Innovative planar electromagnetic component structure

Abstract

The invention relates to an innovative planar transformer structure, the transformer (10) comprising: a primary circuit (11) including a primary winding (12) of N1 turns; a secondary circuit (21) including a secondary winding (22) of N2 turns; a printed circuit board (15) of overlapping layers, forming an opening (18) defining a perimeter (19); vias (27) disposed at the center of the primary (12) and secondary (22) windings on the perimeter (19) of the opening (18), the N1 and N2 turns each being arranged on a layer, according to any alternation between the N1 and N2 turns, each of the N1 and N2 turns winding partially around the vias (27) forming a circular arc (28) per layer; the circular arc (28) of a layer being distinctly oriented with respect to the circular arcs (28) of the other layers. Fig. 2

Description

Description Title of the invention: Innovative structure of an electromechanical component planar genetics

[0001] — The present invention lies in the field of planar magnetic components, such as inductors, coupled inductors, transformers. The invention focuses more specifically on an innovative planar transformer structure.

[0002] — Currently, almost all switched-mode power supplies incorporate Magnetic components. These components can be purchased as components general public and added to the design or developed in-house. The invention relates to this second possibility, and in particular a category of magnetic components called planars (planaires in French). The main idea of ​​this technology is to integrate the Component windings inside the PCB. Magnetic components Planar components are a solution for power integration. These components are in particular made using flattened magnetic cores (ferrite) and windings manufactured using printed circuit boards (PCBs). The advantages of these magnetic components Planars are numerous: they allow for better integration of the component into the design, the reproducibility of the component's electrical characteristics is increased, they allow for a customized component design and therefore, its optimization for use.

[0003] Figure 1 schematically represents an example of the implementation of a planar magnetic component 5 according to the state of the art. This component 5 consists of a electrical circuit 6, consisting of one or more windings 7, themselves made up of of one or more turns (7-1, 7-2, 7-3, 7-4). These windings are designed to produce a Magnetic field. This field can be used for energy storage (inductance). or for transfer (transformer). Component 5 includes a ferroma- core magnetic 8, which allows the magnetic field to be channeled. This is then referred to as a magnetic circuit. genetics. This core 8 can be made from several materials depending on the application target (power / frequency / price / size / performance). The 8 core can including an air gap 9, a small air space in the circuit, extending parallel to the circuit map.

[0004] — The flow of current in the electrical circuit generates losses of the same The way in which the magnetic field circulates in the magnetic circuit. The losses In the two elements, these are respectively called copper losses and iron losses. Losses are interdependent. It is therefore desirable to optimize the dimensions of each element is tailored to the application in order to maximize performance of the whole.

[0005] = The invention aims to overcome all or part of the problems mentioned above by proposing a transformer including an innovative electromagnetic component structure allowing to optimize the performance of the transformer by minimizing losses, improving the integration of the PCB (short for Printed Circuit Board) by limiting vias at the periphery of components, limiting parasitic inductances and improving couplings. To this end, the invention relates to a transformer comprising: a primary circuit comprising a primary winding of N1 turns of a wire electrical conductor, the primary winding extending from a terminal primary input to a primary output terminal; and a secondary circuit comprising a secondary winding of N2 turns of a conductive electric wire, the secondary winding extending from a secondary input terminal to secondary output terminal, NI and N2 each being an integer greater than or equal to | ; The transformer is characterized in that it comprises: a printed circuit board extending along a foreground, and comprising a a plurality of layers superimposed on each other and forming an opening through the first plane around a first axis and defining a perimeter; a ferromagnetic core, arranged around the primary windings and se- secondary, comprising a central part arranged in the opening; a plurality of vias arranged at the center of the primary and se- windings secondary around the perimeter of the opening, and extending through the layers, each along an axis parallel to the first axis, the plurality of vias being configured to interconnect the plurality of layers; in that the N1 turns and the N2 turns of the conducting electric wire are arranged each on one of the plurality of layers, according to any alternation between the NI turns and the N2 turns, each of the NI turns and the N2 turns winding, from a first via of the plurality of vias, partially around the plurality of vias forming an arc of a circle per layer, towards a second via of the plurality of vias; and in that the circular arc of one layer is distinctly oriented with respect to the circular arcs of other layers and of distinct orientation from the circular arcs of other layers. Advantageously, the ferromagnetic core includes an air gap extending along a second axis substantially perpendicular to the first plane. Advantageously, the input terminals are superimposed on the output terminals along a third axis substantially perpendicular to the foreground. Advantageously, at least one among the plurality of layers is a shielding plane, preferably a ground plane. The invention will be better understood and other advantages will become apparent upon reading the detailed description of a given embodiment as an example, illustrated by the attached drawing in which: [Fig.1] schematically represents an example of the implementation of a planar magnetic component according to the state of the art; [Fig.2] schematically represents an example of the arrangement, around the central vias, of the primary and secondary windings of a transformer according to the invention; [Fig.3] schematically represents an example of vias arranged at the center of the primary bearings of an inductance according to the invention; [Fig.4] schematically represents an example of the implementation of the bearings of a transformer according to the invention; [Fig.5] schematically represents the variation of the current density according to a traditional arrangement of the air gap and an arrangement of the air gap according to the invention; [Fig.6] schematically represents the induction between the conductors according to the alternation of turns of the primary and secondary windings; [Fig.7] schematically represents the homogenization of the current density in the input and output terminals of the primary and secondary windings arranged according to an embodiment of the invention; [Fig.8] schematically represents an example of the implementation of a shielding layer in a transformer according to the invention; [Fig.9] schematically represents a classic electrical diagram of a synchronous rectification; Figure 10 schematically represents the optimization of the output terminals for synchronous rectification according to the invention. For clarity, the same elements will have the same reference points in the different figures. For better visibility and improved understanding, the elements are not always shown to scale. Figure 1 schematically represents an example of the implementation of a planar magnetic component 5 according to the state of the art and has already been described in the introduction. Figure 2 schematically represents a transformer 10 according to the invention, with an example of the arrangement of the primary and secondary windings around the central vias. In this figure, the main elements of the transformer are represented by layers (normally superimposed). Note that this is an illustration; the number of layers is given only as a non-limiting example. A person skilled in the art understands that this number of layers may be greater or less than that shown in the figure. The transformer 10 comprises a primary circuit 11 comprising a primary winding 12 of NI turns of a conductive electric wire, the primary winding 12 extending from a primary input terminal 13 to a primary output terminal 14. The transformer 10 includes a secondary circuit 21 comprising a secondary winding 22 of N2 turns of a conductive electric wire, the secondary winding 22 extending from a secondary input terminal 23 to a secondary output terminal 24 (N1 and N2 each being an integer greater than or equal to 1). The transformer 10 includes a printed circuit 15 (decomposed in the figure into several layers) extending along a first plane 16, and comprising a plurality of layers 17-1, 17-2, 17-3, 17-4, 17-5, 17-6, 17-7 superimposed on each other and forming an opening 18 through the first plane 16 around a first axis Z1 and defining a perimeter 19.The transformer 10 comprises a ferromagnetic core 25 (not shown in this figure, but intended to be inserted into the opening 18, and arranged around the primary 12 and secondary 22 windings, comprising a central portion 26 disposed in the opening 18). The transformer 10 comprises a plurality of vias 27 disposed at the center of the primary 12 and secondary 22 windings on the periphery 19 of the opening 18, and extending through the layers 17-1, 17-2, 17-3, 17-4, 17-5, 17-6, 17-7, each along an axis parallel to the first axis Z1, the plurality of vias 27 being configured to interconnect the plurality of layers 17-1, 17-2, 17-3, 17-4, 17-5, 17-6, 17-7. According to the invention, the N1 turns and N2 turns of the electrical conductor are each arranged on one of the plurality of layers, in any alternation between the N1 turns and the N2 turns. In other words, there is one turn (either of the primary winding or of the secondary winding) per layer. This "any alternation" means that, in their superposition, a turn of the primary winding can be superimposed on a turn of either the primary or secondary winding. All combinations of superposition between primary and secondary windings are conceivable. Each of the N1 turns and the N2 turns winds, from a first via of the plurality of vias 27, partially around the plurality of vias 27 forming an arc of a circle 28 per layer, towards a second via of the plurality of vias 27. In other words, per layer, the turn of the winding (primary or secondary) is not a complete turn, the turn does not make the 360° around the opening 18.Thus, some vias per layer are not surrounded by the said tower. The central arrangement of the vias provides great flexibility in the positioning of the layers, which can be intercalated relative to each other, and therefore in the positioning of the towers of the primary and secondary windings. Furthermore, the circular arc 28 of one layer is distinctly oriented with respect to the circular arcs 28 of the other layers and has a distinct orientation from the circular arcs of the other layers. A turn, at the level of the perimeter 19 of the opening 18, can be considered as having a first end and a second end near the perimeter. The first and second ends are spaced a certain number of vias apart. This spacing between the first and second ends is found on each of the layers, and the respective spacings of the layers are not superimposed. The transformer according to the invention allows for better integration and facilitates the implementation of shielding to further limit the impact of leakage flux near the air gap. Minimizing induction at the interconnections reduces losses. All these aspects and advantages of the invention are detailed below. Figure 3 schematically represents an example of vias 27 arranged at the center of the winding 12 of an inductor 10 according to the invention. In this illustration, it should be considered that the scheme (b) is repeated six times and offset each time. This results in an inductor with 7 turns of a conductive electrical wire (therefore NI = 3), implemented in 8 layers (again, only three layers are shown for better readability of the figure). The winding 12 extends from the primary input terminal 13 to the primary output terminal 14. The use of vias at the center of the magnetic component simplifies the construction of the various windings. This allows for the reproduction of an elementary winding on each layer (b) to achieve the desired winding configuration. Only one turn is made per PCB layer. The transition between the different layers is achieved via the central vias 27. One or more vias can be used for this purpose, depending on the desired current in the windings and the size of the core 25 (and its central portion 26). This one-turn-per-layer configuration goes against established practice. Indeed, in power electronics, the number of turns is usually spread across a single layer (as shown in [Fig. 1]). Using one turn per layer here necessitates a large number of PCB layers if a high number of turns is desired. On the other hand, placing the vias in the center, around the edge of the opening, reduces layer-by-layer access resistances and frees up space around the component's periphery, allowing for better integration. Figure 4 schematically represents an example of the implementation of the primary 12 and secondary 22 bearings of a transformer 10 according to the invention. More specifically, the output winding is incorporated within the ring of central vias 27. In order to interlace the primary and secondary windings, the vias enabling the interconnections between the layers 17 are also interlace. The turns of the secondary winding can each be inserted between two turns of the primary winding and / or between a turn of the primary winding and a secondary winding. This configuration is advantageous for a transformer as it allows for better integration and facilitates the implementation of shielding to further limit the impact of proximity effects (and only in cases where the component has an air gap). Minimizing induction at the interconnections reduces losses. Figure 5 schematically represents the variation in current density according to a traditional air gap arrangement (left of the figure) and an air gap arrangement according to the invention (right of the figure). This representation is based on an illustration from the Schafer 2018 publication, Optimal Design of Highly Efficient and Highly Compact PCB Winding Inductors. According to the invention, the ferromagnetic core 25 comprises an air gap 29 extending along a second axis Z2 substantially perpendicular to the first plane 16. The use of a vertical air gap 29 is made possible by machining existing cores or raw material. Commercially available planar cores most often have an air gap arranged on the central leg, which causes the field to radiate in a direction parallel to the planar bearings (see illustration on the left).The configuration on the left of the figure represents a copper conductor in the center subjected to leakage fields emanating from the two air gaps in the magnetic core. The current densities are concentrated at the edges of the conductor, which reduces the efficiency of the solution. More precisely, in a traditional (horizontal) air gap arrangement, the magnetic field propagates through the core. At the air gap, the field lines radiate around it, and these field lines tend to concentrate the currents flowing in the conductor outwards, to such an extent that the current flows only on the outside, where the field lines concentrate it. In other words, only a small portion of the conductor is actually used. In the configuration on the right of the figure, corresponding to the invention, the leakage fields arrive perpendicularly to the conductor, which allows for a reduction in current density and therefore in losses.More specifically, in a vertical arrangement, the field radiates perpendicularly (see illustration on the right), which reduces the effects of proximity to the core and therefore decreases the current concentration at the ends of the electrical circuit. The currents are concentrated at the surface, and the entire conductor is used. This results in a positive impact on the radiation. Thus, the resistance of the winding is reduced. Figure 6 schematically represents the induction between the conductors according to the alternating turns of the primary and secondary windings. The lower part of the figure shows the conductors in a planar transformer. The layers labeled PI represent the primary conductors, while the layers labeled S1 represent the secondary conductors. On the left side of the figure, The turns of the primary winding and the turns of the secondary winding are arranged alternately, and the choice of the alternation mode is facilitated according to the invention. On the right side of the figure, the turns of the primary winding and the turns of the secondary winding follow one another, without any alternation between the primary and secondary windings. In the same diagram, the theoretical magnetic flux density profile is given (H). The magnetic flux density between the conductors increases the concentration of currents in them, which increases losses. It can be seen that without alternation, the maximum magnetic flux density obtained is greater than the maximum magnetic flux density obtained in the case of a transformer according to the invention (with alternating turns). This generates significant conduction losses between the two central layers (P1 and S1), which have a much higher resistance. Figure 7 schematically represents the homogenization of current density in the input and output terminals of the primary and secondary windings arranged according to an embodiment of the invention. This representation is based on an illustration from the Schafer 2018 publication, "Optimal Design of Highly Efficient and Highly Compact PCB Winding Inductors." In this embodiment of the invention, the input terminals 13, 23 are superimposed on the output terminals 14, 24 along a third axis Z3 substantially perpendicular to the first plane 16, as can be seen in the upper right of the figure. This avoids field concentration phenomena between the two planes. With the terminals positioned in two different parallel planes, the current is more evenly distributed throughout the plane and not just concentrated in the middle of a single plane.The lower part of the figure represents the results of a finite element simulation of the current density with adjacent terminals (on the left of the figure) and terminals superimposed according to the invention (on the right of the figure). The results show that interlacing the conductors reduces the induction between them and therefore the current concentrations. A vertical arrangement of the terminals homogenizes the current densities and thus reduces losses in the terminals. Figure 8 schematically represents a cross-sectional view, in a plane perpendicular to the first plane 16, of an example of the implementation of a shielding layer in a transformer according to the invention. In one embodiment of a transformer of the invention, at least one of the plurality of layers 27 is a shielding plane 31, preferably a ground plane. The shielding plane concentrates the eddy currents that generate losses. Thus, thanks to the shielding plane, these losses are generated in the shielding plane and no longer in the bearings. The aim is to limit the total losses. The equivalent resistance of the circuit depends on the various resistances in the circuit. With a shielding plane, this resistance... Resistance is reduced. The shielding plane 31 is most often a ground plane. The leakage field creates an induced current (eddy current) in this plane, which generates losses. The distance from the shield to the air gap, the shield thickness, and the distance from the shield to the conductor depend on the power involved, the operating frequency (and signal shape), and the desired performance relative to the component integration. In general, implementing the solution is beneficial if it reduces total losses. In the specific use case of a resonant converter, reducing the equivalent resistance of the conductors is a factor to consider. Limiting this resistance facilitates primary resonance and therefore smooth switching. In this particular case, it will also be necessary to consider the benefit of this operation on the magnetic sizing. The invention improves the overall performance of a planar magnetic component through a set of features with numerous advantages: The arrangement of the vias in the center in order to achieve the interconnection of the different different layers, particularly in the case of the transformer with the vias of the primary and secondary windings and flexibility in choice interlacing (that is, interspersed with each other); The presence of a shielding layer combined with a vertical air gap allows for limit the effect of leakage flux on conductors. In a re- configuration This advantage is all the more valuable; Optimizing output terminals to improve rectification synchronous. This advantage is particularly valuable in high-power converters output current and high operating frequency requiring the use of one or more GaN transistors. Figure 9 schematically represents a classic electrical circuit of a synchronous rectifier. In this figure, on the left is the transformer (ideal coupler), Rs represents the parasitic series resistance of the secondary winding and the routing, QR the synchronous rectifier transistor, and DQR and CQR the parasitic components associated with this transistor. Cout and Rout represent the output capacitance of the converter and the load, respectively. In the example we will examine, only two planes allow for the secondary winding. It is possible to imagine a different configuration to optimize performance (more copper in the secondary means less loss). Figure 10 schematically represents the optimization of the output terminals for synchronous rectification according to the invention. As described previously, The winding can be achieved using every other via group. By optimizing the transformer terminals, it is possible to improve secondary integration to minimize losses in synchronous rectification. Generally, a voltage drop is applied between the primary and secondary windings. This results in a lower secondary voltage than primary voltage, which also means higher secondary currents. Minimizing the resistance at the secondary terminals is desirable to optimize performance. In the figure, the current path to the output is minimized. This improvement leads to a reduction in the secondary resistance Rs and parasitic inductances. Furthermore, it allows for an easier increase in the number of transistors in the synchronous rectification circuit, which further reduces losses. Finally, it is thus possible to place the drivers as close as possible to the transistors, a critical point for GaN transistors for example. It can be emphasized that the optimization of the various parameters of the magnetic components discussed above is adaptable to most converter configurations. Thus, the invention comprises several technical features, which can be combined with each other, and whose technical effects are listed below: - Use of vias positioned in the center of the planar (near the central part). This configuration allows for easier distribution of the different windings without compromising external integration with the component. This arrangement also simplifies layer interleaving. - Use of a machined air gap on top of the magnetic core. Unlike a horizontal arrangement of the air gap, a vertical arrangement orthogonal to the windings limits the effects of proximity to the windings and therefore reduces copper losses, especially at high frequencies (>500 kHz). — Interleaving / superposition of terminals on a vertical plane. Interleaving reduces induction and therefore high current concentrations. The vertical arrangement allows the full cross-section of the planar conductors to be used, thus reducing AC resistance. - Use of shielding planes. Located as close as possible to the air gap, they limit the effects of proximity on the conductors. The vertical arrangement of the air gap combined with the shielding minimizes the effects of the air gap on the conductors. - Terminal optimization for GaN transistor integration. Since synchronous rectification operates at high frequency and high current, it is necessary to limit parasitic inductances and resistances in the secondary winding. An interleaved and optimized secondary winding arrangement increases the performance of this type of system. It will be more generally apparent to a person skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching that has just been disclosed to them. In the claims that follow, the terms used shall not be interpreted as limiting the claims to the embodiments set forth in this description, but shall be interpreted to include all equivalents that the claims aim to cover by virtue of their formulation and whose prediction is within the grasp of a person skilled in the art based on their general knowledge.

Claims

Demands

1. Transformer (10) comprising: a primary circuit (11) comprising a primary winding (12) of NI turns of a conductive electric wire, the winding primary (12) extending from a primary input terminal (13) to a primary output terminal (14); and a secondary circuit (21) comprising an en- secondary bearing (22) of N2 turns of an electrical wire conductor, the secondary winding (22) extending from a secondary input terminal (23) to a se- terminal secondary output (24), NI and N2 each being a number integer greater than or equal to | ; the transformer (10) being characterized in that it comprises: a printed circuit board (15) extending along a first plane (16), and comprising a plurality of layers (17-1, 17-2, 17-3, 17-4, 17-5, 17-6, 17-7) superimposed on each other and forming a opening (18) through the foreground (16) around a first axis (Z1) and defining a perimeter (19); a ferromagnetic core (25), arranged around the en- primary (12) and secondary (22) bearings, comprising a central part (26) arranged in the opening (18); a plurality of vias (27) arranged at the center of the windings primary (12) and secondary (22) on the perimeter (19) of the opening (18), and extending through the layers (17-1, 17-2, 17-3, 17-4, 17-5, 17-6, 17-7), each along an axis parallel to the first axis (Z1), the plurality of vias (27) being configured to interconnect the plurality of layers; in that the NI turns and the N2 turns of the electrical conductor wire are each arranged on one of the plurality of layers, according to an alternation any between N1 rounds and N2 rounds, each of NI rounds and N2 towers winding their way up, from a first via of the plurality of vias (27), partially around the plurality of vias (27) forming an arc of circle (28) by layer, towards a second via of the plurality of vias (27) and in that the arc of a circle (28) of a layer is distinctly oriented relative to the circular arcs (28) of the other layers and orientation distinct from the arcs of the other layers.

2. Transformer according to claim 1, wherein the ferroma- genetic (25) includes an air gap (29) extending along a second axis (Z2) substantially perpendicular to the first plane (16).

3. Transformer according to claim 1 or 2, wherein the terminals input terminals (13, 23) are superimposed on output terminals (14, 24) according to a third axis (Z3) approximately perpendicular to the foreground {16).

4. Transformer according to any one of claims 1 to 3, in of which at least one among the plurality of layers (27) is a plane of shielding (31), preferably a ground plane.