BACKGROUND
TECHNICAL FIELD
[0002] The present invention relates to a coil component, a method of manufacturing the
coil component, and a coil component set.
RELATED ART
[0003] In this specification, coil component refers to a coil having a conducting wire wound
in an annular or spiral manner, or a component (element) containing such coil, which
is a passive element capable of storing energy in a magnetic field induced by electric
current which flows therethrough. The coil component has variable names depending
on its purpose of use, shape, material, structure and so forth. For example, the coil
component used mainly in the field of power electronics is referred to as reactor,
and the coil component used mainly in control circuits is referred to as inductor.
The coil component directed to block (attenuate) current at a frequency higher than
that of a desired current is referred to as choke coil. For the case where a plurality
of coils, which are electrically isolated and magnetically coupled, are configured
so that one of them stores energy in a magnetic field induced by electric current
which flows therethrough, and the other of them outputs the energy after converting
it into electric current, a coil component including such plurality of coils is referred
to as transformer.
[0004] Patent Document 1 is now exemplified as this sort of technology. Patent Document
1 describes a coil component (reactor) in which a coil core is configured, by combining
a member composed of a pair of flat plate-like magnetic materials, and a pair of columnar
magnetic materials, to form a closed magnetic path structure of a magnetic material.
Patent Document 1 describes that variation in resistivity value of the coil component
may be reduced, by properly adjusting a ratio between the total thickness of gaps
formed between the flat plate-like members and the columnar components, and the thickness
of gaps provided in the middle way of the columnar components.
[0005] Exemplified now are Patent Document 2 and Patent Document 3 which disclose, as techniques
relevant to that described above, specially-shaped coil cores aimed at adjusting magnetic
characteristics of the coil components.
[0006] Patent Document 2 describes a coil component characterized by a special shape of
its so-called toroidal core. The toroidal core is formed so as to gradually increase
or decrease the diameter of winding wound around the outer circumference, along the
circumferential direction. With this configuration, use of only a single coil component
is enough to achieve a high attenuation characteristic over a wide frequency range.
[0007] Patent Document 3 describes a coil component having an annular coil core which is
divided into eight constituents arranged while placing a gap between every adjacent
constituents. The cross-sectional area of the constituents having no winding wound
therearound is smaller than the cross-sectional area of the other constituents having
the winding wound therearound. With this configuration, the coil component is successfully
reduced in size, and also successfully improved in DC superimposition characteristic
of the coil component.
Patent Document 1: Japanese Patent Application Laid-Open No. 2009-259971
Patent Document 2: International Publication WO2008/084684 Patent Document 3: Japanese Patent Application Laid-Open No. 2007-243136
[0008] Although being configured to have a somewhat simple structure, the coil component
has a variety of parameters which are mutually correlated in an intricate manner.
It is therefore not easy to optimize them respectively. In particular, as for the
coil component having a coil core (magnetic core) inserted therein, invisible electromagnetic
action of the coil core heavily affects the characteristics and state of operation
of the coil component. The engineers have therefore had no choice but to work out
details by repeating trial and error, and have had to expend a great deal of labor
to achieve a desired product specification.
[0009] The coil components described in the above individual Patent Documents are intended
to improve the specific parameters by providing the coil cores with some structural
features. All of such structural features however largely affect parameters other
than the targeted parameters. The conventional coil components are therefore still
suffering from the above-described problems, in that they cannot satisfy their desired
product specifications without taking the influences on the other parameters into
consideration.
SUMMARY
[0010] The present invention is conceived considering the above-described problems, and
is to provide a coil component capable of readily achieving desired magnetic characteristics,
a method of manufacturing such coil component, and a coil component set.
[0011] According to the present invention, there is provided a coil component which includes:
an annular coil core composed of a material having a higher permeability than that
of air; and
a winding wound around the coil core in close proximity thereto,
a cross section of the coil core, which is taken orthogonally to the winding axis
of winding, deviating either towards the inner loop side or towards the outer loop
side of the coil core.
[0012] According to the present invention, there is provided a method of manufacturing a
coil component having an annular coil core composed of a material having a higher
permeability than that of air, and a winding wound around the coil core in close proximity
thereto, the method includes:
deriving the degree of deviation of a cross section of the coil core, which is taken
orthogonally to the winding axis of winding, either towards the inner loop side or
towards the outer loop side of the coil core, based on a desired inductance of the
coil component;
determining a shape of the coil core, according to the degree derived in the preceding
step of derivation; and
molding the coil component, according to the shape of coil core determined in the
preceding step of shape determination.
[0013] According to the present invention, there is provided a coil component set which
includes a plurality of coil components each having an annular coil core composed
of a material having a higher permeability than that of air, and a winding wound around
the coil core in close proximity thereto,
and,
among the plurality of coil components having equivalent levels of either one of inductance
and DC superimposition characteristic,
a cross section of the coil core in a first coil component, which is taken orthogonally
to the winding axis of winding, deviating either towards the inner loop side or towards
the outer loop side of the coil core, more largely as compared with the cross section
of the coil core in a second coil component.
[0014] The coil component of the present invention is configured so that the cross section
of the annular coil core, which is taken orthogonally to the winding axis of winding,
deviates either towards the inner loop side or towards the outer loop side of the
coil core.
[0015] With this configuration, ratios of the area of coil core in the cross section thereof
will be different between the side of deviation and the opposite side, resulting in
a stronger magnetic field on the side of deviation. In other words, an effective magnetic
path of the coil component as a whole deviates towards the side of deviation. Accordingly,
the coil component of the present invention will have an effective magnetic path length
(average magnetic path length) which substantially shortens or elongates, and the
inductance will increase or decrease as a consequence, as compared with the coil component
having equivalent DC superimposition characteristic but having a non-deviating cross
section of the core.
[0016] In short, according to the method of manufacturing a coil component of the present
invention, it now becomes possible to manufacture a coil component which satisfies
a desired inductance almost without affecting the DC superimposition characteristic.
Accordingly, a coil component with desired magnetic characteristics may readily be
achieved.
[0017] According to the present invention, a coil component, a method of manufacturing a
coil component and a coil component set, all being aimed at achieving a desired magnetic
characteristics, are successfully provided in an easy manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, advantages and features of the present invention will
be more apparent from the following description of certain preferred embodiments taken
in conjunction with the accompanying drawings, in which:
FIG. 1 is a perspective view illustrating a coil component of a first embodiment.
FIG. 2A is a front view of the coil component of the first embodiment, and FIG. 2B
is a cross-sectional view taken along line II-II in FIG. 2A.
FIG. 3 is a schematic drawing schematically illustrating an effective magnetic path
which generates in the coil component of the first embodiment when the winding is
energized, and the coil winding direction.
FIG. 4 is a perspective view of a coil component of a second embodiment.
FIG. 5A is a front view of the coil component of the second embodiment, and FIG. 5B
is a cross-sectional view taken along line III-III in FIG. 5A.
FIG. 6 is a schematic drawing schematically illustrating an effective magnetic path
which generates in the coil component of the second embodiment, when the winding is
energized, and coil winding direction.
FIGs. 7A and 7B are drawings illustrating a plate member used for a top plate or a
bottom plate, wherein FIG. 7A is a top view of the plate member, and FIG. 7B is a
front view of the plate member.
FIGs. 8A and 8B are drawings illustrating a columnar component, wherein FIG. 8A is
a top view of the columnar component, and FIG. 8B is a front view of the columnar
component.
FIGs. 9A and 9B are drawings illustrating relations of DC current supplied to the
coil component of the first embodiment and the coil component of the second embodiment,
with inductance of the coil components, wherein FIG. 9A represents the case where
the windings are connected in parallel, and FIG. 9B represents the case where the
windings are connected in series.
FIGs. 10A and 10B are drawings illustrating a coil component of a third embodiment,
wherein FIG. 10A is a front view of the coil component of the third embodiment, and
FIG. 10B is a cross-sectional view taken along line IV-IV in FIG. 10A.
FIGs. 11A and 11B are drawings illustrating a coil component according to a modified
example of the first embodiment, wherein FIG. 11A is a front view of the coil component
of the modified example, and FIG. 11B is a cross-sectional view taken along line V-V
in FIG. 11A.
FIG. 12 is a simplified circuit diagram illustrating an electric circuit of a forward
converter.
FIG. 13 is a flow chart illustrating a method of manufacturing a choke coil.
DETAILED DESCRIPTION
[0019] The invention will now be described herein with reference to illustrative embodiments.
Those skilled in the art will recognize that many alternative embodiments can be accomplished
using the teaching of the present invention and that the invention is not limited
to the embodiments illustrated for explanatory purposes. In all drawings, all similar
components will be numbered identically to avoid repetitive explanation for simplicity.
<Configuration of First Embodiment>
[0020] A configuration of a first embodiment of the present invention will be explained
referring FIG. 1 to FIG. 3.
[0021] FIG. 1 is a perspective view of a coil component 100 of the first embodiment.
[0022] FIG. 2A is a front view of the coil component 100, and FIG. 2B is a cross-sectional
view taken along line II-II in FIG. 2A.
[0023] FIG. 3 is a schematic drawing schematically illustrating effective magnetic path
M1 which generates in the coil component 100 when energized through a winding 120,
and the direction of winding of the winding 120.
[0024] The coil component 100 according to the first embodiment of the present invention
has an annular coil core 110, and the winding 120. The annular coil core 110 is composed
of a material having a higher permeability than that of air. The winding 120 is wound
around the coil core 110 in close proximity thereto. The coil component 100 is characterized
in that a cross section of the coil core 110, which is taken orthogonally to the winding
axis of the winding 120, deviates either towards the inner loop side or towards the
outer loop side of the coil core 110.
[0025] In more detail, the coil core 110 is configured to form a ring, contributed by a
pair of columnar parts 116, 118 respectively having a columnar shape and having side
faces opposed to each other, and a pair of sandwiching parts (top plate 112 and bottom
plate 114) supporting the pair of columnar parts 116, 118 so as to hold them in between,
each of which forming one side of a square.
[0026] The winding 120 is spirally wound around each of the pair of columnar parts 116,
118, and the cross-sections of the pair of columnar parts 116, 118 deviates either
towards the inner loop side or towards the outer loop side.
[0027] The coil component 100 in this embodiment will be explained assuming that the cross-section
of the coil core 110 (columnar parts 116, 118) deviates towards the inner loop side,
as illustrated in FIG. 2B.
[0028] As illustrated in FIG. 3, a winding 122 is wound clockwise when viewed from the top
of the columnar part 116, and the winding 124 is wound counterclockwise when viewed
from the top of the columnar part 118. Although not illustrated, each of the winding
122 and the winding 124 has a lead wire so as to be energized therethrough.
[0029] Between the columnar parts 116, 118 and the top plate 112, there is provided a resin
film 130 composed of a resin having a lower permeability than that of the coil core
110, so as to form a so-called coil gap.
[0030] The permeability of the resin film 130 is preferably low enough to be assumed as
air, as compared with the permeability o the coil core 110.
[0031] While the resin film 130 in this embodiment is positioned between the columnar parts
116, 118 and the top plate 112, it may alternatively be positioned between the columnar
parts 116, 118 and the bottom plate 114, or between both of them.
[0032] The coil core 110 is inserted inside the coil (winding 120). The coil core is generally
exemplified by those made of ceramics mainly composed of iron oxide (ferrite core),
those made of amorphous alloy (amorphous core), those obtained by compression molding
of metal powder (dust core), and those having a laminated structure of a plurality
of electrical steel sheets which are electrically isolated from each other (laminated
core).
[0033] The term of "annular" means a geometry which surrounds a certain area on a plane
(circle, square, etc.), or, a geometry which surrounds a certain area on a plane but
the contour of which has a partial omission (C-shape, U-shape, etc.). The omission
herein is made only to a degree enough to allow the coil core 110 to configure a closed
magnetic path. In other words, the site of omission functions as a coil gap of the
coil core 110.
[0034] The term of "inner loop side" means the inner side of the direction in which a first
portion and a second portion are opposed in the annular coil core 110. The term of
"outer loop side" means the outer side of the direction in which a first portion and
a second portion are opposed in the annular coil core 110.
[0035] The phase of "a cross section deviates towards one side" means that the centroid
of area deviates towards one side. More specifically, referring to the columnar parts
116, 118 of this embodiment, when the center of rigidity and the centroid of area
of the cross section of the columnar parts 116, 118 are determined while assuming
that the coil core 110 is composed of a single material, the cross section is then
understood to deviate towards the inner loop side, if the center of rigidity falls
more deeply in the outer loop side than the centroid of area is. On the other hand
on the same assumption, the cross section is understood to deviate towards the outer
loop side, if the center of rigidity of a cross section falls more deeply in in the
inner loop side in the opposing direction than the centroid of area is. The centroid
of area may be determined as the center of gravity of the cross-sectional area, and
the center of rigidity may be determined by dividing cross-sectional primary moment
by the cross-sectional area.
[0036] Now the term of "columnar" means any of column-like shapes, and more specifically
include a shape having the side circumferential surface which stands upright on an
arbitrary plane, a shape having the side circumferential surface bulged at the middle
thereof, a shape having the side circumferential surface thinned at the middle thereof,
and a shape having the side circumferential surface which contains a projection or
a recess.
[0037] The columnar parts 116, 118 in this embodiment can stand upright on the bottom plate
114 or the top plate 112, in both cases where the bottom plate 114 is placed on the
lower side in the perpendicular direction, and where the top plate 112 is placed on
the lower side in the perpendicular direction. In these cases, it suffices that the
columnar parts 116, 118 stand upright on the bottom plate 114 or on the top plate
112 in the assembled coil core 110, or in the form of finished product, even if the
columnar parts 116, 118 are not shaped in a self-supporting manner before the coil
core 110 is assembled.
[0038] Now the term of "side circumferential surface" means a surface other than both end
faces. The phrase of "having side circumferential surfaces opposed to each other"
encompasses the case where there is a hollow space between both side circumferential
surfaces, so that one side circumferential surface is directly visible from the other
side circumferential surface, and the case where both surfaces are opposed to each
other while holding in between some other member (encapsulating resin, for example).
[0039] The phrase of "in close proximity" encompasses both of "being brought into contact",
and "being positioned nearby without being brought into contact".
[0040] In this embodiment, distance between the coil core 110 and the conductor part (coil)
of the winding 120 is preferably minimized as possible. This is because the closer
the positions comes to the coil, the stronger the magnetic field induced by current
supply to the coil, and, the closer the coil core 110 comes to the coil, the more
the magnetic flux which passes through the coil core 110, and thereby, the magnetic
characteristics including inductance are improved when the coil component 100 as a
whole is taken into account.
[0041] For the case where the specific resistance of material composing the coil core 110
is low (Mn-Zn-based ferrite core, for example), and the winding is wound in contact
with the coil core 110, the coil core 110 and the coil would be short-circuited if
the coating layer of winding should be broken by a flash produced at the edge of the
core. In order to avoid such nonconformity, it may be necessary in some cases to preliminarily
provide an insulating finish (forming a coating layer with a tape or resin, for example)
over the surface of the coil core 110.
[0042] The phrase of "a pair of sandwiching parts (top plate 112 and bottom plate 114) holding
in between the columnar parts 116, 118" means that the bottom face of the top plate
112, representing one surface of the sandwiching parts, is opposed to the top faces
of the columnar parts 116, 118, and that the top face of the bottom plate 114, representing
the other surface of the sandwiching parts, is opposed to the bottom faces of the
columnar parts 116, 118, including both cases where the opposed faces are brought
into contact, and where they are not brought into contact. In this embodiment, the
case where the opposed faces are not brought into contact includes an exemplary case
where a gap is provided in between.
[0043] The phrase of "a pair of sandwiching parts (top plate 112 and bottom plate 114) supporting
the pair of columnar parts 116, 118" means that the columnar parts 116, 118 are immobilized
so as not to move relative to the sandwiching part (top plate 112 or bottom plate
114). A variety of embodiments are feasible as modes of supporting the columnar parts
116, 118. For example, the columnar parts 116, 118 may be fixed to the top plate 112
or the bottom plate 114 by adhesion, or by fitting. The columnar parts 116, 118 may
alternatively be fixed using a clamp which keeps them in contact under pressure, on
both of the top faces and bottom faces thereof, with the top plate 112 and the bottom
plate 114. Alternatively, the columnar parts 116, 118, the top plate 112 and the bottom
plate 114 may be arranged in a predetermined positional relation, followed by encapsulation
with an insulating resin.
[0044] In FIG. 3, an effective magnetic path M1 of a coil component 200 is indicated by
a broken line. As illustrated in the drawing, the effective magnetic path M1 which
passes through the coil core 110 is routed so as to deviate from the center towards
the inner loop side. As a result of deviation of the cross section of the coil core
110 towards the inner loop side of the coil core 110, magnetic flux which passes through
the inner loop side of the coil core 110 increases, whereas the magnetic flux which
passes through the outer loop side of the coil core 110 decreases. This is why the
effective magnetic path M1 of the coil component 100 as a whole can deviate towards
the inner loop side.
[0045] Inductance of an ideal coil is given by the equation (1) below:
[Mathematical Formula 1]

where, L represents inductance, 1 represents effective magnetic path length, Ae represents
cross-sectional area of core, and µ represents permeability of core.
[0046] As given by the equation (1), the inductance of an ideal coil is inversely proportional
to the effective magnetic path length. While the inversely proportional relation between
the inductance and the effective magnetic path length in an actual coil may be disordered
to some degree, it still remains that the shorter the effective magnetic path, the
larger the inductance, and that the longer the effective magnetic path length, the
smaller the inductance.
[0047] In the coil component 100 of this embodiment, since the effective magnetic path M1
is routed closer towards the inner loop side to thereby substantially shorten the
effective magnetic path length as described above, so that the inductance will increase
as compared with that of a coil component having equivalent levels of the individual
parameters (core volume, core distance, core material, gap length, way of winding,
number of turns), but no deviation.
[0048] The core volume means the volume of the coil core 110
per se.
[0049] The core distance means the distance between the inner-loop-side lateral face of
the columnar part 116 and the inner-loop-side lateral face of the columnar part 118.
The inner-loop-side lateral face means a part of the side circumferential surface
of the coil core 110, which is placed on the inner loop side.
[0050] The core material means a material composing the coil core 110.
[0051] The way of winding means a way by which the winding 120 is wound around the columnar
parts 116, 118, and specifically includes tension applied to the winding 120, and
pitch of adjacent turns of the winding 120.
[0052] The number of turns means the number of times the winding 120 is wound around the
columnar parts 116, 118.
[0053] The DC superimposition characteristic of the coil component 100 is predominantly
determined by the structure of the coil core 110. More specifically referring to this
embodiment, the DC superimposition characteristic of the coil component 100 is determined
by parameters including cross-sectional area of the columnar parts 116, 118; distance
between the columnar part 116 and the columnar parts 118; volume of the top plate
112 and the bottom plate 114; materials composing the top plate 112, the bottom plate
114 and the columnar parts 116, 118; gap length of the coil core 110 (thickness of
the resin film 130); way of winding of the winding 120; and the number of turns of
the winding 120. Of the parameters exemplified above, the number of winding of the
winding 120 may be arbitrarily increased or decreased, where the upper limit of which
is determined by the size and shape of the coil core 110.
[0054] Now, the coil component 100 of this embodiment is successfully increased in the inductance
of the coil component 100, while focusing on the deviation of cross section of the
coil core 110 (columnar parts 116, 118) which is not included in the parameters enumerated
above, and therefore scarcely affects the DC superimposition characteristic.
[0055] General coil component is adjusted to satisfy desired levels of inductance and DC
superimposition characteristic, by determining a material and a structure of the coil
core based on a target inductance, and then by increasing or decreasing the number
of turns or the gap length. The inductance and the DC superimposition characteristic
are however in a trade-off relation, so that any change in the number of turns and
the gap length for increasing either one will decrease the other.
[0056] Now according to the coil component 100 of this embodiment, it is possible to prepare
the coil component which satisfies a target inductance without due consideration on
the effect on the DC superimposition characteristic, so that it becomes easy to obtain
desired levels of magnetic characteristics.
[0057] The phrase of "prepare the coil component" means to manufacture a coil component
which satisfies desired specifications, by adjusting or selecting various parameters.
More specifically, a possible embodiment is such as deriving a target value of a parameter,
actually measuring the parameter of the coil component, increasing or decreasing the
number of turns or the gap length of the coil core, which are alternately repeated
as necessary, to thereby manufacture the coil component which satisfies the thus derived
target value. Another possible embodiment is such as deriving a target value of a
parameter, and selecting a coil component which satisfies the thus derived target
value, out from a set of a plurality of coil components having different values of
such parameter, to thereby manufacture the coil component.
[0058] In the coil component 100 of this embodiment, the columnar part 116 having the winding
122 round therearound, and the columnar part 118 having the winding 124 wound therearound
are independent, and each of which is held between the pair of sandwiching parts (top
plate 112 and bottom plate 114). With such configuration, the coil component 100 may
be assembled after winding the windings 122, 124 around the columnar parts 116, 118.
This enables machine-assisted automatic winding, and raises benefits of keeping the
tension of the windings 122, 124 at constant during winding, and of reducing the time
consumed for winding.
[0059] Since the columnar parts 116, 118 and the sandwiching parts (top plate 112 and bottom
plate 114) in the coil component 100 of this embodiment are separate and independent
members, so that it is now possible to select and use the columnar parts 116, 118
out from a series of columnar components having various degrees of deviation of the
transverse cross-section. Accordingly, the inductance of the coil component 100 may
be increased or decreased simply by replacement of the columnar parts 116, 118. From
the viewpoint of the sandwiching parts, a material for composing the sandwiching parts
may be standardized, and this successfully improves the productivity and consequently
reduces cost of the coil component 100.
[0060] As illustrated in FIG. 2B, the columnar parts 116, 118 of this embodiment have a
near-trapezoidal transverse cross-section. The columnar parts 116, 118 are arranged
so as to direct the longest side, out of the sides of the transverse cross section
of each of the columnar parts 116, 118, towards the inner loop side of the coil core
110. The columnar parts 116, 118 have nearly same shapes of the transverse cross-sections
at all levels of height, and are respectively vertical to the bottom plate 114 and
the top plate 112.
[0061] In short, the coil component 100 of this embodiment has structural features summarized
below.
[0062] In one columnar part 116, the side circumferential surface includes at least one
flat part, and, the largest flat part 117 having the largest area out of the flat
parts included in the side circumferential surface is positioned on the inner loop
side of the coil core 110, thereby making the cross section of the columnar part 116
deviate towards the inner loop side.
[0063] In the other columnar part 118, the side circumferential surface includes at least
one flat part, and, the largest flat part 119 having the largest area out of the flat
parts included in the side circumferential surface is positioned on the inner loop
side, thereby making the cross section of the columnar part 118 deviate towards the
inner loop side.
[0064] In other words, in the coil component 100 of this embodiment, the pair of columnar
parts 116, 118 respectively have the largest flat parts 117, 119 on the inner loop
side of the coil core 110, and the largest flat parts 117, 119 are arranged in parallel.
[0065] As illustrated in FIG. 1 and FIG. 2A, the coil core 110 of this embodiment has a
square shape. In such square coil core 110 configured to direct either one of the
largest flat part 117 and the largest flat part 119 towards the inner loop side of
the coil core 110, the effective magnetic path length of the coil component 100 may
be shortened, and thereby the inductance of the coil component 100 may be increased,
in a more effective manner. In addition, by arranging the largest flat part 117 and
the largest flat part 119 in parallel to each other on the inner loop side, the effective
magnetic path length of the coil component 100 may become shortest, and the inductance
of the coil component 100 may be increased.
[0066] The top plate 112 and the bottom plate 114 are configured by a pair of flat plates
opposed in parallel to each other. In other words, the top plate 112 and the bottom
plate 114 are opposed in parallel to each other, having no projection other than the
columnar parts 116, 118 in the space held in between. The projection means a part
projected from the top plate 112 and the bottom plate 114, and is composed of a material
same as that composing the individual plates, or a material having an equivalent level
of permeability.
[0067] Assuming now that at least either one of the top plate 112 and the bottom plate 114
has a projection on the opposing surface(s), such projection may deform the magnetic
field formed between the top plate 112 and the bottom plate 114, and is capable of
inhibiting the effect of this embodiment by shifting the magnetic path to be formed
in the coil component 100 towards the outer loop side of the coil core 110. In short,
a preferable configuration is such that, between the top plate 112 and the bottom
plate 114, there is possibly no component with high permeability except for the columnar
parts 116, 118.
[0068] The pair of columnar parts 116, 118 are preferably enclosed in the space formed between
the opposing top plate 112 and bottom plate 114. Since the columnar part 116 has the
winding 122, and the columnar part 118 has the winding 124, so as to be respectively
wound around the side faces thereof in close proximity thereto, so that a magnetic
field generates over the entire side face under current supply. Accordingly, with
the configuration having the columnar part 116 and the columnar part 118 enclosed
in the space formed between the opposing top plate 112 and the bottom plate 114, it
becomes now possible to avoid leakage of magnetic flux which passes through the columnar
parts 116, 118, to thereby improve various magnetic characteristics of the coil component
100 as a whole, typified by increase in inductance.
[0069] Having described the configuration of this embodiment, the embodiment is merely an
illustrative one of the present invention which may be configured in different ways.
[0070] For example, the columnar parts 116, 118, having a near-trapezoidal transverse cross-sectional
shape in this embodiment, may have any other shape, so long as the shape deviates
towards the inner loop side or the outer loop side of the coil core 110. Shape to
be adopted is selectable from a wide variety of shapes including polygons such as
triangle, pentagon or the like; semicircle and arc; convex shape and concave shape;
and shapes surrounded only by a curve and deviates towards one side.
[0071] While the columnar part 116 and the columnar part 118 have been illustrated in this
embodiment, such that they are arranged symmetrically around the center of the transverse
cross section of the coil component 100, they may alternatively be arranged asymmetrically.
<Configuration of Second Embodiment>
[0072] A second embodiment of the present invention will be explained referring to FIG.
4 to FIG. 6.
[0073] FIG. 4 is a perspective view illustrating a coil component 200 of the second embodiment.
[0074] FIG. 5A is a front view of the coil component 200, and FIG. 5B is a cross-sectional
view taken along line III-III in FIG. 5A.
[0075] FIG. 6 is a schematic drawing schematically illustrating an effective magnetic path
M2 induced in the coil component 200 when the winding 220 is energized, and the direction
of winding of the winding 220.
[0076] The coil component 200 according to the second embodiment of the present invention
has an annular coil core 210, a winding 220, and a resin film 230. The coil core 210
has a top plate 212, a bottom plate 214, a columnar part 216, and a columnar part
218.
[0077] The columnar part 216 has a winding 222 wound therearound, and the columnar part
218 has a winding 224 wound therearound. As illustrated in FIG. 6, the winding 222
is wound clockwise when viewed from the top of the columnar part 216, and the winding
224 is wound counterclockwise when viewed from the top of the columnar part 218.
[0078] Although not illustrated, each of the winding 222 and the winding 224 has a lead
wire so as to be energized therethrough.
[0079] The coil core 210 and the coil core 110 in the first embodiment, the winding 220
and the winding 120 in the first embodiment, and the resin film 230 and the resin
film 130 in the first embodiment, are respectively composed of the same materials.
[0080] The top plate 212 and the bottom plate 214 may be configured by a material same as
that used for the top plate 112 and the bottom plate 114 in the first embodiment.
[0081] The coil component 200 of this embodiment is now different from the coil component
100 of the first embodiment, in that, as illustrated in FIG. 5B, the cross section
of the coil core 210 (columnar parts 216, 218) deviates towards the outer loop side.
[0082] In FIG. 6, an effective magnetic path M2 of the coil component 200 is indicated by
a broken line. As illustrated here, in the coil component 200 of this embodiment,
the effective magnetic path M2 which passes through the coil core 210 is routed so
as to deviate from the center towards the outer loop side. In other words, the cross
section of the coil core 210 deviates towards the outer loop side of the coil core
210. Accordingly, the magnetic flux which passes through the outer loop side of the
coil core 210 increases, whereas the magnetic flux which passes through the inner
loop side of the coil core 210 decreases. This is why the effective magnetic path
M2 of the coil component 200 as a whole can deviate towards the outer loop side.
[0083] In the coil component 200 of this embodiment, since the effective magnetic path length
is substantially elongated, so that the inductance will decrease as compared with
that of a coil component having equivalent levels of the individual parameters (core
volume, core distance, core material, gap length, way of winding, number of turns),
but no deviation.
[0084] In short, the coil component 200 of this embodiment has structural features summarized
below.
[0085] In one columnar part 216, the side circumferential surface includes at least one
flat part, and the largest flat part 217 having the largest area out of the flat parts
included in the side circumferential surface, is positioned on the outer loop side
of the coil core 210, thereby making the cross section of the columnar part 216 deviate
towards the outer loop side.
[0086] In the other columnar part 218, the side circumferential surface includes at least
one flat part, and the largest flat part 219 having the largest area out of the flat
parts included in the side circumferential surface, is positioned on the outer loop
side of the coil core 210, thereby making the cross section of the columnar part 218
deviate towards the outer loop side.
[0087] In other words, in the coil component 200 of this embodiment, the pair of columnar
parts 216, 218 respectively have the largest flat parts 217, 219 on the outer loop
side of the coil core 210, and the largest flat parts 217, 219 are arranged in parallel.
[0088] As illustrated in FIG. 4 and FIG. 5A, the coil core 210 of this embodiment has a
square shape. In such square coil core 210 configured to direct either one of the
largest flat part 217 and the largest flat part 219 towards the outer loop side of
the coil core 210, the effective magnetic path length of the coil component 200 may
be elongated, and thereby the inductance of the coil component 200 may be decreased,
in a more effective manner. In addition, by arranging the largest flat part 217 and
the largest flat part 219 in parallel to each other on the outer loop side, the effective
magnetic path length of the coil component 200 may become longest, and the inductance
of the coil component 200 may be decreased.
<Evaluation Tests on First Embodiment and Second Embodiment>
[0089] Evaluation Tests on the magnetic characteristics of the coil component 100 according
to the first embodiment, and on the magnetic characteristics of the coil component
200 of the second embodiment will be explained referring to FIG. 7A to FIG. 9B.
[0090] FIGs. 7A and 7B are drawings illustrating a plate member 12 used for composing the
top plates 112, 212 or the bottom plates 114, 214. FIG. 7A is a top view of the plate
member 12, and FIG. 7B is a side elevation of the plate member 12.
[0091] FIGs. 8A and 8B are drawings illustrating a columnar component 16 used for composing
the columnar parts 116, 118, 216, 218. FIG. 8A is a top view of the columnar component
16, and FIG. 8B is a side elevation of the columnar component 16.
[0092] FIGs. 9A and 9B are drawings illustrating relations of DC current supplied to the
coil components 100, 200, with inductance of the coil components. FIG. 9A represents
the case where the windings 122, 124, or the windings 222, 224 are connected in parallel,
and FIG. 9B represents the case where the windings 122, 124 or the windings 222, 224
are connected in series.
[0093] As illustrated in FIG. 7, the plate member 12 viewed from the top is a square plate
62 mm on a side, with a thickness of 16 mm.
[0094] As illustrated in FIG. 8, the columnar component 16 viewed from the top has a near-trapezoidal
shape, and in more detail, has a shape derived from a trapezoid with the bases of
31 mm and 51 mm, and a height of 20 mm, by round chamfering at both ends of the individual
bases. The columnar component 16 is 20 mm thick.
[0095] A material for composing both of the plate member 12 and the columnar component 16,
used here is an Mn-Zn-based ferrite material called ML24D.
[0096] As illustrated in FIG. 8A, the cross-sectional shape of the columnar component 16
is a near polygon chamfered at the corner parts 15, 17, and more specifically a near
trapezoid.
[0097] The size of chamfering at the corner part 17, positioned on the side to which the
cross section of the columnar component 16 deviates, is smaller than the size of chamfering
at the corner part 15 positioned on the opposite side. In more detail, the corner
part 15 is round chamfered to a radius of 10 mm, and the corner part 17 is round chamfered
to a radius of 6 mm. Having exemplified the case of round chamfering (rounding), the
chamfering may alternatively be 45° chamfering (corner chamfering).
[0098] By chamfering the corner parts 15, 17 of the columnar component 16, the winding (for
example, windings 122, 124, and windings 222, 224) may be wound around the columnar
component 16 in a more strongly adherent manner. In this way, it becomes now possible
to avoid leakage of magnetic flux from the columnar component 16, and to thereby improve
various magnetic characteristics of the coil component (for example, coil component
100 and coil component 200) as a whole, typified by increase in inductance.
[0099] Since the radius of round chamfering at the corner part 17 is smaller than the radius
of round chamfering at the corner part 15, the flat part (largest flat part 117 and
largest flat part 217) on the side of deviation will have a less area of removal by
chamfering at both ends thereof in the direction of circumferential surface. This
way of round chamfering will therefore intensify the effect of the present invention,
aimed at shifting the effective magnetic path produced in the coil device towards
the side to which the cross section of the coil core deviates.
[0100] The coil component 100 of the first embodiment and the coil component 200 of the
second embodiment were manufactured by combining the plate member 12 and the columnar
component 16 respectively illustrated in FIGs. 7A, 7B and FIGs. 8A, 8B.
[0101] The windings 120, 220 used herein was 1 mm in diameter, and the number of turns was
40. The gap length (thickness of the resin films 130, 230) was 1 mm. The plate member
12 and the columnar component 16 were arranged while placing in between a spacer of
11.7 mm thick (not illustrated). Frequency of measurement was set to 100 kHz.
[0102] It is found from FIGs. 9A, 9B that the coil component 100 shows larger inductance
than that of the coil component 200, in both cases of parallel connection and series
connection. Difference in inductance between the coil component 100 and the coil component
200 was found to be approximately 4%.
[0103] As for the DC superimposition characteristic, both of the coil component 100 and
the coil component 200 were found to decrease in inductance to an equivalent degree.
[0104] In short, it was evaluated that the inductance was successfully increased or decreased
by changing the cross-sectional shape of the coil cores 110, 210. It was also evaluated
that such change was found to scarcely affect the DC superimposition characteristic,
when other parameters (core volume, core distance, core material, gap length, way
of winding, the number of turns) remained unchanged.
<Third Embodiment>
[0105] A third embodiment of the present invention will be explained referring to FIGs.
10A, 10B.
[0106] FIGs. 10A, 10B are drawings illustrating a coil component 300 of the third embodiment.
FIG. 10A is a front view of the coil component 300, and FIG. 10B is a cross-sectional
view taken along line IV-IV in FIG. 10A.
[0107] As seen in FIG. 10A, the coil core 310 has a form of bent rod, and the cross section
thereof deviates towards at least one of the inner side or outer side of the bending
curvature of the coil core 310. In this point of view, the coil component 300 of the
third embodiment is different from the coil component 100 of the first embodiment
and the coil component 200 of the second embodiment. More specifically, the coil core
300 of this embodiment is a single-component toroidal core composed of a doughnut-shaped
(annular) member.
[0108] The term "bent" not only relates to the doughnut-shaped mode illustrated above, but
also relates to a mode of bending once in the middle way (L-shaped), a mode of bending
twice in the middle way in the same direction (U-shaped), and a mode of bending like
a bow. It is not always necessary for the coil core 310 to be configured by a single
component, and may instead be configured by linking a plurality of components.
[0109] The coil component 300 of the third embodiment is different from the above-described
embodiments, in that the winding 320 wound around the coil core 310 is a single wire
component, and is wound over almost entire side circumferential surface of the rod-like
coil core 310.
[0110] However, form the viewpoint of electric circuit, this is understood to be equivalent
to a configuration having a plurality of windings (for example, the winding 122 and
the winding 124 in the first embodiment) connected in series.
[0111] While the winding 320 will be explained hereafter as a single entirety, the winding
320 may be configured by a plurality of components, which may occasionally be connected
in parallel.
[0112] The coil gap 330 is not limited to a vacancy, but may be filled with some material
(resin, for example) having permeability sufficiently smaller than that of the coil
core 310. It is not always necessary to provide the coil gap 330, and the coil core
310 in this case may have a form of continuous perfect circle, rectangle, ellipse,
or the like.
[0113] As illustrated in FIG. 10B, the coil component 300 of the third embodiment is similar
to the coil component 100 of the first embodiment, in terms that a cross section of
the coil core 310, which is taken orthogonally to the winding axis of the winding
320, deviates towards the inner loop side of the coil core 310. In other words, the
coil core 310 is made thicker in the inner loop side, than in the outer loop side.
Now the thickness of the coil core 310 means the depth size of the coil core 310 in
the direction the coil core 310 looks like a doughnut, that is, the depth size of
the coil core 310 in a view as illustrated in FIG. 10A.
[0114] Having features equivalent to those of the coil component 100, also the coil component
300 successfully increases in the inductance, as compared with coil components with
equivalent parameters (core volume, core distance, core material gap length, way of
winding, and the number of turns), but no deviation.
[0115] The coil component 300 having a so-called toroidal core causes less leakage of magnetic
flux, and consequently has larger inductance as compared with coil components (coil
component 100, for example) having equivalent levels of the individual parameters
(core volume, core distance, core material, gap length, way of winding, and the number
of turns).
[0116] The paragraphs above explained the embodiment in which the coil core 310 is made
thicker on the inner loop side thereof, than on the outer loop side. In another possible
modified example this embodiment, the coil core 310 may be made thicker on the outer
loop side thereof, than on the inner loop side. Reduced inductance of this modified
example, as compared with the third embodiment, is clearly understood from the principle
explained by comparison between the coil component 100 and the coil component 200.
[0117] While the nearly trapezoidal cross section of the coil core 310 was illustrated in
FIG. 10B merely as an example, the cross section may be varied in various ways, similarly
to the cross-sectional shape of the columnar parts 116, 118 in the first embodiment.
<Modified Example of First Embodiment>
[0118] A modified example of the first embodiment of the present invention will be explained
referring to FIGs. 11A, 11B.
[0119] FIGs. 11A, 11B are drawing illustrating a coil component 400 of the modified example
of the first embodiment. FIG. 11A is a front view of the coil component 400, and FIG.
11B is a cross-sectional view taken along line V-V in FIG. 11A.
[0120] The coil component 400 of the modified example has an annular coil core 410, a winding
420, and a resin film 430. The coil core 410 has a top plate 412, a bottom plate 414,
a columnar part 416, and a columnar part 418. The columnar part 416 has a winding
422 wound therearound, and the columnar part 418 has a winding 424 wound therearound.
[0121] Although not illustrated here, similarly to the coil component 100 of the first embodiment,
the winding 422 is wound clockwise when viewed from the top of the columnar part 416,
and the winding 424 is wound counterclockwise when viewed from the top of the columnar
part 418.
[0122] Although not illustrated here, each of the winding 422 and the winding 424 has a
lead wire so as to be energized therethough.
[0123] The coil core 410 and the coil core 110 in the first embodiment, the winding 420
and the winding 120 in the first embodiment, and the resin film 430 and the resin
film 130 in the first embodiment, are respectively composed of the same materials.
[0124] The top plate 412 and the bottom plate 414 is configured by a material same as that
used for the top plate 112 and the bottom plate 114 in the first embodiment.
[0125] As illustrated in FIG. 11A, the coil component 400 is different from the coil component
100 of the first embodiment, in that the columnar parts 416, 418 are apart from the
sandwiching part (top plate 412), wherein the distance of the columnar parts 416,
418 away from the top plate 412, on the side towards which the cross section of the
columnar parts 416, 418 deviates, is larger than the distance of the columnar parts
416, 418 away from the top plate 412 on the opposite side.
[0126] The resin film 430 provided so as to extend between the columnar parts 416, 418 and
the top plate 412 has a wedge-like shape. Now the wedge-like shape means a shape thickened
on one end, and gradually thinned towards the other end.
[0127] In more detail, the coil component 400 of this modified example is different from
the coil component 100 of the first embodiment, in that the cross section of the columnar
parts 416, 418 deviates towards the inner loop side, and, the distance away from the
top plate 412 is larger on the inner loop side, than on the outer loop side.
[0128] In other words, the resin film 430 provided so as to extend between the columnar
parts 416, 418 and the top plate 412 is thick on one end positioned on the inner loop
side, and is gradually thinned towards the other end positioned on the outer loop
side.
[0129] With such structural features, the coil component 400 of this modified example successfully
acquires a so-called swinging characteristic. The swinging characteristic means a
characteristic of coil capable of ensuring a relatively large inductance when a small
current flows through the winding, whereas capable of keeping a nearly constant inductance
even when the current increases.
[0130] The swinging characteristic is aimed at preventing intermittent oscillation, mainly
in a choke coil used for high-frequency switching power circuit.
[0131] For the case where the wedge-like coil gap is provided to general coil components
with symmetrical cross-sections of the coil cores, aiming at achieving the swinging
characteristic, the characteristic will not largely vary depending on whichever part
of the coil gap is thickened (or thinned). On the other hand, the coil component 400
of this modified example will largely vary the characteristic depending on whichever
part thereof is thickened (or thinned).
[0132] As in the coil component 400 of this modified example, by providing the coil gap
so as to be thickened (expanding the distance) on the side towards which the transverse
cross-sections of the columnar parts 416, 418 deviate (the inner loop side of the
coil core 410), the permeability will decrease on the inner loop side through which
the magnetic flux passes more densely, so that the swinging characteristic may be
more distinctive than in the general coil components, and thereby the DC superimposition
characteristic may be improved.
[0133] Since the coil component 400 of this modified example is configured to have a small
coil gap (distance) on the outer loop side of the coil core 410, so that an additional
effect obtainable now is reduced leakage of magnetic flux outward from the coil component
400.
[0134] While the description in this modified example was made on the case where the core
gap is thickened on the side towards which the transverse cross-sections of the columnar
parts 416, 418 deviate, the present invention is not limited thereto. For example,
another possible embodiment is such as thinning the coil gap on the side towards which
the transverse cross-sections of the columnar parts 416, 418 deviate. In this case,
the permeability becomes high on the inner loop side through which the magnetic flux
passes more densely, so that a large inductance may be obtained in the small current
region.
[0135] While the description in this modified example was made on the coil component 400
which represents the modified example of the first embodiment, it is also possible
without limitation to configure a coil component by providing the swinging characteristic
to the coil component 200 of the second embodiment. More specifically, in another
possible embodiment, the cross section of the columnar part may deviate towards the
outer loop side, and, the distance between the columnar part and the sandwiching part
(top plate or bottom plate) may be larger on the outer loop side, than on the inner
loop side.
[0136] Having explained the wedge-like shape, the coil gap (resin film 430) may have a variety
of shapes without being limited thereto. For example, the distance may be different
between the inner loop side and the outer loop side of the coil core 410, by forming
the top faces of the columnar parts 416, 418 into a stepwise pattern in the front
view.
[0137] The coil components of the present invention were explained referring to a variety
of embodiments and modified examples, merely for illustrative purposes. Various constituents
of the present invention are not always necessarily be independent from each other,
and instead embrace various cases including that a plurality of constituents configure
a single member, a single constituent is configured by a plurality of members, a certain
constituent forms a part of other constituent, and a part of a certain constituent
is shared with a part of other constituent.
[0138] The various constituents of the present invention do not exclude providing an unillustrated
hole, slit, or the like depending on needs.
<Coil Component Set>
[0139] A coil component set having a plurality of coil components according to the above-described
various embodiments and modified examples will be explained.
[0140] That is, the coil component set contains a plurality of coil components (coil component
100 and coil component 200, for example) which respectively have the annular coil
cores (coil core 110 and coil core 210, for example) composed of a material having
a higher permeability than that of air, and the windings (winding 120 and winding
220, for example) wound around the coil cores in close proximity thereto.
[0141] In the coil component set, the plurality of coil components have equivalent levels
of either one of inductance and DC superimposition characteristic. Of the plurality
of coil components contained in the coil component set, a cross section of the coil
core in a first coil component, which is taken orthogonally to the winding axis of
winding, deviates either towards the inner loop side or towards the outer loop side
of the coil core, more largely as compared with the cross section of the coil core
in a second coil component.
[0142] Besides the various coil components described above, the coil component set may contain
any other coil components having symmetrical cross section of the coil core. That
is, what is essential is that, when the cross-sections of the plurality of coil components
are compared in shape, the one deviates more largely than another, without absolutely
needing that the cross section of the coil core deviates within a single coil component.
[0143] Assuming now the coil component set is composed of the plurality of coil components
having equivalent levels of the individual parameters (core volume, core distance,
core material, gap length, way of winding, and the number of turns) and featured as
described above, the plurality of coil components contained in such coil component
set will be given an equivalent level of DC superimposition characteristic and a different
level of inductance.
[0144] Assuming now the coil component set is composed of the plurality of coil components
which differs in at least one of the above-described parameters, in particular in
core material, gap length or the number of turns, and featured as described above,
the plurality of coil components contained in such coil component set will be given
an equivalent level of inductance and a different level of DC superimposition characteristic.
<Method of Manufacturing Coil Component>
[0145] The paragraphs below will describe a method of manufacturing the above-explained
coil components of the various embodiments and modified examples. This is a method
of manufacturing a coil component (for example, coil component 100 and coil component
200) having an annular coil core (coil core 110 and coil core 210, for example) composed
of a material having a higher permeability than that of air, and a winding (winding
120 and winding 220, for example) wound around the coil core in close proximity thereto.
[0146] The method includes a step of derivation, a step of shape determination, and a step
of molding. In the step of derivation, the degree of deviation of a cross section
of the coil core, which is taken orthogonally to the winding axis of winding, either
towards the inner loop side or towards the outer loop side of the coil core, is derived
based on a desired inductance of the coil component. In the step of shape determination,
a shape of the coil core is determined according to the degree derived in the step
of derivation. In the step of molding, the coil component is molded according to the
shape of coil core determined in the step of shape determination.
[0147] For more detailed explanation, assumed now is manufacturing of a choke coil L
1 used for a secondary smoothing circuit RF of a forward converter. Note that the method
of manufacturing described below is merely an illustrative one, by no means limiting
the present invention.
[0148] FIG. 12 is a simplified circuit diagram illustrating an electric circuit of a forward
converter.
[0149] FIG. 13 is a flow chart illustrating a method of manufacturing the choke coil L
1.
[0150] As illustrated in FIG. 12, AC power supplied from an AC power source AC is converted
by an AC/DC converter (indicated as A/D in FIG. 12) to DC power, and then applied
to a switching transistor Tr
1. An input capacitor C
in is provided for the purpose of smoothing the input voltage. The switching transistor
Tr
1 is switched by a control circuit CC according to a predetermined cycle, so as to
convert the DC power into a high-frequency power of several tens kHz or higher. The
high-frequency power converted by the switching transistor Tr
1 is then converted by a transformer T
1 into desired levels of voltage and current. By contribution of a diode D1 and a diode
Dr, surge current which generates when the switching transistor Tr
1 is turned OFF does not flow through the transformer T
1, but is circulated in the output side.
[0151] Voltage and current converted by the transformer T
1 will have ripples superimposed thereon. In order to rectify and smoothen the waveform,
a smoothing circuit RF is provided on the secondary side of the transformer T
1. A circuit indicated by a broken line in FIG. 12 represents the smoothing circuit
RF. The smoothing circuit RF is composed of a choke coil L
1 and a capacitor C
1. Since the smoothing circuit RF is aimed at attenuating the ripples, so that the
inductance of the choke coil L
1 should be one of important parameters, but also DC superimposition characteristic
is important. That is, it is important for the choke coil L
1 to function as a coil, even under the maximum current which possibly flows therethrough.
[0152] If the choke coil magnetically saturates to no longer work as a coil, the smoothing
circuit RF becomes incapable of rectification and smoothing, and thereby becomes incapable
of stable power supply as the forward converter.
[0153] In the forward converter illustrated in FIG. 12, the inductance of the choke coil
L
1 is given by the equation (2) below.
[Mathematical Formula 2]

In the equation (2),
L
1: inductance of choke coil L
1;
V
S: secondary winding voltage of transformer T
1;
V
O: output voltage of forward converter;
Δ I
L: allowable ripple current; and
t
ON: ON time of switching transistor.
[0154] In a switching power circuit, the maximum current I
L(MAX) which flows through the choke coil L
1 is determined taking operational conditions of a protection circuit (not illustrated)
into consideration. Now the protection circuit means a circuit for monitoring voltage,
current, etc. of a main circuit, and for stopping, upon detection of abnormality such
as overload, overvoltage or the like, the inverter in order to prevent damages to
the inverter and induction motor, or for controlling the voltage or current. The maximum
current IL
(MAX) is determined additionally taking allowable ripple current ΔI
L into consideration.
[0155] Assuming now the operational conditions of the protection circuit is 1.2 times of
the rated output current I
O, and the allowable ripple current ΔI
L is 30%
P-P (15% in terms of DC output), the maximum current I
L(MAX) is given by the equation (3) below.
[Mathematical Formula 3]

[0156] As illustrated in FIG. 13, manufacture of the choke coil L
1 starts from calculating a desired inductance of the choke coil L
1 using the equation (2) (step S1).
[0157] Next, the maximum current I
L(MAX) necessary for keeping the desired DC superimposition characteristic of the choke
coil L
1, or the inductance found in step S1, is calculated using the equation (3) (step S2).
[0158] Based on the desired DC superimposition characteristic determined in step S2, the
individual parameters of the choke coil L
1 (core volume, core distance, core material, gap length, way of winding, the number
of turns, for example) are determined (step S3).
[0159] In step S3, another possible embodiment is, for example, such as roughly estimating
the individual parameters (core volume, core distance, core material, gap length,
way of winding, the number of turns, for example) based on the DC superimposition
characteristic determined in step S2 and the desired inductance determined in step
S1. Now the phrase of "roughly estimating" embraces determining a desired value with
a certain numerical range, and, limiting a large number of choices into a predetermined
number of choices.
[0160] In step S3, still another possible embodiment is such as, for example, choosing a
coil component set which contains a plurality of the above-described embodiments and
modified examples, which satisfy the desired DC superimposition characteristic determined
in step S2.
[0161] Based on the desired inductance determined in step S1, the degree of deviation of
the cross section of the coil core in the choke coil L
1 either towards the inner loop side or towards the outer loop side of the coil core
(referred to as the degree of deviation, hereinafter) is derived (step S4, step of
derivation).
[0162] Based on the degree of deviation derived in step S4, the shape of the coil core is
determined (step S5, step of shape determination).
[0163] The choke coil L
1 is molded according to the shape of the coil core determined in step S5 (step S6,
step of molding).
[0164] In step S4, a possible embodiment is such as, for example, calculating the degree
of deviation, based on the individual parameters determined in step S3, and the desired
inductance determined in step S
1. For the calculation, an equation (empirical equation) which depicts a relation among
the degree of deviation, the individual parameters and the inductance, obtained after
repetitive experiments may be used.
[0165] In step S5, a possible embodiment is such as, for example, determining the shape
of the coil core, based on the individual parameters roughly estimated in step S3,
and the degree of deviation derived in step S4.
[0166] As an embodiment implementing step S4 and step S5 in combination, another possible
embodiment is such as, for example, choosing a coil component having a desired inductance,
among from the coil component set selected in step S3.
[0167] In step S6, a possible embodiment is such as, for example, molding the coil component
by placing ferrite particles into a mold corresponded to a shape determined in step
S5. Alternatively, another possible embodiment is such as molding the coil component
by grinding a base coil core into the shape determined in step S5.
[0168] While the paragraphs above have described the method of manufacturing a coil component
of the present invention, assuming the case of manufacturing the choke coil L
1 used for the secondary smoothing circuit RF of the forward converter, the present
invention is also applicable to a method of manufacturing a coil component used for
other purposes.
[0169] For example, the present invention is also applicable to manufacture of a transformer
used for flyback converter for PWM control. In this case, the coil component has a
plurality of windings (for example, the winding 122 and the winding 124 of the coil
component 100) independent from each other, wherein the one is used as the primary
winding, and the other is used as the secondary winding.
[0170] The transformer is used according to the PWM system (continuous conduction mode),
and necessarily has a large inductance than that of transformer used according to
the RCC system (boundary conduction mode) . While a desired inductance is achieved
generally by reducing the gap length, this has consequently degraded the DC superimposition
characteristic, and has sometimes failed in satisfying the desired specification.
[0171] On the contrary, According to the method of manufacturing a coil component of the
present invention, the inductance may be increased or decreased by increasing or decreasing
the degree of deviation of the cross section of the coil core, while keeping the DC
superimposition characteristic almost unchanged. A desired inductance is therefore
achieved easily.
[0172] In short, the method of manufacturing a coil component of the present invention is
preferably applicable to the coil component for which the inductance has been adjustable
only with difficulty by the general method of adjusting inductance (for example, increasing
or decreasing the number of turns, or increasing or decreasing the gap length), due
to the trade-off relation between inductance and DC superimposition characteristic.
[0173] This embodiment embraces the technical spirits below:
- (1) A coil component which includes: an annular coil core composed of a material having
a higher permeability than that of air; and a winding wound around the coil core in
close proximity thereto, characterized in that the coil component further comprises:
a cross section of the coil core, which is taken orthogonally to the winding axis
of winding, deviating either towards the inner loop side or towards the outer loop
side of the coil core.
- (2) The coil component according to (1), wherein the coil core is configured into
a square loop, the sides of which being configured by: a pair of columnar parts which
respectively have a columnar shape and have the side circumferential surfaces opposed
to each other; and a pair of sandwiching parts which support the pair of columnar
parts so as to hold them in between, the winding is wound respectively around each
of the pair of columnar parts, each of the pair of columnar part having a cross section
which deviates either towards the inner loop side or towards the outer loop side.
- (3) The coil component according to (2), wherein in one of the columnar parts, the
side circumferential surface includes at least one flat part, and the cross section
deviates either towards the inner loop side or towards the outer loop side, as a result
of placement of the largest flat part, having the largest area among the flat parts
included in the side circumferential surface, on the inner loop side or on the outer
loop side.
- (4) The coil component according to (3), wherein the cross-sectional shape is a near
polygon with chamfered corner parts, and the size of chamfering of the corner part
positioned on the side to which the cross section deviates is smaller than the size
of chamfering of the corner part positioned on the opposite side.
- (5) The coil component according to (3) or (4), wherein each of the pair of columnar
parts has the largest flat part on the inner loop side, and both largest flat parts
are arranged in parallel.
- (6) The coil component according to (3) or (4), wherein each of the pair of columnar
part has the largest flat part on the outer loop side, and both largest flat parts
are arranged in parallel.
- (7) The coil component according to any one of (2) to (6), wherein the columnar parts
and the sandwiching parts are kept apart, and the distance between the columnar parts
and the sandwiching parts is larger on the side to which the cross section of the
columnar part deviates, than on the opposite side.
- (8) The coil component according to (7), wherein the cross section deviates towards
the inner loop side, and the distance is larger on the inner loop side than on the
outer loop side.
- (9) The coil component according to (1), wherein the coil core has a bent rod form,
and the cross section deviates to at least either towards the inner side or towards
the outer side of the bending curvature of the coil core.
- (10) A method of manufacturing a coil component having an annular coil core composed
of a material having a higher permeability than that of air, and a winding wound around
the coil core in close proximity thereto, characterized in that the method includes:
deriving the degree of deviation of a cross section of the coil core, which is taken
orthogonally to the winding axis of winding, either towards the inner loop side or
towards the outer loop side of the coil core, based on a desired inductance of the
coil component; determining a shape of the coil core, according to the degree derived
in the preceding step of derivation; and molding the coil component, according to
the shape of coil core determined in the preceding step of shape determination.
- (11) A coil component set comprising a plurality of coil components each having an
annular coil core composed of a material having a higher permeability than that of
air, and a winding wound around the coil core in close proximity thereto, and, among
the plurality of coil components having equivalent levels of either one of inductance
and DC superimposition characteristic, a cross section of the coil core in a first
coil component, which is taken orthogonally to the winding axis of winding, deviating
either towards the inner loop side or towards the outer loop side of the coil core,
more largely as compared with the cross section of the coil core in a second coil
component.
- (a) The coil component according to any one of (2) to (8), wherein the pair of sandwiching
parts are configured by a pair of flat plates opposed in parallel to each other.
- (b) The coil component according to (a), wherein the pair of columnar parts are contained
in a space formed between the pair of opposing flat plates.
[0174] It is apparent that the present invention is not limited to the above embodiments,
and may be modified and changed without departing from the scope and spirit of the
invention.