Patent Application
20190311845
The present invention relates to a common mode choke coil included in a rectifier circuit in an electric alternating current device such as a power supply circuit or an inverter, an anti-noise circuit, a waveform shaping circuit, a resonance circuit, various types of switching circuits, and the like, and more specifically to an air-cooled common mode choke coil that can suppress an increase in temperature by improving heat dissipation properties.
A common mode choke coil included in a circuit in various types of electric alternating current devices is formed by winding a coil around an annular core in an insulated manner. The use of a ferrite core formed by sintering a compacted oxide magnetic material as the core is proposed. The core is housed in a resin bobbin, and a coil is wound around the outer circumference of the bobbin, thus forming a common mode choke coil (for example, Patent Document 1).
Patent Document
[Patent Document 1] JP 2012-59754A
A common mode choke coil generates heat when used in a commercial alternating current power supply circuit because Joule heat is generated as a result of the coil being energized. Although the core itself generates little heat, the temperature of the common mode choke coil, in which the core is housed in the bobbin, increases due to conduction, radiation, or convection of the heat generated in the coil. When the temperature of the core increases and exceeds a Curie temperature Tc of the magnetic material, the magnetic properties significantly deteriorate, and the noise suppressing effect is lost. For this reason, it has been necessary to use a material that has a high Curie temperature Tc as the magnetic material of the core, or set the electric current applied to the coil to a low level to suppress heat generation in the coil.
On the other hand, in order to achieve a reduction in the size, weight, and cost of the core while ensuring the effect of suppressing noise over a wide frequency band, an advantageous effect of obtaining an inductance value with fewer windings of the coil can be expected by using a magnetic material that has a high relative magnetic permeability μs. However, in general, a magnetic material with high magnetic permeability has a low Curie temperature Tc, and thus a common mode choke coil that can suppress an increase in the temperature of the core is required.
It is an object of the present invention to provide a bobbin-shaped air-cooled common mode choke coil that can suppress an increase in temperature by improving heat dissipation properties.
An air-cooled common mode choke coil according to the present invention is a common mode choke coil in which an annular core is housed in an annular bobbin, and a coil is wound around an outer circumference of the bobbin. An airflow path that allows an airflow to flow therethrough is formed between the bobbin and the core. The bobbin has at least one opening that is in communication with the airflow path, and a flange is provided in a protruding manner along a peripheral edge of the opening.
The opening may be formed in the outer circumferential surface of the bobbin.
It is desirable that the opening is formed in the outer circumferential surface of the bobbin and reaches upper and lower surfaces of the bobbin.
It is desirable that the flange is flared toward the outer circumference with respect to the opening.
It is desirable that a pair of the openings is provided, and the pair of the openings is formed symmetrically along the diameter of the bobbin.
The core may have a rectangular vertical cross section, and corners of the core may abut against and be supported by an inner surface of the bobbin.
A boss or a rib may be provided protruding on an inner surface of the bobbin, and the core may abut against and be supported by the boss or the rib.
The core may be a ferrite core.
Also, an electric appliance including the common mode choke coil according to the present invention is an electric appliance in which the common mode choke coil described above is mounted on a board housed in a casing. The casing includes an air intake opening and an air exhaust fan, and the common mode choke coil is disposed, with one of the openings pointing toward an upstream side of an airflow formed by the air intake opening and the air exhaust fan.
With the air-cooled common mode choke coil according to the present invention, by introducing an airflow into an opening formed in the bobbin, it is possible to release heat in the bobbin from an opening, and suppress an increase in the temperature of the core caused by heat generated in the coil as much as possible. Accordingly, it is possible to use a material with high magnetic permeability that has a low Curie temperature as the magnetic material of the core.
Hereinafter, an air-cooled common mode choke coil 10 according to an embodiment of the present invention will be described with reference to the accompanying drawings. A single-phase common mode choke coil in which a pair of coils 40 and 40 are wound is used as an example of the common mode choke coil 10.
The core 30 is an annular body made of a magnetic material. The core 30 has a substantially rectangular cross section as shown in the diagrams, but the cross sectional shape is not limited thereto. The core 30 may be, for example, a core (hereinafter also referred to as a “sintered core”) obtained by compact molding a Mn—Zn-based ferrite core material or a Ni—Zn-based ferrite core material and sintering the compacted material.
It is particularly preferable that the present invention is applied to a ferrite core with a high relative magnetic permeability us among sintered cores. Ferrite cores made of a Mn—Zn-based material and a Ni—Zn-based material generally have a relative magnetic permeability us of about 500 to 5000 and a Curie temperature Tc of 180° C. to 250° C. On the other hand, a core 30 mainly made of a Mn—Zn-based material or the like has a high relative magnetic permeability μs as high as 10000 to 18000, and thus an inductance value that is two to three times higher can be obtained even when the number of windings is the same, but the relative magnetic permeability us tends to decrease the closer the Curie temperature Tc of the magnetic material is to 110° C. to 150° C. For this reason, the core 30 needs to be used without increasing the temperature of the core 30 to the Curie temperature Tc or higher.
The bobbin 20 houses the core 30 so as to ensure electric insulation from the coils 40 and 40. The bobbin 20 may be formed of an insulative resin case. In the embodiment shown in the diagrams, the bobbin 20 is configured to be attachable to a coil base 50 that can be attached to a board or the like.
As shown in
The openings 21 and 22 are formed in the circumferential surface of the bobbin 20. For example, as shown in
The openings 21 and 22 are preferably formed at opposing positions across the diameter of the bobbin 20 such that air flows smoothly into and out of the airflow path A. It is most desirable to form two openings in the bobbin 20 as the openings 21 and 22. However, even when only one opening is formed, an airflow can enter the airflow path A in the bobbin 20, and thus an air cooling effect can be expected to a certain degree.
Each of the openings 21 and 22 is provided with flanges 23 and 24 protruding along the peripheral edge thereof. Right and left flanges 23 in each of the openings 21 and 22 secure a creepage distance and a spatial distance specified in safety standards so as to provide electric insulation between the core 30 and the coils 40 and 40 wound around the outer circumference of the bobbin 20, and electric insulation between the coils 40 and 40, as well as preventing these from electrically connecting to each other or from short circuiting and sparking or the like. For this reason, the flanges 23 are designed so as to have a height greater than or equal to the height of the coils 40 and 40 wound near the flanges 23 while having dimensions specified in a safety standard.
In order to increase the airflow that flows through each of the openings 21 and 22, the right and left flanges 23 of each of the openings 21 and 22 have a shape flared toward the outer circumference with respect to the openings 21 and 22. Likewise, in order to increase the amount of air that flows through the openings 21 and 22 and enable smooth guiding of air, the upper and lower flanges 24 of each of the openings 21 and 22 desirably have a vertically flared shape, which is particularly effective when forced-air cooling is performed using a fan or the like.
As described above, the bobbin 20 has, on its inner surface side, a cross-sectional space that is larger than the cross section of the core 30, and a gap provided between the core 30 and the inner surface of the bobbin 20 functions as the airflow path A. The airflow path A is in communication with the openings 21 and 22.
In order to prevent the core 30 from being damaged by mechanical vibrations or impact and suppress magnetostrictive noise caused by a magnetic flux generated by a load current, it is desirable that the bobbin 20 holds the core 30 in the bobbin 20 such that the core 30 does not vibrate in the bobbin 20. For example, as shown in
Also, when the coils 40 and 40 are wound by hand, the coils 40 and 40 are wound into a substantially elliptical bulging shape. By configuring the bobbin 20 to have a substantially elliptical cross section that conforms to the bulging shape, it is possible to avoid an increase in the size of the common mode choke coil 10 while securing the airflow path A in the bobbin 20.
As shown in
As shown in
As shown in
In the bobbin 20 in which the core 30 is housed, each of the coils 40 and 40 is wound around a body portion of the bobbin 20 between the openings 21 and 22. A common mode choke coil 10 is thereby formed. Copper wires with an insulated outer cover can be used as leads used as the coils 40 and 40. Of course, the leads are not limited thereto.
The two coils 40 and 40 can be wound using so-called common mode winding in which each coil 40 is wound between the openings 21 and 22 in a direction that is the same as the direction of the flow of the load current, or in other words, a direction in which magnetic fluxes generated by the coils 40 and 40 cancel each other out.
The common mode choke coil 10 configured as described above may be disposed directly on a board, or may be attached to a coil base 50 as shown in
In the coil base 50, insertion holes 53 and 53 for drawing lead end portions 41 and 41 of the coils 40 and 40 downward may be formed. Accordingly, when the coil base 50 is disposed on a circuit board (not shown), the lead end portions 41 and 41 can be electrically connected to a circuit board.
The following description will be given assuming that the common mode choke coil 10 includes the coil base 50 where appropriate.
The common mode choke coil 10 configured as described above can be mounted on a circuit board in an electric appliance. The casing of the electric appliance includes an air intake opening and an air exhaust fan, or an air intake fan and an air exhaust opening for suppressing an increase in the temperature of electronic components including the common mode choke coil 10, and forcibly generates an airflow in the electronic appliance. Examples of the electric appliance include an IH cooking heater, an IH rice cooker, a microwave oven, a vehicle-mounted DC-DC converter, a vehicle-mounted AC-DC converter, and the like.
The common mode choke coil 10 of the present invention is disposed such that the openings 21 and 22 point in directions on the path of the airflow. If two openings 21 and 22 are formed in the common mode choke coil 10, the common mode choke coil 10 is disposed such that the opening 21, which is one of the openings, points toward the upstream side of the airflow, and the opening 22, which is the other opening, points toward the downstream side. In the case where only one opening is formed, the common mode choke coil 10 is disposed such that the opening points toward the upstream side of the airflow.
With this configuration, as shown in
To be more specific, when an electric current is supplied to the coils 40 and 40 of the common mode choke coil 10, the coils 40 and 40 generate magnetic fluxes due to electromagnetic induction. However, because the coils 40 and 40 are wound in a direction in which the magnetic fluxes cancel each other out, magnetic saturation is suppressed, and the passage of common mode noise is limited by inductance resulting from self-induction. At this time, Joule heat is generated in the coils 40 and 40 through energization and heat is emitted. Then, the heat generated in the coils 40 and 40 is transmitted to the core 30 via the bobbin 20 through conduction, radiation, or convection, and the temperature of the core 30 increases. However, in the common mode choke coil 10 of the present invention, the airflow B flows into the airflow path A from the opening 21 and is discharged from the other opening 22, and thus the heated bobbin 20 and core 30 are cooled through heat exchange with the airflow B.
Accordingly, because an increase in the temperature of the core 30 can be suppressed, it is possible to use a material that has a high relative magnetic permeability us such as a ferrite core that has a low Curie temperature Tc, and apply a large electric current to the coils 40 and 40. Because the core 30 can be formed using a material that has a high relative magnetic permeability μs, it is possible to reduce the number of windings of the coils 40 and 40 and reduce the lead wire diameter while ensuring the same inductance value, and thus achieve a reduction in the size of the common mode choke coil 10. Conversely, if the size of the common mode choke coil 10 is the same, the inductance value can be designed to be higher by increasing the number of windings of the coils 40 and 40, and thus noise reduction can also be achieved.
A common mode choke coil 10 according to the present invention in which two openings 21 and 22 were formed in the bobbin 20 and a common mode choke coil according to a comparative example whose openings 21 and 22 were closed with a 0.5 mm-thick aramid fiber sheet (product name: Nomex®) were placed in a wind tunnel 60 that forcibly generates an airflow C so as to obtain the relationship between a DC current applied to the coils 40 and 40 and a temperature increase in the coils 40 and the core 30.
The common mode choke coil 10 had the following configuration.
Core 30
Magnetic material: ferrite core MA120A available from JFE Ferrite Co., Ltd. (with a relative magnetic permeability μs of 12000)
Inner diameter/outer diameter: 18.5 mm/31.5 mm
Height: 13.4 mm
Cross-sectional area/cross-sectional shape: 87.1 mm2/rectangular shape
Curie temperature Tc: 120° C.
Bobbin 20
Material: polycarbonate resin
Inner diameter/outer diameter: 17.0 mm/33.0 mm
Height: 14.6 mm
Cross-sectional area/cross-sectional shape: 104.0 mm2/elliptical shape
Opening area: 135.1 mm2 each (two openings at diametrically opposing positions)
Cross-sectional area of airflow path A: 16.9 mm2 (bobbin cross-sectional area−core cross-sectional area)
Coil 40
Lead material: polyester copper wire (PEW)
Lead wire diameter: 1.8 mm
Number of windings: 13T each
Direct current resistance: 5.2 mΩ×2
As shown in
An experiment was performed by placing the wind tunnel 60 in an atmosphere of 25° C., and the wind speed was changed from 0 (a no-wind state, or in other words, a state in which the air exhaust fan was deactivated) to 1.2 m/sec. The DC current applied to the coils was set to 0 A, 10 A, 20 A, and 30 A (note that, in the no-wind state, the DC current applied to the coils was set to 0 A, 10 A, and 20 A in consideration of the heat resistance of the bobbin material).
Actual measurement data of the example of the present invention and the comparative example are shown in Tables 1 and 2, respectively. In Tables 1 and 2, the top row shows the DC current value (A) applied to the coils, and the left column shows the wind speed and measurement point. Other numerical values indicate the temperature increase (° C.) from the atmosphere (25° C.). Although not shown in the tables, when the DC current applied to the coils was 0 A, the temperatures of the core 30 and the coil 40 were 25° C., which was the same as that of the atmosphere, and the temperature increase was 0° C.
From
This is because, as shown in
On the other hand, in the common mode choke coil of the comparative example, because the openings were closed, the heat generated in the coils was transmitted to the core via the bobbin, and the heat accumulated in the bobbin, as a result of which the temperature of the core increased together with that of the coil.
As described above, in the common mode choke coil 10 of the present invention, as a result of the airflow path A being formed between the core 30 and the openings 21 and 22 in the bobbin 20, an increase in the temperatures of the core 30 and the coils 40 and 40, in particular, an increase in the temperature of the core 30 can be suppressed. Accordingly, even when the core 30 is formed using a magnetic material that has a relatively low Curie temperature, it is possible to apply a large electric current, and enhance the characteristics of the common mode choke coil 10.
The foregoing description is given to merely illustrate the present invention, and thus should not be construed as limiting the present invention recited in the appended claims or narrowing the scope of the present invention. Also, the constituent elements of the present invention are not limited to those in the example described above, and of course, various modifications can be made within the technical scope of the appended claims.
For example, in the embodiment given above, an example is shown in which the casing of the electric appliance includes an air intake opening and an air exhaust fan. However, as can be seen from the results shown in Tables 1 and 2, it is clear that the present invention is effective even in the no-wind state.
Furthermore, in the foregoing description, a single-phase common mode choke coil 10 is used, but, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-122484 | Jun 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/019642 | 5/26/2017 | WO | 00 |
