JP7050566B2 - High frequency high output transformer - Google Patents

Description

The present invention relates to a high frequency high output transformer.

Electrical and electronic devices usually have built-in inverters and transformers (also called transformers) in order to reduce power consumption. Transformers used at high frequencies generally include a coil around which a wire with a conductor radius smaller than the frequency-determined skin depth is wound around the core in order to suppress the increase in resistance due to the skin effect.
In such a transformer, in order to increase the output, it is necessary to increase the conductor cross section of the electric wire wound around the core. In this case, it is important to avoid the use of electric wires having a large diameter conductor in consideration of the increase in resistance due to the skin effect as described above, and the number of electric wires to be wound is increased. As a method for increasing the number of electric wires, generally, a method of increasing the number of parallel wires by using a plurality of electric wires and a method of using a litz wire obtained by twisting a plurality of strands in a spiral shape as an electric wire can be mentioned.
As a transformer provided with a coil wound by winding a litz wire as an electric wire, for example, a step-up transformer used in a high-frequency heating device is described in Patent Document 1. Specifically, this step-up transformer uses a wire obtained by further covering a litz wire in which a plurality of insulated conductors are bundled with an insulator as a secondary winding (high voltage small current side coil). This step-up transformer is an improvement of the secondary winding as described above. The wire diameter of the wire is reduced to suppress the influence of the skin effect, and the litz wire is covered with an insulator to ensure insulation performance. It is stated that it should be done.

Japanese Unexamined Patent Publication No. 5-13247

A transformer usually includes an input side (primary side) coil and an output side (secondary side) coil, and a voltage and a current value of a current applied to each coil are set. In a transformer, usually, one of the primary side coil and the secondary side coil is a low voltage large current side coil, and the other is a high voltage small current side coil.
In the present invention, the low-voltage high-current side coil means a coil in which a current having a low-pressure high-current value flows relatively among the two coils, and the high-pressure low-current-side coil means a coil in which a low-pressure high-current value current flows relatively. , Means a coil through which a high-voltage, small-current value current flows.

For the low-voltage, high-current side coil of a high-frequency transformer, an electric wire having a conductor designed in consideration of the influence of the skin effect and a thin film insulating layer covering the outer periphery of the conductor has been conventionally used. The reason why the insulating layer is formed in the thin film in this way is that a low voltage current flows through this electric wire. Further, in the case of a transformer (also referred to as a separate winding transformer) having a primary side coil and a secondary side coil having electric wires wound on the outer peripheral surfaces of the core and different from each other, the primary side coil is used. Unlike a transformer in which the side coil and the secondary coil are arranged on the same outer peripheral surface of the core, the primary coil and the secondary coil maintain high insulation. Therefore, the insulating layer of the electric wire used for each coil is set to a thickness sufficient to show the minimum necessary insulating property. Furthermore, it is necessary to set the space factor high for the purpose of preventing Joule loss due to a large current, and for this purpose, forming the insulating layer as thin as possible has been an effective means.

When a high output of 1000 W or more is required for such a high-frequency transformer, the resistance increases especially in the low-voltage large-current side coil, and the transformer loss also increases accordingly. Therefore, it is necessary to further increase the number of electric wires used for the low-voltage high-current side coil. As a result, the DC resistance can be reduced and the loss can be reduced. However, as the number of wires increases, the AC resistance due to the proximity effect acting between the wires increases. The influence of such a proximity effect cannot be ignored when the frequency becomes, for example, about 30 kHz or more. Therefore, in a high-frequency high-output transformer, even if the number of electric wires is simply increased, the effect of reducing the resistance value is limited, and the loss cannot be sufficiently reduced.
As described above, as the electric wire used for the low voltage and large current side coil, the conventional electric wire in which the insulating layer is thinly formed in consideration of the skin effect and the space factor as described above can further reduce the loss of the transformer. There was a limit and improvement was desired.

An object of the present invention is to provide a high-frequency output transformer with reduced loss by suppressing resistance generated in a low-voltage high-current side coil.
In the present invention, the high frequency of the transformer is not particularly limited, but means, for example, that the operating frequency is 30 to 150 kHz. The high output of the transformer is not particularly limited, but is, for example, an output of 1000 W or more, and the upper limit thereof is, for example, 10 kW.

The present inventors have formed a thick insulating layer of the electric wire (set a large outer diameter difference / 2 between the electric wire and the conductor portion), and then the conductor portion, contrary to the electric wire conventionally used for the low-voltage high-current side coil. When an electric wire with the outer diameter ratio (outer diameter of the conductor / outer diameter of the electric wire) set to a specific range is used for the low-voltage high-current side coil, the DC resistance and AC resistance are well-balanced. We have found that it is possible to reduce the resistance, which cannot be achieved by the conventional low-voltage, high-current side coil, and to reduce the loss of the transformer. Based on this finding, the present inventors have further studied and came to the present invention.

That is, the subject of the present invention has been achieved by the following means.
<1> A high-frequency high-output transformer provided with a primary side coil and a secondary side coil having electric wires wound around different outer peripheral surfaces of the core.
The electric wire of the primary side coil and the secondary side coil of the low pressure and high current side coil has a conductor portion and an insulating layer covering the outer periphery of the conductor portion, and the outer diameter of the conductor portion and the electric wire. The outer diameter difference / 2 ([outer diameter of the electric wire-outer diameter of the conductor part] / 2) is in the range of 70 to 260 μm, and the outer diameter ratio (outer diameter of the conductor part / outer diameter of the electric wire) is in the range of 70 to 260 μm. ) Is in the range of 0.48 to 0.84, which is a high output transformer for high frequencies.
<2> The high-frequency output transformer according to <1>, wherein the outer diameter of the conductor portion is 0.35 mm or more and less than 1.00 mm.
<3> When the electric wire is a wire or a litz wire and the wire is a wire, the insulating layer covering the outer periphery of the conductor portion is an insulating layer made of a conducting wire in contact with the conductor portion and heat. The high frequency height according to <1> or <2>, which is a wire insulating layer containing a curable resin, and in the case of a litz wire, includes a stranded wire having a wire insulating layer containing a thermosetting resin in contact with a conducting wire. Output transformer.
<4> The high-frequency output transformer according to <3>, wherein the wire insulating layer containing the thermosetting resin has a thickness of 8 to 18 μm.
<5> The item according to any one of <1> to <4>, wherein the insulating layer covering the outer periphery of the conductor portion has a layer structure of two or more, and the insulating layer of the outermost layer contains a thermoplastic resin. High frequency transformer for high frequency.
<6> The high frequency output transformer according to any one of <1> to <5>, wherein the insulating layer covering the outer periphery of the conductor portion has a layer structure of three or more layers.
<7> The high-frequency high-output transformer according to any one of <1> to <6>, wherein the insulating layer covering the outer periphery of the conductor portion is an extrusion coating layer.

The numerical range represented by using "-" in the present specification means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a high-frequency output transformer with reduced loss by suppressing the resistance generated in the low-voltage high-current side coil.

FIG. 1 is a schematic cross-sectional view showing an example of a preferable electric wire (elementary wire) used for the transformer of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a preferable electric wire (litz wire) used in the transformer of the present invention. FIG. 3 is a schematic cross-sectional view showing another example of a preferable electric wire (litz wire) used in the transformer of the present invention. FIG. 4 is a schematic cross-sectional view showing another example of a preferable electric wire (litz wire) used in the transformer of the present invention. FIG. 5 is a schematic cross-sectional view showing an example of a preferred transformer of the present invention. FIG. 6 is a schematic cross-sectional view showing the coil manufactured in Example 1-1. FIG. 7 is a schematic cross-sectional view showing the coil manufactured in Comparative Example 1-1. FIG. 8 is a graph showing the relationship between the outer diameter ratio and the resistance value of the coil in Example 1 and Comparative Example 1 (frequency 30 kHz). FIG. 9 is a graph showing the relationship between the outer diameter ratio and the resistance value of the coil in Example 1 and Comparative Example 1 (frequency 50 kHz). FIG. 10 is a graph showing the relationship between the outer diameter ratio and the resistance value of the coil in Example 1 and Comparative Example 1 (frequency 150 kHz). FIG. 11 is a schematic cross-sectional view showing the coil manufactured in Example 2-1. FIG. 12 is a schematic cross-sectional view showing the coil manufactured in Comparative Example 2-1. FIG. 13 is a graph showing the relationship between the outer diameter ratio and the resistance value of the coil in Example 2 and Comparative Example 2 (frequency 30 kHz). FIG. 14 is a graph showing the relationship between the outer diameter ratio and the resistance value of the coil in Example 2 and Comparative Example 2 (frequency 50 kHz). FIG. 15 is a graph showing the relationship between the outer diameter ratio and the resistance value of the coil in Example 2 and Comparative Example 2 (frequency 150 kHz). FIG. 16 is a graph showing the relationship between the frequency and the resistance value of the coil in the fourth embodiment. FIG. 17 is for explaining 0.5 times the outer diameter of the conductor and the outer diameter difference between the outer diameter of the conductor portion and the outer diameter of the electric wire when the electric wire used for the transformer of the present invention is a litz wire. It is a schematic end view of the litz wire of.

<< High-frequency output transformer >>
The high-frequency output transformer of the present invention (hereinafter, may be simply referred to as the transformer of the present invention) is a primary coil having an electric wire wound on an outer peripheral surface of a core and different from each other. It is a high-frequency output transformer equipped with a secondary coil. In this transformer, among the primary side coil and the secondary side coil, the electric wire contained in the low voltage large current side coil has the following configurations (1) to (3). By using this electric wire for the low-voltage high-current side coil, the resistance value generated in this coil can be reduced, and the loss of the high-frequency high-output transformer can be further reduced as compared with the conventional transformer. Furthermore, it can also contribute to the recent reduction in size and weight.
(1) It has a conductor portion and an insulating layer that covers the outer periphery of the conductor portion.
(2) The difference in outer diameter between the outer diameter of the conductor and the outer diameter of the electric wire / 2 ([outer diameter of the electric wire-outer diameter of the conductor] / 2) is 70 to 260 μm.
(3) The outer diameter ratio (outer diameter of the conductor / outer diameter of the electric wire) between the outer diameter of the conductor and the outer diameter of the electric wire is 0.48 to 0.84.

<Electric wire>
Regarding the transformer of the present invention, first, the electric wire used for the low-voltage high-current side coil will be described, but the present invention is not limited thereto.
The electric wire used for the low-voltage high-current side coil is not particularly limited as long as it has a conductor portion and an insulating layer covering the outer periphery of the conductor portion. For example, it may be a strand of wire (also referred to as a single wire) composed of a conductor portion and an insulating layer, or may be a stranded wire (also referred to as a litz wire) formed by twisting a plurality of strands.
When the electric wire is a wire, the electric wire has a conducting wire as a conductor portion and an insulating layer covering the outer periphery of the conducting wire.

When the electric wire is a stranded wire, for example, to explain with reference to FIG. 2, the electric wire 10B has a stranded wire portion 13A in which a plurality of strands 10a are twisted together and an outer circumference of the stranded wire portion 13A (plural strands 10a). It has an external insulating layer 14A that covers (integrally). The strand 10a forming the stranded wire portion 13A has a conductor 11 and a strand insulating layer (also referred to as an internal insulating layer) 12A covering the outer periphery of the conductor 11.
In the stranded wire, the conductor portion is a plurality of strands arranged in the outermost row with respect to the radial direction of the stranded wire portion in a cross section perpendicular to the axis of the stranded wire (elements arranged in the center in FIG. 17). A portion defined by a virtual circumscribed circle (a circle shown by a broken line in FIG. 17) circumscribing each conducting wire in six strands 10a) other than the wire. In other words, the portion of the strands arranged in the outermost row with respect to the radial direction of the stranded wire portion, which is defined by the virtual circumscribed circle circumscribed to each portion excluding the strand insulation layer existing on the outer side in the radial direction. say. Further, the insulating layer means a layer existing outside the portion defined by the virtual circumscribed circle in the cross section perpendicular to the axis of the stranded wire. That is, in this cross section, it refers to a layer composed of a wire insulating layer and an external insulating layer existing on the outer side in the radial direction of the strands arranged in the outermost row with respect to the radial direction of the stranded wire portion.
Here, the above-mentioned strands arranged in the outermost row with respect to the radial direction of the stranded wire portion are located in the outermost row among the strands arranged adjacent to each other in the radial direction of the stranded wire portion. The wire to be used.

The electric wire used for the transformer of the present invention (hereinafter, may be referred to as an electric wire used in the present invention) is 0.5 times the outer diameter difference between the outer diameter of the conductor portion and the outer diameter of the electric wire ([Outer diameter of electric wire-]. The outer diameter of the conductor portion] / 2, hereinafter also referred to as a radius difference) is 70 to 260 μm. If this radius difference is too small, the outer diameter of the conductor portion becomes too large, so the reduction of AC resistance is not sufficient. On the other hand, if the radius difference is too large, the outer diameter of the conductor portion becomes too small, so that the AC resistance is reduced. However, the reduction of DC resistance is not sufficient, and in any case, the DC resistance and AC resistance cannot be reduced in a well-balanced manner. That is, as described above, by forming the insulating layer of the electric wire, which is conventionally formed with a thin layer thickness, into a thick layer thickness satisfying the above range, the DC resistance and the AC resistance are combined with the setting of the outer diameter ratio described later. Can be reduced in a well-balanced manner. Therefore, the resistance of the coil and the loss of the transformer can be reduced. Furthermore, it can also contribute to reducing the size and weight of coils and transformers.
In terms of reducing the loss of the transformer, the radius difference is preferably 90 to 260 μm when the electric wire is a strand, and 70 to 240 μm when the electric wire is a litz wire. Further, the fact that the radius difference is large means that the insulating layer is thick, and if the insulating layer having a larger elasticity than the conductor is thick, the contact surface between the electric wires becomes large, and the effect of reducing the thermal resistance is expected.
The radius difference between the conductor portion and the electric wire is half of the difference between the outer diameter of the electric wire and the outer diameter of the conductor portion (Dd shown in FIGS. 1 and 17), and the insulating layer formed outside the conductor portion. It can also be said to be the thickness, that is, the total thickness of the wire insulating layer of the wire arranged in the outermost row of the stranded wire portion and the external insulating layer.

When the wire is a wire, the outer diameter of the wire is the outer diameter of the wire, and when the wire is a litz wire, it is a virtual circumscribed circle that circumscribes the outer peripheral surface of the outer insulating layer in a cross section perpendicular to the axis of the stranded wire. The diameter of. The radius of the wire shall be 0.5 times the outer diameter of the wire. The outer diameter of the electric wire can be adjusted by the outer diameter of the wire, the thickness of the external insulating layer, and the like, and can be measured or calculated by a conventional method.
The outer diameter of the conductor part refers to the outer diameter Dc (see FIG. 1) of the conducting wire described later when the electric wire is a wire, and when the electric wire is a litz wire, the conductor part is defined in the cross section perpendicular to the axis of the stranded wire. The diameter Dc of the virtual circumscribed circle (see FIG. 17). The radius of the conductor portion is 0.5 times the outer diameter Dc of the conductor portion. The outer diameter Dc of the conductor portion can be adjusted by the outer diameter of the conducting wire, the thickness of the wire insulating layer, and the like, and can be measured or calculated by a conventional method.
If the virtual circumscribed circle in the above cross section of the electric wire and the conductor portion is not a perfect circle, the outer diameter shall be the diameter of the perfect circle having the same area as the virtual circumscribed circle, respectively. In the present invention, the diameter of the virtual circumscribed circle is the same.

The electric wire used in the present invention has an outer diameter ratio (outer diameter of the conductor portion / outer diameter of the electric wire) of 0.48 to 0.84 between the outer diameter of the conductor portion and the outer diameter of the electric wire. If the outer diameter ratio is too small, the conductor diameter becomes too small and the DC resistance becomes large, so that the resistance of the coil cannot be reduced. On the other hand, if the outer diameter ratio is too large, the resistance cannot be expected to be reduced while maintaining the coil size. That is, by setting the outer diameter ratio in the above range, in combination with the setting of the radius difference described above, it is possible to reduce the DC resistance and the AC resistance in a well-balanced manner while responding to the miniaturization and weight reduction of the coil and the transformer as necessary. By reducing the outer diameter ratio with respect to the larger radius difference as described above, it is possible to avoid an increase in size and reduce the outer diameter of the conductor portion. As a result, the DC resistance is expected to increase, but the influence of the magnetic field is reduced, and in addition, the distance between the conductor portions is increased to suppress the occurrence of the proximity effect, and the AC resistance can be effectively reduced. Therefore, the resistance of the coil and the loss of the transformer can be reduced.
In terms of reducing the loss of the transformer, the outer diameter ratio is preferably 0.48 to 0.82 when the electric wire is a strand, and 0.51 to 0.84 when the electric wire is a litz wire.

The outer diameter of the electric wire and the outer diameter of the conductor portion are as described above.
The outer diameter ratio can be obtained by obtaining the outer diameters of the electric wire and the conductor portion, respectively, and calculating the ratio of the outer diameter of the conductor portion to the outer diameter of the electric wire. The outer diameter ratio can be set by adjusting the outer diameters of the electric wire and the conductor portion, respectively.
In the present invention, in the above configurations (2) and (3), the outer diameter of the conductor portion is preferably 0.35 mm or more and less than 1.00 mm.
Among them, the outer diameter of the conductor portion is more preferably 0.35 to 0.9 mm, still more preferably 0.4 to 0.9 mm when the electric wire is a wire. On the other hand, when the electric wire is a litz wire, 0.35 to 0.85 mm is more preferable, and 0.4 to 0.85 mm is further preferable.

By using the electric wire satisfying the above configurations (1) to (3) for the low voltage and large current side coil, it is possible to secure a sufficient distance between the electric wires in the coil and reduce the proximity effect, and also to reduce the DC resistance value and the AC resistance. The resistance value can be reduced by balancing the above. As a result, the loss of the high-frequency output transformer can be further reduced as compared with the conventional transformer.
The conventional electric wire used for the low-voltage high-current side coil is formed in a thin layer necessary for ensuring the insulation performance as described above. However, in the present invention, by thickening the insulating layer of the electric wire used, the distance between the conductors is increased, the proximity effect is reduced, and the resistance value of the coil is reduced. On the other hand, simply thickening the insulating layer increases the size of the coil or transformer, so the outer diameter of the conductor portion is reduced. When the outer diameter of the conductor portion is reduced, the DC resistance is increased, but the AC resistance due to the proximity effect is reduced due to the factor that the magnetic field is less likely to be received due to the smaller diameter and the factor that the distance between the conductors is increased. In the present invention, the coil is balanced between DC resistance and AC resistance by satisfying the above radius difference and further setting the outer diameter ratio between the outer diameter of the conductor portion and the outer diameter of the electric wire to a specific range. It is possible to reduce the resistance value of. In the present invention that defines the radius difference and the outer diameter ratio, the ratio of the resin that forms the insulating layer is higher than that of copper or the like that forms the conducting wire, and in addition to the resistance reduction effect and miniaturization, cost reduction is achieved. It also has the effect of trying.

The outer diameter of the electric wire used in the present invention is not particularly limited as long as the above-mentioned radius difference and outer diameter ratio are satisfied. As an example, for example, 0.5 to 1.2 mm is preferable.
In the electric wire used in the present invention, the outer diameter of the conductor portion is not particularly limited as long as the above-mentioned radius difference and outer diameter ratio are satisfied. As an example, for example, 0.2 to 1.0 mm is preferable.
The electric wire used in the present invention is preferably a litz wire obtained by twisting a plurality of strands in order to prevent a skin effect, to secure a conductor cross section required for a large current, and to suppress an increase in the size of a coil. ..
The cross-sectional shape of the electric wire used in the present invention is not particularly limited and may be circular or rectangular (flat shape), but circular (round wire) is preferable.

In the present invention, the layer forming the electric wire may be a single layer or a plurality of two or more layers. In the present invention, the number of layers is determined by observing a cross section of the layer regardless of the type and content of the resin and the additive forming the layer. Specifically, when the cross section of a certain layer is observed at a magnification of 200 times, if the annual ring-shaped boundary cannot be confirmed, the total number of the certain layers is set to 1, and if the annual ring-shaped boundary can be confirmed, the number of layers of the certain layer. Is (number of boundaries + 1).

-Strand wire-
When the electric wire used in the present invention is a wire, the wire has a conducting wire and an insulating layer, and if the wires satisfy the above configurations (2) and (3), the other configurations are particularly limited. Not done.

(Conductor)
As the conducting wire, those conventionally used for windings for coils and the like can be used. Preferred are copper wires made of low oxygen copper or plain copper having an oxygen content of 30 ppm or less (more preferably 20 ppm or less).
The cross-sectional shape of the conducting wire may be circular or rectangular (flat shape), but circular shape is preferable.
The outer diameter φ (wire diameter) of the conducting wire is not particularly limited as long as it satisfies the above configurations (2) and (3).
In the present invention, particularly in the case of litz wire, 0.1 to 0.3 mm is preferable, and 0.15 to 0.25 mm is more preferable.

(Insulation layer)
The insulating layer of the wire is formed on the outer periphery of the conductor. This insulating layer preferably has a wire insulating layer (also referred to as an enamel layer) containing a thermosetting resin as a resin component, and further, as shown in FIG. 1, of the enamel layer 12A. An external insulating layer 12B containing preferably a thermoplastic resin as a resin component may be provided on the outer periphery.

As the thermosetting resin forming the wire insulating layer, any thermosetting resin usually used for electric wires can be used without particular limitation. For example, polyamide-imide (PAI), polyimide (PI), polyetherimide (PEI), polyesterimide (PEsI), polyurethane (PU), polyester (PEst), polybenzoimidazole, melamine resin, epoxy resin and the like can be mentioned. Of these, polyamideimide, polyimide, polyetherimide, polyesterimide, polyurethane or polyester are preferable. The thermosetting resin may be contained alone or in combination of two or more.

This wire insulating layer may contain various additives usually used for electric wires. In this case, the content of the additive is not particularly limited, but is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, based on 100 parts by mass of the resin component.

The thickness of the wire insulating layer is not particularly limited, but is preferably 8 to 18 μm in terms of ensuring the insulating property between the electric wires and further increasing the space factor of the conducting wire.

The wire insulating layer can be formed by a known method. For example, a method of applying a varnish of a resin component such as a thermosetting resin to the outer periphery of a conducting wire or the like and baking it is preferable. This varnish contains a resin component, a solvent, and if necessary, a curing agent for the resin component or various additives. The solvent is preferably an organic solvent, and a solvent capable of dissolving or dispersing the resin component is appropriately selected.
As the method for applying the varnish, a normal method can be selected, and examples thereof include a method using a varnish coating die having an opening similar to or substantially similar to the cross-sectional shape of the conducting wire. The varnish is usually baked in a baking oven. The conditions at this time cannot be uniquely determined depending on the type of resin component or solvent, and examples thereof include conditions where the furnace temperature is 400 to 650 ° C. and the transit time is 10 to 90 seconds.

The external insulating layer that the wire may have is not particularly limited as long as it is an insulating layer that an electric wire usually has. The external insulating layer that the strands may have is synonymous with, for example, the external insulating layer of the litz wire described later, except that it covers one conducting wire, and the preferred embodiment is also the same.

Although not particularly limited, the wire shown in FIG. 1 is mentioned as an example of a preferable wire used in the present invention.
The wire 10A includes a conductor 11, a wire insulating layer 12A arranged on the outer peripheral surface of the conductor 11, and an external insulating layer 12B arranged on the outer peripheral surface of the wire insulating layer 12A. In the wire 10A, the insulating layer 12 is composed of a wire insulating layer 12A and an external insulating layer 12B.

-Ritz line-
As described above, the litz wire has a stranded wire portion in which a plurality of strands are twisted together and an external insulating layer covering the outer periphery of the stranded wire portion, and satisfies the above configurations (2) and (3). As long as it is a thing, other configurations are not particularly limited.
The strands forming the litz wire are synonymous with the above strands, but those composed of a conducting wire and a strand insulating layer (those having no external insulating layer) are preferable.

(Strand wire part)
The number of strands forming the stranded wire portion is not particularly limited as long as it is two or more, but considering the alignment of the strands, seven or more wires in which six wires are arranged around one wire are preferable, and AC resistance. Considering practical workability, 100 or less is preferable. Especially considering the alignment, the number is more preferably 7 to 37.
The arrangement, twisting direction, twisting pitch, etc. of the strands when twisting the strands can be appropriately set according to the application and the like.

(External insulation layer)
The external insulating layer may be a layer that covers a plurality of strands, and a layer containing a thermoplastic resin described later as a resin component is preferable. The thickness of the external insulating layer is not particularly limited as long as the above-mentioned radius difference and outer diameter ratio are satisfied. For example, the thickness of the external insulating layer is preferably 52 to 252 μm.
As long as the external insulating layer can cover a plurality of strands, the mode of covering the strands is not particularly limited. The external insulating layer is preferably a layer (extruded coating layer) formed by extrusion molding (extrusion coating).

The external insulating layer may have a laminated structure of two or more layers as described above, but may preferably have a laminated structure of three or more layers, more preferably three to five layers. When the laminated structure has three or more layers, a sufficient creepage distance of the electric wire can be secured, so that the insulating tape normally used for ensuring the insulating property can be omitted in the transformer of the present invention. This is also effective in reducing the size of the transformer.
When the external insulating layer has a laminated structure, the thickness of each layer is not particularly limited as long as the total thickness of each layer satisfies the above-mentioned radius difference and outer diameter ratio. For example, when having an inner layer, an intermediate layer and an outer layer, the thickness of each layer is preferably 13 to 130 μm. The thickness of each layer may be the same or different.

The external insulating layer preferably contains a thermoplastic resin as a resin component. The thermoplastic resin is not particularly limited as long as it is a thermoplastic resin usually used for electric wires or windings. For example, polyamide (nylon), polyacetal (POM), polycarbonate (PC), polyphenylene ether (including PPE and modified polyphenylene ether), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), super In addition to general-purpose engineering plastics such as high-molecular-weight polyethylene, polysulfone (PSF), polyethersulfone (PES), polyphenylene sulfide (PPS), polyallylate (PAR), polyetherketone (PEK), polyaryletherketone (PAEK), Tetrafluoroethylene / ethylene copolymer (ETFE), polyetheretherketone (including PEEK and modified PEEK), polyetherketoneketone (PEKK), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polytetra Super engineering plastics such as fluoroethylene (PTFE), thermoplastic polyimide resin (TPI), thermoplastic polyamideimide (TPAI), liquid crystal polyester, and polymer alloys based on polyethylene terephthalate or polyethylene naphthalate, ABS / polycarbonate, Examples thereof include polymer alloys containing the above engineering plastics such as nylon 6,6, aromatic polyamide resin, polyphenylene ether / nylon 6,6, polyphenylene ether / polystyrene, and polybutylene terephthalate / polycarbonate. The thermoplastic resin may be contained alone or in combination of two or more.

When the external insulating layer has a laminated structure, the resin components contained in each layer at the maximum content may be the same or different from each other.

The external insulating layer may contain various additives usually used for electric wires. In this case, the content of the additive is not particularly limited, but is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, based on 100 parts by mass of the resin component.

The external insulating layer is preferably formed by extruding a resin composition on the outer periphery of the stranded wire portion. The resin composition contains the above-mentioned resin component and, if necessary, various additives. The extrusion method cannot be uniquely determined depending on the type of the resin component, etc., but for example, using an extrusion die having an opening similar to or substantially similar to the cross-sectional shape of the stranded wire portion, the temperature of the resin component is higher than the melting temperature. The method of extruding at the temperature of is mentioned.
The external insulating layer is not limited to extrusion molding, and can be formed in the same manner as the enamel layer by using a varnish containing the above-mentioned thermoplastic resin, a solvent and the like, and if necessary, various additives.
In the present invention, as described above, the thickness of the insulating layer is increased contrary to the conventional electric wire. Therefore, from the viewpoint of productivity, it is preferable to form the external insulating layer by extrusion molding.
When forming an insulating layer thicker than before, the number of turns increases when the tape is wound, and the production speed decreases. On the other hand, in the case of extrusion molding, the processing speed does not depend on the thickness of the coating, so that the production speed does not decrease.
Further, if the tape is wound, the flexibility is impaired as compared with the extruded coating layer, and there is a possibility that the bobbin with a small diameter cannot be wound.

(Litz wire structure)
The specific structure of the litz wire used in the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.
In each figure, the contour shape of the electric wire is shown in an annular shape, but in the electric wire used in the present invention, the shape of the outer contour line is not limited to the annular shape and can be appropriately determined. For example, examples of the contour shape of the electric wire include an elliptical shape, a flat knurled shape (gear shape or a wavy shape), and the like, in addition to the circular shape.

An example of a preferable litz wire used in the present invention is the litz wire 10B.
As shown in FIG. 2, the litz wire 10B has a stranded wire portion 13A formed by twisting seven strands 10a, and an external insulating layer 14A covering the outer periphery of the stranded wire portion 13A. The stranded wire portion 13A is formed by twisting seven strands 10a in a pattern in which six strands 10a are arranged around one strand 10a. The six strands 10a are all strands arranged in the outermost row in the radial direction and are strands for determining the conductor portion. Each wire 10a has a conductor 11 and a wire insulating layer 12A arranged on the outer peripheral surface of the conductor 11.

In the present invention, the method of thickening the insulating layer of the electric wire to reduce the AC resistance and the DC resistance in a well-balanced manner only needs to satisfy the above configurations (2) and (3), so that the insulating layer has a laminated structure. You can also. Examples of such a litz wire include the litz wire 10C shown in FIG. The litz wire 10C is the same as the litz wire 10B except that it has an external insulating layer 14B having a three-layer laminated structure. Each of the constituent layers 14b1, 14b2 and 14b3 constituting the external insulating layer 14B is set to have the same thickness. In the present invention, the relationship between the thicknesses of the constituent layers of the external insulating layer having a laminated structure is not particularly limited.

Another preferred example of the litz wire used in the present invention is the litz wire 10D.
The litz wire 10D shown in FIG. 4 is the same as the litz wire 10B except that it has a stranded wire portion 13B formed of 19 strands 10a and an external insulating layer 14A. The stranded wire portion 13B of the litz wire 10D has a total of 12 strands 10a (10a-1 and 10a-2) outside the stranded wire portion 13A of the litz wire 10B so as to have a hexagonal shape in the cross section shown in FIG. ) Are arranged and twisted together. In this arrangement, of the 12 strands 10a arranged in the outermost row, the 6 strands 10a-1 located at the apex of the hexagon in the cross section shown in FIG. 4 are the most in the radial direction. It is a wire arranged in the outer row and is a wire that determines the conductor portion. On the other hand, the remaining 6 strands, that is, the 6 strands 10a-2 located at the center of each side of the hexagon in the cross section shown in FIG. 4, are the strands arranged in the outermost row and are conductors. It is a wire that does not determine the part. Since the litz wire 10D has a pattern in which six strands 10a are arranged around one strand like the litz wire 10A, the space factor of the conductor portion is the same as that of the litz wire 10B. The resistance value can be reduced. Here, the area ratio of the conductor portion means the area ratio of the cross-sectional area of the conductor to the area of the unit grid (cross-sectional area of the conductor / area of the unit grid) in the cross-sectional shape of the electric wire. When the cross-sectional shape of the electric wire is circular, the unit grid of the electric wire is a regular hexagon circumscribing the outer shape of the electric wire, and when the cross-sectional shape of the electric wire is rectangular, the unit grid is a quadrangle circumscribing the outer shape of the electric wire.

In the present invention, the litz wire structure used in the present invention may be a structure in which the structures of the litz wires 10B to 10D are appropriately combined. Further, in the litz wires 10B to 10D, the strands shown in FIG. 1 can be used for all or part of the strands 10a.

<Electric wire used for high voltage and small current side coil>
The electric wire used for the high-voltage small-current side coil in the transformer of the present invention is not particularly limited, and a normal electric wire used for the high-voltage small-current side coil of the transformer can be used. Examples of such an electric wire include the litz wire used for the secondary winding described in Patent Document 1. Further, the electric wire used in the present invention described above can also be used.

<Coil>
The low-voltage, high-current-side coil of the transformer of the present invention is the above-mentioned electric wire used in the present invention wound around the outer peripheral surface of the core. Therefore, this low voltage large current side coil is the same as the conventional low voltage large current side coil except that the electric wire used in the present invention described above is used.
The low-voltage high-current side coil is not particularly limited, and is wound around the outer peripheral surface of the core 6 (the inner peripheral surface of the slot 7 formed in the bobbin 5), for example, as shown in FIG. 6 or 11. , The above-mentioned coils 4A and 4B having the electric wires 10A or 10B used in the present invention are preferably mentioned. In FIG. 6 or FIG. 11, the wire insulating layer 12A included in the electric wires 10A and 10B is not shown because it is a thin layer and cannot be clearly shown as the contour line of the conducting wire 11. The same applies to FIGS. 5 and 12.
Further, the high-voltage small-current side coil of the transformer of the present invention is an outer peripheral surface different from the outer peripheral surface of the core in which the above-mentioned known electric wire or the above-mentioned electric wire used in the present invention is wound with the electric wire used for the low-voltage high-current side coil. It is wound around.
In the present invention, the material (iron core, magnetic core, air core, etc.) and size of the core (also referred to as core) around which each electric wire is wound are appropriately selected according to the intended use and the like. Further, the winding method, the number of turns (two or more turns), the pitch, etc. of the electric wire are also appropriately selected according to the application and the like.

<Transformer of the present invention>
The transformer of the present invention is the same as the conventional transformer except that the electric wire used in the present invention described above is used for the low voltage and large current side coil.
A transformer is a device for converting the high voltage of AC power by using electromagnetic induction. A transformer generally has two coils, namely an input side coil (primary side coil) and an output side coil (secondary side coil). In the transformer, an alternating current is passed through the primary coil to generate an alternating magnetic field, which is received by the magnetically coupled secondary coil, and the current is generated again to be output. At this time, the ratio of the voltage generated between the primary side coil and the secondary side coil is the same as the ratio of the number of turns of the electric wire in each coil. The number of turns is determined.
A transformer in which the voltage of the primary coil is set relatively higher than that of the secondary coil is called a step-down transformer. In this step-down transformer, a high-voltage small-current current flows through the primary side coil (high-pressure small-current side coil), and a low-voltage large-current current flows through the secondary side coil (low-voltage large-current side coil). On the other hand, a transformer in which the voltage of the primary coil is set relatively lower than that of the secondary coil is called a step-up transformer. In this step-up transformer, a low-voltage large-current current flows through the primary side coil (low-pressure large-current side coil), and a high-pressure small-current current flows through the secondary side coil (high-pressure small-current side coil).

In the transformer of the present invention, whether it is a step-down transformer or a step-up transformer, a coil wound with the above-mentioned electric wire used in the present invention is used as the low-voltage large-current side coil.
The structure or size of the transformer of the present invention is not particularly limited as long as it has a coil around which the above-mentioned electric wire used in the present invention is wound as a low-voltage high-current side coil. For example, in the primary side coil and the secondary side coil, the voltage and the current value of the current are relatively determined. Therefore, in addition to the low voltage large current side coil, the high pressure small current side coil may be used in the present invention. It is also possible to use a coil wound around the above-mentioned electric current to be used.

In the transformer of the present invention, the current flowing through each coil is appropriately determined according to the application and characteristics as described above. Although not particularly limited, for example, the current flowing through the low-voltage large-current side coil is preferably 100 V or more and less than 500 V, and the current value is preferably 1 A or more and 30 A or less. The current flowing through the high-voltage small-current side coil preferably has a voltage of 500 V or more and 4000 V or less, and a current value of 0.3 A or more and less than 1 A.

The transformer configuration of the present invention is established in principle if it has a primary coil and a secondary coil, but it is usually preferable to have a core (bobbin) around which an electric wire is wound. Further, in order to strengthen the magnetic coupling between the primary side coil and the secondary side coil, it is preferable that the bobbin has a core, and this core is made of a magnetic material (not an air core). preferable.
The transformer of the present invention is a transformer (also referred to as a split winding transformer) in which a primary side coil and a secondary side coil are wound around different outer peripheral surfaces of the core to ensure insulation by space. Specifically, using one bobbin having two slots (forming a core) separated in the axial direction, the primary side coil and the secondary side coil are wound around different slots to ensure insulation. Examples are mentioned. Further, the primary side coil and the secondary side coil are wound around different bobbins (usually having one slot), and the axes of these two bobbins are aligned and arranged in a line in the axial direction. , An embodiment in which insulation is ensured can be mentioned. With the above-mentioned split winding transformer, it is possible to avoid dielectric breakdown of the electric wire wound around each coil even at a high output for high frequency. In the split winding transformer, the core may be an integral type and the electric wire may be wound around different outer peripheral surfaces thereof as in each of the above-mentioned aspects, or the core may be one using separate cores. An electric wire may be wound around each of the outer peripheral surfaces of the core.

In the transformer of the present invention, the shape, dimensions, or material of the core and bobbin used in a normal transformer can be appropriately selected.

The transformer of the present invention may have the above configuration, and examples thereof include a transformer having coils 4A and / or 4B shown in FIG. 6 or FIG. In the transformer of the present invention, the low-voltage high-current side coil and the high-voltage low-current side coil are wound around different outer peripheral surfaces of the core. The low-voltage high-current side coil and the high-voltage low-current side coil are arranged so that the cores (bobbins) are adjacent to each other in the axial direction of the cores, and form a transformer. The electric wire used in the present invention is wound around the outer peripheral surface of the core of the low-pressure high-current side coil, and the above-mentioned known electric wire or the above-mentioned electric wire used in the present invention is wound around the high-pressure small-current side coil. There is.

An example of a preferred transformer of the present invention is the transformer 1 shown in FIG. This transformer 1 has a low voltage large current side coil 4B shown in FIG. 11 as a primary side coil 2 and a conventional high voltage small current side coil as a secondary coil 3, and a primary side coil 2 and a secondary side coil. 3 is arranged in a row in the axial direction with the axes aligned with each other. As will be described later, the low-voltage high-current side coil 4B has a litz wire 10B wound around the outer peripheral surface of the core 6A of the bobbin 5A, and the high-voltage low-current side coil 3 is conventionally mounted on the outer peripheral surface of the core 6B of the bobbin 5B. The electric wire (litz wire) 101 is wound around.

Since the transformer of the present invention has a coil in which an electric wire having the above configurations (1) to (3) is wound as a low-voltage high-current side coil, even a high-frequency high-output transformer is described above. In addition, the loss can be effectively suppressed. Further, the transformer of the present invention uses an electric wire in which the conductor portion and the outer diameter of the electric wire are set as described above, instead of increasing the number of windings of the electric wire and the number of strands of the litz wire. Therefore, it is possible to respond to the recent miniaturization or weight reduction without increasing the size of the coil or transformer, and it is also possible to contribute to cost reduction.

<Use>
The transformer of the present invention is suitably used in applications where high output for high frequency is required, and further in applications in which a current having a large current value flows. For example, it is more preferably used for an alternating current (AC) / direct current (DC) converter that transforms and rectifies an alternating current commercial power source and converts it into a direct current with a voltage suitable for electrical and electronic equipment, specifically a microwave oven. It is suitably used as each transformer for producing a high voltage for supplying a magnetron in a power supply board for a current device.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Example 1>
In this example, the coil 4A shown in FIG. 6 using a wire as the electric wire used in the present invention was manufactured and evaluated.
-Example 1-1-
First, the electric wire (wire) 10A shown in FIG. 1 used for the low voltage and large current side coil 4A was manufactured.
A wire insulating layer (enamel layer) 12A having a thickness of 16 μm was formed in a step of applying a polyamide-imide resin varnish to the surface of a lead wire (copper wire having a circular cross section) 11 having an outer diameter of 0.85 mm and baking it. Then, polyethylene terephthalate (PET) resin was extruded to a thickness of 77 μm to form an external insulating layer 12B. As a result, an electric wire (elementary wire) 10A having a conducting wire 11 and an insulating layer 12 having a total thickness of 93 μm was produced.
The manufactured electric wire 10A has an outer diameter of the conducting wire (conductor portion) 11 of 0.85 mm, a thickness of the insulating layer 12 of 0.093 mm, and an outer diameter (finished diameter) of the electric wire 10A of 1.036 mm. rice field. The radius difference in the electric wire 10A is 93 μm, and the outer diameter ratio is 0.82. Further, in the core 6 and the bobbin 5 used, the diameter of the outer peripheral surface (inner peripheral surface of the slot 7) around which the electric wire 10A was wound was 30.2 mm, and the axis length was 6 mm (shown in FIG. 6 (schematic cross-sectional view)). The dimensions of the core 6 and the bobbin 5 do not exactly match the above dimensions described in Example 1-1). As shown in FIG. 6, the electric wire 10A is wound around the outer peripheral surface of the core 6 in two rows (number of parallels 2) consisting of five turns, for a total of 10 turns (number of turns), and the low-voltage high-current side coil is wound. 4A was produced.

Examples 1-2 to 1-4
The low-voltage large-current side coils 4A of Examples 1-2 to 1-4 were manufactured in the same manner as in Example 1-1 except that the radius difference and the outer diameter ratio of the electric wires were changed as follows.
In the electric wire used for the coil of Example 1-2, the outer diameter of the conducting wire (conductor portion) 11 is 0.8 mm, the thickness of the insulating layer 12 is 118 μm (the thickness of the enamel layer 12A is unchanged, and the external insulation is performed. The thickness of the layer 12B was changed), and the outer diameter (finished diameter) of the electric wire 10A was 1.036 mm. The radius difference in the electric wire 10A is 118 μm, and the outer diameter ratio is 0.77.
In the electric wire used for the coil of Example 1-3, the outer diameter of the conducting wire (conductor portion) 11 is 0.6 mm, the thickness of the insulating layer 12 is 218 μm (the thickness of the enamel layer 12A is unchanged, and the external insulation is performed. The thickness of the layer 12B was changed), and the outer diameter (finished diameter) of the electric wire 10A was 1.036 mm. The radius difference in the electric wire 10A is 218 μm, and the outer diameter ratio is 0.58.
In the electric wire used for the coil of Example 1-4, the outer diameter of the conducting wire (conductor portion) 11 is 0.5 mm, the thickness of the insulating layer 12 is 268 μm (the thickness of the enamel layer 12A is unchanged, and the external insulation is performed. The thickness of the layer 12B was changed), and the outer diameter (finished diameter) of the electric wire 10A was 1.036 mm. The radius difference in the electric wire 10A is 268 μm, and the outer diameter ratio is 0.48.

<Comparative Example 1>
-Comparative Example 1-1-
Comparative Example 1-1 is an example using the electric wire 110A in which the radius difference is smaller than the range specified in the present invention and the outer diameter ratio is larger than the range specified in the present invention.
In the same manner as in Example 1-1, except that the outer diameter of the conductor of the electric wire 110A is set to 1.0 mm and the thickness of the wire insulating layer is set to 18 μm (the external insulating layer is not provided). The low-voltage, high-current-side coil 104A of Comparative Example 1-1 shown in FIG. 7 was manufactured. The electric wire 110A in the low pressure large current side coil 104A had an outer diameter (finished diameter) of 1.036 mm, a radius difference of 18 μm, and an outer diameter ratio of 0.97.

-Comparative example 1-2-
Comparative Example 1-2 is an example in which an electric wire having a radius difference larger than the range specified by the present invention and an outer diameter ratio smaller than the range specified by the present invention is used.
Except for the fact that the outer diameter of the conductor was set to 0.2 mm and the thickness of the insulating layer was set to 418 μm (the thickness of the enamel layer 12A was unchanged and the thickness of the external insulating layer 12B was changed). The low-voltage, high-current-side coil of Comparative Example 1-2 was produced in the same manner as in Example 1-1. The electric wire in the low voltage and large current side coil had an outer diameter (finished diameter) of 1.036 mm, a radius difference of 418 μm, and an outer diameter ratio of 0.19.

<Measurement of resistance>
Using the coils manufactured in Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2, the resistance value generated in the coil is measured by changing the frequency with a precision LCR meter (trade name: E4980A, KEY SIGHT). Measurements were made using TECHNOLOGIES (formerly Agilent).
Specifically, in the range of about 40 mm from both ends of each low-voltage and high-current side coil, the exposed conductor wire after peeling off the external insulating layer and the wire insulating layer was covered with solder. The contact resistance was sufficiently reduced and the resistance value was measured by sandwiching the soldered portion between the measuring jigs of the precision LCR meter and pressing the soldered portion. The obtained resistance value was divided by the coil length excluding the solder portion to calculate the resistance value (Ω / m) per 1 m.

The relationship between the resistance values at frequencies of 30 Hz, 50 Hz and 150 Hz and the outer diameter ratio is shown in FIGS. 8 to 10. In FIGS. 8 to 10, the resistance value generated in the low-voltage large-current side coil of Comparative Example 1-2 is not shown because it is too large as shown in Table 1.
In Example 1 and Comparative Example 1, the relationship between the resistance value and the radius difference can be understood by setting the horizontal axis as the radius difference in each figure.
Table 1 shows the minimum resistance values of Examples 1-1 to 1-4 at each frequency. Specifically, when the frequency is 30 kHz, the resistance value of the low-voltage high-current side coil 4B manufactured in Example 1-1 is used, and when the frequency is 50 kHz, the low-voltage high-current side coil 4B manufactured in Example 1-3 is used. When the frequency is 150 kHz, the resistance value of the low-voltage large-current side coil 4B manufactured in Example 1-4 is shown.
Further, for each of the above-mentioned minimum resistance values, the resistance ratio (minimum resistance value of the example coil / resistance value of the coil of the comparative example) to each resistance value of the coils of Comparative Examples 1-1 and 1-2 is set. It is shown in Table 1.
The resistivity ratio is obtained from the corresponding resistance values below and is rounded off to five decimal places.

The following can be seen from FIGS. 8 to 10 and Table 1.
At high frequencies of 30 kHz or higher, the proximity effect cannot be ignored, but when the radius difference and outer diameter ratio of the wires used for the low voltage and large current side coils are within the specific ranges specified in the present invention, the DC resistance and AC resistance The balance is improved, and the resistance value can be suppressed to be smaller than that of Comparative Examples 1-1 and 1-2. Further, the higher the frequency, the larger the proximity effect and the higher the resistance value generated in the coil, but the low voltage and large current side coil of Example 1 becomes smaller as the frequency increases with respect to the resistance ratio to the coil of Comparative Example 1-1. It can be seen that the effect of reducing the resistance value is excellent. In the case of a step-up transformer used in an inverter type microwave oven, an operating frequency of 30 to 150 kHz is common. Therefore, it can be seen that when the step-up transformer having the low-voltage large-current side coil of Example 1 is used in the inverter type microwave oven, the resistance of the low-voltage large-current side coil can be effectively reduced and the loss of the step-up transformer can be reduced.

<Example 2>
In this example, the coil 4B shown in FIG. 11 using the litz wire 10C shown in FIG. 3 as the electric wire used in the present invention was manufactured and evaluated.
-Example 2-1-
The stranded wire portion 13A was manufactured using the strand wire prepared as follows.
First, in a step of applying a polyurethane resin varnish to the surface of a conductor wire (copper wire having a circular cross section) 11 having an outer diameter of 0.25 mm and baking it, the wire wire 10a having a wire insulating layer (enamel layer) 12A having a thickness of 11 μm. Was produced. In the produced wire 10a, the outer diameter of the conductor 11 was 0.25 mm, the thickness of the wire insulating layer 12A was 11 μm, and the outer diameter (finished diameter) of the wire 10a was 0.272 mm.
With the one strand 10a produced in this way as the center and six strands 10a arranged around it, these strands 10a are twisted at a twist pitch of 18 mm to produce a stranded wire portion 13A. bottom.
Next, PET resin was extruded on the outer periphery of the stranded wire portion 13A so as to have a thickness of 26 μm. This extrusion molding was repeated three times to manufacture an electric wire (litz wire) 10C having a stranded wire portion 13A and an extruded coating layer having a three-layer structure composed of an external insulating layer 14B having a thickness of 78 μm. The outer diameter of the conductor portion of the litz wire 10C was 0.794 mm, and the outer diameter (finished diameter) of the litz wire 10C was 0.972 mm. Therefore, the radius difference was 89 μm, and the outer diameter ratio was 0.82.
The core 6 and the bobbin 5 used had a diameter of the outer peripheral surface around which the litz wire 10C was wound 30.2 mm and an axis length of 6 mm (the dimensions of the core 6 and the bobbin 5 shown in FIG. 11 (schematic sectional view) are It does not exactly match the above dimensions described in Example 2-1). As shown in FIG. 11, the litz wire 10C is wound around the outer peripheral surface of the core 6 in two parallel rows (number of parallels 2) in which one row consists of 5 turns, for a total of 20 turns (number of turns) to reduce the voltage. A high current side coil 4B was manufactured.

Examples 2-2 and 2-3
The low voltage large current side coil 4B of Examples 2-2 to 2-4 was manufactured in the same manner as in Example 2-1 except that the radius difference and the outer diameter ratio of the litz wire were changed as follows.
In the electric wire used for the coil of Example 2-2, the outer diameter of the conducting wire 11 is 0.2 mm, the thickness of the wire insulating layer 12A is 10 μm, and the outer diameter of the wire 10a is 0.22 mm. rice field. The outer diameter of the conductor portion of the litz wire 10C is 0.64 mm, and the outer diameter (finished diameter) of the litz wire 10C is 0.972 mm by adjusting the thickness of the external insulating layer 14B. Therefore, the radius difference was 166 μm, and the outer diameter ratio was 0.66.
In the electric wire used for the coil of Example 2-3, the outer diameter of the conductor 11 is 0.15 mm, the thickness of the wire insulating layer 12A is 8 μm, and the outer diameter of the wire 10a is 0.166 mm. rice field. The outer diameter of the conductor portion of the litz wire 10C is 0.482 mm, and the outer diameter (finished diameter) of the litz wire 10C is 0.972 mm by adjusting the thickness of the external insulating layer 14B. Therefore, the radius difference was 245 μm, and the outer diameter ratio was 0.50.

<Comparative Example 2>
-Comparative example 2-1-
Comparative Example 2-1 is an example using the electric wire 110B in which the radius difference is smaller than the range specified in the present invention and the outer diameter difference is larger than the range specified in the present invention.
For the wire, adjust the outer diameter of the conductor wire to 0.3 mm, the thickness of the wire insulating layer to 9 μm, the outer diameter of the conductor to 0.936 mm, and the outer diameter of the litz wire 110B to adjust the thickness of the outer insulating layer. The low-voltage, high-current-side coil 104B of Comparative Example 2-1 shown in FIG. 12 was produced in the same manner as in Example 2-1 except that it was set to 0.972 mm. The electric wire 110B in the low voltage large current side coil 104B had a radius difference of 18 μm and an outer diameter ratio of 0.96.

-Comparative example 2-2-
Comparative Example 2-2 is an example in which an electric wire having a radius difference larger than the range specified by the present invention and an outer diameter difference smaller than the range specified by the present invention is used.
For the wire, adjust the outer diameter of the conductor to 0.1 mm, the thickness of the wire insulating layer to 7 μm, the outer diameter of the conductor to 0.328 mm, and the outer diameter of the litz wire to the thickness of the outer insulating layer. A low-voltage, high-current-side coil of Comparative Example 2-2 was produced in the same manner as in Example 2-1 except that it was set to 0.972 mm. The electric wire in the low voltage and large current side coil had a radius difference of 322 μm and an outer diameter ratio of 0.34.

<Measurement of resistance>
Using the coils manufactured in Examples 2-1 to 2-3 and Comparative Examples 2-1 and 2-2, the resistance generated in the coil was measured by changing the frequency in the same manner as in Example 1.

The relationship between the resistance values at frequencies of 30 Hz, 50 Hz and 150 Hz and the outer diameter ratio is shown in FIGS. 13 to 15. In FIGS. 13 and 14, the resistance value generated in the low voltage and large current side coil of Comparative Example 2-2 is not shown because it is too large as shown in Table 2.
In Example 2 and Comparative Example 2, the relationship between the resistance value and the radius difference can be understood by setting the horizontal axis as the radius difference in each figure.
Table 2 shows the minimum resistance values of Examples 2-1 to 2-3 at each frequency. Specifically, when the frequency is 30 kHz, the resistance value of the low-voltage high-current side coil 4B manufactured in Example 2-1 is used, and when the frequency is 50 kHz, the low-voltage high-current side coil 4B manufactured in Example 2-2 is used. When the frequency is 150 kHz, the resistance value of the low-voltage large-current side coil 4B manufactured in Example 2-3 is shown.
Further, for each of the above-mentioned minimum resistance values, the resistance ratio to each resistance value of the coils of Comparative Examples 2-1 and 2-2 (minimum resistance value of the coil of the example / resistance value of the coil of the comparative example). Is shown in Table 2.

Since the coil of the second embodiment uses more strands (number of turns) than the coil of the first embodiment, the proximity effect between the electric wires is strengthened and a large AC resistance is generated. However, as shown in FIGS. 13 to 15 and Table 2, the low-voltage, high-current-side coil around which the electric wire specified in the present invention is wound has a resistance value at a high frequency of 30 kHz or higher, as in the first embodiment. The increase can be suppressed. Further, as the frequency becomes higher, the resistance ratio to the coil of Comparative Example 2-1 becomes smaller, and the effect of reducing the resistance value is excellent. Therefore, it can be seen that when the step-up transformer having the low-voltage large-current side coil of Example 2 is used in the inverter type microwave oven, the resistance of the low-voltage large-current side coil can be effectively reduced and the loss of the step-up transformer can be reduced.

<Example 3>
A comparison was made between the coil manufactured in Example 2 and the coil used for the transformer described in Patent Document 1 (referred to as the coil of Patent Document 1).
The coil manufactured in Example 2 is as described above. In Example 3, when the frequency was set to 30 kHz, the low voltage large current side coil 4B manufactured in Example 2-1 was used. Similarly, when the frequency is set to 50 kHz, the low-voltage high-current side coil 4B manufactured in Example 2-2 is used, and when the frequency is set to 150 kHz, the low-voltage high-current side coil manufactured in Example 2-3 is used. 4B was used.
The coil of Patent Document 1 was manufactured in the same manner as in Example 2-1 except that the electric wire described in paragraph [0010] of Patent Document 1 was used. The electric wire described in paragraph [0010] of Patent Document 1 has a radius difference of 33 μm and an outer diameter ratio of 0.83.
For the above coil, the resistance generated in the coil was measured by changing the frequency in the same manner as in Example 1.
The ratio of the resistance value at frequencies of 30 Hz, 50 Hz and 150 Hz to the resistance value of the coil manufactured in Patent Document 1 to the resistance value of the coil manufactured in Example 2 (resistance value of the coil manufactured in Example 2 / the resistance value of Patent Document 1). The resistance value of the coil) is shown in Table 3.

As is clear from Table 3, even if the electric wire described in Patent Document 1 is used for the low-voltage high-current side coil, the increase in resistance value cannot be sufficiently suppressed. On the other hand, when the electric wire specified in the present invention is used for the low voltage large current side coil, the increase in resistance value can be effectively suppressed at any frequency, and the electric wire described in Patent Document 1 is used. It can be seen that the effect of reducing the resistance value is high with respect to the coil (the resistance ratio is large), and the loss of the transformer can be effectively suppressed.

<Example 4>
A coil in which an electric wire (litz wire) 10C manufactured by the following method was wound in the same manner as in Example 2 was produced, and the resistance value was measured. In addition, as a coil for comparison, the resistance value was also measured for the low-voltage, high-current side coil of the transformer built in the steam range ER-ND7 (trade name, operating frequency 30 Hz, output 1430 W, manufactured by Toshiba).
Further, the low-voltage large-current side coil of Example 4 manufactured as described below is mounted as the low-voltage large-current side coil of the transformer mounted on the steam range (the transformer of the present invention is manufactured) to form a steam range. Loss was measured. As the coil on the high voltage and small current side, the coil of the transformer mounted on the steam range was used as it was. The steam range loss was calculated by subtracting the output from the input when the steam range was operated for 1 minute at the maximum output setting. The input wattage was measured using a power meter: Power High Tester 3334 (trade name, manufactured by Hioki Electric Co., Ltd.), and the output wattage was calculated from the temperature rise of the water heated in 1 minute.

-Manufacturing of the electric wire and coil of Example 4-
The litz wire 10C shown in FIG. 3 was manufactured as the electric wire used in Example 4.
A wire 10a having a wire insulating layer 12A having a thickness of 0.010 mm was produced by a step of applying a polyurethane resin varnish to the surface of a conductor wire (copper wire having a circular cross section) 11 having an outer diameter of 0.18 mm and baking it. In the produced wire 10a, the outer diameter of the conductor 11 is 0.18 mm, the thickness of the wire insulating layer 12A is 0.010 mm, and the outer diameter (finished diameter) of the wire 10a is 0.20 mm. rice field.
With the one strand 10a produced in this way as the center and six strands 10a arranged around it, these strands 10a are twisted at a twist pitch of 18 mm to produce a stranded wire portion 13A. bottom.
Next, PET resin was extruded on the outer circumference of the stranded wire portion 13A. This extrusion molding is repeated three times, and an electric wire (litz wire) having a stranded wire portion 13A and an external insulating layer (three-layer structure extrusion coating layer, the thickness of each constituent layer is the same) 14B having a thickness of 0.10 mm. ) 10C was manufactured. The outer diameter of the conductor portion of the litz wire 10C was 0.58 mm, and the outer diameter (finished diameter) of the litz wire 10C was 0.8 mm. Therefore, the radius difference is 110 μm, and the outer diameter ratio is 0.73.
The core used had a diameter of the outer peripheral surface around which the litz wire 10C was wound was 22 mm and a shaft length of 15 mm. Ten wires 10C are bundled and twisted at a twist pitch of 10 mm, wound around the outer peripheral surface of this core for 5 turns, folded back for another 4 turns, folded back for 5 turns, and folded back for 4 turns for a total of 4 layers and 18 turns. A low-voltage, high-current side coil was created by winding.

As a coil on the low voltage and high current side for comparison, the coil originally mounted on the microwave oven was used as a comparison target. The electric wire wound around this coil is made by twisting 16 strands having a wire insulating layer with a thickness of 0.017 mm on the surface of a conductor wire (copper wire having a circular cross section) having an outer diameter of 0.20 mm at a twist pitch of 10 mm. It was a thing. The outer diameter (finished diameter) of this electric wire is 1.17 mm, the radius difference is 17 μm, and the outer diameter ratio is 0.97.
Five litz wires for comparison are bundled on the outer peripheral surface of the same core as the core used in Example 4, twisted at a twist pitch of 10 mm, wound around the outer peripheral surface of this core for 5 turns, folded back, and further 4 A total of 4 layers and 18 turns were wound with turns, folded back for 5 turns, and turned back for 4 turns to manufacture a low-voltage, high-current side coil.

With respect to the low voltage large current side coil of Example 4 and the low voltage large current side coil for comparison, the resistance value generated in the low voltage large current side coil was measured in the same manner as in Example 1. The result is shown in FIG.
From FIG. 16, it can be seen that the low voltage large current side coil of Example 4 has a smaller resistance value than the comparative low voltage large current side coil at a frequency of 50 Hz or higher. Here, the operating frequency of the microwave oven is 30 kHz, but since it is a rectangular wave, harmonics of 90 kHz and 150 kHz are carried. Therefore, the actual frequency is about 50 kHz on average. Therefore, it can be seen that the low-voltage, high-current-side coil of Example 4 can reduce its loss when used in a high-frequency transformer.
Moreover, the electric wire 10C produced in Example 4 has a lead dose (copper usage amount) of 30% less by mass ratio than the electric wire used for the low-pressure large-current side coil for comparison. Therefore, the low-voltage, high-current-side coil and transformer manufactured in Example 4 are smaller, lighter, and cheaper than the comparative coil and transformer.

The loss of the microwave oven when the microwave oven was operated at the maximum output for 1 minute was measured by incorporating the coil of Example 4 and the comparison coil into a transformer as a low-voltage high-current side coil. As a result, both when the coil for comparison was used and when the coil of Example 4 was used, the loss was 621 W and the efficiency was 46%. As described above, it can be seen that the low-voltage large-current side coil of Example 4 exhibits the same performance as the comparative low-voltage large-current side coil even if it is small and lightweight, and can be manufactured at a low cost. In other words, when the low-voltage large-current side coil of Example 4 is used with an increased number of windings (number of parallels) so that the amount of copper used is the same as that of the comparative low-voltage large-current side coil, it is 10 in terms of the above-mentioned conducting dose. Since it can be increased by / 7, the resistance value becomes 7/10 of the reciprocal. That is, it can be seen that the resistance value generated in the coil of the fourth embodiment can be reduced by 30% with respect to the low-voltage large-current side coil for comparison.

From Examples 1 to 4, it can be seen that the coil using the electric wire specified in the present invention exhibits a small resistance when used in a transformer as a low voltage and large current side coil, and can effectively reduce the loss of the transformer.
In each of Examples 1 to 4, a step-up transformer was manufactured and its excellent characteristics were evaluated. It can be seen that if the above-mentioned excellent characteristics are obtained for this step-up transformer, the step-down transformer also exhibits excellent characteristics as well.

1 Transformer 2 Primary side coil 3 Secondary side coil (high voltage small current side coil)
4A, 4B, 104A, 104B (low voltage, large current side) coil 5, 5A, 5B Bobbin 6, 6A, 6B Core 7 Slot 10A, 110A Wire (wire)
10B, 10C, 10D, 101, 110B electric wire (litz wire)
11 Conductor 12 Insulation layer 12A Wire insulation layer (enamel layer)
12B External Insulation Layer 13A, 13B Stranded Wire 10a Wire 10a-1 Wire arranged in the outermost row in the radial direction and determining the conductor part 10a-2 Outermost in the radial direction Wires arranged in a row but whose conductor part is not determined 14A, 14B External insulation layer 14b1, 14b2, 14b3 Constructible layer Dc Outer diameter of conductor part Dd Outer diameter difference / 2 (radius difference)

Claims (7)

A high-frequency high-output transformer provided with a primary coil and a secondary coil having wires wound around different outer peripheral surfaces of the core.
The electric wire of the primary side coil and the secondary side coil of the low pressure and high current side coil has a conductor portion and an insulating layer covering the outer periphery of the conductor portion, and the outer diameter of the conductor portion and the electric wire. The outer diameter difference / 2 ([outer diameter of the electric wire-outer diameter of the conductor part] / 2) is in the range of 70 to 260 μm, and the outer diameter ratio (outer diameter of the conductor part / outer diameter of the electric wire) is in the range of 70 to 260 μm. ) Is in the range of 0.48 to 0.84, which is a high output transformer for high frequencies. The high-frequency output transformer according to claim 1, wherein the outer diameter of the conductor portion is 0.35 mm or more and less than 1.00 mm. When the electric wire is a wire or a litz wire and the wire is a wire, the insulating layer covering the outer periphery of the conductor portion is an insulating layer made of a conducting wire in contact with the conductor portion and is a thermosetting resin. The high output transformer for high frequency according to claim 1 or 2, wherein the wire insulating layer includes a stranded wire having a wire insulating layer containing a thermosetting resin in contact with a conducting wire in the case of a litz wire. The high-frequency high-output transformer according to claim 3, wherein the wire insulating layer containing the thermosetting resin has a thickness of 8 to 18 μm. The high frequency high output according to any one of claims 1 to 4, wherein the insulating layer covering the outer periphery of the conductor portion has a layer structure of two or more layers, of which the outermost insulating layer contains a thermoplastic resin. Trance. The high-frequency high-output transformer according to any one of claims 1 to 5, wherein the insulating layer covering the outer periphery of the conductor portion has a layer structure of three or more layers. The high-frequency high-output transformer according to any one of claims 1 to 6, wherein the insulating layer covering the outer periphery of the conductor portion is an extrusion coating layer.

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