Transformer

Abstract

The present invention provides a transformer comprising: a magnetic core that includes a central leg and at least two outer legs which are branched from the central leg; and primary windings and a secondary winding that are wound around the magnetic core. The transformer is configured such that the primary windings are wound respectively around the central leg, a first outer leg, and a second outer leg, the secondary winding is wound around the central leg, and magnetic fluxes that are generated by the primary windings wound around the first and second outer legs weaken each other at the central leg.

Description

Transformer

[0001] The present invention relates to a transformer.

[0002] JP2008-166624A discloses a technique in which a transformer is connected to a power conversion circuit (switching power supply circuit) using resonance characteristics, and the inductance of a winding provided on the transformer is used as an inductance element in the power conversion circuit. In this technique, the inductance required for the power conversion circuit is ensured by utilizing the leakage inductance of the winding.

[0003] JP2008-166624A uses a transformer including an E-type magnetic core (a magnetic core including one central leg forming a magnetic path and outer legs branched into at least two from the central leg), and adjusts the leakage inductance of the transformer by adjusting the arrangement of the primary winding and the secondary winding in the magnetic core and the number of turns. However, since leakage magnetic flux from the primary winding and leakage magnetic flux from the secondary winding interlink and affect the excitation inductance, there is a problem that it is difficult to adjust the leakage inductance to a desired range.

[0004] Accordingly, an object of the present invention is to provide a transformer capable of adjusting leakage inductance to a desired range while suppressing the influence on excitation inductance.

[0005] According to an aspect of the present invention, there is provided a transformer including: a magnetic core including a central leg and at least two outer legs branched from the central leg; and a primary winding and a secondary winding wound around the magnetic core. The primary winding is respectively wound around the central leg, a first outer leg, and a second outer leg, the secondary winding is wound around the central leg, and the transformer is configured such that magnetic fluxes generated by the respective primary windings wound around the first outer leg and the second outer leg cancel each other out at the central leg.

[0006] Figure 1 is a diagram illustrating the structure of a transformer according to the first embodiment of the present invention. Figure 2 is a diagram illustrating the equivalent circuit of the transformer. Figure 3 is a diagram illustrating the structure of a transformer according to the second embodiment. Figure 4 is a diagram illustrating the structure of a transformer according to the third embodiment. Figure 5 is a diagram illustrating the layer structure of the laminated structure constituting the transformer in Figure 4. Figure 6 is a diagram illustrating the structure of a transformer according to the fourth embodiment. Figure 7 is a diagram illustrating the layer structure of the laminated structure constituting the transformer in Figure 6.

[0007] The embodiments of the present invention will be described below with reference to the drawings.

[0008] [First Embodiment] Figure 1 is a diagram illustrating the structure of the transformer 1 according to the first embodiment. Figure 2 is a diagram showing the equivalent circuit of the transformer. The transformer 1 of this embodiment is used in various power conversion circuits (power converters) such as resonant switching power supply circuits such as resonant converters and DC-DC converters.

[0009] As shown in Figure 1, the transformer 1 mainly comprises a magnetic core 10 having an EE core shape or an EI core shape, and a primary winding 12 and a secondary winding 14 wound around the magnetic core 10.

[0010] The magnetic core 10 is composed of a central leg 10A and two outer legs (a first outer leg 10B and a second outer leg 10C) branching off from the central leg 10A. A primary winding 12 (particularly the primary winding 12A) and a secondary winding 14 (particularly the secondary winding 14A) are wound around the central leg 10A, and these primary winding 12A and secondary winding 14A are magnetically coupled through the magnetic core 10.

[0011] Furthermore, a primary winding 12 (particularly primary winding 12B) is wound around the first outer leg 10B, and a primary winding 12 (particularly primary winding 12C) is wound around the second outer leg 10C. In particular, in this embodiment, the number of turns of the primary winding 12B located on the first outer leg 10B and the primary winding 12C located on the second outer leg 10C are the same (number of turns = 1 in Figure 1).

[0012] The primary winding 12B of the first outer leg 10B is supplied with the operating current (indicated by the symbol "I" in Figure 1) of the power conversion circuit into which the transformer 1 is incorporated. The supplied current then flows from the primary winding 12B through the primary winding 12A of the central leg 10A to the primary winding 12C of the second outer leg 10C, and is output.

[0013] Therefore, when current flows through the primary winding 12A of the central leg 10A, a magnetic flux is generated, and at least a portion of this magnetic flux links with the secondary winding 14A. This magnetic flux then generates mutual inductance (excitation inductance) in the transformer 1. On the other hand, when current flows through the primary winding 12B of the first outer leg 10B, a magnetic flux Mf1 shown in Figure 1 is generated. On the other hand, when current flows through the primary winding 12C of the second outer leg 10C, a magnetic flux Mf2 shown in Figure 1 is generated. These magnetic fluxes Mf1 and Mf2 generated in each of these outer legs 10B and 10C generate inductance (leakage inductance) necessary for them to function as inductance elements in the power conversion circuit.

[0014] In particular, the primary winding 12B is positioned on the first outer leg 10B such that when current flows, a magnetic flux Mf1 in a first direction (upward in the figure) is generated at the first outer leg 10B. On the other hand, the primary winding 12C is positioned on the second outer leg 10C such that when current flows, a magnetic flux Mf2 in a second direction (downward in the figure) is generated at the second outer leg 10C.

[0015] As a result, the magnetic flux Mf1 generated by the primary winding 12B and the magnetic flux Mf2 generated by the primary winding 12C will move in directions that weaken each other (cancel each other out) within the magnetic core 10 (especially the central leg 10A).

[0016] With the above configuration, the magnetic flux generated from the primary winding 12A wound around the central leg 10A, specifically the flux linked with the secondary winding 14A wound around the central leg 10A, generates mutual inductance. On the other hand, the induced voltages generated at the ends of the respective primary windings 12B and 12C wound around the outer legs 10B and 10C, which are linked, are in opposite directions. Therefore, these cancel each other out, achieving a state where they do not act as excitation inductance in effect.

[0017] Furthermore, the induced voltage generated by the magnetic flux Mf1 generated from the winding wound around one of the outer legs 10B, 10C (for example, the primary winding 12B) that links with the primary winding 12A and secondary winding 14A of the central leg 10A is in the opposite direction to the induced voltage generated by the magnetic flux Mf2 generated from the winding wound around the other of the outer legs 10B, 10C (for example, the primary winding 12C). In other words, these induced voltages cancel each other out, making it possible to achieve a state in which they do not act as an excitation inductance in effect.

[0018] On the other hand, the voltage induced by the magnetic flux Mf1 generated from the winding wound on one of the outer legs 10B, 10C (e.g., primary winding 12B) that links with the winding wound on the other leg (e.g., primary winding 12C), and the voltage induced by the magnetic flux Mf2 generated from the winding wound on the other leg (e.g., primary winding 12C) that links with the winding wound on one leg (e.g., primary winding 12B), are in the same direction. Therefore, these voltages act as leakage inductance.

[0019] Therefore, by appropriately adjusting the number of turns of the primary winding 12A and secondary winding 14A wound around the central leg 10A, only the excitation inductance (mutual inductances M1 and M2 shown in Figure 2) can be adjusted. Furthermore, by appropriately adjusting the number of turns of the primary windings 12B and 12C wound around each of the outer legs 10B and 10C, only the leakage inductance (self-inductance L1 shown in Figure 2) can be adjusted. In other words, the excitation inductance and leakage inductance in the transformer 1 can be adjusted independently.

[0020] Here, for example, in the circuit of an isolated resonant converter, a resonant inductance is generally inserted in series with the isolation transformer, and it is required to operate in the high-frequency range in order to miniaturize the passive components. Therefore, by using transformer 1 with the above configuration as the isolation transformer for such a resonant converter, it is possible to easily design the circuit while taking into account the adjustment of leakage inductance.

[0021] In particular, in the transformer 1 of this embodiment, the primary winding 12C wound around the second outer leg 10C and the secondary winding 14A wound around the central leg 10A are arranged in close proximity horizontally within the window portion W2 of the magnetic core 10. Furthermore, the direction of the current flowing through the end of the primary winding 12C on the side of the secondary winding 14A (towards the back of the paper) and the direction of the current flowing through the end of the secondary winding 14A on the side of the primary winding 12C (towards the front of the paper) are opposite to each other. Therefore, the proximity effect that may occur due to the currents flowing through the closely arranged primary winding 12C and secondary winding 14A can be suppressed. In particular, when the transformer 1 is used in applications where high-frequency currents are expected to flow through each winding, such as the isolated resonant converter described above, suppressing the proximity effect in this way can achieve a high loss reduction effect. From the viewpoint of reducing the influence (loss) due to the skin effect, it is preferable that the cross-sectional shape of each winding be thinner than the skin thickness determined according to the frequency.

[0022] Furthermore, as described above, the number of turns in the primary windings 12B and 12C of each outer leg 10B and 10C is the same. This allows windings carrying currents in opposite directions to be placed in close proximity to each other in the window section W2, thereby further improving the effect of suppressing proximity effects.

[0023] [Effects] In this embodiment, a transformer 1 is provided that includes a magnetic core 10 having a central leg 10A and at least two outer legs (10B, 10C) branching from the central leg 10A, and a primary winding 12 and a secondary winding 14 wound around the magnetic core 10. The primary windings 12 (12A, 12B, 12C) are wound around the central leg 10A, the first outer leg 10B, and the second outer leg 10C, respectively, and the secondary winding 14 (14A) is wound around the central leg 10A. The magnetic fluxes (Mf1, Mf2) generated by each primary winding (12B, 12C) wound around the first outer leg 10B and the second outer leg 10C destructively cancel each other out at the central leg 10A.

[0024] This makes it possible to suppress the influence of the magnetic flux (Mf1, Mf2) generated by the primary windings (12B, 12C) wound around each outer leg (10B, 10C) on the flux linkage (excited flux) generated by the primary winding 12A and secondary winding 14A of the central leg 10A. Therefore, a transformer 1 is realized in which the excitation inductance and leakage inductance can be adjusted independently.

[0025] In particular, in the transformer 1 of this embodiment, the secondary winding 14A wound around the central leg 10A and the primary windings 12B and / or 12C wound around the first outer leg 10B and / or the second outer leg 10C are formed on the same plane (at the same height).

[0026] This allows the size of the transformer 1 in the height direction to be suppressed. In addition, the proximity of each winding (especially the secondary winding 14A and the primary winding 12C), which have currents flowing in opposite directions, within the window (especially window W2) surrounded by the magnetic core mitigates the bias in the current density distribution within the windings. Therefore, while suppressing the size in the height direction, it is possible to reduce AC resistance and suppress losses (especially losses in the high-frequency range).

[0027] Furthermore, in the transformer 1 of this embodiment, the primary windings (12B, 12C) wound around the first outer leg 10B and the second outer leg 10C have the same number of turns.

[0028] This allows windings carrying currents in opposite directions to be placed closer together more reliably, thereby further improving the effect of suppressing proximity effects.

[0029] [Second Embodiment] The second embodiment will be described below. In the following description, elements similar to those in the previous embodiment will be denoted by the same reference numerals, and their descriptions will be omitted.

[0030] Figure 3 is a diagram illustrating the structure of the transformer 1 according to the second embodiment. This embodiment differs from the transformer 1 shown in Figure 1 in that, at the central leg 10A, the primary winding 12A and the secondary winding 14A are wound alternately with the same number of turns. That is, the portions of the primary winding 12A and the portions of the secondary winding 14A are spaced apart from each other.

[0031] By adopting the above structure, the magnetic coupling between the primary winding 12A and the secondary winding 14A of the central leg 10A can be strengthened, and the independence of the leakage inductance and the excitation inductance can be increased. Furthermore, at the central leg 10A, the portions of the primary winding 12A and the secondary winding 14A, where the direction of the current flowing is opposite, are adjacent to each other. In other words, it is possible to separate (prevent from being close together) portions of the primary winding 12A where the direction of the current is the same. As a result, the current density distribution of the winding cross-section at the central leg 10A can be improved, and the resistance component to current (especially high-frequency current) can be reduced.

[0032] Here, for example, if the transformer 1 described above is incorporated into a resonant converter and the leakage inductance of the transformer 1 is used as the resonant inductance of the resonant converter, a current corresponding to the switching frequency of the resonant converter will flow through each winding constituting the transformer 1. In contrast, with the structure of the transformer 1 according to this embodiment, the bias in the current density distribution of the winding cross-section at the central leg 10A is mitigated, thereby suppressing an increase in losses.

[0033] [Effects] In the transformer 1 of this embodiment, the primary winding 12A and the secondary winding 14A are wound alternately around the central leg 10A.

[0034] This allows the primary winding 12A and the secondary winding 14A, whose current flows in opposite directions, to be placed close together at the central leg 10A. In other words, the portions of the primary winding 12A whose current flows in the same direction can be spaced apart. This reduces the bias in the current density distribution inside the windings caused by the proximity effect between the windings at the central leg 10A, thereby reducing AC resistance and suppressing losses. Furthermore, as described above, by reducing the effect of the proximity effect, the distance between the primary winding 12A and the secondary winding 14A at the central leg 10A can be made as short as possible while avoiding contact between them. This reduces the size of the transformer 1 in the height direction, while strengthening the electromagnetic induction coupling between the primary winding 12A and the secondary winding 14A, and further increasing the independence of the excitation inductance from the inductance (leakage inductance) added in series.

[0035] In particular, in the transformer 1 of this embodiment, the primary winding 12A and the secondary winding 14A are wound around the central leg 10A with the same number of turns.

[0036] This allows the primary winding 12A and the secondary winding 14A to be wound alternately around the central leg 10A. In other words, by having different numbers of turns, it is possible to avoid situations where portions of the primary winding 12A or portions of the secondary winding 14A are placed in close proximity to each other. Therefore, the bias in the current density distribution caused by the proximity effect between the windings of the central leg 10A can be more reliably mitigated.

[0037] [Third Embodiment] Figure 4 is a diagram illustrating the structure of the transformer 1 according to the third embodiment. Figure 5 is a diagram illustrating the layer structure of the laminated structure that constitutes the transformer 1 in Figure 4.

[0038] The transformer 1 of this embodiment is configured as a laminated structure (a so-called planar transformer) formed by stacking a plurality of (six in Figure 5) substrate layers 20a to 20f, each having a predetermined winding pattern, in this order (in the order of Figures 5(a) to 5(f)). In particular, the primary winding 12A and secondary winding 14A of the central leg 10A, the primary winding 12B of the first outer leg 10B, and the primary winding 12C of the second outer leg 10C are each formed by the respective winding patterns formed on at least one of the substrate layers 20a to 20f. Specifically, each substrate layer 20a to 20f has the central leg portions 10Aa to 10Af, the first outer leg portions 10Ba to 10Bf, and the second outer leg portions 10Ca to 10Cf formed thereon, which constitute the central leg 10A, the first outer leg 10B, and the second outer leg 10C of the magnetic core 10, respectively.

[0039] The transformer 1, configured as the above-described laminated structure, can be manufactured by, for example, preparing multiple (six in this embodiment) substrates, each with holes provided at positions corresponding to the central leg portions 10Aa to 10Af, the first outer leg portions 10Ba to 10Bf, and the second outer leg portions 10Ca to 10Cf for forming these magnetic material portions, and printing the respective winding patterns at the necessary locations of each magnetic material portion, stacking the six substrates and connecting them with solder or pins, and adding the magnetic material that constitutes each leg portion.

[0040] More specifically, the transformer 1 of this embodiment has a structure in which the first substrate layers 20a, 20c, and 20e and the second substrate layers 20b, 20d, and 20f are alternately stacked in the order shown in Figure 5. In particular, the first substrate layers 20a, 20c, and 20e have primary winding patterns 12Aa, 12Ac, and 12Ae that constitute the primary winding 12A formed on their respective central leg portions 10Aa, 10Ac, and 10Ae. Furthermore, no winding patterns are formed on the first outer leg portions 10Ba, 10Bc, and 10Be and the second outer leg portions 10Ca, 10Cc, and 10Ce of the first substrate layers 20a, 20c, and 20e.

[0041] On the other hand, in the second substrate layers 20b, 20d, and 20f, secondary winding patterns 14Ab, 14Ad, and 14Af, which constitute the secondary winding 14A, are formed on the central leg portions 10Ab, 10Ad, and 10Af. In addition, in some of the second substrate layers 20b and 20f, primary winding patterns 12Bb and 12Bf, which constitute the primary winding 12B, are formed on the first outer leg portions 10Bb and 10Bf. Furthermore, in the second outer leg portions 10Cb and 10Cf of these second substrate layers 20b and 20f, primary winding patterns 12Cb and 12Cf, which constitute the primary winding 12C, are formed. Furthermore, in the remaining part of the second substrate layer 20d, neither the first outer leg portion 10Bd nor the second outer leg portion 10Cd has a winding pattern formed on it.

[0042] In this embodiment of the transformer 1, a connection terminal 30 for connecting to an external circuit is provided at one end of the primary winding pattern 12Bb in the first outer leg portion 10Bb of the second substrate layer 20b. The other end terminal α1 of the primary winding pattern 12Bb is connected to terminal α2 at one end of the primary winding pattern 12Bf in the first outer leg portion 10Bf of the second substrate layer 20f. The other end terminal α3 of the primary winding pattern 12Bf is connected to terminal α4 at one end of the primary winding pattern 12Ae in the central leg portion 10Ae of the first substrate layer 20e. Furthermore, the other end terminal α5 of the primary winding pattern 12Ae is connected to terminal α6 at one end of the primary winding pattern 12Ac in the central leg portion 10Ac of the first substrate layer 20c. Furthermore, terminal α7 at the other end of the primary winding pattern 12Ac is connected to terminal α8 at one end of the primary winding pattern 12Aa in the central leg portion 10Aa of the first substrate layer 20a. In addition, terminal α9 at the other end of the primary winding pattern 12Aa is connected to terminal α10 at one end of the primary winding pattern 12Cb in the second outer leg portion 10Cb of the second substrate layer 20b. Also, terminal α11 at the other end of the primary winding pattern 12Cb is connected to terminal α12 at one end of the primary winding pattern 12Cf in the second outer leg portion 10Cf of the second substrate layer 20f. Finally, a connection terminal 32 for connecting to an external circuit is provided at the other end of the primary winding pattern 12Cf.

[0043] On the other hand, a connection terminal for connecting to an external circuit is provided at one end of the secondary winding pattern 14Ab in the central leg portion 10Ab of the second substrate layer 20b. A terminal β1 at the other end of the secondary winding pattern 14Ab is connected to a terminal β2 at one end of the secondary winding pattern 14Ad in the central leg portion 10Ad of the second substrate layer 20d. Further, a terminal β3 at the other end of the secondary winding pattern 14Ad is connected to a terminal β4 at one end of the secondary winding pattern 14Af in the central leg portion 10Af of the second substrate layer 20f. A connection terminal for connecting to an external circuit is provided at the other end of the secondary winding pattern 14Af.

[0044] In the transformer 1 having the above layer structure, the windings of the first outer leg 10B, the central leg 10A, and the second outer leg 10C can all be flush with each other on the same plane in the height direction. More specifically, the primary winding pattern 12Bf, the secondary winding pattern 14Af, and the primary winding pattern 12Cf can be arranged on the same plane, and the primary winding pattern 12Bb, the secondary winding pattern 14Ab, and the primary winding pattern 12Cb can be arranged on the same plane. This reduces the size of the transformer 1 in the height direction, enabling miniaturization. Furthermore, in the present embodiment, the structure in which the windings of the first outer leg 10B, the central leg 10A, and the second outer leg 10C are on the same plane (the structure shown in FIG. 4) can be realized by a simple manufacturing process of laminating base materials corresponding to the respective substrate layers 20a to 20f shown in FIG. 5 in the order of FIGS. 5(a) to 5(f).

[0045] Furthermore, in the transformer 1 of the present embodiment, the ends of the primary winding patterns 12Bb and 12Bf of the first outer leg 10B and the ends of the secondary winding patterns 14Ab and 14Af of the central leg 10A are arranged close to each other in the window W1. However, currents in opposite directions flow through these winding patterns. Therefore, the proximity effect caused by the flow of current (particularly high-frequency current) through each winding pattern can be reduced, thereby suppressing loss.

[0046] On the other hand, in the transformer 1 of the present embodiment, the ends of the primary winding patterns 12Bb, 12Bf on the first outer leg 10B and the ends of the primary winding patterns 12Ab, 12Af on the central leg 10A are arranged close to each other in the window W1. Currents in the same direction flow through each of these winding patterns. In contrast, in the transformer 1 of the present embodiment, between the respective second substrate layers 20b, 20f (multiple winding pattern layers) where the primary winding patterns 12Bb, 12Bf, 12Cb, 12Cf are formed on the portions of the first outer leg 10B and the second outer leg 10C, a structure is adopted in which a second substrate layer 20d (single winding pattern layer) where no winding pattern is formed is sandwiched. Therefore, the distance between the respective windings on the first outer leg 10B and the second outer leg 10C (more specifically, between primary winding patterns 12Bb and 12Bf, and between primary winding patterns 12Cb and 12Cf) can be secured to reduce the influence of the proximity effect and suppress loss.

[0047] It should be noted that the number of respective substrate layers constituting the laminated structure of the transformer 1 and the specific arrangement of winding patterns on each substrate layer are not limited to the above embodiments. In particular, these can be appropriately changed in consideration of factors such as excitation inductance and leakage inductance required in a power conversion circuit using the transformer 1.

[0048] [Functions and Effects] The transformer 1 of the present embodiment is configured by laminating a plurality of substrate layers (20a-20f) each provided with a winding pattern. Each of the substrate layers (20a-20f) is provided with a central leg portion (10Aa-10Af) constituting the central leg 10A, a first outer leg portion (10Ba-10Bf) constituting the first outer leg 10B, and a second outer leg portion (10Ca-10Cf) constituting the second outer leg 10C, respectively, and the same number of first substrate layers 20a, 20c, 20e and second substrate layers 20b, 20d, 20f are alternately laminated. In particular, on the first substrate layers 20a, 20c, 20e, primary winding patterns 12Aa, 12Ac, 12Ae constituting the primary winding 12A are formed on the central leg portions 10Aa, 10Ac, 10Ae. On the other hand, on the second substrate layers 20b, 20d, 20f, secondary winding patterns 14Ab, 14Ad, 14Af constituting the secondary winding 14A are formed on the central leg portions 10Ab, 10Ad, 10Af.

[0049] As a result, the structure of the transformer 1 described above is realized by stacking substrate layers 20a to 20f, each having a desired winding pattern applied (printed) to it, thus simplifying the manufacturing process of the transformer 1. Furthermore, by adopting a structure in which the same number of first substrate layers 20a, 20c, 20e, each having primary winding patterns 12Aa, 12Ac, 12Ae formed on the central leg portions 10Aa, 10Ac, 10Ae, and second substrate layers 20b, 20d, 20f, each having secondary winding patterns 14Ab, 14Ad, 14Af formed on the central leg portions 10Ab, 10Ad, 10Af, are stacked, the size of the transformer 1 in the height direction is reduced while keeping the number of turns of the primary winding 12A and the secondary winding 14A the same.

[0050] In particular, each second substrate layer 20b, 20d, 20f includes at least one (two in this embodiment) double winding pattern layer (second substrate layers 20b, 20f) in which primary winding patterns 12Bb, 12Bf, 12Cb, 12Cf are formed on the first outer leg portions 10Bb, 10Bf and the second outer leg portions 10Cb, 10Cf, respectively.

[0051] This makes it possible to realize an example of the arrangement of each winding pattern in each substrate layer that is suitable for simplifying the manufacturing process in order to obtain the above-described structure of transformer 1. In particular, with this structure, inductance (leakage inductance) is added in series to both ends of the input and output of transformer 1. Therefore, when the transformer 1 is mounted in a circuit such as a resonant converter, the balance of capacitance to ground can be improved and electromagnetic noise can be suppressed.

[0052] Furthermore, each second substrate layer 20b, 20d, and 20f includes at least two double winding pattern layers (20b, 20f) and at least one single winding pattern layer (in this embodiment, the first substrate layer 20c, the second substrate layer 20d, and the first substrate layer 20e) on which the winding patterns are not formed on either the first outer leg portion 10Bd or the second outer leg portion 10Cd. The single winding pattern layers (20c, 20d, and 20e) are arranged between the two double winding pattern layers (20b and 20f).

[0053] As a result, even in a structure in which windings are arranged on each outer leg 10B, 10C (particularly a structure in which fewer turns are arranged than the winding on the central leg 10A), by adopting an configuration in which a single winding pattern layer with a winding pattern formed only on the central leg 10A is arranged between each double winding pattern layer, it is possible to secure the vertical spacing between the windings on each outer leg 10B, 10C and suppress the proximity effect.

[0054] Furthermore, as in the fourth embodiment described later, a structure may be adopted in which at least two of the first substrate layers 20a, 20c, and 20e are double winding pattern layers, and at least one single winding pattern layer is placed between them.

[0055] In particular, according to this embodiment, each first substrate layer 20a, 20c, 20e is configured as a single winding pattern layer in which no winding pattern is formed on any of the first outer leg portions 10Ba, 10Bc, 10Be or the second outer leg portions 10Ca, 10Cc, 10Ce. At least one of each second substrate layer 20b, 20d, 20f (in this embodiment, the second substrate layers 20b, 20f) is configured as a double winding pattern layer.

[0056] This makes it possible to realize a structure in transformer 1 in which the windings are arranged on the same plane (at the same height) on the central leg 10A and each of the outer legs 10B, 10C. In particular, a structure comprising a secondary winding 14A wound on the central leg 10A and primary windings 12B, 12C wound on each of the outer legs 10B, 10C can be manufactured using a common substrate (more specifically, the substrates of substrate layers 20b, 20f) on which these windings are formed. Therefore, the number of substrates required to obtain the desired inductance (excitation inductance or leakage inductance) can be reduced, thereby reducing size and manufacturing costs. Furthermore, with the above structure, the direction of the current in each winding can be reversed in the portion where the windings arranged on the central leg 10A and each outer leg 10B, 10C are in close proximity (more specifically, the portion of the window W1 where the primary winding pattern 12Bb and the secondary winding pattern 14Ab, or the primary winding pattern 12Bf and the secondary winding pattern 14Af are in close proximity), thereby suppressing the proximity effect.

[0057] [Fourth Embodiment] Figure 6 is a diagram illustrating the structure of the transformer 1 according to the fourth embodiment. Figure 7 is a diagram illustrating the layer structure of the laminated structure that constitutes the transformer 1 in Figure 6.

[0058] The transformer 1 of this embodiment, like the third embodiment, is composed of a laminated structure formed by stacking a plurality (six in Figure 6) of substrate layers 20a to 20f in this order (in the order of Figures 7(a) to 7(f)). It also shares with the third embodiment the fact that primary winding patterns 12Aa, 12Ac, and 12Ae, which constitute the primary winding 12A, are formed on the central leg portions 10Aa, 10Ac, and 10Ae of the first substrate layers 20a, 20c, and 20e, respectively, and that secondary winding patterns 14Ab, 14Ad, and 14Af, which constitute the secondary winding 14A, are formed on the central leg portions 10Ab, 10Ad, and 10Af of the second substrate layers 20b, 20d, and 20f, respectively.

[0059] On the other hand, in the transformer 1 of this embodiment, primary winding patterns 12Ba and 12Be are formed on the first outer leg portions 10Ba and 10Be of the first substrate layers 20a and 20c and 20e, respectively. Also, primary winding patterns 12Ca and 12Ce are formed on the second outer leg portions 10Ca and 10Ce of the first substrate layers 20a and 20e, respectively. In other words, in this embodiment, each of the first substrate layers 20a and 20e becomes a double winding pattern layer. Furthermore, in each of the second substrate layers 20b, 20d, and 20f, no winding patterns are formed on the first outer leg portions 10Bb, 10Bd, and 10Bf and the second outer leg portions 10Cb, 10Cd, and 10Cf, respectively. In other words, in this embodiment, each of the second substrate layers 20b, 20d, and 20f becomes a single winding pattern layer.

[0060] The transformer 1 of this embodiment, which is formed by stacking the above-mentioned first substrate layers 20a, 20c, 20e and second substrate layers 20b, 20d, 20f, can also be manufactured using a simple manufacturing process, similar to that of the third embodiment. Furthermore, as shown in Figure 6, a structure is realized in which the windings of the first outer leg 10B, the central leg 10A, and the second outer leg 10C are on the same plane (flush in the height direction).

[0061] Furthermore, in this embodiment, the primary winding pattern 12Aa of the central leg portion 10Aa and the primary winding pattern 12Ca of the second outer leg portion 10Ca in the first substrate layer 20a are integrally formed. In addition, the primary winding pattern 12Ae of the central leg portion 10Ae and the primary winding pattern 12Be of the first outer leg portion 10Be in the first substrate layer 20e are also integrally formed.

[0062] More specifically, in the first substrate layer 20a, when the primary winding pattern 12Aa and the primary winding pattern 12Ca are configured as separate components, windings carrying currents in opposite directions are placed in close proximity to each other in the portion between the central leg portion 10Aa and the second outer leg portion 10Ca. For this reason, in the first substrate layer 20a, the primary winding pattern 12Aa and the primary winding pattern 12Ca are integrated as a ring shape (single-stroke shape) spanning the central leg portion 10Aa and the second outer leg portion 10Ca. Hereafter, the winding pattern structure in which the primary winding pattern 12Aa and the primary winding pattern 12Ca are integrated will be referred to as the shared winding pattern [12Aa, 12Ca].

[0063] In particular, the shared winding pattern [12Aa, 12Ca] is formed in a shape that extends from terminal α6 located near the central leg portion 10Aa to terminal α7 located near the second outer leg portion 10Ca, surrounding the outside of the central leg portion 10Aa and the second outer leg portion 10Ca.

[0064] On the other hand, in the first substrate layer 20e, when the primary winding pattern 12Ae and the primary winding pattern 12Be are configured as separate components, windings carrying current in the same direction are placed in close proximity to each other in the portion between the first outer leg portion 10Be and the central leg portion 10Aa. For this reason, in the first substrate layer 20e, the primary winding pattern 12Be and the primary winding pattern 12Ae are integrated as an S-shape spanning the first outer leg portion 10Ba and the central leg portion 10Ae. Hereafter, the winding pattern structure in which the primary winding pattern 12Be and the primary winding pattern 12Ae are integrated will be referred to as the shared winding pattern [12Be, 12Ae].

[0065] In particular, the shared winding pattern [12Be, 12Ae] is formed in such a shape that it extends from terminal α2 above the first outer leg portion 10Ba, enclosing one side of the first outer leg portion 10Ba (the side opposite to the central leg portion 10Ae), forming a shared wide winding portion between the first outer leg portion 10Ba and the central leg portion 10Ae, enclosing one side of the central leg portion 10Ae (the side opposite to the first outer leg portion 10Ba), and extending down to terminal α3 below the central leg portion 10Ae.

[0066] In this embodiment of the transformer 1, a connection terminal 30 for connecting to an external circuit is provided at one end of the primary winding pattern 12Ba in the first outer leg portion 10Ba of the first substrate layer 20a. The other end terminal α1 of the primary winding pattern 12Ba is connected to the terminal α3 at one end of the common winding pattern [12Be, 12Ae] of the first substrate layer 20e. The other end terminal α3 of the common winding pattern [12Be, 12Ae] is connected to the terminal α4 at one end of the primary winding pattern 12Ac in the central leg portion 10Ac of the first substrate layer 20c. Furthermore, the other end terminal α5 of the primary winding pattern 12Ac is connected to the terminal α6 at one end of the common winding pattern [12Aa, 12Ca] of the first substrate layer 20a. Furthermore, terminal α7 at the other end of the shared winding pattern [12Aa, 12Ca] is connected to terminal α8 at one end of the primary winding pattern 12Ce in the second outer leg portion 10Ce of the first substrate layer 20e. A connection terminal 32 for connecting to an external circuit is provided at the other end of the primary winding pattern 12Ce.

[0067] On the other hand, the wiring configuration of each secondary winding pattern 14Ab, secondary winding pattern 14Ad, and secondary winding pattern 14Af constituting the secondary winding 14 is the same as in the third embodiment (Figure 5).

[0068] As described above, in each of the first substrate layers 20a and 20e, which are double winding pattern layers, shared winding patterns [12Aa, 12Ca] and shared winding patterns [12Be, 12Ae] are formed in a form that takes into account the direction of the current. Compared to the case where each primary winding pattern is configured in an independent shape (separate), the overall length of the primary winding 12 can be shortened, reducing the resistance component and suppressing losses.

[0069] Furthermore, current flows in opposite directions through the primary winding pattern 12Ba and the shared winding patterns [12Aa, 12Ca] that are not integrated in the first substrate layer 20a. Similarly, current flows in opposite directions through the primary winding pattern 12Be and the shared winding patterns [12Be, 12Ae] that are not integrated in the first substrate layer 20e. Therefore, proximity effects that may occur between the closely spaced primary winding pattern 12Ba and the shared winding patterns [12Aa, 12Ca], and between the primary winding pattern 12Be and the shared winding patterns [12Be, 12Ae] can be reduced, thereby decreasing the bias in the current density distribution and suppressing losses.

[0070] [Effects] In the transformer 1 of this embodiment, at least one of the first substrate layers 20a, 20c, and 20e (in this embodiment, the first substrate layers 20a and 20e) is configured as a double winding pattern layer. On the other hand, the second substrate layers 20b, 20d, and 20f are configured as single winding pattern layers in which no winding patterns are formed on any of the first outer leg portions 10Bb, 10Bd, and 10Bf or the second outer leg portions 10Cb, 10Cd, and 10Cf. In the first substrate layer 20a, which is configured as a double winding pattern layer, the primary winding pattern 12Aa formed on the central leg portion 10Aa and the primary winding pattern 12Ca formed on the second outer leg portion 10Ca are integrally configured. Furthermore, in the first substrate layer 20e configured as a double winding pattern layer, the primary winding pattern 12Ae formed in the central leg portion 10Ae and the primary winding pattern 12Be formed in the first outer leg portion 10Be are integrally configured.

[0071] This makes it possible to realize a structure in transformer 1 in which the windings are arranged on the same plane (at the same height) on the central leg 10A and each of the outer legs 10B, 10C. In particular, a structure comprising a secondary winding 14A wound on the central leg 10A and primary windings 12B, 12C wound on each of the outer legs 10B, 10C can be manufactured using a common substrate (more specifically, the substrates of substrate layers 20b, 20f) on which these windings are formed. Therefore, the number of substrates required to obtain the desired inductance (excitation inductance or leakage inductance) can be reduced, thereby reducing size and cost. Furthermore, with the above structure, the wiring can be made common between the central leg portion 10Aa (or central leg portion 10Ae) and the second outer leg portion 10Ca (or first outer leg portion 10Be) of the first substrate layers 20a, 20e, and the overall length of the primary winding 12 can be shortened. Therefore, the DC resistance can be reduced and losses can be suppressed.

[0072] Although embodiments of the present invention have been described above, the configurations described in each of the above embodiments represent only a part of the application examples of the present invention and are not intended to limit the technical scope of the present invention.

[0073] This application claims priority under Japanese Patent Application No. 2025-29405, filed with the Japan Patent Office on 26 February 2025, and all contents of that application are incorporated herein by reference.

Claims

1. A transformer comprising a magnetic core having a central leg and at least two outer legs branching from the central leg, and a primary winding and a secondary winding wound around the magnetic core, wherein the primary winding is wound around the central leg, a first outer leg, and a second outer leg, respectively, and the secondary winding is wound around the central leg, and the magnetic flux generated by each primary winding wound around the first outer leg and the second outer leg is destructively offset at the central leg.

2. A transformer according to claim 1, wherein the secondary winding wound around the central leg and the primary winding wound around the first and / or second outer leg are formed on the same plane.

3. A transformer according to claim 1, wherein the primary windings wound around the first and second outer legs have the same number of turns.

4. A transformer according to claim 1, wherein the primary winding and the secondary winding are wound alternately around the central leg.

5. A transformer according to claim 4, wherein the primary winding and the secondary winding are wound around the central leg with the same number of turns.

6. A transformer according to claim 1, wherein the primary winding and the secondary winding are formed by laminating a plurality of substrate layers on which winding patterns are applied.

7. A transformer according to claim 6, wherein each substrate layer is provided with a central leg portion, a first outer leg portion, and a second outer leg portion, respectively, and an equal number of first and second substrate layers are alternately stacked, and a primary winding pattern constituting the primary winding is formed on the central leg portion of the first substrate layer, and a secondary winding pattern constituting the secondary winding is formed on the central leg portion of the second substrate layer.

8. A transformer according to claim 7, wherein each first substrate layer or each second substrate layer includes at least one double winding pattern layer on which the primary winding pattern is formed on each of the first outer leg portion and the second outer leg portion.

9. A transformer according to claim 8, wherein each of the first substrate layers or each of the second substrate layers includes at least two of the double winding pattern layers and at least one single winding pattern layer on which no winding pattern is formed on either the first outer leg portion or the second outer leg portion, and at least one of the single winding pattern layers is disposed between the two of the double winding pattern layers.

10. A transformer according to claim 8, wherein each of the first substrate layers is configured as a single winding pattern layer in which no winding pattern is formed on either the first outer leg portion or the second outer leg portion, and at least one of the second substrate layers is configured as the double winding pattern layer.

11. A transformer according to claim 8, wherein at least one of the first substrate layers is configured as the double winding pattern layer, each of the second substrate layers is configured as a single winding pattern layer in which no winding pattern is formed on either the first outer leg portion or the second outer leg portion, and in the first substrate layer configured as the double winding pattern layer, the primary winding pattern formed on the central leg portion and the primary winding pattern formed on the first outer leg portion or the second outer leg portion are integrally configured.

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