JP7218599B2 - Noise filter - Google Patents

Description

The technology disclosed in this specification relates to noise filters.

In order to suppress electromagnetic noise superimposed on conductive lines, noise filters are being developed. Many noise filters of this type have a capacitor for bypassing electromagnetic noise and suppressing transmission of the electromagnetic noise to the output. However, the capacitor has a parasitic inductance called equivalent series inductance (ESL), and the wiring to which the capacitor is connected also has a parasitic inductance. Therefore, it is known that such a noise filter cannot exhibit good filtering performance against electromagnetic noise in a high frequency band due to the influence of these parasitic inductances.

Patent Literature 1 discloses a noise filter that utilizes magnetic coupling of a pair of inductors connected in series with conductive lines. The noise filter disclosed in Patent Document 1 improves filter performance by reducing the equivalent series inductance of the capacitor by mutual inductance generated between a pair of inductors.

U.S. Pat. No. 6,937,115

In the technique of Patent Document 1, a conductive wire formed in a specific pattern is used to form a pair of magnetically coupled inductors on the conductive wire. However, there is a problem that the area of the noise filter increases depending on the specific pattern of the conductive lines. Also, depending on the specific pattern of the conductive line, the width of the conductive line is narrowed, increasing the parasitic resistance. Therefore, there is a problem that the heat generated due to the energy loss of the noise filter cannot be suppressed. Since it is necessary to consider such problems, the technology using conductive lines formed in a specific pattern has a significantly low degree of freedom in design. Therefore, it can be said that the technique using the conductive line formed in a specific pattern is a technique lacking in versatility. An object of the present specification is to provide a noise filter that suppresses the equivalent series inductance of a capacitor and the parasitic inductance of wiring to which the capacitor is connected, and is highly versatile.

An embodiment of the noise filter disclosed herein can comprise a first conductive line, a second conductive line, a third conductive line, and a magnetic material. The first conductive line extends between a first input port and a first output port, and extends between the first input port and a first branch. a first output conductive line extending between the output port and the first branch. the second conductive line extending between a second input port and a second output port, a second input conductive line extending between the second input port and a second branch; a second output conductive line extending between the output port and the second branch. The third conductive line is connected between the first branched portion of the first conductive line and the second branched portion of the second conductive line, and has a capacitor interposed therebetween. The magnetic body is provided so as to cross each of the first input-side conductive line, the second input-side conductive line, the first output-side conductive line, and the second output-side conductive line. The magnetic body magnetically couples the first input-side conductive line, the second input-side conductive line, the first output-side conductive line, and the second output-side conductive line to each other, and by these magnetic couplings, The resulting mutual inductance is configured to reduce the equivalent series inductance of the capacitor and the parasitic inductance of the third conductive line. In the noise filter of the above embodiment, there is no need to form any particular pattern on each of the first conductive lines and the second conductive lines. Therefore, the technique of arranging the magnetic material on each of the first conductive line and the second conductive line can be applied to various types of conductive lines, and is a highly versatile technique. be.

In the noise filter of the above embodiment, the magnetic body may have an annular shape. According to this embodiment, the magnetic path passing through the magnetic material provided around the first conductive line and the magnetic path passing through the magnetic material provided around the second conductive line are shared. can be done. Therefore, the number of parts can be reduced as compared with the case where separate magnetic bodies are provided for each of the first conductive line and the second conductive line. Further, a gap may be formed in the magnetic body to separate the magnetic bodies along the circumferential direction of the annular shape. When such a gap is provided, the mutual inductance caused by magnetic coupling can be adjusted by adjusting the width of the gap.

In the noise filter of the above embodiment, the magnetic bodies may be configured to extend in the same plane. Since the magnetic body of this noise filter is configured in a flat form, it has a feature of being easy to manufacture. Alternatively, in the noise filter of the above embodiment, both the first conductive line and the second conductive line may extend in the same plane. The first conductive line and the second conductive line of this noise filter can be arranged on, for example, a printed board or a thick copper board.

In the noise filter of the above embodiment, when the magnetic coupling is ignored, the inductance of the first input-side conductive line and the inductance of the second input-side conductive line match, and the inductance of the first output-side conductive line It may be configured such that the inductances of the second output-side conductive lines are the same. Furthermore, in the noise filter of the above embodiment, when the magnetic coupling is considered, the inductance of the first input-side conductive line and the inductance of the second input-side conductive line match, and the inductance of the first output-side conductive line The inductance may match the inductance of the second output-side conductive line. According to this embodiment, the conversion of electromagnetic noise from normal mode to common mode can be suppressed.

In the noise filter of the above embodiment, each of the first conductive line and the second conductive line may be configured by a flat busbar. Even if each of the first conductive line and the second conductive line is a flat bus bar, by arranging the magnetic material around such a bus bar, the equivalent series inductance of the capacitor and the third Parasitic inductance of conductive lines can be reduced.

(A) is a diagram showing an equivalent circuit of a noise filter; (B) is a diagram showing an equivalent circuit of the noise filter of FIG. 1 (A) when excited in normal mode; 1B is a diagram for explaining the noise transfer characteristic of the noise filter of FIG. 1B; FIG. 1B is a diagram for explaining noise transfer characteristics when magnetic coupling is considered in the noise filter of FIG. 1B; FIG. FIG. 2 is a diagram showing an equivalent circuit in which a differential noise generation source and a load are connected in the noise filter of FIG. 1(A); FIG. 2 is a diagram showing an equivalent circuit when considering magnetic coupling in the noise filter of FIG. 1(A); The perspective view of the noise filter of this embodiment is shown typically. The perspective view of the example by which the GND board was arrange|positioned above and below the noise filter of this embodiment is shown typically. The perspective view of the modification of the noise filter of this embodiment is shown typically. The perspective view of the modification of the noise filter of this embodiment is shown typically. The perspective view of the modification of the noise filter of this embodiment is shown typically. The perspective view of the modification of the noise filter of this embodiment is shown typically.

(About noise transfer characteristics of noise filters)
Before describing specific embodiments of the noise filter disclosed in the present specification, noise transfer characteristics of the noise filter 1 will be described with reference to FIGS. 1 to 3. FIG. 1 and 2 are equivalent circuits without a magnetic body, which will be described later, and FIG. 3 is an equivalent circuit with a magnetic body, which will be described later.

As shown in FIG. 1A, the noise filter 1 includes a first conductive line 11 extending between a first input port IN1 and a first output port OUT1, a second input port IN2 and a second output port. A second conductive line 12 extending between OUT2, and a third conductive line 13 having one end connected to the first conductive line 11 and the other end connected to the second conductive line 12. there is A capacitor C<b>1 is inserted in the third conductive line 13 . The noise filter 1 further includes a pair of inductors L1 and L3 serially connected to the first conductive line 11, a pair of inductors L2 and L4 serially connected to the second conductive line 12, and a third conductive line 13. and a pair of inductors L5 and L6 connected in series. _The inductance of inductor L1 is L1, the inductance of inductor L2 is L2 _, the _inductance of inductor L3 is L3, the inductance of inductor L4 is _L4 , the inductance of inductor L5 is _L5 , The inductance of inductor L6 is _L6 . Each of the inductors L1, L2, L3, L4, L5, and L6 may be a parasitic inductor of wiring. Also, the equivalent series inductance ₍ ESL) of the capacitor C1 is added to the inductances L5 and _L6 .

When the first input port IN1 and the second input port IN2 are excited in the normal mode and the normal mode transmission to the first output port OUT1 and the second output port OUT2 is observed, the equivalent circuit of FIG. It can be regarded as the two-port circuit of FIG.

FIG. 2 shows an equivalent circuit in which a noise source and a load are connected to the two-port circuit of FIG. 1(B). _{ZE is the internal impedance of the noise source and Z Load is} the impedance of the load. _L12 is the combined inductance of inductors L1 and L2, _L34 is the combined inductance of inductors L3 and L4, and _L56 is the combined inductance of inductors L5 and L6.

Although the specific configuration will be described later, the noise filter 1 disclosed in the specification of the present application is configured such that the inductor L1, the inductor L2, and the inductor L3 are formed by magnetic bodies disposed around the first conductive line 11 and the second conductive line 12. and inductor L4 are magnetically coupled to each other. That is, in the noise filter 1 disclosed in this specification, any inductor is magnetically coupled to all other inductors. Considering the mutual inductance M caused by these magnetic couplings, the equivalent circuit in FIG. 2 can be expressed as the equivalent circuit in FIG. As shown in FIG. 3, the inductance L ₅₆ of the third conductive line 13 is reduced by the mutual inductance M. As shown in FIG.

Here, assuming that the noise voltage of the noise source is E _noise , the noise voltage V _Load applied to the load is expressed by the following equation.

Z _L12 : Impedance (jω(L ₁₂ +M)) corresponding to inductance L ₁₂
Z _L34 : Impedance (jω(L ₃₄ +M)) corresponding to inductance L ₃₄
Z _L56 : Impedance (jω(L ₅₆ −M)) corresponding to inductance L ₅₆
Z _Cap : Impedance of capacitor C1 (1/(jωC))
ω: Angular frequency (2πf)

In order to reduce the noise voltage V _Load applied to the load, the denominator of Equation 1 may be increased or the numerator of Equation 1 may be decreased. Since _ZE and Z _Load are outside the noise filter 1, they are outside the scope of design.

Since the amplitude of the noise voltage V _Load is represented by an absolute value, taking the absolute value of Equation 1 above and letting V _num be the numerator on the right side, it can be represented by the following equation.

According to Equation 2 above, it can be seen that setting the mutual inductance M so that {ω(L ₅₆ −M)−1/ωC} is 0 maximizes the filter performance. However, such a condition is fulfilled only at certain frequencies. Therefore, it is desirable for the noise filter circuit to reduce noise in a wide range of frequencies, and such conditions are not set.

Here, the mutual inductance M is the mutual _inductance between the inductance _L12 and the inductance L34, and can be expressed by the following formula using the coupling coefficient k.

The coupling coefficient k is a value indicating the degree of magnetic coupling, and takes a value of 0≦k≦1 in the structure disclosed in this specification. As shown in Equations 2 and 3 above, if the values of k, L ₁₂ , and L ₃₄ are adjusted so that the inductance L ₅₆ and the mutual inductance M match, the numerator of Equation 1 above is the capacity of the capacitor C1. Only the product of the impedance and the impedance of the load remains. Since the angular frequency ω increases as the frequency increases, matching the inductance L ₅₆ and the mutual inductance M improves the filter performance against electromagnetic noise in the high frequency band.

In this way, the noise filter 1 disclosed in the specification of the present application magnetically couples the inductors L1, L2, L3, and L4 to each other, so that the mutual inductance M generated by these magnetic couplings reduces the inductance _L56. configured to be The technology disclosed in this specification can utilize this phenomenon to improve filter performance against electromagnetic noise in a high frequency band.

(Regarding the effect of suppressing conversion from normal mode to common mode)
Before describing a specific embodiment of the noise filter disclosed in the specification of the present application, referring to FIGS. explain. FIG. 4 shows an equivalent circuit without a magnetic body, which will be described later, and FIG. 5 shows an equivalent circuit with a magnetic body, which will be described later.

なお、上記数式４の分母は、以下の数式で表される。

FIG. 4 shows an equivalent circuit in which a differential noise source and a load are connected to the noise filter 1 of FIG. 1(A). Z _E1 and Z _E2 are the internal impedances of the noise sources, respectively, and Z _Load1 and Z _Load2 are the impedances of the loads. _Zc is the common mode impedance of the common mode current path. The current _Ic flowing through the common mode impedance _Zc is expressed by the following equation.

Note that the denominator of Equation 4 above is represented by the following equation.

Here, impedances Z ₁ , Z ₂ , Z ₃ , Z ₄ , and Z ₅ respectively represent the following composite impedances.

Z ₁ =Z _E1 +jωL ₁
Z ₂ =Z _E2 +jωL ₂
Z ₃ =Z _Load 1 +jωL _3
Z4 = _ZLoad2 + _jωL4
Z ₅ =jω(L ₅ +L ₆ )+1/(jωC)

Since the equivalent circuit shown in FIG. 4 is excited using a normal mode noise source, Ic represents the amount of conversion from normal mode to common mode. According to Equation 4, Ic=0 when Z ₁ =Z ₂ and Z ₃ =Z ₄ , and conversion from normal mode to common mode is suppressed. When the internal impedances Z _E1 and Z _E2 of the noise source match, and the impedances Z _Load1 and Z _Load2 of the load match, the following formula 6 is established in order to establish Z ₁ =Z ₂ . In order for Z ₃ =Z ₄ to hold, Equation 7 below needs to hold.

Since the magnitude of the inductance is determined by the structure, in order for the above formulas 6 and 7 to hold, the form of wiring on the input side of each of the first conductive line 11 and the second conductive line 12 should be matched, and the first conductive line The form of wiring on the output side of each of the line 11 and the second conductive line 12 should be matched.

Although the specific configuration will be described later, the noise filter 1 disclosed in the specification of the present application is configured such that the inductor L1, the inductor L2, and the inductor L3 are formed by magnetic bodies disposed around the first conductive line 11 and the second conductive line 12. and inductor L4 are magnetically coupled to each other. FIG. 5 shows an equivalent circuit in consideration of magnetic coupling in the noise filter of FIG. 1(A). The presence of the magnetic material increases the self-inductance of each of inductor L1, inductor L2, inductor L3, and inductor L4. Considering the increased self-inductance, the inductance of inductor L1 is L ₁ ', the inductance of inductor L2 is L ₂ ', the inductance of inductor L3 is L ₃ ', and the inductance of inductor L4 is L ₄ '. . In the equivalent circuit of FIG. 5, the voltages V ₁ , V ₂ , V ₃ and V ₄ generated in the inductors L1, L2, L2 and L4 when the closed circuit currents I _l12 and I _l34 flow have the following relationships: holds.

Here, M _nm (n=1 to 4, m=1 to 4) represents the mutual inductance between the inductances L ₁ ′ to L ₄ ′, and the mutual inductance between Ln′ and Lm′ is M _nm (= M _mn ). In this circuit, when the normal mode noise source, load, and common mode path in FIG. ₄ are connected, in order to suppress the return from the normal mode to the common mode, in _FIG . It is required that V ₃ =V ₄ . For that purpose, the following formula must be established.

となる。また、上記数式１２において、Ｍ_３４＝Ｍ_４３であることから、

となる。 Since M ₁₂ =M ₂₁ in Equation 9 above,

becomes. Further, since M ₃₄ =M ₄₃ in Equation 12 above,

becomes.

In order for the above formula 13 to hold, the positional relationship between the inductor L1 and the magnetic material crossing it should be the same as the positional relationship between the inductor L2 and the magnetic material crossing it. The same applies to Equation 14 above.

In order for the above formula 10 to hold, the coupling amount of the magnetic flux generated in each of the inductors L3 and L4 with respect to the inductor L1 must be the same as the amount of magnetic flux generated in each of the inductors L3 and L4 with respect to the inductor L2. not. If L ₃ '=L ₄ ', it can be easily realized. The same applies to Equation 11 above, and it suffices if L ₁ '=L ₂ '.

As described above, if the above formulas 6, 7, 13, and 14 hold, the noise filter 1 can suppress the conversion of electromagnetic noise from normal mode to common mode. As will be described later, in the noise filter disclosed in this specification, the above formulas 6, 7, 13, and 14 are established by making the input-side conductive line and the output-side conductive line symmetrical with respect to the capacitor. is configured to

(Regarding noise filter embodiment)
A noise filter to which the technology disclosed in this specification is applied will be described below. In each figure referred to below, components having substantially the same function as the circuit elements of the noise filter 1 described above are denoted by the same reference numerals, and description thereof may be omitted.

FIG. 6 shows a perspective view of the noise filter 10. As shown in FIG. The noise filter 10 includes a first conductive line 11 extending between a first input port IN1 and a first output port OUT1 and a second conductive line extending between a second input port IN2 and a second output port OUT2. 12, a third conductive wire 13 having one end connected to the first branch portion 11C of the first conductive wire 11 and the other end connected to the second branch portion 12C of the second conductive wire 12; and have. A capacitor C<b>1 is inserted in the third conductive line 13 .

Each of the first conductive line 11 and the second conductive line 12 is composed of a metal bus bar shaped like a flat plate. A first input port IN1 of the first conductive line 11 and a second input port IN2 of the second conductive line 12 are connected to a power supply that is a source of noise. The first conductive line 11 is the positive power line and the second conductive line 12 is the negative power line. The power supply may be a DC power supply or an AC power supply. A load is connected between the first output port OUT1 of the first conductive line 11 and the second output port OUT2 of the second conductive line 12 . The first conductive line 11 and the second conductive line 12 extend in parallel.

A portion of the first conductive line 11 between the first input port IN1 and the first branch portion 11C is referred to as a first input side conductive line 11A. A portion of the first conductive line 11 between the first output port OUT1 and the first branch portion 11C is called a first output side conductive line 11B. A portion of the second conductive line 12 between the second input port IN2 and the second branch portion 12C is referred to as a second input side conductive line 12A. A portion of the second conductive line 12 between the second output port OUT2 and the second branch portion 12C is called a second output side conductive line 12B.

As for the first conductive line 11, the first input-side conductive line 11A, the first output-side conductive line 11B, and the first branch portion 11C are not arranged on the same plane. The first conductive line 11 has a stepped shape. The first input-side conductive line 11A is arranged on the upper side in the drawing with respect to the first branch portion 11C, and the first output-side conductive line 11B is arranged on the lower side in the drawing with respect to the first branch portion 11C. In this manner, the first input-side conductive line 11A and the first output-side conductive line 11B are arranged on different sides with respect to the first branch portion 11C.

As for the second conductive wire 12, the second input-side conductive wire 12A, the second output-side conductive wire 12B, and the second branch portion 12C are not arranged on the same plane. The second conductive line 12 has a stepped shape. The second input-side conductive line 12A is arranged below the second branch portion 12C in the drawing, and the second output-side conductive line 12B is arranged above the second branch portion 12C in the drawing. In this way, the second input-side conductive line 12A and the second output-side conductive line 12B are arranged on different sides with respect to the second branch portion 12C.

More specifically, the first input-side conductive line 11A of the first conductive line 11 and the second input-side conductive line 12A of the second conductive line 12 are not arranged on the same plane, and the first input-side conductive line 11A is arranged above the second input-side conductive line 12A in the drawing. With such a positional relationship, a portion of the linearly extending magnetic body 30 crosses the illustrated lower side of the first input-side conductive line 11A and the illustrated upper side of the second input-side conductive line 12A. can be traversed. Also, the first output-side conductive line 11B of the first conductive line 11 and the second output-side conductive line 12B of the second conductive line 12 are not arranged on the same plane, and the first output-side conductive line 11B is the second output side conductive line. It is arranged below the side conductor 12B in the drawing. With such a positional relationship, a portion of the linearly extending magnetic body 30 crosses the illustrated upper side of the first output-side conductive line 11B and the illustrated lower side of the second output-side conductive line 12B. can be traversed.

The third conductive wire 13 is composed of a metal bus bar formed into a flat plate shape. The third conductive line 13 is orthogonal to each of the first conductive line 11 and the second conductive line 12, extends from the side surface of the first branch portion 11C of the first conductive line 11, and extends from the second conductive line 12. extends from the side surface of the second branch portion 12C. A capacitor C<b>1 is inserted in the third conductive line 13 . For the capacitor C1, a capacitor with good frequency characteristics and high withstand voltage is used. A film capacitor or a ceramic capacitor, for example, is used for the capacitor C1.

Thus, the noise filter 10 is composed of the parasitic inductance of the first conductive line 11, the parasitic inductance of the second conductive line 12, and the capacitor C interposed in the third conductive line 13. noise filter.

The magnetic body 30 is composed of a magnetic sheet in which ferrite powder, which is a magnetic material, is kneaded into resin. The magnetic body 30 has a first magnetic body portion 31, a second magnetic body portion 32, a third magnetic body portion 33, and a fourth magnetic body portion 34, and is configured to have an annular shape. . The first magnetic body part 31, the second magnetic body part 32, the third magnetic body part 33, and the fourth magnetic body part 34 are configured to extend in the same plane, and are rectangular in plan view. is configured to be When the magnetic body 30 is configured to extend in the same plane as described above, the manufacturing of the magnetic body 30 is facilitated. The magnetic body 30 may be a magnetic plate formed of ferrite or the like obtained by sintering materials such as Mn--Zn and Ni--Zn.

The first magnetic portion 31 linearly extends across the first input-side conductive line 11A of the first conductive line 11 and the second input-side conductive line 12A of the second conductive line 12 . The first magnetic portion 31 crosses the lower side of the first input-side conductive line 11A in the drawing so as to be orthogonal to the first input-side conductive line 11A. The first magnetic body portion 31 further crosses the illustrated upper side of the second input-side conductive line 12A so as to be orthogonal to the second input-side conductive line 12A.

The second magnetic portion 32 extends parallel to the first conductive line 11 outside the first conductive line 11 . The second magnetic portion 32 has one end connected to the first magnetic portion 31 and the other end connected to the third magnetic portion 33 .

The third magnetic portion 33 linearly extends across each of the first output-side conductive line 11B of the first conductive line 11 and the second output-side conductive line 12B of the second conductive line 12 . The third magnetic portion 33 crosses the illustrated upper side of the first output-side conductive line 11B so as to be orthogonal to the first output-side conductive line 11B. The third magnetic body portion 33 further crosses the illustrated lower side of the second output-side conductive line 12B so as to be orthogonal to the second output-side conductive line 12B.

The fourth magnetic body portion 34 extends parallel to the second conductive line 12 outside the second conductive line 12 . The fourth magnetic portion 34 has one end connected to the third magnetic portion 33 and the other end connected to the first magnetic portion 31 .

It should be noted that the magnetic body 30 in this example is configured in a continuous annular form. Instead of this example, the magnetic body 30 may be formed with a gap that separates the magnetic bodies 30 along the circumferential direction of the annular shape. For example, a gap may be formed between the first magnetic portion 31 and the second magnetic portion 32 and a gap may be formed between the first magnetic portion 31 and the fourth magnetic portion 34 . In this case, the magnetic body 30 includes an I-shaped portion (first magnetic body portion 31), a C-shaped portion (second magnetic body portion 32, third magnetic body portion 33, and fourth magnetic body portion 34), consists of two parts. When the magnetic body 30 is divided in this way, it becomes easy to mount the magnetic body 30 around the conductive wires 11 and 12 . Also, as will be described later, it is possible to adjust the mutual inductance by adjusting the width of the gap. Note that the positions where the gaps are formed and the number of gaps are not particularly limited.

Here, consider a case where normal mode (differential mode) noise is superimposed on the first conductive line 11 and the second conductive line 12 . In this case, the noise current flows through the first conductive line 11 and the second conductive line 12 in opposite phases. For example, a noise current flows through the first conductive line 11 from the first input port IN1 toward the first output port OUT1, and flows through the second conductive line 12 from the second output port OUT2 toward the second input port IN2. . When such normal mode noise current flows, magnetic flux is generated in the magnetic body 30 . In the first magnetic body portion 31, magnetic flux is generated in the direction from the second input-side conductive line 12A to the first input-side conductive line 11A. In the third magnetic body portion 33, magnetic flux is generated in the direction from the first output-side conductive line 11B to the second output-side conductive line 12B. Thus, a magnetic flux is generated in the magnetic body 30 in the clockwise direction in the drawing. In this manner, when the magnetic body 30 is arranged around the first conductive line 11 and the second conductive line 12, the first input conductive line 11A, the second input conductive line 12A and the first output conductive line are connected. Each of the line 11B and the second output-side conductive line 12B can be magnetically coupled to each other.

In this noise filter 10, by adjusting the material and form of each of the first magnetic portion 31, the second magnetic portion 32, the third magnetic portion 33, and the fourth magnetic portion 34, the first input side The mutual inductance generated between each of the conductive line 11A, the second input conductive line 12A, the first output conductive line 11B and the second output conductive line 12B is adjusted. Further, as described above, when a gap is formed in a part of the magnetic body 30, the mutual inductance generated between these conductive lines is adjusted by adjusting the width of the gap. Thereby, the sum of the equivalent series inductance of the capacitor C1 and the parasitic inductance of the third conductive line 13 is reduced by the mutual inductance generated between these conductive lines (see FIG. 3). As a result, the noise filter 10 can exhibit high filtering performance against electromagnetic noise in a high frequency band, as shown in Equation 2 above. It should be noted that the mutual inductance generated between these conductive lines does not necessarily have to match the sum of the equivalent series inductance of the capacitor C1 and the parasitic inductance of the third conductive line 13. Let M be the mutual inductance, and L ₅₆ be the sum of the equivalent series inductance of the capacitor C1 and the parasitic inductance of the third conductive line 13. Adjust M so that |L ₅₆ −M|<L ₅₆ This allows the capacitor C1 to maintain low impedance up to high frequencies. This bypasses noise currents through capacitor C1 and prevents noise currents from being transferred to the output. The noise filter 10 can have high filter performance.

In the noise filter 10, the sum of the equivalent series inductance of the capacitor C1 and the parasitic inductance of the third conductive line 13 is reduced simply by arranging the magnetic body 30 around the first conductive line 11 and the second conductive line 12. In this example, the first conductive line 11 and the second conductive line 12 are busbars, but the same applies to other types of conductive lines. Moreover, regardless of the shape of the first conductive line 11 and the second conductive line 12, the equivalent series inductance of the capacitor C1 and the third conductive line 13 can be reduced by arranging the magnetic body 30 around them. can reduce the sum of the parasitic inductances of In particular, the magnetic body 30 made of a magnetic sheet can be easily arranged with respect to the first conductive wire 11 and the second conductive wire 12 . Thus, the technique of arranging the magnetic material 30 around the first conductor wire 11 and the second conductor wire 12 can be applied to various types of conductor wires, and thus is a technique with high versatility.

One of the characteristics of the noise filter 10 is that the magnetic body 30 is annularly formed so as to surround the first conductive line 11 and the second conductive line 12 . For example, a magnetic body configured to extend between the first input-side conductive line 11A and the first output-side conductive line 11B of the first conductive line 11 and the second input-side conductive line 12A of the second conductive line 12 The filter performance of the noise filter 10 is improved even if two magnetic bodies, ie, a magnetic body configured to extend between the second output-side conductive wires 12B, are employed, and magnetic flux is generated in each magnetic body. can be improved. However, as in the present embodiment, the magnetic body 30 having a common magnetic path can be made smaller in volume than the two magnetic bodies when the magnetic flux of the same magnitude flows.

In the noise filter 10, the first input-side conductive line 11A and the second input-side conductive line 12A have a common shape (length, width and thickness). Similarly, the first output-side conductive line 11B and the second output-side conductive line 12B have a common shape (length, width and thickness). Therefore, in the noise filter 10, ignoring the magnetic coupling of the magnetic body 30, the inductance of the first input-side conductive line 11A and the inductance of the second input-side conductive line 12A match, and the inductance of the first output-side conductive line 11B The inductance matches the inductance of the second output-side conductive line 12B. Therefore, the noise filter 10 satisfies Equations 6 and 7 above.

In the noise filter 10, the relative positional relationship of the magnetic body 30 with respect to the first input-side conductive line 11A and the relative positional relationship of the magnetic body 30 with respect to the second input-side conductive line 12A match. Similarly, in the noise filter 10, the relative positional relationship of the magnetic body 30 with respect to the first output-side conductive line 11B and the relative positional relationship of the magnetic body 30 with respect to the second output-side conductive line 12B match. Therefore, in the noise filter 10, when the magnetic coupling of the magnetic body 30 is considered, the inductance of the first input-side conductive line 11A and the inductance of the second input-side conductive line 12A match, and the inductance of the first output-side conductive line 11B The inductance matches the inductance of the second output-side conductive line 12B. Therefore, the noise filter 10 satisfies Equations 13 and 14 above.

As described above, the noise filter 10 is configured to satisfy the above equations 6, 7, 13, and 14, so that the conversion of electromagnetic noise from normal mode to common mode can be suppressed.

In the example shown in FIG. 6, a GND plate fixed to a reference potential may be arranged around the noise filter 10 . Such a GND plate may be arranged only partially around the noise filter 10 or may be arranged so as to surround the noise filter 10 . Further, when the GND plate is arranged so as to surround the noise filter 10, the GND plate can also function as an electromagnetic noise shield. Note that the GND plate may be composed of a braided wire.

For example, FIG. 7 schematically shows an example in which a pair of GND plates 42 and 44 are arranged above and below the noise filter 10 . In this case, if the distances D1, D2, D3 between the GND plates 42, 44 and the conductive lines 11, 12 are configured to have the relationships shown in the figure, even if the proximity effect due to the GND plates is considered, The relationships of Equations 6 and 7 can be maintained, and the noise suppression effect can be maintained even for high-frequency noise (for example, 10 MHz or higher). Specifically, between the lower GND plate 42 and the first input conductive line 11A, between the lower GND plate 42 and the second output conductive line 12B, and between the upper GND plate 44 and the first output conductive line 11B. and the distance D1 between the upper GND plate 44 and the second input-side conductive line 12A. Between the lower GND plate 42 and the first output conductive line 11B, between the lower GND plate 42 and the second input conductive line 12A, between the upper GND plate 44 and the first input conductive line 11A, and on the upper side. The distance D2 between the GND plate 44 and the second output-side conductive line 12B is common. Between the lower GND plate 42 and the first branch portion 11C, between the lower GND plate 42 and the second branch portion 12C, between the upper GND plate 44 and the first branch portion 11C, and between the upper GND plate 44 and the second branch portion 11C. A distance D3 between the branch portions 12C is common.

In the noise filter 10 shown in FIG. 6, the magnetic body 30 has a planar rectangular shape. Instead of this example, in the noise filter 100 shown in FIG. 8, the magnetic body 110 may have an annular shape when viewed from above. Such an annular magnetic body 110 has the effect of allowing magnetic flux to pass easily. Part of the magnetic body 110 may be annular or elliptical. In addition, a gap may be formed in the magnetic body 110 to separate the magnetic bodies 110 along the circumferential direction of the annular shape. When such a gap is formed, mutual inductance generated by magnetic coupling can be adjusted by adjusting the gap width, and the magnetic body 110 can be easily arranged around the conductive lines 11 and 12. becomes.

In the noise filter 10 shown in FIG. 6, each of the first conductive wire 11 and the second conductive wire 12 has a stepped shape. Instead of this example, in noise filter 102 shown in FIG. 9, each of first conductive line 11 and second conductive line 12 may be arranged in the same plane. In this case, the magnetic bodies 120 are arranged three-dimensionally. In addition, as shown in FIG. 10, a gap may be formed in the magnetic body 120 to separate the magnetic bodies 120 along the circumferential direction of the annular shape. When such a gap is formed, mutual inductance generated by magnetic coupling can be adjusted by adjusting the gap width, and the magnetic body 110 can be easily arranged around the conductive lines 11 and 12. becomes. The noise filter 102 shown in FIGS. 9 and 10 is particularly useful when each of the first conductive lines 11 and the second conductive lines 12 is arranged on a printed board or a thick copper board.

In the noise filter 10 shown in FIG. 6, the first conductive wire 11 and the second conductive wire 12 extend in parallel. Instead of this example, in the noise filter 103 shown in FIG. 11, each of the first conductive line 11 and the second conductive line 12 extends in a meandering manner and approaches at the position where the capacitor C1 is arranged. may be configured. In this example, a part of the first branched portion 11C of the first conductive wire 11 and a part of the second branched portion 12C of the second conductive wire 12 are wiring (capacitor C1 wiring on both sides). Thus, the wires on both sides of capacitor C1 are shortened, and the parasitic inductance of these wires can be reduced. Therefore, the mutual inductance required to reduce the parasitic inductance of these wires can be suppressed, so the amount of the magnetic material 120 can be reduced. Further, in this noise filter 103, the first conductive line 11 and the second conductive line 12 are arranged in close proximity to each other in the vicinity of the port and extend in parallel. Therefore, the parasitic inductance of the first conductive line 11 and the second conductive line 12 can be reduced.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. In addition, the technical elements described in this specification or in the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in this specification or drawings can simultaneously achieve a plurality of purposes, and achieving one of them has technical utility in itself.

10: Noise filter 11: First conductive wire 11A: First input conductive wire 11B: First output conductive wire 11C: First branch 12: Second conductive wire 12A: Second input conductive wire 12B: Second Output-side conductive line 12C: Second branch portion 13: Third conductive line 30: Magnetic body 31: First magnetic body part 32: Second magnetic body part 33: Third magnetic body part 34: Fourth magnetic body part IN1: First input port IN2: Second input port OUT1: First output port OUT2: Second output port C1: Capacitor

Claims (4)

a first input-side conductive line extending between a first input port and a first output port, the first input-side conductive line extending between the first input port and a first branch; a first conductive line having a first output conductive line extending between an output port and the first branch;
a second input-side conductive line extending between a second input port and a second output port, the second input-side conductive line extending between the second input port and a second branch; a second conductive line having a second output conductive line extending between the output port and the second branch;
a third conductive line connected between the first branch of the first conductive line and the second branch of the second conductive line and having a capacitor inserted therein;
and a magnetic body provided so as to cross each of the first input-side conductive line, the second input-side conductive line, the first output-side conductive line, and the second output-side conductive line. ,
The magnetic body is adapted to connect each of the first input-side conductive line, the second input-side conductive line, the first output-side conductive line, and the second output-side conductive line when a normal mode noise current flows. are magnetically coupled to each other, and the mutual inductance generated by these magnetic couplings reduces the equivalent series inductance of the capacitor and the parasitic inductance of the third conductive line ,
When the magnetic coupling is ignored, the inductance of the first input-side conductive line and the inductance of the second input-side conductive line match, and the inductance of the first output-side conductive line and the inductance of the second output-side conductive line The inductance is matched and
Considering the magnetic coupling, the inductance of the first input-side conductive line and the inductance of the second input-side conductive line match, and the inductance of the first output-side conductive line and the inductance of the second output-side conductive line The inductance is matched and
Both the first conductive line and the second conductive line are configured to extend in the same plane,
A noise filter in which each of the first conductive wire and the second conductive wire is not wound with the magnetic material . 2. The noise filter according to claim 1, wherein said magnetic body has an annular shape. 3. The noise filter according to claim 2, wherein the magnetic body is provided with a gap that separates the magnetic body along the circumferential direction of the annular shape. 4. The noise filter according to any one of claims 1 to 3 , wherein each of said first conductive line and said second conductive line is composed of a flat busbar.

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