Electromagnetic interference suppression circuit and method and power adapter

Abstract

The invention discloses an electromagnetic interference suppression circuit and method and a power adapter, and belongs to the technical field of power adapters, the electromagnetic interference suppression circuit comprises a common mode inductor, a first end of the common mode inductor is connected to a live wire input end of the power adapter, a second end of the common mode inductor is connected to a null line input end of the power adapter, and the common mode inductor is used for generating magnetic flux; common-mode noise of the live line input end and the zero line input end of the power adapter is suppressed; the differential mode filter is connected with the common mode inductor in parallel and is used for suppressing differential mode noise between the live wire and the zero wire; and the first end of the grounding resistor is connected with the zero line input end of the power adapter, the second end of the grounding resistor is grounded, and the grounding resistor is used for providing a low-impedance path and guiding an electromagnetic interference signal passing through the input end of the power adapter to the ground. Through the combined action of the common mode inductor, the differential mode filter and the grounding resistor, the electromagnetic compatibility of the power adapter can be effectively improved, and the electromagnetic interference is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of power adapters, and in particular relates to an electromagnetic interference suppression circuit, method and power adapter. Background Art

[0002] Electromagnetic interference (EMI) refers to the interference of electromagnetic radiation or conducted noise to electronic equipment and system signals, which is usually generated by switches, motors, transformers, etc. in electrical equipment. EMI interference can affect the normal operation of equipment through transmission paths such as cables and power cords, reduce signal integrity, and even cause equipment failure. In power adapters, the power cord is the main propagation channel for electromagnetic interference. The interference signal is transmitted to the input end of the device through the power supply line, thus causing an impact.

[0003] Electromagnetic interference usually originates from the switching action of the power supply or the noise caused by other nonlinear loads, which can easily cause interference to the electronic circuits inside the power adapter. Existing electromagnetic interference suppression technologies mostly use magnetic flux leakage to suppress electromagnetic interference, which not only has a poor suppression effect on common-mode noise, but also has limited suppression effect on differential-mode noise. Therefore, how to effectively suppress electromagnetic interference at the input end of the power adapter is a technical problem that needs to be solved urgently. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides an electromagnetic interference suppression circuit, method and power adapter, aiming to solve the electromagnetic interference problem at the input end of the power adapter in the traditional technical solution and improve the electromagnetic compatibility of the power adapter.

[0005] A first aspect of an embodiment of the present invention provides an electromagnetic interference suppression circuit, which is applied to a power adapter. The electromagnetic interference suppression circuit includes: A common mode inductor, a first end of which is connected to the live line input end of the power adapter, and a second end of which is connected to the neutral line input end of the power adapter, for generating a magnetic flux to suppress the common mode noise at the live line input end and the neutral line input end of the power adapter; A differential mode filter, which is connected in parallel with the common mode inductor, and is used to suppress differential mode noise at the live wire input terminal and the neutral wire input terminal of the power adapter; A grounding resistor, a first end of which is connected to the neutral line input terminal of the power adapter, and a second end of which is grounded, is used to provide a low impedance path to guide the electromagnetic interference signal passing through the input terminal of the power adapter to the ground.

[0006] In one embodiment, the common mode inductor includes: a first winding and a second winding; the first winding is connected to the live wire input terminal, and the second winding is connected to the neutral wire input terminal. The directions of the first winding and the second winding are opposite, and are used to form a reverse magnetic field through magnetic flux coupling.

[0007] In one embodiment, the first winding and the second winding are disposed on different magnetic layers.

[0008] In one embodiment, the common mode inductor further includes: a first capacitor, a first end of the first capacitor is connected to the live wire input end, and a second end of the first capacitor is connected to the ground wire, for filtering out high frequency noise signals.

[0009] In one embodiment, the differential mode filter includes an adjustable inductor and a second capacitor; a first end of the adjustable inductor is connected to the live line input end, a second end of the adjustable inductor is connected to the neutral line input end, and the second capacitor is connected in parallel to both ends of the adjustable inductor.

[0010] In one embodiment, the electromagnetic interference suppression circuit further includes an electronic control module, which adjusts the inductance value of the adjustable inductor according to the frequency of the differential mode noise at the input end of the power adapter.

[0011] In one embodiment, the second capacitor is a ceramic capacitor with low equivalent series resistance and high frequency response, and the capacitance value of the second capacitor is positively correlated with the frequency of the differential mode noise at the input end of the power adapter.

[0012] In one embodiment, the resistance of the grounding resistor is expressed as: in, is the grounding resistor value, f is the noise frequency at the power adapter input, C is the capacitance value of the second capacitor.

[0013] A second aspect of an embodiment of the present invention provides an electromagnetic interference suppression method, comprising: The common-mode inductor connected in series to the input end of the power adapter generates magnetic flux to suppress the common-mode noise at the live input end and the neutral input end of the power adapter. The differential mode noise between the live wire input terminal and the neutral wire input terminal of the power adapter is suppressed by a differential mode filter connected in parallel to the input terminal of the power adapter; A grounding resistor connected between the neutral line input terminal of the power adapter and the ground line provides a low impedance path, thereby guiding the electromagnetic interference signal passing through the input terminal of the power adapter to the ground line.

[0014] A third aspect of an embodiment of the present invention provides a power adapter, which includes the electromagnetic interference suppression circuit of the first aspect above.

[0015] The beneficial effects of the embodiments of the present application are as follows: the first end of the common-mode inductor is connected to the live input end of the power adapter, and the second end of the common-mode inductor is connected to the neutral input end of the power adapter, which is used to generate magnetic flux to suppress the common-mode noise of the live input end and the neutral input end of the power adapter; the differential-mode filter connected in parallel with the common-mode inductor suppresses the differential-mode noise of the live input end and the neutral input end of the power adapter; the first end of the grounding resistor is connected to the neutral input end of the power adapter, and the second end of the grounding resistor is grounded to provide a low-impedance path to guide the electromagnetic interference signal passing through the input end of the power adapter to the ground. By setting the combination of the common-mode inductor and the differential-mode filter, the common-mode noise and the differential-mode noise are effectively suppressed respectively, ensuring that the noise level of the input end of the power adapter is low, and the effect of the coordinated grounding resistor solves the electromagnetic interference problem of the input end of the power adapter in the traditional technical solution, and improves the electromagnetic compatibility of the power adapter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 A schematic diagram of the circuit structure of an electromagnetic interference suppression circuit provided in one embodiment of the present application; Figure 2 A schematic diagram of a power adapter provided in an embodiment of the present application; Figure 3 A schematic diagram of the circuit structure of a common-mode inductor provided in one embodiment of the present application; Figure 4 A schematic diagram of the circuit structure of a common-mode inductor provided in another embodiment of the present application; Figure 5 A schematic diagram of the circuit structure of a differential mode filter provided in one embodiment of the present application; Figure 6 A schematic diagram of the circuit structure of an electromagnetic interference suppression circuit provided in another embodiment of the present application; Figure 7 A schematic diagram of a flow chart of an electromagnetic interference suppression method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0020] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0021] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0023] In the description of the embodiments of the present application, the term "multi-frame" refers to more than two (including two).

[0024] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0025] The embodiments of the present invention provide an electromagnetic interference suppression circuit, method and power adapter, which can solve the electromagnetic interference problem at the input end of the power adapter in the traditional technical solution and improve the electromagnetic compatibility of the power adapter.

[0026] See also Figure 1 As shown, Figure 1 Schematic diagram of the circuit structure of an electromagnetic interference suppression circuit provided in an embodiment of the present application. The electromagnetic interference circuit provided in an embodiment of the present application is applied to a power adapter. Figure 2 As shown, Figure 2 A schematic diagram of a power adapter provided in an embodiment of the present application. Figure 2 It can be seen that the power adapter 100 includes an electromagnetic interference suppression circuit 110. The electromagnetic interference suppression circuit 110 can effectively solve the electromagnetic interference problem at the input end of the power adapter 100 and improve the electromagnetic compatibility of the power adapter 100.

[0027] Depend on Figure 1 It can be seen that the electromagnetic interference suppression circuit 110 provided in the embodiment of the present application includes: a common-mode inductor 200, a first end of which is connected to the live wire input terminal 120 of the power adapter 100, and a second end of which is connected to the neutral wire input terminal 130 of the power adapter 100, for generating a magnetic flux to suppress the common-mode noise of the live wire input terminal 120 and the neutral wire input terminal 130 of the power adapter 100; a differential-mode filter 300, which is connected in parallel with the common-mode inductor 200, for suppressing the differential-mode noise of the live wire input terminal 120 and the neutral wire input terminal 130 of the power adapter 100; a grounding resistor 400, a first end of which is connected to the neutral wire input terminal 130 of the power adapter 100, and a second end of which is grounded, for providing a low-impedance path to guide the electromagnetic interference signal passing through the input terminal of the power adapter 100 to the ground.

[0028] The common-mode noise between the live wire and the neutral wire is suppressed by the common-mode inductor 200. Specifically, the common-mode inductor 200 effectively suppresses the common-mode noise by connecting the live wire and the neutral wire of the power adapter 100 to the two ports of the common-mode inductor 200 and generating a reverse magnetic field through its magnetic flux. Among them, the common-mode noise refers to the noise signal that appears simultaneously in the live wire and the neutral wire of the power adapter 100. Due to the reverse coupling effect of the magnetic flux of the common-mode inductor 200, when the common-mode noise passes through, the common-mode inductor 200 generates a reverse magnetic field to offset the noise signal, thereby achieving attenuation or suppression of the common-mode noise.

[0029] The differential mode noise between the live wire and the neutral wire is suppressed by the differential mode filter 300. The differential mode filter 300 is connected in parallel between the live wire and the neutral wire, and is mainly used to suppress the differential mode noise. Differential mode noise generally refers to the noise generated between the live wire and the neutral wire of the power adapter 100 due to current imbalance or interference source. In the present application, the differential mode filter 300 can generate impedance to the differential mode signal and reduce the conduction of the differential mode noise signal.

[0030] The grounding resistor 400 provides a low impedance path between the neutral line input terminal 130 of the power adapter 100 and the ground. When the input terminal of the power adapter 100 generates redundant electromagnetic interference signals other than common mode noise or differential mode noise, the grounding resistor 400 guides these electromagnetic interference signals to the ground line through its low impedance characteristics, thereby preventing these electromagnetic interference signals from entering the power adapter 100. The grounding resistor 400 further effectively reduces the noise in the power adapter 100, thereby enhancing the anti-interference capability of the power adapter 100.

[0031] In one embodiment, see Figure 3 As shown, Figure 3 This is a schematic diagram of the circuit structure of a common mode inductor provided in an embodiment of the present application. Figure 3 It can be seen that the common mode inductor 200 includes: a first winding 210 and a second winding 220; the first winding 210 is connected to the live line input terminal 120, and the second winding 220 is connected to the neutral line input terminal 130. The directions of the first winding 210 and the second winding 220 are opposite, and are used to form a reverse magnetic field (such as Figure 3 As shown by the arrow in the middle, it indicates the reverse magnetic field formed by the first winding 210 and the second winding 220 through the magnetic flux coupling effect). In this application, Figure 3 It can be seen that the first winding 210 and the second winding 220 are arranged on different magnetic layers.

[0032] In the present application, when current passes through the first winding 210 and the second winding 220, a magnetic field is generated. Since the first winding 210 and the second winding 220 are in opposite directions, their magnetic fields cancel each other out, and this reverse magnetic field can effectively suppress common mode noise. Further, by arranging the first winding 210 and the second winding 220 on different magnetic layers, this multi-layer structure helps to increase the magnetic coupling area of ​​the common mode inductor 200, thereby improving the overall performance of the common mode inductor 200 and the ability to suppress high frequency common mode noise.

[0033] In one embodiment, see Figure 4 As shown, Figure 4 A schematic diagram of the circuit structure of a common mode inductor provided in another embodiment of the present application. Figure 4 It can be known that the common mode inductor 200 further includes: a first capacitor 230 , a first end of the first capacitor 230 is connected to the live wire input end, and a second end of the first capacitor 230 is connected to the ground wire, for filtering high frequency common mode noise.

[0034] Specifically, the first capacitor 230 has a low impedance characteristic, and through its low impedance characteristic, the high-frequency noise signal is guided to the ground line, thereby filtering out the high-frequency noise and preventing it from being transmitted to the power adapter 100. In the present application, the first capacitor 230 receives the high-frequency noise signal by connecting to the live wire, and transmits the high-frequency common-mode noise to the ground line, thereby reducing the impact of the high-frequency common-mode noise.

[0035] See also Figure 5 As shown, Figure 5 The circuit structure diagram of the differential mode filter provided in one embodiment of the present application is shown in FIG. Figure 5 It can be seen that the differential mode filter 300 includes an adjustable inductor 310 and a second capacitor 320; the first end of the adjustable inductor 310 is connected to the live line input terminal 120, the second end of the adjustable inductor 310 is connected to the neutral line input terminal 130, and the second capacitor 320 is connected in parallel to both ends of the adjustable inductor 310.

[0036] Differential mode noise is noise caused by the current imbalance between the live wire and the neutral wire of the power adapter 100. The function of the differential mode filter 300 is to suppress this noise and reduce its impact on the power adapter 100. Specifically, the responsiveness of the adjustable inductor 310 to the differential mode noise of different frequencies is changed by adjusting the inductance value of the adjustable inductor 310. When the frequency of the differential mode noise changes, the inductance value of the adjustable inductor 310 is adjusted, thereby effectively suppressing the differential mode noise of different frequencies. By connecting the second capacitor 320 in parallel at both ends of the adjustable inductor 310, it helps to further filter out the high-frequency differential mode noise.

[0037] See also Figure 6 As shown, Figure 6 This is a schematic diagram of the circuit structure of an electromagnetic interference suppression circuit provided by another embodiment of the present application. Figure 6 It can be seen that the electromagnetic interference suppression circuit provided in this embodiment is Figure 1 Compared with the electromagnetic interference suppression circuit shown in FIG. 1 , the electromagnetic interference suppression circuit 10 further includes an electronic control module 500 . The electronic control module 500 adjusts the inductance value of the adjustable inductor 310 according to the frequency of the differential mode noise at the input end of the power adapter 100 .

[0038] In the present application, the function of the electronic control module 500 is to monitor the differential mode noise frequency of the input end in real time, and adjust the inductance value of the adjustable inductor 310 according to the differential mode noise frequency. Through this adjustment, the differential mode filter can dynamically adapt to the differential mode noise of different frequencies, and effectively suppress the differential mode noise interference at the input end of the power adapter 100.

[0039] Exemplarily, the electronic control module 500 adjusts the inductance value of the adjustable inductor 310 according to the frequency of the differential mode noise at the input end of the power adapter 100 .

[0040] In one embodiment, the second capacitor 320 is a ceramic capacitor with low equivalent series resistance and high frequency response, and the capacitance value of the second capacitor 320 is positively correlated with the frequency of the differential mode noise at the input end of the power adapter 100. The high frequency differential mode noise at the input end is filtered by the second capacitor 320, and its low equivalent series resistance and high frequency response characteristics enable the high frequency differential mode noise to be efficiently filtered out.

[0041] In one embodiment, the resistance of the grounding resistor 400 is expressed as: in, is the grounding resistor value, f is the noise frequency at the power adapter input, C is the capacitance value of the second capacitor.

[0042] The function of the grounding resistor 400 is to provide a low impedance path for the input end of the power adapter 100 , through which the excess noise can be guided to the ground line, thereby reducing the interference of the noise on the power adapter 100 .

[0043] Furthermore, by setting the resistance value of the grounding resistor 400 to be closely related to the noise frequency at the input end of the power adapter 100 and the capacitance value of the second capacitor, the noise suppression effect can be improved. Here, the noise frequency at the input end of the power adapter 100 is the noise suppressed or filtered by the common mode inductor and the differential mode filter.

[0044] The electromagnetic interference suppression circuit works in coordination through components such as common-mode inductors, differential-mode filters, first capacitors, second capacitors, electronic control modules, and grounding resistors. The common-mode inductors and differential-mode filters suppress common-mode noise and differential-mode noise respectively, the first capacitors and second capacitors help filter out high-frequency common-mode noise and high-frequency differential-mode noise respectively, and the grounding resistor provides a low-impedance path to guide excess interference signals to the ground wire. The electronic control module dynamically adjusts the inductance value of the adjustable inductor according to the input differential-mode noise frequency, thereby improving the overall noise suppression effect on the power adapter.

[0045] See also Figure 7 As shown, Figure 7 A flow chart of an electromagnetic interference suppression method provided in an embodiment of the present application. Figure 7 It can be seen that the electromagnetic interference suppression method provided in the embodiment of the present application includes: S700: The common-mode inductor connected in series to the input end of the power adapter generates magnetic flux to suppress the common-mode noise at the live input end and the neutral input end of the power adapter.

[0046] S710: Suppress differential mode noise between the live wire input terminal and the neutral wire input terminal of the power adapter by connecting a differential mode filter in parallel to the input terminal of the power adapter.

[0047] S720: A low impedance path is provided by connecting a grounding resistor between the neutral line input terminal of the power adapter and the ground line, so as to guide the electromagnetic interference signal passing through the input terminal of the power adapter to the ground line.

[0048] It should be noted that the specific implementation process of the above steps can be referred to Figures 1 to 6 The specific description of the illustrated embodiments will not be repeated here.

[0049] The beneficial effects of the embodiment of the present application are as follows: the first end of the common-mode inductor is connected to the live input end of the power adapter, and the second end of the common-mode inductor is connected to the neutral input end of the power adapter, which is used to generate magnetic flux and suppress the common-mode noise of the live input end and the neutral input end of the power adapter; the differential-mode filter is connected in parallel between the live input end and the neutral input end of the power adapter, which is used to suppress the differential-mode noise of the live input end and the neutral input end of the power adapter; the first end of the grounding resistor is connected to the neutral input end of the power adapter, and the second end of the grounding resistor is connected to the ground wire, which is used to provide a low-impedance path to guide the electromagnetic interference signal passing through the input end of the power adapter to the ground wire. By setting the combination of the common-mode inductor and the differential-mode filter, the common-mode noise and the differential-mode noise are effectively suppressed respectively, ensuring that the noise level of the input end of the power adapter is low, and the effect of the coordinated grounding resistor solves the electromagnetic interference problem of the input end of the power adapter in the traditional technical solution, and improves the electromagnetic compatibility of the power adapter.

[0050] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into a processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0051] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0052] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. An electromagnetic interference suppression circuit, applied to a power adapter, characterized in that: The electromagnetic interference suppression circuit comprises: A common mode inductor, wherein a first end of the common mode inductor is connected to a live line input end of the power adapter, and a second end of the common mode inductor is connected to a neutral line input end of the power adapter, and is used to generate a magnetic flux to suppress common mode noise of the live line input end and the neutral line input end; A differential mode filter, wherein the differential mode filter and the common mode inductor are used to suppress differential mode noise at the live line input end and the neutral line input end; A grounding resistor, wherein a first end of the grounding resistor is connected to the neutral line input terminal of the power adapter, and a second end of the grounding resistor is grounded, for providing a low impedance path to guide the electromagnetic interference signal passing through the input terminal of the power adapter to the ground.

2. The electromagnetic interference suppression circuit according to claim 1, characterized in that: The common-mode inductor includes: a first winding and a second winding; the first winding is connected to the live wire input end, the second winding is connected to the neutral wire input end, and the first winding and the second winding have opposite directions and are used to form a reverse magnetic field through magnetic flux coupling.

3. The electromagnetic interference suppression circuit according to claim 2, characterized in that: The first winding and the second winding are arranged on different magnetic layers.

4. The electromagnetic interference suppression circuit according to claim 3, characterized in that: The common mode inductor further includes: a first capacitor, a first end of the first capacitor is connected to the live line input end, and a second end of the first capacitor is connected to a ground line, for filtering out high frequency noise signals.

5. The electromagnetic interference suppression circuit according to claim 1, characterized in that: The differential mode filter comprises an adjustable inductor and a second capacitor; a first end of the adjustable inductor is connected to the live line input end, a second end of the adjustable inductor is connected to the neutral line input end, and the second capacitor is connected in parallel to both ends of the adjustable inductor.

6. The electromagnetic interference suppression circuit according to claim 5, characterized in that: The electromagnetic interference suppression circuit also includes an electronic control module, which adjusts the inductance value of the adjustable inductor according to the frequency of the differential mode noise at the input end of the power adapter.

7. The electromagnetic interference suppression circuit according to claim 6, characterized in that: The second capacitor is a ceramic capacitor with low equivalent series resistance and high frequency response, and the capacitance value of the second capacitor is positively correlated with the frequency of the differential mode noise at the input end of the power adapter.

8. The electromagnetic interference suppression circuit according to claim 7, characterized in that: The resistance value of the grounding resistor is expressed as: in, is the grounding resistance, f is the noise frequency at the power adapter input, C is the capacitance value of the second capacitor.

9. A method for suppressing electromagnetic interference, characterized in that: include: The common-mode inductor connected in series to the input end of the power adapter generates magnetic flux to suppress the common-mode noise at the live input end and the neutral input end of the power adapter. The differential mode noise between the live wire input terminal and the neutral wire input terminal of the power adapter is suppressed by a differential mode filter connected in parallel with the common mode inductor; A low impedance path is provided by connecting a grounding resistor between the neutral line input terminal of the power adapter and the ground line, so that the electromagnetic interference signal passing through the input terminal of the power adapter is guided to the ground line.

10. A power adapter, characterized in that: The power adapter comprises the electromagnetic interference suppression circuit according to any one of claims 1-8.

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