WO2023025674A1

WO2023025674A1 - Planar transformer

Info

Publication number: WO2023025674A1
Application number: PCT/EP2022/073180
Authority: WO
Inventors: Thomas WASSERBAUER; Markus Kratzer
Original assignee: Magna powertrain gmbh & co kg
Priority date: 2021-08-26
Filing date: 2022-08-19
Publication date: 2023-03-02
Also published as: DE102021209402A1

Abstract

The invention relates to a planar transformer (1) for energy transmission, comprising: a multi-layer circuit board (2) having at least three layers (L1, L2, L3, L4, L5, L6) to form electrical conductive tracks (16, 17, 18, 19); at least two current circuits which are galvanically separated from one another and of which a first current circuit comprises a primary winding and each additional one of these current circuits comprises a secondary winding of the planar transformer (1), the primary winding and each additional secondary winding being in the form of conductive tracks (16, 17, 18, 19) on an outer layer (L1, L6) and/or an inner layer (L2, L3, L4, L5) of the circuit board (2); a magnetic core (3a, 3b), which core (3a, 3b) at least partially surrounds the multi-layer circuit board (2) and penetrates the circuit board at least partially in the region of the primary winding and of the secondary winding and thus acts at least on the first current circuit and on the additional current circuit, an intermediate voltage being tapped on the penultimate turn of the secondary winding relative to an outermost and thus last turn of at least one secondary winding.

Description

planar transformer

field of invention

The present invention relates to a planar transformer for energy transmission, comprising a multi-layer printed circuit board with at least three layers for forming electrical conductor tracks, two of these layers each forming an outer layer of the printed circuit board and each additional layer forming an inner layer of the printed circuit board, at least two galvanically isolated layers Circuits, wherein a first circuit comprises a primary winding and each further of these circuits comprises a secondary winding of the planar transformer, wherein the primary winding and each further secondary winding are formed in the form of conductor tracks on an outer layer and/or an inner layer of the printed circuit board and a magnetic core, wherein the core at least partially encloses the multilayer printed circuit board and at least partially penetrates it in the area of the primary winding and the secondary winding and thus acts at least on the first circuit and on the further circuit.

State of the art

It is known from practice that transformers generally represent an important component for the electrical isolation of circuits in many electronic products, with both energy and signals and/or data being able to be transmitted via the transformer. A planar transformer is a special type of transformer. The essential components of the planar transformer are a magnetic core that is inserted into a printed circuit board and windings that are designed in the form of conductor tracks on the printed circuit board.

To realize an intermediate voltage tap in a winding of a For planar transformers in DC/DC converter applications, it is necessary to switch to another layer using a via, also called "VIA"("Vertical Interconnect Access"), which is usually routed through the entire circuit board for cost reasons to provide a connection for further use. A distance to the through-hole plating in all layers of the planar transformer must therefore be taken into account, especially in applications with required galvanic isolation of circuits and the associated insulation strength requirements. Due to the air and creepage distances to be maintained, these distances are often large. This reduces the filling factor of the winding and thus there is a reduction in the magnetic coupling, with the coupling factor being an important criterion for every transformer. The coupling factor determines the proportion of energy that can be transported to the secondary side(s) or how high the proportion of losses and voltage overshoots are at the switching transistor. A perfect coupling cannot be realized under real conditions - there are always voltage peaks at the switching transistor. RCD snubbers are commonly used to protect the transistor. These limit the height of the voltage peaks. The height of the voltage peaks depends on the magnetic coupling and the resulting so-called leakage inductance of the transformer.

Summary of the Invention

It is an object of the invention to provide an improved planar transformer.

This need can be met by the subject matter of the present invention according to independent claim 1. Advantageous embodiments of the present invention are described in the dependent claims.

The planar transformer according to the invention is used in particular for energy transfer carrying.

According to the invention, the planar transformer has a multi-layer printed circuit board with at least three layers for forming electrical conductor tracks, with two of these layers forming an outer layer of the printed circuit board and each additional layer forming an inner layer of the printed circuit board, at least two circuits that are galvanically isolated from one another, with a first Circuit comprises a primary winding and each further of these circuits comprises a secondary winding of the planar transformer, the primary winding and each further secondary winding being in the form of conductor tracks on an outer layer and/or an inner layer of the circuit board and a magnetic core, the core being the multi-layer circuit board at least partially encloses and at least partially penetrates this in the area of the primary winding and the secondary winding and thus acts at least on the first circuit and on a further circuit.

According to the present invention, an intermediate voltage tap is implemented on the penultimate turn of this secondary winding in relation to an outermost and thus last turn of at least one secondary winding. The number of turns must be selected in such a way that after the intermediate voltage tap, only one turn of the winding remains, thus significantly increasing the fill factor. In this respect, an intermediate voltage tap of a secondary winding of the planar transformer has the effect that two different voltage levels can be provided with the secondary winding—corresponding to the winding on which the intermediate voltage tap is attached or electrically conductively fixed. According to the invention, all turns of the secondary winding lie along a winding plane. For example, the secondary winding can have turns running spirally along the winding plane.

According to the invention, it can optionally be provided that a winding end of at least one secondary winding faces an upper side of the secondary winding assigned layer is performed and the Zwischenspannungsabgriff is led to a bottom opposite the top - or vice versa with respect to the top / bottom. Accordingly, the end of the winding and the intermediate voltage tap run along two opposite sides—top and bottom—of the layer.

The conductor tracks are preferably formed on at least one inner layer of the printed circuit board for all circuits.

In a preferred embodiment of the present invention, the core is formed in at least two parts, comprising a first core part and a second core part, with the first core part forming an E-shape with a base part and three legs, namely two outer legs and a middle leg, and the second core part with forms an I-shape in one part.

The printed circuit board preferably has three recesses, in each of which a leg of the first core part is inserted, with the outer legs thus at least partially penetrating the printed circuit board. The two outer legs are preferably connected to the second core part at the ends remote from the middle part of the first core part. An air gap is preferably realized on the middle leg.

In a preferred variant of the planar transformer, an “RCD snubber” is arranged directly above all turns, between a start and end of the primary winding on one of the two outer layers of the printed circuit board.

A planar transformer with a reduced leakage inductance is generated by means of the design of the planar transformer according to the invention, in particular the realization of an intermediate voltage tap in a winding space without the use of a VIA. A distance between the conductor tracks of the individual windings in the other layers and the VIA must be taken into account, especially in the case of applications of planar transformers with required galvanic isolation and the associated insulation strength requirements. Due to the air and creepage distances to be maintained, these distances are often large. The fill factor of the winding increases as a result of the design of the planar transformer according to the invention, in particular the intermediate voltage tap, as a result of which an increase in the magnetic coupling is achieved.

At the same time, this also reduces the leakage inductance of the transformer. The energy stored as a result can be dissipated again via the "RCD snubber". Since this energy must be dissipated very quickly, in the nanosecond range, it is advantageous if the current loop via the “RCD snubber” and the primary winding of the transformer is designed to be as small and as short as possible. Such an optimized arrangement is realized by the geometric arrangement of the “RCD snubber” according to the invention.

Brief description of the drawings

The invention is described below by way of example with reference to the drawings.

Fig. 1 shows a schematic cross-sectional view of a

planar transformer.

FIG. 2 shows a schematic representation of a layer structure of a planar transformer according to FIG. 1.

Fig. 3 shows a schematic representation of a circuit board of a

Planar transformer according to FIG. 1 with cutouts for a core. 4 shows a schematic representation (top view) of a primary winding in a third layer (first conductor track) and a fifth layer (second conductor track).

FIG. 5 shows a schematic representation (top view) of a primary winding according to FIG. 4 with vias.

Fig. 6 shows a schematic representation (top view) of a first

Secondary winding in a second layer (third track).

Fig. 7 shows a schematic representation (top view) of a first

Secondary winding according to FIG. 6 with vias.

8 shows a schematic representation (top view) of a second secondary winding in a fourth layer (fourth conductor track).

FIG. 9 shows a schematic representation (top view) of a second secondary winding according to FIG. 8 with vias.

Fig. 10 shows a schematic representation of FIG. 4 with a

"RCD snubber".

Detailed description of the invention

The one shown in Fig. 1 to Fig. 9 in different degrees of detail

Planar transformer 1 is used for energy transmission and has a printed circuit board 2 for forming electrical conductor tracks, three galvanically isolated circuits and a magnetic core 3a, 3b (Fig. 1).

The printed circuit board 2 is multi-layered, i.e. constructed like a sandwich, and comprises a total of six layers, namely a first layer L1, a second layer L2, a third layer L3, a fourth layer L4, a fifth layer L5 and a sixth layer L6 (Fig. 2 ).

As shown in FIGS. 1 , 2 and 3 , the circuit board 2 has a vertical extension along a direction Y and a horizontal extension along a direction X1 and a direction X2.

The individual layers L1, L2, L3, L4, L5, L6 are stacked one on top of the other along the Y direction, with the first layer L1 and the sixth layer L6 each being an outer layer of the printed circuit board 2 and the second layer L2, the third layer L3, the fourth Layer L4 and the fifth layer L5 each form an inner layer of the circuit board 2 (Fig. 2).

An insulation element is arranged in each case between the individual layers L1, L2, L3, L4, L5, L6. In the present exemplary embodiment, the printed circuit board 2 itself assumes this insulating function.

The magnetic core 3a, 3b encloses or partially covers the printed circuit board 2 on the outer layers L1, L6. The magnetic core 3a, 3b is composed of two interconnected magnetic core parts, namely a first core part 3a and a second core part 3b. The first core part 3a forms an E-shape with a base part 4 and three legs 5a, 5b, 6, namely two outer legs 5a, 5b and a middle leg 6. The second core part 3b forms an I-shape with a straight part ( FIG. 1 ).

In the circuit board 2 three recesses 7 are introduced, each with a

Legs 5a, 5b, 6 of the first core part 3a in one of these recesses 7 is used (Fig. 1, Fig. 3). The two outer legs 5a, 5b of the first core part 3a completely penetrate the printed circuit board 2 in direction Y and are connected to the second core part 3b at the ends of the outer legs 5a, 5b remote from the base part 4 of the first core part 3a. The middle limb 6 of the first core part 3a partially penetrates the printed circuit board in direction Y—in this way, an air gap 8 is realized in the area of the middle limb 6 of the first core part 3a.

As already mentioned above, the planar transformer 1 shown in FIGS. 1 to 9 has three circuits that are galvanically isolated from one another, namely a first circuit, a second circuit and a third circuit.

The first circuit, called the primary circuit in the following, includes a primary winding with five turns (Fig. 4, Fig. 5). The second circuit, hereinafter referred to as the first secondary circuit, includes a first secondary winding with three turns (FIG. 6, FIG. 7). The third circuit, referred to below as the second secondary circuit, includes a second secondary winding with five turns (FIG. 8, FIG. 9).

The primary winding and the two secondary windings are designed in the form of essentially spiral conductor tracks on the inner layers L2, L3, L4, L5 of the printed circuit board 2.

Current can be fed in via the primary circuit and at least one output current can be discharged via the secondary circuits for the purpose of energy transmission.

In the present exemplary embodiment, the five turns of the primary winding of the primary circuit are arranged on two layers, namely the third layer L3 and the fifth layer L5. Five turns of the primary winding are made on the third layer L3 and five turns on the fifth layer L5. Both partial windings of the primary winding, ie the five-turn partial winding on the third layer L3 and the five-turn partial winding ment on the fifth layer L5 of the primary circuit are connected to one another via a first via arrangement 9 and a second via arrangement 10 and connected in parallel. The first through-contact arrangement 9 and the second through-contact arrangement 10 each have two through-contacts in the present exemplary embodiment. However, each of these two via arrangements 9, 10 can also have only one via or more than two vias. For the sake of simplicity, the first through-contacting arrangement 9 and the second through-contacting arrangement 10 expediently run through the entire printed circuit board 2, ie through all layers L1, L2, L3, L4, L5, L6, and are continuously filled with electrically conductive material. For the arrangement of the five turns of the primary winding on the third layer L3, a first conductor track 16 is formed accordingly and for the other five turns of the primary winding a second conductor track 17 is formed on the fifth layer L5. The first conductor track 16 and the second conductor track 17 are each routed from the first through-contact arrangement 9 to the second through-contact arrangement 10 . The first via arrangement 9 and the second via arrangement 10 each form a connection a, b in the first layer L1. The primary circuit can be electrically contacted via the outwardly routed connection connections a, b, with the current flow taking place, for example, from connection connection a in the direction of connection connection b, although this does not necessarily have to be the case.

Furthermore, the three turns of the first secondary winding of the first secondary circuit are arranged on the second layer L2 of the circuit board 2 . For the arrangement of the three turns of the first secondary winding on the second layer L2 of the printed circuit board 2, a third conductor track 18 is formed accordingly on this. The third conductor track 18 is routed from a third via arrangement 11 to a fourth via arrangement 12 . The third through-contact arrangement 11 and the fourth through-contact arrangement 12 each have two through-contacts in the present exemplary embodiment. Each of these two via arrangements 11, 12 can however, also have only one via or more than two vias. For the sake of simplicity, the third through-contact arrangement 11 and the fourth through-contact arrangement 12 expediently lead through the entire printed circuit board 2, ie through all layers L1, L2, L3, L4, L5, L6, and are continuously lined with electrically conductive material. The third via arrangement 11 and the fourth via arrangement 12 each form a connection c, d in the first layer L1. Electrical contact can be made with the first secondary circuit via the outwardly routed connections c, d, with the current flow taking place, for example, from the connection c in the direction of the connection d, although this does not necessarily have to be the case.

An intermediate voltage tap is embodied on the third conductor track 18 at the penultimate turn of the first secondary winding in relation to an outermost and thus last turn of the first secondary winding of the first secondary circuit. This intermediate voltage tap is routed via a fifth via arrangement 13 to a connection e in the first layer L1. The fifth via arrangement 13 has two vias in the present exemplary embodiment. However, the fifth via arrangement 13 can also have only one via or more than two vias. For the sake of simplicity, the fifth via arrangement 13 runs through the entire printed circuit board 2, i.e. through all layers L1, L2, L3, L4, L5, L6, and is continuously filled with electrically conductive material.

Furthermore, the five turns of the second secondary winding of the second secondary circuit are arranged on the fourth layer L4 of the circuit board 2 . For the arrangement of the five turns of the second secondary winding on the fourth layer L4 of the printed circuit board 2, a fourth conductor track 19 is formed accordingly on this. The fourth conductor track 19 is routed from a sixth via arrangement 14 to a seventh via arrangement 15 . The sixth via arrangement 14 and the seventh via tion arrangement 15 each have two vias in the present exemplary embodiment. However, each of these two via arrangements 14, 15 can also have only one via or more than two vias. For the sake of simplicity, the sixth via arrangement 14 and the seventh via arrangement 15 expediently lead through the entire printed circuit board 2, ie through all layers L1, L2, L3, L4, L5, L6, and are continuously lined with electrically conductive material. The sixth via arrangement 14 and the seventh via arrangement 15 each form a connection f, g in the first layer L1. Electrical contact can be made with the second secondary circuit via the outwardly routed connections f, g, with the current flow taking place, for example, from the connection f in the direction of the connection g, although this does not necessarily have to be the case.

In this exemplary embodiment, all of the connection connections a, b, c, d, e, f, g, h are routed outwards into the first layer L1 of the printed circuit board 2 . However, it goes without saying that it would also be possible to route the connecting connections a, b, c, d, e, f, g, h into the further outer layer, namely the sixth layer L6.

In FIG. 10, an “RCD snubber” 20 is arranged on a primary winding as already shown in FIG. 4 and as previously described. The “RCD snubber” 20 has a diode D, a resistor R and a capacitor C. The "RCD snubber" 20 is arranged directly over the windings of the first conductor track 16 between a winding start 21 and a winding end 22 of the primary winding on the first layer L1 (or the last layer L6) of the printed circuit board 2, thereby creating the current loop between the winding start 21 and the winding end 22 of the primary winding are kept as short as possible. Reference character list

1 planar transformer

Circuit board a First core part b Second core part

base part

outer thigh

middle thigh

recesses

air gap

9 First via arrangement

10 Second via arrangement

11 Third via arrangement

12 Fourth via arrangement

13 Fifth via arrangement

14 Sixth via arrangement

15 Seventh via arrangement

16 First track

17 Second trace

18 Third track

19 Fourth track

20 "RCD snubber"

21 Start of the primary winding

22 Winding end of the primary winding

L1 First position

L2 Second layer

L3 Third position

L4 Fourth position

L5 Fifth position L6 Sixth layer

D diode

R resistance

C capacitor a, b, c, d, e, f, g terminal connections

X1 , X2, Y direction

Claims

Claims Planar transformer (1) for energy transmission comprising a multi-layer printed circuit board (2) with at least three layers (L1, L2, L3, L4, L5, L6) for forming electrical conductor tracks (16, 17, 18, 19), wherein two of these layers (L1, L6) each form an outer layer of the printed circuit board (2) and each additional layer (L2, L3, L4, L5) forms an inner layer of the printed circuit board (2), at least two circuits that are galvanically isolated from one another, with a first circuit a primary winding and each further of these circuits comprises a secondary winding of the planar transformer (1), the primary winding and each further secondary winding being in the form of conductor tracks (16, 17, 18, 19) on an outer layer (L1, L6) and/or an inner layer (L2, L3, L4, L5) of the circuit board (2), a magnetic core (3a, 3b), wherein the core (3a, 3b) at least partially encloses the multi-layer circuit board (2) and this in the area of primary winding and the second The primary winding penetrates at least partially and thus acts at least on the first circuit and on the further circuit, characterized in that an intermediate voltage tap is implemented on the penultimate turn of the secondary winding in relation to an outermost and thus last turn of at least one secondary winding. Planar transformer (1) according to claim 1, characterized in that the conductor tracks (16, 17, 18, 19) for all circuits on at least one inner layer (L2, L3, L4, L5) of the printed circuit board (2) are formed. Planar Transform ator (1) according to claim 1 or 2, characterized in that the core (3a, 3b) at least two parts to comprising a first core part (3a) and a second core part (3b), the first core part (3a) having a base part (4) and three legs (5a, 5b, 6), namely two outer legs (5a, 5b ) and a middle leg (6), forms an E-shape and the second core part (3b) forms an I-shape. Planar transformer (1) according to Claim 3, characterized in that the printed circuit board (2) has three recesses (7) and one leg (5a, 5b, 6) of the first core part (3a) in each case in one of these recesses (7 ) is inserted and thus penetrates the printed circuit board (2) at least partially and that at least the two outer legs (5a, 5b) of the first core part (3a), at the ends remote from the base part (4) of the first core part (3a), connect to the second Core part (3b) are connected. Planar transformer (1) according to any one of claims 1 to 4, characterized in that an "RCD snubber" (20) directly over all turns between a winding start (21) and a winding end (22) of the primary winding on one of the two Outer layers (L1, L6) of the circuit board (2) is arranged. Planar transformer (1) according to any one of claims 1 to 4, characterized in that a winding end of at least one secondary winding is routed to an upper side of the layer associated with the secondary winding and the intermediate voltage tap is routed to an underside opposite the upper side. Planar transformer (1) according to any one of claims 1 to 4, characterized in that the winding end of at least one secondary winding is routed to the underside of the layer associated with the secondary winding and the intermediate voltage tap is routed to the top side opposite the underside.