Planar transformer windings

Abstract

This winding (12) for a planar power transformer comprises at least one stack (50) of conductor tracks (52, 53, 54A, 55, 56, 57, 58). These conductor tracks comprise a first set of at least one conductor track, referred to as the primary conductor track (52, 53), forming a primary turn of the winding (12), and a second set of at least one conductor track, referred to as the secondary conductor track (55, 56, 57, 58), forming a secondary turn of the winding (12). The first set comprises at least one pair (134) of primary conductor tracks (52, 53) electrically connected to each other by at least one first electrical connection (136). The at least one secondary conductor track (55, 56, 57, 58) extends perpendicular to the first electrical connection (136).

Description

[Technical Field]

[0001] The present invention relates to a coil for a planar power transformer of the type comprising at least one stack of conductive tracks, said conductive tracks including a first set made up of at least one so-called primary conductive track forming the primary winding of the coil and a second set made up of at least one so-called secondary conductive track forming the secondary winding of the coil.

[0002] Such a coil can be combined with a magnetic circuit to form a planar power transformer, which has the advantage of being very compact and capable of providing high amplitude, high frequency currents.

[0003] The invention also relates to a method for manufacturing such a coil. [Background technology]

[0004] The electrical energy demands of modern aircraft necessitate the implementation of high-performance, reliable electrical energy conversion between the onboard electrical energy source and the equipment that consumes this electrical energy, such as lighting, pressure regulators, and avionics equipment. Specifically, while electrical energy sources typically generate alternating current at a voltage of 115 volts or direct current at a voltage of 28 volts, newer equipment usually requires supply current at a higher voltage, typically 540 volts. In such cases, static power transformers are used to convert the voltage generated by the energy source to a voltage that meets the requirements of the equipment.

[0005] These transformers traditionally consist of a copper coil associated with a magnetic circuit. The coil is made up of two types of windings: one with a primary turn, commonly known as the primary winding, and another with a secondary turn, commonly known as the secondary winding. The first of the windings, typically the primary winding, receives electrical energy and generates a magnetic field. The other winding passes through the magnetic field generated by the first winding and generates an alternating current of the same frequency but with a voltage greater or less than the voltage across the terminals of the first winding.

[0006] Two main transformer technologies are known.

[0007] One conventional transformer technology is the so-called coil transformer technology, in which the primary and secondary windings are made of enamel-coated copper wire. These transformers are relatively heavy, have considerable volume, and are expensive to produce. Furthermore, these transformers suffer from inconsistent electrical performance due to their manufacturing methods. Finally, these transformers have high AC (alternating current) losses. These AC losses are due to the alternating current characteristics of the current flowing through the transformer, particularly due to the skin effect, proximity effect, and stacking effect. Similar to effective impedance, AC losses increase with the operating frequency of the transformer. Therefore, AC losses limit the applications of high-frequency wound transformers.

[0008] A more recent transformer technology is the planar transformer, where the winding turns are formed by thin conductive tracks. These conductive tracks can be formed by the conductive layers of a PCB (Printed Circuit Board), or by "foils" cut from sheets of conductive material and pressed flat onto an insulating backing.

[0009] The primary and secondary turns of these planar transformers are often stacked, i.e., they are arranged on different planes (or layers). Typically, the turns are then electrically connected to one another by an electrical connection that extends over the entire height of the stack. Each conductive track then comprises a turn-forming portion and an offset portion that electrically connects the turn-forming portion to a connection hole.

[0010] These planar transformers have the advantages of being compact, particularly due to their low height and small size, as well as high efficiency and high power density. Furthermore, they have reduced AC losses compared to coil transformers. However, while the AC losses of planar transformers are already low, it is desirable to further reduce the AC losses to improve the performance of these transformers, particularly to enable their use at even higher frequencies. Summary of the Invention [Problem to be solved by the invention]

[0011] One object of the present invention is to reduce AC losses in planar transformers with stacked turns. [Means for solving the problem]

[0012] To this end, the present invention provides, as subject matter, according to a first aspect, a coil for a planar power transformer comprising at least one stack of conductive tracks, the stack being constituted by a printed circuit made up of a plurality of printed circuit boards, said conductive tracks comprising a first set made up of at least one so-called primary conductive track forming the primary winding of the coil, and a second set made up of at least one so-called secondary conductive track forming the secondary winding of the coil, the first set being formed on the same printed circuit board and comprising at least one pair of primary conductive tracks made up of primary conductive tracks electrically connected to each other by at least one first electrical connection, and at least one secondary conductive track of the second set having a coil formed in the same printed circuit board, belonging to an outer layer of said printed circuit board and extending perpendicular to the first electrical connection connecting the primary conductive tracks of a pair of primary conductive tracks.

[0013] According to particular embodiments of the invention, the coil also has one or more of the following characteristics, taken separately or according to any technically possible combination: - the coil comprises at least one sintered metal disk inserted between two printed circuit boards of the stack, the at least one sintered metal disk electrically connecting two of the conductive tracks belonging to the outer layers of the printed circuit boards of the stack to each other; - the conductive tracks electrically connected to each other by the sintered metal disc are secondary conductive tracks, and at least one primary conductive track extends perpendicular to the sintered metal disc; - the conductive tracks electrically connected to each other by sintered metal discs are secondary conductive tracks, each of said secondary conductive tracks forming one turn; - each of the primary conductive tracks of which a pair of primary conductive tracks is composed forms one turn; - the second set comprises, for the pair or at least one pair of primary conductive tracks, a pair of secondary conductive tracks formed in the same printed circuit board as the pair of primary conductive tracks and sandwiching said pair of primary conductive tracks, said secondary conductive tracks each forming one turn and being electrically connected to each other by at least one second electrical connection across the printed circuit board; - each primary conductive track of a pair of primary conductive tracks forms one turn with two longitudinal branches laterally spaced apart from each other, each having a first longitudinal end and an opposite second longitudinal end, and an end cross bar connecting the two longitudinal ends of the two branches, and each primary conductive track of a pair further comprises an intermediate cross bar connecting the two branches to each other at a distance from their respective longitudinal ends, the intermediate cross bar being inserted between the or each first electrical connection and the or each second electrical connection, and each secondary conductive track of a pair of secondary conductive tracks extends perpendicular to said intermediate cross bar, - each primary conductive track of the pair also comprises a bend extending from the first longitudinal end of the first longitudinal branch to the second longitudinal branch, said bend having a free end spaced apart from the second longitudinal branch, thus leaving a passage between the second longitudinal branch and the bend; the second set comprises a plurality of pairs of secondary conductive tracks, and insulating layers are interposed between the second electrical connections electrically connecting the secondary conductive tracks of different pairs; - the stack is constituted by a printed circuit and the or each first electrical connection is constituted by a blind connection hole; - the or each second electrical connection is constituted by a connection hole, and the or each first electrical connection is constituted by a sunk connection hole;

[0014] The present invention also has as its subject matter, according to a second aspect, a planar transformer comprising a coil according to the first aspect.

[0015] The present invention also provides, as another subject matter, according to a third aspect, a method for manufacturing a coil for a planar power transformer according to any of the preceding claims, comprising the step of fabricating a printed circuit board, said fabricating step comprising: - providing a substrate made of a dielectric material; - producing conductive tracks forming a first turn on a first side of the substrate; - producing conductive tracks forming a second turn on the second side of the substrate; - making at least one first electrical connection through the substrate to electrically connect the first conductive track and the second conductive track to each other, said first conductive tracks forming a first set of primary conductive track pairs forming a primary winding of a coil; - depositing a first insulating layer on the first side of the substrate, the first insulating layer covering the or each first electrical connection; - making a third turn-forming conductive track on the side of the first insulating layer opposite the substrate, said third conductive track belonging to a second set forming a secondary winding of a coil extending perpendicular to the or each first electrical connection connecting the primary conductive tracks of a pair of primary conductive tracks; The present invention also has a method, which includes:

[0016] According to a particular embodiment of the invention, the manufacturing method also has one or more of the following characteristics, taken separately or according to any technically possible combination: the method comprises the additional steps of: depositing a second insulating layer on the second side of the substrate, the second insulating layer covering the or each contact hole; and making a fourth turn-forming conductive track on the face of the second insulating layer facing away from the substrate, - a fourth conductive track extends perpendicular to the or each first contact hole; the manufacturing method comprises the additional step of making at least one second contact hole through the substrate and the two insulating layers to electrically connect the third conductive track and the fourth conductive track to each other; the producing step is repeated in such a way as to produce at least a first printed circuit board and a second printed circuit board, the method of manufacturing further comprising the steps of: superimposing a first printed circuit board and a second printed circuit board; and o sinter laminating the first printed circuit board and the second printed circuit board in such a way as to form an electrical connection between one of the turns forming conductive tracks of the first printed circuit board and one of the turns forming conductive tracks of the second printed circuit board.

[0017] Other characteristics and advantages of the invention will become apparent on reading the following description, given purely by way of example and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view of a planar power transformer in accordance with an exemplary embodiment of the present invention. [Figure 2] This is a wiring diagram of the transformer in Figure 1. [Figure 3] FIG. 2 is a perspective view of the coil of the planar transformer of FIG. 1. [Figure 4] FIG. 4 is a top view of the coil of FIG. 3, with the dielectric material layers of which the coil is constructed remaining transparent to allow some fabrication details to be visible. [Figure 5] 4 is a cross-sectional view of the coil of FIG. 3 taken along the plane marked VV in FIG. 4, in which the dielectric material layers of which the coil is constructed remain transparent to allow some fabrication details to be visible. [Figure 6] 6 is a cross-sectional view similar to that of the coil of FIG. 5, showing only the first set of conductive tracks of which the coil is made up; FIG. [Figure 7] 6 is a cross-sectional view similar to that of the coil of FIG. 5, showing only the second set of conductive tracks of which the coil is made up; FIG. [Figure 8] FIG. 4 is a top view of a first type of conductive track on which the first winding of the coil of FIG. 3 is made up. [Figure 9] FIG. 4 is a top view of a second type of conductive track on which the first winding of the coil of FIG. 3 is made up. [Figure 10] FIG. 4 is a top view of a third type of conductive track on which the first winding of the coil of FIG. 3 is made up. [Figure 11] FIG. 4 is a top view of a first type of conductive track on which the second winding of the coil of FIG. 3 is made up. [Figure 12] FIG. 4 is a top view of a second type of conductive track on which the second winding of the coil of FIG. 3 is made up. [Figure 13] FIG. 4 is a top view of a third type of conductive track on which the second winding of the coil of FIG. 3 is made up. [Figure 14] FIG. 4 is a top view of a fourth type of conductive track on which the second winding of the coil of FIG. 3 is made up. [Figure 15] 2A to 2C are diagrams illustrating a method for manufacturing the planar transformer of FIG. 1. [Figure 16] 16A to 16C illustrate steps for manufacturing a printed circuit board according to the manufacturing method of FIG. 15. DETAILED DESCRIPTION OF THE INVENTION

[0019] The planar power transformer 10 shown in Fig. 1 is typically equipped with an isolated DC-DC voltage converter (not shown) operating at a cutoff frequency between 100 kHz and a few MHz. This voltage converter is, for example, an independent voltage converter. In one variant, the voltage converter belongs to a conversion line intended to convert an AC voltage into a DC voltage (or vice versa), said conversion line comprising a DC-AC voltage converter upstream or downstream of the DC-DC converter.

[0020] The isolated DC-DC voltage converter is, for example, part of a plasma propulsion engine (not shown), and typically the isolated DC-DC voltage converter supplies power to an anode (not shown) of the plasma engine. In one variant, the isolated DC-DC converter is installed on board an aircraft and supplies power to at least one piece of equipment of the aircraft, such as a lighting system, a pressurization system, or an avionics system.

[0021] The planar power transformer 10 comprises a coil 12 and contact pads 14, 15, 16, 17. In the illustrated example, the planar power transformer 10 also comprises a magnetic circuit 18.

[0022] 2, coil 12 includes a primary winding 20 electrically connected to first contact pad 14 and second contact pad 15 of contact pads 14, 15, 16, and 17. Coil 12 also includes a secondary winding 22 electrically connected to third contact pad 16 and fourth contact pad 17 of contact pads 14, 15, 16, and 17.

[0023] Typically, the primary winding 20 is connected to an electrical energy source, for example a battery, and the secondary winding 22 is connected to an electrical energy consumer. The primary winding 20 is preferably connected to the electrical energy source via a low-voltage DC bus, for example between 70 and 100 volts, advantageously via a high-frequency inverter, for example of the full-bridge or half-bridge type, which converts the DC voltage to an AC voltage and supplies it to the primary winding 20. The secondary winding is preferably connected to the energy consumer via a high-voltage DC bus, for example between 300 and 600 volts, advantageously via a controlled or uncontrolled rectifier, for example with one or two phases, which converts the AC voltage to a DC voltage and supplies the current from the secondary winding 22 to the high-voltage DC bus.

[0024] The primary winding 20 comprises a plurality, preferably an even number, of primary turns 24. These primary turns 24 are distributed among a number of branches 26A, 26B, 26C, which in this case are connected in parallel with the first and second contact pads 14, 15. Each branch 26A, 26B, 26C comprises a number of primary turns 24, in this case two, connected in series. In the example shown, the number of these branches 26A, 26B, 26C is three.

[0025] The secondary winding 22 comprises a plurality, preferably an even number, of secondary turns 28. These secondary turns 28 are connected in series, in this case between the third contact pad 16 and the fourth contact pad 17. In the illustrated example, the number of secondary turns 28 is equal to the number of primary turns 24.

[0026] As can be seen in Figure 3, the primary turns 24 and secondary turns 28 are stacked on top of each other in this case along the stacking direction Z. Each primary turn 24 and each secondary turn 28 extends in particular around a recess 30 oriented along the stacking direction Z, which is common to said turns 24, 28.

[0027] Here and in the rest of this specification, the terms direction should be understood with reference to the Cartesian coordinate system of reference characters X, Y, Z shown in the figures, and in addition to the stacking direction Z, it is possible to recognize: - the longitudinal direction X, which is perpendicular to the stacking direction Z, and - The horizontal direction Y, which is perpendicular to the vertical direction X and the stacking direction Z The horizontal direction Y, together with the vertical direction U, forms a so-called horizontal plane.

[0028] Each turn 24, 28 extends in a substantially horizontal plane.

[0029] In the illustrated example, the primary turns 24 and secondary turns 28 are interleaved, i.e., the coil 12 has alternating primary turns 24 and secondary turns 28 arranged along the stacking direction Z. In particular, each pair of primary turns 24 belonging to the same branch 26A, 26B, 26C is sandwiched between a pair of secondary turns 28. The turns 28 of the secondary turns 28 of this pair are unique to the pair, i.e., each turn 28 of a pair of secondary turns 28 is distinct from other turns 28 belonging to a pair of secondary turns 28 that sandwich another pair of primary turns 24. Furthermore, the two turns 24 that make up a pair of primary turns 24 are arranged consecutively along the stacking direction Z, i.e., no secondary turns 28 are inserted between the two primary turns 24.

[0030] Thus, the stack for turns 24 and 28 comprises the following sequence of turns: - 1 secondary turn 28, - two primary turns 24 connected in series, - 2 secondary turns 28, - two primary turns 24 connected in series, - 2 secondary turns 28, - two primary turns 24 connected in series, and - 1 secondary turn 28.

[0031] This interleaving of the primary turns 24 and secondary turns 28 allows for good coupling between the primary winding 20 and secondary winding 22, while minimizing losses by minimizing H-flux.

[0032] 1, the magnetic circuit 18 is formed, in a manner well known to those skilled in the art, from a block 32 of ferromagnetic material, typically made of ferrite, which is perforated with two longitudinal windows 34, 36 through which the turns 24, 28 of the coil 12 pass. The magnetic circuit 18 therefore comprises an upper plate 38 and a lower plate 40, as well as two outer legs 42 and a central leg 44 which connect the upper and lower plates 38, 40 to one another. The central leg 44 fits within the recess 30, with each turn 24, 28 surrounding said central leg 44.

[0033] In the example shown, the block 32 has a double-E type topology, i.e., the block 32 is formed of two superimposed bodies 46, 48, each of which is E-shaped, with the branches of the E forming part of the legs 42, 44 and the bar of the E forming one of the plates 38, 40. In one variant, the block 32 has an EI, CI, CC type topology, or any other topology known to those skilled in the art.

[0034] 5, the coil 12 is constituted by a stack 50 of conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 insulated in pairs by layers of dielectric material 59. This stack 50 is in this case constituted by a printed circuit 51, the conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 being constituted by conductive layers of said printed circuit 51. In a variant (not shown), the conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 are each constituted by a conductive material foil.

[0035] The printed circuit 51 is in particular made up of a number of multi-layer PCBs (Printed Circuit Boards) 61 sintered and laminated together. Each printed circuit board 61 has a thickness measured along the stacking direction Z that is, for example, substantially equal to 3 mm. In practice, this parameter is adjusted accordingly according to the application.

[0036] The conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 are made, for example, of copper. In one variant, the conductive tracks are made of silver or aluminum.

[0037] The conductive tracks include a first set 60A (FIG. 6) that is made up of so-called primary conductive tracks 52, 53, 54A, 54B (track 54B, see FIG. 3) forming the primary winding 20. The conductive tracks also include a second set 60B (FIG. 7) that is made up of so-called secondary conductive tracks 55, 56, 57, 58 forming the secondary winding 22.

[0038] The primary conductive tracks comprise a first type of conductive track 52, a second type of conductive track 53, and a third type of conductive tracks 54A, 54B. The secondary conductive tracks comprise, in the stacking direction Z, an end conductive track 55 of a first type, an end conductive track 56 of a second type, an intermediate conductive track 57 of a first type, and an intermediate conductive track 58 of a second type. Conductive tracks of the same type are substantially identical to each other.

[0039] 8 , each primary conductive track 52 of the first type forms one turn. To this end, the primary conductive track 52 comprises two longitudinal branches 62, 63 laterally spaced apart from one another, each having a first longitudinal end 64 and an opposite second longitudinal end 66, and an end cross bar 68 connecting the two longitudinal ends 66 of the two branches 62, 63 to one another. The primary conductive track 52 also comprises a bend 70 extending from the first longitudinal end 64 of the first longitudinal branch 62 to the second longitudinal branch 63 of the longitudinal branches 62, 63. The bend 70 has a free end 71 spaced apart from the second longitudinal branch 63, thereby leaving a passage 72 between the second longitudinal branch 63 and the bend 70.

[0040] The length of the bend 70 measured along the transverse direction Y is greater than half the transverse separation distance between the longitudinal branches 62, 63, in particular greater than two-thirds of this separation distance. In particular, the length of the bend 70 is substantially equal to three-quarters of the transverse separation distance between the longitudinal branches 62, 63.

[0041] The longitudinal branches 62, 63, the bar 68 and the bend 70 are of substantially the same width. For the longitudinal branches 62, 63, the width is measured along the transverse direction Y. For the bar 68 and the bend 70, the width is measured along the longitudinal direction X.

[0042] The second branch 63 is in particular longer than the first branch 62, such that a first longitudinal end 64 of the second branch 63 projects longitudinally relative to the first longitudinal end 64 of the first branch 62. This first longitudinal end 64 of the second branch 63 therefore has a through orifice 73 for the passage of the first interconnection pad 14.

[0043] In the example shown, each primary conductive track 52 of the first type also comprises an intermediate cross bar 74 connecting the two branches 62, 63 to each other at a position away from the respective longitudinal ends 66 of the two branches 62, 63.

[0044] The intermediate cross bar 74 is interposed between the bend 70 and the end cross bar 68. The intermediate cross bar 74 is specifically closer to the end cross bar 68 than the bend 70.

[0045] Intermediate cross bar 74, together with longitudinal branches 62, 63 and bend 70, bounds a portion of recess 30. Intermediate cross bar 74, together with longitudinal branches 62, 63 and end bar 68, bounds window 76.

[0046] 9, each primary conductive track 53 of the second type is constituted by a mirror image of a primary conductive track 52 of the first type with respect to the longitudinal plane XZ. The above description of the primary conductive tracks 52 of the first type is therefore applicable mutatis mutandis, apart from the detail that the through orifices 73 apply in this case to the passages of the second interconnect pads 15 (and not to the passages of the first interconnect pads 14 as in the case of the primary conductive tracks 52 of the first type).

[0047] 10 , each primary conductive track 54A, 54B of the third type has a thin strip shape 80 perforated at a first end 82 of its longitudinal ends 82, 84 with a through orifice 86 for the passage of the first interconnection pad 14 or the second interconnection pad 15. This thin strip 80 has a transverse dimension substantially equal to the width of the longitudinal branches 62, 63 of said primary conductive track 52 of the first type and said primary conductive track 53 of the second type. The thin strip 80 has a longitudinal dimension less than the difference in length between the longitudinal branches 62, 63 of said primary conductive track 52 of the first type and said primary conductive track 53 of the second type.

[0048] 11 , the first type of end secondary conductive track 55 forms one turn. To this end, the end secondary conductive track 55 comprises two laterally spaced-apart longitudinal branches 90, 92, each having a first longitudinal end 94 and an opposite second longitudinal end 96, and a cross bar 98 connecting the first longitudinal ends 94 of the branches 90, 92 to each other. The end secondary conductive track 55 also comprises a bend 100 extending from the second longitudinal end 96 of the first longitudinal branch 90 to the second longitudinal end 92 of the longitudinal branches 90, 92. The bend 100 has a free end 101 spaced apart from the second longitudinal end 192, thus leaving a passage 102 between the second longitudinal branch 92 and the bend 100.

[0049] The lateral separation distance between the longitudinal branches 90, 92 of the secondary conductive track 55 is substantially equal to the lateral separation distance between the longitudinal branches 62, 63 of the first type primary conductive track 52 and the second type primary conductive track 53.

[0050] The length of the bend 100 measured along the transverse direction Y is greater than half the transverse separation distance between the longitudinal branches 90, 92, in particular greater than two-thirds of this separation distance. In particular, the length of the bend 100 is substantially equal to three-quarters of the transverse separation distance between the longitudinal branches 90, 92.

[0051] The longitudinal branches 90 , 92 , the bar 98 and the bend 100 together bound a portion of the recess 30 .

[0052] The longitudinal branches 90, 92, the bar 98 and the bend 100 are of substantially equal width. For the longitudinal branches 90, 92, the width is measured along the transverse direction Y. For the bar 98 and the bend 100, the width is measured along the longitudinal direction X. This width is substantially equal to the width of the longitudinal branches 62, 63 of the first type primary conductive track 52 and the second type primary conductive track 53, the width of the bar 68 and the width of the bend 70.

[0053] The second branch 92 is longer than the first branch 90 such that a second longitudinal end 96 of the second branch 92 projects longitudinally relative to the second longitudinal end 96 of the first branch 90. The difference in length between the longitudinal branches 90, 92 is greater than the length, measured along the longitudinal direction X, of the branch extensions 74, 76 of the first type primary conductive track 52 and the second type primary conductive track 53.

[0054] This first longitudinal end 94 of the second branch 92 has a through orifice 103 for the passage of, in this case, the third interconnection pad 16 .

[0055] The first type of secondary conductive track 55 also comprises a protruding portion 104 that protrudes longitudinally outward from the bend 100. This protruding portion 104 is spaced apart from the second branch 92. The protruding portion 104 has a longitudinal dimension that is less than the difference in length between the longitudinal branches 90, 92. This longitudinal dimension is typically in the range of 1.5 to 2 times the width of the bend 100.

[0056] In the illustrated example, the first longitudinal branch 90 is extended as a tapered edge 106 to fill the space between the protruding portion 104 and the second end 96 of the first longitudinal branch 90 .

[0057] 12, the second type of end secondary conductive track 56 is configured as a mirror image of the first type of end secondary conductive track 55 with respect to the longitudinal plane XZ. The above description of the first type of end secondary conductive track 55 is therefore applicable mutatis mutandis, except for the detail that the through orifice 103 applies in this case to the passage of the fourth interconnection pad 17 (and not to the passage of the third interconnection pad 16 as in the case of the first type of end secondary conductive track 55).

[0058] 13 , each intermediate secondary conductive track 57 of the first type forms one turn. To this end, the intermediate secondary conductive track 57 comprises two laterally spaced-apart longitudinal branches 110, 112, each having a first longitudinal end 114 and an opposite second longitudinal end 116, and a cross bar 118 connecting the first longitudinal ends 114 of the two branches 110, 112 to each other. The intermediate secondary conductive track 57 also comprises a first bend 120 extending from the second longitudinal end 116 of the first longitudinal branch 110 to the second longitudinal branch 112 of the longitudinal branches 110, 112. This first bend 120 has a free end 121 spaced apart from the second longitudinal branch 112, thus leaving a passage 122 between the second longitudinal branch 112 and the bend 120.

[0059] The lateral separation distance between the longitudinal branches 110, 112 is substantially equal to the lateral separation distance between the longitudinal branches 62, 63 of the first type primary conductive track 52 and the second type primary conductive track 53.

[0060] The length of the bend 120 measured along the transverse direction Y is greater than half the transverse separation distance between the longitudinal branches 110, 112, in particular greater than two-thirds of this separation distance. In particular, the length of the bend 120 is substantially equal to three-quarters of the transverse separation distance between the longitudinal branches 110, 112.

[0061] The longitudinal branches 110 , 112 , the bar 118 and the bend 110 together bound a portion of the recess 30 .

[0062] The second branch 112 is longer than the first branch 110 such that a second longitudinal end 116 of the second branch 112 projects longitudinally relative to the second longitudinal end 116 of the first branch 110. The difference in length between the longitudinal branches 110, 112 is substantially equal to the length, measured along the longitudinal direction X, of the branch extensions 74, 76 of the first type primary conductive track 52 and the second type primary conductive track 53.

[0063] Each intermediate secondary conductive track 57 of the first type also comprises a second bend 124 that projects laterally from the second longitudinal end 116 of the second longitudinal branch 112 towards the first longitudinal branch 110. This second bend 124 has a lateral dimension substantially equal to the lateral dimension of the first bend 120. The second bend 124 has a free end 125 opposite the junction of the second bend 124 with the second longitudinal branch 112.

[0064] The longitudinal branches 110, 112, the bar 118, the first bend 120 and the second bend 124 are of substantially equal width. In the case of the longitudinal branches 110, 112, the width is measured along the transverse direction Y. In the case of the bar 118 and the two bends 120, 124, the width is measured along the longitudinal direction X. This width is substantially equal to the width of the longitudinal branches 62, 63, the width of the bar 68 and the width of the bend 70 of the first type primary conductive track 52 and the second type primary conductive track 53.

[0065] Each intermediate secondary conductive track 57 of the first type further comprises a protruding portion 126 protruding longitudinally outward from the bend 120. This protruding portion 126 is spaced apart from the second branch 112. The protruding portion 126 has a longitudinal dimension that is smaller than the longitudinal separation between the first bend 120 and the second bend 124. This longitudinal dimension is greater than half of the longitudinal space between the first bend 120 and the second bend 124, in particular greater than two-thirds of this space, and typically substantially equal to three-quarters of this space.

[0066] Furthermore, the longitudinal dimension of the protruding portion 126 is substantially equal to the longitudinal dimension of the protruding portion 104 of the end secondary conductive tracks 55,56.

[0067] In the illustrated example, the first longitudinal branch 110 is extended as a tapered portion 128 to fill the space between the protruding portion 126 and the second end 116 of the first longitudinal branch 110 .

[0068] 14, each intermediate secondary conductive track 58 of the second type is constituted by a symmetric image of an intermediate secondary conductive track 57 of the first type with respect to the longitudinal plane XZ. The above description of the intermediate secondary conductive track 57 of the first type is therefore applicable mutatis mutandis.

[0069] The first longitudinal ends 64, 94, 114 of the longitudinal branches 62, 63, 90, 92, 110, 112 of the conductive tracks 52, 53, 55, 56, 57, 58 are arranged on the same first side 130 (FIG. 3) of the recess 30. The second longitudinal ends 66, 96, 116 of the longitudinal branches 62, 63, 90, 92, 110, 112 of the conductive tracks 52, 53, 55, 56, 57, 58 are arranged on the same second side 132 (FIG. 3) of the recess 30, opposite the first side.

[0070] The conductive tracks 52, 53, 55, 56, 57, 58 are: - the intermediate bars 74 of the primary conductive tracks 52, 53 are aligned with each other along the stacking direction Z, as well as with the bends 100 of the end secondary tracks 55, 56 and the first bends 120 of the intermediate secondary tracks 57, 58, substantially aligned; the first longitudinal branches 62, 90, 110 of the primary tracks 52, 53 and of the secondary tracks 55, 56, 57, 58 are substantially aligned with one another along the stacking direction Z; the second longitudinal branches 63, 92, 112 of the primary tracks 52, 53 and of the secondary tracks 55, 56, 57, 58 are substantially aligned with one another along the stacking direction Z; the bends 70 of the primary tracks 52, 53 are aligned with each other along the stacking direction Z and are substantially aligned with the bars 98, 118 of the secondary tracks 55, 56, 57, 58; and the end bars 68 of the primary tracks 52, 53 are aligned with each other along the stacking direction Z and are substantially aligned with the second bends 124 of the intermediate secondary tracks 57, 58; are arranged as follows.

[0071] Thus, the overlap of the primary turn 24 and the secondary turn 28 is optimized, which allows for good electromagnetic coupling of said turns 24, 28 and reduces AC losses.

[0072] 6, the first type primary conductive tracks 52 and the second type primary conductive tracks 53 are grouped into primary conductive track pairs 134. Each pair 134 consists of a first type primary conductive track 52 and a second type primary conductive track 53 electrically connected to each other by a sunk first connection hole 136.

[0073] Each pair 134 forms a branch 26 A, 26 B, 26 C of the primary winding 20 .

[0074] The primary conductive tracks 52, 53 of each of these pairs 134 are formed on the same printed circuit board 61, in particular belonging to an inner layer of the printed circuit board 61, and the first connection holes 136 are made in said printed circuit board 61. The primary conductive tracks 52, 53 of different pairs 134 are formed on different printed circuit boards 61.

[0075] 8 and 9, first connection holes 136 are formed at the free ends 71 ​​of the bent portions 70 of each of the conductive tracks 52, 53. In the example shown, the first connection holes 136 are four in number and are aligned along the width direction of the bent portions 70 in this case.

[0076] 5, each of the secondary conductive tracks 55, 56, 57, 58 extends perpendicular to the connection hole 136 along the stacking direction Z. In particular, the bars 98, 118 of each of the secondary tracks 55, 56, 57, 58 extend perpendicular to the connection hole 136 along the stacking direction Z.

[0077] Thus, the primary conductive tracks 52, 53 of each pair 134 are electrically connected to each other with no offset relative to the secondary conductive tracks 55, 56, 57, 58, which allows for reduced AC losses.

[0078] 3 and 6, the third type of primary conductive tracks 54A, 54B include a first third type primary conductive track 54A (FIG. 6) and a second third type primary conductive track 54B (FIG. 3). The primary conductive tracks 54A, 54B include, in particular, at least one first third type primary conductive track 54A and at least one second third type primary conductive track 54B per board 61. The first third type primary conductive tracks 54A are aligned with each other along the stacking direction Z, and the second third type primary conductive tracks 54B are aligned with each other along the stacking direction Z. Each third type primary conductive track 54A, 54B belongs to one outer layer (not referenced) of the printed circuit board 61.

[0079] In the example shown, each of the printed circuit boards 61 comprises two primary conductive tracks 54A of the third type and two primary conductive tracks 54B of the third type, except that the printed circuit boards 61 arranged at opposite ends of the stack 50 one comprises a single first primary conductive track 54A of the third type and the other comprises a single second primary conductive track 54B of the third type. In a variant (not shown), each of the printed circuit boards 61, including the printed circuit boards 61 arranged at opposite ends of the stack, comprises two first primary conductive tracks 54A of the third type and two second primary conductive tracks 54B of the third type.

[0080] The primary conductive track 52 of the first type of each pair 134 is electrically connected to the or each first primary conductive track 54A of a third type formed on the same printed circuit board 61. Said primary conductive track 52 of the first type is electrically connected to this or each first primary conductive track 54A of the third type via a through-hole 137A made through the printed circuit board 61.

[0081] Similarly, the primary conductive track 53 of the second type of each pair 134 is electrically connected to the or each second primary conductive track 54B of a third type formed on the same printed circuit board 61. Said primary conductive track 53 of the second type is electrically connected to this or each second primary conductive track 54B of the third type by means of a through-hole 137B (FIG. 4) made through the printed circuit board 61.

[0082] These connection holes 137A, 137B are insulated from the corresponding connection holes 137A, 137B made through the or each adjacent printed circuit board 61 by an insulating layer 59. This insulating layer 59 is typically obtained during sintering lamination of the printed circuit boards 61 from which the stack is made.

[0083] 4, 8 and 9, the connection holes 137A are made in the first longitudinal ends 64 of the second branches 63 of the first type of primary conductive tracks 52, and the connection holes 137B are made in the first longitudinal ends 64 of the second branches 63 of the second type of primary conductive tracks 52. In the example shown, the connection holes 137A, or connection holes 137B, respectively, are four in number and are aligned along the width of the second branches 63 of the primary conductive tracks 52, 53 in this case.

[0084] 5 and 7, the secondary conductive tracks 55, 56, 57, 58 are also grouped into pairs of secondary conductive tracks 138. Each pair of secondary conductive tracks 138 sandwiches a corresponding pair 134 of primary tracks.

[0085] The secondary conductive tracks 55, 56, 57, 58 of each pair 138 are formed on the same printed circuit board 61 as the primary tracks 52, 53 of the sandwiched pair 134, and belong to an outer layer of said printed circuit board 61. The secondary conductive tracks 55, 56, 57, 58 are electrically connected to each other by second via holes 140 that traverse the printed circuit board 61. Thus, each printed circuit board 61 comprises a first portion 134 of tracks formed by the primary conductive tracks 52, 53 electrically connected to each other by the sunk first via holes 136, and a second pair 138 of tracks formed by the secondary conductive tracks 55, 56, 57, 58 electrically connected to each other by the second via holes 140 that sandwich said first pair 134.

[0086] In particular, each pair 138 comprises an intermediate or end secondary conductive track 55, 57 of a first type and an intermediate or end secondary conductive track 56, 58 of a second type. As can be seen in Figures 11 to 14, second connection holes 140 are formed in the protruding portions 104, 126 of each of the conductive tracks 55, 56, 57, 58. In the example shown, the second connection holes 140 are four in number and are arranged in this case in a square.

[0087] 5, the second contact holes 140 extend through the windows 79 of the primary conductive tracks 52, 53 of which the sandwiched pair 134 is made up. The intermediate bar 74 of each of these conductive tracks 52, 53 is therefore inserted between the first contact hole 136 on the one hand and the second contact hole 140 on the other hand. The term "inserted" in this case should be understood in the remainder of this specification to mean that the bar 74 extends through a straight line connecting the first contact hole 136 and the second contact hole 140.

[0088] This arrangement minimizes the length of the offset portions 104, 126 required to interconnect the secondary conductive tracks 55, 56, 57, 58 of each pair 138. Furthermore, the surface area of ​​overlapping conductive material between the primary winding 20 and the secondary winding 22 in the series interconnection region of the secondary turns 28 is maximized, thereby improving electromagnetic coupling between the primary winding 20 and the secondary winding 22 and reducing AC losses.

[0089] 7, the secondary conductive tracks 55, 56, 57, 58 of different pairs 138 are formed on different printed circuit boards 61, with an insulating layer 59 being inserted between the second connection holes 140 that electrically connect the secondary conductive tracks 55, 56, 57, 58 of different pairs 138. This insulating layer 59 is typically obtained during sintering lamination of the printed circuit boards 61 from which the stack is constructed.

[0090] 5, the coil 12 also comprises sintered metal discs 142, 144 which provide electrical connections between the conductive tracks 54A, 54B, 57, 58 belonging to the outer layers of the printed circuit boards 61 of which the stack is made up. Each sintered metal disc 142, 144 is therefore inserted between two of the printed circuit boards 61 of which the stack is made up.

[0091] Each sintered metal disc is typically made of silver.

[0092] The sintered metal discs 142, 144 include a first sintered metal disc 142, each connecting two primary conductive tracks 54A, 54B of a third type to each other, and a second sintered metal disc 144, each connecting an intermediate secondary conductive track 57 of the first type to an intermediate secondary conductive track 58 of the second type.

[0093] 6 and 10, each first sintered metal disk 142 is placed perpendicular to the second end 84 of the thin strip 80 forming the third type primary conductive tracks 54A, 54B, opposite the through orifice 86. Thus, when each of the third type primary conductive tracks 54A, 54B is connected by the first sintered metal disk 142, the connecting holes 137A, 137B are inserted between the through orifice 86 and the first sintered metal disk 142 along the longitudinal direction X.

[0094] The third type of primary conductive tracks 54A, 54B, the connection holes 137A, 137B and the second sintered metal disk 142 together provide a parallel electrical connection of the pairs 134. They allow the pairs 134 to be electrically connected to each other in the absence of electrical bonding of the insertion orifices of the contact pads 14, 15, which is not possible with current technological means.

[0095] Meanwhile, a second sintered metal disk 144 provides the series electrical connection of the pair 138 .

[0096] For this purpose, as can be seen in Figures 14 and 15, each second sintered metal disk 144 is placed perpendicular to the second bends 124 of the intermediate secondary conductive tracks 57, 58. Each second sintered metal disk 144 is in contact with the second bends 124 of the first type of intermediate secondary conductive track 57 and the second bends 124 of the second type of intermediate secondary conductive track 58.

[0097] 5, the first type primary conductive tracks 52 and the second type primary conductive tracks 53 extend perpendicular to the second sintered metal disc 144 along the stacking direction Z. In particular, the second cross bars 78 of each of the first type primary conductive tracks 52 and the second type primary conductive tracks 53 extend perpendicular to the second sintered metal disc 144 along the stacking direction Z.

[0098] Thus, the pairs 138 are electrically connected to each other without any offset relative to the primary conductive tracks 52, 53 that form the turns, thereby making it possible to reduce AC losses.

[0099] A method 200 of manufacturing the planar power transformer 10 will now be described with reference to FIG.

[0100] The method 200 includes a first step 201 of manufacturing the coil 12 .

[0101] Step 201 begins with a first sub-step 202 in which a printed circuit board 61 is fabricated.

[0102] Referring to FIG. 16, this fabricating step 202 begins with substep 210 of providing a substrate (not shown) made of a dielectric material.

[0103] Substep 210 is followed by substep 220 of producing a first inner conductive layer (not referenced) of the printed circuit board 61 on a first side of the board. This substep 220 comprises producing 222 primary conductive tracks 52 of a first type on said first side of the board.

[0104] Substep 210 is followed by substep 230 of producing a second inner conductive layer (not referenced) of printed circuit board 61 on a second side of the substrate, which substep 230 comprises producing 232 primary conductive tracks 53 of a second type on said second side of the substrate.

[0105] Sub-steps 220 and 230 may be performed in parallel or sequentially.

[0106] Sub-steps 220 and 230 are followed by sub-step 240, in which sunk contact holes are made through the substrate to electrically connect the first type of primary conductive tracks 52 and the second type of primary conductive tracks 53 to one another. These sunk contact holes constitute the first contact holes 136.

[0107] Following this sub-step 240, the step 202 of preparing the printed circuit board 61 includes a sub-step 250 of depositing a first insulating layer 59 on the first side of the board, the first insulating layer 59 covering the first connection hole 136.

[0108] Substep 250 is followed by substep 260 of making a first outer conductive layer (not referenced) on the side of the first insulating layer opposite the substrate. This substep 260 includes making 262 at least one, and preferably two, primary conductive tracks 54A, 54B of a third type perpendicular to the first longitudinal end 64 of the second longitudinal branch 63 of at least one of the primary conductive tracks 52 of the first type and the primary conductive tracks 53 of the second type. Substep 260 also includes making 264 intermediate or end secondary conductive tracks 55, 57 of the first type, the bars 98, 118 of said tracks 55, 57 extending perpendicular to each first connection hole 136.

[0109] Following sub-step 240, step 202 of preparing printed circuit board 61 also includes sub-step 270 of depositing a second insulating layer 59 on the second side of the substrate, the second insulating layer 59 covering the first contact hole 136.

[0110] Substep 270 is followed by substep 280 of fabricating a second outer conductive layer (not referenced) on the side of the second insulating layer opposite the substrate. This substep 280 includes a step 282 of fabricating at least one, and preferably two, primary conductive tracks 54A, 54B of a third type perpendicular to the first longitudinal end 64 of the second longitudinal branch 63 of at least one of the primary conductive tracks 52 of the first type and the second type conductive tracks 53. Substep 280 also includes a step 284 of fabricating intermediate or end secondary conductive tracks 56, 58 of the second type, the bars 98, 118 of said tracks 56, 58 extending perpendicular to each first connection hole 136.

[0111] Sub-steps 270 and 280 may be performed in parallel or sequentially with sub-steps 250 and 260.

[0112] Sub-steps 260 and 280 are followed by sub-step 290 of making through-connection holes through the substrate and the two insulating layers 59. This sub-step 290 includes step 292 of making second connection holes 140 for electrically connecting the secondary conductive tracks 55, 57 of the first type to the secondary conductive tracks 56, 58 of the second type. Sub-step 290 also includes step 294 of making third connection holes 137A, 137B for electrically connecting each of the primary conductive tracks 52 of the first type and the primary conductive track 53 of the second type to at least one primary conductive track 54A, 54B of a third type.

[0113] A printed circuit board 61 is thus obtained.

[0114] Returning to FIG. 15, sub-step 202 is repeated until all printed circuit boards 61 in the stack have been fabricated.

[0115] Next, the step 201 of manufacturing the coil 12 includes a sub-step 203 of stacking the thus produced printed circuit boards 61. During this stacking step, a metal paste is inserted between the printed circuit boards 61 perpendicular to the third type of primary conductive tracks 54A, 54B on the one hand and perpendicular to the second bends 124 of the intermediate secondary conductive tracks 57, 58 on the other hand. The remaining spaces between the printed circuit boards 61 are filled with a dielectric material.

[0116] Sub-step 203 is followed by sub-step 204 of sinter laminating the printed circuit boards 61. During this sub-step 204, the metal inserted between the printed circuit boards 61 becomes sintered and intimately joined with the conductive tracks of the outer layers, thereby forming an electrical connection between the third type primary conductive tracks 54A, 54B on the one hand and the second bends 124 of the intermediate secondary conductive tracks 57, 58 on the other hand. Furthermore, the dielectric material contained between the printed circuit boards 61 hardens and forms an insulating layer. The principle of sinter lamination is well known to those skilled in the art, and therefore, they will know how to perform this step without any particular difficulty.

[0117] The coil 12 is thus obtained.

[0118] Step 201 is followed by step 205 of providing the interconnection pads 14, 15, 16, 17. During this step 205, the pads 14, 15, 16, 17 are inserted into the through orifices 72, 86, 103 provided for this purpose, and washers are then fitted onto the pads 14, 15, 16, 17 to electrically connect the pads to the conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58. In particular: - first washers (not referenced) are mounted on the first pads 14 to provide an electrical connection between said first pads 14 and first primary conductive tracks 54A of the third type at the surface of the stack; - second washers (not referenced) are mounted on the second pads 15 to provide an electrical connection between said second pads 15 and second primary conductive tracks 54B of a third type at the surface of the stack; a third washer (not referenced) is mounted on the third pad 16 to provide an electrical connection between said third pad 16 and the end secondary conductive track 55 of the first type; a fourth washer (not referenced) is mounted on the fourth pad 17 to provide an electrical connection between said fourth pad 17 and the end secondary conductive track 56 of the second type;

[0119] Step 205 is followed by step 206 of installing the magnetic circuit 18. During this step 206, a block 32 of ferromagnetic material is placed around the coil 12.

[0120] The planar transformer 10 is thus obtained.

[0121] Thanks to the exemplary embodiment described above, the overlap of the conductive tracks 52, 53, 55, 56, 57, 58 forming the turns 24 of the primary winding 20 and the turns 28 of the secondary winding 22 is optimized, which allows for improved electromagnetic coupling between the primary winding 20 and the secondary winding 22 and reduces AC losses. Furthermore, the offset of the conductive tracks 52, 53, 55, 56, 57, 58 forming these turns 24, 28 is significantly reduced, which further contributes to reducing AC losses. Therefore, the planar transformer 10 can be easily used at high frequencies.

Claims

1. A coil (12) for a planar power transformer (10) comprising at least one stack (50) with conductive tracks (52, 53, 54A, 54B, 55, 56, 57, 58), the stack being constituted by a printed circuit (51) comprising a plurality of printed circuit boards (61), the conductive tracks comprising a first set (60A) with at least one so-called primary conductive track (52, 53) forming a primary winding (20) of the coil (12) and a second set (60B) with at least one so-called secondary conductive track (55, 56, 57, 58) forming a secondary winding (22) of the coil (12), The coil (12) comprises a first set (60A) formed on the same printed circuit board (61) and comprising at least one pair (134) of primary conductive tracks comprising primary conductive tracks (52, 53) electrically connected to each other by at least one first electrical connection (136), and at least one secondary conductive track (55, 56, 57, 58) of the second set (60B) formed on the same printed circuit board (61), belonging to an outer layer of said printed circuit board (61), and extending perpendicular to said first electrical connection (136) connecting the primary conductive tracks (52, 53) of the pair (134) of primary conductive tracks.

2. 2. The coil (12) according to claim 1, comprising at least one sintered metal disk (144) inserted between two printed circuit boards (61) of the stack, the at least one sintered metal disk (144) electrically connecting two of the conductive tracks (52, 53, 54A, 54B, 55, 56, 57, 58) belonging to the outer layers of the printed circuit boards (61) of the stack (50) to each other.

3. 3. The coil (12) of claim 2, wherein the conductive tracks (52, 53, 54A, 54B, 55, 56, 57, 58) electrically connected to one another by the sintered metal disc (144) are secondary conductive tracks (55, 56, 57, 58), and at least one primary conductive track (52, 53) extends perpendicular to the sintered metal disc (144).

4. 4. The coil (12) according to claim 2 or 3, wherein the conductive tracks (52, 53, 54A, 54B, 55, 56, 57, 58) electrically connected to one another by the sintered metal disc (144) are secondary conductive tracks (55, 56, 57, 58), each of said secondary conductive tracks (55, 56, 57, 58) forming one turn.

5. 5. A coil (12) according to any one of claims 1 to 4, wherein each of the primary conductive tracks (52, 53) constituting the pair (134) of primary conductive tracks of the printed circuit board (61) forms one turn.

6. 6. A coil (12) according to any one of claims 1 to 5, wherein the second set (60B) comprises, for the pair or at least one pair (134) of primary conductive tracks, a pair (138) of secondary conductive tracks comprising secondary conductive tracks (55, 56, 57, 58) formed on the same printed circuit board (61) as the pair (134) of primary conductive tracks and sandwiching said pair (134) of primary conductive tracks, said secondary conductive tracks (55, 56, 57, 58) each forming one turn and being electrically connected to each other by at least one second electrical connection (140) across the printed circuit board (61).

7. each primary conductive track (52, 53) of the pair (134) of primary conductive tracks forms a turn with two longitudinal branches (62, 63) laterally spaced apart from one another, each having a first longitudinal end (64) and an opposite second longitudinal end (66), and an end cross bar (68) connecting the two longitudinal ends (66) of the two branches (62, 63) to one another; each primary conductive track of the pair further comprises an intermediate cross bar (74) connecting the two branches (62, 63) to each other at a distance from their respective longitudinal ends (66), the intermediate cross bar (74) being inserted between the or each first electrical connection (136) and the or each second electrical connection (140); 7. The coil (12) of claim 6, wherein each secondary conductive track (55, 56, 57, 58) of a pair (138) of secondary conductive tracks extends perpendicular to the intermediate cross bar (74).

8. 8. A coil (12) according to claim 7, wherein each primary conductive track of the pair also comprises a bend (70) extending from the first longitudinal end (64) of the first longitudinal branch (62) to the second longitudinal branch (63) of the longitudinal branches (62, 63), said bend (70) having a free end (71) spaced apart from the second longitudinal branch (63), thus leaving a passage (72) between the second longitudinal branch (63) and the bend (70).

9. A planar transformer (10) comprising a coil (12) according to any one of claims 1 to 8.

10. 10. A method for manufacturing a coil (12) for a planar power transformer (10) according to any one of claims 1 to 9, comprising the step of fabricating (202) a printed circuit board (61), said fabricating step (202) comprising: - providing a substrate (210) made of a dielectric material; a substep (222) of making conductive tracks (52) forming a first turn on the first side of the substrate; a substep (232) of making conductive tracks (53) forming a second turn on the second face of the substrate; - a substep (240) of making at least one first electrical connection (136) through the substrate to electrically connect the first conductive track (52) and the second conductive track (53) to each other, said first conductive tracks (52, 53) forming a pair (134) of primary conductive tracks of a first set (60A) forming the primary winding (20) of the coil (12); - a substep (250) of depositing a first insulating layer (59) on the first side of the substrate, the first insulating layer (59) covering the or each first electrical connection (136); - making, on the face of the first insulating layer facing away from the substrate, a conductive track (55) forming a third turn, said third conductive track (55) belonging to a second set (60B) forming a secondary winding (22) of the coil (12) extending perpendicular to the or each first electrical connection (136) connecting the primary conductive tracks (52, 53) of the pair (134) of primary conductive tracks; A method comprising:

Images