Transformer

Abstract

To provide a transformer with small AC resistance despite its low magnetic coupling.SOLUTION: A transformer 1 comprises: a primary winding 2; a secondary winding 3; and a core 7 that has a center leg part 71 where the primary winding 2 and the secondary winding 3 are wound with a gap therebetween, and a side leg part 72 provided on the outer peripheral side of the primary winding 2 and the secondary winding 3. The transformer comprises: a first magnetic member 21 that is arranged in contact with at least part of a surface of winding material of the primary winding 2, and is formed of magnetic composite material including magnetic powder and matrix material; a second magnetic member 31 that is arranged in contact with at least part of a surface of winding material of the secondary winding 3, and is formed of magnetic composite material including magnetic powder and matrix material; and a third magnetic member 4 that is arranged between the primary winding 2 and the secondary winding 3, and is formed of magnetic composite material including magnetic powder and matrix material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a transformer with low magnetic coupling, such as a leakage transformer.

[0002] Transformers are used in various electric circuits. For example, electric circuits include power supply circuits such as DC-DC (direct current-direct current) converters. Increasing the switching frequency is effective for miniaturizing DC-DC converters. The development of gallium nitride (GaN) and silicon carbide (SiC) power devices, which have characteristics that exceed those of silicon-based power devices, has made it possible for DC-DC converters to function at higher switching frequencies. Power devices incur switching losses as their frequencies increase. The LLC resonant DC-DC converter is a low-loss DC-DC converter that can reduce switching losses at high frequencies by soft switching. The LLC resonant DC-DC converter is so named because it utilizes resonance with two Ls (inductors) and one C (capacitor).

[0003] An LLC resonant DC-DC converter uses a resonant inductor and a transformer. A leakage transformer, which is a transformer with low magnetic coupling, is used as the resonant inductor and transformer (for example, Patent Document 1). This is because the leakage inductance of the leakage transformer can be used as a substitute for the resonant inductor. When a leakage transformer is used, it is not necessary to provide a resonant inductor as a component, so the number of components can be reduced and the converter can be made smaller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-12554 Summary of the Invention [Problem to be solved by the invention]

[0005] In low magnetic coupling transformers such as leakage transformers, the coupling coefficient between the primary and secondary windings is small, which causes high leakage flux, and when this leakage flux passes through the transformer's winding conductor, eddy currents are generated inside the conductor, increasing the AC resistance. For this reason, suppressing this increase in AC resistance has become an issue.

[0006] The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a transformer having low magnetic coupling and low AC resistance. [Means for solving the problem]

[0007] The transformer described in claim 1 is a transformer comprising a core having a primary winding, a secondary winding, a central leg around which the primary winding and the secondary winding are wound with a gap therebetween, and side legs provided on the outer periphery of the primary winding and the secondary winding, and is characterized in comprising: a first magnetic member formed of a magnetic composite material containing magnetic powder and a matrix material and arranged in contact with at least a portion of a surface of the winding material of the primary winding; a second magnetic member formed of a magnetic composite material containing magnetic powder and a matrix material and arranged in contact with at least a portion of a surface of the winding material of the secondary winding; and a third magnetic member formed of a magnetic composite material containing magnetic powder and a matrix material and arranged between the primary winding and the secondary winding.

[0008] The transformer described in claim 2 is the transformer described in claim 1, characterized in that the first magnetic member is attached in layers so as to be in contact with and cover a surface of the winding material of the primary winding, so that adjacent layers of the first magnetic member do not come into contact with each other, and the second magnetic member is attached in layers so as to be in contact with and cover a surface of the winding material of the secondary winding, so that adjacent layers of the second magnetic member do not come into contact with each other.

[0009] The transformer described in claim 3 is the transformer described in claim 1, characterized in that the first magnetic member is provided to seal the primary winding, and the second magnetic member is provided to seal the secondary winding.

[0010] The transformer described in claim 4 is the transformer described in claim 1, characterized in that the first magnetic member is provided in contact with the outer circumferential and inner circumferential ends of the surface of the winding material of the primary winding, and the second magnetic member is provided in contact with the outer circumferential and inner circumferential ends of the surface of the winding material of the secondary winding.

[0011] The transformer described in claim 5 is the transformer described in claim 1, characterized in that the third magnetic member is provided so as not to come into contact with the central leg portion and the side leg portion.

[0012] The transformer described in claim 6 is the transformer described in claim 1, characterized in that the secondary winding is divided into two parts so that it is positioned so that the primary winding is sandwiched between them, and a first of the third magnetic members is arranged between the secondary winding and the primary winding of one of the two parts, and a second of the third magnetic members is arranged between the secondary winding and the primary winding of the other of the two parts. Effect of the Invention

[0013] In a transformer to which the present invention is applied, a first magnetic member made of a magnetic composite material is disposed in contact with the surface of the winding material of the primary winding, a second magnetic member made of a magnetic composite material is disposed in contact with the surface of the winding material of the secondary winding, and a third magnetic member made of a magnetic composite material is disposed between the primary winding and secondary winding. Since magnetic composite material has low loss at high frequencies, low magnetic permeability, and high saturation magnetic flux density, magnetic flux that penetrates the winding and generates losses is induced and shielded by the magnetic composite material, so that eddy currents generated inside the winding can be reduced despite low magnetic coupling, resulting in a transformer with low AC resistance. [Brief description of the drawings]

[0014] [Figure 1] 1 is a vertical sectional view of a transformer to which the present invention is applied; [Diagram 2] FIG. 2 is an enlarged view of the area enclosed by the dashed line in FIG. [Diagram 3] FIG. 1 is a circuit diagram of a transformer to which the present invention is applied. [Figure 4] FIG. 11 is a vertical sectional view of another transformer to which the present invention is applied. [Diagram 5] FIG. 5 is an enlarged view of a portion enclosed by a dashed line frame in FIG. [Figure 6] FIG. 11 is a vertical sectional view of still another transformer to which the present invention is applied. [Figure 7] FIG. 7 is an enlarged view of a portion enclosed by a dashed line frame in FIG. 6. [Figure 8] FIG. 11 is a partially enlarged cross-sectional view of a transformer according to Comparative Example 2. [Figure 9] FIG. 11 is a partially enlarged cross-sectional view of a transformer according to Comparative Example 3. [Figure 10] This is the gain characteristic of an LLC resonant DC-DC converter. [Figure 11] 1 shows the frequency characteristics of the complex relative permeability of the core material MC2 and the magnetic composite material. [Figure 12] 13 is a frequency characteristic showing a simulation result of a primary side inductance when the secondary side is open. [Figure 13] 13 is a frequency characteristic showing a simulation result of the primary side resistance when the secondary winding 3a is short-circuited. [Figure 14] 13 is a frequency characteristic showing a simulation result of the primary inductance when the secondary winding 3a is short-circuited. [Figure 15] 13 is a frequency characteristic showing a simulation result of a coupling coefficient k. [Figure 16] 13 is a graph showing a simulation result of the magnetic flux density of the third magnetic member. [Figure 17] 1 is a photograph showing the appearance and manufacturing process of a manufactured leakage transformer. [Figure 18] 13 is a frequency characteristic showing the measured value and the simulation result of the primary side inductance when the secondary side is open. [Figure 19]13 is a frequency characteristic showing the measured value and the simulation result of the primary side resistance when the secondary winding 3a is short-circuited. [Figure 20] 13 is a frequency characteristic showing the measured value and the simulation result of the primary side inductance when the secondary winding 3a is short-circuited. [Figure 21] 13 is a frequency characteristic showing the measured value and the simulation result of the coupling coefficient k. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In addition, common parts in the drawings may be denoted by the same or corresponding reference numerals, and the description thereof may be omitted.

[0016] First, the main configuration of transformers 1, 101, and 201 to which the present invention is applied will be described. Transformer 1 is shown in Figures 1 to 3, transformer 201 is shown in Figures 4 and 5, and transformer 301 is shown in Figures 6 and 7. The transformers 1, 101, 201 to which the present invention is applied include a primary winding 2, a secondary winding 3 (3a, 3b), a central leg 71 (71a, 71b) around which the primary winding 2 and the secondary winding 3 (3a, 3b) are wound with a gap between them, and a core 7 (one side core piece 7a, the other side core piece 7b) having side legs 72 (72a, 72b) provided on the outer periphery of the primary winding 2 and the secondary winding 3 (3a, 3b). This transformer 1, 101, 201 includes a first magnetic member 21, 22, 23 formed of a magnetic composite material containing magnetic powder and a matrix material and arranged in contact with at least a portion of the surface of the winding material of the primary winding 2, a second magnetic member 31, 32, 33 formed of a magnetic composite material containing magnetic powder and a matrix material and arranged in contact with at least a portion of the surface of the winding material of the secondary winding 3 (3a, 3b), and a third magnetic member 4 (4a, 4b) formed of a magnetic composite material containing magnetic powder and a matrix material and arranged between the primary winding 2 and the secondary winding 3 (3a, 3b). Each embodiment will be described below.

[0017] [First embodiment] Fig. 1 is a vertical cross-sectional view of a transformer 1 to which the present invention is applied. Fig. 2 is an enlarged view of a portion enclosed by a dashed line frame in Fig. 1. Fig. 3 is a circuit diagram of the transformer 1.

[0018] The transformer 1 of the first embodiment to which the present invention is applied is characterized in that a first magnetic member 21 is attached in layers so as to contact and cover the surface of the winding material of the primary winding 2, and adjacent layered first magnetic members 21 are arranged so as not to contact each other, and a second magnetic member 31 is attached in layers so as to contact and cover the surface of the wire material of the secondary winding, and adjacent layered second magnetic members 31 are arranged so as not to contact each other. The details will be explained below.

[0019] The transformer 1 includes a primary winding 2, a secondary winding 3 (3a, 3b), a first magnetic member 21, a second magnetic member 31, a third magnetic member 4 (4a, 4b), and a core .

[0020] FIG. 3 shows a circuit diagram of the transformer 1. The transformer 1 is composed of a primary winding 2 and a secondary winding 3. The secondary winding 3 is divided into two parts, a secondary winding (first winding part) 3a and a secondary winding (second winding part) 3b. The secondary winding 3 is composed of one of the two divided parts, the secondary winding 3a, and the other of the two divided parts, the secondary winding 3b, which are connected in series, and the connection part is the center tap of the secondary winding 3. The secondary winding 3a is composed of two windings (winding materials) connected in parallel, as an example. The secondary winding 3b is composed of two windings (winding materials) connected in parallel, as an example. Note that the circuit of this transformer 1 is just an example, and although an example has been shown in which the secondary windings 3a and 3b are each composed of two windings connected in parallel, the secondary windings 3a and 3b may each be composed of one winding. The secondary winding 3 may also be composed of a configuration without a center tap.

[0021] As shown in the longitudinal cross-sectional view of FIG. 1, the core 7 is configured with a pair of one-side (upper) core piece 7a and the other-side (lower) core piece 7b facing each other. The one-side core piece 7a and the other-side core piece 7b are formed symmetrically. The one-side core piece 7a has a central leg 71a and a side leg 72a. The central leg 71a and the side leg 72a are connected to a base portion 73a. The other-side core piece 7b has a central leg 71b and a side leg 72b. The central leg 71b and the side leg 72b are connected to a base portion 73b. The central leg 71a and the central leg 71b face each other to form the central leg 71, and the side leg 72a and the side leg 72b face each other to form the side leg 72. In this example, the one-side core piece 7a and the other-side core piece 7b are arranged facing each other with a gap therebetween. The presence or absence of a gap and the gap interval may be appropriately determined according to the required characteristics.

[0022] The core 7 (one-side core piece 7a, the other-side core piece 7b) is made of a known magnetic material, and can be made of, for example, a magnetic composite material containing iron-based amorphous magnetic powder such as FeSiCrB, ferrite, electromagnetic steel sheet, sendust, permalloy, Ni-based, Fe-based ferromagnetic material, etc. The core 7 is manufactured, for example, by compression molding a known magnetic material and subjecting it to heat treatment. The core 7 may also be a dust core made by forming an insulating layer around soft magnetic metal powder and pressure molding it.

[0023] The primary winding 2 and the secondary winding 3 (3a, 3b) are wound separately around a central leg 71 (71a, 71b) of the core 7 without overlapping or contacting each other. At least a part of the outer periphery of the primary winding 2 and the secondary winding 3 (3a, 3b) is covered by a side leg 72 (72a, 72b) of the core 7. In other words, the central leg 71 (71a, 71b) is located on the inner periphery of the primary winding 2 and the secondary winding 3 (3a, 3b), and the side leg 72 (72a, 72b) is located on the outer periphery of the primary winding 2 and the secondary winding 3 (3a, 3b).

[0024] The cross-sectional shape (not shown) of the central leg 71 (71a, 71b) of the core 7 is not limited, and may be any shape, such as a prismatic shape, a cylindrical shape, an elliptical shape, a polygonal shape, an oval shape, or a rounded rectangular shape (like the track of an athletics stadium). When the central leg 71 is prismatic, the one-side core piece 7a and the other-side core piece 7b are also called E cores. When the central leg 71 is cylindrical, the one-side core piece 7a and the other-side core piece 7b are also called ER cores. Here, as an example, the central leg 71 is assumed to be rectangular with rounded corners.

[0025] The primary winding 2 is wound around the central leg 71 (central leg 71a and central leg 71b) so that the middle position of the central leg 71 (the position where the central leg 71a and the central leg 71b face each other) is approximately in the center. The primary winding 2 may be wound around the central leg 71 via a bobbin, an insulating sheet, or the like (not shown) so as not to directly contact the central leg 71. Fig. 1 shows an example in which the primary winding 2 is wound with 10 turns.

[0026] The secondary winding 3 is divided into two parts, a secondary winding (first winding part) 3a and a secondary winding (second winding part) 3b, so that the secondary winding 3 is wound around the central leg 71 with the primary winding 2 sandwiched between them. The secondary winding 3a is wound around the central leg 71 (central leg 71a) on one side (upper side) of the primary winding 2 with a gap between it and the primary winding 2. The secondary winding 3b is wound around the central leg 71 (central leg 71b) on the other side (lower side) of the primary winding 2 with a gap between it and the primary winding 2. The secondary winding 3 (3a, 3b) may be wound around the central leg 71 via a bobbin, an insulating sheet, or the like (not shown) so as not to directly contact the central leg 71.

[0027] The secondary winding 3a is formed, for example, by winding two wire materials in parallel with a gap therebetween (parallel winding). These two wire materials are electrically connected in parallel. FIG. 1 shows an example in which the secondary winding 3a is wound with two turns. Similarly, the secondary winding 3b is formed, for example, by winding two wire materials in parallel with a gap therebetween (parallel winding). These two wire materials are electrically connected in parallel. FIG. 1 shows an example in which the secondary winding 3b is wound with two turns.

[0028] The winding material of the primary winding 2 and the secondary winding 3 (3a, 3b) is, for example, a conductor having a plate-like (rectangular) cross section. A rectangular wire or a ribbon wire may be used as such a winding material. The winding material of the primary winding 2 may be a Litz wire made by twisting together a plurality of wires and having a substantially rectangular cross section.

[0029] A first third magnetic member 4a for forming leakage inductance is disposed between one of the secondary windings 3a and the primary winding 2. The first third magnetic member 4a is formed in an annular plate shape (ring shape). The first third magnetic member 4a is formed of a magnetic composite material including magnetic powder and a matrix material.

[0030] A second third magnetic member 4b for forming leakage inductance is disposed between the other secondary winding 3b and the primary winding 2. The second third magnetic member 4b is formed in an annular plate shape (ring shape). The second third magnetic member 4a is formed of a magnetic composite material including magnetic powder and a matrix material. The magnetic composite material will be described later.

[0031] Figure 2 shows an enlarged view of the portion enclosed by the dashed line frame in Figure 1. Note that the middle portion of the dashed line frame is omitted from the illustration.

[0032] As shown in the figure, a first magnetic member 21 is attached in layers to the primary winding 2 so as to contact and cover the entire surface of the winding material. In this example, the first magnetic member 21 is attached in layers to contact and cover the front surface (upper surface in the figure), back surface (lower surface in the figure), outer periphery (left side in the figure), and inner periphery (right side in the figure) of the plate-shaped winding material of the primary winding 2.

[0033] A gap is provided between adjacent first magnetic members 21 so that the layered first magnetic members 21 attached to adjacent winding materials of the primary winding 2 do not come into contact with each other. This gap is formed by sandwiching an insulating sheet (not shown), such as a resin sheet, between the adjacent first magnetic members 21. The first magnetic member 21 is formed of a magnetic composite material containing magnetic powder and a matrix material. The magnetic composite material will be described later.

[0034] As shown in the figure, the secondary winding 3 (3a) is provided with a layer of second magnetic member 31 in contact with and covering the entire surface of the winding material. In this example, the second magnetic member 31 is provided in layers in contact with and covering the front surface (upper surface in the figure), back surface (lower surface in the figure), outer periphery (left side in the figure), and inner periphery (right side in the figure) of the plate-shaped winding material of the secondary winding 3a.

[0035] A gap is provided between adjacent second magnetic members 31 so that the layered second magnetic members 31 attached to adjacent winding materials of the secondary winding 3a do not come into contact with each other. This gap is formed by sandwiching an insulating sheet (not shown), such as a resin sheet, between the adjacent second magnetic members 31. The second magnetic member 31 is formed of a magnetic composite material containing magnetic powder and a matrix material. The magnetic composite material will be described later.

[0036] Although not shown, the secondary winding 3b is similar to the secondary winding 3a, and the second magnetic members 31 are attached in layers to contact the surface of the winding material and cover the entire surface, with gaps being provided between adjacent second magnetic members 31. Similarly, an insulating sheet is sandwiched in this gap.

[0037] The third magnetic member 4 (4a) is provided with a gap from the first magnetic member 21 so as not to come into contact with the first magnetic member 21 of the primary winding 2. The third magnetic member 4 (4a) is also provided with a gap from the second magnetic member 31 of the secondary winding 3a so as not to come into contact with the second magnetic member 31. These gaps are formed by sandwiching an insulating sheet (not shown), such as a resin sheet.

[0038] Although not shown, the third magnetic member 4b is similar to the third magnetic member 4a, and is provided with a gap therebetween so as not to come into contact with the first magnetic member 21 of the primary winding 2, and is also provided with a gap therebetween so as not to come into contact with the second magnetic member 31 of the secondary winding 3b. This gap is similarly formed by sandwiching an insulating sheet therebetween.

[0039] It is preferable that the third magnetic member 4 (4a, 4b) is provided so as not to come into contact with the central leg 71 and the side leg 72. As will be described later, if the third magnetic member 4 comes into contact with the central leg 71 and the side leg 72, the magnetic flux density of the third magnetic member 4 increases, which may increase the loss generated in the third magnetic member 4.

[0040] The first magnetic member 21, the second magnetic member 31, and the third magnetic member 4 (4a, 4b) are all formed of a magnetic composite material in which magnetic powder is dispersed in a matrix material. Such a magnetic composite material is characterized by being easy to mold, having little loss at high frequencies, low magnetic permeability, and high saturation magnetic flux density. The magnitude of the magnetic permeability in the composite magnetic material can be controlled by changing the shape, type, and size of the magnetic powder, which will be described later, and the mixing ratio of the magnetic powder to the matrix material. The magnitude of the relative magnetic permeability is preferably 5 or more and 50 or less, taking into account the balance between the coupling coefficient between the primary winding 2 and the secondary winding 3 and the shielding effect of the magnetic composite material.

[0041] The shape of the magnetic powder is arbitrary. For example, one or more types of powder selected from spherical, lumpy, and flat powders can be used as the magnetic powder. Also, powders of different shapes and sizes can be mixed and used as the magnetic powder. There is no limitation on the shape of the magnetic powder, but shapes without magnetic anisotropy such as spherical and cubic shapes are preferable. There is no limitation on the size of the magnetic powder, but as an example, a size of several hundred nm to about 100 μm is preferable.

[0042] The magnetic powder is not limited to any material as long as it is a soft magnetic material. For example, one or more types of magnetic powder selected from iron powder, Si-Fe powder, amorphous powder, ferrite powder (Mn-Zn, Ni-Zn), Finemet (registered trademark) powder, Sendust powder, and Fe-Si-Al powder can be used as the magnetic powder. A coated magnetic powder whose surface is covered with an insulating material may be used as the magnetic powder. The amount of magnetic powder is not limited, but it is preferable that the magnetic composite contains about 60 to 80% by volume, for example.

[0043] The matrix material is a base material in a composite material, and is not particularly limited as long as it is a non-magnetic, insulating material that hardens from a liquid state (slurry state). For example, resin materials such as silicone, epoxy, and acrylic, and inorganic materials such as water glass can be used as the matrix material. Among these, resin materials are preferred in terms of improving mechanical strength. As the resin, resins that harden from a liquid state, such as thermoplastic resins, thermosetting resins such as silicone elastomers, or resins that can be crosslinked by a hardener, can be used. For example, silicone and epoxy can be preferably used among the resin materials.

[0044] The magnetic powder is mixed with the liquid matrix material, the magnetic powder is uniformly dispersed in the matrix material, and the liquid matrix material is cured to form a magnetic composite material. When mixing, solvents, additives, binders, etc. may be added as necessary.

[0045] The types and amounts of magnetic powder used in the first magnetic member 21, the second magnetic member 31, and the third magnetic member 4 may be the same or different. The types and amounts of matrix material used in the first magnetic member 21, the second magnetic member 31, and the third magnetic member 4 may be the same or different. The types and amounts of magnetic powder used in each may be appropriately determined according to the required characteristics. The results of the electromagnetic field simulation of transformer 1 and the measurement results of the prototype will be described later.

[0046] [Second embodiment] Fig. 4 is a vertical cross-sectional view of a transformer 101 to which the present invention is applied. Fig. 5 is an enlarged view of a portion enclosed by a dashed line frame in Fig. 4. The circuit diagram of the transformer 101 is the same as that in Fig. 3.

[0047] The second embodiment of the transformer 101 to which the present invention is applied is characterized in that a first magnetic member 22 is provided to seal the primary winding 2, and a second magnetic member 32 is provided to seal the secondary winding 3 (3a, 3b). The details will be explained below.

[0048] The transformer 101 has a primary winding 2, a secondary winding 3 (3a, 3b), a first magnetic member 22, a second magnetic member 32, a third magnetic member 4 (4a, 4b), and a core 7. The primary winding 2, the secondary winding 3 (3a, 3b), the third magnetic member 4 (4a, 4b), and the core 7 are similar to those of the transformer 1 already described.

[0049] Fig. 5 shows an enlarged view of the portion enclosed by the dashed line frame in Fig. 4. Note that the middle portion of the dashed line frame is omitted from the illustration.

[0050] As shown in the figure, the primary winding 2, including the spaces between the windings, is entirely sealed (molded, enclosed) by the first magnetic member 22. The first magnetic member 22 is made of the same material as the first magnetic member 21 of the transformer 1 already described, and is formed of a magnetic composite material containing magnetic powder and a matrix material. A gap is formed between the first magnetic member 22 and the third magnetic member 4 (4a). A gap is formed between the first magnetic member 22 and the core 7 (center leg 71, side leg 72).

[0051] As shown in the figure, the entire secondary winding 3a, including the spaces between the windings, is sealed (molded, enclosed) by the second magnetic member 32 (first second magnetic member). The second magnetic member 32 is made of the same material as the second magnetic member 31 of the transformer 1 already described, and is formed of a magnetic composite material containing magnetic powder and a matrix material. A gap is formed between the second magnetic member 32 and the third magnetic member 4 (4a). A gap is formed between the second magnetic member 32 and the core 7 (center leg 71, side leg 72).

[0052] Although not shown, the secondary winding 3b is similar to the secondary winding 3a, and is entirely sealed by the second magnetic member 32 (second second magnetic member). A gap is formed between the second magnetic member 32 and the third magnetic member 4b. A gap is formed between the second magnetic member 32 and the core 7 (center leg 71, side leg 72). The results of an electromagnetic field simulation of the transformer 101 will be described later.

[0053] [Third embodiment] Fig. 6 is a vertical cross-sectional view of a transformer 201 to which the present invention is applied. Fig. 7 is an enlarged view of a portion enclosed by a dashed line frame in Fig. 6. The circuit diagram of the transformer 201 is the same as that in Fig. 3.

[0054] A transformer 201 of the third embodiment to which the present invention is applied is characterized in that a first magnetic member 23 is provided in contact with the outer circumferential and inner circumferential ends of the surface of the winding material of the primary winding 2, and a second magnetic member 33 is provided in contact with the outer circumferential and inner circumferential ends of the surface of the winding material of the secondary winding 3 (3a, 3b). The details will be explained below.

[0055] The transformer 201 has a primary winding 2, a secondary winding 3 (3a, 3b), a first magnetic member 23, a second magnetic member 33, a third magnetic member 4 (4a, 4b), and a core 7. The primary winding 2, the secondary winding 3 (3a, 3b), the third magnetic member 4 (4a, 4b), and the core 7 are similar to those of the transformer 1 already described.

[0056] Fig. 7 shows an enlarged view of the portion enclosed by the dashed line frame in Fig. 6. Note that the middle portion of the dashed line frame is omitted from the illustration.

[0057] As shown in the figure, the primary winding 2 is provided with a first magnetic member 23 (first magnetic member on the outer periphery) in contact with the winding material at the end of the winding material on the outer periphery side, and a first magnetic member 23 (first magnetic member on the inner periphery) in contact with the winding material at the end of the winding material on the inner periphery side. The first magnetic member 23 is provided so as to hang not only on the end face of the winding material on the outer periphery side, but also on the front and back surfaces of the winding material on the outer periphery side. The first magnetic member 23 is provided so as to hang not only on the end face of the winding material on the inner periphery side, but also on the front and back surfaces of the winding material on the inner periphery side. The first magnetic member 23 is not provided in the center of the front and back surfaces of the winding material except for the outer periphery side and the inner periphery side. Also, as shown in the figure, a gap may be provided so that the first magnetic members 23 provided on adjacent winding materials of the primary winding 2 do not come into contact with each other. The gap is formed by, for example, sandwiching an insulating sheet (not shown) such as a resin sheet.

[0058] The first magnetic member 23 is made of the same material as the first magnetic member 21 of the transformer 1 already described, and is formed of a magnetic composite material containing magnetic powder and a matrix material.

[0059] As shown in the figure, the secondary winding 3 (3a) is provided with a second magnetic member 33 (second magnetic member on the outer periphery) in contact with the winding material at the end of the winding material on the outer periphery side, and a first magnetic member 33 (second magnetic member on the inner periphery) in contact with the winding material at the end of the winding material on the inner periphery side. The second magnetic member 33 is provided so as to hang not only on the end face of the winding material on the outer periphery side, but also on the front and back surfaces of the winding material on the outer periphery side. The second magnetic member 33 is provided so as to hang not only on the end face of the winding material on the inner periphery side, but also on the front and back surfaces of the winding material on the inner periphery side. The first magnetic member 33 is not provided in the center of the front and back surfaces of the winding material except for the outer periphery side and the inner periphery side. Also, as shown in the figure, a gap may be provided so that the second magnetic members 33 provided on adjacent winding materials of the secondary winding 3 (3a) do not come into contact with each other. The gap is formed by sandwiching an insulating sheet (not shown), such as a resin sheet.

[0060] The second magnetic member 33 is made of the same material as the second magnetic member 31 of the transformer 1 already described, and is formed of a magnetic composite material containing magnetic powder and a matrix material.

[0061] Although not shown, the secondary winding 3b is similar to the secondary winding 3a, and a second magnetic member 33 (second magnetic member on the outer periphery) is provided at the end of the winding material on the outer periphery side, and a first magnetic member 33 (second magnetic member on the inner periphery) is provided at the end of the winding material on the inner periphery side. The results of an electromagnetic field simulation of the transformer 201 will be described later.

[0062] In the transformer 1 of the first embodiment, the combination of the primary winding 2 and the secondary winding 3 to which the magnetic composite material is applied in layers has been described, in the transformer 101 of the second embodiment, the combination of the primary winding 2 and the secondary winding 3 sealed with the magnetic composite material has been described, and in the transformer 201 of the third embodiment, the combination of the primary winding 2 and the secondary winding 3 to which the magnetic composite material is applied on the outer and inner peripheral sides has been described. However, the combination of the positions of the magnetic composite material provided on the primary winding 2 and the secondary winding 3 may be changed. For example, the transformer may be a combination of a primary winding 2 with a layer of magnetic composite material and a secondary winding 3 sealed with magnetic composite material, a combination of a primary winding 2 sealed with magnetic composite material and a secondary winding 3 with a layer of magnetic composite material, a combination of a primary winding 2 with a layer of magnetic composite material and a secondary winding 3 with a magnetic composite material on the outer peripheral side and the inner peripheral side, a combination of a primary winding 2 with a magnetic composite material on the outer peripheral side and the inner peripheral side and a secondary winding 3 with a layer of magnetic composite material, a combination of a primary winding 2 sealed with magnetic composite material and a secondary winding 3 with a magnetic composite material on the outer peripheral side and the inner peripheral side, or a combination of a primary winding 2 with a magnetic composite material on the outer peripheral side and the inner peripheral side and a secondary winding 3 with a magnetic composite material on the outer peripheral side and the inner peripheral side. The position of the magnetic composite material to be arranged in the primary winding 2 is arbitrary. The position of the magnetic composite material to be arranged in the secondary winding 3 is arbitrary. This can be determined appropriately according to the required specifications.

[0063] [Simulation using electromagnetic field analysis] Simulations were performed using electromagnetic field analysis. Here, the simulations were performed for the embodiment 1 shown in Figures 1 and 2 (transformer 1 in which a magnetic composite material is provided in a layer on the entire surface of the winding material of the primary winding 2 and secondary winding 3), the embodiment 2 shown in Figures 4 and 5 (transformer 101 in which the winding material of each of the primary winding 2 and secondary windings 3a and 3b is sealed with a magnetic composite material) as the embodiment 2, and the embodiment 3 shown in Figures 6 and 7 (transformer 301 in which a magnetic composite material is provided on the outer and inner peripheries of the winding material of the primary winding 2 and secondary winding 3) as the embodiment 3.

[0064] As Comparative Example 1, a simulation was performed on a configuration in which all magnetic composite materials were removed from the transformer 1 of Example 1, i.e., a configuration in which the primary winding 2 did not have the first magnetic member 21, the secondary winding 3 (3a, 3b) did not have the second magnetic member 31, and the third magnetic member 4 (4a, 4b) was not provided.

[0065] As Comparative Example 2, a simulation was performed on a transformer 901 shown in the enlarged view of the dashed line portion in Fig. 8. As shown in the figure, the transformer 901 differs from the transformer 1 in that the primary winding 2 does not have a first magnetic member, and the secondary winding 3 (3a, 3b) does not have a second magnetic member. The figure corresponds to the enlarged view of the dashed line portion of the transformer 1 shown in Fig. 2. The transformer 901 has a third magnetic member 4 (4a, 4b) similar to that of the transformer 1.

[0066] As Comparative Example 3, a simulation was performed on a transformer 902 shown in an enlarged view of the dashed line portion in FIG. 9. As shown in the figure, the transformer 902 is different from the transformer 1 in that the primary winding 2 is not provided with a first magnetic member, the secondary winding 3 (3a, 3b) is not provided with a second magnetic member, and a third magnetic member 94 (94a, 94b) is provided. The third magnetic member 94 (94a, 94b) is a third magnetic member 4 (4a, 4b) that has been made wider, and is in contact (close contact) with the central leg 71 and the side leg 72 of the core 7. The material of the third magnetic member 94 (94a, 94b) is the same as that of the third magnetic member 4 (4a, 4b) of the transformer 1.

[0067] [LLC resonant DC-DC converter and leakage transformer specifications] The target specifications were set assuming that the transformer used in the electromagnetic field simulation was a leakage transformer used in an LLC resonant DC-DC converter (hereinafter also referred to as LLC converter). The basic specifications of the LLC converter were a bus converter with an input voltage of 360 to 400 V, an output voltage of 48 V, and an output power of 1 kW. The resonant frequency was 1 MHz, and the switching frequency was 0.7 to 1 MHz. The dead time was set to 20 to 30 ns, which is 2.0% to 3.0% of the period of the resonant frequency of 1 MHz. The excitation inductance was determined to be 9.8 to 14.8 μH based on the dead time, the output capacitance of the primary side power device, the maximum switching frequency, and the zero voltage switching condition. The type name GS-065-060-3-T (GaN Systems Inc.) was used for the primary power device, and the output capacitance Coss was set to 127 pF. As the leakage transformer is used in an LLC converter that uses a half-bridge technique and center-tap rectification, which can reduce the number of components, the turns ratio of the leakage transformer is set to number of turns of primary winding 2: number of turns of secondary winding 3a: number of turns of secondary winding 3b = 5:1:1 (see Figure 1).

[0068] Figure 10 shows the gain characteristic of the LLC converter. As the coupling coefficient increases, the operating frequency shifts to lower frequencies. Therefore, to enable operation at high frequencies where the excitation current can be reduced, the coupling coefficient of the leakage transformer must be 0.8 to 0.9.

[0069] [Simulation conditions] The core material used is MC2 (JFE Ferrite Corporation), which has excellent high-frequency characteristics. The core is EERI (JFE Ferrite Corporation), which has a rounded rectangular central leg.

[0070] The length from the center y shown in FIG. 1 to the inner peripheral end of the primary winding 2 and the secondary winding 3a, 3a was 3.7 mm, and the length to the outer peripheral end was 9.9 mm. The thickness of the conductor of the primary winding 2 and the secondary winding 3a, 3a was 0.1 mm and 0.2 mm, respectively. The distance between adjacent winding materials of the primary winding 2 and the secondary winding 3a, 3a was 0.2 mm, and the distance from the primary winding 2 to the secondary winding 3a, 3a was 0.9 mm. The length from the center y shown in FIG. 1 to the inner peripheral end of the third magnetic members 4a, 4b was 3.5 mm, and the length to the outer peripheral end was 10.1 mm. The thickness of the third magnetic composite member was 0.5 mm.

[0071] The width of the central leg 71 from the center y of the core 7 was 3.16 mm, the distance from the center y of the core 7 to the inside of the side leg 72 was 10.415 mm, the distance to the outside of the side leg was 12.5 mm, the length from the bottom to the top of the core 7 in the state shown in Figure 1 was 12.58 mm, and the gap between one side core piece 7a and the other side core piece 7b was 0.3 mm.

[0072] The primary winding 2 has 10 turns, one secondary winding 3a has 2 turns, and the other secondary winding 3b has 2 turns. The secondary windings 3a and 3b have two parallel windings. To reduce the coupling coefficient, the primary and secondary windings are wound independently.

[0073] In the case of the first embodiment shown in Figures 1 and 2, the thickness of the magnetic composite layer attached to the front and back surfaces of the primary winding 2 and the secondary windings 3a, 3a is 0.05 mm, and the thickness of the magnetic composite layer attached to both side surfaces is 0.2 mm.

[0074] In the second embodiment shown in Figures 4 and 5, the primary winding 2 and the secondary windings 3a, 3a are internally sealed with a magnetic composite material, but the magnetic composite material protrudes outward by 0.05 mm from both the upper and lower end faces of the primary winding 2 and the secondary windings 3a, 3a, and by a thickness of 0.2 mm from both side faces.

[0075] In the case of the third embodiment shown in Figures 6 and 7, the layer of the magnetic composite material portion attached outward from both side surfaces of the primary winding 2 and the secondary windings 3a, 3a has a thickness of 0.2 mm, and the magnetic composite material portion is provided in layers on the front and back surfaces with a thickness of 0.05 mm, extending 0.1 mm inward from both end faces.

[0076] Figure 11 shows the frequency characteristics of the complex relative permeability (catalog value) of the core material MC2 and the complex relative permeability (measured value) of the magnetic composite material. The magnetic composite material is made by mixing amorphous spherical powder, the main component of which is iron, with resin, and is characterized by low loss at high frequencies. The complex relative permeability was measured using an impedance analyzer (Agilent Technologies, Inc., model 4294A). The complex relative permeability was derived from the inductance of a single-turn inductor formed by inserting a toroidal core, the material under test, into a jig (KEYSIGHT Technologies, model 16454A). Since the magnetic composite material has low loss, the contact resistance of the jig has a large effect on the imaginary part of the complex relative permeability μ'″ of the magnetic composite material. Therefore, μ″ of the magnetic composite material increases at low frequencies. Here, the simulation was performed with μ″ of the magnetic composite material set to 0.01. Table 1 shows the simulation conditions.

[0077] [Table 1]

[0078] The primary inductance Lp when the secondary side is open, the primary resistance (AC resistance) Rsh1 when one of the secondary windings 3a is shorted, and the primary inductance Lsh1 when one of the secondary windings 3a is shorted are simulated. The primary impedance characteristics when the other secondary winding 3b is shorted are the same as when one of the secondary windings 3a is shorted, so they are omitted here. The coupling coefficient k is calculated from the following equation (1).

[0079]

number

[0080] [Simulation results] Fig. 12 shows the primary inductance Lp with the secondary side open. The leakage transformer Lp at a frequency of 1 MHz was 14.1 μH for Example 1, 14.8 μH for Example 2, 13.8 μH for Example 3, 13.1 μH for Comparative Example 1, and 13.5 μH for Comparative Example 2. The magnetic composite material is disposed between the primary winding and the secondary winding or on at least a part of the surface of the winding material, and forms a magnetic path with a shorter path length than the main magnetic path. As a result, the inductance Lp is increased when the magnetic composite material is provided as in Examples 1 to 3.

[0081] FIG. 13 shows the primary resistance Rsh1 when the secondary winding 3a is short-circuited. The leakage transformer Rsh1 at a frequency of 1 MHz was 358 mΩ for Example 1, 388 mΩ for Example 2, 460 mΩ for Example 3, 584 mΩ for Comparative Example 1, and 507 mΩ for Comparative Example 2. The primary resistance Rsh1 of Examples 1 to 3 was smaller than that of Comparative Examples 1 and 2. This is because the magnetic flux that penetrates the winding and generates losses is induced and shielded by the magnetic composite material. By applying the magnetic composite material in layers as in Example 1, it was possible to reduce Rsh1 by 39% compared to Comparative Example 1 in which the magnetic composite material was not applied. The structure of Example 1 had the smallest resistance. The structure of Example 2 is prone to leakage flux because all the windings are sealed in the magnetic composite material, and showed a higher resistance value than the layered magnetic composite material of Example 1. The structure of Example 3 is effective in reducing AC resistance due to the skin effect. However, since only a portion (the outer and inner periphery) of the winding conductor surface is covered with the magnetic composite material, the reduction in AC resistance due to the proximity effect is small.

[0082] 14 shows the primary inductance Lsh1 when the secondary winding 3a is short-circuited. The leakage transformer's Lsh1 at a frequency of 1 MHz was 3.9 μH for Example 1, 4.5 μH for Example 2, 3.9 μH for Example 3, 1.5 μH for Comparative Example 1, and 2.8 μH for Comparative Example 2. When the magnetic composite material was disposed between the primary winding and secondary winding or on the outer periphery of the conductor as in Examples 1 to 3, a leakage flux path was created, and Lsh1 increased.

[0083] Fig. 15 shows the coupling coefficient k. The coupling coefficient k of the leakage transformer at a frequency of 1 MHz was 0.85 for Example 1, 0.83 for Example 2, 0.88 for Example 3, 0.94 for Comparative Example 1, and 0.89 for Comparative Example 2. By appropriately arranging the magnetic composite material as in Examples 1 to 3, it is possible to create a path for leakage magnetic flux and reduce the coupling coefficient.

[0084] [Magnetic flux density of the third magnetic member] A simulation was performed on the magnetic flux density of the third magnetic member. FIG. 16 shows the magnetic flux density of the third magnetic member at a frequency of 1 MHz and a current of 8 A. In Comparative Example 3, the third magnetic member is in contact (close contact) with the core, while in Comparative Example 2 and Examples 1 to 3, the third magnetic member is not in contact with the core. As shown in Comparative Example 3 in the figure, the magnetic flux density of the third magnetic member increases when it is in contact with the core. Since iron loss increases with increasing magnetic flux density, when the magnetic flux density of the third magnetic member increases, the loss generated in the third magnetic member increases. In addition, the third magnetic member is not magnetically saturated in this simulation, but there is a possibility that magnetic saturation or the function as a shield will decrease when the current is further increased.

[0085] [Making a leakage transformer] A leakage transformer was fabricated as Example 4. The leakage transformer to be fabricated was a transformer corresponding to Example 1, which had the lowest resistance value in the simulation. Also, as Comparative Example 4, a transformer corresponding to Comparative Example 1 was fabricated without using a magnetic composite material, that is, without the first magnetic member 21, the second magnetic member 31, and the third magnetic member 4.

[0086] FIG. 17 shows photographs showing the appearance and manufacturing process of the leakage transformer. The magnetic composites of the first magnetic member 21, the second magnetic member 31, and the third magnetic member 4 were made of the same material. Iron-based amorphous spherical powder was used as the magnetic powder of the magnetic composite, and silicone resin was used as the matrix material. Silicone resin was mixed with the iron-based amorphous spherical powder to prepare magnetic composite slurry. For each turn (one sheet) of winding material of the primary winding and the secondary winding, the magnetic composite slurry was applied onto the winding material using a metal mask. Note that the size of the metal mask is shown small in the figure. The opening of the metal mask was formed slightly larger than the size of the winding material, so that when the magnetic composite slurry was applied to one side of the winding material, the magnetic composite slurry was also applied to the side end surface of the winding material. After the applied magnetic composite slurry was heated and hardened, the magnetic composite slurry was similarly applied to the back side of the winding material and heated and hardened. Similarly, a magnetic composite material was formed in layers on all the winding materials of the primary winding and the secondary winding. A third magnetic member was also fabricated on a resin sheet using the magnetic composite material slurry and a metal mask.

[0087] As shown in Figures 1 and 2, the winding material with magnetic composite material that will become the primary winding and secondary winding, and the third magnetic member were set on the core 7. A resin sheet was sandwiched between one side core piece 7a and the other side core piece 7b to form a predetermined gap. A resin sheet was sandwiched between the winding materials and on both sides of the third magnetic member to form a predetermined gap. The winding materials were electrically connected so as to form the connection of the primary winding and secondary winding shown in Figure 3, and the transformer of Example 4 was produced.

[0088] As Comparative Example 4, a transformer was produced without using a magnetic composite material, by setting the winding materials to become the primary winding and secondary winding on the core 7, and electrically connecting each winding material to form the primary winding and secondary winding.

[0089] [Evaluation of the fabricated leakage transformer] The impedance characteristics of the leakage transformers fabricated in Example 4 and Comparative Example 4 were measured. An impedance analyzer (E4990A, manufactured by KEYSIGHT Technologies) was used for the measurements. The measurement results are shown in Figs. 18 to 21. In addition, each figure also shows the simulation results of Example 1 and Comparative Example 1 described above.

[0090] Figure 18 shows the primary inductance Lp when the secondary side is open. Lp in Example 4 was 13.8 μH, and Lp in Comparative Example 4 was 13.8 μH. There was no difference in Lp with or without the magnetic composite material. This is thought to be due to the dimensional tolerance of the core and the error in the gap length.

[0091] FIG. 19 shows the primary resistance Rsh1 when the secondary winding 3a is short-circuited. Rsh1 in Comparative Example 4 was 743 mΩ, and Rsh1 in Example 4 was 501 mΩ. By applying the magnetic composite material, Rsh1 was reduced by 33% compared to when the magnetic composite material was not applied. As in the simulation, it is believed that by applying the magnetic composite material, the magnetic flux that causes loss is blocked and induced, reducing Rsh1. Due to differences between the prototype and the simulation model (lead wire, via), the actual measured value of Rsh1 was higher than the simulation result.

[0092] Fig. 20 shows the primary inductance Lsh1 when the secondary winding 3a is short-circuited. Lsh1 in Comparative Example 4 was 1.8 μH, and Lsh1 in Example 4 was 4.5 μH. As in the simulation, Lsh1 increased by creating a leakage flux path using the magnetic composite material. The difference between the prototype and the simulation results is the same as the reason for the increase in Rsh1.

[0093] 21 shows the coupling coefficient k, where k was 0.93 for Comparative Example 4 and 0.82 for Example 4. As with the simulation results, the coupling coefficient could be reduced by forming a leakage magnetic path made of a magnetic composite material.

[0094] In the above examples, the dimensions of each part were determined to conform to the above-mentioned [Specifications of the LLC resonant DC-DC converter and leakage transformer]. In the case of the present specifications, the leakage transformer with the smallest AC resistance was transformer 1 of embodiment 1. However, depending on the target specifications, transformer 101 of embodiment 2 or transformer 201 of embodiment 3 may be optimal.

[0095] Although there were some differences between the measured values ​​and the simulation values, these were thought to be errors caused by the influence of the leads and vias, and the simulation settings and calculated values ​​were generally considered to be correct. [Explanation of symbols]

[0096] 1, 101, and 201 are transformers, 2 is a primary winding, 3 is a secondary winding, 3a is one of the two divided secondary windings, 3b is the other of the two divided secondary windings, 4 is a third magnetic member, Reference numeral 4a denotes a first third magnetic member, 4b denotes a second third magnetic member, 7 denotes a core, 7a denotes one side core piece, 7b denotes the other side core piece, 21, 22, and 23 denote first magnetic members, 31, 32, and 33 denote second magnetic members, 71, 71a, and 71b denote central legs, 72, 72a, and 72b denote side legs, 73, 73a, and 73b denote base portions, 94 denotes a third magnetic member, 94a denotes a first third magnetic member, 94b denotes a second third magnetic member, and 901 and 902 denote transformers.

Claims

1. A primary winding; A secondary winding; a core having a central leg around which the primary winding and the secondary winding are wound with a gap therebetween, and side legs provided on outer circumferential sides of the primary winding and the secondary winding, a first magnetic member that is disposed in contact with at least a portion of a surface of the winding material of the primary winding and is made of a magnetic composite material that contains magnetic powder and a matrix material; a second magnetic member formed of a magnetic composite material containing magnetic powder and a matrix material and disposed in contact with at least a portion of a surface of the winding material of the secondary winding; a third magnetic member disposed between the primary winding and the secondary winding, the third magnetic member being made of a magnetic composite material containing magnetic powder and a matrix material.

2. the first magnetic member is provided in layers so as to contact and cover a surface of the winding material of the primary winding, and adjacent layers of the first magnetic member are provided so as not to come into contact with each other; 2. The transformer according to claim 1, wherein the second magnetic member is provided in layers so as to contact and cover a surface of the winding material of the secondary winding, and adjacent layers of the second magnetic member are provided so as not to come into contact with each other.

3. the first magnetic member is provided to seal the primary winding, 2. The transformer according to claim 1, wherein the second magnetic member is provided so as to seal the secondary winding.

4. the first magnetic member is provided in contact with ends of an outer periphery side and an inner periphery side of a surface of a winding material of the primary winding, 2. The transformer according to claim 1, wherein the second magnetic member is provided in contact with ends of an outer periphery side and an inner periphery side of a surface of a wire material of the secondary winding.

5. 2. The transformer according to claim 1, wherein the third magnetic member is provided so as not to come into contact with the central leg and the side legs.

6. The secondary winding is divided into two parts so as to sandwich the primary winding therebetween, a first third magnetic member is disposed between one of the two split secondary windings and the primary winding; 2. The transformer according to claim 1, wherein a second of the third magnetic members is disposed between the other of the two split secondary windings and the primary winding.

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