KR20210074073A - Electro Magnetic Interference Filter - Google Patents

Abstract

According to the invention, an EMI filter is disposed between a power input unit to which external power is input and a noise source. The EMI filter comprises: a first noise filter unit connected to first and second terminals of the power input unit; and a second noise filter unit connected to a third terminal of the power input unit. Here, the second noise filter unit may include an inductor and a capacitor connected in parallel to each other. Accordingly, compared to a structure in which the second noise filter unit is excluded, conducted noise by the third terminal can be reduced and compared to a structure in which the second noise filter unit includes only the inductor, an increase in impedance of the second noise filter unit is prevented, thereby preventing intensification of radiated noise.

Description

EMF filter {Electro Magnetic Interference Filter}

The present invention relates to an EMI filter provided in an electronic device and filtering EMI noise.

An electronic device or an electrical system is provided with an EMI filter for reducing the effect of electromagnetic interference (EMI, hereinafter referred to as "EMI").

EMI includes Conducted Emissions Noise by a conductor through which current flows, and Radiated Emissions Noise emitted around a conductor through which current flows.

EMI filters are intended to reduce the effects of EMI on electronic devices. Illustratively, the EMI filter may be provided in a power supply device for stably supplying power required for driving an electronic device or an electrical system. Such an EMI filter is to block EMI generated by an electronic device from being emitted, or to block EMI generated by another electronic device from being introduced.

In relation to such a noise filter, Prior Document 1 (Korean Patent Publication No. 10-2005-0078537, published on Aug. 5, 2005, applied to LG Electronics Co., Ltd.) discloses an X capacitor for suppressing differential mode noise and common mode noise suppression. Disclosed is an EMI filter including a Y capacitor and a common choke for

Prior Document 1 has a problem in that it does not propose a method for reducing conducted noise caused by the chassis when the chassis housing the noise source is a conductor.

In this regard, Prior Document 2 (Korean Patent Publication No. 10-2011-0055924, published on May 26, 2011, filed by Samsung Electro-Mechanics) is provided at both ends of the first capacitor, the line filter and the first capacitor connected to the active and neutral wires. Disclosed is an EMI filter that includes a ferrite bead, a Y capacitor connected to a line filter, and blocks conductive noise. That is, Prior Document 2 discloses reducing conduction noise caused by an iron case of an electronic product by providing ferrite beads provided at both ends of the first capacitor.

However, Prior Document 2 has a problem in that it does not suggest a method for reducing conduction noise due to a path including the ground.

In addition, Prior Document 2 has a problem in that it does not suggest a method for reducing radiation noise.

Korean Patent Publication No. 10-2005-0078537 Korean Patent Publication No. 10-2011-0055924

It is an object of the present invention to provide an EMI filter capable of reducing conducted noise.

Another object of the present invention is to provide an EMI filter capable of reducing radiation noise.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention not mentioned may be understood by the following description, and will be more clearly understood by the examples of the present invention. Moreover, it will be readily apparent that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

The EMI filter according to the present invention is disposed between a power input unit to which external power is input and a noise source, a first noise filter unit connected to the first and second terminals of the power input unit, and a third terminal connected to the power input unit It may include a second noise filter unit. Here, the second noise filter unit may include an inductor and a capacitor connected in parallel to each other.

Accordingly, compared to the structure in which the second noise filter unit is excluded, there is an advantage in that the conduction noise caused by the third terminal can be reduced.

In addition, since the second noise filter unit further includes a capacitor connected in parallel to the inductor compared to the structure including only the inductor, an increase in the impedance of the second noise filter unit may be prevented. Therefore, the deepening of the radiation noise can be prevented.

That is, according to the present invention, the third terminal is connected to the earth ground, the noise source and the first noise filter unit are accommodated in a chassis made of a conductive material, and the second noise filter unit may be disposed between the chassis and the third terminal. . In this case, the chassis may be grounded by the third terminal.

In addition, the EMI filter according to the present invention may further include a clamp unit respectively connected to the first, second, and third lines corresponding to the first, second, and third terminals.

At this time, the impedance of the first current path including at least one of the first and second lines and the third line is the second current path including the chassis capacitor and the earth ground corresponding to the parasitic capacitance between the chassis and the earth ground. less than the impedance. To this end, in a high frequency region of 30 MHz or higher, the impedance of the second noise filter unit is smaller than the reference impedance, and the reference impedance may be derived as the sum of the impedance of the clamp unit connected to the third line and the impedance of the chassis capacitor.

The capacitance of the capacitor of the second noise filter unit may be 100pF to 300pF.

The EMI filter according to the present invention includes a second noise filter unit connected to a third terminal of a power input unit corresponding to a ground line of an external power source, and the second noise filter unit includes an inductor and a capacitor connected in parallel to each other.

Accordingly, due to the inductor of the second noise filter unit, there is an advantage that the common mode conduction noise including the third terminal can be reduced.

Also, as the second noise filter unit further includes a capacitor connected in parallel with the inductor, it is possible to prevent the impedance of the second noise filter unit from increasing due to the inductor. Accordingly, the impedance of the current path including the third terminal may be prevented from increasing due to the impedance of the second noise filter unit. Accordingly, since the impedance of the current path including the third terminal may be smaller than the impedance of the current path including the earth ground, the deepening of radiation noise may be prevented.

In addition to the above-described effects, the specific effects of the present invention will be described together while describing specific details for carrying out the invention below.

1 is a diagram illustrating an EMI filter according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of the first noise filter unit of FIG. 1 .
FIG. 3 is a diagram illustrating a first current path of the EMI filter of FIG. 1 .
FIG. 4 is a diagram illustrating a second current path of the EMI filter of FIG. 1 .
5 is a view showing the EMI filter of Comparative Example 1 having a structure in which the second noise filter unit is removed.
6 is a diagram illustrating an EMI filter of a second comparative example in which a second noise filter unit includes only a ground inductor.
7 is a view showing radiation noise according to Comparative Examples 1 and 2;
8 is a reference impedance and an impedance of a clamp unit according to an embodiment and a second comparative example of the present invention, an impedance of a second noise filter unit according to a second comparative example, and an impedance of a second noise filter unit according to an embodiment of the present invention; is a diagram showing
9 is a view showing common mode conducted noise according to Comparative Examples 1 and 2 and an embodiment of the present invention.
10 is a view showing differential mode conduction noise according to Comparative Examples 1 and 2 and an embodiment of the present invention.
11 is a view showing the impedance of the second noise filter unit according to the second comparative example and the first, second, and third embodiments of the present invention, respectively.
12 is a view showing common mode conducted noise currents according to Comparative Examples 1 and 2 and Examples 1, 2, and 3 of the present invention, respectively.
13 is a diagram illustrating an example implementation of the second noise filter unit of FIG. 1 .

The above-described objects, features and advantages will be described below in detail with reference to the accompanying drawings, and accordingly, those of ordinary skill in the art to which the present invention pertains will be able to easily implement the technical idea of the present invention. In describing the present invention, if it is determined that a detailed description of a known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

Although the first, second, etc. are used to describe various elements, these elements are not limited by these terms, of course. These terms are only used to distinguish one component from other components, and unless otherwise stated, the first component may be the second component, of course.

Also, when it is described that a component is "connected", "coupled" or "connected" to another component, the components may be directly connected or connected to each other, but other components are "interposed" between each component. It is to be understood that “or, each component may be “connected,” “coupled,” or “connected” through another component.

Throughout the specification, unless otherwise stated, each element may be singular or plural.

As used herein, the singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as "consisting of" or "comprising" should not be construed as necessarily including all of the various components or various steps described in the specification, some of which components or some steps are It should be construed that it may not include, or may further include additional components or steps.

Throughout the specification, when “A and/or B” is used, it means A, B or A and B, unless specifically stated to the contrary, and when “C to D” is used, it means that there is no specific contrary description. Unless otherwise specified, it means C or more and D or less.

Hereinafter, an EMI filter according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a diagram illustrating an EMI filter according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of the first noise filter unit of FIG. 1 . FIG. 3 is a diagram illustrating a first current path of the EMI filter of FIG. 1 . FIG. 4 is a diagram illustrating a second current path of the EMI filter of FIG. 1 .

As shown in FIG. 1 , the EMI filter 100 according to an embodiment of the present invention is disposed between a power input unit 20 to which an external power source 10 is input and a predetermined noise source 30 . The EMI filter 100 is to reduce EMI introduced into the noise source 30 or EMI emitted from the noise source 30 .

For example, the external power supply 10 supplies AC power and may include an active line (L; Live Line), a neutral line (N; Neutral Line) and a ground line (G; Ground Line).

In addition, the power input unit 20 includes a first terminal 21 corresponding to the active line L of the external power source 10 , a second terminal 22 corresponding to the neutral line N of the external power source 10 and an external A third terminal 23 corresponding to the ground line G of the power source 10 may be included.

The power input unit 20 may be a plug connected to a socket for supplying the external power 10 .

The noise source 30 collectively refers to various electronic circuits connected to the power input unit 20 . For example, the noise source 30 may be a power converter that converts AC power supplied through the power input unit 20 into DC power.

Here, the power conversion device may be provided in an electronic device such as an air conditioner. In addition, although not shown in FIG. 1 , the noise source 30 implemented as a power converter may include a converter, a DC link capacitor, and an inverter.

The converter is connected to the power input unit 20 through the EMI filter 100 , and converts the AC voltage supplied through the power input unit 20 into a DC voltage. As an example, the converter does not include a switch element, and may rectify an AC voltage without a switch element. Alternatively, the converter may include a switch element and may perform step-up, power factor improvement, and DC power conversion by using a switching operation of the switch element.

The DC link capacitor is disposed in parallel between the output terminal of the converter and the input terminal of the inverter, and is charged with the output of the converter.

The inverter supplies the driving voltage to the motor by converting the voltage of the DC link capacitor. For example, the motor may be provided in a compressor for compressing a refrigerant among the air conditioners.

The EMI filter 100 according to an embodiment of the present invention includes a first noise filter unit 110 connected to the first and second terminals 11 and 12 of the power input unit 20 , and a power input unit 20 . and a second noise filter unit 120 connected to a third terminal 23 corresponding to an earth ground 40 . Here, the second noise filter unit 120 includes an inductor 121 and a capacitor 122 connected in parallel to each other. Hereinafter, for concise description, the inductor 121 and the capacitor 122 of the second noise filter unit 120 are referred to as a ground inductor 121 and a ground capacitor 122 .

In addition, the EMI filter 100 has first, second and third lines 21', 22', 23 corresponding to the first, second and third terminals 21, 22, 23 of the power input unit 20. ') may further include a clamp unit 130 respectively connected to the. The first, second and third lines 21 ′, 22 ′, and 23 ′ connect between the first, second and third terminals 21 , 22 , 23 of the power input unit 20 and the noise source 30 . Connect.

The clamp unit 130 may be formed of a ferrite ring core surrounding each of the first, second, and third lines 21', 22', and 23'. The ferrite ring core may be part of the current transformer. The clamp unit 130 may be for detecting an overcurrent of each of the first, second, and third lines 21', 22', and 23'.

The first noise filter unit 110 may be accommodated in a predetermined chassis 50 together with the noise source 30 .

The first noise filter unit 110 filters EMI conducted through the first and second lines 21' and 22'.

As shown in FIG. 2 , the first noise filter unit 110 may include at least one of a common choke 111 and Y capacitors 112 and 113 . The common choke 111 and the Y capacitors 112 and 113 are for suppressing common mode conduction noise.

For example, the first noise filter unit 110 includes a common choke 111 disposed between the first and second terminals 21 and 22 and the noise source 30 , and a common choke 111 disposed at both ends of the common choke 111 . A pair of Y capacitors 112 and 113 may be included.

Common Mode (CM) Conducted noise is generated by the current of a common component moving between the conductor and the ground. That is, the common mode conduction noise is noise existing between each of the active line (L) and the neutral line (N) and the earth ground (40).

Alternatively, although not shown in FIG. 2 , the first noise filter unit 110 may further include an X capacitor (not shown) for suppressing differential mode conduction noise. For example, the first noise filter unit 110 may further include a pair of X capacitors (not shown) disposed at both ends of the common choke 111 .

Differential Mode Conducted noise is generated by a differential current that reciprocates in a conductor. That is, the differential mode conduction noise is noise existing between the first and second lines 21' and 22' for single-phase power supply such as the active line (L) and the neutral line (N).

For reference, PI_w in FIG. 2 is a parasitic inductance of a line connecting the Y capacitors 112 and 113 and the ground. In this case, the ground may be the second noise filter unit 120 connected to the third terminal 23 or the chassis 50 connected to the second noise filter unit 120 .

As shown in FIG. 1 , the second noise filter unit 120 is connected between the third terminal 23 and the first noise filter unit 110 . The second noise filter unit 120 filters EMI conducted through the third line 23 ′ corresponding to the earth ground 40 of the power input unit 20 .

According to an embodiment of the present invention, the second noise filter unit 120 includes a ground inductor 121 connected in series between the third terminal 23 and the first noise filter unit 110 and connected in parallel with each other; and a ground capacitor 122 .

The ground inductor 121 may be formed of a core. Conduction noise caused by the current of the third line 23 ′ may be reduced by the ground inductor 121 .

However, when the second noise filter unit 120 is made of only the ground inductor 121 for reducing the conduction noise, compared to the structure excluding the second noise filter unit 120, the conduction noise is reduced while the radiation noise is deepened. There is a problem being

The radiation noise may be noise corresponding to a high-frequency region of 30 MHz or higher.

The common mode conduction noise is generated by a current between at least one of the first and second lines 21' and 22' and the ground line (G).

For example, as shown in FIG. 3 , the common mode conduction noise between the external power source 10 and the noise source 30 is connected to at least one of the first and second terminals 21 and 22 of the power input unit 20 and It may be generated by the first current path CP1 including the third terminal 23 of the power input unit 20 .

And, as shown in FIG. 4 , when the chassis 50 accommodating the first noise filter unit 110 and the noise source 30 is made of a conductive material, the chassis 50 is formed for electrical stability and user safety. need to be grounded. Accordingly, the chassis 50 is grounded by being connected to the third terminal 23 of the power input unit 20 . In addition, the ground line G or the third terminal 23 is connected to the ground ground 40 .

At this time, since a parasitic capacitance exists between the chassis 50 and the earth ground 40 , the second current path is affected by the chassis capacitor 51 corresponding to the parasitic capacitance between the chassis 50 and the earth ground 40 . (CP2) may occur.

That is, the common mode conducted noise between the external power supply 10 and the noise source 30 includes at least one of the first and second lines 21 ′ and 22 ′, the chassis capacitor 51 and the earth ground 40 . It may also be generated by the second current path CP2.

However, as the current of the second current path CP2 increases compared to the current of the first current path CP1, there is a problem in that the radiation noise increases.

Accordingly, the EMI filter 100 according to an embodiment of the present invention includes the ground inductor 121 to reduce conduction noise corresponding to the third line 23 ′, and is parallel to the ground inductor 121 . By including the ground capacitor 122 connected to , it is possible to prevent an increase in the impedance of the first current path CP1 due to the ground inductor 121 . Accordingly, it is possible to prevent the radiation noise from being deepened due to the ground inductor 121 .

In order to explain the effects of an embodiment of the present invention, first and second comparative examples will be described as follows.

5 is a view showing the EMI filter of Comparative Example 1 having a structure in which the second noise filter unit is removed. 6 is a diagram illustrating an EMI filter of a second comparative example in which a second noise filter unit includes only a ground inductor. 7 is a view showing radiation noise according to Comparative Examples 1 and 2;

As shown in FIG. 5 , the EMI filter REF1 according to the first comparative example includes only the first noise filter unit 110 and the clamp unit 130 , and includes a second noise filter unit ( 120 in FIG. 1 ). structure is excluded.

According to this first comparative example REF1, there is a problem in that there is a limitation in suppressing the common mode conduction noise caused by the first current path CP1, in particular, the conduction noise of the third line 23' corresponding to the ground line. have.

On the other hand, as shown in FIG. 6 , the EMI filter REF2 according to the second comparative example includes a first noise filter unit 110 , a second noise filter unit 120 ′, and a clamp unit 130 , The second noise filter unit 120 ′ has a structure including only the ground inductor 121 .

There is an advantage that conduction noise of the third line 23 ′ can be suppressed by the ground inductor 121 .

However, as the impedance of the first current path CP1 increases due to the ground inductor 121 , the difference between the impedance of the first current path CP1 and the impedance of the second current path CP2 decreases. Therefore, there is a problem in that the size of the noise current generated by the second current path CP2 increases, so that radiation noise corresponding to a high frequency region of 30 MHz or higher is increased.

As shown in FIG. 7 , the differential mode conduction noise (DP noise) in the high frequency region of 30 MHz or higher according to the second comparative example REF2 in which the second noise filter unit 120 ′ includes only the ground inductor 121 . ) is increased by about 20 dBpW or more compared to the first comparative example REF1 having a structure that does not include the ground inductor 121 .

However, according to an embodiment of the present invention, the second noise filter unit 120 further includes a ground capacitor 122 connected in parallel to the ground inductor 121, so that an increase in impedance due to the ground inductor 121 is reduced. can be offset. Accordingly, it is possible to prevent the radiation noise from being deepened due to the second noise filter unit 120 .

8 is a reference impedance and an impedance of a clamp unit according to an embodiment and a second comparative example of the present invention, an impedance of a second noise filter unit according to a second comparative example, and an impedance of a second noise filter unit according to an embodiment of the present invention; is a diagram showing 9 is a view showing common mode conducted noise according to Comparative Examples 1 and 2 and an embodiment of the present invention. 10 is a diagram illustrating conducted noise in differential mode according to Comparative Examples 1 and 2 and an embodiment of the present invention.

The first current path CP1 includes at least one of the first and second lines 21 ′ and 22 ′ and a third line 23 ′.

Accordingly, as shown in Equation 1 below, the impedance Z _{in1 of the first current path CP1 is the impedance Z NF2} of the second noise filter unit 120 disposed on the third line 23 ′ and Corresponds to the sum of _{the impedances Z cable1} of the cables implementing the first current path CP1. At this time, since the clamp unit 130 connected to at least one of the first and second lines 21 ′ and 22 ′ and the clamp unit 130 connected to the third line 23 ′ cancel each other out, the first _{The impedance Z in1} of the first current path CP1 may not be affected by the impedance of the clamp unit 130 .

In addition, the second current path CP2 includes at least one of the first and second lines 21 ′ and 22 ′, the chassis capacitor 51 and the earth ground 40 .

Accordingly, as shown in Equation 2 below, the impedance Z _{in2 of the second current path CP2 is the impedance Z ch} of the chassis capacitor 51 and the clamp unit connected to the third line 23 ′ ( 130) corresponds to the impedance (Z _{clamp ) and the impedance (Z cable2} ) of the cable implementing the second current path (CP2).

At this time, in order to prevent the aggravation of the radiation noise, since the magnitude of the current by the second current path CP2 must be smaller than the magnitude of the current by the first current path CP1, the impedance Z _{in2 of the second current path CP2} ) is very large compared to _{the impedance Z in1} of the first current path CP1 occurs. (|Z _in2 | >> |Z _in1 |)

And, assuming the impedance of the cable to implement the first current path (CP1) the impedance (Z _cable1) and the second current path (CP2) of the cable to implement the (Z _cable2) is that the mutual similarity, the expressions (1) and (2) _{When the condition (|Z in2} | >> |Z _in1 |) for preventing the deepening of the radiation noise is applied, as shown in Equation 3 below, the impedance Z _NF2 of the second noise filter unit 120 is the reference impedance The condition that it is much smaller than (Z _{base ) occurs.} Here, the reference impedance (Z _base) is the sum of the chassis capacitor 51 impedance (Z _ch) and the impedance (Z _clamp) of the clamp portion 130 connected to the third line (23 ') of.

As shown in FIG. 8 , in the high frequency region of 30 MHz or higher, the impedance Z _ch of the chassis capacitor 51 is negligible compared to _{the impedance Z clamp} of the clamp unit 130 connected to the third line 23 ′. Since it is small enough, it can be seen that the reference impedance Z _base is derived similarly to _{the impedance Z clamp} of the clamp unit 130 connected to the third line 23 ′.

And, as mentioned above, since the second noise filter unit 120 ′ according to the second comparative example REF2 includes only the ground inductor 121 , the second noise filter unit according to the second comparative example REF2 . The impedance (|Z _NF2 | of REF2) of (120') corresponds to the impedance of the ground inductor 121 . Accordingly, in the high frequency region of 30 MHz or higher, the impedance |Z _NF2 | of REF2 of the second noise filter unit 120 ′ according to the second comparative example REF2 is smaller than the reference impedance _{Z base , and the reference impedance Z base} ) is adjacent.

On the other hand, since the second noise filter unit 120 according to an embodiment of the present invention further includes a ground capacitor 122 connected in parallel to the ground inductor 121, the second noise filter unit 120 according to an embodiment of the present invention further includes a ground capacitor 122 connected in parallel to the ground inductor 121. The impedance (|Z _NF2 | of EM) of the part 120 may be reduced by the grounding capacitor 122 .

Accordingly, in a high frequency region of 30 MHz or higher, the impedance (|Z _NF2 | of EM) of _{the second noise filter unit 120 according to an embodiment of the present invention is not only the reference impedance (Z base} ), but also the chassis capacitor 51 . It can be seen that it is smaller than the impedance (Z _{ch ) of}

As described above, the EMI filter 100 according to the embodiment of the present invention and the EMI filter REF2 according to the second comparative example are disposed on the third line 23', unlike the first comparative example REF1. a grounded inductor 121 .

Therefore, as shown in FIG. 9, in the region of 30 MHz or less, the common mode conducted noise (CM CE) according to the exemplary embodiment (EM) and the second comparative example (REF) of the present invention is the second 1 It can be seen that the decrease compared to Comparative Example (REF1).

In addition, the EMI filter 100 according to the embodiment of the present invention further includes a ground capacitor 122 connected in parallel to the ground inductor 121 unlike the second comparative example REF2. Accordingly, it is possible to prevent the impedance of the second noise filter unit 120 connected to the third line 23' from increasing, so that the magnitude of the current of the second current path CP2 is the current of the first current path CP1. Oversize can be prevented.

Accordingly, as shown in FIG. 10 , in a high frequency region of 30 MHz or higher, it can be confirmed that the differential mode conduction noise (DP noise) according to the exemplary embodiment (EM) of the present invention is lower than that of the second comparative example (REF2). . In particular, in the high frequency region of 30 MHz or higher, it can be seen that the differential mode conduction noise (DP noise) according to the embodiment (EM) of the present invention is similar to the first comparative example (REF1) of the structure not including the second noise filter unit. have.

As described above, the EMI filter 100 according to an embodiment of the present invention has the advantage of preventing an increase in radiation noise while reducing conduction noise.

On the other hand, the capacitance of the ground capacitor 122 of the EMI filter 100 according to an embodiment of the present invention is selected within a range that satisfies the condition that _{the second noise filter unit Z NF2} is smaller than the reference impedance Z _{base .} can

11 is a view showing the impedance of the second noise filter unit according to the second comparative example and the first, second, and third embodiments of the present invention, respectively. 12 is a view showing common mode conducted noise currents according to Comparative Examples 1 and 2 and Examples 1, 2, and 3 of the present invention, respectively.

11 and 12, in the first embodiment (EM1) of the present invention, the capacitance of the grounding capacitor 122 is 100pF, and in the second embodiment (EM2) of the present invention, the capacitance of the grounding capacitor 122 is 200pF, and in the third embodiment EM3 of the present invention, the capacitance of the ground capacitor 122 is 300pF.

11 , according to the first embodiment EM1 of the present invention in which the capacitance of the ground capacitor 122 is 100 pF, the impedance (|Z _NF2 | of EM1) of the second noise filter unit 120 is It can be seen that it is derived as about 1/10 of the reference impedance (Z _{base ).}

And, according to the second embodiment (EM2) of the present invention in which the capacitance of the ground capacitor 122 is 200 pF, the impedance (|Z _NF2 | of EM2) of the second noise filter unit 120 is the reference impedance (Z _base ) It can be seen that it is derived by about 1/20 of

In addition, according to the third embodiment (EM3) of the present invention in which the capacitance of the ground capacitor 122 is 300 pF, the impedance (|Z _NF2 | of EM3) of the second noise filter unit 120 is It can be confirmed that it is derived with a smaller value than the example (|Z _{NF2 | of EM2).}

_{As described above, the impedances |Z NF2} | of EM1, EM2, EM3 of the second noise filter unit 120 according to the first to third embodiments of the present invention _{are smaller than the reference impedance Z base} , and in particular, the ground It can be seen that the structure is smaller than that of the second comparative example REF2 in which the capacitor 122 is not included.

Also, as in the first to third embodiments of the present invention, as the capacitance of the grounding capacitor 122 increases in the range of 100pF to 300pF, the impedance (|Z _NF2 | of EM1) of the second noise filter unit 120 increases. , EM2, EM3) can be seen to decrease.

12, in the high-frequency region of 30 MHz to 100 MHz, the common mode conducted noise current (I _CM ) according to the first, second, and third embodiments (EM1, EM2, EM3) of the present invention is a ground inductor It can be seen that the structure including only (121) is smaller than that of the second comparative example (REF2).

In particular, in the high-frequency region of 30 MHz to 100 MHz, the common mode conducted noise current I _CM according to the second and third embodiments EM2 and EM3 is the first of the structure that does not include the second noise filter unit 120 . A similar thing to the comparative example (REF1) can be confirmed.

However, in the case of the first embodiment (EM1), in the 30 MHz region, _{it can be seen that the common mode conduction noise current (I CM} ) is similar to that of the second comparative example (REF2).

Accordingly, the ground capacitor 122 of the second noise filter unit 120 of the EMI filter 100 according to an embodiment of the present invention has a capacitance of 100 pF to 300 pF to offset the impedance of the ground inductor 121 . can In particular, the ground capacitor 122 may have a capacitance of 200 pF to 300 pF.

13 is a diagram illustrating an implementation example of the second noise filter unit of FIG. 1 .

13 , the ground inductor 121 and the ground capacitor 122 of the second noise filter unit 120 may be bonded to the substrate 123 disposed outside the chassis 50 .

For example, the grounding inductor 121 may be formed in a form in which a wire having a diameter of 1.15 mm is wound multiple times on a core having a diameter of 16 mm.

The ground capacitor 122 may be bonded to the substrate 123 together with the ground inductor 121 . In addition, a plurality of ground capacitors 122 connected in parallel to the ground inductor 121 may be provided. In this case, the plurality of ground capacitors 122 may be connected in parallel to each other.

The substrate 123 may be implemented separately from a substrate (not shown) corresponding to the first noise filter unit 110 . In addition, the substrate 123 may be installed on the outer wall of the chassis 50 .

As described above, the present invention has been described with reference to the illustrated drawings, but the present invention is not limited by the embodiments and drawings disclosed in this specification, and various methods can be obtained by those skilled in the art within the scope of the technical spirit of the present invention. It is obvious that variations can be made. In addition, although the effects according to the configuration of the present invention are not explicitly described and described while describing the embodiments of the present invention, it is natural that the effects predictable by the configuration should also be recognized.

10: external power
L, N, G: active wire, neutral wire, ground wire
20: power input unit
21, 22, 23: first, second, and third terminals
21', 22', 23': first, second, third line
30: noise source 40: earth ground
50: chassis 51: chassis capacitor
100: EMI filter 110: first noise filter unit
120: second noise filter unit 121: ground inductor
122: ground capacitor
CP1, CP2: first and second current paths

Claims (8)

In the EMI filter disposed between the power input unit to which external power is input and the noise source,
a first noise filter unit connected to the first and second terminals of the power input unit; and
and a second noise filter unit connected to the third terminal of the power input unit and including an inductor and a capacitor connected in parallel to each other.
The method of claim 1,
The third terminal is connected to the earth ground,
The noise source and the first noise filter unit are accommodated in a chassis made of a conductive material,
The second noise filter unit is disposed between the chassis and the third terminal,
The chassis is an EMI filter grounded through the third terminal.
3. The method of claim 2,
The EMI filter further comprising a clamp unit respectively connected to the first, second and third lines corresponding to the first, second and third terminals of the power input unit.
4. The method of claim 3,
The impedance of the first current path including at least one of the first and second lines and the third line is,
An EMI filter smaller than an impedance of a second current path including at least one of the first and second lines, a chassis capacitor corresponding to a parasitic capacitance between the chassis and the ground ground, and the ground ground.
5. The method of claim 4,
In a high frequency region of 30 MHz or higher, the impedance of the second noise filter unit is smaller than the reference impedance,
The reference impedance is an EMI filter derived from the sum of the impedance of the clamp unit connected to the third line and the impedance of the chassis capacitor.
6. The method of claim 5,
The capacitance of the capacitor of the second noise filter unit is 100pF to 300pF EMI filter.
The method of claim 1,
The first noise filter unit
a common mode choke disposed between the first and second terminals and the noise source; and
An EMI filter including a one-phase Y capacitor disposed at both ends of the common mode choke.
The method of claim 1,
The first terminal corresponds to a live line of the external power source,
The second terminal corresponds to a neutral line of the external power source,
The third terminal is an EMI filter corresponding to a ground line of the external power source.

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