Planar transformer

Abstract

The planar transformer (100) comprises: - a first printed circuit board (110); - a second printed circuit board (112); - a primary winding (114) consisting of at least one turn; - a secondary winding (116) consisting of at least one turn; and - a magnetic core (102) for coupling the primary (114) and secondary (116) windings. Each turn of the primary winding (114) is formed in an internal conductive layer (110INT1-4) of at least one of the first printed circuit board (110) and the second printed circuit board (112), this internal conductive layer being covered on each side with insulating material.

Description

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 different countries. In particular, an ambitious standard applies to both new types of aircraft and those already 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 less energy-intensive and more environmentally friendly aeronautical components and products 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, particularly 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 some 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 galvanic isolation using a power transformer. For isolated DC / DC applications, this transformer is generally planar (from the English "planar") because it allows for high-frequency operation (several hundred kilohertz) and therefore 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, with the primary winding located in one part of the conductive layers and the secondary winding in another. The primary and secondary windings can be interleaved to improve magnetic coupling and reduce losses. However, there are also cases where the primary and secondary windings are not interleaved, but grouped into two separate sets.

[0010] As is well known, the conductive layers of a multilayer printed circuit board (PCB) include a top layer, one or more internal layers, and a bottom layer. These conductive layers are separated from each other by electrically insulating material. More specifically, a multilayer PCB typically consists of several core boards, with two conductive layers deposited on either side of each core board. Layers of prepreg are then sandwiched between the core boards to cover the conductive layers (which are thus "internal") and bond the core boards 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] Therefore, such a planar transformer does not meet the stringent requirement for segregating 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 prepreg layer, depending on the configuration). This is thus 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 directly opposite the lower conductive layer of the upper printed circuit board, without any insulation.

[0013] Even if the upper printed circuit board lacks a lower layer, as is the case, for example, in the article "Design and Analysis of Planar Transformers in Modern 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, we again obtain a simple barrier whose integrity is difficult to guarantee.

[0014] This uncertainty is more important for aeronautical applications where altitude and the environment (which may be unpressurized) will promote 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 is therefore proposed according to claim 1.

[0017] Thus, because only internal layers are used to form the turns, the primary and secondary windings are separated by at least one thickness of insulating material of a printed circuit board, which enhances the insulation.

[0018] The invention may further include one or more of the optional features of claims 2 to 9, according to any technically feasible combination.

[0019] A DC-DC converter is also proposed according to claim 10.

[0020] An aircraft is also proposed according to claim 11. Brief description of the figures

[0021] 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: there figure 1 is a cross-sectional view of a planar transformer according to a first embodiment of the invention, the figure 2 is a cross-sectional view of a planar transformer according to a second embodiment of the invention, and the figure 3 is a cross-sectional view of a planar transformer according to a third embodiment of the invention. Detailed description of the invention

[0022] With reference to the figure 1 , a planar transformer 100 according to the invention will now be described.

[0023] 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 1091, 1092 connecting respectively the ends of the legs 104, 106, 108. The core is for example made of ER51 ferrite.

[0024] 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).

[0025] Thus, each of the multilayer printed circuit boards 110, 112 comprises at least one substrate plate 110 SUB1-2, 112 SUB1-3 having two opposite faces on which are respectively deposited two internal conductive layers 110 1NT1-4, 112 INT1-6. Each of the multilayer printed circuit boards 110, 112 further comprises prepreg layers (indicated by a dot fill on the figure 1 ) sandwiched between the substrate plates (substrate plate 110 SUB1-2, 112 SUB1-3), 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 (110 INT1-4, 112 INT1-6) is covered on both sides with insulating material: substrate plate on one side and a prepreg layer on the other. The prepreg layers are, for example, made of epoxy.

[0026] For example, as in the illustrated example, the first multilayer printed circuit 110 has two substrate plates 110 SUB1-2 and four inner layers 110 INT1-4: two 110 INT1-2 on each side of the first substrate plate 110 SUB1 and two 110 INT3-4 on each side of the second substrate plate 110 SUB2.

[0027] Again, for example, as in the illustrated example, the second multilayer printed circuit 112 has three substrate plates 110 SUB1-3 and six internal layers 112 INT1-6: two 112 INT1-2 on each side of the first substrate plate 112 SUB1, two 112 INT3-4 on each side of the second substrate plate 112 SUB2, and two 112 INT5-6 on each side of the third substrate plate 112 SUB3.

[0028] 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) 110 INT1-4 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 110 INT1-4. In the illustrated example, only one turn is formed in each of the internal conductive layers 110 INT1-4, so that the primary winding 114 has 4 turns.

[0029] A top conductive layer may be provided, for example to form an upper connection terminal 114T of the first winding 114, but no turns. Similarly, a bottom conductive layer may be provided, for example to form a lower connection terminal 114B, but no turns.

[0030] For example, the conductive layers are connected to each other by vias.

[0031] 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) 112 INT1-6 of the second multilayer printed circuit board 112. More precisely, at least one turn of the primary winding 114 is formed in each internal conductive layer 110 INT1-4. In the illustrated example, two turns are formed in each of the internal conductive layers 110 INT1-3, 5-6, except for the internal conductive layer 112 INT4 in which only one turn is formed, so that the secondary winding 116 has 11 turns.

[0032] An upper conductive layer may be provided, for example to form an upper connection terminal 116T of the second winding 116, but no turn. Similarly, a lower conductive layer may be provided, for example to form a lower connection terminal 116B, but no turn.

[0033] For example, the conductive layers are connected to each other by vias.

[0034] The first planar transformer 100 may also 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 1091, 1092.

[0035] The structure illustrated on the figure 1 It 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, for example, have a thickness of 140 µm, while the prepreg layers, for example, have a thickness of 350 µm.

[0036] The secondary winding consists of four 8.6mm wide secondary layers connected in parallel. The primary winding consists of six layers of conductors connected in series, including one 7.3mm turn and five 3.4mm turns.

[0037] With reference to the figure 2 , another planar transformer 200 according to the invention will now be described.

[0038] The 200 planar transformer is similar to that of the figure 1The only difference is that the turns of the primary winding 114 are formed in the inner layers of the first printed circuit board 110 and in the inner layers of the second printed circuit board 112. In the illustrated example, three turns are formed in the first printed circuit board 110: two turns are formed in each of the internal conductive layers 110 INT1, 2, and one turn is formed in the internal conductive layer 110 INT3. Furthermore, six turns are formed in the second printed circuit board 112: two turns are formed in each of the internal conductive layers 112 INT1-3. The primary winding 116 thus has 9 turns.

[0039] The planar transformer 200 further includes a conductive plate 202 extending between the first printed circuit board 110 and the second printed circuit board 112, and the secondary winding 116 is formed by this conductive plate 202.

[0040] The planar transformer 200 further comprises a first electrical insulating screen 118A between the first printed circuit board 110 and the conductive plate 202 and a second electrical insulating screen 118B between the conductive plate 202 and the second printed circuit board 112.

[0041] With reference to the figure 3 , another planar transformer 300 according to the invention will now be described.

[0042] The 300 planar transformer is similar to that of the figure 2except that, instead of the conductive plate 202 and the insulating plates 118A, 118B, it includes a third printed circuit board 302 between the first printed circuit board 110 and the second printed circuit board 112. Each turn of the secondary winding 116 is then formed in an internal conductive layer 302 INT1-4 of the third printed circuit board 302. In the illustrated example, the third printed circuit board 302 has four internal conductive layers 302 INT1-4, in each of which a single turn is formed, so that the secondary winding 116 has 4 turns.

[0043] In conclusion, it should be noted that the invention is not limited to the embodiment described above. Indeed, it will 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 provided.

[0044] 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 order of positioning of the printed circuits.

[0045] 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 to include 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

1. Planar transformer (100; 200; 300) comprising: - a first printed circuit board (110); - a second printed circuit board (112); - a primary winding (114) formed of at least one turn; - a secondary winding (116) formed of at least one turn; and - a magnetic core (102) for coupling the primary (114) and secondary (116) windings; characterized in that Each turn of the primary winding (114) is formed in an internal conductive layer (110 INT1-4 ) of at least one of the first printed circuit board (110) and the second printed circuit board (112), this internal conductive layer being covered on each side with insulating material.

2. Planar transformer (100; 200; 300) 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; 200; 300) according to claim 1 or 2, 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).

4. Planar transformer (100) according to any one of claims 1 to 3, in which each turn of the primary winding (114) is formed in an internal conductive layer (110 INT1-4 ) of the first printed circuit board (110), and in which each turn of the secondary winding (116) is formed in an internal conductive layer (112 INT1-6 ) of the second printed circuit board (112).

5. Planar transformer (100) according to claim 4, further comprising an electrical insulating screen (118) between the first printed circuit board (110) and the second printed circuit board (112).

6. Planar transformer (200; 300) according to any one of claims 1 to 3, wherein each of some of the turns of the primary winding (114) is formed in an internal conductive layer (110 INT1-4 ) of the first printed circuit board (110) and each of the other turns of the primary winding (114) is formed in an internal conductive layer (110 INT1-4 ) of the second printed circuit board (112).

7. Planar transformer (200) according to claim 6, further comprising a conductive plate (202) extending between the first printed circuit board (110) and the second printed circuit board (112), and in which the secondary winding (116) is formed by this conductive plate (202).

8. Planar transformer (200) according to claim 7, further comprising a first electrical insulating screen (118A) between the first printed circuit board (110) and the conductive plate (202) and a second electrical insulating screen (118B) between the conductive plate (202) and the second printed circuit board (112).

9. Planar transformer (300) according to claim 6, further comprising a third printed circuit board (302) between the first printed circuit board (110) and the second printed circuit board (112), and in which each turn of the secondary winding (116) is formed in an internal conductive layer (302 INT1-4 ) of the third printed circuit board (302).

10. DC-DC converter comprising a planar transformer (100; 200; 300) according to any one of the preceding claims.

11. Aircraft comprising a planar transformer (100; 200; 300) according to any one of the preceding claims or a DC-DC converter according to the preceding claim.

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