transformer

Abstract

To provide a transformer in which a plurality of flat surface coils are laminated, that reduces a parasitic capacitance.SOLUTION: A transformer is a transformer in which eight flat surface coils of a first coil to an eight coil are laminated in this order. When one end of each coil is named as an A end, and the other end is named as a B end, the following relationship is established. The A ends of the first coil and the eight coil are connected to a first input end on a primary side. The B end of the first coil, the B end of the eight coil, the A end of the fourth coil, and the A end of the fifth coil are connected. The B ends of the fourth coil and the fifth coil are connected to a second input end on the primary side. The A ends of the second coil and the sixth coil are connected to a first output end on a secondary side. The B end of the second coil and the A end of the third coil are connected. The B end of the sixth coil and the A end of the seventh coil are connected. The B ends of the third coil and the seventh coil are connected to a second output end on the secondary side. Since the second coil and the third coil which are adjacent become the same electric potential, no parasitic capacitance occurs between them.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present specification relates to a transformer, and more particularly to a transformer in which a plurality of planar coils are stacked. [Background technology]

[0002] There are known transformers in which multiple planar coils, each of which has a winding wound in a plane, are stacked (Patent Documents 1-3, Non-Patent Document 1). It is known that in a transformer in which planar coils are stacked, the AC resistance of the winding increases as the magnetomotive force of the primary coil (or secondary coil) increases (Non-Patent Document 1).

[0003] Therefore, Non-Patent Document 1 proposes the following structure to suppress AC resistance. Each of the primary coil and secondary coil is realized by multiple planar coils connected in series. The planar coil on the primary side and the planar coil on the secondary side are alternately stacked. Multiple primary coils and multiple secondary coils are alternately stacked one by one. The magnetomotive force generated in the primary coil is consumed by the adjacent secondary coil. Therefore, the magnetomotive force of the entire primary coil is reduced. By stacking the primary coil and the secondary coil, the magnetomotive force is offset, the magnetomotive force in the entire transformer is reduced, and the AC resistance is suppressed. According to Non-Patent Document 1, the above structure also has the effect of reducing leakage inductance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-096725 A [Patent Document 2] JP 2013-168401 A [Patent Document 3] JP 2009-105180 A [Non-patent literature]

[0005] [Non-Patent Document 1] Riccardo Pittini, Zhe Zhang, Michael AE Andersen: “High Current Planar Transformer for Very High Efficiency Isolated Boost DC-DC Converters”, Proceedings of IEEE The 2014 International Power Electronics Conference, pp. 3905-3912, 2014 Summary of the Invention [Problem to be solved by the invention]

[0006] When multiple planar coils are stacked, parasitic capacitance occurs due to the potential difference between adjacent planar coils. The parasitic capacitance affects the performance of a transformer. In particular, in a transformer through which a high-frequency current flows, the parasitic capacitance increases the power loss generated in the transformer. Furthermore, the parasitic capacitance reduces the drive frequency of the transformer. This specification realizes a transformer that reduces the AC resistance and also reduces the parasitic capacitance. [Means for solving the problem]

[0007] One embodiment of the transformer (10, 10a) disclosed in this specification is embodied in a transformer in which eight planar coils, from the first coil (11) to the eighth coil (18), are stacked in this order. For ease of explanation, one end of each coil is called end A and the other end is called end B. The eight planar coils are electrically connected as follows: ends A of the first coil and the eighth coil are connected to a first input end of the primary side; ends B of the first coil and the eighth coil are connected to ends A of the fourth coil (14) and the fifth coil (15) at one point; ends B of the fourth coil and the fifth coil are connected to a second input end of the primary side; ends A of the second coil (12) and the sixth coil (16) are connected to a first output end of the secondary side; and ends B of the second coil and the A of one of the third coil (13) and the seventh coil (17) are connected to each other. The B end of the sixth coil is connected to the A end of the other of the third coil or the seventh coil. The B ends of the third coil and the seventh coil are connected to the second output terminal of the secondary side. As a modified example, the B ends of the second coil and the sixth coil and the A ends of the third coil and the seventh coil may be connected.

[0008] The first, fourth, fifth, and eighth coils correspond to the primary coils. Multiple primary coils can be electrically represented as one equivalent coil. The second, third, sixth, and seventh coils correspond to the secondary coils. Multiple secondary coils can be electrically represented as one equivalent coil. The above eight-layer transformer is electrically equivalent to a transformer consisting of one primary coil and one secondary coil.

[0009] Meanwhile, physically, both the primary coil and the secondary coil are composed of four planar coils each, which are stacked. The primary coils and secondary coils are stacked alternately, which reduces AC resistance. Also, the fourth coil and the fifth coil are electrically connected in parallel. Therefore, the fourth coil and the fifth coil are at the same potential, and no parasitic capacitance occurs between them even if the fifth coil is stacked next to the fourth coil. The above connection relationship reduces parasitic capacitance.

[0010] Another embodiment of the transformer disclosed in this specification is embodied in a transformer (20) in which six planar coils, from a first coil (21) to a sixth coil (26), are stacked in this order. In this case, too, for convenience of explanation, one end of each coil is called an A end and the other end is called an B end. The six planar coils are electrically connected as follows: A ends of the first coil and the sixth coil are connected to a first input end of the primary side; B ends of the first coil and the sixth coil are connected to A ends of the third coil (23) and the fourth coil (24) at one point; B ends of the third coil and the fourth coil are connected to a second input end of the primary side; A end of the second coil (22) is connected to a first output end of the secondary side; B end of the second coil is connected to A end of the fifth coil (25); B end of the fifth coil is connected to a second output end of the secondary side.

[0011] In the six-layer transformer described above, the third coil and the fourth coil are stacked next to each other but are electrically connected in parallel, so no parasitic capacitance occurs in the third coil and the fourth coil.

[0012] This specification also provides a technology for improving the heat dissipation of stacked planar coils. Each planar coil includes a winding pattern (11) formed on a substrate, and a heat dissipation pattern (34). The heat dissipation pattern is formed on the substrate so as to surround the winding pattern. The heat dissipation pattern surrounding the winding pattern dissipates heat from the winding pattern. It is more preferable to include a thermal coupling member (35) that contacts the multiple stacked heat dissipation patterns. Since the multiple heat dissipation patterns are thermally coupled via the thermal coupling member, the heat from the winding pattern is diffused in the stacking direction. The winding pattern is effectively cooled.

[0013] The transformer disclosed in this specification is particularly suitable for implementation on a multi-layer PCB (Printed Circuit Board). Each planar coil is embodied as a conductive pattern on a multi-layer PCB substrate. Details and further improvements of the technology disclosed in this specification will be described in the following "Form for carrying out the invention." [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a circuit diagram of a transformer according to a first embodiment. [Diagram 2] FIG. 2 is an equivalent circuit diagram of a transformer according to the first embodiment. [Diagram 3] FIG. 2 is a plan view of the transformer of the first embodiment. [Figure 4] 4 is a cross-sectional view of the transformer taken along line IV-IV in FIG. [Diagram 5] FIG. 4 is a cross-sectional view of the transformer taken along line VV in FIG. [Figure 6] FIG. 11 is a circuit diagram of a transformer according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a circuit diagram of a transformer according to a third embodiment. [Figure 8] FIG. 11 is a cross-sectional view of a transformer according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] (First embodiment) A transformer 10 of the first embodiment will be described with reference to Figs. 1 to 5. Fig. 1 is a circuit diagram of the transformer 10. Fig. 1 shows an application example of the transformer 10, in which a DC / DC converter 2 is configured by the transformer 10, a DC / AC conversion circuit 50, and a rectifier circuit 60. The DC / AC conversion circuit 50 is connected to the primary side (input terminals 19a, 19b) of the transformer 10, and the rectifier circuit 60 is connected to the secondary side (output terminals 19c, 19d) of the transformer 10. The rectifier circuit 60 is a bridge-type rectifier circuit.

[0016] The DC / DC converter 2 is a device that converts the voltage of input DC power. Fig. 1 shows an example in which a DC power supply 98 is connected to input terminals 50a, 50b of the DC / DC converter 2, and a load device 99 is connected to output terminals 60a, 60b of the DC / DC converter 2. In Fig. 1, the load device 99 is represented by a resistor symbol. The load device 99 is, for example, a DC motor.

[0017] 1, the DC / AC conversion circuit 50 is composed of four switching elements 51a-51d, and a DC power supply 98 is connected to input terminals 50a, 50b of the DC / AC conversion circuit 50. Output terminals of the DC / AC conversion circuit 50 are connected to input terminals 19a, 19b of the transformer 10. The DC / AC conversion circuit 50 appropriately turns on and off the four switching elements 51a-51d to convert DC power output by the DC power supply 98 into AC power and supply it to the transformer 10.

[0018] 1, the rectifier circuit 60 is composed of four switching elements 61a-61d, a reactor 62, and a smoothing capacitor 63. The rectifier circuit 60 converts AC power supplied from the transformer 10 into DC power and outputs it from output terminals 60a and 60b. A load device 99 that operates on DC power is connected to the output terminals 60a and 60b.

[0019] The DC / AC conversion circuit 50 and the rectifier circuit 60 in FIG. 1 are well known, so a detailed description thereof will be omitted.

[0020] The transformer 10 will now be described. The transformer 10 is composed of eight coils 11-18, and converts the voltage of AC power input to primary input terminals 19a and 19b, and outputs it to secondary output terminals 19c and 19d. Coils 11 and 18 are connected in parallel, and coils 14 and 15 are also connected in parallel. The parallel connection of coils 11 and 18 and the parallel connection of coils 14 and 15 are connected in series. Coils 11, 14, 15, and 18 correspond to the primary coils of the transformer 10.

[0021] Coils 12, 13, 16, and 17 correspond to the secondary coils of transformer 10. Coils 12 and 16 are connected in parallel, and coils 13 and 17 are connected in parallel. The parallel connection of coils 12 and 16 and the parallel connection of coils 13 and 17 are connected in series.

[0022] A circuit electrically equivalent to transformer 10 is shown in Figure 2. Transformer 10 in Figure 1 is electrically equivalent to transformer 100 in Figure 2. Transformer 100 is the simplest transformer consisting of one primary coil 101 and one secondary coil 102. The entire circuit of coils 11, 14, 15, and 18 in Figure 1 is electrically equivalent to primary coil 101 in Figure 2, and the entire circuit of coils 12, 13, 16, and 17 in Figure 1 is electrically equivalent to secondary coil 102 in Figure 2. However, a special effect can be obtained by configuring the primary side and secondary side with multiple coils each as in Figure 2.

[0023] The connection relationship of the eight coils 11-18 will be described in detail. An enlarged view of the circuit of the transformer 10 is shown at the bottom of FIG. 1. For convenience of explanation, the eight coils 11-18 are called the first coil 11, the second coil 12, the third coil 13, the fourth coil 14, the fifth coil 15, the sixth coil 16, the seventh coil 17, and the eighth coil 18. Each coil has two ends, and for convenience of explanation, one end of the coil is called the A end, and the other end is called the B end. The designations "A end" and "B end" are given because they are easier to refer to than simply "one end" and "the other end." The A end of the first coil 11 is represented by the symbol 11a, and the B end is represented by the symbol 11b. The same applies to the other coils.

[0024] The eight coils 11-18 are connected as follows: A-terminals 11a and 18a of the first coil 11 and the eighth coil 18 are connected to the first input terminal 19a of the primary side. B-terminal 11b of the first coil 11, B-terminal 18b of the eighth coil 18, A-terminal 14a of the fourth coil 14, and A-terminal 15a of the fifth coil 15 are connected to the second input terminal 19b of the primary side. As described above, the first coil 11 and the eighth coil 18 are connected in parallel, and the fourth coil 14 and the fifth coil 15 are also connected in parallel. The parallel connection of the coils 11 and 18 and the parallel connection of the coils 14 and 15 are connected in series. The coils 11, 14, 15, and 18 constitute the primary side of the transformer 10.

[0025] The A terminals 12a and 16a of the second coil 12 and the sixth coil 16 are connected to the first output terminal 19c on the secondary side. The B terminal 12b of the second coil 12 is connected to the A terminal 13a of the third coil 13. The B terminal 16b of the sixth coil 16 is connected to the A terminal 17a of the seventh coil 17. The B terminals 13b and 17b of the third coil 13 and the seventh coil 17 are connected to the second output terminal 19d on the secondary side. The second coil 12 and the third coil 13 are connected in series, and the sixth coil 16 and the seventh coil 17 are also connected in series. The series connection of the second coil 12 and the third coil 13 and the series connection of the sixth coil 16 and the seventh coil 17 are connected in parallel. The coils 12, 13, 16, and 17 constitute the secondary side of the transformer 10.

[0026] All of the eight coils 11-18 are planar type coils (planar coils 30). Figure 3 shows a plan view of the transformer 10. The transformer 10 has a core 39, but in Figure 3, the core 39 is drawn with imaginary lines so that the structure of the first coil 11 can be seen.

[0027] The planar coil 30 is realized by a winding pattern formed in a spiral shape with copper foil on an insulating substrate 31. To facilitate understanding, the winding pattern is drawn in bold lines in FIG. 3. The winding pattern in FIG. 3 corresponds to the first coil 11. The winding pattern is formed on one surface of the substrate 31, and the A end 11a of the first coil 11 is the outermost end of the spiral winding pattern and is formed on the same surface as the winding pattern. The B end 11b is located at the innermost position of the spiral winding pattern. The B end 11b is led to the outside of the winding pattern through the back surface of the substrate 31.

[0028] A heat dissipation pattern 34 is formed on the substrate 31 so as to surround the winding pattern of the first coil 11. To facilitate understanding, the heat dissipation pattern 34 is shown by gray hatching in Fig. 3. The heat dissipation pattern 34 is also made of copper foil, but is insulated from the spiral winding pattern corresponding to the first coil 11.

[0029] A through hole 32 is provided in the center of the substrate 31 (the center of the winding pattern), and a through hole 33 is also provided in the substrate 31 outside the winding pattern. A cross section taken along line IV-IV in Fig. 3 is shown in Fig. 4. In Fig. 4, the right half from the center line CL is omitted. In Fig. 4, the reference numerals of parts are omitted for some of the planar coils 30.

[0030] Cores 39 penetrate the stacked substrates 31. The cores penetrating through the through holes 32 and the cores 39 penetrating through the through holes 33 are connected to both sides of the stacked substrates 31 in the stacking direction.

[0031] The substrate 31, the winding pattern corresponding to the first coil 11, and the heat dissipation pattern 34 are collectively referred to as a planar coil 30.

[0032] All eight coils 11-18 have the same structure as the planar coil 30 in FIG. 3. As shown in FIG. 4, the eight planar coils 30 are stacked. In FIG. 4, the spiral winding patterns (i.e., coils 11-18) are simplified and depicted as simple rectangles. The stack of multiple planar coils 30 is preferably realized on a multi-layer PCB (Printed Circuit Board). Each planar coil 30 is embodied as a conductive pattern on a multi-layer PCB substrate.

[0033] The transformer 10 is a laminate of eight planar coils 30. All eight planar coils 30 have the same structure, but in order to match the arrangement of each coil in the laminate with the circuit diagram in Fig. 1, the eight laminated planar coils 30 are associated with the eight coils 11-18 in order from the end. That is, the eight coils 11-18 shown in Fig. 1 are laminated in this order.

[0034] The advantages of the transformer 10 having the connection relationship in FIG. 1 and the structure in FIG. 3 and FIG. 4 will be described. Generally, when a transformer is realized as a laminate of multiple planar coils, the transformer can be made smaller. However, on the other hand, parasitic capacitance occurs between adjacent planar coils. Parasitic capacitance reduces the performance of the transformer. In particular, the higher the frequency of the AC current flowing through the transformer, the greater the loss caused by the parasitic capacitance. When the frequency of the AC current supplied to the transformer exceeds the cutoff frequency determined by the parasitic capacitance and the inductance of the coil, the transformer will no longer function as a transformer.

[0035] In the transformer 10 of the embodiment, the fourth coil 14 and the fifth coil 15 are adjacent to each other as shown in Fig. 4. The fourth coil 14 and the fifth coil 15 are connected in parallel and therefore have the same potential. Therefore, no parasitic capacitance occurs between the adjacent fourth coil 14 and fifth coil 15. The transformer 10 of the first embodiment can suppress the parasitic capacitance in a transformer realized by a laminate of planar coils.

[0036] Other advantages of the transformer 10 are explained below. It is generally known that the greater the magnetomotive force of the primary coil (or secondary coil), the greater the influence of the proximity effect in the laminate of planar coils, and the greater the winding AC resistance. By arranging the coils in parallel, the transformer 10 can reduce the magnetomotive force per coil to obtain the same inductance as when there is only one coil. In addition, the primary coils and secondary coils are alternately laminated. The magnetomotive force generated in the primary planar coil 30 is cancelled out by the adjacent secondary planar coil 30. This makes it possible to suppress the winding AC resistance.

[0037] Furthermore, the second coil 12 and the third coil 13, which are connected in series, are stacked adjacent to each other. Since the conductive path connecting the second coil 12 and the third coil 13 is shortened, the internal resistance of the transformer 10 can be reduced. The sixth coil 16 and the seventh coil 17, which are connected in series, are also arranged adjacent to each other in the stack. Since the conductive path connecting the sixth coil 16 and the seventh coil 17 is shortened, the internal resistance of the transformer 10 can be further reduced.

[0038] The effect of the heat dissipation pattern 34 formed on the substrate 31 of each planar coil 30 will be described. The heat dissipation pattern 34 is made of copper foil and has excellent heat dissipation properties. The first coil 11 generates heat when an alternating current flows. The heat of the winding pattern that constitutes the first coil 11 is dissipated to the outside via the heat dissipation pattern 34 that surrounds the winding pattern. The heat dissipation pattern 34 has the advantage of effectively dissipating the heat of the first coil 11.

[0039] Each of the laminated planar coils 30 has a heat dissipation pattern 34. The transformer 10 has a metal pin 35 penetrating the laminated planar coils 30. FIG. 5 shows a cross section along line VV in FIG. 3. FIG. 5 shows a cross section of the transformer 10 cut on a plane passing through the center CL of the coil 11 (12-18) and the metal pin 35. In FIG. 5, the right side of the center line CL is also omitted. The metal pin 35 is in contact with all the laminated heat dissipation patterns 34. The multiple heat dissipation patterns 34 are thermally connected via the metal pin 35. The metal pin 35 diffuses the heat of the multiple winding patterns (coils 11-18) in the lamination direction. The multiple heat dissipation patterns 34 and the metal pin 35 in contact with them effectively cool the coils 11-18.

[0040] The metal pins 35 penetrate the substrate 31 and the heat dissipation patterns 34 in each planar coil 30. The metal pins 35 correspond to thermal coupling members that thermally couple to the heat dissipation patterns 34.

[0041] (Second embodiment) Fig. 6 shows a circuit diagram of a DC / DC converter 2a including a transformer 10a of a second embodiment. The transformer 10a differs from the transformer 10 of the first embodiment in that the B end 12b of the second coil 12, the B end 16b of the sixth coil 16, the A end 13a of the third coil 13, and the A end 17a of the seventh coil 17 are connected. Other than that, the connection structure of the transformer 10a is the same as that of the transformer 10. The physical structure of the transformer 10a is shown in Figs. 3 and 4.

[0042] The connection point of the B end 12b of the second coil 12, the B end 16b of the sixth coil 16, the A end 13a of the third coil 13, and the A end 17a of the seventh coil 17 corresponds to the center tap 19e on the secondary side of the transformer 10a.

[0043] The transformer 10a of the second embodiment has a center tap 19e on the secondary side. Therefore, a rectifier circuit 70 having a three-pole input terminal is connected to the secondary side of the transformer 10a. The rectifier circuit 70 is composed of two switching elements 71a and 71b, a reactor 72, and smoothing capacitors 73 and 74. The rectifier circuit 70 is also a well-known general circuit. The transformer 10a of FIG. 6 has the same advantages as the transformer 10 of the first embodiment.

[0044] Third embodiment A transformer 20 of a third embodiment will be described with reference to Figs. 7 and 8. Fig. 7 is a circuit diagram of a DC / DC converter 2b including a transformer 20. Like the DC / DC converter 2 of the first embodiment, the DC / DC converter 2b is a device that changes the voltage of input DC power and outputs it. A DC / AC conversion circuit 50 is connected to the primary side of the transformer 20, and a rectifier circuit 70 is connected to the secondary side.

[0045] FIG. 8 is a vertical cross-sectional view of transformer 20. In FIG. 8, the right side of center line CL is also omitted. Transformer 20 has a structure in which six planar coils 30 are stacked. Each of the multiple planar coils 30 has the same structure as planar coil 30 in the first embodiment. For ease of explanation, six planar coils 30 are referred to as first coil 21 to sixth coil 26. Six planar coils 30 (first coil 21 to sixth coil 26) are stacked in this order (see FIG. 8).

[0046] The connection relationship of the six coils 21 to 26 will be described with reference to FIG. 7. The A-ends 21a and 26a of the first coil 21 and the sixth coil 26 are connected to the first input end 29a on the primary side. The B-end 21b of the first coil 21, the B-end 26b of the sixth coil 26, the A-end 23a of the third coil 23, and the A-end 24a of the fourth coil 24 are connected to the second input end 29b on the primary side. The A-end 22a of the second coil 22 is connected to the first output end 29c on the secondary side. The B-end 22b of the second coil 22 is connected to the A-end 25a of the fifth coil 25. The connection point of the B-end 22b of the second coil 22 and the A-end 25a of the fifth coil 25 corresponds to the center tap 29e on the secondary side. The B-end 25b of the fifth coil 25 is connected to the second output end 29d on the secondary side.

[0047] The transformer 20 of the third embodiment is obtained by replacing the second coil 12 and the sixth coil 16 connected in parallel with one coil (second coil 22) in the transformer 10 of the first embodiment, and by replacing the third coil 13 and the seventh coil 17 connected in parallel with another coil (fifth coil 25). That is, the transformer 20 is obtained by simplifying the secondary side structure of the transformer 10.

[0048] As shown in Fig. 8, the first coil 21 to the sixth coil 26 are stacked in this order. The third coil 23 and the fourth coil 24 are adjacent to each other. Meanwhile, as shown in Fig. 7, the third coil 23 and the fourth coil 24 are connected in parallel and therefore have the same potential. Therefore, no parasitic capacitance is generated between the adjacent third coil 23 and fourth coil 24. The transformer 20 of the third embodiment also has the effect of reducing parasitic capacitance.

[0049] Points to note regarding the technology described in the embodiment will be described. In Fig. 1, the third coil 13 and the seventh coil 17 may be interchanged. That is, it is sufficient that the B end 12b of the second coil 12 is connected to the A end of either the third coil 13 or the seventh coil 17, and the B end 16b of the sixth coil 16 is connected to the A end of the other of the third coil 13 or the seventh coil 17.

[0050] The black dots in the transformer symbol represent the polarity of the coil. In Fig. 1, the first input terminal 19a corresponds to the positive pole of the primary side, and the second input terminal 19b corresponds to the negative pole of the primary side. The first output terminal 19c corresponds to the positive pole of the secondary side, and the second output terminal 19d corresponds to the negative pole of the secondary side.

[0051] 1, the terminals A of the primary coils 11, 14, 15, and 18 are positive, and the terminals A of the secondary coils 12, 13, 16, and 17 are positive. The terminals B of the primary coils 11, 14, 15, and 18 may be positive. Alternatively, the terminals B of the secondary coils 12, 13, 16, and 17 may be positive.

[0052] The thermal connection member, typified by the metal pin 35, may be made of a material having high thermal conductivity, i.e., a material having a thermal conductivity equivalent to that of copper or aluminum.

[0053] The heat dissipation pattern 34 may be connected to the ground of the circuit. The heat dissipation pattern, which is made of a conductive pattern and surrounds the winding pattern, functions as a magnetic shield that blocks electromagnetic waves emitted by the winding pattern (coil).

[0054] The DC / DC converter 2 (2a, 2b) of the embodiment can be expressed as follows: The DC / DC converter 2 (2a, 2b) includes a transformer having the above-mentioned characteristics, a DC / AC circuit connected to the primary side (input end) of the transformer, and a rectifier circuit connected to the secondary side (output end) of the transformer.

[0055] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0056] 2, 2a, 2b: DC / DC converter 10, 10a, 20: transformer 11-18, 21-26: coil 19a, 19b, 29a, 29b: input terminal 19c, 19d, 29c, 29d: output terminal 19e, 29e: center tap 30: planar coil 31: substrate 32, 33: through hole 34: heat dissipation pattern 35: metal pin 39: core 50: DC / AC conversion circuit 50a, 50b: input terminal 51a-51d, 61a-61d, 71a-71d: switching element 60, 70: rectifier circuit 60a, 60b: output terminal 62, 72: reactor 63, 73, 74: capacitor 98: DC power supply 99: load device 100: transformer 101: primary coil 102: Secondary coil

Claims

1. The transformer (10, 10a) has eight planar coils, from a first coil (11) to an eighth coil (18), stacked in this order. When one end of each coil is designated as end A and the other end is designated as end B, The A terminals of the first coil and the eighth coil are connected to the first input terminal of the primary side, The B end of the first coil, the B end of the eighth coil, the A end of the fourth coil (14), and the A end of the fifth coil (15) are connected together, The B terminals of the fourth coil and the fifth coil are connected to the second input terminal of the primary side, The A terminals of the second coil (12) and the sixth coil (16) are connected to a first output terminal on the secondary side, The B end of the second coil is connected to the A end of either the third coil (13) or the seventh coil (17), The B end of the sixth coil is connected to the A end of the other of the third coil or the seventh coil, The B terminals of the third coil and the seventh coil are connected to the second output terminal of the secondary side. transformer.

2. The transformer (10a) according to claim 1, wherein the B terminals of the second coil and the sixth coil and the A terminals of the third coil and the seventh coil are connected to each other.

3. A transformer (20) in which six planar coils, from a first coil (21) to a sixth coil (26), are stacked in this order, and when one end of each coil is designated as end A and the other end is designated as end B, The A terminals of the first coil and the sixth coil are connected to the first input terminal of the primary side, The B end of the first coil, the B end of the sixth coil, the A end of the third coil (23), and the A end of the fourth coil (24) are connected together, The B terminals of the third coil and the fourth coil are connected to the second input terminal of the primary side, The A terminal of the second coil (22) is connected to the first output terminal of the secondary side, The B end of the second coil and the A end of the fifth coil (25) are connected to each other, The B end of the fifth coil is connected to the second output end of the secondary side. transformer.

4. Each planar coil is A winding pattern (11) formed on a substrate; a heat dissipation pattern (34) formed on the substrate so as to surround the winding pattern, the heat dissipation pattern being insulated from the winding pattern; The transformer according to claim 1 , further comprising:

5. 5. The transformer according to claim 4, further comprising a thermal connecting member (35) in contact with the plurality of laminated heat dissipation patterns.

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