PLANAR TRANSFORMER

Abstract

The planar transformer (100) comprises: - a first printed circuit board (110); - a second printed circuit board (112); - a primary winding (114) formed of at least one turn, each turn of the primary winding (114) being formed in a conductive layer (110INT1-4) of the first printed circuit board (110); - a secondary winding (116) formed of at least one turn, each turn of the secondary winding (116) being formed in a conductive layer (112INT1-6) of the second printed circuit board (112); and - a magnetic core (102) for coupling the primary (114) and secondary (116) windings. The conductive layers (110INT1-4, 112INT1-6) in which the turns of the primary (114) and secondary (116) windings are formed are internal conductive layers, covered on each side with insulating material. See Fig. 1 for abbreviations.

Description

Title of the invention: PLANAR TRANSFORMER Technical field of the invention

[0001] The present invention relates to a planar transformer. Technological background

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0006] In the aeronautical field, the increase in electrical power expected in new aircraft is accompanied by an evolution of the onboard network. In certain aircraft network architectures, high voltage (between 500 V and 1000 V DC) and low voltage (for example 28 V DC) networks are required to coexist with isolated DC-DC converters at the interfaces of these two networks.

[0007] The isolation of this converter is essential because it is the main barrier between these networks and makes it possible in particular to prevent the propagation of a fault from the high voltage to the low voltage.

[0008] Traditional solutions involve achieving this galvanic isolation using a power transformer. For isolated DC / DC applications, this transformer is generally planar because it allows for high-frequency operation (several hundred kilohertz) and therefore enables a more compact converter. This technology is thus well-suited for aeronautical applications, especially since it is more easily industrialized than wound-winding technologies.

[0009] Traditional planar technologies involve using a multilayer printed circuit board, thus comprising several conductive layers, and carrying the primary winding in one part of the conductive layers and the secondary winding in another part of the conductive layers. The primary and secondary windings can be interlaced to improve magnetic coupling and reduce losses. However, there are also cases where the primary and secondary windings are not interlaced, but grouped into two separate sets.

[0010] As is known, the conductive layers of a multilayer printed circuit board include a top conductive layer, one or more inner conductive layers, and a bottom layer. These conductive layers are separated from each other by electrically insulating material. More specifically, a multilayer printed circuit board generally comprises several substrate (core) plates, with two conductive layers deposited on either side of each substrate plate. Layers of prepreg are then sandwiched between the substrate plates to cover the conductive layers (which are thus "inner") and to bond the substrate plates together to form a stack.The top and bottom conductive layers are then deposited onto the top and bottom prepreg layers of the stack, respectively. Such a stack is described, for example, by following the internet link https: / / tspcb.pl / en / blog / quality / structure-characteristics-and-design-of-multilayer-printed-circuit-boards.

[0011] Thus, such a planar transformer does not meet the stringent requirement for segregation of high-voltage and low-voltage networks across the multilayer printed circuit board. Indeed, the internal conductive layer of the first winding and the internal conductive layer of the second winding, facing each other, are separated only by a thickness of insulating material (substrate plate or layer of pre-impregnated according to the configuration). It is therefore a simple barrier whose integrity is difficult to guarantee.

[0012] Furthermore, it is also known to use two different printed circuit boards, placed one above the other, for the first and second windings respectively. However, in this case, the upper conductive layer of the lower printed circuit board is located opposite the lower conductive layer of the upper printed circuit board, without insulation.

[0013] Even if the upper printed circuit board does not have a lower layer, as is the case, for example, in the article "Design and Analysis of Planar Transformers in Modem Switching Mode Power Supply" by Hassan et al., 2021, a single layer of insulating material separates the upper conductive layer of the lower printed circuit board from the conductive layer closest to the upper printed circuit board. Thus, a simple barrier is again obtained, the integrity of which is difficult to guarantee.

[0014] This uncertainty is more important for aeronautical applications where altitude and the environment (which may be unpressurized) will favor the appearance of electric arcs as soon as the voltage becomes close to 1000 V DC.

[0015] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. Summary of the invention

[0016] A planar transformer comprising: is therefore proposed. - a first printed circuit board; - a second printed circuit board; - a primary winding consisting of at least one turn, each turn of the primary winding being formed in a conductive layer of the first printed circuit; - a secondary winding consisting of at least one turn, each turn of the secondary winding being formed in a conductive layer of the second printed circuit board; and - a magnetic coupling core of the primary and secondary windings; characterized in that the conductive layers in which the turns of the primary and secondary windings are formed are internal conductive layers, covered on each side with insulating material.

[0017] Thus, by placing the two printed circuits one above the other, the two conductive layers respectively of the nearest primary and secondary windings are separated by two thicknesses of insulating material, which strengthens the insulation.

[0018] The invention may further include one or more of the following optional features, according to any technically possible combination.

[0019] Preferably, the first printed circuit board and / or the second printed circuit board is multilayer.

[0020] Preferably also, the planar transformer further comprises an electrical insulating screen between the first and second printed circuits.

[0021] Preferably also, the first printed circuit board and / or the second printed circuit board has an upper and / or lower conductive layer forming a connection terminal for the corresponding winding.

[0022] A DC-DC converter comprising a planar transformer according to the invention is also proposed.

[0023] An aircraft comprising a planar transformer according to the invention or a DC-DC converter according to the invention is also proposed. Brief description of the figures

[0024] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which: - [Fig.1] is a cross-sectional view of a planar transformer according to the invention. Detailed description of the invention

[0025] With reference to [Fig.1], a planar transformer 100 according to the invention will now be described.

[0026] The planar transformer 100 first of all comprises a magnetic core 102 having several legs, for example three legs 104, 106, 108 as in the illustrated example, with a central leg 106 and two lateral legs 104, 108, and two cross members 109i, 1092 connecting respectively the ends of the legs 104, 106, 108. The core is for example made of ER51 ferrite.

[0027] The planar transformer 100 comprises two printed circuits, for example first and second multilayer printed circuits 110, 112 as in the illustrated example, formed of a stack of conductive layer(s), substrate plate(s) and prepreg layer(s).

[0028] Thus, each of the multilayer printed circuit boards 110, 112 comprises at least one substrate plate HOsubi 2, H2subi 3 having two opposite faces on which are respectively deposited two internal conductive layers 1101NTi 4, 1121NTi 6. Each of the multilayer printed circuit boards 110, 112 further comprises prepreg layers (indicated by dot filling in [Fig. 1]) interleaved between the substrate plates HOsubi 2, H2subi 3, as well as a top prepreg layer at the top of the stack and a bottom prepreg layer at the base of the stack. Thus, each internal conductive layer 1101NTX 4, 1 121NTi_6 is covered on each side with insulating material: a substrate plate on one side and a prepreg layer on the other. The prepreg layers are, for example, made of epoxy.

[0029] For example, as in the illustrated example, the first multilayer printed circuit 110 comprises two substrate plates 1 IOsubi 2 and four internal layers 1 10inti-4: two 1101NTi 2 on each side of the first substrate plate 1 10Subi and two 1101NT3 4 on each side of the second substrate plate 1 10Sub2-

[0030] Again, for example, as in the illustrated example, the second multilayer printed circuit 112 comprises three substrate plates 110Subi 3 and six internal layers 1121Nn_ 6: two 112^.2 on each side of the first substrate plate 112SUBb, two 1121nt3 4 on each side of the second substrate plate 112SUb2, and two 112IXT 5 _ 6 on each side of the third substrate plate 112SUb3-

[0031] The first planar transformer 100 further comprises a primary winding 114 having at least one turn wound around one of the legs 104, 106, 108 of the magnetic core 102, for example the central leg 106 as in the illustrated example. The turn(s) of the primary winding 114 are formed in the internal conductive layer(s) 110inti-4 of the first multilayer printed circuit board 110. More precisely, at least one turn of the primary winding 114 is formed in each internal conductive layer 1101NTi 4. In the illustrated example, only one turn is formed in each of the internal conductive layers 1101NTX 4, so that the primary winding 114 has 4 turns.

[0032] A top conductive layer may be provided, for example to form an upper connection terminal 114T of the first winding 114, but no turn. Similarly, a bottom conductive layer may be provided, for example to form a lower connection terminal 114B, but no turn.

[0033] The conductive layers are for example connected to each other by vias.

[0034] The first planar transformer 100 further comprises a secondary winding 116 having at least one turn wound around one of the legs 104, 106, 108 of the magnetic core, preferably the same as the primary winding 114, for example the central leg 106 as in the illustrated example. The turn(s) of the secondary winding 116 are formed in the internal conductive layer(s) 112INTX_ 6 of the second multilayer printed circuit 112. More precisely, at least one turn of the primary winding 114 is formed in each internal conductive layer 110INTX_ 4. In the illustrated example, two turns are formed in each of the internal conductive layers 110INTX| 3.3 except for the internal conductive layer 112INT4 in in which a single turn is formed, so that the secondary winding 116 has 11 turns.

[0035] A top conductive layer may be provided, for example to form an upper connection terminal 116T of the second winding 116, but no turn. Similarly, a bottom conductive layer may be provided, for example to form a lower connection terminal 116B, but no turn.

[0036] The conductive layers are for example connected to each other by vias.

[0037] The first planar transformer 100 may further include, as in the illustrated example, an electrical insulating screen 118 interposed between the first and second printed circuit boards 110, 112. The electrical insulating screen 118 is made of an electrical insulating material preferably with good thermal conductivity (at least 4 W / mK, for example around 5 W / mK). The thickness of the electrical insulating screen 118 is chosen to be consistent with the thicknesses of the printed circuit boards so that the total thickness is permissible within the winding window, extending vertically between the two cross members 109i, 1092.

[0038] The structure illustrated in [Fig. 1] is suitable for a power transfer of 1.5 kW, and can operate over a frequency range of 100 kHz to 1 MHz. The conductive layers have, for example, a thickness of 140 µm, while the prepreg layers have, for example, a thickness of 350 µm.

[0039]

[0040] The secondary winding is made from 4 secondary layers, each 8.6 mm wide, connected in parallel. The primary winding consists of 6 layers of conductors connected in series, including one turn of 7.3 mm and 5 others of 3.4 mm.

[0041] In conclusion, it should be noted that the invention is not limited to the embodiment described above. It will indeed be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in light of the information just disclosed to them.

[0042] In particular, the number of turns, the number of conductive layers, the thickness of the conductive layers and the thickness of the prepreg layers may be different from the values ​​given above, as well as the positioning order of the printed circuits.

[0043] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiments set forth in this description, but shall be interpreted as including all equivalents which can be foreseen by a person skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Demands

1. Planar transformer (100) comprising: - a first printed circuit board (110); - a second printed circuit board (112); - a primary winding (114) formed of at least one turn, each turn of the primary winding (114) being formed in a conductive layer (1101NTi_4) of the first printed circuit board (110); - a secondary winding (116) formed of at least one turn, each turn of the secondary winding (116) being formed in a conductive layer (1121NTi_6) of the second printed circuit board (112); and - a magnetic core (102) for coupling the primary (114) and secondary (116) windings; characterized in that the conductive layers (1 10iNTi-4, H2inti-6) in which the turns of the primary (114) and secondary (116) windings are formed are internal conductive layers, covered on each side with insulating material.

2. Planar transformer (100) according to claim 1, wherein the first printed circuit board (110) and / or the second printed circuit board (112) is multilayer.

3. Planar transformer (100) according to claim 1 or 2, further comprising an electrical insulating screen (118) between the first and second printed circuits (110, 112).

4. Planar transformer (100) according to any one of claims 1 to 3, wherein the first printed circuit board (110) and / or the second printed circuit board (112) has an upper and / or lower conductive layer forming a connection terminal (114T, 114B, 116T, 116B) of the corresponding winding (114, 116).

5. DC-DC converter comprising a planar transformer (100) according to any one of the preceding claims.

6. Aircraft comprising a planar transformer (100) according to any one of the preceding claims or a DC-DC converter according to the preceding claim.

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