LLC transformer and method of manufacturing the same

Abstract

The application discloses an LLC transformer and a manufacturing method thereof, and the LLC transformer comprises a primary winding and a secondary winding, a magnetic core and a skeleton, characterized in that the magnetic core and the skeleton are assembled together, the secondary winding is a planar winding and is embedded in the skeleton, the primary winding is a vertical winding and is wound on the skeleton, and only a predetermined number of layers of the primary winding and the secondary winding are coupled with each other to increase the leakage inductance of the LLC transformer. The LLC transformer can realize the effect of small volume and large leakage inductance, and the manufacturing method of the LLC transformer can conveniently and accurately debug the inductance value of the product to be prepared.

Description

Technical Field

[0001] This invention relates to the field of transformer technology, and in particular to an LLC transformer and its manufacturing method. Background Technology

[0002] The LLC (Resonant Circuit) architecture uses a resonant inductor, magnetizing inductor, and resonant capacitor connected in series. It boasts advantages such as high operating frequency, low loss, high efficiency, and small size, and is widely used in the high-power PD (Power Delivery) fast charging market. Unlike traditional pulse-width modulation (PWM) converters, LLC transformers are resonant circuits that achieve a fixed output voltage by controlling the switching frequency (frequency regulation). They offer better EMI (Electromagnetic Interference) characteristics, making them suitable for high-efficiency, high-power power supply applications such as automotive converters. Its advantages include achieving zero-voltage turn-on (ZVS) for the two primary MOS switches and zero-current turn-off (ZCS) for the secondary rectifier diodes. Through soft-switching technology, it can reduce switching losses and improve efficiency and power density. Traditional LLC transformer designs generally fall into two categories:

[0003] 1. A double-slot bobbin structure is used, where the primary and secondary windings are wound in two separate slots (with the bobbin acting as an isolation element). Alternatively, a long bobbin can be used, with the primary and secondary windings wound at opposite ends, using the bobbin between the two windings for isolation, thus achieving a larger leakage flux. This winding structure leaves a certain distance between the primary and secondary windings. To obtain even higher leakage inductance, the baffle or distance between the primary and secondary windings needs to be increased. This results in a larger LLC transformer, and controlling the leakage inductance becomes more difficult.

[0004] 2. Transformer + Resonant Inductor Solution: Minimize the leakage inductance of the transformer and connect a resonant inductor in series with the primary side. This makes it easier to control the leakage inductance of the LLC transformer. However, it requires two components, which increases the cost. Furthermore, it occupies a large PCB board space when used by the client, thus limiting its application range. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art, this application provides an LLC transformer, including a primary winding and a secondary winding, a magnetic core and a frame. The magnetic core and the frame are assembled together. The secondary winding is a planar winding embedded in the frame. The primary winding is a vertical winding wound on the frame. The primary winding and the secondary winding are coupled together in only a predetermined number of layers to increase the leakage inductance of the LLC transformer.

[0006] The present invention may also employ the following optional / preferred solutions:

[0007] The predetermined number of layers of mutual coupling specifically means that only one layer of the secondary winding is coupled to the primary winding.

[0008] The secondary winding is made of copper sheets.

[0009] The secondary winding has 1-3 layers.

[0010] The magnetic core includes a core post, and the frame has a frame hole. The magnetic core and the frame are assembled together by inserting the core post into the frame hole.

[0011] The magnetic core includes a left magnetic core and a right magnetic core, which are assembled with the skeleton from the left and right sides, respectively.

[0012] This invention also provides a method for manufacturing an LLC transformer, comprising the following steps:

[0013] The integrated skeleton and secondary winding are formed by embedding the planar wound secondary winding into the skeleton material, and then obtaining the integrated skeleton and secondary winding by injection molding.

[0014] The primary winding is wound vertically on the integrated frame and the secondary winding frame, so that there are only a predetermined number of layers of mutual coupling between the primary winding and the secondary winding.

[0015] The assembly of the magnetic core and the frame involves assembling the magnetic core, the integrated frame, and the frame of the secondary winding to obtain the LLC transformer.

[0016] Preferably, the secondary winding formed by planar winding has 1-3 layers.

[0017] Preferably, in the molding step of the integrated skeleton and secondary winding, the PIN pins are also simultaneously embedded into the skeleton for injection molding.

[0018] The assembly of the magnetic core and the frame preferably adopts a dual-core assembly method, that is, the magnetic core includes a left magnetic core and a right magnetic core, the frame has a central hole, and the central post of the left magnetic core and the central post of the right magnetic core are inserted into the central hole from the left and right sides respectively for assembly.

[0019] The one or more technical solutions provided in this application have at least the following advantages compared with the prior art:

[0020] The LLC transformer of this application reduces coupling by decreasing the contact area between the primary and secondary coils. One winding uses a planar winding method, while the other uses a vertical winding method. This results in only a limited number of layers coupling with each other, increasing leakage inductance by reducing mutual coupling, ultimately achieving a small size and high leakage inductance in the LLC transformer. Furthermore, the manufacturing method of the LLC transformer of this application allows for different inductance values ​​to be obtained during product manufacturing by adjusting the wall thickness of the bobbin and the wire diameter of the windings. This method is both convenient and allows for precise adjustment. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural diagram of the LLC transformer according to an embodiment of this application;

[0022] Figure 2 for Figure 1 A schematic diagram of the LLC transformer with the left magnetic core and primary winding hidden;

[0023] Figure 3 for Figure 1 A schematic diagram of the cross-sectional structure;

[0024] Figure 4 This is an exploded view of the magnetic core and frame assembly;

[0025] Figure 5 This is a schematic diagram illustrating the process principle of injection molding of the skeleton, secondary coil, and PIN pin in the manufacturing method embodiment of this application;

[0026] Figure 6 This is a schematic diagram of the skeleton structure after the secondary coil and PIN pin have been embedded and injection molded according to an embodiment of this application;

[0027] Figure 7 for Figure 6 A schematic diagram of the skeleton from another perspective. Detailed Implementation

[0028] The technical solution in this application is to solve the problem that LLC transformers cannot achieve small size and large leakage inductance and are limited in application. The general idea is as follows: by reducing the contact area between the primary and secondary coils to reduce coupling (the primary and secondary windings are separated), the leakage inductance is increased, and finally, the LLC transformer can achieve small size and large leakage inductance. Specifically, the secondary winding is wound in a planar manner and embedded in the frame, while the primary winding is wound vertically, thereby reducing the coupling between them to increase the leakage inductance and greatly reducing the size of the transformer.

[0029] To better understand the above technical solutions, the following is in conjunction with the appendix. Figure 1-7The present invention will be further described below with reference to specific embodiments, wherein the same reference numerals denote the same parts unless otherwise specifically stated. It should be emphasized that the following description is merely exemplary and not intended to limit the scope or application of the invention. The background section of the invention may contain background information about the problems or environment of the invention, and is not necessarily a description of prior art. Therefore, the content included in the background section is not an admission of prior art by the applicant.

[0030] A specific implementation of an LLC transformer, for example Figure 1-3 As shown, the LLC transformer includes a primary winding 801 and a secondary winding 802, a magnetic core 200, and a frame 300. The magnetic core 200 and the frame 300 are assembled together. The secondary winding 802 is a planar winding embedded in the frame 300. The primary winding 801 is a vertical winding wound on the frame 300. The primary winding 801 and the secondary winding 802 are coupled in only a predetermined number of layers to increase the leakage inductance of the LLC transformer. The secondary winding 802 is configured to be embedded in the frame 300, which provides more winding space for the primary winding 801, thus creating favorable conditions for the miniaturization of the LLC transformer product. Specifically, the predetermined number of layers of mutual coupling means that the secondary winding 802 has only one layer coupled with the primary winding 801, but it is not limited to this. The number of layers of the secondary winding 802 can be 1-3 layers, such as 1.5 layers, 2 layers, etc., as long as the number of layers of mutual coupling with the primary winding 801 is relatively limited and can be embedded in the skeleton 300. In this way, the effect of small volume and large leakage inductance can be achieved.

[0031] The secondary winding 802 is preferably made of copper sheets so that the LLC transformer can be adapted to handle large output currents. Figure 4 As shown, the magnetic core 200 preferably includes a core post 201, and the frame 300 correspondingly has a frame hole 301. The magnetic core 200 and the frame 300 are assembled together by inserting the core post 201 into the frame hole 301. The core post 201 has a groove structure 202 around it for accommodating or partially accommodating the frame 300. The internal shape of the groove structure 202 is preferably consistent with the outer contour of the frame 300. Furthermore, the magnetic core 200 is more preferably composed of a left magnetic core and a right magnetic core, which are assembled to the frame 300 from the left and right sides, respectively.

[0032] A specific embodiment of a method for manufacturing an LLC transformer includes the following steps:

[0033] The integrated frame and secondary winding are formed by embedding the planar wound secondary winding into the frame material, and then obtaining the integrated frame and secondary winding through injection molding. The planar wound secondary winding 802 can have a relatively small number of layers, such as 1, 1.5, 2, 2.5, or 3 layers, so that the number of layers that can be embedded in the frame and coupled with the primary winding 801 is relatively limited. The planar wound secondary winding can be obtained by combining two copper sheets 700 together, with the ends of the two copper sheets 700 bent to form three terminals 100, which extend beyond the frame 300. This method of obtaining a secondary winding can increase the output current and helps to reduce the size of the LLC transformer and improve operating efficiency. Furthermore, it is preferable to simultaneously embed the PIN pins into the frame during injection molding to save processing steps and improve processing efficiency. The process principle of this preferred method is as follows: Figure 5 As shown.

[0034] The primary winding is wound vertically on the integrated frame and the secondary winding frame. An isolation section is formed in the frame 300 between the primary coil 801 and the secondary coil 802. The primary winding 801 and the secondary winding 802 are coupled only through a predetermined number of layers. In this product, the primary winding 801 typically has a large number of layers (turns), therefore the predetermined number of layers of coupling is usually determined by the number of layers in the secondary winding 802. Figure 6-7 As shown, this step specifically includes: bobbin winding-coating-wire arrangement steps. The primary winding is made of two copper wires. The first copper wire is hung on pin 402, then passed through lead groove 502 and wound in winding groove 600. Finally, the end of the copper wire is led out from lead groove 501 and hung on pin 401. The second copper wire is hung on pin 404, then passed through lead groove 504 and wound in winding groove 600. Finally, the end of the copper wire is led out from lead groove 503 and hung on pin 403. A tinning step is then performed, with the preferred tinning temperature being 420±10℃. Finally, a core adhesive dispensing step is performed, where adhesive is applied to both sides of the groove structure 202 on the core surface that forms the core air gap.

[0035] The assembly of the magnetic core and the frame involves assembling the magnetic core 200 with the integrated frame and the frame 300 in the secondary winding to obtain the LLC transformer. Preferably, a dual-core structure is adopted, i.e., the magnetic core 200 includes a left core and a right core, and the frame 300 has a central hole 301. The central posts 201 of the left and right cores are inserted into the central hole 301 from the left and right sides, respectively, for assembly. A wrapping step is also preferred, i.e., using high-temperature tape to fix the assembled transformer. This method is simple, convenient, and easy to operate.

[0036] In addition, after assembly, the transformer is placed in an oven for baking only to accelerate molding. Preferably, the baking temperature is 130°C and the baking time is 60 minutes.

[0037] Finally, the obtained product undergoes comprehensive testing, specifically testing its electrical characteristics such as inductance and leakage inductance after baking and cooling. The LLC transformer manufactured using this embodiment exhibits a small size and high leakage inductance. Under conditions comparable in size to conventional products, the leakage inductance of a single LLC transformer unit manufactured using this embodiment can reach 20–80 μH, which is 5%–20% of the inductance value. Through turns ratio feedback, the leakage inductance in client applications can reach 200 μH, approximately 50% of the maximum inductance value.

[0038] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0039] Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

[0040] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An LLC transformer, comprising a primary winding and a secondary winding, a magnetic core and a frame, characterized in that, The magnetic core and the frame are assembled together. The secondary winding is a planar winding embedded in the frame. The primary winding is a vertical winding wound on the frame. The primary winding and the secondary winding are coupled together in only a predetermined number of layers to increase the leakage inductance of the LLC transformer.

2. The LLC transformer as described in claim 1, characterized in that, The predetermined number of layers of mutual coupling specifically means that only one layer of the secondary winding is coupled to the primary winding.

3. The LLC transformer as described in claim 1, characterized in that, The secondary winding is made of copper sheets.

4. The LLC transformer as described in claim 1, characterized in that, The secondary winding has 1-3 layers.

5. The LLC transformer as described in claim 1, characterized in that, The magnetic core includes a core post, and the frame has a frame hole. The magnetic core and the frame are assembled together by inserting the core post into the frame hole.

6. The LLC transformer as described in claim 5, characterized in that, The magnetic core includes a left magnetic core and a right magnetic core, which are assembled with the skeleton from the left and right sides, respectively.

7. A method for manufacturing an LLC transformer, characterized in that, Includes the following steps: The integrated skeleton and secondary winding are formed by embedding the planar wound secondary winding into the skeleton material, and then obtaining the integrated skeleton and secondary winding by injection molding. The primary winding is wound vertically on the integrated frame and the secondary winding frame, so that there are only a predetermined number of layers of mutual coupling between the primary winding and the secondary winding. The assembly of the magnetic core and the frame involves assembling the magnetic core, the integrated frame, and the frame of the secondary winding to obtain the LLC transformer.

8. The method for manufacturing an LLC transformer as described in claim 7, characterized in that, The secondary winding formed by planar winding has 1-3 layers.

9. The method for manufacturing an LLC transformer as described in claim 7 or 8, characterized in that, In the molding process of the integrated skeleton and secondary winding, the PIN pins are also simultaneously embedded into the skeleton for injection molding.

10. The method for manufacturing an LLC transformer as described in claim 7, characterized in that, The magnetic core assembly step adopts a dual-core assembly method, that is, the magnetic core includes a left magnetic core and a right magnetic core, the frame is provided with a central hole, and the central post of the left magnetic core and the central post of the right magnetic core are inserted into the central hole from the left and right sides respectively for assembly.

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