Planar transformer for energy transmission

Abstract

Planar transformer (100) for energy transmission having a vertical dimension and a horizontal dimension - a sandwich-like constructed printed circuit board (7) with at least three layers (L1, L2, L3) for forming electrical conductors (1a, 1b, 2a, 2b, 3a, 3b), wherein a first and a second of these layers form outer layers (L1, L2) of the printed circuit board (7) and each further of these layers forms an inner layer (L3) of the printed circuit board (7), and wherein an insulating material (y) with a minimum thickness is arranged between all these layers (L1, L2, L3), - a number of at least three galvanically isolated circuits (1, 2, 3), wherein a first circuit (1) forms a primary circuit, a second circuit (2) a first secondary circuit, and each further circuit (3) a further equivalent secondary circuit of the planar transformer (100), and wherein current is fed in via the primary circuit (1) for energy transfer and an output current is carried out via the secondary circuits (2, 3), - a magnetic core (5) that at least partially encloses the sandwich-like structure of the circuit board (7) and acts at least on the first circuit (1), on the second circuit (2) and on the third circuit (3); - wherein the magnetic core (5) is composed of two interconnected magnetic core parts (5a, 5b), wherein a first core part (5a) forms a U-shape with a central part (5m) and two outer legs (5s1, 5s2), and wherein the circuit board (7) has two recesses (7a, 7b) and the two outer legs (5s1, 5s2) of the first core part (5a) are inserted into these recesses (7a, 7b) and are connected at their ends, away from the central part (5m), to the second core part (5b), wherein for exactly one single circuit (1) of the at least three circuits (1, 2, 3) has a conductor track (1a, 1b) on at least one of the outer layers (L1, L2) and for all further of the at least three circuits (1, 2, 3) conductor tracks (2a, 2b, 3a, 3b) are formed on an inner layer (L3) or several inner layers - and wherein a conductor track (1a, 1b, 2a, 2b, 3a, 3b) of at least one circuit (2) of the at least three circuits (1, 2, 3) is wound only around a first outer leg (5s1) and conductor tracks (1a, 1b, 2a, 2b, 3a, 3b) of at least two further circuits (1, 3) of the at least three circuits (1, 2, 3) are wound around the second outer leg (5s2).

Description

[0001] The present invention relates to a planar transformer for energy transmission.

[0002] Transformers are often used for the galvanic isolation of circuits according to various standards. Depending on the design of the transformers, they can transmit energy, signals and / or data.

[0003] Planar transformers, i.e. transformers which are characterised by a flat construction due to a special design, are used for energy transmission, particularly in the context of isolation amplifiers, which can provide galvanic isolation of several circuits and / or connect different AC voltage levels.

[0004] JP 2013 - 175657 A describes a planar transformer comprising a multilayer substrate with multiple substrate layers separated from one another by an insulation layer. Furthermore, each of the substrates has conductive structures that can be interconnected via vias. Furthermore, the planar transformer comprises a core with a first core portion and a second core portion, wherein the first core portion can be passed through the multilayer substrate with the aid of openings.

[0005] US 2007 / 0139151 A1 describes a coil on a printed circuit with several layers that can be connected to each other via vias.

[0006] Furthermore, WO 2011 / 047819 A1 describes an inductive electronic assembly for providing a transformer, in particular in planar technology.

[0007] US 2006 / 0 152 326 A1 discloses a planar transformer arrangement for use in an implantable medical device, which comprises a circuit board and two cores, as well as a secondary winding located on inner layers of the planar transformer arrangement and a secondary winding located on outer layers of the planar transformer arrangement.

[0008] US 2012 / 0 112 866 A1 also describes a coil transformer which has a very flat design with improved heat radiation and several layers.

[0009] A highly simplified block diagram concerning the use of a transformer within an isolation amplifier for galvanic isolation between a primary circuit and at least one secondary circuit in the signal processing of analog signals is shown in the attached Fig. 15.

[0010] Accordingly, during operation, an input signal to be processed, in particular an analog input voltage or an analog input current, is applied to the connection marked 1, and the connection marked 2 is connected to ground (GND1).

[0011] With regard to the Fig. In the signal processing chain outlined in Figure 15, the analog input signal is generally fed to an input signal processing circuit, and the signal processed via this circuit is then applied, for example, to the primary circuit of a transformer adapted for signal transmission. The signal is tapped via the secondary circuit of the transformer and fed to an output signal processing circuit, which may include, for example, an amplifier circuit and possibly also a filter circuit, before the output signal can be tapped at the connection marked 5 at the end of the signal processing chain. The connection marked 6 is in turn connected to ground (GND2). By means of the transformer adapted for signal transmission, the input signal processing circuits and the output signal processing circuits can therefore be galvanically isolated from one another.

[0012] With regard to the Fig. 15, also outlined in Figure 15, for supplying individual active circuits in the signal processing chain with the necessary operating voltage, a separate transformer is typically used, adapted for power transmission. In the illustrated case, this transformer ensures galvanic isolation of a primary circuit and two secondary circuits. A power supply circuit is connected to the primary circuit of the transformer via the connection marked 7, which provides, for example, an input voltage of 20 to 30 V. The connection marked 8 is in turn connected to ground (GND3).

[0013] Energy is then transferred to the voltage supply via one of the secondary circuits, e.g. the input signal processing circuit, and via the other secondary circuit, e.g. the amplifier circuit. The currents in the primary and secondary circuits are therefore much greater than the currents in the circuits of a transformer adapted for signal transmission, which generally leads to significantly increased heat generation. Furthermore, the smaller the transformer is, the greater the heat generation. However, this in turn runs counter to the general aim of continually miniaturizing electrical and electronic components.Although the heat generated by electronic components can often be dissipated to the environment by convection, this can often no longer be guaranteed, even with the aid of ventilation openings, due to the increasing volume-specific heat output of such components due to miniaturization, and can consequently lead to the risk of exceeding the permissible component temperatures.

[0014] Furthermore, transformers for power transmission are often housed in devices together with other electrical / electronic components, with a plurality of such devices arranged adjacent to one another, e.g., along a mounting rail. This leads to a further significant increase in overall heat generation and consequently requires the use of additional heat dissipation elements, e.g., a heat sink arranged between each two such devices, as provided, for example, in DE 10 2008 059 320 A1.

[0015] Depending on the application of such or similar isolation amplifiers, intrinsically safe galvanic isolation of individual or all circuits may be necessary for energy transmission, particularly in the case of circuits used in Ex areas, i.e. in potentially explosive areas, which must be supplied with energy.

[0016] Intrinsically safe means that the transformer's geometry is designed and optimized to ensure a specific level of protection against interference and to ensure prescribed separation distances. This can generally be achieved using wound coils as well as coils printed or etched onto circuit boards. The advantage of printed or etched coils is that no additional winding processes are required and good reproducibility can be guaranteed. Further advantages include fundamentally improved thermal properties compared to wound coils with the same core volume, and lower manufacturing costs.

[0017] DE 41 37 776 discloses a high-frequency power transformer using multilayer technology. Based on an EE core, it forms primary and secondary windings on various multilayer plates, each with a core hole for accommodating at least the middle leg of the core. Consequently, the circuit routing is limited horizontally by the two outer legs, and any separate circuits must necessarily be formed in different layers. This leads to a large vertical expansion and, if heat dissipation is necessary, requires correspondingly larger dimensions.

[0018] WO 03 / 003391 A1 discloses an EI or EE transformer that has two coils wound around the central web and two coils wound around the same outer leg. This allows for two primary and two secondary coils to be implemented, with the first primary and secondary coils forming a first transmission path and being arranged around the central web, and the second primary and secondary coils forming a second transmission path and being arranged around the outer leg. This transformer is therefore not suitable for applications in which energy is to be transmitted from one primary circuit to two secondary circuits, where galvanic, particularly intrinsically safe, isolation must be provided for all three circuits.

[0019] Planar transformers (or planar transmitters) are also known in which individual turns or (partial) windings or even entire circuits of the transformer are arranged essentially next to one another in one plane. This enables a flat design, so that the transformer can, for example, also be integrated into devices with a low overall height. For example, the prior applications DE 10 2012 016 569 A1 and DE 10 2012 003 364 A1 of the present applicant describe planar transmitters which have a layered structure with a plurality of circuits, wherein a first circuit can be a primary winding and is galvanically isolated from a second circuit, which can be a secondary winding, and with at least one magnetic core. The first circuit and the second circuit therefore lie essentially in a horizontal plane and form a layer within the layered structure.In the planar transformer according to DE 10 2012 016 569 A1, at least the first circuit or the second circuit is further divided into a plurality of galvanically isolated circuits, wherein the galvanically isolated circuits of the first circuit or the second circuit are arranged vertically one above the other. In the planar transformer according to DE 10 2012 003 364 A1, the circuits each extend vertically into a plurality of subcircuits, which are electrically connected to one another by connecting elements.

[0020] In order to maintain prescribed separation distances between the circuits, including their turns or (partial) windings, and from the magnetic core, according to both prior applications, the turns or (partial) windings of the circuits are each formed on inner layers of the layered structure and led to the outside via through-holes for electrical contact. For example, if a minimum insulation thickness of T0 is prescribed as the separation distance in a solid insulation medium between two galvanically isolated circuits, the prior applications teach that and how this thickness is to be maintained between all galvanically isolated circuits, including their turns or (partial) windings, and that and how only half such a thickness is to be maintained from the magnetic core.

[0021] The classic approach to dimensioning planar transformers can therefore be seen as positioning all windings or (partial) windings on top of each other around a common hole on the circuit board in a multi-layer structure, whereby the thickness of the individual insulation layers must be selected according to the insulation requirements. A magnetic core is passed through a central hole. To close the resulting magnetic circuit, two additional holes are typically made in the circuit board and the magnetic core is also passed through these. To close the magnetic circuit without splitting the circuit board, the magnetic core consists of two parts that are either glued or clamped together. The cores used in this way are, for example, E cores or ER or EQ cores.

[0022] The stacked arrangement of the windings or (partial) windings of circuits achieves a high main inductance and good coupling or low stray inductance, which has a positive impact on signal quality. A disadvantage is that complex circuit board technology is required for high insulation requirements and many windings or (partial) windings of different circuits that need to be galvanically isolated.

[0023] This disadvantage can be avoided by arranging the windings or (partial) coils partly side by side and partly one above the other. This simply requires two holes to be made in the circuit board, e.g., by milling, through which one leg of a U-shaped magnetic core is inserted. Here, too, the magnetic circuit is closed by using two partial cores.

[0024] At least one turn or (partial) winding is placed around each hole. This allows some of the insulation requirements to be shifted to the horizontal plane. This measure makes the planar transformer thinner and allows for fewer layers, which is advantageous for cost reasons. The potential disadvantage of resulting lower coupling or higher stray inductance can often be compensated for by circuit design.

[0025] If planar transformers or planar transformers for isolation amplifiers or similar functions are required, there are often special requirements for the insulation properties of the transformers. This is expressed, for example, in clearance and creepage distances of a few millimeters for insulation strengths in the kV range, which are regulated in special standards and regulations. However, there are also safety distances between the individual galvanically isolated windings within the printed circuit boards. For example, the DIN EN 61010-1 standard specifies that for voltage classes up to 300 V, two conductors belonging to different circuits or windings and arranged next to each other on the same inner layer must be at least 0.4 mm apart. There are also special requirements for the dielectric strength of the individual insulation layers of the PCB's layer structure. This applies, for example, toTwo conductor tracks of different circuits or windings that intersect at different layers. To meet insulation requirements, a certain minimum thickness of the individual insulation layers may be required.

[0026] If planar transformers are to be dimensioned for explosion-hazard areas, the requirements are often even stricter. For example, according to DIN EN 60079-11, conductor tracks with solid insulation must not be less than 1 mm thick for voltage class 375 V and protection level ia, ib. This applies to conductor tracks on the inner layers of a printed circuit board, both horizontally (side by side on the same layer) and vertically (on top of each other on different layers with an insulation layer between them).

[0027] Clearances and creepage distances on the surface of the printed circuit board are designated LS in the following description, solid insulation in the horizontal direction with "x" and in the vertical direction with "y". If there are several circuits with different insulation requirements, LSij can be used to access the insulation between circuit i including its turns or winding and circuit j including its turns or winding for better clarity. For example, LS23 would characterize the clearance and creepage distance between circuit 2 and circuit 3.

[0028] By using special coatings, clearance and creepage distances can be partially avoided or reduced. Certain standards also stipulate that clearance and creepage distances can be divided; for example, a required clearance of 5 mm can be divided into two 2.5 mm sections. This may be necessary, for example, because the magnetic core is generally assumed to be electrically conductive. For example, the primary circuit to the magnetic core can have a clearance and creepage distance of 2.5 mm, and the magnetic core to the secondary circuit can also have a clearance and creepage distance of 2.5 mm. The core is then at a virtual "intermediate potential."

[0029] It is an essential object of the invention to further improve heat dissipation in a planar transformer for energy transmission, which is intended to provide at least three galvanically isolated circuits, in particular also with improved utilization of the volume enclosed by the vertical and horizontal expansion of a planar transformer, in order to expediently simultaneously advance the further miniaturization of electrical and / or electronic components, so that such a planar transformer can also be used in particular within isolating amplifiers, wherein additional heat sinks can preferably also be dispensed with in the adjacent arrangement of a large number of devices with such isolating amplifiers, e.g. along a mounting rail.The aim of the invention is therefore, in particular, to provide a planar transformer with as many galvanically “well” (i.e. high insulation classes) separated circuits as possible, including their turns or windings, using the most cost-effective printed circuit board technology.

[0030] The invention solves the problem in a surprising manner by an article having the feature of claim 1, wherein preferred embodiments are the subject of the subclaims.

[0031] Accordingly, a planar transformer for energy transmission with a vertical extension and a horizontal extension is provided, which has a sandwich-like printed circuit board with at least three layers for forming electrical conductor tracks, wherein a first and a second of these layers form outer layers of the printed circuit board and each further of these layers forms an inner layer of the printed circuit board, and wherein an insulating material with a minimum thickness is arranged between all of these layers. Furthermore, a number of at least three electrically isolated circuits is included, wherein a first circuit forms a primary circuit, a second circuit forms a first secondary circuit, and each further circuit forms a further equal secondary circuit of the planar transformer. For energy transmission, current is fed in via the primary circuit and an output current is discharged via the secondary circuits.A magnetic core at least partially encloses the sandwich-like structure and acts on at least the first, second, and third circuits. The magnetic core is composed of two interconnected magnetic core parts, wherein a first core part forms a U-shape with a central part and two outer legs. The circuit board has two recesses, and the two outer legs of the first core part are inserted into these recesses and connected to the second core part at their ends remote from the central part.For exactly one single circuit of the at least three circuits, a conductor track is formed on at least one of the outer layers and for all further circuits of the at least three circuits, conductor tracks are formed on one inner layer or several inner layers, wherein a conductor track of at least one circuit of the at least three circuits is wound only around a first outer leg and conductor tracks of at least two further circuits of the at least three circuits are wound around the second outer leg.

[0032] A suitable embodiment provides that conductor tracks are formed on one and the same inner layer for at least two further circuits of the at least three circuits.

[0033] A suitable embodiment provides that for each conductor track formed on a layer for forming electrical conductor tracks, at least one end is electrically connected to a through-plating, which is electrically connected to a connection arranged on another layer for electrically contacting the conductor track.

[0034] A useful further development provides that the through-hole connection is continuously routed through all layers of the circuit board and is lined with electrically conductive material.

[0035] A supplementary or alternative development provides that a specified minimum distance of an air and creepage distance between two circuits determines the minimum distance between the through-contact of a circuit and the edges of the two recesses.

[0036] A further supplementary or alternative development provides that a through-plating associated with a conductor track wound around an outer leg is always arranged in the interior of the conductor track wound around the outer leg.

[0037] Further expedient embodiments provide that for at least one of the circuits, conductor tracks are wound around both outer legs and / or are formed on two different layers.

[0038] A further advantageous embodiment provides that the planar transformer according to the invention is integrated in the housing of an isolation amplifier.

[0039] Further expedient embodiments provide that at least one conductor track formed on an outer layer is coated with a protective varnish and / or the core is assigned to the potential of the conductor track formed on an outer layer with regard to the galvanic isolation of the circuits.

[0040] As a PCB technology, a standard multilayer stackup is therefore considered, typically with four or six layers. The thicknesses of the insulation layers are selected depending on the insulation requirements. It is also possible for an insulation layer to be composed of several sublayers.

[0041] In such a layered structure in standard printed circuit board technology, there are conductive inner and outer layers separated from each other by insulating layers. The insulating layers can be cores or so-called "prepregs" (pre-impregnated fibers). Preferably, conductive paths of a common circuit between different layers are connected to each other using vias through all layers.

[0042] Particularly preferred within the scope of the invention is only such "normal" vias. However, there are also other contacting options that, for example, only extend from one specific layer to another, particularly to a layer adjacent to a specific layer. However, such technologies are more complex to manufacture and therefore more expensive.

[0043] When using the preferred standard technology with vias through all layers, which vias are consequently also expediently lined with electrically conductive material, the invention expediently takes into account that minimum distances to these vias are also maintained if necessary. If, for example, in a winding which is arranged in a 4-layer structure with a respective partial winding on the outer layer 1 and on the outer layer 4, the two partial windings on layers 1 and 4 are to be connected to one another, the vias also go through layers 2 and 3. Thus, in the practical implementation of the invention, another winding which is arranged, for example, on the inner layer 2, maintains a minimum distance from the via. This means that, for example, a certain area on the circuit board cannot be used.Conversely, the first winding must also maintain safety distances (air and creepage distances) to each via of the second winding, since each via for the second winding is also conveniently present on the outer layers.

[0044] Consequently, the invention makes it possible to manage with as few layers as possible, whereby the layer structure can also be extended to a 4-, 5-, 6-, 7-, 8- or even more layer structure, and thus additional inner layers and also insulation layers can be added.

[0045] Another relevant aspect is the preferred use of a protective varnish, in particular a solder resist. If conductor tracks are formed on outer layers to form windings of a circuit of the planar transformer, it may happen that the magnetic core is located in the immediate vicinity of these conductor tracks. Expedient embodiments of the invention even provide for the magnetic core to lie directly above these conductor tracks or even to be glued there. Since the magnetic core can have a certain electrical conductivity (albeit typically poor), and this conductivity is in turn detrimental to function due to resulting eddy currents and losses, this magnetic core is not considered an insulator within the scope of the invention. To prevent the core from directly short-circuiting the individual turns of a winding, protective varnish, in particular a solder resist, is preferably used.This ensures appropriate insulation of the (partial) winding arranged on an outer layer from the magnetic core located directly above it. However, since the protective varnish often has only low insulating properties, it is not included in the calculation of the insulating properties within the scope of the invention. This means that, for mathematical purposes, the magnetic core is expediently placed at the same potential as the (partial) winding arranged on an outer layer. This, in turn, leads to the fact that only the turns of a single winding are preferably applied to both outer layers, since the core is located in close proximity to both outer layers and the insulating properties of a protective varnish are generally not sufficient to insulate two windings from each other.However, if only the turns of a single winding are located on the outer layers, the potential of the magnetic core is assigned to this winding within the scope of the invention, and there is a single potential on both outer layers in the area of ​​the core, the associated holes, and the conductor tracks on the outer layers, to which all other windings must maintain corresponding clearance and creepage distances. This will be explained in more detail in the following exemplary embodiments.

[0046] Key advantages and features of the invention can be seen in the fact that, using just a few layers (typically 4, max. 6), standard printed circuit board technology, and a "simple" U-shaped core, highly flexible planar transformers with multiple windings and customized insulation requirements can be generated. This makes it possible, for example, for the first time to realize a quadruple transformer with one core and a 4-layer layout. These and other advantages and features of the invention will also become apparent from the following description of some exemplary embodiments with reference to the accompanying drawings. They show: Fig. 1 an equivalent circuit diagram of a transformer comprising four circuits, Fig. 2 a schematic view of a planar transformer according to the invention for realizing the equivalent circuit according to Fig. 1 and with the circuit board kept transparent for display purposes, Fig. 3 a schematic sectional view through the planar transformer according to Fig. 2, Fig. 4 a schematic detail from the sectional view according to Fig. 3, Fig. 5 a schematic plan view opposite to the y-direction according to Fig. 2 to a printed circuit board layer of the planar transformer forming a first outer layer of the printed circuit board according to Fig. 2, Fig. 6 a schematic plan view opposite to the y-direction according to Fig. 2 to a printed circuit board layer of the planar transformer forming a first inner layer of the printed circuit board according to Fig. 2, Fig. 7 a schematic plan view opposite to the y-direction according to Fig. 2 on a printed circuit board layer of the planar transformer forming a second inner layer of the printed circuit board according to Fig. 2, Fig. 8 a schematic plan view opposite to the y-direction according to Fig. 2 on a printed circuit board layer of the planar transformer forming a second outer layer of the printed circuit board according to Fig. 2, Fig. 9 is a schematic plan view of a device according to the arrangement Fig. 5 and Fig. 8 modified design of conductor tracks wound on the outer layers of a printed circuit board within the scope of the invention, Fig. 10 an equivalent circuit diagram of a transformer comprising three circuits, Fig. 11 is an equivalent circuit diagram of a four-circuit transformer with center tap, Fig. 12 a first schematic view of a planar transformer according to the invention for realizing the equivalent circuit diagram according to Fig. 11 and with the circuit board kept transparent for illustration purposes, Fig. 13 another schematic view of the planar transformer according to Fig. 12 with transparent circuit board, Fig. 14 a schematic sectional view through the planar transformer according to Fig. 12, Fig. 15 a highly simplified diagram concerning the use of a transformer within an isolation amplifier for the galvanic isolation of analog signals.

[0047] All figures are schematic representations and are not to scale. Similar or identical elements are designated by the same reference numerals throughout the figures.

[0048] The following will first be based on the Fig. 1 to 8, preferred embodiments according to the invention are discussed in more detail.

[0049] A preferred embodiment of a planar transformer for energy transmission according to the invention is intended, for example, to be the Fig. 1 shown equivalent circuit diagram of a transformer.

[0050] Accordingly, the winding of a first circuit 1 should comprise, for example, 10 turns and form a primary circuit of the planar transformer for supplying current for energy transmission. The winding of a second circuit 2 should comprise, for example, 4 turns and form a first secondary circuit of the planar transformer for dissipating current. The winding of a third circuit 3 should comprise, for example, 13 turns and form a second secondary circuit of the planar transformer for tapping current. According to the equivalent circuit diagram according to Fig. 1, in a suitable embodiment, a fourth circuit 4, for example, should further comprise a winding with 13 turns and form a third secondary circuit of the planar transformer for dissipating current.

[0051] Viewed clockwise and starting from the primary circuit (circuit 1) and moving on to the secondary circuits (circuits 4, 2, and 3), a 4-way transformer with a turns ratio of 10:13:4:13 is to be implemented. For energy transfer, current is fed into one "way" and discharged from three "ways," meaning that, within the scope of the invention, energy is transferred from one primary circuit to three secondary circuits. A sandwich-type printed circuit board with four layers is sufficient for forming electrical conductors. In a preferred embodiment, all turns of the circuits should also be designed for intrinsically safe isolation of 300V in accordance with DIN EN 61010 and have a test voltage of 3 kV. This results in a clearance and creepage distance LS of 5.2 mm between all 4 windings, i.e. LS12 = LS13 = LS14 = LS23 = LS24 = LS34 = LS = 5.2 mm. Where: LS12 the clearance and creepage distance between circuits 1 and 2, LS13 the clearance and creepage distance between circuits 1 and 3, LS14 the clearance and creepage distance between circuits 1 and 4, LS23 the clearance and creepage distance between circuits 2 and 3, LS24 the clearance and creepage distance between circuits 2 and 4 and

[0052] LS34 the clearance and creepage distance between circuits 3 and 4.

[0053] The letters A to F are Fig. 1 respective exposed connection connections for electrical contacting of the windings are marked from the outside.

[0054] A practical construction of an equivalent circuit diagram according to Fig. 1 corresponding planar transformer for energy transmission according to the invention is Fig. 2 to 8.

[0055] In Fig. 2 shows a schematic view of such a planar transformer according to the invention, designated as a whole by the reference numeral 100.

[0056] The planar transformer 100 for energy transmission has a vertical extension, in particular along the direction marked Y according to Fig. 2, and a horizontal extension, in particular along the direction marked x1 and along the direction marked x2 according to Fig. 2.

[0057] The planar transformer 100 has a sandwich-like printed circuit board 7 with at least three layers for forming electrical conductor tracks, as shown in particular in the Fig. 3 to 8. A first and a second of these layers, e.g. according to Fig. 4 the layers L1 and L2, form outer layers of the printed circuit board and each further of these layers, e.g. according to Fig. 4, layers L3 and L4, an inner layer of the circuit board. A suitable insulating material with a specific minimum thickness is arranged between each of these layers, whereby the relevant teachings of DE 10 2012 003 364 A1 and / or DE 10 2012 016 569 A1 are incorporated into the disclosure content within the scope of the present invention, as part of the knowledge of the person skilled in the art.

[0058] A schematic view against the y-direction according to Fig. 2 to the PCB layer L1 of the planar transformer, which in the present example forms a first outer layer of the PCB, is in Fig. 5, a schematic plan view opposite the y-direction according to Fig. 2 to the PCB layer L3 of the planar transformer, which in the present example forms a first inner layer of the PCB, is in Fig. 6, a schematic plan view opposite the y-direction according to Fig. 2 to the PCB layer L4 of the planar transformer, which in the present example forms a second inner layer of the PCB, is in Fig. 7 and a schematic plan view opposite the y-direction according to Fig. 2 to the PCB layer L2 of the planar transformer, which in this example forms the second outer layer of the PCB, is in Fig. 8 shown.

[0059] As in particular the Fig. 2 to 4, a magnetic core, designated overall by the reference numeral 5, at least partially encloses the sandwich-like structure. The magnetic core 5 is composed of two interconnected magnetic core parts, wherein a first core part 5a forms a U-shape with a central part 5m and two outer legs 5s1 and 5s2 extending from this central web, wherein this U-shape can, in particular within the scope of the invention, also transition into a C-shape or V-shape. Two recesses 7a and 7b are made in the circuit board 7, and the two outer legs 5s1 and 5s2 of the first core part are inserted into these recesses. The second core part 5b is connected to the first core part 5a at the ends of the outer legs 5s1 and 5s2 remote from the central web 5m.

[0060] In the present example, the second core part 5b also has a U-shape, so that in this case the two core parts 5a and 5b are expediently connected to each other via the ends of the outer legs remote from the central part. It will be apparent to a person skilled in the art that the outer legs 5s1 and 5s2 therefore do not have to completely penetrate the recesses 7a and 7b, but that the respective interconnected outer legs can also be connected to each other within the sandwich-like printed circuit board, as is the case, for example, with the Fig. 3 and Fig. 4. Alternatively, the second core part 5b can, for example, also have merely an elongated web or a plate and form an approximately I-shape. In this case, the two core parts 5a and 5b would be connected to one another via the ends of the outer legs 5s1 and 5s2 remote from the central part 5m with the elongated web of the second core part, with the outer legs 5s1 and 5s2 then expediently completely penetrating the recesses 7a and 7b.

[0061] The Fig. 2 to 8 it can be seen that the planar transformer shown has a number of at least three circuits 1, 2, 3. These are furthermore galvanically isolated from each other, according to the above explanations regarding Fig. 1 in a preferred embodiment, in particular intrinsically safe galvanically isolated. A first circuit 1 can therefore form a primary circuit, a second circuit 2 a first secondary circuit and the third circuit 3 a second secondary circuit equal to the first secondary circuit, wherein the magnetic core 5 acts at least on the first circuit 1, on the second circuit 2 and on the third circuit 3. Consequently, current can be fed in via the primary circuit and an output current can be discharged via the equal secondary circuits for the purpose of energy transmission, in particular The feed and discharge takes place in particular via the exposed connection connections for electrical contacting of the windings. Fig. The planar transformer shown in Figures 2 to 8 is used to implement the equivalent circuit diagram according to Fig. 1, a fourth circuit 4 is further configured such that, in the present example, it forms a secondary circuit of equal importance to the first two secondary circuits. In this case, the magnetic core 5 thus acts at least on the first circuit 1, the second circuit 2, the third circuit 3, and the fourth circuit 4.

[0062] For exactly one single circuit, a conductor track is formed on at least one of the outer layers, according to the illustrated embodiment for the circuit 1. It should be noted here that external supply lines on outer layers, which are also provided as conductor tracks that are far enough away, for example, are not taken into account, e.g. a connection contact on the outer layer to via 6-2 on connection C.

[0063] In detail, in the present example, the 10 turns of the winding of this circuit 1, which serves as the primary circuit, are arranged on the two outer layers L1 and L2. Five turns on layer L1 and five turns on layer L2. For the arrangement of the first five turns on layer L1, a conductor track 1a is formed accordingly. Correspondingly, for the other five turns on layer L2, a conductor track 1b is formed on layer L2. The conductor track 1a is separated from the outwardly led connection A ( Fig. 5) to a through-plating 6-1 and the conductor track 1b is led from the through-plating 6-1 to the outwardly led connection B ( Fig. 8). The through-plating 6-1 leads from layer L1 through the entire circuit board to layer L2 and, for the sake of simplicity, is conveniently lined with electrically conductive material throughout. Both partial windings, i.e. the five-turn partial winding on layer L1 and the five-turn partial winding on layer L2, of circuit 1 are consequently connected to one another via the through-plating 6-1 across all layers and connected in series. The circuit can be electrically contacted with a circuit belonging to circuit 1 (not shown in the figures for reasons of clarity) at the externally led connections A and B, whereby the current flow is thereby used to implement the equivalent circuit diagram according to Fig. 1, for example, from connection A towards connection B. It should be noted that the current flow does not necessarily have to go from A to B (alternating signals). The points in the equivalent circuit only indicate the winding direction. If the winding direction is the same, a positive signal edge at one winding results in a positive edge at the other winding. If the winding direction is the opposite, a positive signal edge at one winding results in a negative edge at the other winding, and vice versa.

[0064] Furthermore, for all further circuits of the at least three circuits, ie according to the present embodiment for circuits 2, 3 and 4, conductor tracks are formed on one inner layer or several inner layers.

[0065] According to the embodiment shown, a conductor track 2a or 3a is formed for the circuit 2 and 3, for example, on the layer L3, as is the Fig. 6. The conductor track 2a of the circuit 2 is routed on the layer L3 between a through-plating 6-2 arranged inside the windings formed by the conductor track 2a and the connection D leading to the outside on the layer 3 ( Fig. 6). The conductor track 3a of the circuit 3 is arranged between a through-plating 6-3 arranged inside the windings formed by the conductor track 3a and the connection F ( Fig. 6). For the sake of simplicity, the vias 6-2 and 6-3 are expediently routed through the entire circuit board from layer L1 to layer L2 and are lined throughout with electrically conductive material. The conductor track 2a of the circuit 2 further forms all four turns on layer L3, so that the via 6-2 simultaneously provides a connection C, e.g. on one of the outer layers. The circuit 2 can be electrically contacted at the connections C and D with another circuit belonging to the circuit 2, which is not shown in the figures for reasons of clarity, whereby the current flow is thereby used to implement the equivalent circuit diagram according to Fig. 1 then, for example, be specified from the connection C in the direction of the connection D, whereby the current flow does not necessarily have to go from C to D.

[0066] Furthermore, the conductor track 3a of the circuit 3 forms only eleven turns on the layer L3.

[0067] As can also be seen from the figures, in the illustrated embodiment, a conductor track of at least one of the at least three circuits is wound around a first outer leg, and conductor tracks of at least two further circuits of the at least three circuits are wound around the second outer leg. For example, the conductor track 2a of the circuit 2 is wound around the outer leg 5s1, which is inserted into the recess 7a, and the conductor track 1a of the circuit 1 and the conductor track 3a of the circuit 3 are wound around the outer leg 5s2, which is inserted into the recess 7b.

[0068] Furthermore, according to the embodiment shown, a conductor track 3b or 4a is formed for the circuit 3 and 4, for example, on the layer L4, as is the Fig. 7. The conductor track 3b of the circuit 3 is routed on the layer L4 between the connection E, which is routed to the outside on the layer L4, and the through-plating 6-3 ( Fig. 7). Both windings or partial windings of the circuit 3 formed by the conductor tracks 3a and 3b are consequently connected to each other via the through-plating 6-3 and connected in series. The circuit 3 can be electrically contacted with an associated circuit (not shown in the figures for reasons of clarity) at the connection points E and F, whereby the current flow is thereby used to realize the equivalent circuit diagram according to Fig. 1 then, for example, be specified from the connection E in the direction of the connection F, whereby the current flow does not necessarily have to go from E to F.

[0069] The conductor track 4a of the circuit 4 is arranged between a through-plating 6-4 arranged inside the windings formed by the conductor track 4a and the connection H ( Fig. 7). The conductor track 4a of the circuit 4 thus forms all four turns on the layer L4, so that the through-plating 6-4 also simultaneously provides the connection G, e.g. on one of the outer layers. The circuit 4 can be electrically contacted at the connections G and H with another circuit belonging to the circuit 4, which is not shown in the figures for reasons of clarity, whereby the current flow is thereby used to realize the equivalent circuit diagram according to Fig. 1 then, for example, be specified from the connection G in the direction of the connection H, whereby the current flow does not necessarily have to go from G to H.

[0070] When dimensioning the conductor tracks, it is preferable to use conductor tracks that are as wide as possible so that ohmic losses are as small as possible, while at the same time not making the conductor tracks too wide so that a planar transformer that is as space-saving as possible can be realized and stray fields do not become too large. With regard to the distance between two adjacent conductor tracks, the technologically permissible minimum distance is generally selected. This also applies to the distance of the conductor tracks to the edges, e.g. a milling contour, of the recesses 7a and 7b. According to the invention, this also applies to the circuit for which a conductor track is formed on at least one of the outer layers, i.e., according to the illustrated embodiment, for circuit 1.

[0071] However, according to the invention, a conductor track on an outer layer, and thus according to the illustrated embodiment the conductor tracks 1a and 1b on the outer layers L1 and L2 of the circuit 1, are preferably coated with a protective varnish 10, e.g. a solder resist (cf. Fig. 4), which provides insulation between the respective conductor track of an outer layer and the respective region of the core part 5a or 5b of the core 5 located on the side of this outer layer.

[0072] The two core parts 5a and 5b are further preferably bonded together by means of an adhesive 55, although another connection, e.g., clamping, is also possible. They may have an air gap 50 in the region of the contact surface, which, however, should preferably be kept small. Furthermore, at least one of the core halves, the core half, is advantageously attached to the circuit board 7 by adhesive bonding. This adhesive bond initially provides mechanical stability and prevents vibrations.

[0073] Furthermore, however, due to the adhesive bonding of the magnetic core 5 to the circuit board 7, the insulation between the windings formed by a conductor track on the corresponding outer layer—according to the illustrated embodiment, in particular between the windings 1b and the core 5b—is very low, since the conductor tracks on layer L2 are only surrounded by the protective varnish 10. However, a high dielectric strength of the protective varnish cannot be guaranteed, since such a protective varnish generally only has a thickness in the range of approximately ≥ 5 µm. According to the invention, the insulation provided by the protective varnish 10 is therefore not taken into account for the calculations of the insulation between the windings, and the magnetic core 5 is assigned to the potential of the windings on the outer layer. Thus, the windings of all other circuits must not only maintain the clearance and creepage distances LS12, LS13, LS14 to the conductor track on each outer layer, but also to the magnetic core 5.

[0074] With reference to the illustrated embodiment, the conductor tracks and the windings formed thereby in circuits 2, 3, and 4 must therefore not only maintain the clearance and creepage distances LS12, LS13, and LS14 to the conductor tracks 1a and 1b, but also to the magnetic core 5. If, according to preferred embodiments, the circuit board includes through-hole platings, these must also be assigned to the potential of the respective circuits containing these through-hole platings. Thus, the clearance and creepage distances must also be maintained for such through-hole platings, at least in the areas lined with electrically conductive material.

[0075] In the illustrated embodiment, in which preferably only through-contacts 6-1, 6-2, 6-3 and 6-4 are provided which are guided through the entire circuit board and completely lined with electrically conductive material, a distance sufficient for the air and creepage distances LS12, LS13, LS14 to the conductor tracks 1a and 1b and to the magnetic core 5 must therefore also be maintained during the positioning of the through-contacts 6-2, 6-3 and 6-4. In order that the magnetic core 5 can assume slightly different arrangements in the recesses or holes 7a and 7b due to possible tolerances, these air and creepage distances are maintained for the windings of all circuits that are not assigned to the potential of the windings on the outer layer, ie according to the illustrated embodiment for the windings of the circuits 2 to 4, and also expediently to the edges of the recesses 7a and 7b, since these represent the limiting "barriers" for the magnetic core.If one of the two core parts is designed merely as an elongated web or as a plate, this can result in even greater positioning tolerances. For example, this core part may protrude further beyond the recesses, making it necessary to further enlarge the safety zone around the core. The aforementioned clearance and creepage distances are then appropriately maintained for the core part ends that protrude further beyond the recesses.

[0076] Due to the inventive design of conductor tracks for only a single circuit on at least one of the outer layers, in particular such that the magnetic core 5 can consequently be mathematically assigned to the potential of this circuit, circuits 2 to 4 and thus their conductor tracks or windings can no longer be placed on the outer layers. In the example shown, these outer layers are blocked by circuit 1, in particular by conductor track 1b of circuit 1 on layer L2. For the reasons mentioned, this also applies to outer leg 5s1 in recess 7a, although no conductor tracks of the first circuit 1 are arranged around it on the outer layers.

[0077] Consequently, all conductor tracks for further circuits are distributed across the inner layers. However, since the assembled magnetic core forms a closed magnetic circuit, or at least a substantially closed magnetic circuit, the conductor tracks for forming the respective windings can be placed around either leg 5s1 with the associated hole 7a or the other leg 5s2 with the associated hole 7b. It should be noted that slightly different electrical and magnetic properties can result depending on whether conductor tracks of two different windings are positioned directly above one another on one leg or next to one another on different legs. While higher magnetic and capacitive coupling occurs in the first case, it is somewhat lower when arranged side by side. However, these properties can be taken into account in the circuit design within the scope of specialist knowledge.Therefore, this will not be discussed in detail within the scope of the invention. However, it may be useful, for example, to place several secondary sides of a secondary circuit or of different secondary circuits, whose clock edges must be as synchronous as possible, directly above one another. Within the scope of the invention, "directly above one another" means that the corresponding conductor tracks on different layers are largely routed directly above one another and / or the corresponding windings on different layers are wound around the same outer leg. The better secondary circuits are placed directly above one another, the more optimal the coupling.

[0078] As already mentioned above, for example, the thirteen-turn winding of circuit 3 is placed asymmetrically on the two inner layers L3 and L4 around hole 7b, the thirteen-turn winding of circuit 4 is placed on inner layer L4 around hole 7a, and the four-turn winding of circuit 2 is placed on inner layer L3 around hole 7a. Thus, all layers are utilized as effectively as possible, and the ohmic resistances of the individual circuit ends are minimized.

[0079] In the Fig. 2 to 8, the conductor tracks 3a and 3b are now, as shown above, distributed asymmetrically between layers L3 and L4 to form the thirteen turns of the circuit 3 and placed around the hole 7b. Thus, the first eleven turns are arranged on layer L3, in particular in a spiral shape, and the innermost turn is expediently connected to the through-plating 6-3. Since this, in turn, extends over all layers due to the preferred technology, the outer layers are also affected, and the air and creepage distance LS13 of 5.2 mm here to the conductor tracks 1a and 1b of the turns of the circuit 1 on the two outer layers L1 and L2 must be maintained (see also Fig. 5, Fig. 8). For this reason, all eleven turns of circuit 3 located on layer L3 are expediently "pulled out" as far as they will go, i.e., they are also routed around the through-hole plating 6-3. This measure, in turn, results in a larger stray field, which can, however, be technically taken into account. The remaining two turns of circuit 3, which are placed on layer L4 via conductor track 3b, are also connected to the through-hole plating 6-3. Conductor track 3b, and the turns formed thereby, are also expediently routed around the through-hole plating 6-3.

[0080] As already mentioned above, in a practical implementation of the invention, the insulation properties of the conductor tracks must be taken into account. Thus, the conductor tracks of all circuits with windings are placed only on the inner layers, just close enough to the holes 7a and 7b, in particular to their edges or their milling contours, to ensure that the minimum value for solid insulation is maintained. This allows the magnetic core to theoretically extend to the edge of the recesses 7a and / or 7b, depending on tolerances.

[0081] In the present example, for example, the minimum value for the solid insulation between two conductor tracks belonging to different circuits on the same inner layer is specified as x=0.4 mm. If tolerances regarding the conductor pattern, e.g., 0.1 mm, and the recess, e.g., also 0.1 mm, are added, a minimum distance of xA=0.6 mm to the edges, e.g., the milling contours, of recesses 7a and 7b is selected.

[0082] Consequently, there is a minimum distance of xA13=XA=0.6 mm between the conductor tracks 3a, 3b and the edge of the recess 7b (cf. Fig. 6, Fig. 7). Likewise, in accordance with the appropriate design of the through-holes, care must be taken to ensure that the minimum distance of x=0.4 mm is also maintained between the conductor tracks 3a, 3b and the through-hole 6-1, which is to be assigned to circuit 1. The tolerance of a milling or a recess edge is generally not important here. However, a tolerance of the conductor pattern, e.g., of 0.1 mm, is appropriately taken into account and consequently a safety distance, e.g., of x13=0.5 mm, is appropriately maintained between the respective winding 3a or 3b and the through-hole 6-1 (cf. Fig. 6, Fig. 7).

[0083] The layer structure and an insulation layer between layers L1 and L3 with a minimum thickness y13 of, for example, 0.2 mm further ensure that conductor track 3a does not extend too close to conductor track 1a of winding 1a. Conductor track 3b on layer L4 is designed similarly to layer L3, but with the difference that two turns are used instead of eleven. Therefore, the insulation layer between layers L2 and L4 with a minimum thickness of y24=y13 is also expediently provided, ensuring that conductor track 3b on layer L4 does not extend too close to conductor track 1b on layer L2.

[0084] The asymmetry (11 and 2 turns, respectively) of circuit 3 further facilitates the formation of circuits 2 and 4, whose conductor tracks 2a and 4a, respectively, can thus be wound one above the other around the outer leg 5s1 and consequently around the recess 7a. Since only two inner layers L3 and L4 are available for the turns of two galvanically isolated circuits, in particular two intrinsically safe galvanically isolated circuits, it is advantageous to use only one layer for the turns of each circuit. The conductor track 4a for forming the thirteen turns of circuit 4 is thus formed entirely on layer L4, in particular in a spiral shape, so that all 13 turns are placed next to each other on layer L4 (cf. Fig. 7). Since there is only limited space available in the gap between the two cutouts 7a and 7b, the turns of conductor track 4a protrude relatively close to the cutout 7b. For this reason, too, only space is reserved for a small number of turns on layer L4 for circuit 3, in the example shown for the two turns of circuit 3 formed with conductor track 3b. Between conductor tracks 3b and 4a, the safety distance of, for example, x34=0.5 mm (minimum distance plus a tolerance of the conductor pattern) is again maintained in a practical design. The layer structure also ensures that the insulation with a thickness of y34 between layers L3 and L4 is sufficient to galvanically and, in particular, intrinsically safely separate the individual circuits 2 and 4 as well as 3 and 4. The insulation thickness y34 therefore corresponds appropriately to the insulation thickness y13 and y24.

[0085] The via 6-4, which belongs to the circuit 4, is in turn located far enough away from the magnetic core 5, in particular from the edge of the recess 7a, and from the conductor tracks 1a and 1b of the circuit 1 in the x-direction (i.e., in the x1 and x2 directions) that the air and creepage distance of LS14 is maintained. At the via 6-4, the circuit 4 can be contacted with the associated circuit at one of the layers L1, L2, or L3, so that the via 6-4 provides the connection G.

[0086] Furthermore, between the conductor track 4a and the edge of the recess 7a, a minimum distance of xA14=xA=0.6 mm is expediently provided and between the conductor track 4a and the through-plating 6-2, a safety distance of, for example, x24=0.5 mm is expediently maintained (cf. Fig. 7).

[0087] The dimensioning of the conductor track 2a on layer L3 for the windings of the circuit 2 is preferably similar to the conductor track 4a for the windings of the circuit 4. The through-plating 6-2 is thus again far enough away from the hole 7a that the air and creepage distance LS12 = 5.2 mm is maintained and that the distance between the through-plating 6-2 and the conductor tracks 4a of the windings of the circuit 4, preferably x24 = 0.5 mm, is not undercut on the inner layer L4. Furthermore, a minimum distance of xA12 = xA = 0.6 mm is expediently provided between the conductor track 2a and the edge of the recess 7a, and a safety distance of, for example, x23 = 0.5 mm (minimum distance plus a tolerance of the conductor pattern) is again expediently maintained between the conductor tracks 2a and 3a.

[0088] Thus, all circuits 1 to 4 are galvanically isolated from each other in accordance with the insulation requirements, in particular also intrinsically safe, and the planar transformer according to the invention is complete. It should be noted that a mixed form can also be provided within the scope of the invention, such that the circuits can be arranged partially galvanically isolated from each other and partially intrinsically safe.

[0089] Theoretically, within the scope of the invention, using four layers of a printed circuit board for forming electrical conductor tracks, a protective varnish, in particular solder resist, on a conductor track located on an outer layer, and normal vias, i.e., vias extending through the entire printed circuit board with electrical material lined throughout, five galvanically isolated, in particular intrinsically safe, electrically isolated circuits are possible. To form the associated windings of a first circuit, either one conductor track is arranged on an outer layer or two conductor tracks are arranged on both outer layers.

[0090] Furthermore, especially from the point of view of optimal copper utilization, the formation of conductor tracks on outer layers can be advantageous compared to the Fig. 5 and Fig. 8 can be further improved. Are the Fig. 5 and Fig. 8 on the outer layers only windings placed around the recess 7b, shows Fig. 9 shows a modified or alternative embodiment in which further windings 1c, 1d of the first circuit 1 are also guided around the other recess 7a. These windings must then be adapted in terms of winding direction or winding sense so that the magnetic fluxes in the core overlap in the same direction. In the specific embodiment according to Fig. 9, that the turns formed by conductor tracks 1a and 1b and the turns formed by conductor tracks 1c and 1d are connected anti-serially, i.e., the turn formed by conductor track 1a and the turn formed by conductor track 1c are electrically connected, which is indicated by the dashed line between the connection points marked A' and B'. However, the basic properties remain unaffected by this measure; however, in this case, the conductor tracks on the inner layers and the vias 6-2 and 6-4 (cf. Fig. 5 and Fig. 8) must be adjusted or moved, since LS12 and LS14 are moved and at least one new via 6-1a must be added (cf. Fig. 9). For example, according to a design according to Fig. 9 Consequently, for at least one of the circuits, ie in the illustrated case for circuit 1, conductor tracks and thus also windings are wound around both outer limbs. Furthermore, in an expedient addition for this circuit, conductor tracks and thus also windings are also formed on two different layers, ie in the illustrated case on layers L1 and L2. For a second circuit, a conductor track for forming associated windings is arranged on a first inner layer with windings around a first outer limb, e.g. around the one inserted into the recess 7a. For a third circuit, a conductor track for forming associated windings is arranged on the same inner layer with windings around the second outer limb of the magnetic core, e.g. around the one inserted into the recess 7b.For a fourth circuit, a conductor track for forming associated windings is arranged on a second inner layer with windings around the first outer leg, and for a fifth circuit, a conductor track for forming associated windings is arranged on the same second inner layer with windings around the second outer leg of the magnetic core.

[0091] Can be modified to the equivalent circuit diagram according to Fig. 1, for example, circuit 4 should be omitted and only three circuits should be used, for example according to Fig. 10 starting from a primary winding (circuit 1) to two secondary windings (circuits 2 and 3) in the winding ratio 11:12:12, three layers of a printed circuit board may be sufficient for forming electrical conductor tracks within the scope of the invention. Based on the equivalent circuit diagram according to Fig. 10, for example, a conductor track can be formed on at least one of the outer layers for a first circuit of the at least three circuits 1, 2, 3. The windings formed thereby can be wound around a first outer leg and / or around the second outer leg of the magnetic core.

[0092] For the remaining two circuits, a conductor track can be formed on the then single inner layer, wherein the conductor track of one of the remaining two circuits is wound around a first outer leg and the conductor track of the other of the remaining two circuits is wound around the second outer leg. Due to the number of Fig. However, a planar transformer based on this with only three layers has a somewhat larger horizontal dimension than the 10 turns specified, since either twelve turns of circuits 2 and 3 are arranged on the inner layer, or eleven turns of circuit 1 and twelve turns of circuit 2 or 3 are arranged on the inner layer. The turns of the remaining circuit are arranged on one or both outer layers.

[0093] The other general properties of such a planar transformer are identical to those described previously.

[0094] A further preferred embodiment according to the invention will be explained with reference to the Fig. 11 to 14 and is based on e.g. the equivalent circuit diagram according to Fig. 11. Based on the equivalent circuit diagram according to Fig. 11 a planar transformer with four circuits 1, 2, 3 and 4 is to be realized, where, for example, one of the circuits 1, 4 and 3 is the primary circuit and the remaining circuits are in turn equal secondary circuits.

[0095] Even in a planar transformer according to the invention that implements this equivalent circuit, the general properties are identical to those described previously, so that again only the differences will be discussed.

[0096] A special feature is, for example, that there are different insulation regulations. For reasons of simplicity, the insulation regulations for circuits 1, 2 and 3 correspond to those of the planar transformer according to the Fig. 1 to 8, however, circuit 4 with the connection points G and H should be designed for a safe separation of more than 300 V, e.g. 1000 V. In this specific context, this means that the air and creepage distances of LS14, LS24 and LS34 are increased, e.g. to 11.2 mm, whereas for all other air and creepage distances, e.g. a distance of 5.2 mm must be maintained. Furthermore, with regard to circuit 4, the horizontal and vertical requirements for the solid insulation have also increased, whereas with regard to all other circuits, the horizontal and vertical requirements for the solid insulation of the embodiment according to Fig. 1 to 8 correspond.

[0097] Another difference is, for example, that according to the illustration for circuit 2, there should also be a center tap or a middle connection C`.

[0098] In order to nevertheless realize a flat design with a planar transformer according to the invention with continued good heat dissipation, according to the Fig. 12 to 14, so that the transformer can be integrated, for example, into devices with a low overall height, preferably only the windings of circuit 4 are wound around one leg and the windings of all other circuits are wound around the other leg, whereby none of the windings of these other circuits are arranged directly above or below the windings of circuit 4. As a result, the overall height can continue to be kept low, despite the increased vertical requirements with regard to circuit 4 and the heat development in the entire horizontal and vertical area of ​​circuit 4 is solely due to this.Furthermore, for further improved heat dissipation, the circuit 4 is expediently distributed over inner layers, so that the windings of a further circuit are arranged on one outer layer or several outer layers, whereby in particular these windings can further contribute to improved heat dissipation via direct heat dissipation to the ambient air.

[0099] Based on this, a sandwich-like printed circuit board 7 with six layers L1 to L6 is selected for the formation of electrical conductor tracks (cf. Fig. 12 to 14). The printed circuit board is therefore slightly thicker overall than in the embodiment according to the Fig. 1 to 8. The windings of the circuit 4 are expediently formed on the innermost two layers L4 and L5, and none of the windings of the further circuits are arranged directly above or below the windings of the circuit 4. For example, a first conductor track 4a for forming 5 windings of the circuit 4 is arranged on the layer L4 around the recess 7a, and a second conductor track 4b for forming 5 windings of the circuit 4 on the layer L5 is also arranged around the recess 7a (cf. Fig. 14).

[0100] With the increased vertical requirement with regard to circuit 4, an increased distance of y14 must be maintained only between layers L1 and L4 and between layers L5 and L2. Since the vertical requirements with regard to the other circuits correspond to those according to the embodiment according to the Fig. 1 to 8, a distance of only 0.2 mm, for example, must be maintained between the other layers. The thickness of the entire circuit board 7 is thus determined by twice the increased distance y14 and once the smaller distance of 0.2 mm, or by five times the smaller distance of 0.2 mm, for example, if 0.4 mm is sufficient for y14 in the example.

[0101] Since the clearance and creepage distances of LS14, LS24 and LS34 also increase with respect to circuit 4, this justifies the great distance of the through-plating 6-4, which electrically connects the conductor tracks 4a and 4b, from the hole 7a. If, for example, the windings of circuit 1 are arranged on at least one of the outer layers, this great distance of the through-plating 6-4, which electrically connects the conductor tracks 4a and 4b, from the hole 7a corresponds to the clearance and creepage distance LS14. Since the horizontal requirements for the solid insulation with respect to circuit 4 have also increased, the distance of the conductor tracks 4a and 4b of circuit 4 from the edge of the recess 7a is also greater than before. If the windings of the circuits 1 are arranged on at least one of the outer layers, this distance of the conductor tracks 4a and 4b of the circuit 4 from the edge of the recess 7a can be determined in accordance with the embodiments according to the Fig. 1 to 8 are marked with xA14 (cf. Fig. 13).

[0102] However, when using six layers, the turns of circuits 1, 2 and 3 can each be distributed across two layers, which in turn reduces the required horizontal extension. For example, if the conductor tracks of circuit 1 are distributed across the two outer layers L1 and L2, the conductor tracks of circuit 2 can be distributed across the two layers L3 and L4, and the conductor tracks of circuit 3 can be distributed across the two layers L5 and L6, in particular the number of them can be distributed as evenly as possible. The inner end of each turn of circuits 1 and 3 is then expediently electrically connected to a through-hole 6-1 or 6-3, to which in turn a connection is made that leads to the outside on another layer but is not explicitly shown for reasons of clarity.In the reference of circuit 2, due to the required center tap C', two vias 6-2-1 and 6-2-2 are electrically connected to the windings. This not only provides a connection to the outside (not explicitly shown for reasons of clarity), but also allows the center tap C' to be provided to the outside on another layer. The total area of ​​the conductor tracks, especially copper conductor tracks, and thus the amount of heat-absorbing and heat-dissipating material can therefore be dimensioned larger than in the previous version, while maintaining otherwise identical dimensions of the planar transformer.

[0103] Theoretically, with this technology used in preferred embodiments, ie with a sandwich-like printed circuit board 7 with six layers L1 to L6 for forming electrical conductor tracks, protective lacquer and normal through-holes, nine galvanically isolated, in particular also intrinsically safe, circuits can be realized.

[0104] To form the associated windings of a first circuit, either one conductor track is arranged on an outer layer or two conductor tracks are arranged on both outer layers. To form windings belonging to four additional circuits, the four inner layers can be used around a first outer leg of the magnetic core, and to form further windings belonging to four additional circuits, the same four inner layers can be used around the second outer leg of the magnetic core.

[0105] Theoretically, therefore, with this technology, ie with a sandwich-like printed circuit board 7 with a plurality of N layers for forming electrical conductor tracks, protective lacquer and normal through-holes ((N-2)*2)+1, galvanically isolated, in particular intrinsically safe, circuits can be realized.

[0106] In practice, however, it is preferable to combine several inner layers to enable lower copper losses.

[0107] A planar transformer according to the invention can thus, in a preferred embodiment, be integrated within an isolating amplifier, in particular in the housing of an isolating amplifier, which, however, is not shown further in the figures for reasons of clarity. List of reference symbols 1, 2, 3, 4 circuit or potential group or winding of the transformer; 1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b conductor tracks; A, A', B, B', C, C', D, E, F, G, H connection connections for electrical contact; 5 magnetic core; 5a first part of the magnetic core; 5b second part of the magnetic core; 5m middle part of the first part of the magnetic core; 5s1, 5s2 outer legs of the first part of the magnetic core; 6-1, 6-1a, 6-2, 6-2-1, 6-2-3, 6-3, 6-4a vias; 7 circuit board; 7a, 7b Recesses in the circuit board; L1, L2, L3, L4L5, L6 layers for forming conductive paths; LS clearance and creepage distances; x, y insulation distances within the insulation material between two different circuits; xA Insulating distances within the insulating material between a circuit and the edge of a recess; 100 inventive planar transformer.

Claims

[1] Planar transformer (100) for energy transmission having a vertical extension and a horizontal extension - a sandwich-like printed circuit board (7) with at least three layers (L1, L2, L3) for forming electrical conductor tracks (1a, 1b, 2a, 2b, 3a, 3b), wherein a first and a second of these layers form outer layers (L1, L2) of the printed circuit board (7) and each further of these layers forms an inner layer (L3) of the printed circuit board (7), and wherein an insulating material (y) with a minimum thickness is arranged between all of these layers (L1, L2, L3), - a number of at least three electrical circuits (1, 2, 3) which are each galvanically isolated from one another, wherein a first circuit (1) forms a primary circuit, a second circuit (2) forms a first secondary circuit and each further circuit (3) forms a further equal secondary circuit of the planar transformer (100), and wherein, for energy transmission, current is fed in via the primary circuit (1) and an output current is discharged via the secondary circuits (2, 3), - a magnetic core (5) which at least partially encloses the sandwich-like structure of the printed circuit board (7) and acts at least on the first circuit (1), on the second circuit (2) and on the third circuit (3); - wherein the magnetic core (5) is composed of two interconnected magnetic core parts (5a, 5b), wherein a first core part (5a) forms a U-shape with a central part (5m) and two outer legs (5s1, 5s2), and wherein the printed circuit board (7) has two recesses (7a, 7b) and the two outer legs (5s1, 5s2) of the first core part (5a) are inserted into these recesses (7a, 7b) and are connected to the second core part (5b) at their ends remote from the central part (5m), wherein for exactly one single circuit (1) of the at least three circuits (1, 2, 3), a conductor track (1a, 1b) is formed on at least one of the outer layers (L1, L2) and for all other of the at least three circuits (1, 2, 3), conductor tracks (2a, 2b, 3a, 3b) are formed on one inner layer (L3) or several inner layers - and wherein a conductor track (1a, 1b, 2a, 2b, 3a, 3b) of at least one circuit (2) of the at least three circuits (1, 2, 3) is wound only around a first outer leg (5s1) and conductor tracks (1a, 1b, 2a, 2b, 3a, 3b) of at least two further circuits (1, 3) of the at least three circuits (1, 2, 3) are wound around the second outer leg (5s2). [2] Planar transformer according to claim 1, wherein conductor tracks (1a, 1b, 2a, 2b, 3a, 3b) are formed on one and the same inner layer (L3) for at least two further circuits (2, 3) of the at least three circuits (1, 2, 3). [3] Planar transformer according to claim 1 or 2, wherein for each conductor track (1a, 1b, 2a, 2b, 3a, 3b) formed on a layer for forming electrical conductor tracks, at least one end is electrically connected to a via which is electrically connected to a terminal connection arranged on another layer for electrically contacting the conductor track. [4] Planar transformer according to claim 3, wherein the through-plating is continuously guided through all layers of the printed circuit board (7) and is lined with electrically conductive material. [5] Planar transformer according to claim 3 or 4, wherein a predetermined minimum distance of an air and creepage distance between two circuits (1, 2, 3) determines the minimum distance between the through-hole of a circuit and the edges of the two recesses. [6] Planar transformer according to claim 3, 4 or 5, wherein a via associated with a conductor track wound around an outer leg (5s1, 5s2) is always arranged in the interior of the conductor track wound around the outer leg (5s1, 5s2). [7] Planar transformer according to one of the preceding claims, wherein for at least one of the circuits conductor tracks are wound around both outer legs (5s1, 5s2) and / or are formed on two different layers. [8] Planar transformer according to one of the preceding claims, wherein it is integrated in the housing of an isolation amplifier. [9] Planar transformer according to one of the preceding claims, wherein at least one conductor track formed on an outer layer (L1, L2) is coated with a protective varnish (10) and / or the core is to be assigned to the potential of the conductor track formed on an outer layer (L1, L2) with respect to the galvanic isolation of the circuits.

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