Noise reduction unit, power supply device, and method for disposing cores in noise reduction unit

A noise reduction unit includes a plurality of cores each having formed therein a through hole, a plurality of wires connected to a noise source and each wound around the corresponding core through the through hole, and a core supporting member that supports the plurality of cores. The core supporting member supports the plurality of cores in such a manner that the plurality of cores is disposed parallel to each other along a through direction of the through holes and spaced apart from each other with a predetermined gap in the through direction.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2012-124285, which was filed on May 31, 2012, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a noise reduction unit that includes a plurality of cores for noise filters, a power supply device that includes the noise reduction unit, and a method for disposing cores in the noise reduction unit.

2. Description of Related Art

A power supply device is known that supplies power from an (external) power supply to a load such as an electrical device. A switching power supply circuit is known in which the input alternating current through a power input terminal is output as direct current via a rectifying section and a plurality of DC-DC converters to obtain a plurality of direct current outputs. There is also a technique by which the noise generated in a DC-DC converter and conducted through a power line is reduced with a noise reduction unit (common-mode filter) provided between a power input terminal and a rectifying section in a power supply device.

SUMMARY OF THE INVENTION

The frame of a power supply device is typically provided with a frame grounding wire to ensure safety (prevention of electric shock). Some power supply devices are further provided with a noise filter (normal-mode filter) for the purpose of reducing the noise conducted through the frame grounding wire, because the noise in the power supply device may leak into external peripherals or other such devices via the frame grounding wire. In some cases, the noise filter is provided for each output line of the direct current output from the power supply device, because these output lines are likely to conduct different forms of noise. Such noise filters are often configured from a wire wound around a magnetic core of material such as metal oxide. The filers using the core have a simple structure, and are advantageous in terms of design freedom. A drawback, however, is the relatively large number of components it requires. Thus, using a plurality of cores requires some ingenuity for the downsizing of the noise reduction unit to be provided with the multiple cores.

The inventors of the present application conducted intensive studies to downsize the noise reduction unit that includes a plurality of cores, and found that the noise reduction effects of the cores disposed close to each other deteriorate in a manner that depends on the placement or positions of the cores.

According to an aspect of the present invention, there are provided a noise reduction unit that can be downsized without deteriorating the noise reduction effect, a power supply device that includes the noise reduction unit, and a method for disposing cores in the noise reduction unit.

A noise reduction unit according to an embodiment of the present invention includes a plurality of cores, a plurality of wires, and a core supporting member. The cores each have formed therein a through hole. The wires are connected to a noise source and each wound around the corresponding core through the through hole. The core supporting member supports the plurality of cores. The core supporting member supports the plurality of cores in such a manner that the plurality of cores is disposed parallel to each other along a through direction of the through holes and spaced apart from each other with a predetermined gap in the through direction.

A power supply device of an embodiment of the present invention includes: a noise reduction unit, a plurality of power input terminals, a power conversion circuit, a plurality of power lines, and a frame grounding wire. The power input terminals are configured to receive the externally input power. The power conversion circuit is configured to convert the input power through the plurality of power input terminals into a predetermined power, and output the converted predetermined power. The power lines connect the plurality of power input terminals to a plurality of input terminals of the power conversion circuit. The frame grounding wire connects a ground terminal in the plurality of power input terminals to a frame configured to protect the power conversion circuit. The noise reduction unit includes a plurality of cores, a plurality of wires, and a core supporting member. The cores each have formed therein a through hole. The wires are connected to a noise source and each wound around the corresponding core through the through hole. The core supporting member supports the plurality of cores. The core supporting member supports the plurality of cores in such a manner that the plurality of cores is disposed parallel to each other along a through direction of the through holes and spaced apart from each other with a predetermined gap in the through direction. The noise source is the power conversion circuit. At least one of the plurality of power lines is used as the wires of the noise reduction unit and wound around at least one first core selected from the plurality of cores. The frame grounding wire is used as one of the wires of the noise reduction unit and wound around at least one second core different from the first core and selected, from the plurality of cores.

A power supply device according to an embodiment of the present invention is one that supplies an externally input power to a load with the foregoing noise reduction unit. The power supply device includes a plurality of power input terminals, a plurality of power conversion circuits, and a plurality of output lines. The power input terminals are configured to receive the externally input power. The power conversion circuits are connected in parallel with respect to the plurality of power input terminals, and configured to convert the input power through the plurality of power input terminals into different predetermined powers. The output lines connect a plurality of output terminals of the plurality of power conversion circuits to the load. The noise source is the plurality of power conversion circuits. The plurality of output lines are used as the wires of the noise reduction unit and wound around different cores of the plurality of cores.

A method for disposing cores in a noise reduction unit according to an embodiment of the present invention is a method for disposing cores in a noise reduction unit that includes a plurality of cores each having formed therein a through hole, and a plurality of wires connected to a Boise source and each wound around the corresponding core through the through hole. The method includes the step of disposing the plurality of cores in such a manner that the plurality of cores is disposed parallel to each other along a through direction of the through holes and spaced apart from each other with a predetermined gap in the through direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A power supply device according to First Embodiment of the present invention is described below with reference to the accompanying drawings.

Referring toFIG. 1, the overall structure of a power supply device101is described first. The power supply device101includes a power input section10, an AC-DC conversion circuit20, a protective frame100, and a noise reduction unit50.

The power input section10includes two external input terminals10aand10b. The input primary alternating-current power from an alternating-current source5is applied between the external input terminals10aand10b. The external input terminal10bground terminal10b) is connected to earth (grounded to the earth). The external input terminals10aand10bof the present embodiment correspond to power input terminals.

The AC-DC conversion circuit20converts the input primary alternating-current power through the power input section10into a predetermined secondary direct-current power, and supplies the secondary direct-current power to a load R0of an electrical device or the like. The protective frame100is made of, for example, metallic material and houses and protects the AC-DC conversion circuit20inside. The frame ground FG of the protective frame100and the ground terminal10bare connected to each other by a frame grounding wire31via earth. The noise reduction unit50reduces the noise generated in the AC-DC conversion circuit20. The AC-DC conversion circuit20of the present embodiment corresponds to a power conversion circuit.

The AC-DC conversion circuit20is described below. The AC-DC conversion circuit20includes a primary rectifying circuit21that converts the primary alternating-current power into a primary direct-current power, and a DC-DC converter25that converts the primary direct-current power into the predetermined secondary direct-current power.

The primary rectifying circuit21includes a bridge rectifying circuit22(full-wave rectifying circuit), undo smoothing capacitor23. The bridge rectifying circuit22rectifies the alternating-current power into the direct-current power. The bridge rectifying circuit22has input terminals22aand22brespectively connected to the external input terminals10aand10bvia power lines30aand30b. The smoothing capacitor23is provided to smooth the output direct-current power of a pulsating waveform from the bridge rectifying circuit22, and is connected to output terminals22cand22dof the bridge rectifying circuit22.

The DC-DC converter25includes a transformer T, a switching element Q, a secondary rectifying circuit26, and a switching control circuit29.

The transformer T is provided to transmit power from the primary side to the secondary side, and includes a primary coil n1and a secondary coil n2. The primary coil n1generates voltage from switching current to provide excitation energy to the transformer T. The secondary coil n2generates voltage from the excitation energy generated by the primary coil n1. One of the terminals, T1, of the primary coil n1is connected to a positive terminal23aof the smoothing capacitor23.

The switching, element Q is a transistor that induces a voltage in the primary coil n1of the transformer T by switching the current flowing through the primary coil n1of the transformer T. The switching element Q is connected between the other terminal, T2, of the primary coil n1and a negative terminal23bof the smoothing capacitor23. The switching element Q, and the primary coil n1of the transformer T constitute a series circuit that receives the primary direct-current power from the primary rectifying circuit21.

The secondary alternating-current power output according to the generated voltage in the secondary coil n2of the transformer T is converted into the secondary direct-current power by the secondary rectifying circuit26. The secondary rectifying circuit26includes a diode27and a smoothing capacitor28. The diode27rectifies the secondary alternating-current power to direct-current power. The anode of the diode27is connected to one of the terminals, T3, of the secondary coil n2. The smoothing capacitor28generates the secondary direct-current power by smoothing the current flowing out of the diode27. The smoothing capacitor28has a positive terminal28aconnected to the cathode of the diode27, and a negative terminal28bconnected to the other terminal, T4, of the secondary coil n2of the transformer T. The positive terminal28aof the smoothing capacitor28is the positive output terminal of the AC-DC conversion circuit20, and the negative terminal28bis the negative output terminal of the AC-DC conversion circuit20. The positive terminal28aand the negative terminal28bare connected to the load R0via output lines33aand33b, respectively. The negative terminal28bis connected to the protective frame100, and grounded to the chassis.

The switching control circuit29detects the output voltage across the output terminals (terminals28aand28b) of the AC-DC conversion circuit20, and uses the detection result to control the ON/OFF of the switching element Q with a pulsed drive signal supplied to the switching element Q.

The operation of the AC-DC conversion circuit20is described below. First, the input primary alternating-current power between the external input terminals10aand10bof the power input section10from the alternating-current source5is converted into the primary direct-current power by the primary rectifying circuit21. The converted primary direct-current power is input to the series circuit formed by the switching element Q and the primary coil n1of the transformer T. The switching control circuit29then controls the ON/OFF of the switching element Q, and the secondary alternating-current power is induced in the secondary coil n2of the transformer T. The secondary rectifying circuit26converts the secondary alternating-current power into the secondary direct-current power, which is then supplied to the load R0via the output lines33aand33b. The switching control circuit29detects the output voltage across the output terminals (terminals28aand28b) of the AC-DC conversion circuit20. By using the detection result, the switching control circuit29increases or decreases the duty of the pulse that controls the ON/OFF of the switching, element Q, and thereby varies the ON time of the switching element Q to control the output voltage.

Various elements in the AC-DC conversion circuit20generate noise during the operation of the AC-DC conversion circuit20. For example, switching of the switching element Q produces switching noise on the primary side of the transformer T. The current flow through the primary rectifying circuit21also generates noise. On the secondary side of the transformer T, for example, the current flow through the secondary rectifying circuit26generates noise. The noise generated on the primary side of the transformer T transfers to the secondary side via the transformer T, and the noise generated on the secondary side of the transformer T transfers to the primary side via the transformer T. The noise on the primary side of the transformer T is undesirably conducted to the power lines30aand30band leaks into the alternating-current source5. The noise on the secondary side of the transformer T is also problematic, because it is conducted to the frame grounding wire31via the frame ground FG and leaks into external devices such as peripherals.

As a countermeasure, in the present embodiment, the noise reduction unit50reduces the noise generated in the noise source, specifically, the AC-DC conversion circuit20, and conducted through the power lines30aand30band the frame grounding wire31. Note that the noise conducted through the power lines30aand30band the noise conducted through the frame grounding wire31have different noise components (for example, the frequency components, and the magnitudes of the frequency components of the noise), because the circuit structures (routes) for the element (for example, the switching element Q) are different. On the other hand, the noise conducted through the power line30aand the noise conducted through the power line30bhave essentially the same noise components, because the circuit structures for the noise generating element are essentially the same.

The noise reduction unit50has a chassis85, as illustrated inFIGS. 2A and 2B. Inside the chassis85are disposed a common-mode filter L1, a normal-mode filter L2, a core supporting member80, and a belt90. The chassis85may be realized by, for example, the frame of the power supply device101.

The common-mode filter L1prevents the noise from leaking toward the alternating-current source5, and, as depicted inFIG. 1,FIG. 2A, andFIG. 3A, includes a core60(first core), and the power lines30aand30b. The core60is a magnetic core (ferrite core) of materials such as metal oxide, and has a form of a cylinder with a through hole60a. The power lines30aand30bare wound around the core60through the through hole60a. The power lines30aand30bare wound around the core60in opposite directions. As described above, the noise components are essentially the same for the noise conducted in the power lines30aand30b, and thus the magnetic fluxes due to the noise conducted in the power lines30aand30badd together in the core60and produce a large impedance. The noise conducted in the power lines30aand30bcan thus be reduced.

The normal-mode filter L2prevents the noise from leaking into external devices such as peripherals via the frame ground FG, and, as depicted inFIG. 2AandFIG. 3B, includes a core70(second core) and the frame grounding wire31. As with the core60, the core70is a magnetic core of material such as metal oxide, and has a form of a cylinder with a through hole70a. The frame grounding wire31is wound around the core70through the through hole70a. In this way, a magnetic flux generates inside the core70, and an impedance is produced for the noise conducted through the frame grounding wire31. The noise conducted through the frame grounding wire31can thus be reduced. In the present embodiment, the core70and the core60have the same shape.

The core supporting member80is cylindrical in shape, and anchors and supports the core60and the core70inside. The core supporting member80is an insulating heat-shrinkable tube used after being shrunk under heat.

The core60and the core70need to be disposed close to each other in order to downsize the noise reduction unit50. However, the noise reduction effects of the cores60and70may deteriorate in a manner that depends on the placement or positions of the cores60and70. For example, as shown inFIG. 3C, the magnetic flux generated inside the core60or70interacts with the other core by magnetic coupling when the cores60and70are disposed parallel to each other along the through direction of the through holes60aand70aand spaced apart from each other on a plane orthogonal to the through direction. For example, a change may occur in the noise component of one of the cores when the magnetic flux flowing in the other core transfers and interacts with the magnetic flux of the core. The cores cannot accommodate such noise component changes, because the core materials and dimensions are designed in a manner that reduces the noise component of the predetermined range. This may lead to the deterioration of the noise reduction effect.

As a countermeasure, in the present embodiment, the core supporting member80anchors and supports the cores60and70in such a manner that the cores60and70are disposed parallel to each other along the through direction of the through holes60aand70aand spaced apart from each other with a predetermined gap along the through direction, as shown inFIGS. 2A and 2B. The magnetic fluxes generated in the cores60and70are therefore parallel to each other, and do not interact with each other. Because the cores60and70can be brought close to each other in this fashion without deteriorating the noise reduction effects, the noise reduction unit50can be downsized.

Further, in the present embodiment, the core supporting member80anchors and supports the cores60and70in such a manner that the centers60band70bof the through holes60aand70aoverlap as viewed from the through direction, as shown inFIG. 2B. The centers60band70balso coincide with the cylinder axis of the core supporting member80. In this way, the projected areas of the cores60and70as viewed from the through direction can be reduced, and the noise reduction unit50can be downsized even further.

Further, in the present embodiment, the cores60and70are disposed in such a manner that the power lines30aand30bwound around the core60do not overlap the frame grounding wire31wound around the core70as viewed, from the through direction, as shown inFIG. 2B. Further, the center of gravity combining the center of gravity of each projected area of the power lines30aand30bwound around the core60with the center of gravity of the projected area of the frame grounding wire31wound around the core70coincides with the centers60band70bof the through holes60aand70aas viewed from the through direction. In this way, the wires wound around the cores60and70are unlikely to directly contact each other between the adjacent cores even when the cores60and70anchored and supported by the core supporting member80are accidentally released. In the event where the cores60and70come in direct contact with each other, there are cases where the magnetic fluxes transfer between the cores60and70and deteriorate the noise reduction effect of the noise reduction unit50. Note that it is not necessarily required that the combined center of gravity coincides with the centers60band70bof the through holes60aand70aas viewed from the through direction, provided that the power lines30aand30bwound around the core60do not overlap the frame grounding wire31wound around the core70as viewed from the through direction. As a variation, the cores60and70may be disposed so that the center of gravity of the projected areas of the power lines30aand30bwound around the core60coincides with the center60bof the through hole60a, and that the center of gravity of the projected area of the frame grounding wire31wound around the core70coincides with the center70bof the through hole70aas viewed from the through direction.

The belt90is a banding band that anchors the core supporting member80on the chassis85. As illustrated inFIG. 2A, the belt90includes a long band portion91, and a lock portion92formed at one end of the band portion91.

The lock portion92has a band insertion hole and a band locking portion formed in the band insertion hole (neither is shown). An engaging portion (not shown) that engages the band locking portion in the band insertion hole is continuously formed along the longitudinal direction of the band portion91. Inserting the band portion91in the band insertion hole of the lock portion92engages the engaging portion of the band portion91with the band locking portion, and restricts the movement of the band portion91in one direction relative to the lock portion92. Specifically, the band portion91can only be moved so as to be inserted into the band insertion hole, and cannot be drawn out of the band insertion hole.

The following describes the method of anchoring the cores60and70with the core supporting member80, and the method of anchoring the core supporting member80on the chassis85with the belt90, with reference toFIGS. 4A to 4C.

First, as illustrated inFIG. 4A, the cores60and70are disposed in the core supporting member80(heat-shrinkable tube). Note that the inner diameter of the core supporting member80before thermal shrinkage is one size larger than the outer diameters of the cores60and70.

The cores60and70are disposed in the core supporting member80parallel to each other along the through direction of the through holes60aand70aand spaced apart from each other with a predetermined gap in the through direction. Here, the centers60band70bof the through holes60aand70aof the cores60and70overlap as viewed from the through direction, and the power lines30aand30bwound around the core60do not overlap the frame grounding wire31wound around the core70as view from the through direction.

Then, the core supporting member80is heated to shrink in the radial direction, as illustrated inFIG. 4B. This anchors and supports the cores60and70on the inner wall of the core supporting member80. Here, the region of the core supporting member80between the cores60and70adjacent to each other in the through direction shrinks inward of the outer circumferences of the cores60and70in the radial direction under the applied heat. As a result, an annular depression81is formed that is depressed inwardly in the radial direction of the core supporting member80between the cores60and70disposed adjacent to each other in the through direction.

For anchoring the core supporting member80on the chassis85with the belt90, as illustrated inFIG. 4C, the band portion91is wound around the annular depression81of the core supporting member80, and the front end portion of the band portion91is inserted into the band insertion hole of the lock portion92. The band portion91is then drawn out of the lock portion92and tightened, and the front end portion of the band portion91drawn out of the lock portion92is anchored on the chassis85. Because the band portion91is wound around the annular depression81in this fashion, the belt90does not easily come off the core supporting member80. This ensures that the core supporting member80is reliably anchored on the chassis85.

In the present embodiment described above, the cores60and70are disposed parallel to each other along the through direction of the through holes60aand70aand spaced apart from each other with a predetermined gap in the through direction. Accordingly, the magnetic fluxes generated in the cores60and70are also parallel to each other, and do not interfere with each other. Because the cores60and70can be brought close to each other in this fashion without deteriorating the noise reduction effect, the noise reduction unit50can be downsized.

Further, in the present embodiment, because the core supporting member80is a heat-shrinkable member used after being shrunk under heat, the cores60and70can be anchored and supported with a simple structure.

Second Embodiment

A power supply device201according to Second Embodiment of the present invention is described, below with reference toFIGS. 5 and 6. Second Embodiment differs from First Embodiment in that the power supply device201is a multi-output power supply device provided with multiple DC-DC converters125and126. Further, in Second Embodiment, common-mode filters L3and L4are provided the noise reduction between each output terminal of the DC-DC converters125and126and the load R0. In the following, the constituting elements and/or features already described in the foregoing First Embodiment are appended with the same reference numerals, and explanations thereof are omitted as appropriate.

In the present embodiment, as illustrated inFIG. 5, the DC-DC converters125and126are connected in parallel with respect to the primary rectifying circuit21. The output voltages from the DC-DC converters125and126are different because the ON/OFF time ratio (duty ratio) of the switching element Q as determined by the switching control circuit29is different for the DC-DC converters125and126.

The output terminals28aand28bof the DC-DC converter125are connected to the load R0via output lines133aand133b. The output terminals28aand28bof the DC-DC converter126are connected to the load R0via output lines134aand134b. The DC-DC converters125and126of the present embodiment correspond to power conversion circuits. Further, the output terminals of the primary rectifying circuit21(the positive terminal23aand the negative terminal23bof the smoothing capacitor23) of the present embodiment correspond to power input terminals.

During the operation of the DC-DC converters125and126, switching of the switching elements Q in the DC-DC converters125and126produces noise or other disturbances. The noise generated in the DC-DC converters125and126may undesirably leak into the load R0through the output lines133a,133b,134a, and134b.

As described above, the ON/OFF time ratio of the switching element Q is different for the DC-DC converters125and126. Accordingly, the noise component of the noise due to the switching of the switching element Q is also different for the DC-DC converters125and126. The noise component is thus different for the noise conducted through the output lines133aand133b, and the noise conducted through the output lines134aand134b. Further, the noise components greatly differ for the noise conducted through the output lines133a,133b,134a, and134b, and the noise conducted through the power lines30aand30band the frame grounding wire31, because the circuit structures for the noise-producing elements are different. On the other hand, the noise conducted through the output line133aand the noise conducted through the output line133bhave essentially the same noise components. Similarly; the noise components are essentially the same for the noise conducted through the output line134aand the noise conducted through the output line134b.

In the present embodiment, the noise reduction unit150is capable of reducing the noise conducted through the output lines133a,133b,134a, and134b, in addition to the noise conducted through the power lines30aand30band the frame grounding wire31. Specifically, the noise reduction unit150includes a common-mode filter L3and a common-mode filter L4, in addition to the common-mode filter L1and the normal-mode filter L2.

The common-mode filter L3prevents the generated noise in the DC-DC converter125from leaking toward the load R0, and, as illustrated inFIGS. 5 and 6, includes a core110and the output lines133aand133b. The core110is a magnetic core of material such as metal oxide, and has a form of a cylinder with a through hole (not illustrated). The output lines133aand133bare wound around the core110through the through hole. The output lines1.33aand133bare wound around the core110in opposite directions. As described above, the noise components are essentially the same for the noise conducted through the output lines133aand133b, and thus the magnetic fluxes due to the noise conducted in the output lines133aand133badd together in the core110and produce a large impedance. The noise conducted in the output lines133aand133bcan thus be reduced.

The common-mode filter L4prevents the generated noise in the DC-DC converter126from flowing toward the load R0, and, as illustrated inFIGS. 5 and 6, includes a core120and the output lines134aand134b. The core120and the output lines134aand134bwill not be described, because these are the counterparts of the core110and the output lines133aand133b. In the present embodiment, the cores60,70,110, and120have the same shape.

The core supporting member80anchors and supports the cores110and120, in addition to the cores60and70. As illustrated inFIG. 6, the core supporting member80anchors and supports the cores60,70,110, and120in such a manner that the cores60,70,110, and120are parallel to one another along the through direction of the through holes60a,70a,110a, and120aand spaced apart from one another with predetermined gaps in the through direction. Accordingly the magnetic fluxes generated in the cores60,70,110, and120are parallel to one another, and do not interfere with one another. Because the cores60,70,110, and120can be brought close to one another in this fashion without deteriorating the noise reduction effect, the noise reduction unit150can be downsized.

Further, as illustrated inFIG. 6, the core supporting member80anchors and supports the cores110and120so that the centers110band120bof the through holes11.0aand120aoverlap as viewed from the through direction. Here, the output lines133aand133bwound around the core110do not overlap the output lines134aand134bwound around the core120as viewed from the through direction. Further, the output lines133aand133bwound around the core110do not overlap the power lines30aand30bwound around the core60adjacent to the core110, as viewed from the through direction. In this way, the wires wound around the cores60,70,110, and120are unlikely to directly contact one another between the adjacent cores even when the cores60,70,110, and120anchored and supported by the core supporting member80are accidentally released.

As described above, in the present embodiment, the noise conducted through the output lines133a,133b,134a, and134bcan be reduced with the common-mode filters L3and L4. Further, the magnetic fluxes generated in the cores60,70,110, and120are parallel to one another, and do not interfere with one another, because the cores60,70,110, and120are disposed parallel to one another along the through direction of the through holes60a,70a,110a, and120aand spaced apart from one another with predetermined gaps in the through direction. Because the cores60,70,110, and120can be brought close to one another in this fashion without deteriorating the noise reduction effect, the noise reduction unit150can be downsized.

The core shape, described as being cylindrical in the foregoing embodiments, is not particularly limited. For example, the core may be a cuboid with a through hole. Further, the core, described in the foregoing embodiments as having an annular shape as viewed from the through direction of the through hole, may have the shape of the letter C. In other words, a slit may be formed along the through direction.

Further, even though the foregoing embodiments were described through the case where the core supporting member is an insulating heat-shrinkable tube used after being shrunk under heat, the core supporting member is not particularly limited as long as it is an insulator capable of anchoring and supporting the plurality of cores disposed parallel to one another along the through direction of the through holes and spaced apart from one another with predetermined gaps in the through direction. A variation of the core supporting member is described below with reference toFIGS. 8A and 8B.

As illustrated inFIGS. 8A and 8B, a core supporting member180according a variation of the invention includes an annular member181, a step portion182, and a plurality of projecting portions183. The annular member181is cylindrical in shape, and has an inner diameter slightly larger than the outer diameter of the core. With the core housed inside, the annular member181can restrict the core movement in the radial direction.

The step portion182radially projects out of the center of the inner wall relative to the cylinder axis direction of the annular member181. The projecting portions183radially project out of the inner wall at the both ends relative to the cylinder axis direction of the annular member181, and are spaced apart from one another with predetermined gaps along the circumferential direction of the annular member181. The core housed inside the annular member181can thus be restricted from moving in the cylinder axis direction by the step portion182and the projecting portions183formed at one end of the cylinder axis direction. The annular member181, the step portion182, and the projecting portions183anchor and support the core in this fashion.

The projecting portions183are flexible, and bend when the force applied in the cylinder axis direction exceeds a predetermined value. In order to house the core in the annular member181, the core is pushed into the annular member181from one end of the annular member181in the cylinder axis direction with a force exceeding a predetermined value. The force applied to the core bends the projecting portions183, and the core is housed inside the annular member181.

In the foregoing embodiments, the plurality of cores (60and70, or110and120) is disposed so as to overlap each other as viewed from the through direction. However, this is not necessarily required as long as the plurality of cores is disposed parallel to each other along the through direction of the through holes and spaced apart from each other with a predetermined gap in the through direction. That is, the plurality of cores (60and70, or110and120) may be disposed so as not to overlap each other as viewed from the through direction. The noise reduction unit can also be downsized in the through direction, because the magnetic flux flowing in one of the cores does not interfere with the other core.

The shapes of the plurality of cores (60and70, or110and120), described as being the same in the foregoing embodiments, may be different from each other.

Further, in the foregoing First Embodiment, the core supporting member80anchors and supports the cores60and70in such a manner that the centers60band70bof the through holes60aand70aoverlap each other as viewed from the through direction. However, the centers60band70bof the through holes60aand70aare not necessarily required to overlap each other as viewed from the through direction, as long as the cores60and70are anchored and supported with through holes60aand70aat least partially overlapping each other as viewed from the through direction.

The present invention is not limited to the foregoing embodiments, and is also applicable to various types of noise reduction units in which the noise component of the Boise conducted through each wire from a noise source is different for each of the cores wound with a plurality of wires.