Winding for planar transformer

Abstract

This winding (12) for a planar power transformer comprises at least one stack (50) of conductive tracks (52, 53, 54A, 55, 56, 57, 58). These conductive tracks comprise a first set, forming a primary winding of the winding (12), composed of at least one so-called primary conductive track (52, 53), and a second set, forming a secondary winding of the winding (12), composed of at least one so-called secondary conductive track (55, 56, 57, 58). The first set comprises at least one pair of primary conductive tracks (134) composed of primary conductive tracks (52, 53) electrically connected to each other by at least one first electrical connection (136). At least one secondary conductive track (55, 56, 57, 58) extends in line with said first electrical connection (136). Figure for the abstract: Fig. 5

Description

Title of the invention: Winding for planar transformer Field of invention

[0001] The present invention relates to a winding for a planar power transformer, of the type comprising at least one stack of conductive tracks, said conductive tracks comprising a first assembly, forming a primary winding of the winding, composed of at least one conductive track called primary, and a second assembly, forming a secondary winding of the winding, composed of at least one conductive track called secondary.

[0002] Such a winding can be combined with a magnetic circuit to form a planar power transformer (also called, by Anglicism, "planar transformer"). Such a transformer has the advantage of being very compact and of being able to supply high amplitude and high frequency currents.

[0003] The invention also relates to a method of manufacturing such a winding. Technological background

[0004] The electrical energy needs of modern aircraft require the implementation of efficient and reliable conversions of electrical energy between the electrical energy sources on board the aircraft and the equipment that consumes this electrical energy, such as lighting, pressurization and avionics equipment. Indeed, while electrical energy sources generally produce an alternating current at a voltage of 115 volts or a direct current at a voltage of 28 volts, new equipment most often requires a supply current at a higher voltage, typically 540 volts. Static power transformers then make it possible to transform the voltages produced by the energy sources into voltages corresponding to the needs of the equipment.

[0005] These transformers are conventionally composed of a copper winding associated with a magnetic circuit. The winding is formed of two types of windings of turns: a winding of primary turns, commonly called the primary winding, and a winding of secondary turns, commonly called the secondary winding. A first of the windings, typically the primary winding, receives the electrical energy and generates a magnetic field. The other winding is crossed by the magnetic field produced by the first winding and provides an alternating current of the same frequency but with a voltage which may be higher or lower than the voltage at the terminals of the first winding.

[0006] Two main transformer technologies are known.

[0007] A conventional transformer technology is that of so-called transformers wound, in which the primary and secondary windings are made of enameled copper wire. These transformers are relatively heavy and have a large footprint and a high production cost. In addition, they have a troublesome dispersion of their electrical performance, linked to their manufacturing process. Finally, they have significant so-called AC (alternating current) losses. These AC losses consist of losses induced by the alternating nature of the current flowing in the transformer and are notably caused by the skin effect, the proximity effect and the swarm effect. Similar to a real impedance, they increase with the operating frequency of the transformer. They therefore limit the use of wound transformers at high frequencies.

[0008] A more recent transformer technology is that of so-called planar transformers in which the turns of the windings are formed by thin conductive tracks. These conductive tracks can be made up of the conductive layers of a printed circuit board (better known by the acronym PCB for "Printed Circuit Board"), or by "strips" cut from plates of conductive material and plated on insulating supports.

[0009] Often, the primary and secondary turns of these planar transformers are stacked, that is to say they are placed in different planes (or strata). Most often, said turns are then electrically connected to each other by electrical connections extending over the entire height of the stack. Each conductive track then comprises a portion forming a turn and a remote portion electrically connecting the portion forming a turn to a connection hole.

[0010] These planar transformers have the advantage of being compact, in particular having a reduced height and a small footprint, and of having a high efficiency and a good power density. In addition, they have reduced AC losses compared to wound transformers. However, even if the AC losses of planar transformers are already low, it is desirable to lower them even further so as to improve the performance of these transformers and in particular to allow their use at ever higher frequencies. Statement of the invention

[0011] An objective of the invention is to reduce the AC losses of a planar transformer with stacked turns.

[0012] To this end, the invention relates, according to a first aspect, to a winding for a power transformer of the aforementioned type, in which the first assembly comprises at least one pair of primary conductive tracks composed of conductive tracks primaries electrically connected to each other by at least one first electrical connection, at least one secondary conductive track extending in line with said first electrical connection.

[0013] According to particular embodiments of the invention, the winding also has one or more of the following characteristics, taken in isolation or in any technically possible combination(s): - the winding comprises at least one sintered metal pad electrically connecting two of the conductive tracks of the stack to each other; - the conductive tracks electrically connected to each other by the sintered metal pad are secondary conductive tracks, and at least one primary conductive track extends in line with the sintered metal pad; - the conductive tracks electrically connected to each other by the sintered metal pad are secondary conductive tracks, each of said secondary conductive tracks forming a turn; - each of the primary conductive tracks making up the pair of primary conductive tracks forms a turn; - the second set comprises, for the or at least one of the pair(s) of primary conductive tracks, a pair of secondary conductive tracks composed of secondary conductive tracks sandwiching said pair of primary conductive tracks, said secondary conductive tracks each forming a turn and being electrically connected to each other by at least one second electrical connection; - each primary conductive track making up the pair of primary conductive tracks forms a turn comprising a portion interposed between the or each first electrical connection and the or each second electrical connection, and each secondary conductive track making up the pair of secondary conductive tracks extends in line with said portion; - the second set comprises a plurality of pairs of secondary conductive tracks, an insulating layer being interposed between the second electrical connections electrically connecting the secondary conductive tracks of different pairs; - the stack is constituted by a printed circuit, the or each first electrical connection being constituted by a non-through connection hole; - the or each second electrical connection is constituted by a connection hole; and - the first electrical connection or connections are made by a buried connection hole.

[0014] The invention also relates, according to a second aspect, to a transformer planar comprising a winding according to the first aspect.

[0015] The invention also relates, according to a third aspect, to a method for manufacturing a winding for a power transformer, comprising a step of producing a printed circuit board, said production step including the following sub-steps: - supply of a substrate made of dielectric material, - production of a first conductive track forming a turn on a first face of the substrate, - production of a second conductive track forming a turn on a second face of the substrate, - making at least a first electrical connection through the substrate to electrically connect the first and second conductive tracks to each other, - depositing a first insulating layer on the first face of the substrate, the first insulating layer covering the or each first electrical connection, and - production of a third conductive track forming a turn on one face of the first insulating layer opposite the substrate, said third conductive track extending in line with the or each first electrical connection.

[0016] According to particular embodiments of the invention, the manufacturing method also has one or more of the following characteristics, taken in isolation or in any technically possible combination(s): - the method comprises the following additional steps: • depositing a second insulating layer on the second face of the substrate, the second insulating layer covering the or each first bonding hole, and • production of a fourth conductive track forming a turn on one face of the second insulating layer opposite the substrate; - the fourth conductive track extends in line with the or each first connection hole; - the manufacturing method comprises an additional step of producing at least one second via through the substrate and the two insulating layers to electrically connect the third and fourth conductive tracks to each other; and - the production step is repeated so as to produce at least a first printed circuit board and a second printed circuit board, the manufacturing method further comprising the following steps: • stacking the first and second printed circuit boards, and • laminating-sintering the first and second printed circuit boards so as to form an electrical connection between one of the conductive tracks forming a turn of the first printed circuit board and one of the conductive tracks forming a turn of the second printed circuit board. Brief description of the Figures

[0017] Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which: - [Fig. 1] is a perspective view of a planar power transformer according to an exemplary embodiment of the invention, - [Fig.2] is an electrical diagram of the transformer of [Fig.l], - [Fig.3] is a perspective view of the planar transformer winding of [Fig.l], - [Fig.4] is a top view of the winding of [Fig.3], the layers of dielectric material making up this winding being left transparent to reveal certain production details, - [Fig.5] is a sectional view of the winding of [Fig.3] along a plane marked VV in [Fig.4], the layers of dielectric material making up this winding being left transparent to reveal certain production details, - [Fig.6] is a view similar to that of [Fig.5], only a first set of conductive tracks making up the winding being shown, - [Fig.7] is a view similar to that of [Fig.5], only a second set of conductive tracks making up the winding being shown, - [Fig.8] is a top view of a first type of conductive track making up a first winding of the coil of [Fig.3], - [Fig.9] is a top view of a second type of conductive track making up the first winding of the coil of [Fig.3], - [Fig. 10] is a top view of a third type of conductive track making up the first winding of the coil of [Fig. 3], - [Fig. 11] is a top view of a first type of conductive track making up a second winding of the coil of [Fig. 3], - [Fig. 12] is a top view of a second type of conductive track making up the second winding of the coil of [Fig. 3], - [Fig. 13] is a top view of a third type of conductive track composing the second winding of the winding of [Fig.3], - [Fig. 14] is a top view of a fourth type of conductive track composing the second winding of the winding of [Fig.3], - [Fig. 15] is a diagram illustrating a manufacturing process of the planar transformer of [Fig.l], and - [Fig. 16] is a diagram illustrating a step in the manufacturing of a printed circuit board in the manufacturing process of [Fig. 15]. Detailed description of an example of implementation

[0018] The planar power transformer 10 shown in [Fig.l] typically equips an isolated DC-DC voltage converter (not shown) operating at switching frequencies between 100 kHz and a few MHz. This voltage converter is for example an independent voltage converter. Alternatively, it belongs to a conversion chain intended to convert an alternating voltage into a direct voltage (or vice versa), said conversion chain comprising a direct-alternating voltage converter upstream or downstream of the direct-direct voltage converter.

[0019] Said isolated DC-DC voltage converter is for example part of a plasma engine (not shown); typically, it powers the anode (not shown) of said plasma engine. Alternatively, the isolated DC-DC voltage converter is on board an aircraft and powers at least one piece of equipment of the aircraft such as a lighting system, a pressurization system, or an avionics system.

[0020] This planar power transformer 10 comprises a winding 12 and connection pads 14, 15, 16, 17. In the example shown, it also comprises a magnetic circuit 18.

[0021] As visible in [Fig.2], the winding 12 comprises a primary winding 20 electrically connected to a first 14 and a second 15 of the connection pads 14, 15, 16, 17. It also comprises a secondary winding 22 electrically connected to a third 16 and a fourth 17 of the connection pads 14, 15, 16, 17.

[0022] 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 consuming equipment. The primary winding 20 is preferably connected to the electrical energy source by a low voltage DC bus, for example between 70 and 100 Volts, advantageously with a high frequency inverter, for example of the full bridge or half-bridge type, ensuring the conversion of the DC voltage into AC voltage to power the primary winding 20. The secondary winding is preferably connected to the energy consuming equipment by a high voltage DC bus, for example between 300 and 600 V, advantageously with a rectifier, for example of the controlled or non-controlled type, single or double alternation, ensuring the conversion of the alternating voltage into direct voltage for the supply of said high voltage direct bus with the current leaving the secondary winding 22.

[0023] The primary winding 20 comprises a plurality of primary turns 24, preferably an even number. These primary turns 24 are here distributed between several branches 26A, 26B, 26C connected in parallel to the first and second connection pads 14, 15. Each branch 26A, 26B, 26C comprises several primary turns 24, here two, connected in series. In the example shown, these branches 26A, 26B, 26C are three in number.

[0024] The secondary winding 22 comprises a plurality of secondary turns 28, preferably an even number. These secondary turns 28 are here connected in series between the third and fourth connection pads 16, 17. In the example shown, the number of secondary turns 28 is equal to the number of primary turns 24.

[0025] As visible in [Fig. 3], the primary 24 and secondary 28 turns are here stacked one above the other in a stacking direction Z. Each primary turn 24 and each secondary turn 28 extends in particular around a recess 30, oriented in the stacking direction Z, common to said turns 24, 28.

[0026] Here and hereinafter, the terms of orientation extend with reference to a direct orthogonal reference frame X, Y, Z shown in the Figures and in which we distinguish, in addition to the stacking direction Z: - a longitudinal direction X, orthogonal to the stacking direction Z, and - a transverse direction Y, orthogonal to the longitudinal direction X and to the stacking direction Z, this transverse direction Y forming with the longitudinal direction Y a so-called horizontal plane.

[0027] Each turn 24, 28 extends substantially in a horizontal plane.

[0028] In the example shown, the primary 24 and secondary 28 turns are interlaced, that is to say that the winding 12 has an alternation of primary turns 24 and secondary turns 28 following 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 this pair of secondary turns 28 is specific to said pair, that is to say that each turn 28 of the pair of secondary turns 28 is distinct from any other turn 28 belonging to a pair of secondary turns 28 sandwiching another pair of primary turns 24. Furthermore, the two turns 24 composing the pair of primary turns 24 are arranged consecutively according to the stacking direction Z, that is to say that there is no secondary turn 28 interposed between said two primary turns 24.

[0029] Thus, the stack of turns 24, 28 comprises the following sequence of turns: a secondary turn 28, two primary turns 24 connected in series, two secondary turns 28, two primary turns 24 connected in series, two secondary turns 28, two primary turns 24 connected in series, and one secondary turn 28.

[0030] This alternation of the primary 24 and secondary 28 turns allows good coupling of the primary 20 and secondary 22 windings and minimizes losses thanks to a minimization of the H field.

[0031] Returning to [Fig.l], the magnetic circuit 18 is, in a manner well known to those skilled in the art, formed from a block 32 of ferromagnetic material, typically ferrite, pierced with two longitudinal windows 34, 36 crossed by the turns 24, 28 of the winding 12. The magnetic circuit 18 thus has an upper plate 38 and a lower plate 40, as well as two outer legs 42 and a central leg 44 connecting the upper 38 and lower 40 plates to each other. The central leg 44 is engaged in the recess 30 and each turn 24, 28 surrounds said central leg 44.

[0032] In the example shown, the block 32 has a double E type topology, that is to say that it is formed of two superimposed bodies 46, 48, each in the shape of an E, the branches of the E partly forming the legs 42, 44 while the bar of the E forms one of the plates 38, 40. As a variant, the block 32 has a topology of type El, CI, CC or any other topology known to those skilled in the art.

[0033] With reference to [Fig. 5], the winding 12 is constituted by a stack 50 of conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 insulated two by two by layers of dielectric material 59. This stack 50 is here 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. As a variant (not shown), the conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 are each constituted by a strip of conductive material.

[0034] The printed circuit 51 is in particular composed of several printed circuit boards 61 (better known by the English acronym PCB for "printed circuit board") multi-layer laminated-sintered with each other. Each printed circuit board 61 has for example a thickness, measured in the stacking direction Z, substantially equal to 3 mm. In practice, this parameter is adapted according to the application.

[0035] The conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58 are for example made of copper. Alternatively, they are made of silver or aluminum.

[0036] The conductive tracks comprise a first set 60A ([Fig.6]), forming the primary winding 20, composed of so-called primary conductive tracks 52, 53, 54A, 54B, (track 54B, see [Fig.3]). The conductive tracks also comprise a second set 60B ([Fig.7]), forming the secondary winding 22, composed of so-called secondary conductive tracks 55, 56, 57, 58.

[0037] The primary conductive tracks comprise conductive tracks of a first type 52, conductive tracks of a second type 53 and conductive tracks of a third type 54A, 54B. The secondary conductive tracks comprise, relative to the stacking direction Z, an end conductive track of a first type 55, an end conductive track of a second type 56, intermediate conductive tracks of a first type 57 and intermediate conductive tracks of a second type 58. The conductive tracks of the same type are substantially identical to each other.

[0038] With reference to [Fig. 8], each primary conductive track of the first type 52 forms a turn. For this purpose, it comprises two longitudinal branches 62, 63 spaced transversely from one another, each having a first longitudinal end 64 and an opposite second longitudinal end 66, and a transverse end bar 68 connecting the second longitudinal ends 66 of the two branches 62, 63 to one another. It also comprises an elbow 70 extending from the first longitudinal end 64 of a first 62 of the longitudinal branches 62, 63 towards the second longitudinal branch 63. The elbow 70 has a free end 71 spaced from the second longitudinal branch 63, thus leaving a passage 72 between the second longitudinal branch 63 and the elbow 70.

[0039] The length of the elbow 70, measured along the transverse direction Y, is greater than half of the transverse distance between the longitudinal branches 62, 63, in particular greater than 2 / 3 of this distance. The length of the elbow 70 is in particular substantially equal to ¾ of the transverse distance between the longitudinal branches 62, 63.

[0040] The longitudinal branches 62, 63, the bar 68 and the elbow 70 are of substantially equal widths. For the longitudinal branches 62, 63, the width is measured in the transverse direction Y. For the bar 68 and the elbow 70, the width is measured in the longitudinal direction X.

[0041] The second branch 63 is in particular longer than the first branch 62, so that its first longitudinal end 64 protrudes longitudinally relative to the first longitudinal end 64 of the first branch 62. This first longitudinal end 64 of the second branch 63 here has a through-orifice 73 for the passage of the first interconnection pad 14.

[0042] In the example shown, each primary conductive track of the first type 52 also comprises an intermediate transverse bar 74 connecting the two branches 62,63 to each other, at a distance from their respective longitudinal ends 66.

[0043] This intermediate transverse bar 74 is interposed between the elbow 70 and the end transverse bar 68. It is in particular closer to the end transverse bar 68 than to the elbow 70.

[0044] The intermediate transverse bar 74 delimits with the longitudinal branches 62, 63 and the elbow 70 a section of the recess 30. It also delimits with the longitudinal branches 62, 63 and the end bar 68, a window 76.

[0045] With reference to [Fig.9], each primary conductive track of the second type 53 is constituted by the symmetrical aspect of a primary conductive track of the first type 52 relative to a longitudinal plane XZ. The above description of a primary conductive track of the first type 52 therefore applies mutatis mutandis, with the exception that the through-orifice 73 is here adapted to the passage of the second interconnection pad 15 (and not of the first interconnection pad 14 as is the case for the primary conductive tracks of the first type 52).

[0046] With reference to [Fig. 10], each primary conductive track of the third type 54A, 54B has a strip shape 80 pierced at a first 82 of its longitudinal ends 82, 84 with a through-orifice 86 for the passage of the first or second interconnection pad 14, 15. This strip 80 has a transverse dimension substantially equal to the width of the longitudinal branches 62, 63 of the primary conductive tracks of the first and second types 52, 53. The strip 80 has a longitudinal dimension less than the difference in length between the longitudinal branches 62, 63 of the primary conductive tracks of the first and second types 52, 53.

[0047] With reference to [Fig. 11], the secondary end conductive track of the first type 55 forms a turn. For this purpose, it comprises two longitudinal branches 90, 92 spaced transversely from one another, each having a first longitudinal end 94 and an opposite second longitudinal end 96, and a transverse bar 98 connecting the first longitudinal ends 94 of the two branches 90, 92 to one another. It also comprises an elbow 100 extending from the second longitudinal end 96 of a first 90 of the longitudinal branches 90, 92 towards the second longitudinal branch 92. The elbow 100 has a free end 101 spaced from the second longitudinal branch 92, thus leaving a passage 102 between the second longitudinal branch 92 and the elbow 100.

[0048] The transverse distance between the longitudinal branches 90, 92 of the secondary conductive track 55 is substantially equal to the transverse distance between the longitudinal branches 62, 63 of the primary conductive tracks of the first and second types 52, 53.

[0049] The length of the elbow 100, measured along the transverse direction Y, is greater than half of the transverse distance between the longitudinal branches 90, 92, in particular greater than 2 / 3 of this distance. The length of the elbow 100 is in particular substantially equal to ¾ of the transverse distance between the longitudinal branches 90, 92.

[0050] The longitudinal branches 90, 92, the bar 98 and the elbow 100 together delimit a section of the recess 30.

[0051] The longitudinal branches 90, 92, the bar 98 and the elbow 100 are of substantially equal widths. For the longitudinal branches 90, 92, the width is measured along the transverse direction Y. For the bar 98 and the elbow 100, the width is measured along the longitudinal direction X. This width is substantially equal to that of the longitudinal branches 62, 63, the bar 68 and the elbow 70 of the primary conductive tracks of the first and second types 52, 53.

[0052] The second branch 92 is longer than the first branch 90, so that its second longitudinal end 96 protrudes 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 in the longitudinal direction X, of the branch extensions 74, 76 of the primary conductive tracks of the first and second types 52, 53.

[0053] This first longitudinal end 94 of the second branch 92 here has a through orifice 103 for the passage of the third interconnection pad 16.

[0054] The secondary conductive track of the first type 55 also comprises a projecting portion 104 projecting longitudinally outwards from the elbow 100. This projecting portion 104 is spaced from the second branch 92. It has a longitudinal dimension less than the difference in length between the longitudinal branches 90, 92. This longitudinal dimension is typically between 1.5 and 2 times the width of the elbow 100.

[0055] In the example shown, the first longitudinal branch 90 is extended by a beveled portion 106 filling the space between the projecting portion 104 and the second end 96 of said first longitudinal branch 90.

[0056] With reference to [Fig. 12], the secondary end conductive track of the second type 56 is constituted by the symmetrical aspect of the secondary end conductive track of the first type 55 relative to a longitudinal plane XZ. The above description of the secondary end conductive track of the first type 55 therefore applies mutatis mutandis, except that the through-orifice 103 is here adapted to the passage of the fourth interconnection pad 17 (and not of the third interconnection pad 16 as is the case for the secondary end conductive track of the first type 55).

[0057] With reference to [Fig. 13], each intermediate secondary conductive track of the first type 57 forms a turn. For this purpose, it comprises two longitudinal branches 110, 112 spaced transversely from one another, each having a first longitudinal end 114 and a second longitudinal end 116. opposite, and a transverse bar 118 connecting the first longitudinal ends 114 of the two branches 110, 112 to each other. It also comprises a first elbow 120 extending from the second longitudinal end 116 of a first 110 of the longitudinal branches 110, 112 towards the second longitudinal branch 112. This first elbow 120 has a free end 121 spaced from the second longitudinal branch 112, thus leaving a passage 122 between the second longitudinal branch 112 and the elbow 120.

[0058] The transverse distance between the longitudinal branches 110, 112 is substantially equal to the transverse distance between the longitudinal branches 62, 63 of the primary conductive tracks of the first and second types 52, 53.

[0059] The length of the elbow 120, measured along the transverse direction Y, is greater than half of the transverse distance between the longitudinal branches 110, 112, in particular greater than 2 / 3 of this distance. The length of the elbow 120 is in particular substantially equal to ¾ of the transverse distance between the longitudinal branches 110, 112.

[0060] The longitudinal branches 110, 112, the bar 118 and the elbow 110 together delimit a section of the recess 30.

[0061] The second branch 112 is longer than the first branch 110, so that its second longitudinal end 116 protrudes 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 in the longitudinal direction X, of the branch extensions 74, 76 of the primary conductive tracks of the first and second types 52, 53.

[0062] Each intermediate secondary conductive track of the first type 57 also comprises a second elbow 124 projecting transversely from the second longitudinal end 116 of the second longitudinal branch 112 towards the first longitudinal branch 110. This second elbow 124 has a transverse dimension substantially equal to that of the first elbow 120. It has a free end 125 opposite its junction with the second longitudinal branch 112.

[0063] The longitudinal branches 110, 112, the bar 118 and the first and second elbows 120, 124 are of substantially equal widths. For the longitudinal branches 110, 112, the width is measured along the transverse direction Y. For the bar 118 and the two elbows 120, 124, the width is measured along the longitudinal direction X. This width is substantially equal to that of the longitudinal branches 62, 63, the bar 68 and the elbow 70 of the primary conductive tracks of the first and second types 52, 53.

[0064] Each intermediate secondary conductive track of the first type 57 further comprises a projecting portion 126 projecting longitudinally outwards from the elbow 120. This projecting portion 126 is spaced from the second branch 112. It has a longitudinal dimension less than the longitudinal space between the first and second elbows 120, 124. This longitudinal dimension is greater than half of the longitudinal space between the first and second elbows 120, 124, in particular greater than 2 / 3 of this space, typically substantially equal to ¾ of this space.

[0065] The longitudinal dimension of the projecting portion 126 is moreover substantially equal to the longitudinal dimension of the projecting portion 104 of the secondary end conductive tracks 55, 56.

[0066] In the example shown, the first longitudinal branch 110 is extended by a beveled portion 128 filling the space between the projecting portion 126 and the second end 116 of said first longitudinal branch 110.

[0067] With reference to [Fig. 14], each intermediate secondary conductive track of the second type 58 is constituted by the symmetrical of an intermediate secondary conductive track of the first type 57 relative to a longitudinal plane XZ. The above description of an intermediate secondary conductive track of the first type 57 therefore applies mutatis mutandis.

[0068] 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 located 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 located on the same second side 132 ([Fig.3]), opposite the first side, of the recess 30.

[0069] The conductive tracks 52, 53, 55, 56, 57, 58 are arranged so that: - the intermediate bars 74 of the primary tracks 52, 53 are substantially aligned with each other in 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, - the first longitudinal branches 62, 90, 110 of the primary tracks 52, 53 and secondary tracks 55, 56, 57, 58 are substantially aligned with each other in the stacking direction Z, - the second longitudinal branches 63, 92, 112 of the primary tracks 52, 53 and secondary tracks 55, 56, 57, 58 are substantially aligned with each other in the stacking direction Z, - the elbows 70 of the primary tracks 52, 53 are substantially aligned with each other in the stacking direction Z, as well as 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 substantially aligned with each other in the stacking direction Z and with the second bends 124 of the intermediate secondary tracks 57, 58.

[0070] Thus, the superposition of the primary 24 and secondary 28 turns is optimized, which allows good electromagnetic coupling of said turns 24, 28 and reduces AC losses.

[0071] With reference to [Fig.6], the primary conductive tracks of the first and second types 52, 53 are grouped in pairs of primary conductive tracks 134. Each pair 134 is composed of a primary conductive track of the first type 52 and a primary conductive track of the second type 53 electrically connected to each other by first buried connection holes 136.

[0072] Each pair 134 forms a branch 26A, 26B, 26C of the primary winding 20.

[0073] The primary conductive tracks 52, 53 making up each of these pairs 134 are formed in the same printed circuit board 61 and belong in particular to internal layers of the printed circuit board 61, the first connection holes 136 being provided in said printed circuit board 61. The primary conductive tracks 52, 53 of different pairs 134 are formed in different printed circuit boards 61.

[0074] With reference to Figures 8 and 9, the first connecting holes 136 are formed at the free end 71 of the elbow 70 of each of the conductive tracks 52, 53. In the example shown, the first connecting holes 136 are four in number and are here aligned along the width of the elbow 70.

[0075] As visible in [Fig. 5], each of the secondary conductive tracks 55, 56, 57, 58 extends in line with the connecting holes 136 in the stacking direction Z. In particular, the bar 98, 118 of each of the secondary tracks 55, 56, 57, 58 extends in line with the connecting holes 136 in the stacking direction Z.

[0076] Thus, the primary conductive tracks 52, 53 of each pair 134 are electrically connected to each other without a portion offset from the secondary conductive tracks 55, 56, 57, 58, which makes it possible to reduce the AC losses.

[0077] With reference to Figures 3 and 6, the primary conductive tracks of the third type 54A, 54B comprise first primary conductive tracks of the third type 54A ([Fig.6]) and second primary conductive tracks of the third type 54B ([Fig.3]). They comprise in particular at least one first primary conductive track of the third type 54A and at least one second primary conductive track of the third type 54B per card 61. The first primary conductive tracks of the third type 54A are aligned with each other along the stacking direction Z and the second primary conductive tracks of the third type 54B are aligned with each other along the stacking direction Z. Each primary conductive track of the third type 54A, 54B belongs to an external layer (not referenced) of one of the printed circuit cards 61.

[0078] In the example shown, each of the printed circuit boards 61 comprises two first primary conductive tracks of the third type 54A and two second primary conductive tracks of the third type 54B, with the exception of the printed circuit boards 61 arranged at the ends of the stack 50, one comprising a single first primary conductive track of the third type 54A and the other comprising a single second primary conductive track of the third type 54B. Alternatively (not shown), each of the printed circuit boards 61 comprises two first primary conductive tracks of the third type 54A and two second primary conductive tracks of the third type 54B, including the printed circuit boards 61 arranged at the ends of the stack.

[0079] The primary conductive track of the first type 52 of each pair 134 is electrically connected to the or each first primary conductive track of the third type 54A formed in the same printed circuit board 61. Said primary conductive track of the first type 52 is electrically connected to this or these first primary conductive track(s) of the third type 54A by through-holes 137A provided through the printed circuit board 61.

[0080] Similarly, the primary conductive track of the second type 53 of each pair 134 is electrically connected to the or each second primary conductive track of the third type 54B formed in the same printed circuit board 61. Said primary conductive track of the second type 53 is in particular electrically connected to this or these second primary conductive track(s) of the third type 54B by through-holes 137B ([Fig.4]) provided through the printed circuit board 61.

[0081] These connecting holes 137A, 137B are isolated from the corresponding connecting holes 137A, 137B provided through the or each neighboring printed circuit board 61 by an insulating layer 59. This insulating layer 59 is typically obtained during the lamination-sintering of the printed circuit boards 61 making up the stack.

[0082] As visible in Figures 4, 8 and 9, the connecting holes 137A are provided at the first longitudinal end 64 of the second branch 63 of the primary conductive track of the first type 52 and the connecting holes 137B are provided at the first longitudinal end 64 of the second branch 63 of the primary conductive track of the second type 52. In the example shown, the connecting holes 137A, respectively the connecting holes 137B, are four in number and are here aligned along the width of the second branch 63 of the primary conductive track 52, 53.

[0083] With reference to Figures 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 pair of tracks primary 134 respectively.

[0084] The secondary conductive tracks 55, 56, 57, 58 composing each pair 138 are formed in the same printed circuit board 61 as the primary tracks 52, 53 composing the sandwiched pair 134 and each belong to an outer layer of said printed circuit board 61. They are electrically connected to each other by second through holes 140 passing through the printed circuit board 61. Thus, each printed circuit board 61 comprises a first pair of tracks 134, consisting of primary conductive tracks 52, 53 electrically connected to each other by first buried through holes 136, and a second pair of tracks 138, consisting of secondary conductive tracks 55, 56, 57, 58 electrically connected to each other by second through holes 140 passing through and sandwiching said first pair 134.

[0085] In particular, each pair 138 is composed of an intermediate or end secondary conductive track of the first type 55, 57 and an intermediate or end secondary conductive track of the second type 56, 58. As visible in Figures 11 to 14, the second connecting holes 140 are formed in the projecting portion 104, 126 of each of these conductive tracks 55, 56, 57, 58. In the example shown there are four of them and they are arranged in a square here.

[0086] As visible in [Fig. 5], the second connecting holes 140 extend through the windows 79 of the primary conductive tracks 52, 53 making up the sandwiched pair 134. Thus, the intermediate bar 74 of each of these conductive tracks 52, 53 is interposed between the first connecting holes 136 on the one hand and the second connecting holes 140 on the other hand. By “interposed”, it is understood here and hereinafter that the bar 74 extends across the straight line connecting the first connecting holes 136 to the second connecting holes 140.

[0087] Thanks to this arrangement, the length of the offset portion 104, 126 necessary for the interconnection of the secondary conductive tracks 55, 56, 57, 58 of each pair 138 is minimized. In addition, the surface area of ​​conductive material superimposed between the primary and secondary windings 20, 22 in the series interconnection zone of the secondary turns 28 is maximized. This improves the electromagnetic coupling between the primary and secondary windings 20, 22 and makes it possible to reduce AC losses.

[0088] Returning to [Fig.7], the secondary conductive tracks 55, 56, 57, 58 of different pairs 138 are formed in different printed circuit boards 61 and an insulating layer 59 is interposed between the second connection holes 140 electrically connecting the secondary conductive tracks 55, 56, 57, 58 of different pairs 138. This insulating layer 59 is typically obtained during the lamination-sintering of the printed circuit boards 61 making up the stack.

[0089] With reference to [Fig.5], the winding 12 also comprises metal pellets sintered 142, 144 providing an electrical connection between conductive tracks 54A, 54B, 57, 58 belonging to external layers of the printed circuit boards 61 making up the stack. Each sintered metal pad 142, 144 is thus interposed between two of the printed circuit boards 61 making up the stack.

[0090] Each sintered metal pellet is typically silver.

[0091] These sintered metal pads 142, 144 comprise first sintered metal pads 142 each connecting two primary conductive tracks of the third type 54A, 54B to each other. They also comprise second sintered metal pads 144, each connecting an intermediate secondary conductive track of the first type 57 to an intermediate secondary conductive track of the second type 58.

[0092] As visible in Figures 6 and 10, each first sintered metal pad 142 is placed in line with the second end 84 of the strip 80 forming the primary conductive track of the third type 54A, 54B, opposite the through-hole 86. Thus, for each of the primary conductive tracks of the third type 54A, 54B connected by the first sintered metal pad 142, the connecting holes 137A, 137B are interposed in the longitudinal direction X between the through-hole 86 and the first sintered metal pad 142.

[0093] Together, the primary conductive tracks of the third type 54A, 54B, the connection holes 137A, 137B and the first sintered metal pads 142 ensure the parallel electrical connection of the pairs 134. They allow the pairs 134 to be electrically connected to each other in the absence of metallization of the insertion holes of the connection pads 14, 15, metallization impossible to achieve with current technological means.

[0094] The second sintered metal pellets 144 ensure the electrical connection in series of the pairs 138.

[0095] For this purpose, as visible in Figures 14 and 15, each second sintered metal pellet 144 is placed in line with the second bends 124 of the intermediate secondary conductive tracks 57, 58. It is in contact with the second bend 124 of an intermediate secondary conductive track of the first type 57 and with the second bend 124 of an intermediate secondary conductive track of the second type 58.

[0096] Thus, as visible in [Fig. 5], each of the primary conductive tracks of the first and second types 52, 53 extends in line with the second sintered metal pad 144 in the stacking direction Z. In particular, the second transverse bar 78 of each of the primary conductive tracks of the first and second types 52, 53 extends in line with the second sintered metal pad 144 in the stacking direction Z.

[0097] As a result, the pairs 138 are electrically connected to each other without portion offset from the primary conductive tracks forming turns 52, 53, which makes it possible to reduce AC losses.

[0098] A method 200 for manufacturing the planar power transformer 10 will now be described, with reference to [Fig. 15].

[0099] The method 200 comprises a first step 201 of manufacturing the winding 12.

[0100] Step 201 begins with a first sub-step 202 of producing a printed circuit board 61.

[0101] With reference to [Fig. 16], this production step 202 begins with a sub-step 210 of providing a substrate (not shown) made of dielectric material.

[0102] Sub-step 210 is followed by a sub-step 220 of producing a first internal conductive layer (not referenced) of the printed circuit board 61 on a first face of the substrate. This sub-step 220 comprises the production 222 of a primary conductive track of the first type 52 on said first face of the substrate.

[0103] Sub-step 210 is also followed by a sub-step 230 of producing a second internal conductive layer (not referenced) of the printed circuit board 61 on a second face of the substrate. This sub-step 230 comprises the production 232 of a primary conductive track of the second type 53 on said second face of the substrate.

[0104] Sub-steps 220 and 230 are carried out in parallel or successively to one another.

[0105] Substeps 220 and 230 are followed by a substep 240 of making buried bonding holes through the substrate to electrically connect the primary conductive tracks of the first and second types 52, 53 to each other. These buried bonding holes constitute the first bonding holes 136.

[0106] Following this sub-step 240, the production 202 of the printed circuit board 61 comprises a sub-step 250 of depositing a first insulating layer 59 on the first face of the substrate. This first insulating layer 59 covers the first connection holes 136.

[0107] Sub-step 250 is followed by a sub-step 260 of producing a first external conductive layer (not referenced) on a face of the first insulating layer opposite the substrate. This sub-step 260 comprises the production 262 of at least one, preferably two, primary conductive track(s) of the third type 54A, 54B in line with the first longitudinal end 64 of the second longitudinal branch 63 of at least one of the primary conductive tracks of the first and second types 52, 53. It also comprises the production 264 of an intermediate or end secondary conductive track of the first type 55, 57, the bar 98, 118 of said track 55, 57 extending in line with each first connection hole 136.

[0108] Following sub-step 240, production 202 of the printed circuit board 61 also comprises a sub-step 270 of depositing a second insulating layer 59 on the second face of the substrate. This second insulating layer 59 covers the first bonding holes 136.

[0109] Sub-step 270 is followed by a sub-step 280 of producing a second external conductive layer (not referenced) on a face of the second insulating layer opposite the substrate. This sub-step 280 comprises the production 282 of at least one, preferably two, primary conductive track(s) of the third type 54A, 54B in line with the first longitudinal end 64 of the second longitudinal branch 63 of at least one of the primary conductive tracks of the first and second types 52, 53. It also comprises the production 284 of an intermediate or end secondary conductive track of the second type 56, 58, the bar 98, 118 of said track 56, 58 extending in line with each first connection hole 136.

[0110] Sub-steps 270 and 280 are carried out in parallel or successively with sub-steps 250 and 260.

[0111] Sub-steps 260 and 280 are followed by a sub-step 290 of producing through-holes through the substrate and the two insulating layers 59. This sub-step 290 comprises producing 292 the second through-holes 140 to electrically connect the secondary conductive track of the first type 55, 57 to the secondary conductive track of the second type 56, 58. It also comprises producing 294 the third through-holes 137A, 137B to electrically connect each of the primary conductive tracks of the first and second types 52, 53 to at least one primary conductive track of the third type 54A, 54B.

[0112] A printed circuit board 61 is thus obtained.

[0113] Returning to [Fig. 15], substep 202 is repeated until all the printed circuit boards 61 of the stack have been produced.

[0114] Then, the manufacturing 201 of the winding 12 comprises a sub-step 203 of stacking the printed circuit boards 61 thus produced. During this stacking step, a metal paste is interposed between the printed circuit boards 61, at the level of the primary conductive tracks of the third type 54A, 54B on the one hand and the second bends 124 of the intermediate secondary conductive tracks 57, 58 on the other hand. The remainder of the space between the printed circuit boards 61 is filled with a dielectric material.

[0115] Sub-step 203 is followed by a sub-step 204 of rolling-sintering the printed circuit boards 61. During this sub-step 204, the metal interposed between the printed circuit boards 61 sinters and bonds intimately to the conductive tracks of the external layers, thus forming an electrical connection between the primary conductive tracks of the third type 54A, 54B on the one hand and the second bends 124 of the tracks intermediate secondary conductors 57, 58 on the other hand. Furthermore, the dielectric material housed between the printed circuit boards 61 hardens and forms an insulating layer. The principle of lamination-sintering (better known by its English name of “sinter lamination”) is well known to those skilled in the art, who will therefore be able to implement this step without any particular difficulty.

[0116] This gives winding 12.

[0117] Step 201 is followed by a step 205 of installing the interconnection pads 14, 15, 16, 17. During this step 205, the pads 14, 15, 16, 17 are inserted into the through-holes 72, 86, 103 provided for this purpose, then washers are mounted on the pads 14, 15, 16, 17 to electrically connect them to the conductive tracks 52, 53, 54A, 54B, 55, 56, 57, 58. In particular: - a first washer (not referenced) is mounted on the first pad 14 to ensure the electrical connection between said first pad 14 and a first primary conductive track of the third type 54A on the surface of the stack, - a second washer (not referenced) is mounted on the second pad 15 to ensure the electrical connection between said second pad 15 and a second primary conductive track of the third type 54B on the surface of the stack, - a third washer (not referenced) is mounted on the third pad 16 to ensure the electrical connection between said third pad 16 and the secondary end conductive track of the first type 55, and - a fourth washer (not referenced) is mounted on the fourth pad 17 to ensure the electrical connection between said fourth pad 17 and the secondary end conductive track of the second type 56.

[0118] Step 205 is followed by a step 206 of placing the magnetic circuit 18. During this step 206, the block 32 of ferromagnetic material is positioned around the winding 12.

[0119] We thus obtain the planar transformer 10.

[0120] Thanks to the embodiment described above, the superposition of the conductive tracks 52, 53, 55, 56, 57, 58 forming the turns 24, 28 of the primary and secondary windings 20, 22 is optimized, which makes it possible to improve the electromagnetic coupling between the primary and secondary windings 20, 22 and reduces the AC losses. In addition, the offset portions of said conductive tracks 52, 53, 55, 56, 57, 58 forming these turns 24, 28 are greatly reduced, which contributes even further to the reduction of the AC losses. The planar transformer 10 can thus be easily used at high frequency.

Claims

Claims

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

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

3. A coil (12) according to claim 2, wherein the conductive tracks (52, 53, 54A, 54B, 55, 56, 57, 58) electrically connected to each other by the sintered metal pad (144) are secondary conductive tracks (55, 56, 57, 58), and at least one primary conductive track (52, 53) extends in line with the sintered metal pad (144).

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

5. A coil (12) according to any preceding claim, wherein each of the primary conductive tracks (52, 53) composing the pair of primary conductive tracks (134) of a printed circuit board (61) forms a turn.

6. A coil (12) according to any preceding claim, wherein the second assembly (60B) comprises, for the or at least one of the pairs of primary conductive tracks (134), a pair of secondary conductive tracks (138) composed of secondary conductive tracks (55, 56, 57, 58) formed in the same printed circuit board (61) as the pair of primary conductive tracks (134) sandwiching said pair of primary conductive tracks (134), said secondary conductive tracks (55, 56, 57, 58) each forming a turn and being electrically connected to each other by at least one second electrical connection (140) passing through the printed circuit board (61).

7. A coil (12) according to claim 6, wherein each primary conductive track (52, 53) making up the pair of primary conductive tracks (134) forms a turn comprising two longitudinal branches (62, 63) spaced transversely from one another, each having a first longitudinal end (64) and an opposite second longitudinal end (66), and an end transverse bar (68) connecting the second longitudinal ends (66) of the two branches (62, 63) to one another, each primary conductive track of the pair further comprising an intermediate transverse bar (74) connecting the two branches (62, 63) to one another, at a distance from their respective longitudinal ends (66) and interposed between the or each first electrical connection (136) and the or each second electrical connection (140), and each secondary conductive track (55, 56, 57,58) composing the pair of secondary conductive tracks (138) extends in line with said intermediate transverse bar (74).,

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

9. A planar transformer (10) comprising a winding (12) according to any one of the preceding claims.

10. A method of manufacturing a winding (12) for a planar power transformer (10) according to any one of the preceding claims, comprising a step (202) of producing a printed circuit board (61), said producing step (202) including the following sub-steps: - providing (210) a substrate made of dielectric material, - production (222) of a first conductive track (52) forming a turn on a first face of the substrate, - production (232) of a second conductive track (53) forming a turn on a second face of the substrate, - making (240) at least one first electrical connection (136) through the substrate to electrically connect the first and second conductive tracks (52, 53) to each other, said conductive tracks (52, 53) forming a pair of primary conductive tracks (134) of a first set (60A) forming a primary winding (20) of the coil (12), - deposition (250) of a first insulating layer (59) on the first face of the substrate, the first insulating layer (59) covering the or each first electrical connection (136), and production of a third conductive track (55) forming a turn on a face of the first insulating layer opposite the substrate, said third conductive track (55) belonging to a second assembly (60B) forming a secondary winding (22) of the coil (12) extending in line with the or each first electrical connection (136) connecting the primary conductive tracks (52, 53) of the pair of primary conductive tracks (134).

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