Planar transformer

Abstract

The utility model provides a planar transformer. The planar transformer comprises a magnetic core, the primary Litz coil winding is arranged on the magnetic core in a sleeving manner; the magnetic core is sleeved with the PCB multilayer board, the PCB multilayer board and the primary Litz coil winding are arranged in a staggered mode in the axis direction of the primary Litz coil winding, the PCB multilayer board at least comprises two outer layers and a plurality of inner layers, the two outer layers are two secondary windings of the transformer respectively, the two secondary windings are further provided with a first copper foil layer and a second copper foil layer respectively, and the first copper foil layer and the second copper foil layer are arranged in a staggered mode. The first copper foil layer and the second copper foil layer are arranged according to the shapes of the corresponding secondary windings and are directly connected in parallel with the secondary windings on the respective sides, and the inner layer directly opposite to the two secondary windings is an insulating layer; a rectifier tube, a filter capacitor and an optional driving circuit are integrated at the output end of the PCB multilayer board, and the output end of each secondary winding passes through the rectifier tube and the filter capacitor and then is connected in series and in parallel with the output of the secondary winding. The scheme can reduce the parasitic capacitance of the secondary winding, reduce the alternating current loss and improve the efficiency of the transformer.

Description

Technical Field

[0001] This utility model belongs to the field of transformer technology, and in particular relates to a planar transformer. Background Technology

[0002] Transformers utilize the principle of electromagnetic induction to convert voltage. Their main components are the primary winding, secondary winding, and magnetic core. Users can adjust the number of turns in the primary or secondary winding to adapt to different voltage ranges according to product requirements. Traditional wound transformers are heavy and bulky, limiting the miniaturization of power supplies. Planar transformers, because they eliminate the need for a winding frame, are small in size, simple in manufacturing, and offer high operating frequencies, good heat dissipation, and good consistency, and have been widely used in switching power supplies in recent years.

[0003] Currently, planar transformers mostly use multilayer PCBs with multiple layers. Each copper layer in a multilayer PCB can be used to set the primary and secondary windings. However, since the insulation layer between copper layers in a multilayer PCB is thinner than that of a single-layer board, and the distance is an important parameter affecting the size of parasitic capacitance, the parasitic capacitance between the primary and secondary windings, and between the secondary windings, is also larger. Utility Model Content

[0004] The technical objective of this invention is to provide a planar transformer that aims to reduce parasitic capacitance of the secondary winding, reduce AC losses, and improve transformer efficiency.

[0005] To solve the above technical problems, the present invention is implemented as follows: a planar transformer is provided, comprising: a magnetic core; a primary Litz coil winding, sleeved on the magnetic core; and a PCB multilayer board, sleeved on the magnetic core, arranged alternately with the primary Litz coil winding along the axial direction of the primary Litz coil winding. The PCB multilayer board includes at least two outer layers and optionally multiple inner layers. The two outer layers are the two secondary windings of the transformer. The two secondary windings also have a first copper foil layer and a second copper foil layer, respectively. The first copper foil layer and the second copper foil layer are arranged according to the shape of the corresponding secondary winding and are directly connected in parallel with the secondary winding on their respective sides. The inner layer directly opposite the two secondary windings is an insulating layer. The output terminal of the PCB multilayer board integrates a rectifier tube, a filter capacitor, and an optional drive circuit. The output terminal of each secondary winding is connected in series and parallel through the rectifier tube and the filter capacitor.

[0006] Furthermore, the secondary winding includes an outer copper foil layer of the PCB and a copper foil layer of the same shape connected in parallel therewith. The PCB multilayer board is equipped with a rectifier tube and a filter capacitor. The secondary winding includes a surrounding part and a connecting part. The surrounding part surrounds the central column of the magnetic core and has two ends. There are two connecting parts. One end of the two connecting parts is connected to the two ends of the surrounding part, and the other end of the two connecting parts is connected to the rectifier tube and the filter capacitor, respectively.

[0007] Furthermore, there are two pairs of rectifier tubes and filter capacitors, which are respectively installed on the two outer layers facing away from each other. One end of each of the two filter capacitors is connected to one of the connection portions of the first copper foil layer and the second copper foil layer, and the other end of each filter capacitor is connected to one end of the adjacent rectifier tube in the same layer. The other end of each rectifier tube is connected to the other connection portion of the first copper foil layer and the second copper foil layer.

[0008] Furthermore, when using diode rectification, the driving circuit and multiple inner layers are eliminated, and the filter capacitor is connected to the cathode of the rectifier tube; when using synchronous rectification, the driving circuit is retained and multiple optional inner layers are set according to the wiring, and the filter capacitor is connected to the source of the rectifier tube.

[0009] Furthermore, the PCB multilayer board includes a circular ring portion and an outer portion. The circular ring portion is sleeved on the magnetic core, and the outer portion is located on one radial side of the circular ring portion and is integrally formed with the circular ring portion. The surrounding portion is located on the circular ring portion, and the connecting portion, the filter capacitor, and the rectifier tube are all located on the outer portion.

[0010] Furthermore, the two connecting portions of the secondary winding are arranged at intervals, with a distance between them greater than 3mm.

[0011] Furthermore, the primary Litz coil winding is a double-layer coil, with both ends of the double-layer coil located radially outward.

[0012] Furthermore, the thicknesses of the first copper foil layer and the second copper foil layer are calculated using the skin effect formula, which is related to the operating frequency f. The total thickness of the copper foil plus the PCB layer of a single secondary winding satisfies less than twice the skin depth δ=sqrt(ρ / (πμf)), where ρ is the resistivity of the material and μ is the permeability of the conductor.

[0013] Furthermore, both the primary Litz coil winding and the PCB multilayer board are provided in multiple ways, and the multiple primary Litz coil windings and the multiple PCB multilayer boards are arranged alternately, with the primary Litz coil windings distributed on the outermost two sides of the entire transformer winding.

[0014] Furthermore, the magnetic core has an air gap, and the distance between the air gap and the primary Litz coil winding is smaller than the distance between the air gap and the PCB multilayer board.

[0015] Compared with existing technologies, the planar transformer of this invention has the following advantages: This application uses a multi-layer PCB board as the carrier of the secondary winding. The outer layers have a first copper foil layer and a second copper foil layer connected in parallel as the secondary winding, and the inner layer corresponding to the winding is an insulating layer without a secondary winding. Therefore, the distance between the boards is the distance of the entire PCB board's insulating layer, which is greater than the distance when copper foil layers are set on each layer. The thickness of the parallel copper foil can be determined according to the needs and operating frequency of the planar transformer, thereby reducing parasitic capacitance without affecting the current magnitude. Furthermore, by incorporating the rectifier tube and filter capacitor as part of the winding circuit, each side of the PCB winding is first rectified and filtered before being connected in series and parallel. This also increases the distance between the PCB winding inlet and outlet ports, reducing AC losses at the output terminals and improving the efficiency of the planar transformer. Attached Figure Description

[0016] Figure 1 This is a three-dimensional exploded view of the planar transformer in an embodiment of this utility model;

[0017] Figure 2 yes Figure 1 A schematic front view of the PCB multilayer board in the embodiment;

[0018] Figure 3 yes Figure 2 A magnified view of region A in the middle.

[0019] In the accompanying drawings, the reference numerals indicate: magnetic core 100; primary Litz coil winding 200; PCB multilayer board 300; annular portion 301; external portion 302; first copper foil layer 310; surrounding portion 311; connecting portion 312; port distance 313; rectifier tube 320; filter capacitor 330; and drive circuit 340. Detailed Implementation

[0020] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this utility model, and should not be construed as limiting this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

[0021] In the description of this utility model, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "circumferential", "radial", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In this utility model, "optional" means that there are two possibilities: either the corresponding component is present or it is not.

[0023] See Figure 1 , Figure 1 An exploded three-dimensional structural diagram of a planar transformer is shown. In one embodiment, this application provides a planar transformer that, compared to existing planar transformers, has smaller parasitic capacitance and lower port AC losses under the same conditions. The specific structure includes a magnetic core 100, a primary Litz coil winding 200, and a multilayer PCB board 300. In this embodiment, the magnetic core 100 is an E-shaped iron core with a circular center post. The primary Litz coil winding 200 is mounted on the magnetic core 100. The PCB multilayer board 300 is also mounted on the magnetic core 100 and is staggered with the primary Litz coil winding 200 along the length of the magnetic core 100. The PCB multilayer board 300 includes at least two outer layers and multiple optional inner layers, such as no inner layers or one, two, or three inner layers. The two outer layers are the two secondary windings of the transformer. The two secondary windings are also connected in parallel with a first copper foil layer 310 and a second copper foil layer, respectively. The first copper foil layer 310 and the second copper foil layer are set according to the shape of the corresponding secondary winding and are directly connected in parallel with the secondary winding on their respective sides. The inner layer directly opposite the two secondary windings is an insulating layer. The output end of the PCB multilayer board 300 integrates a rectifier tube 320, a filter capacitor 330, and an optional drive circuit 340. The output end of each secondary winding is connected in series and parallel through the rectifier tube 320 and the filter capacitor 330. Due to the viewing angle, the second copper foil layer is located on the other side of the first copper foil layer 310, so it is not shown in the attached figure.

[0024] In this implementation, a multilayer PCB board 300 is used as the carrier of the secondary winding. Since the PCB board has an outer layer and an inner layer, the outer layer has a first copper foil layer 310 and a second copper foil layer connected in parallel as the secondary winding. The thickness of these two layers can be determined according to the requirements of the planar transformer and the operating frequency. The inner layer of the winding of the multilayer PCB board 300 is an insulating layer and does not have a secondary winding, which increases the distance between the first copper foil layer 310 and the second copper foil layer, reducing parasitic capacitance.

[0025] In other embodiments, the shape of the magnetic core 100 can be specifically adjusted, such as being prism-shaped or elliptical-cylindrical.

[0026] Preferably, the first copper foil layer 310 and the second copper foil layer of the PCB multilayer board 300 can be thickened or externally connected with copper foil, thereby reducing parasitic capacitance while being able to carry a larger current.

[0027] See Figure 2 and Figure 3 , Figure 2 A schematic diagram of the PCB board structure is shown. Figure 3 Showing Figure 2 Enlarged view of region A. In one embodiment, the secondary winding includes an outer copper foil layer of the PCB and a copper foil layer of the same shape connected in parallel therewith. The PCB multilayer board 300 is equipped with a rectifier tube 320 and a filter capacitor 330. Both the first copper foil layer 310 and the second copper foil layer include a surrounding portion 311 and a connecting portion 312. The surrounding portion 311 surrounds the central column of the magnetic core 100. Two connecting portions 312 are provided. One end of the two connecting portions 312 is connected to the two ends of the surrounding portion 311, and the other end of the two connecting portions 312 is connected to the filter capacitor 320 and the rectifier tube 330, respectively.

[0028] Specifically, from Figure 2 As can be seen from this embodiment, both the first copper foil layer 310 and the second copper foil layer resemble circles with notches. These notches create two ports, and two connecting portions 312 connect these ports to the rectifier tube 320 and the filter capacitor 330, respectively. After passing through the rectifier tube 320 and the filter capacitor 330, the voltage is DC, which can be connected via a copper busbar or other PCB board. The filter capacitor 320 and the rectifier tube 330 are existing devices, and their structure and function will not be described in detail in this application.

[0029] Preferably, the first copper foil layer 310 and the second copper foil layer are connected in parallel to form a single secondary winding or in series to form a double secondary winding with a center tap after passing through the rectifier tube 320 and the filter capacitor 330, as required, to increase the output capacity of the transformer. The primary Litz coil winding 200 can be connected in parallel, in series, or in parallel and series in parallel according to the voltage and current levels.

[0030] In the above embodiments, the rectifier 320 can be a diode or a synchronous rectifier. When it is a diode, the driver circuit 340 can be omitted. When using diode rectification, the driver circuit 340 and multiple inner layers are eliminated, and the filter capacitor 330 is connected to the cathode of the rectifier 320. When using synchronous rectification, the driver circuit 340 is retained, and multiple optional inner layers are set according to the wiring difficulty. The filter capacitor 330 is connected to the source of the rectifier 320.

[0031] See Figure 2 In one embodiment, the two connecting portions 312 of the first copper foil layer 310 and the second copper foil layer are arranged at intervals to form a port distance 313. The port distance 313 is greater than 3 mm. The specific distance can be determined according to the operating frequency of the planar transformer. A suitable port distance 313 can reduce the proximity effect in physical phenomena.

[0032] Preferably, in one embodiment, there are two (groups) of filter capacitors 320, which are respectively installed on both sides of the PCB multilayer board 300. Figure 2 and Figure 3 The image shows one of the filter capacitors 330. The two filter capacitors 330 are connected one-to-one with the first copper foil layer 310 and the second copper foil layer. When only one side of the PCB multilayer board 300 has the filter capacitors 330 installed, and the other side does not, the winding on the other side needs to pass through a via on the PCB board to connect to the filter capacitor 330 on the opposite side. This increases the equivalent series resistance and inductance in the filter circuit, and also causes the impedance of the windings on the two sides to be inconsistent. Furthermore, there is a proximity effect between the vias, leading to increased AC losses.

[0033] See Figure 2 In one embodiment, the PCB multilayer board 300 includes an annular portion 301 and an outer portion 302. In this embodiment, the outer portion 302 is approximately rectangular in shape, but its actual shape is not limited as long as it meets the requirements for current and board area. The annular portion 301 is fitted onto the magnetic core 100, and the outer portion 302 is located on one radial side of the annular portion 301 and is integrally formed with it. The surrounding portions 311 of the first copper foil layer 310 and the second copper foil layer are located on the front and back surfaces of the annular portion 301, and the connecting portion 312, rectifier tube 320, and filter capacitor 330 are all located on the outer portion 302. This allows the first copper foil layer 310 and the second copper foil layer within the annular portion 301 to have a larger thickness and width, and the outer portion 302 can avoid the primary Litz coil winding 200 when mounting the rectifier tube 330 and the filter capacitor 320. At the same time, the rectifier tube 320 and the filter capacitor 330, as part of the secondary winding, can minimize the loop length, thereby reducing losses at the winding ends. Figure 3 The middle external connection 302 is also equipped with a drive circuit 340, which can reduce losses under high current output conditions when synchronous rectification is used.

[0034] Preferably, in one embodiment, the primary Litz coil winding 200 is a double-layer coil, with both ends of the double-layer coil located radially outward. Specifically, the primary Litz coil winding 200 adopts a double-layer, multi-turn Litz coil winding structure to avoid end-point wire problems. The Litz wire specifications (wire diameter and number of strands) are selected based on the primary-side current, switching frequency, and secondary-side winding width. When the coil has an odd number of layers, one of its winding joints needs to be folded out from the inside of the coil along the surface, which will create a gap between the primary and secondary coils, leading to increased leakage inductance. A double-layer coil does not have this problem.

[0035] Preferably, in one embodiment, the dielectric between the first copper foil layer 310 and the second copper foil layer is an insulating layer or air to reduce the parasitic capacitance between them. The thickness of the first copper foil layer 310 and the second copper foil layer can be determined according to the requirements of the planar transformer. The thickness range values ​​of the first copper foil layer 310 and the second copper foil layer provided in this application are all calculated by the skin effect formula and are related to the operating frequency f. The total thickness of the copper foil plus the PCB layer of a single winding satisfies less than twice the skin depth δ=sqrt(ρ / (πμf)), and the target current is achieved by connecting multiple PCB windings in parallel, where ρ is the resistivity of the material and μ is the permeability of the conductor.

[0036] Preferably, in one embodiment, multiple primary Litz coil windings 200 and multiple PCB multilayer boards 300 are provided, and the multiple primary Litz coil windings 200 and multiple PCB multilayer boards 300 are staggered. The primary Litz coil windings are distributed on the outermost two sides of the entire transformer winding to reduce magnetomotive force. Here, staggered arrangement does not mean that one primary Litz coil winding 200 and one PCB multilayer board 300 are arranged alternately. Within one arrangement cycle, the number of primary Litz coil windings 200 and PCB multilayer boards 300 is not limited. For example, the arrangement sequence can be two primary Litz coil windings 200 and two PCB multilayer boards 300.

[0037] Preferably, in one embodiment, a plurality of primary Litz coil windings 200 and a plurality of PCB multilayer boards 300 form winding ends, with the windings on both sides of the winding ends being primary Litz coil windings 200. The primary Litz coil windings 200 can separate the inner surface of the magnetic core 100 from the PCB multilayer boards 300, thereby avoiding excessively large parasitic capacitance caused by an excessively large facing area between the first copper foil layer 310 and the second copper foil layer and the magnetic core.

[0038] In one embodiment, the magnetic core 100 has an air gap, the distance between the air gap and the primary Litz coil winding 200 is smaller than the distance between the air gap and the PCB multilayer board 300, thereby reducing the influence of leakage flux.

[0039] In the above embodiments, all primary Litz coil windings 200 can be assembled using a simple PCB multilayer board 300, and the series and parallel connections can be achieved through wiring on the PCB multilayer board 300.

[0040] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A planar transformer, characterized in that, include: Magnetic core (100); The primary Litz coil winding (200) is sleeved on the magnetic core (100); A PCB multilayer board (300) is sleeved on the magnetic core (100) and is staggered with the primary Litz coil winding (200) along the axial direction of the primary Litz coil winding (200). The PCB multilayer board (300) includes at least two outer layers and optional multiple inner layers. The two outer layers are the two secondary windings of the transformer. The two secondary windings also have a first copper foil layer (310) and a second copper foil layer, respectively. The first copper foil layer (310) and the second copper foil layer are arranged according to the shape of the corresponding secondary winding and are directly connected in parallel with the secondary winding on their respective sides. The inner layer directly opposite the two secondary windings is an insulating layer. The output terminal of the PCB multilayer board (300) integrates a rectifier tube (320), a filter capacitor (330), and an optional drive circuit (340). The output terminals of each secondary winding are connected in series and parallel after passing through the rectifier tube (320) and the filter capacitor (330).

2. The planar transformer according to claim 1, characterized in that, The secondary winding includes an outer copper foil layer of the PCB and a copper foil layer of the same shape connected in parallel with it. The PCB multilayer board (300) is equipped with a rectifier tube (320) and a filter capacitor (330). The secondary winding includes a surrounding part (311) and a connecting part (312). The surrounding part (311) surrounds the central column of the magnetic core (100) and has two ends. There are two connecting parts (312). One end of the two connecting parts (312) is connected to the two ends of the surrounding part (311), and the other end of the two connecting parts (312) is connected to the rectifier tube (320) and the filter capacitor (330) respectively.

3. The planar transformer according to claim 2, characterized in that, Two pairs of rectifier tubes (320) and filter capacitors (330) are provided, respectively installed on the two outer layers opposite to each other. One end of each filter capacitor (330) is connected to one of the connecting parts (312) of the first copper foil layer (310) and the second copper foil layer, respectively. The other end of each filter capacitor (330) is connected to one end of the rectifier tube (320) adjacent to it in the same layer. The other end of each rectifier tube (320) is connected to the other connecting part (312) of the first copper foil layer (310) and the second copper foil layer, respectively.

4. The planar transformer according to claim 3, characterized in that, When diode rectification is used, the driving circuit (340) and multiple inner layers are eliminated, and the filter capacitor (330) and the cathode of the rectifier tube (320) are connected. When synchronous rectification is used, the driving circuit (340) is retained and multiple optional inner layers are set according to the wiring. The filter capacitor (330) and the source of the rectifier tube (320) are connected.

5. The planar transformer according to claim 3, characterized in that, The PCB multilayer board (300) includes an annular portion (301) and an external portion (302). The annular portion (301) is sleeved on the magnetic core (100). The external portion (302) is located on one radial side of the annular portion (301) and is integrally formed with the annular portion (301). The surrounding portion (311) is located on the annular portion (301). The connecting portion (312), the filter capacitor (320), and the rectifier tube (330) are all located on the external portion (302).

6. The planar transformer according to claim 2, characterized in that, The two connecting parts (312) of the secondary winding are arranged at intervals, and the distance between them is greater than 3mm.

7. The planar transformer according to claim 1, characterized in that, The primary Litz coil winding (200) is a double-layer coil, with both ends of the double-layer coil located radially outward.

8. The planar transformer according to claim 1, characterized in that, The thicknesses of the first copper foil layer (310) and the second copper foil layer are calculated using the skin effect formula and are related to the operating frequency f. The total thickness of the copper foil plus the PCB layer of a single secondary winding satisfies less than twice the skin depth δ=sqrt(ρ / (πμf)), where ρ is the resistivity of the material and μ is the permeability of the conductor.

9. The planar transformer according to claim 1, characterized in that, Both the primary Litz coil winding (200) and the PCB multilayer board (300) are provided in multiple ways, and the multiple primary Litz coil windings (200) and the multiple PCB multilayer boards (300) are arranged alternately, with the primary Litz coil windings distributed on the outermost two sides of the entire transformer winding.

10. The planar transformer according to claim 8, characterized in that, The magnetic core (100) has an air gap, and the distance between the air gap and the primary Litz coil winding (200) is less than the distance between the air gap and the PCB multilayer board (300).

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