EMI Filter Circuit

Abstract

The present application provides an EMI filter circuit that combines a first filter circuit, a second filter circuit, and a third filter circuit based on the transformer principle and connects them to the power supply system. This circuit achieves the goal of suppressing common-mode and differential-mode interference at the power input or output port using a filter circuit that is simple in structure, small in size, and lightweight, and achieves full-band interference reduction while providing enhanced filtering for fixed-frequency interference. The EMI filter circuit provided by this application has a superior low-frequency interference suppression effect compared to traditional inductive filtering, effectively resolving the difficulty of low-frequency interference suppression efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of circuit interference suppression, and in particular to an EMI filter circuit. Background Art

[0002] The switching process of semiconductors inside the power supply system generates a very high rate of change of voltage or current, which causes the voltage or current to contain abundant high-order harmonics. Transient noise is generated through the parasitic inductance and distributed capacitance in the line, thus generating conducted interference in the circuit. On the one hand, it affects the electromagnetic compatibility within the system, and on the other hand, it may cause electromagnetic interference (EMI) to other equipment outside the system. Therefore, it is necessary to suppress the electromagnetic interference generated by the power supply device.

[0003] High-power power supply systems often feature high currents and voltages. Traditional filter circuits often suffer from drawbacks such as bulk, weight, high cost, low reliability, and leakage current. Especially for suppressing low-frequency interference, the filtering efficiency is often poor. A new filter circuit is needed that can address these issues. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide an EMI filtering circuit.

[0005] Based on the above purpose, the present application provides an EMI filter circuit, characterized in that it includes: a first filter circuit, a second filter circuit and a third filter circuit;

[0006] The first filter circuit is provided between the positive electrode of the power supply and the input terminal of the power module, and is used to improve the differential mode impedance of the EMI filter circuit and reduce the harmonics returned to the power supply; wherein the first filter circuit is connected to the input terminal through the second filter circuit;

[0007] The second filter circuit is connected to the first filter circuit, the negative electrode of the power supply and the input terminal respectively, and is used to improve the common mode impedance of the EMI filter circuit;

[0008] The third filter circuit is provided between the output terminal of the power module and the load, and is used to further improve the common mode impedance of the EMI filter circuit.

[0009] As can be seen from the above, the EMI filter circuit provided by this application suppresses differential and common-mode interference at the input or output ports of the power supply by setting up multiple filter circuits, achieving full-band interference reduction. At the same time, enhanced filtering can be performed for fixed-frequency interference. Compared with traditional inductor filtering, this method has good low-frequency interference suppression effect, effectively solving the difficulty of low-frequency interference suppression efficiency. Each filter circuit is obtained by connecting an inductor and a transformer, and has the advantages of simple circuit structure, small size, light weight, and no leakage current. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in this application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0011] Figure 1 A schematic diagram of an EMI filter circuit provided in an embodiment of the present application;

[0012] Figure 2a A schematic diagram of a first filtering circuit provided in an embodiment of the present application;

[0013] Figure 2b A schematic diagram of a second filtering circuit provided in an embodiment of the present application;

[0014] Figure 2c A schematic diagram of a third filtering circuit provided in an embodiment of the present application;

[0015] Figure 3 A schematic diagram of an equivalent circuit of the first filtering circuit, the second filtering circuit, or the third filtering circuit provided in an embodiment of the present application;

[0016] Figure 4 An impedance curve diagram of the first filter circuit provided in an embodiment of the present application;

[0017] Figure 5a This is a schematic diagram of the first filter circuit provided by an embodiment of the present application after an auxiliary transformer is added;

[0018] Figure 5b A schematic diagram of a second filter circuit provided in an embodiment of the present application with a first auxiliary common-mode transformer added;

[0019] Figure 5c A schematic diagram of a third filtering circuit provided in an embodiment of the present application with a second auxiliary common-mode transformer added;

[0020] Figure 6This is an impedance curve diagram of the first filter circuit provided by an embodiment of the present application after an auxiliary transformer is added;

[0021] Figure 7 Schematic diagram of a third filtering circuit implemented using a common-mode magnetic ring provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of this application more clear, this application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0023] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should have the usual meanings understood by people with ordinary skills in the field to which this application belongs. The "first", "second" and similar words used in the embodiments of the present application do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0024] In order to reduce electromagnetic interference in the power supply system, technicians have adopted a variety of methods, among which EMI filter circuits are mainly used to suppress electromagnetic interference at the power input or output ports. However, the traditional EMI filter circuits used in the prior art have problems such as complex circuit structure, poor low-frequency filtering effect, leakage current, and unsuitability for variable frequency speed regulation output ports; or active filtering requires the addition of active circuits, controllers and other equipment, which has disadvantages such as low cost-effectiveness and high failure rate. Relying on existing technology cannot achieve the purpose of suppressing electromagnetic interference in the power supply system with an EMI filter circuit with simple structure, high reliability and good interference suppression effect.

[0025] To solve the above problems, the present application provides an EMI filter circuit, which is composed of multiple separate EMI filter circuits and can be used to suppress common-mode and differential-mode interference, thereby achieving the purpose of simple circuit structure. Moreover, through parameter design, it can not only suppress interference in the entire frequency band, but also enhance the suppression of a certain fixed interference frequency point of the system. In particular, it has a good suppression effect on low-frequency interference of tens of Hz to tens of kHz, and will not generate leakage current. It can be suitable for EMI filtering of high-power power supply devices.

[0026] As an optional embodiment, the EMI filter circuit provided by this application refers to Figure 1 ,include:

[0027] The first filter circuit is provided between the positive electrode of the power supply and the input terminal of the second filter circuit, and is used to increase the differential mode impedance of the EMI filter circuit and reduce the harmonics returning to the power supply.

[0028] Reference Figure 2a The first filter circuit is a differential mode filter circuit, which is composed of an inductor and a transformer, wherein the input end of the first filter circuit is one end of the inductor, the other end of the inductor is connected to the positive pole of the primary winding of the transformer, the negative pole of the primary winding is the output end of the first filter circuit, and the secondary winding of the transformer is connected in series with the capacitor.

[0029] The second filter circuit is connected to the first filter circuit, the negative electrode of the power supply and the input end respectively, and is used to improve the common mode impedance of the EMI filter circuit.

[0030] Reference Figure 2b , the second filtering circuit is a common-mode filtering circuit, which is composed of a first common-mode inductor, a second common-mode inductor and a first common-mode transformer; wherein,

[0031] The first input end of the second filter circuit is one end of the first common-mode inductor, which is connected to the output end of the first filter circuit; the other end of the first common-mode inductor is connected to the positive pole of the first primary winding of the first common-mode transformer, and the negative pole of the first primary winding of the first common-mode transformer is the first output end of the second filter circuit, which is connected to the first input end of the power module.

[0032] The second input end of the second filter circuit is one end of the second common-mode inductor, connected to the negative electrode of the power supply; the other end of the second common-mode inductor is connected to the positive electrode of the second primary winding of the first common-mode transformer; the negative electrode of the second primary winding of the first common-mode transformer is the second output end of the second filter circuit, and is connected to the second input end of the power module;

[0033] The secondary winding of the first common-mode transformer is connected in series with the capacitor.

[0034] The third filter circuit is provided between the output terminal of the power module and the load, and is used to further improve the common mode impedance of the EMI filter circuit.

[0035] Reference Figure 2c , the third filtering circuit is also a common-mode filtering circuit, which is composed of a third common-mode inductor, a fourth common-mode inductor, a fifth common-mode inductor and a second common-mode transformer; wherein,

[0036] The first input end of the third filter circuit is one end of the third common-mode inductor, which is connected to the first output end of the power module; the other end of the third common-mode inductor is connected to the positive pole of the first primary winding of the second common-mode transformer, and the negative pole of the first primary winding of the second common-mode transformer is the first output end of the third filter circuit, which is connected to the load.

[0037] The second input end of the third filter circuit is one end of the fourth common-mode inductor, which is connected to the second output end of the power module; the other end of the fourth common-mode inductor is connected to the positive pole of the second primary winding of the second common-mode transformer, and the negative pole of the second primary winding of the second common-mode transformer is the second output end of the third filter circuit, which is connected to the load.

[0038] The third input end of the third filtering circuit is one end of the fifth common-mode inductor, which is connected to the third output end of the power module; the other end of the fifth common-mode inductor is connected to the positive pole of the third primary winding of the second common-mode transformer, and the negative pole of the third primary winding of the second common-mode transformer is the third output end of the third filtering circuit, which is connected to the load.

[0039] The secondary winding of the second common-mode transformer is connected in series with the capacitor.

[0040] As an optional embodiment, the EMI filter circuit provided in this application is most effective in reducing electromagnetic interference at the parallel resonant frequency of the first filter circuit, the second filter circuit, and the third filter circuit. These parallel resonant frequency points can be regarded as the interference filter frequency points of the entire EMI filter circuit. The interference filter frequency point of a single filter circuit can be calculated according to the following formula:

[0041]

[0042] Wherein, Lm is the magnetizing inductance of the first, second, or third filter circuit; L2′ is the inductance of the secondary winding of the transformer in the first, second, or third filter circuit after being converted to the primary winding; and C2′ is the capacitance of the secondary winding of the transformer in the first, second, or third filter circuit after being converted to the primary winding. Lm is obtained by solving the equivalent circuit of the first, second, or third filter circuit.

[0043] As an optional embodiment, the equivalent circuits of the first filtering circuit, the second filtering circuit or the third filtering circuit are as follows: Figure 3As shown; where Z1 is the inductance model, Z2 is the T-type equivalent circuit model of the transformer, R1 and L1 in the transformer model are the primary winding resistance and leakage inductance, R2' and L2' are the resistance and inductance of the secondary winding after conversion to the primary, C2' is the secondary capacitance after conversion of the secondary winding to the primary, Rm is the excitation resistance, and Lm is the excitation inductance.

[0044] Assuming the number of turns of the primary winding of the transformer is N1 and the number of turns of the secondary winding is N2, the known data of the number of turns and the parameters of the equivalent circuit can be converted to:

[0045] When the secondary side resistance is R2, its resistance converted to the primary side is:

[0046] When the secondary inductance is L2, its inductance converted to the primary side is:

[0047] When the secondary capacitance is C2, its capacitance converted to the primary side is:

[0048] As an optional embodiment, refer to Figure 4 , taking the first filter circuit as an example, Figure 4 The impedance curve of the first filter circuit is obviously different from the impedance curves of the other filter schemes. According to the filter circuit, at low frequencies, the filter circuit impedance is approximately equal to the inductor impedance + transformer excitation impedance, and at high frequencies, the filter circuit impedance is approximately equal to the inductor impedance; and near the transformer parallel resonant frequency, the filter circuit impedance is approximately equal to the inductor impedance + transformer parallel resonant impedance. Figure 4 It can be concluded that near the transformer parallel resonance frequency (9kHz), the parallel resonance exhibits a high-impedance characteristic, which significantly increases the equivalent impedance of the filter circuit by 15dB (the impedance increases by 5 times) compared to the traditional solution with only inductance.

[0049] As an optional embodiment, refer to Figure 5a ,to Figure 5c , it is also possible to connect in series at least one auxiliary transformer with parameters different from those of the transformer between the inductor of the first filter circuit and the transformer; or connect in series at least one first auxiliary common-mode transformer with parameters different from those of the first common-mode transformer between the first common-mode inductor, the second common-mode inductor and the first common-mode transformer, and connect in series at least one second auxiliary common-mode transformer with parameters different from those of the second common-mode transformer between the third common-mode inductor, the fourth common-mode inductor, the fifth common-mode inductor and the second common-mode transformer.

[0050] A new interference frequency point is obtained according to the parallel resonant frequency point of the auxiliary transformer, the first auxiliary common mode transformer or the second auxiliary common mode transformer, thereby obtaining a multi-frequency filter circuit. Figure 5a Take the differential mode filter circuit as an example, its impedance curve is as follows Figure 6 As shown, the main filtering frequency point 1 and the main filtering frequency point 2 are the interference filtering frequency points of the auxiliary transformer and the transformer. At these two points, the interference suppression effect of the first filtering circuit is outstanding.

[0051] As an optional embodiment, the EMI filtering circuit provided in the present application can also adjust the interference frequency point by adjusting the turns ratio of the primary winding and the secondary winding of the transformer, auxiliary transformer, first common-mode transformer, first auxiliary common-mode transformer, second common-mode transformer or second auxiliary common-mode transformer in the first filtering circuit, the second filtering circuit or the third filtering circuit, so as to adjust the interference suppression performance of the EMI filtering circuit according to needs.

[0052] As an optional embodiment, when the EMI filter circuit provided by the present application is actually applied to the power supply system: for the first filter circuit, a differential mode reactor can be used to act as an inductor; for the second filter circuit and the third filter circuit, the corresponding common mode inductor and common mode transformer can be obtained by passing the cable through the common mode magnetic ring, referring to Figure 7 The three cables pass through the common-mode magnetic ring and the second common-mode magnetic ring, respectively. The portions passing through the first common-mode magnetic ring form the third, fourth, and fifth common-mode inductors. The portion passing through the second common-mode magnetic ring and the capacitor loop also passing through the second common-mode magnetic ring form the second common-mode transformer.

[0053] In summary, the EMI filter circuit provided by this application combines a differential-mode filter circuit and a common-mode filter circuit based on the transformer principle and connects them to the power supply system. This achieves the use of a filter circuit with a simple structure, small size, and light weight to suppress common-mode and differential-mode interference at the power input or output port. It also reduces interference across the entire frequency band and can perform enhanced filtering for fixed-frequency interference. Compared to traditional inductive filtering, this method has a good low-frequency interference suppression effect, effectively solving the difficulty of low-frequency interference suppression efficiency.

[0054] It should be noted that the above description is limited to some embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in an order different from that described in the above embodiments and still achieve the desired results. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0055] It should be noted that the embodiments of the present application can be further described in the following manner:

[0056] An EMI filter circuit, characterized by comprising: a first filter circuit, a second filter circuit and a third filter circuit;

[0057] The first filter circuit is provided between the positive electrode of the power supply and the input terminal of the power module, and is used to improve the differential mode impedance of the EMI filter circuit and reduce the harmonics returned to the power supply; wherein the first filter circuit is connected to the input terminal through the second filter circuit;

[0058] The second filter circuit is connected to the first filter circuit, the negative electrode of the power supply and the input terminal respectively, and is used to improve the common mode impedance of the EMI filter circuit;

[0059] The third filter circuit is provided between the output terminal of the power module and the load, and is used to further improve the common mode impedance of the EMI filter circuit.

[0060] As an optional embodiment, the parallel resonant frequency points of the first filter circuit, the second filter circuit, and the third filter circuit are all interference filter frequency points of the EMI filter circuit, and the interference filter frequency points of the first filter circuit, the second filter circuit, and the third filter circuit are all calculated by the following formula:

[0061]

[0062] In which, Lm is the excitation inductance of the first filter circuit, the second filter circuit or the third filter circuit, L2′ is the inductance of the secondary winding of the transformer in the first filter circuit, the second filter circuit or the third filter circuit after being converted to the primary winding, and C2′ is the capacitance of the secondary winding of the transformer in the first filter circuit, the second filter circuit or the third filter circuit after being converted to the primary winding.

[0063] As an optional embodiment, the first filtering circuit is a differential mode filtering circuit, including an inductor and a transformer, one end of the inductor is the input end of the first filtering circuit, the other end of the inductor is connected to the positive pole of the primary winding of the transformer, the negative pole of the primary winding is the output end of the first filtering circuit, and the secondary winding of the transformer is connected in series with the capacitor.

[0064] As an optional embodiment, the second filtering circuit is a common-mode filtering circuit, comprising: a first common-mode inductor, a second common-mode inductor and a first common-mode transformer;

[0065] One end of the first common-mode inductor is the first input end of the second filter circuit, and is connected to the output end of the first filter circuit;

[0066] The other end of the first common-mode inductor is connected to the positive electrode of the first primary winding of the first common-mode transformer, and the negative electrode of the first primary winding of the first common-mode transformer is the first output end of the second filter circuit and is connected to the first input end of the power module;

[0067] One end of the second common-mode inductor is the second input end of the second filter circuit, and is connected to the negative electrode of the power supply;

[0068] The other end of the second common-mode inductor is connected to the positive electrode of the second primary winding of the first common-mode transformer, and the negative electrode of the second primary winding of the first common-mode transformer is the second output end of the second filter circuit and is connected to the second input end of the power module;

[0069] The secondary winding of the first common-mode transformer is connected in series with the capacitor.

[0070] As an optional embodiment, the third filtering circuit is a common-mode filtering circuit, comprising: a third common-mode inductor, a fourth common-mode inductor, a fifth common-mode inductor, and a second common-mode transformer;

[0071] One end of the third common-mode inductor is the first input end of the third filter circuit, and is connected to the first output end of the power module;

[0072] The other end of the third common-mode inductor is connected to the positive electrode of the first primary winding of the second common-mode transformer, and the negative electrode of the first primary winding of the second common-mode transformer is the first output end of the third filter circuit and is connected to the load;

[0073] One end of the fourth common-mode inductor is the second input end of the third filter circuit, and is connected to the second output end of the power module;

[0074] The other end of the fourth common-mode inductor is connected to the positive electrode of the second primary winding of the second common-mode transformer, and the negative electrode of the second primary winding of the second common-mode transformer is the second output end of the third filter circuit and is connected to the load;

[0075] One end of the fifth common-mode inductor is the third input end of the third filter circuit, and is connected to the third output end of the power module;

[0076] The other end of the fifth common-mode inductor is connected to the positive electrode of the third primary winding of the second common-mode transformer, and the negative electrode of the third primary winding of the second common-mode transformer is the third output end of the third filter circuit, which is connected to the load;

[0077] The secondary winding of the second common-mode transformer is connected in series with the capacitor.

[0078] As an optional embodiment, at least one auxiliary transformer having parameters different from those of the transformer is connected in series between the inductor and the transformer of the first filter circuit;

[0079] At least one first auxiliary common-mode transformer having parameters different from those of the first common-mode transformer is further connected in series between the first common-mode inductor, the second common-mode inductor, and the first common-mode transformer. At least one second auxiliary common-mode transformer having parameters different from those of the second common-mode transformer is further connected in series between the third common-mode inductor, the fourth common-mode inductor, the fifth common-mode inductor, and the second common-mode transformer.

[0080] As an optional embodiment, adjusting the turns ratio of the primary winding to the secondary winding of the transformer or the auxiliary transformer;

[0081] Adjust the turns ratio of each primary winding and the corresponding secondary winding of the first common-mode transformer, the first auxiliary common-mode transformer, the second common-mode transformer, or the second auxiliary common-mode transformer.

[0082] As an optional embodiment, the inductor of the first filter circuit is a differential mode reactor.

[0083] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present application (including the claims) is limited to these examples. Within the scope of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0084] In addition, for simplicity of description and discussion, and in order not to make the embodiment of the application difficult to understand, the known power supply / ground connection with integrated circuit (IC) chip and other components may or may not be shown in the accompanying drawings provided. In addition, the device can be shown in the form of a block diagram to avoid making the embodiment of the application difficult to understand, and this also takes into account the following fact, that is, the details of the embodiment of these block diagram devices are highly dependent on the platform to be implemented in the embodiment of the application (that is, these details should be fully within the scope of understanding of those skilled in the art). When specific details (for example, circuit) are set forth to describe exemplary embodiments of the application, it will be apparent to those skilled in the art that the embodiment of the application can be implemented without these specific details or when these specific details are changed. Therefore, these descriptions should be considered to be illustrative rather than restrictive.

[0085] Although the present invention has been described in conjunction with specific embodiments thereof, many alternatives, modifications, and variations of these embodiments will be apparent to those skilled in the art based on the foregoing description. For example, other memory architectures (e.g., dynamic RAM (DRAM)) may utilize the embodiments discussed.

[0086] The embodiments of the present application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the scope of protection of this application.

Claims

1. An EMI filter circuit, characterized in that: include: a first filtering circuit, a second filtering circuit, and a third filtering circuit; The first filter circuit is provided between the positive electrode of the power supply and the input terminal of the power module, and is used to improve the differential mode impedance of the EMI filter circuit and reduce the harmonics returned to the power supply; wherein the first filter circuit is connected to the input terminal through the second filter circuit; The second filter circuit is connected to the first filter circuit, the negative electrode of the power supply and the input terminal respectively, and is used to improve the common mode impedance of the EMI filter circuit; A third filter circuit is provided between the output terminal of the power module and the load, and is used to further improve the common mode impedance of the EMI filter circuit; The first filter circuit is a differential mode filter circuit, including an inductor and a transformer; One end of the inductor is the input end of the first filter circuit, the other end of the inductor is connected to the positive pole of the primary winding of the transformer, the negative pole of the primary winding is the output end of the first filter circuit, and the secondary winding of the transformer is connected in series with the capacitor; The second filtering circuit is a common-mode filtering circuit, comprising: a first common-mode inductor, a second common-mode inductor and a first common-mode transformer; One end of the first common-mode inductor is the first input end of the second filter circuit, and is connected to the output end of the first filter circuit; The other end of the first common-mode inductor is connected to the positive electrode of the first primary winding of the first common-mode transformer, and the negative electrode of the first primary winding of the first common-mode transformer is the first output end of the second filter circuit and is connected to the first input end of the power module; One end of the second common-mode inductor is the second input end of the second filter circuit, and is connected to the negative electrode of the power supply; The other end of the second common-mode inductor is connected to the positive electrode of the second primary winding of the first common-mode transformer, and the negative electrode of the second primary winding of the first common-mode transformer is the second output end of the second filter circuit and is connected to the second input end of the power module; The secondary winding of the first common mode transformer is connected in series with the capacitor; The third filtering circuit is a common-mode filtering circuit, comprising: a third common-mode inductor, a fourth common-mode inductor, a fifth common-mode inductor and a second common-mode transformer; One end of the third common-mode inductor is the first input end of the third filter circuit, and is connected to the first output end of the power module; The other end of the third common-mode inductor is connected to the positive electrode of the first primary winding of the second common-mode transformer, and the negative electrode of the first primary winding of the second common-mode transformer is the first output end of the third filter circuit and is connected to the load; One end of the fourth common-mode inductor is the second input end of the third filter circuit and is connected to the second output end of the power module; The other end of the fourth common-mode inductor is connected to the positive electrode of the second primary winding of the second common-mode transformer, and the negative electrode of the second primary winding of the second common-mode transformer is the second output end of the third filter circuit and is connected to the load; One end of the fifth common-mode inductor is the third input end of the third filter circuit, and is connected to the third output end of the power module; The other end of the fifth common-mode inductor is connected to the positive electrode of the third primary winding of the second common-mode transformer, and the negative electrode of the third primary winding of the second common-mode transformer is the third output end of the third filter circuit, which is connected to the load; The secondary winding of the second common-mode transformer is connected in series with the capacitor.

2. The EMI filter circuit according to claim 1, wherein: The parallel resonant frequency points of the first filter circuit, the second filter circuit, and the third filter circuit are all interference filter frequency points of the EMI filter circuit, and the interference filter frequency points of the first filter circuit, the second filter circuit, and the third filter circuit are all calculated by the following formula: in, is the excitation inductance of the first filter circuit, the second filter circuit or the third filter circuit, is the inductance of the secondary winding of the transformer in the first filtering circuit, the second filtering circuit, or the third filtering circuit after being converted to the primary winding, It is the capacitance of the secondary winding of the transformer in the first filtering circuit, the second filtering circuit or the third filtering circuit after being converted to the primary winding.

3. The EMI filter circuit according to claim 1, wherein: Also includes: At least one auxiliary transformer having parameters different from those of the transformer is connected in series between the inductor of the first filter circuit and the transformer; At least one first auxiliary common-mode transformer having parameters different from those of the first common-mode transformer is further connected in series between the first common-mode inductor, the second common-mode inductor, and the first common-mode transformer. At least one second auxiliary common-mode transformer having parameters different from those of the second common-mode transformer is further connected in series between the third common-mode inductor, the fourth common-mode inductor, the fifth common-mode inductor, and the second common-mode transformer.

4. The EMI filter circuit according to claim 3, characterized in that: Further including: adjusting the turns ratio of the primary winding to the secondary winding of the transformer or the auxiliary transformer; Adjust the turns ratio of each primary winding and the corresponding secondary winding of the first common-mode transformer, the first auxiliary common-mode transformer, the second common-mode transformer, or the second auxiliary common-mode transformer.

5. The EMI filter circuit according to claim 1, wherein: The inductor of the first filter circuit is a differential mode reactor.

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