JP2567360Y2 - Noise prevention choke coil - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a noise prevention choke coil used as a part of a noise filter circuit in a power input portion of an electronic device or the like.

[0002]

2. Description of the Related Art A coil inserted into a power supply input section of an electronic device is most commonly a common mode choke coil used for the purpose of preventing switching noise generated from a switching power supply, for example. In addition, harmonics that have recently become a problem due to voltage distortion in the power system (harmonics refer to frequencies from the second to the 20th order with respect to 50 or 60 Hz, and failures are evident in some devices. Therefore, in order to suppress international regulations such as the IEC standard pub-555-2, etc.), a large inductance (1 mH
A reactor having a normal mode inductance of 10 to 10 mH) is used.

[0003] In FIG. 12, a theoretical equation showing the ratio of the n-th harmonic current of the power supply rectifier circuit 100 when there is no reactor 102 is as follows. _{i n / i i = 2 sinnπ} / 2 · (sinnπα · cosπα-n cosnπα sinπα) / n (n 2 -1) (πα- sinπα · cosπα) where α = (π-2γ) / 2π γ: flowing start Angle On the other hand, when the reactor 102 is inserted, the flow start angle in the above equation is advanced, and harmonic current can be suppressed. Also,
By inserting the common mode choke coil 101, the common mode impedance can be increased and the common mode noise current can be suppressed.

When a reactor 102 and a common mode choke coil 101 for suppressing a harmonic current shown in FIG. 12 are formed, a winding 111 and a core 113 made of ferrite or amorphous magnetic material are conventionally used as shown in FIG.
The common mode choke coil 1
01. Further, a reactor 102 for suppressing harmonics, in which a winding 122 is wound around a core 121 made of silicon steel or the like, is connected in series with the common mode choke coil 101.

[0005]

As described above, conventionally, the common mode choke coil 101 and the reactor 102 for suppressing harmonics are respectively configured as individual parts independent of each other, and are connected to each other so that the power supply shown in FIG. The circuit was configured. Therefore, three windings and two cores are required, and connection work between them is required.
In addition, since the number of components is increased, the mounting area increases,
It has the disadvantage that it is expensive and the device becomes large.

The present invention eliminates the above-mentioned drawbacks and, when used in a power supply circuit of an electronic device, has a common mode noise and harmonic suppression effect, is small, has a small mounting space, and is inexpensive. It is intended to provide a coil.

[0007]

According to the present invention, a power supply 2 is provided.
A two-line choke coil having two windings connected to each line between an electric wire and a load, and penetrating the windings to form a magnetic circuit (outer magnetic path); Is formed of an outer core with a magnetic gap in part,
A noise prevention choke coil characterized by providing a midfoot core constituting a short-circuit magnetic path for short-circuiting the outer magnetic path is obtained.

According to the present invention, there are also provided two windings connected to each line between the power source 2 and the load, and a magnetic circuit (outer magnetic path) is formed through the windings. In the two-line choke coil, the outer magnetic path is formed through a part of an outer core, a magnetic gap, and a midfoot core,
The midfoot core is configured to short-circuit the outer magnetic path, thereby obtaining a noise prevention choke coil.

[0009]

According to the above construction, the outer magnetic path having a gap functions as a magnetic path for securing a normal mode inductance for suppressing harmonics while preventing magnetic saturation due to a large amplitude fundamental wave or harmonic current. However, the midfoot core acts as a magnetic path for obtaining a common mode inductance for preventing common mode noise.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to suppress harmonics, a large normal mode inductance is required as described above, and it is necessary not to be saturated by a fundamental wave having a large amplitude or a harmonic current. On the other hand, in order to prevent common mode noise, a common mode inductance having an appropriate magnitude of inductance (for example, 1 mH to 10 mH) and high frequency characteristics (for example, 10 kHz to 30 MHz) is required.

FIG. 1 is a schematic diagram showing a first embodiment of the present invention. In FIG. 1, a core A and a core B are formed by punching / lamination or powder pressing / sintering a magnetic material having a relatively high saturation magnetic flux density, such as silicon steel, an amorphous magnetic material, or ferrite. E-shaped core. These cores have shorter leg portions on both sides than the central leg portion. When the central leg portions of the core A and the core B are arranged in abutment, a magnetic gap 3 is formed between the opposing side leg portions. It is formed. The legs on both sides, together with the core body connecting them,
Act as an outer core for forming the outer magnetic path 4 having The central leg acts as a midfoot core for forming a short-circuit magnetic path 5 for short-circuiting the outer magnetic path 4.

The outer core legs 41 and 42 have windings 6 and 7 respectively connected to the input terminals 61 and 71 or the output terminals 6 and 71, respectively.
It is wound so that the winding directions viewed from 2, 72 are the same as each other. In practice, the windings 6, 7 are wound on a bobbin, into which the legs 41 and 42 of the outer core are inserted.

When this noise preventing choke coil 1 is inserted in series into two lines between a power supply line and a load, the winding 6, the current flowing through the winding 6,
Part of the magnetic fluxes Φ ₁ and Φ ₂ (Φ ₁ −Φ ₃ and Φ ₂ −Φ ₄ ) generated at 7 are added to Φ ₂ and Φ ₁ at the windings 7 and 6 at the windings 7 and 6 via the outer magnetic path 4. Thus, the others (Φ ₃ and Φ ₄ ) flow in directions to cancel each other out at the short-circuit magnetic path 5. In this case, the magnitude of the added magnetic flux (Φ ₁ −Φ ₃ and Φ ₂ −Φ ₄ ) and the amount of the canceled magnetic flux (Φ ₃ and Φ ₄ ) are determined by the magnetic gaps on both side legs. 3, length, cross-sectional area, cross-sectional area of the metatarsal core,
It is determined by the relationship between the magnetic path length of the short-circuit magnetic path 5 and the outer magnetic path 4. Actually, since the magnetic gap 3 is provided in the outer magnetic path 4, the magnetic resistance is large and Φ ₂ -Φ ₄ can be considered to be substantially 0 and Φ ₁ -Φ ₃ can be considered to be substantially 0.

In this manner, the normal mode inductance which is effective for the fundamental wave and the harmonic current is applied to each winding by the magnetic flux Φ ₁ flowing through the winding 6 and the magnetic flux Φ ₂ flowing through the winding 7 of the outer core. It is the sum of the generated inductances. Common mode when the noise component of the current flows, the common mode noise of the magnetic flux current due to each of the magnetic flux [Phi ₆ components one flowing to the magnetic flux [Phi ₅ and winding 7 according to the common mode noise component of the current flowing through the winding 6 parts are superimposed on the metatarsal core section as [Phi _7, [Phi _8, in the direction opposite to the [Phi ₆ as [Phi ₅ - [Phi] ₇ in the winding 7 parts of the outer core, the winding 6 parts [Phi as [Phi ₆ - [Phi] ₈ Flows in the opposite direction to ₅ .

On the other hand, since the outer magnetic path 4 has the magnetic gap 3, the magnetic resistance is large as in the case of the normal mode noise, Φ ₅ -Φ ₇ is substantially 0, and Φ ₆ -Φ ₈ is also substantially. It may be regarded as 0. Therefore, the common mode inductance is an inductance generated in each winding by the magnetic flux flowing through a part of the outer magnetic path having the short circuit path 5 and each winding 6 or 7. Therefore, in theory, the common mode inductance is 1 of the normal mode inductance.
/ 2. The magnetic flux generated for the common mode noise is superimposed on the middle foot core portion. However, the common mode noise has a small current (several tens mA to several hundreds) as compared with a fundamental wave or a harmonic current (for example, 1 A to 10 A). mA), and the magnetic fluxes generated in the normal mode noise cancel each other out, so that magnetic saturation hardly occurs, and the cross-sectional area can be made sufficiently smaller than the cross-sectional area of the outer core.

The outer core is made of two U-shaped cores,
Even if a magnetic circuit similar to that of FIG. 1 is formed by using one I-shaped core as the middle foot core, the same effect can be obtained in terms of inductance. Instead of using the two cores, silicon steel, an amorphous magnetic material, ferrite, or the like may be formed from the shape shown in FIG. 1 by punching / lamination or powder pressing / sintering. However, the first of the present invention
As shown in the embodiment of the present invention, it is more preferable to form the outer core and the midfoot core with a core having an integral structure by punching and laminating silicon steel, amorphous magnetic material, or powder pressing and sintering of ferrite. It is inexpensive and has a great effect on assembly.

FIG. 2 is a perspective view showing a second embodiment of the present invention. The outer magnetic path includes two U-shaped outer cores 14, a part of an I-shaped metatarsal core 15, and the magnetic gap 3. Further, the winding is wound around a core main body which is a connecting portion of two legs in the outer core 14 so that a winding direction viewed from an input end or an output end is the same.
Since the state of the magnetic flux, the normal mode inductance, and the common mode inductance of the present embodiment are the same as those of the first embodiment, the description will be omitted.

A feature of the second embodiment is that the metatarsal core 15 is completely separated from the outer core 14, and a core having magnetic characteristics different from that of the outer core 14 can be used as the metatarsal core 5.
As described above, large normal mode inductance is used to suppress harmonics and common mode noise.
While a large common-mode inductance is required, the outer magnetic path is provided with a magnetic gap to prevent magnetic saturation, so the effective magnetic permeability is reduced. Winding needs to be performed. Therefore, it is necessary to increase the so-called window area for the winding, and it is inevitably a large choke coil. On the other hand, in order to make the choke coil as small as possible, it is important how to effectively secure the window area for the winding. The second embodiment further solves this problem. That is, as described in the description of the first embodiment, the cross-sectional area of the midfoot core 15 can be further reduced by making the permeability of the midfoot core 15 larger than the permeability of the outer core 14. When the road has the same size, the length of the leg of the outer core 14 can be increased, and a large window area can be secured accordingly.

A noise preventing choke coil 1 'shown in FIG.
In the above, an amorphous core is used for the outer core 14 and a ferrite core is used for the midfoot core 15, and the magnetic gap 3 is set to 0.1.
3 mm, coils A and B each wound with a 0.5 mm-diameter wire with 75 turns. The measurement circuit shown in FIG. 3 shows the DC current superposition characteristics of normal mode inductance, and the measurement circuit shown in FIG. FIG. 5 shows the results obtained by measuring the DC current superposition characteristics of the respective samples. FIG. 5 shows, for comparison, DC current superposition characteristics of a choke coil having both the normal mode inductance and the common mode inductance shown in FIG. 6 which are conventionally known. In the illustrated conventional choke coil, the outer core 61 is formed of an endless high-permeability ferrite without a magnetic gap, and
For No. 2, a dust iron core having a lower magnetic permeability than ferrite is used. The coils A and B are wound so that the winding directions viewed from the input terminal and the output terminal are opposite to each other to obtain a common mode inductance and a normal mode inductance.

In the conventional choke coil, as shown in FIG. 5, the normal mode inductance is only about 10% of the common mode inductance. In addition, even when the difference in the magnetic materials used is taken into account, the reduction of both inductances due to the superposition of direct current is remarkable, and the effect for suppressing harmonics is extremely low. This is because the ferrite having high magnetic permeability is used in the outer core portion 61 without providing a magnetic gap, and a large common mode inductance is obtained when there is no DC superimposed current. This is because the outer core 61 is rapidly saturated and the inductance is reduced. On the other hand, in the noise prevention choke coil according to the present invention, the normal mode inductance and the common mode inductance do not decrease at all up to the rated current of 2 A, for example, and the magnitude of the common mode inductance is approximately 50% of the normal mode inductance.
%, And an inductance that can never be obtained in the conventional example is obtained.

Usually, the value of inductance required as a reactance for suppressing harmonics is said to be 1 mH to 10 mH (General Publication No. 232, Electric Cooperative Research Vol. 46, No. 2, "Harmonics in Power System and Its Countermeasures ”), common mode inductance for noise suppression is generally 1mH to 10mH
The inductance in the range is often used. Therefore, the configuration of the choke coil according to the present invention, which has a common mode inductance of 50% of the normal mode inductance and has a good DC superposition property, is much more effective than the conventional method. As shown in FIG. 7, the frequency characteristics of the inductance of the choke coil according to the embodiment of the present invention are obtained up to 1 MHz or more in the normal mode.
Not only harmonics of 00Hz to 1kHz, but also 10kHz to 1MHz
Needless to say, a great effect can be obtained in suppressing the normal mode noise.

Next, the effect when a noise filter is constructed by connecting two 6800 pF capacitors to the noise prevention choke coil of the present invention as shown in FIG. 8 will be described. FIG. 9 shows a common mode attenuation characteristic of the noise filter measured by MIL-STD-220A. According to FIG. 9, 20 dB or more at 150 kHz and 40 dB at 1 MHz to 30 MHz
It can be seen that the above attenuation is obtained. FIG. 10 shows the result of mounting the same noise filter on the switching power supply and measuring the voltage between noise terminals according to the FCC standard. 5
It can be seen that at around 00 kHz, the switching noise is attenuated by 30 dB or more, and the switching noise generated from 450 kHz to 15 MHz is effectively suppressed. FIG. 11 shows the harmonic suppression effect in that case. For harmonics in the measurement range of 150 Hz to 650 Hz,
An inhibitory effect of 9.5% to 75.6% is obtained.

[0023]

[Effect of the invention] As described above, according to the invention,
Although it is a single component, it can also effectively suppress common mode noise, normal mode noise, and harmonics, and can provide a small, inexpensive noise-prevention choke coil with a small mounting space. It makes a significant contribution to the realization of small, low-cost electronic devices with a noise suppression function.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a noise prevention choke coil according to the present invention.
FIG. 1 is a schematic diagram showing a configuration of an example of FIG.

FIG. 2 shows a second embodiment of the noise prevention choke coil according to the present invention.
FIG. 1 is a schematic diagram showing a configuration of an example of FIG.

FIG. 3 is a circuit for measuring a normal mode inductance of the noise prevention choke coil according to the present invention.

FIG. 4 is a circuit diagram for measuring the common mode noise of the noise prevention choke coil according to the present invention.

FIG. 5 is a diagram showing actual measured values of DC superposition characteristics of inductances in both common and normal modes of the noise prevention choke coil according to the present invention and the conventional noise prevention choke coil.

FIG. 6 is a perspective view of an example of a conventional type noise canceling choke coil for both common mode and normal mode.

FIG. 7 is a diagram showing a frequency characteristic of a normal mode inductance of the noise prevention choke coil according to the present invention.

FIG. 8 is an example of a circuit configured as a noise filter using the noise prevention choke coil according to the present invention.

FIG. 9 shows the MIL-STD- of the noise filter shown in FIG.
The figure which showed the example of the attenuation characteristic measurement of the common mode by 220A.

10 is an example showing an actually measured value of a voltage between noise terminals, that is, a noise suppression effect when the noise filter shown in FIG. 8 is mounted on a switching power supply.

11 is a diagram showing actually measured values of a harmonic suppression effect when the noise filter shown in FIG. 8 is mounted on a switching power supply.

FIG. 12 is a diagram illustrating an example of a power supply input circuit to an electronic device using a conventional choke coil.

FIG. 13 is a diagram showing a specific connection state of a conventional choke coil.

[Explanation of symbols]

 1, 1 'Noise prevention choke coil according to the present invention 3 Magnetic gap 4 Outer magnetic path 5 Short circuit path 6, 7 Winding 61, 71 Winding input terminal

Claims (3)

(57) [Scope of request for utility model registration] 1. A two-line choke having two windings connected to each line between a power supply 2 electric wire and a load, and penetrating the windings to form a magnetic circuit (outer magnetic path). In the coil, the outer magnetic path is formed by an outer core partially having a magnetic gap, and a midfoot core that forms a short-circuit magnetic path for short-circuiting the outer magnetic path is provided. choke coil. 2. A two-line choke having two windings connected to each line between a power supply 2 electric wire and a load, and penetrating the windings to form a magnetic circuit (outer magnetic path). In the coil, the outer magnetic path is formed through an outer core, a magnetic gap, and a part of a middle foot core, and the middle foot core short-circuits the outer magnetic path. . 3. The noise prevention choke coil according to claim 1, wherein the middle foot core is made of a material having a magnetic permeability equal to or higher than that of the outer core.