Power supply EMI filter

Abstract

The application relates to the technical field of filters, in particular to a power EMI filter. The power EMI filter has an input end and an output end; the power EMI filter comprises a filter circuit, the filter circuit comprises a differential mode filter circuit and a common mode filter circuit; the common mode filter circuit comprises a first common mode inductor and a first common mode capacitor group; the first common mode capacitor group comprises a first capacitor and a second capacitor, and a connecting point between the first capacitor and the second capacitor is grounded; the differential mode filter circuit comprises a first differential mode inductor, a second differential mode inductor and a third capacitor and a fourth capacitor arranged in parallel; in the direction from the input end to the output end, the first common mode inductor is located between the third capacitor and the fourth capacitor, the third capacitor is located upstream of the fourth capacitor, and the first differential mode inductor and the second differential mode inductor are located upstream of the first common mode capacitor group. The application can improve the overall attenuation capability of low-frequency electromagnetic interference.

Description

Technical Field

[0001] This application relates to the field of filter technology, and more specifically, to a power supply EMI filter. Background Technology

[0002] With the rapid development of electronic equipment and power systems, power supplies inevitably generate electromagnetic interference (EMI) during operation. This interference not only affects the performance of the power supply itself but can also adversely affect the normal operation of surrounding electronic components, control systems, and communication equipment, even leading to equipment malfunctions or signal distortion. In modern complex power and electronic systems, EMI problems are becoming increasingly prominent, especially in high-precision electronic instruments, communication base stations, industrial automation equipment, and new energy vehicles, placing higher demands on electromagnetic compatibility (EMC). To address these interferences, EMI filters are typically added to the power supply input or output to weaken or isolate unwanted electromagnetic noise, thereby improving the system's EMC performance. Currently, power supply EMI filters exhibit good suppression capabilities in the high-frequency range, effectively filtering out interference signals in the range of hundreds of kilohertz to tens of megahertz. However, in the low-frequency range, such as around 10 kHz, the filtering capability is relatively limited. Utility Model Content

[0003] The purpose of this application is to provide a power EMI filter, which aims to solve the technical problem that the power EMI filter has relatively limited filtering capability in the low-frequency band in related technologies.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a power EMI filter, which has an input terminal and an output terminal; The power supply EMI filter includes a filter circuit, which includes a differential-mode filter circuit and a common-mode filter circuit. The common-mode filter circuit includes a first common-mode inductor and a first common-mode capacitor group. The first common-mode capacitor group includes a first capacitor and a second capacitor. The connection point between the first capacitor and the second capacitor is grounded. The differential-mode filter circuit includes a first differential-mode inductor, a second differential-mode inductor, and a third capacitor and a fourth capacitor connected in parallel. From the input terminal to the output terminal, the first common-mode inductor is located between the third capacitor and the fourth capacitor, the third capacitor is located upstream of the fourth capacitor, and the first differential-mode inductor and the second differential-mode inductor are located upstream of the first common-mode capacitor group.

[0005] In some implementations, the first input terminal of the first common-mode inductor is connected to one end of the third capacitor, and the second input terminal of the first common-mode inductor is connected to the other end of the third capacitor; The first output terminal of the first common-mode inductor is connected to one end of the fourth capacitor, and the second output terminal of the first common-mode inductor is connected to the other end of the fourth capacitor.

[0006] In some implementations, one end of the first differential mode inductor is connected to one end of the fourth capacitor, and the other end of the first differential mode inductor is connected to one end of the first capacitor. One end of the second differential mode inductor is connected to the other end of the fourth capacitor, and the other end of the second differential mode inductor is connected to one end of the second capacitor; The other end of the first capacitor is connected to the other end of the second capacitor.

[0007] In some implementations, the differential mode filter circuit further includes a third differential mode inductor, which is a differential mode inductor formed by the leakage inductance of the first common mode inductor; The third capacitor and the third differential mode inductor form the first stage differential mode filter network of the differential mode filter circuit; The fourth capacitor, the first differential mode inductor, and the second differential mode inductor form the second-stage differential mode filter network of the differential mode filter circuit.

[0008] In some implementations, the filter circuit further includes a first resistor connected in parallel with the third capacitor, and the first resistor is located upstream of the third capacitor.

[0009] In some implementations, the first resistor is a color-coded resistor.

[0010] In some implementations, the first capacitor and the second capacitor are both Y2 type safety capacitors; the third capacitor and the fourth capacitor are both X2 type safety capacitors.

[0011] In some implementations, the power EMI filter further includes a circuit board on which the filtering circuitry is integrated.

[0012] In some implementations, the power EMI filter further includes a housing that is fixedly connected to the circuit board; the housing is made of aluminum or stainless steel.

[0013] In some implementations, the magnetic ring of the first common-mode inductor is made of nanocrystalline material.

[0014] The main advantages of the power supply EMI filter provided in this application are: The common-mode filter circuit of this application employs a first common-mode inductor in conjunction with a grounded first capacitor and a second capacitor. This structure provides a low-impedance discharge path for common-mode noise and, through local resonance with upstream differential-mode capacitors (a third capacitor and a fourth capacitor), effectively extends the low-frequency cutoff frequency of the common-mode filter, significantly enhancing the suppression capability for low-frequency common-mode interference (e.g., around 10 kHz). The differential-mode filter circuit introduces a first differential-mode inductor, a second differential-mode inductor, and a third capacitor and a fourth capacitor connected in parallel, forming a multi-stage differential-mode filter network, significantly widening the differential-mode suppression bandwidth. The first and second differential-mode inductors are positioned upstream of the first common-mode capacitor group, effectively improving the impedance matching and attenuation slope of low-frequency differential-mode interference. By placing the first common-mode inductor between the third and fourth capacitors, and placing the first differential-mode inductor and the second differential-mode inductor upstream of the first common-mode capacitor group, a staggered and coordinated layout of differential-mode and common-mode filter circuits is formed. This layout enables the power supply EMI filter to maintain excellent high-frequency suppression performance while improving the overall attenuation capability of low-frequency (e.g., 10 kHz) electromagnetic interference. Attached Figure Description

[0015] 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.

[0016] Figure 1 This is a schematic diagram (perspective view) of the power EMI filter provided in the embodiments of this application. Figure 2 This is a structural schematic diagram (perspective view) of the housing of the power EMI filter provided in the embodiments of this application. Figure 3 This is a schematic diagram of the internal structure of the power EMI filter provided in the embodiments of this application; Figure 4 This is a schematic diagram of the principle structure of the filter circuit provided in the embodiment of this application; Figure 5 This is an equivalent circuit diagram used to analyze the common-mode noise suppression performance of the power supply EMI filter in the embodiments of this application; Figure 6 This is an equivalent circuit diagram used to analyze the differential-mode noise suppression performance of the power supply EMI filter in the embodiments of this application; Figure 7 This is a simulation curve of the common-mode insertion loss of the power EMI filter in the embodiments of this application; Figure 8 This is a simulation curve of the differential-mode insertion loss of the power EMI filter in the embodiments of this application.

[0017] Explanation of key figure labels: L1, First common-mode inductor; C3, First capacitor; C4, Second capacitor; L2, First differential-mode inductor; L3, Second differential-mode inductor; C1, Third capacitor; C2, Fourth capacitor; L, Live wire input; L', Live wire output; N, Neutral wire input; N', Neutral wire output; R1, First resistor; Lg, Third differential-mode inductor; G, Ground wire; 101. Ground terminal; 102. Housing; 103. Input pin; 104. Output pin. Detailed Implementation

[0018] In related technologies, power supply EMI filters exhibit good suppression capabilities at high frequencies, effectively filtering out interference signals in the range of hundreds of kilohertz to tens of megahertz. However, at low frequencies, such as around 10 kHz, their filtering capability is relatively limited.

[0019] Therefore, this application provides a power EMI filter to solve the problems in related technologies.

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0021] Combination Figures 1 to 4 As shown, this application embodiment provides a power EMI filter, which has an input terminal and an output terminal. The power EMI filter includes a filter circuit, which includes a differential mode filter circuit and a common mode filter circuit. The common mode filter circuit includes a first common mode inductor L1 and a first common mode capacitor group, which includes a first capacitor C3 and a second capacitor C4. The connection point between the first capacitor C3 and the second capacitor C4 is grounded. The differential mode filter circuit includes a first differential mode inductor L2, a second differential mode inductor L3, and a third capacitor C1 and a fourth capacitor C2 connected in parallel. From the input terminal to the output terminal, the first common mode inductor L1 is located between the third capacitor C1 and the fourth capacitor C2. The third capacitor C1 is located upstream of the fourth capacitor C2. The first differential mode inductor L2 and the second differential mode inductor L3 are located upstream of the first common mode capacitor group.

[0022] The common-mode filter circuit in this embodiment uses a first common-mode inductor L1 in conjunction with a grounded first capacitor C3 and a second capacitor C4. This structure provides a low-impedance discharge path for common-mode noise and, through local resonance with the upstream differential-mode capacitors (third capacitor C1 and fourth capacitor C2), effectively extends the low-frequency cutoff frequency of the common-mode filter, significantly enhancing the suppression capability for low-frequency common-mode interference (e.g., around 10 kHz). The differential-mode filter circuit introduces a first differential-mode inductor L2, a second differential-mode inductor L3, and the third capacitor C1 and fourth capacitor C2 connected in parallel to form a multi-stage differential-mode filter network, significantly widening the differential-mode suppression bandwidth. The first differential-mode inductor L2 and the second differential-mode inductor L3 are positioned upstream of the first common-mode capacitor group, effectively improving the impedance matching and attenuation slope of low-frequency differential-mode interference. By placing the first common-mode inductor L1 between the third capacitor C1 and the fourth capacitor C2, and placing the first differential-mode inductor L2 and the second differential-mode inductor L3 upstream of the first common-mode capacitor group, a staggered and coordinated layout of differential-mode and common-mode filter circuits is formed. This layout enables the power supply EMI filter to maintain excellent high-frequency suppression performance while improving the overall attenuation capability of low-frequency (e.g., 10 kHz) electromagnetic interference.

[0023] In some embodiments, the power EMI filter is an AC filter, connected in series between the live wire (L), neutral wire (N) of the AC power supply and the load, ensuring that the electronic system to which the filter is used meets electromagnetic compatibility requirements. For example, the power EMI filter is suitable for use at the power interface of the electronic system, installed at the front end of the power module, and can simultaneously filter out electromagnetic interference transmitted from the power grid to the system and interference signals conducted from the system to the power grid, providing a stable and reliable power environment for the electronic system. This power EMI filter is suitable for 50 / 60Hz AC power supply systems requiring a high withstand voltage of 1000V. The operating temperature range of the power EMI filter is -55℃ to 125℃. The input terminals of the power EMI filter include a live wire input terminal L and a neutral wire input terminal N, and the output terminals include a live wire output terminal L' and a neutral wire output terminal N'. The power EMI filter also includes a ground terminal 101. The live wire input terminal L and the live wire output terminal L' correspond to each other, and the neutral wire input terminal N and the neutral wire output terminal N' correspond to each other. It is understood that in this embodiment, the direction from upstream to downstream is the direction from the input end to the output end; the live wire input end L is used for live wire connection, and the neutral wire input end N is connected to the neutral wire.

[0024] In some embodiments, the filter circuit further includes a first resistor R1, which is connected in parallel with the third capacitor C1. The first resistor R1 is located upstream of the third capacitor C1, so that the first resistor R1 acts as a bleeder resistor to protect the circuit and can safely discharge the charge on the third capacitor C1 after power is cut off, preventing the risk of electric shock. For example, the first resistor R1 is a color-coded resistor. One end of the first resistor R1 is connected to the live wire input terminal L, and the other end of the first resistor R1 is connected to the neutral wire input terminal N.

[0025] In some embodiments, the first input terminal of the first common-mode inductor L1 is connected to one end of the third capacitor C1, and the second input terminal of the first common-mode inductor L1 is connected to the other end of the third capacitor C1; the first output terminal of the first common-mode inductor L1 is connected to one end of the fourth capacitor C2, and the second output terminal of the first common-mode inductor L1 is connected to the other end of the fourth capacitor C2. This helps to reduce the 10 kHz common-mode cutoff frequency, thereby improving low-frequency insertion loss. For example, the first input terminal of the first common-mode inductor L1 is connected to the live wire input terminal L, and the second input terminal of the first common-mode inductor L1 is connected to the neutral wire input terminal N; the first input terminal of the first common-mode inductor L1 corresponds to the first output terminal of the first common-mode inductor L1, and the second input terminal of the first common-mode inductor L1 corresponds to the second output terminal of the first common-mode inductor L1.

[0026] In some embodiments, one end of the first differential mode inductor L2 is connected to one end of the fourth capacitor C2, and the other end of the first differential mode inductor L2 is connected to one end of the first capacitor C3; one end of the second differential mode inductor L3 is connected to the other end of the fourth capacitor C2, and the other end of the second differential mode inductor L3 is connected to one end of the second capacitor C4; the other end of the first capacitor C3 is connected to the other end of the second capacitor C4. This is beneficial for improving the low-frequency differential mode impedance. For example, the fourth capacitor C2 is located upstream of the first differential mode inductor L2 and the second differential mode inductor L3, the first differential mode inductor L2 is connected in series between the live wire input terminal L and the live wire output terminal L', and the second differential mode inductor L3 is connected in series between the neutral wire input terminal N and the neutral wire output terminal N'. The first capacitor C3 and the second capacitor C4 are connected in series. The other end of the first capacitor C3 is connected to the other end of the second capacitor C4 and then grounded. One end of the first capacitor C3 is connected to the live wire output terminal L'. One end of the second capacitor C4 is connected to the neutral wire output terminal N'. Thus, the first capacitor C3 is connected between the live wire and the ground wire G, and the second capacitor C4 is connected between the neutral wire and the ground wire G. It can be understood that grounding can refer to a direct or indirect connection to the ground terminal 101.

[0027] In some embodiments, the differential-mode filter circuit further includes a third differential-mode inductor Lg, which is a differential-mode inductor formed by the leakage inductance of the first common-mode inductor L1; the third capacitor C1 and the third differential-mode inductor Lg form the first-stage differential-mode filter network of the differential-mode filter circuit; the fourth capacitor C2, the first differential-mode inductor L2, and the second differential-mode inductor L3 form the second-stage differential-mode filter network of the differential-mode filter circuit. By utilizing the differential-mode inductor formed by the leakage inductance of the first common-mode inductor L1, an additional differential-mode inductor is unnecessary, which helps reduce cost and size.

[0028] In some embodiments, the power EMI filter further includes a circuit board on which the filter circuitry is integrated for ease of manufacturing. The circuit board has a ground wire G connected to a ground terminal 101. Exemplarily, potting compound can be filled into the housing to improve mechanical strength and insulation. The circuit board can be a PCB; the potting compound needs to withstand temperatures up to 200°C to adapt to long-term operation in high-temperature, high-humidity, and moldy environments.

[0029] In some embodiments, the power EMI filter further includes a housing 102, which is fixedly connected to the circuit board. The housing 102 is made of metal, which enhances the shielding effect against external noise interference and provides a safe grounding function. For example, the metal can be stainless steel. The inner and outer surfaces of the housing 102 can have a plating layer, which can be a nickel layer. The power EMI filter also includes two input pins 103 and two output pins 104. One input pin 103 is connected to the live wire input terminal L, and the other input pin 103 is connected to the neutral wire input terminal N. One output pin 104 is connected to the live wire output terminal L', and the other output pin 104 is connected to the neutral wire output terminal N'. The input pins 103 and 104 can be fixed to the housing 102 by insulating components. The ground terminal 101 is fixed to the housing 102 and can be directly electrically connected to the housing 102. The length, width, and height of the housing 102 are 63mm, 31mm, and 30mm, respectively. The temperature resistance of both the housing 102 and the PCB board needs to be greater than 260℃. Furthermore, since the housing 102 is made of metal with a melting point as high as 470℃, it can withstand long-term operation in environments up to 180℃ and exhibits strong chemical resistance.

[0030] It should be noted that in some other possible embodiments, the outer casing 102 may also be made of aluminum.

[0031] In some embodiments, the first capacitor C3 and the second capacitor C4 are both Y2 type safety capacitors; the third capacitor C1 and the fourth capacitor C2 are both X2 type safety capacitors. Thus, the X2 type safety capacitor acts between the live wire and the neutral wire. The X2 type safety capacitor can withstand high-voltage pulse impacts, ensuring that the capacitor will not short-circuit and break down when a transient surge occurs in the AC power. Furthermore, the failure mode of the X2 type safety capacitor is open circuit mode, preventing the live wire and neutral wire from being directly connected after a short circuit. The X2 type safety capacitor used in this embodiment needs to have a withstand voltage of 2000V. The Y2 type safety capacitor acts between the live wire and the ground wire G and between the neutral wire and the ground wire G, has high insulation strength, and its failure mode is open circuit mode, preventing the metal casing 102 from being directly connected to the live wire, causing a short circuit. The Y2 type safety capacitor used in this embodiment needs to have a withstand voltage of 2700V. For example, the first capacitor C3, the second capacitor C4, the third capacitor C1, and the fourth capacitor C2 can all be film capacitors used for AC electrode filtering. Film capacitors are characterized by good high-frequency characteristics, high reliability, and high insulation. The operating temperature range of film capacitors is -55℃ to 125℃.

[0032] In some embodiments, the magnetic ring of the first common-mode inductor L1 is made of nanocrystalline material. Nanocrystalline material has high initial permeability, which can provide higher inductance performance when applied in the low-frequency range. For example, to improve insertion loss in the low-frequency range, the inductance of the first common-mode inductor L1 at 1kHz is greater than or equal to 70mH, which is beneficial for achieving low-frequency filtering characteristics. The magnetic rings of the first differential-mode inductor L2 and the second differential-mode inductor L3 are both iron-nickel-molybdenum magnetic rings with high saturation flux density. The first common-mode inductor L1, the first differential-mode inductor L2, and the second differential-mode inductor L3 are all wound with single-strand enameled copper wire to meet the 6A rated current requirement of the power supply EMI filter. The operating temperature range of the high-permeability nanocrystalline magnetic ring is -55℃ to 125℃. The temperature rating of the enameled copper wire is 180℃.

[0033] In the embodiments of this application, for accurate analysis and evaluation Figure 4 The power supply EMI filter shown needs to be examined separately in common-mode and differential-mode to assess its ability to suppress different types of noise.

[0034] Figure 5This is an equivalent circuit diagram used to analyze the common-mode noise suppression performance of the power EMI filter in the embodiments of this application. The equivalent circuit diagram shows the equivalent connection of each inductor and capacitor element in the power EMI filter under common-mode noise. Under common-mode noise, the signals on the live wire and neutral wire are in the same direction and at the same potential relative to the ground wire G; therefore, the live wire and neutral wire can be considered as the same node in the circuit. The diagram shows the equivalent parallel connection of the first common-mode inductor L1, the first capacitor C3, and the second capacitor C4 under common-mode noise, forming a bypass path for the common-mode noise.

[0035] Figure 6 This is an equivalent circuit diagram used to analyze the differential-mode noise suppression performance of the power EMI filter in the embodiments of this application. The diagram illustrates the equivalent connection of each inductor and capacitor in the power EMI filter under differential-mode noise. Under differential-mode noise, the signals on the live wire and neutral wire are opposite in direction and have opposite potentials, with the voltage mainly existing between the live wire and neutral wire. The diagram shows the differential-mode filter network formed by the equivalent series connection of the third capacitor C1, the fourth capacitor C2, the third differential-mode inductor Lg, the first differential-mode inductor L2, the second differential-mode inductor L3, and the first capacitor C3 and the second capacitor C4, used to attenuate the differential-mode noise between the neutral and live wires.

[0036] Figure 7 This is a simulation curve of the common-mode insertion loss of the power EMI filter in the embodiments of this application; Figure 8 This is a simulation curve of the differential-mode insertion loss of the power EMI filter in the embodiments of this application. Combined with... Figure 5 and Figure 7 ,as well as Figure 6 and Figure 8 As can be seen, the power EMI filter in this embodiment meets the requirement of a common-mode insertion loss of not less than 30dB at 10kHz and a differential-mode insertion loss of not less than 20dB at 10kHz. Compared with related technologies where filters of the same size typically have an insertion loss of less than 10dB at low frequencies (e.g., 10kHz), the power EMI filter provided in this embodiment exhibits significantly better anti-interference performance at low frequencies (e.g., 10kHz). Therefore, the power EMI filter in this embodiment achieves the characteristics of small size and high insertion loss at low frequencies.

[0037] In summary, this application provides a small-volume, low-frequency, high-insertion-loss power EMI filter, employing a novel circuit topology combined with common materials. Through optimization of structure, materials, and processes, this power EMI filter achieves high withstand voltage, high power, and high low-frequency suppression characteristics. In terms of performance, this power EMI filter significantly improves low-frequency suppression capability within the same volume, possessing high insertion loss performance, good withstand voltage capability, and a wide operating frequency band. It balances high and low-frequency noise suppression performance, effectively suppressing conducted interference on electronic system transmission lines, thereby significantly improving the system's electromagnetic compatibility (EMC) performance. Specifically, this power EMI filter meets the CE102 conducted interference standard. Targeting major interference sources such as transient currents and voltage spikes generated during startup of the switching power supply, it meets the CE102 conducted interference requirements in the 10kHz-10MHz range, effectively suppressing interference signals generated by the switching power supply. By implementing bidirectional filtering, it prevents internal system interference signals from entering the power network and also prevents interference signals in the power network from affecting subsequent circuits, thereby improving the overall reliability and electrical performance of the system. Furthermore, this application fully considers environmental adaptability requirements such as vibration resistance, shock resistance, moisture resistance, and salt spray resistance in its structural and process design, enabling the power supply EMI filter to maintain stable performance over a wide operating temperature range, with high reliability and environmental applicability, and meeting the engineering requirements of harsh application scenarios.

[0038] It should be understood that, in the embodiments of this application, unless otherwise expressly specified and limited, the terms "connection," "fixed connection," "contact," etc., should be interpreted broadly. Those skilled in the art can understand the specific meanings of the various terms in the embodiments of this application according to the specific circumstances.

[0039] For example, the "connection" can be a fixed connection, a rotating connection, a flexible connection, a sliding connection, a one-piece molding, an electrical connection, a contact connection, or other connection methods; it can be a direct connection, or an indirect connection through an intermediate medium, or a connection within two components or an interaction between two components.

[0040] For example, a "fixed connection" can be a component that can be directly or indirectly fixedly connected to another component; a fixed connection can include mechanical connection, welding, bonding or integral molding, etc., wherein mechanical connection can include riveting, bolting, threaded connection, keying, snap-fit ​​connection, locking connection, plugging, etc., and bonding can include adhesive bonding and solvent bonding, etc.

[0041] It should also be understood that the “parallel” or “perpendicular” described in the embodiments of this application can be understood as “approximately parallel” or “approximately perpendicular”.

[0042] It should also be understood that 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. Features specified as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0043] In the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature and the second feature are in direct contact, or that the first feature and the second feature are in indirect contact through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0044] It should also be understood that the terms “length,” “width,” “up,” “down,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” and “outer,” etc., indicate the orientation or positional relationship (if any) based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application 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 application.

[0045] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims. In conclusion, the above description is merely a preferred embodiment of the technical solution of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A power supply EMI filter, characterized in that, The power EMI filter has an input terminal and an output terminal; The power supply EMI filter includes a filter circuit, which includes a differential-mode filter circuit and a common-mode filter circuit. The common-mode filter circuit includes a first common-mode inductor and a first common-mode capacitor group. The first common-mode capacitor group includes a first capacitor and a second capacitor. The connection point between the first capacitor and the second capacitor is grounded. The differential-mode filter circuit includes a first differential-mode inductor, a second differential-mode inductor, and a third capacitor and a fourth capacitor connected in parallel. From the input terminal to the output terminal, the first common-mode inductor is located between the third capacitor and the fourth capacitor, the third capacitor is located upstream of the fourth capacitor, and the first differential-mode inductor and the second differential-mode inductor are located upstream of the first common-mode capacitor group.

2. The power EMI filter as described in claim 1, characterized in that, The first input terminal of the first common-mode inductor is connected to one end of the third capacitor, and the second input terminal of the first common-mode inductor is connected to the other end of the third capacitor; The first output terminal of the first common-mode inductor is connected to one end of the fourth capacitor, and the second output terminal of the first common-mode inductor is connected to the other end of the fourth capacitor.

3. The power EMI filter as described in claim 1, characterized in that, One end of the first differential mode inductor is connected to one end of the fourth capacitor, and the other end of the first differential mode inductor is connected to one end of the first capacitor; One end of the second differential mode inductor is connected to the other end of the fourth capacitor, and the other end of the second differential mode inductor is connected to one end of the second capacitor; The other end of the first capacitor is connected to the other end of the second capacitor.

4. The power EMI filter as described in any one of claims 1-3, characterized in that, The differential mode filter circuit further includes a third differential mode inductor, which is a differential mode inductor formed by the leakage inductance of the first common mode inductor; The third capacitor and the third differential mode inductor form the first stage differential mode filter network of the differential mode filter circuit; The fourth capacitor, the first differential mode inductor, and the second differential mode inductor form the second-stage differential mode filter network of the differential mode filter circuit.

5. The power EMI filter as described in any one of claims 1-3, characterized in that, The filter circuit further includes a first resistor, which is connected in parallel with the third capacitor and is located upstream of the third capacitor.

6. The power EMI filter as described in claim 5, characterized in that, The first resistor is a color-coded resistor.

7. The power EMI filter as described in any one of claims 1-3, characterized in that, The first capacitor and the second capacitor are both Y2 type safety capacitors; the third capacitor and the fourth capacitor are both X2 type safety capacitors.

8. The power EMI filter as described in any one of claims 1-3, characterized in that, The power EMI filter also includes a circuit board, on which the filtering circuit is integrated.

9. The power EMI filter as described in claim 8, characterized in that, The power EMI filter also includes a housing, which is fixedly connected to the circuit board; the housing is made of aluminum or stainless steel.

10. The power EMI filter as described in any one of claims 1-3, characterized in that, The magnetic ring of the first common-mode inductor is made of nanocrystalline material.

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