the coil 103 are a pair of ferrite magnetic cores 10.
In the internal space S formed by one member, the filler 10
They are insulated from each other by 4 and laminated and fixed.

Since the transformer of the switching power supply is used at a high frequency, a skin effect appears in its coil. Therefore, in the thin transformer, the planar coils 102, 1
The thickness h'of 03 was designed to be almost the same as the skin depth (depth of skin effect) δ of the conductive plate processed in the planar coils 102 and 103. The skin depth δ is a value calculated by the following equation, where the conductivity of the conductive plate is σ, the transmittance is μ ₀ , and the frequency of the current flowing through the planar coils 102 and 103 is f.

[0004]

[Equation 1]

A design example of a thin transformer in which the thickness of such a plane coil is almost the same as the skin depth is as follows.
A. F. Gold Burke, J.M. G. Kasakian, M.A.
F. "Lee shoes Rireiteddo-to-1-10MH _Z transformer design" by Messrs Shurehito (IEEE Trans.onPower Ele
ctron. , 4, January 1989) and "finite element analysis of Copper loss-in-1-10MH _Z transformer"
(IEEE Trans. On Power Elec
tron. , 4, April 1989) and the like.

[0006]

However, in the thin transformer of the above-mentioned conventional technique, the loss of the coil cannot be reduced even if the thickness of the plane coil is more than the skin depth. Therefore, the reduction of the loss remains a problem. Was there. FIG. 7 is a calculation diagram showing the loss of the coil when the thickness of the plane coil is changed. There is a value h _opt that minimizes the loss in the thickness of the plane coil, and the thickness of the winding is more than that. It is shown that there is no effect even if is increased.

The present invention was devised to solve the above problems, and an object of the present invention is to provide a thin transformer capable of reducing the loss of the planar coil that causes the skin effect.

[0008]

In order to achieve the above object, in the structure of the thin transformer of the present invention, at least three plane coils each obtained by processing a conductive plate into a spiral shape are used.
A structure is provided in which a coil portion that is laminated individually and a pair of flat ferrite cores that sandwich the coil portion are provided, and among the three planar coils, the planar coils that are arranged above and below sandwich the planar coil that is arranged in the middle. The upper and lower flat coils are electrically connected in parallel or in series to form one coil, and the intermediate flat coil is the other coil.

[0009]

The present invention analyzes the relationship between the configuration of a plane coil and the loss of the plane coil, and based on the analysis result, presents a configuration of a coil that minimizes the loss of the plane coil. At least one of the coils constituting the thin transformer is made into two plane coils sandwiching the other coil, and these two plane coils are connected in parallel or in series to reduce the magnetomotive force due to the current flowing in one coil. .. Due to this decrease in the magnetomotive force, the magnitude of the magnetic flux changing in the thickness direction of each coil is reduced, the influence of the skin effect of the coil is reduced, and the loss due to it is reduced.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings.

1A and 1B are configuration diagrams showing a first embodiment of a thin transformer according to the present invention. FIG. 1A is a sectional view of the thin transformer, and FIG. 1B is a coil connection. It is a figure. In the configuration of the present embodiment, 1 is a pair of ferrite magnetic cores each having a recess for forming a ring-shaped space S therein, 2
a and 2b (hereinafter referred to as "2" when represented) are a pair of coils each made into a flat coil of 6 turns by processing a conductive plate into a spiral shape, and 3 are 3 turns by similarly processing a conductive plate into a spiral shape. The coil 4 is a plane coil, and 4 is a filler. The pair of plane coils 2a and 2b are arranged so as to sandwich the plane coil 3 from above and below.
The a and the planar coil 2b are electrically connected in parallel externally as shown in FIG. 1 (b). Therefore, the turn ratio of the plane coil 2 and the plane coil 3 is 6: 3, but it goes without saying that this turn ratio can be designed freely. The ferrite core 1 is formed in a thin disk shape, and an internal space S formed by a pair of recesses facing each other.
The coils 2a, 2b and the coil 3 are sandwiched therein, and are insulated in a desired thickness by the filling material 4 and fixed in a laminated state.

The operation and effect of the first embodiment constructed as above will be described.

In this embodiment, two plane coils 2a and 2b are used.
Are arranged above and below one plane coil 3, and the two plane coils 2a and 2b are connected in parallel to form two plane coils 2
The current flowing in a and 2b is divided into two, and one flat coil 2
The purpose is to reduce the magnetomotive force due to the current flowing through a or 2b. By reducing the magnetomotive force in this way, the magnitude of the magnetic flux that changes in the thickness direction of each coil can also be reduced at the same time, so that the effect of the skin effect of the coil can be reduced.

The increase in loss due to the skin effect of the coil will be evaluated by the AC resistance (equivalent to the loss when an effective value current of 1 A is passed through the coil), and the effect of the above embodiment will be described below. The winding structure in comparison with the shape of the thin transformer used for the calculation is shown in FIGS. (G) is a perspective view in which a winding portion is broken, and (a) to (f) are cross-sectional views of the fractured surface A, showing six types (hereinafter, (a) to
Regarding (f) structure, only the coil portion is shown in an enlarged manner. In the cross-sectional view of (g), 1 is a pair of ferrite magnetic cores (cores) each having a recess for forming a ring-shaped space S therein, 2 is a flat coil having four turns by processing a conductive plate into a spiral shape. The primary coil 3 and the secondary coil 3 are similarly secondary coils each formed by processing a conductive plate into a spiral shape to form a one-turn flat coil. The space S is filled with the filler. In the winding structure, (a) structure is the basic structure described in the above-mentioned paper, (b) structure is the structure according to the present embodiment, and (c) to (f) structures reduce the magnetomotive force to reduce the AC resistance. This is the targeted structure.

Table 1 shows the calculation conditions. In the table, W is the width of the conductive plate of the planar coil 3, D is the distance between the conductive plates of the planar coil 3, and H is the thickness of the conductive plate.

[0016]

[Table 1]

The value of the skin depth of the conductive plate is 50
It becomes 93 μm at 0 kHz, which is almost equal to the thickness H of the conductive plate and decreases to half of H at 2 MHz. When the skin depth is less than the thickness of the conductive plate, the value of the skin effect due to each winding structure becomes remarkable, so the frequency for calculation is 2 MH.
z. A commercially available finite element method program "Maxwell" (Ansoft Corp.) was used for the calculation. The AC resistance of each winding structure (a) to (f) was calculated by using the primary coil as an example, and the result normalized by the DC resistance is shown in FIG.
Shown in. In the structure (b) of this embodiment, the increase rate (Rac / Rdc) of the DC resistance can be reduced as compared with the structure (a). However, it can be seen that the rate of increase in AC resistance cannot be reduced with other winding structures. This is (c)-(e)
When magnetic flux is dispersed like a structure or a winding that blocks the flow of magnetic flux is inserted, leakage flux or magnetic flux concentrated in a part causes
This is because the eddy current loss increases. Further, even if the conductive plate is divided as in the case of (f) structure, the current concentrates on the boundary between the primary coil 2 and the secondary coil 3 having low impedance, and the AC resistance cannot be reduced. Therefore, the AC resistance (coil loss) cannot be reduced by any method other than this embodiment.

Next, a second embodiment of the present invention will be described.

4 (a) and 4 (b) are views showing the structure thereof, FIG. 4 (a) is a partial sectional view, and FIG. 4 (b) is an electrical connection diagram of a coil. In this embodiment, an intermediate flat coil 3 is sandwiched between upper and lower flat coils 2a and 2b in the coil portion composed of the flat coils 2a, 2b and 3 of the first embodiment.
A thin transformer in which the upper and lower flat coils 2a and 2b are connected in series to form one coil portion and the intermediate flat coil 3 serves as the other coil portion is shown. These coil parts are
Similar to the above embodiment, the flat ferrite magnetic core 1 is sandwiched between the flat ferrite magnetic cores 1 and stacked and fixed by the filler 4.

In the second embodiment thus constructed, the loss of each coil portion can be reduced by the same action as in the first embodiment, and the coils 2a and 2b are connected in series. Therefore, a larger inductance can be obtained than in the first embodiment.

Next, a third embodiment of the present invention will be described.

5 (a), 5 (b), and 5 (c) are views showing the structure, (a) is a partial sectional view, and (b) and (c) are electrical connection diagrams of coils. Is. In this embodiment, as an example of the case where the coil portion is formed by laminating four or more plane coils, a case where the coil portion is composed of five layers of plane coils is shown. In the coil portion of this embodiment, the plane coil 3a is sandwiched between the plane coils 2a and 2b from above and below, and the plane coil 2b and the plane coil 2c are sandwiched between the plane coil 2a and the plane coil 3b.
a, 2b, 2c as one coil part, and the planar coil 3
a and 3b are used as the other coil portion. Similar to the first embodiment, these coil portions are sandwiched between the spaces S in the pair of flat ferrite magnetic cores 1 and stacked and fixed by the filler 4. In this embodiment, as shown in FIG. 5B, the planar coils 2a, 2 are
It is possible to configure two types, that is, a group of b and 2c and a group of planar coils 3a and 3b are connected in parallel, and a series of each group is connected as shown in FIG. 5C.

In the configuration of the above third embodiment,
The configuration by the connection of (b) corresponds to the first embodiment,
It is clear that the configuration by the connection of (c) corresponds to the second embodiment, and the same effects can be obtained respectively. However, since the number of plane coils forming each coil portion is large, the effect can be further enhanced.

The shape of the thin transformer of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that it can be applied to various shapes. As described above, the present invention can be applied in various ways in accordance with its gist and can take various embodiments.

[0025]

As is apparent from the above description, according to the thin transformer of the present invention, the thickness of the plane coil is set to about skin depth to reduce the loss of the coil portion as compared with the plane coil of the conventional structure. It is possible to obtain the advantage that the switching power supply can be made compact and economical.

[Brief description of drawings]

1A and 1B are configuration diagrams showing a first embodiment of the present invention.

2A and 2B are winding structure diagrams in which coil losses are compared in order to clarify the effect of the first embodiment.

FIG. 3 is an explanatory diagram showing that the coil loss of the first embodiment can be reduced as compared with the conventional example.

4A and 4B are configuration diagrams showing a second embodiment of the present invention.

5A, 5B and 5C are configuration diagrams showing a third embodiment of the present invention.

6A and 6B are configuration diagrams showing a configuration of a conventional example.

FIG. 7 is an explanatory diagram showing the relationship between the thickness and the loss of the conductive plate of the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ferrite magnetic core, 2a, 2b, 2c ... The plane coil which comprises one coil part, 3, 3a, 3b ... The plane coil which comprises the other coil part, 4 ... Filler.

Claims (1)

Claim: What is claimed is: 1. A coil portion, in which at least three planar coils obtained by processing a conductive plate into a spiral shape are laminated, and a pair of flat ferrite magnetic cores sandwiching the coil portion. Among the plane coils, the plane coils arranged above and below have a structure sandwiching the plane coils arranged in the middle, and the top and bottom plane coils are electrically connected in parallel or in series to form one coil, A thin transformer characterized by using the flat coil as the other coil.