Emi filter and access circuit therefor

Abstract

The application belongs to the technical field of filters, and provides an EMI filter and an access circuit thereof. The EMI filter realizes stable transmission of a 20A rated current under a compact size of length* width* height ≤ 35mm*25mm*12mm. A hollow layout of a low magnetic ring and a double-wire enameled copper wire side-by-side winding common-mode inductor design in the middle of a PCB board not only compresses the space occupation in the vertical direction of the components, but also guarantees the anti-saturation performance and heat dissipation efficiency under a large-current working condition. Small package ceramic capacitors cooperate with common-differential mode composite filtering topology, and the capacitor series connection structure of the common-mode branch forms an equivalent differential-mode capacitor, without the need for additional independent large-capacity differential-mode capacitors. In a limited space, the common-mode and differential-mode insertion loss of the 150kHz-30MHz frequency band is all ≥ 50dB, meeting the CE102 conducted interference requirements.

Description

Technical Field

[0001] This application belongs to the field of filter technology, and more specifically, relates to an EMI filter and its connection circuit. Background Technology

[0002] Power supply EMI filters, as key components for suppressing conducted interference, have evolved into various sizes and structures, but miniaturization under high-current conditions remains a technical bottleneck. In conventional designs, to handle rated currents of 20A and above, large-size magnetic cores and increased winding wire diameters are often required, significantly increasing the size of the common-mode inductor. Simultaneously, to meet wide-band insertion loss requirements, multiple sets of capacitors are needed, further reducing internal space. Therefore, there is an urgent need for a new type of filter that can achieve stable high-current transmission and possess excellent filtering performance within a very small size. Summary of the Invention

[0003] This application provides an EMI filter and its connection circuit to solve the technical problem of large size of existing high-current transmission filters.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: An EMI filter is provided, comprising: The shell, with an internal space for containment; A circuit board is disposed within the receiving space of the housing, and the middle area of ​​the circuit board has a hollow structure; A common-mode inductor is disposed within the hollow structure of the circuit board, and the common-mode inductor is made of two strands of enameled copper wire wound side by side; Multiple ceramic capacitors are soldered to the periphery of the circuit board to form a filter circuit.

[0005] As a further improvement to the above technical solution: Optionally, the filtering circuit includes a common-mode filtering circuit; the common-mode filtering circuit includes a common-mode inductor, a first common-mode capacitor, a second common-mode capacitor, a third common-mode capacitor, and a fourth common-mode capacitor; The first common-mode capacitor and the second common-mode capacitor are connected in series between the positive and negative terminals of the input terminal, and the third common-mode capacitor and the fourth common-mode capacitor are connected in series between the positive and negative terminals of the output terminal. The ground terminal is connected between the first common-mode capacitor and the second common-mode capacitor, and between the third common-mode capacitor and the fourth common-mode capacitor. One end of the common-mode inductor is connected in parallel between the first common-mode capacitor and the third common-mode capacitor, and the other end of the common-mode inductor is connected in parallel between the second common-mode capacitor and the fourth common-mode capacitor.

[0006] Optionally, the filtering circuit further includes a differential-mode filtering circuit; the differential-mode filtering circuit includes a differential-mode inductor equivalent to a common-mode inductor, a first differential-mode capacitor, a second differential-mode capacitor, a first equivalent differential-mode capacitor, and a second equivalent differential-mode capacitor. The first differential-mode capacitor and the first equivalent differential-mode capacitor are connected in parallel between the positive and negative terminals of the input terminal, the second differential-mode capacitor and the second equivalent differential-mode capacitor are connected in parallel between the positive and negative terminals of the output terminal, one end of the differential-mode inductor is connected in parallel to one end of the first differential-mode capacitor and the second differential-mode capacitor, and the other end of the differential-mode inductor is connected in parallel to the other end of the first differential-mode capacitor and the second differential-mode capacitor. The first equivalent differential mode capacitor is formed by connecting the first common mode capacitor and the second common mode capacitor in series, and the second equivalent differential mode capacitor is formed by connecting the third common mode capacitor and the fourth common mode capacitor in series.

[0007] Optionally, the common mode inductor is further fixed to the circuit board with adhesive, and the circuit board is grounded to the inner wall of the housing after being installed in the housing.

[0008] Optionally, the housing is a metal housing, and the surface of the metal housing is plated with a nickel layer, the thickness of which is ≥5.0μm.

[0009] Optionally, the housing is provided with flange mounting structures on both sides, and the flange mounting structures are provided with mounting holes.

[0010] Compared to existing technologies, the beneficial effects of the EMI filter provided in this application are as follows: The EMI filter provided in this application achieves stable transmission of a rated current of 20A within a compact size of ≤35mm×25mm×12mm (length×width×height). The design of a low-profile magnetic ring with a central cutout on the PCB and a common-mode inductor wound with parallel double-strand enameled copper wire not only reduces the vertical space occupied by components but also ensures anti-saturation performance and heat dissipation efficiency under high current conditions. Small-package ceramic capacitors, combined with a common-mode / differential-mode composite filter topology, reuse the capacitor series structure of the common-mode branch to form an equivalent differential-mode capacitor, eliminating the need for an additional large-capacity differential-mode capacitor. Within a limited space, it achieves common-mode and differential-mode insertion losses of ≥50dB in the 150kHz-30MHz frequency band, meeting the CE102 conducted interference requirements.

[0011] This application also provides an EMI filter access circuit, including: power supply; The source impedance is connected in series with the power supply. The aforementioned EMI filter has its input port connected in parallel with the power supply and the source impedance; The load impedance forms a parallel structure with the output port of the EMI filter. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a cross-sectional structural diagram of the EMI filter provided in this application; Figure 2 A circuit diagram of the EMI filter provided in this application.

[0014] The following are the labeling elements in the figure: 1. Shell; 2. Circuit board; 3. Common mode inductor; 4. Ceramic capacitor; 41. First common-mode capacitor; 42. Second common-mode capacitor; 43. Third common-mode capacitor; 44. Fourth common-mode capacitor; 45. First differential-mode capacitor; 46. Second differential-mode capacitor. Detailed Implementation

[0015] Embodiments of the present invention are described in detail below, examples of which are illustrated 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 the present invention, and should not be construed as limiting the present invention.

[0016] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention 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. Therefore, they should not be construed as limitations on this invention.

[0017] 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 as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0018] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0019] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0020] Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of the present invention.

[0021] In the following description, suffixes such as "circuit," "component," "assembly," or "unit" are used only for the purpose of illustrative purposes and do not have any specific meaning in themselves. Therefore, they can be used interchangeably.

[0022] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0023] like Figure 1 and Figure 2As shown, this application provides an EMI filter, including a housing 1, a circuit board 2, a common-mode inductor 3, and multiple ceramic capacitors 4. The housing 1 is made of steel and precision-stamped in one piece, forming an internal accommodating space. Its length, width, and height are controlled within 35mm, 25mm, and 12mm, respectively. The outer surface is plated with a nickel layer with a thickness of not less than 5.0μm to provide electromagnetic shielding and environmental protection. Flange mounting holes and electronic wire exit channels are provided on both sides. The circuit board 2 is a 1.5mm thick FR4 fiberglass board, horizontally fixed within the accommodating space of the housing 1. A hollow structure with a shape adapted to the common-mode inductor 3 is opened in its central area, and conductive lines and pads are arranged in the surrounding area. The common-mode inductor 3 is housed within the hollow structure of the circuit board 2 to reduce the overall assembly height. Its magnetic core is a high-permeability manganese-zinc ferrite core with a height of 5mm. The winding uses double-strand enameled copper wire wound side-by-side on the core. This winding method ensures that the conductor cross-sectional area meets the 20A rated current carrying capacity while effectively controlling the vertical dimensions of the component. Multiple ceramic capacitors 4, using small-package surface-mount devices with dimensions of 3.2mm × 2.5mm × 2.0mm, are soldered to the periphery of circuit board 2. They are electrically connected to the pins of common-mode inductor 3 and the input / output harness through the internal traces of circuit board 2, jointly constructing a common-mode and differential-mode filtering network. After assembly, the gaps inside the housing 1 are filled with potting compound resistant to 200℃ to fix the internal components and improve vibration and shock resistance.

[0024] In some specific embodiments of this application, the filtering circuit includes a common-mode filtering circuit, mainly used to suppress common-mode interference signals between the power line and ground. The common-mode filtering circuit specifically includes a common-mode inductor 3, a first common-mode capacitor 41, a second common-mode capacitor 42, a third common-mode capacitor 43, and a fourth common-mode capacitor 44. The first common-mode capacitor 41 and the second common-mode capacitor 42 are connected in series across the positive and negative terminals of the input. The third common-mode capacitor 43 and the fourth common-mode capacitor 44 are connected in series across the positive and negative terminals of the output. The grounding terminal is connected to the common connection point of the first common-mode capacitor 41 and the second common-mode capacitor 42, and the common connection point of the third common-mode capacitor 43 and the fourth common-mode capacitor 44, forming a two-stage common-mode filtering architecture. One end of the common-mode inductor 3 is connected in parallel to the line between the first common-mode capacitor 41 and the third common-mode capacitor 43, and the other end is connected in parallel to the line between the second common-mode capacitor 42 and the fourth common-mode capacitor 44. This allows the interference current to flow through the common-mode inductor 3 for impedance blocking after being coupled by the voltage divider of the two stages of common-mode capacitors. The first common-mode capacitor 41, the second common-mode capacitor 42, the third common-mode capacitor 43, and the fourth common-mode capacitor 44 are all multilayer ceramic chip capacitors with dimensions of 3.2mm×2.5mm×2.0mm, and are soldered to the periphery of the circuit board 2. Combined with the low-profile layout of the common-mode inductor 3 in the cutout area of ​​the circuit board 2, a highly efficient common-mode noise suppression path is constructed within a limited space, ensuring that the common-mode insertion loss of the filter in the 150kHz to 30MHz frequency band is not less than 50dB.

[0025] In some specific embodiments of this application, the filtering circuit further includes a differential-mode filtering circuit, mainly used to suppress differential-mode interference signals between lines. The differential-mode filtering circuit utilizes the leakage inductance characteristic of the common-mode inductor 3 to be equivalent to a differential-mode inductor, and specifically includes a first differential-mode capacitor 45, a second differential-mode capacitor 46, a first equivalent differential-mode capacitor formed by connecting a first common-mode capacitor 41 and a second common-mode capacitor 42 in series, and a second equivalent differential-mode capacitor formed by connecting a third common-mode capacitor 43 and a fourth common-mode capacitor 44 in series. The first differential-mode capacitor 45 and the first equivalent differential-mode capacitor are connected in parallel and then connected across the positive and negative terminals of the input terminal. The second differential-mode capacitor 46 and the second equivalent differential-mode capacitor are connected in parallel and then connected across the positive and negative terminals of the output terminal. One end of the differential-mode inductor equivalent to the common-mode inductor 3 is connected in parallel to the line between the first differential-mode capacitor 45 and the second differential-mode capacitor 46, and the other end is connected in parallel to the line between the first equivalent differential-mode capacitor and the second equivalent differential-mode capacitor. This architecture uses the capacitor series connection structure in the common-mode branch to form an equivalent differential-mode capacitor, eliminating the need for an additional large-capacity differential-mode capacitor and effectively reducing the component footprint. With the layout of the first differential-mode capacitor 45 and the second differential-mode capacitor 46 on circuit board 2, differential-mode noise is shunted by two stages of capacitors and attenuated by the impedance of the differential-mode inductor along the transmission path. This ensures that the differential-mode insertion loss of the filter in the 150kHz to 30MHz frequency band is not less than 50dB, meeting the CE102 conducted interference standard requirements.

[0026] In some specific embodiments of this application, after the common-mode inductor 3 is placed within the hollow structure of the circuit board 2, epoxy adhesive is applied between it and the circuit board 2 for secondary fixation to offset shear stress under vibration or impact conditions and prevent fatigue fracture of the pin solder joints. A grounding pad is pre-set in the edge area of ​​the circuit board 2. After the circuit board 2 is fully inserted into the receiving space of the housing 1, the grounding pad is tightly fitted to the top inner wall of the housing 1, and the two are fully soldered together using high-temperature tin-lead solder to achieve low-impedance electrical conduction between the circuit board 2 and the housing 1. This connection method allows the metal housing 1 to simultaneously serve as the common ground point for the filter circuit, providing a low-impedance discharge path for common-mode noise, while utilizing the electromagnetic shielding characteristics of the housing 1 to suppress internal electromagnetic radiation leakage. After the internal components are assembled, potting compound with a temperature resistance of not less than 200°C is injected through the top opening of the housing 1. The potting compound fully fills the gaps inside the housing 1 and wraps all components and solder joints. After curing, the circuit board 2 assembly is fixed to the housing 1 as a whole, further improving the overall structure's vibration resistance, impact resistance, and airtightness.

[0027] In some specific embodiments of this application, the housing 1 is a steel metal housing, integrally formed by precision stamping, and plated with a nickel layer with a thickness ≥5.0μm. This nickel layer can improve the corrosion resistance and salt spray resistance of the housing 1, making it suitable for harsh application environments such as high humidity and high salt spray. At the same time, it ensures the wettability of the solder when the housing 1 is grounded and soldered to the circuit board 2, reduces the grounding loop impedance, ensures stable electromagnetic shielding performance, and also improves the wear resistance of the surface of the housing 1, meeting the requirements of repeated disassembly and assembly of the flange mounting structure.

[0028] In some specific embodiments of this application, the two sides of the housing 1 extend outward to form flange mounting structures. Through mounting holes with a diameter of 3.5mm are provided on the flange mounting structures. The corners of the flange mounting structures and the openings of the mounting holes are rounded to reduce stress concentration and prevent scratching of cables or operators during assembly. This flange structure is used to fix the filter to the external equipment substrate. Combined with the integral curing structure formed by the potting compound inside the housing 1, vibration and impact stress can be evenly distributed to the mounting interface, improving the overall vibration and impact resistance performance. The positional accuracy of the mounting holes and the flatness of the flange meet the requirements of batch assembly, ensuring that the filter will not become loose due to deformation caused by thermal expansion and contraction within the operating temperature range of -55℃ to 125℃, thus guaranteeing the reliability of the connection during long-term operation.

[0029] This application also provides an EMI filter access circuit, including a power supply, a source impedance, the EMI filter described in the above embodiment, and a load impedance. The power supply provides DC or AC power, and the source impedance is connected in series in the output circuit of the power supply to simulate the output impedance characteristics of an actual power grid or power supply system, ensuring impedance matching between the test and application scenarios. The input port of the EMI filter is connected to the node between the power supply and the source impedance via an electronic wire, forming a parallel structure with the filter input, the power supply, and the source impedance to receive the supplied power and attenuate conducted interference from the power supply side. The load impedance is connected in parallel to the output port of the EMI filter to simulate the input characteristics of downstream electrical equipment. Under this connection, the filter presents a high impedance to electromagnetic noise from the power supply side, blocking noise from entering the load end, while simultaneously bypassing and suppressing interference noise generated at the load end and fed back to the power supply side, achieving bidirectional filtering and ensuring electromagnetic compatibility between the power supply and the load.

[0030] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An EMI filter, characterized in that, include: The shell (1) has an internal space for receiving the contents; The circuit board (2) is disposed in the receiving space of the housing (1), and the middle area of ​​the circuit board (2) is provided with a hollow structure; A common-mode inductor (3) is disposed in the hollow structure of the circuit board (2), and the common-mode inductor (3) is made of two strands of enameled copper wire wound side by side; Multiple ceramic capacitors (4) are soldered to the periphery of the circuit board (2) to form a filter circuit.

2. The EMI filter as described in claim 1, characterized in that, The filtering circuit includes a common-mode filtering circuit; the common-mode filtering circuit includes a common-mode inductor (3), a first common-mode capacitor (41), a second common-mode capacitor (42), a third common-mode capacitor (43), and a fourth common-mode capacitor (44); The first common-mode capacitor (41) and the second common-mode capacitor (42) are connected in series between the positive and negative terminals of the input terminal, and the third common-mode capacitor (43) and the fourth common-mode capacitor (44) are connected in series between the positive and negative terminals of the output terminal. The ground terminal is connected between the first common-mode capacitor (41) and the second common-mode capacitor (42), as well as between the third common-mode capacitor (43) and the fourth common-mode capacitor (44). One end of the common-mode inductor (3) is connected in parallel between the first common-mode capacitor (41) and the third common-mode capacitor (43), and the other end of the common-mode inductor (3) is connected in parallel between the second common-mode capacitor (42) and the fourth common-mode capacitor (44).

3. The EMI filter according to claim 2, characterized in that, The filtering circuit further includes a differential-mode filtering circuit; the differential-mode filtering circuit includes a differential-mode inductor equivalent to a common-mode inductor (3), a first differential-mode capacitor (45), a second differential-mode capacitor (46), a first equivalent differential-mode capacitor, and a second equivalent differential-mode capacitor. The first differential-mode capacitor (45) and the first equivalent differential-mode capacitor are connected in parallel between the positive and negative terminals of the input terminal, the second differential-mode capacitor (46) and the second equivalent differential-mode capacitor are connected in parallel between the positive and negative terminals of the output terminal, one end of the differential-mode inductor is connected in parallel to one end of the first differential-mode capacitor (45) and the second differential-mode capacitor (46), and the other end of the differential-mode inductor is connected in parallel to the other end of the first differential-mode capacitor (45) and the second differential-mode capacitor (46); The first equivalent differential mode capacitor is formed by connecting the first common mode capacitor (41) and the second common mode capacitor (42) in series, and the second equivalent differential mode capacitor is formed by connecting the third common mode capacitor (43) and the fourth common mode capacitor (44) in series.

4. The EMI filter according to claim 1, characterized in that: The common mode inductor (3) is further fixed to the circuit board (2) by adhesive. After the circuit board (2) is installed in the housing (1), it is grounded to the inner wall of the housing (1).

5. The EMI filter according to claim 1, characterized in that, The housing (1) is a metal housing (1), and the surface of the metal housing (1) is plated with a nickel layer, the thickness of which is ≥5.0μm.

6. The EMI filter according to claim 1, characterized in that, The housing (1) has flange mounting structures on both sides, and the flange mounting structures have mounting holes.

7. An EMI filter access circuit, characterized in that, include: power supply; The source impedance is connected in series with the power supply. The EMI filter according to any one of claims 1 to 6 has its input port connected in parallel with the power supply and the source impedance; The load impedance forms a parallel structure with the output port of the EMI filter.

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