Wire-wound coil

Details Wire-wound coil Wire-wound coil

2002-10-16

2004-08-03

Nguyen, Tuyen T. (Department: 2832)

Inductor devices

With closed core interrupted by an air gap

C336S212000

Reexamination Certificate

active

06771157

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wire-wound coil, and more particularly, to a wire-wound coil for use in, for example, an inductor, a common-mode choke coil, a normal-mode choke coil, a transformer, or other suitable device.
2. Description of the Related Art
In general, the insertion loss versus frequency characteristic of a common-mode choke coil is significantly influenced by an inductance component due to the common-mode inductance L in the region of frequencies lower than the self-resonant frequency, and is significantly influenced by a capacitance component due to the stray capacitance C produced in the common-mode choke coil in the region of frequencies higher than the self-resonant frequency. The self-resonant frequency measured when the impedance is about 50 &OHgr; is represented by the following Expression f0, the insertion loss versus frequency characteristic in the region of frequencies lower than the self-resonant frequency is represented by the following Approximate Expression 1, and the insertion loss versus frequency characteristic in the region of frequencies higher than the self-resonant frequency is represented by the following Approximate Expression 2:
f
0
:fr=
1/[2&pgr;(
LC
)
1/2
]
Approximate Equation 1:
insertion loss=10 log [1+(&ohgr;
L/
100)
2
]
Approximate Equation 2:
insertion loss=10 log [1+1/(100&ohgr;
C
)
2
]
In order to improve the noise-eliminating performance of the common-mode choke coil in the high-frequency region, the stray capacitance C must be decreased. The stray capacitance C is principally caused by the influences of a winding structure of windings, bobbins, and a magnetic core. In order to reduce the influence of the bobbins, it is necessary to change the material of the bobbins to a material having a lower dielectric constant, or to reduce the thickness of the bobbins. However, when the common-mode choke coil is used for an AC supply line, flame retardancy, relative thermal index, an insulation distance according to the safety standards must be ensured. Since existing common-mode choke coils generally adopt thick bobbins having a thickness of 0.5 mm to 1.0 mm and are made of a material having a dielectric constant ∈ of 2 to 4, it is difficult to reduce the influence of the bobbins on the stray capacitance C by changing the material and thickness of the bobbins.
Accordingly, in order to reduce the stray capacitance C produced in the common-mode choke coil, it is important to reduce the influence of the winding structure of the windings, and the influence of the magnetic core. The ratio of the influences varies depending on the winding structure of the windings. For example, so-called sectional winding for winding windings in sections is known as a winding structure that produces little stray capacitance.
FIG. 21
shows the configuration of a known common-mode choke coil
1
in which windings
7
and
17
are wound in sections. The common-mode choke coil
1
includes a magnetic core constituted by two U-shaped core members
20
and
21
, and two bobbins
2
and
12
. The bobbins
2
and
12
include cylindrical body portions
3
and
13
, and flange portions
4
,
5
, and
6
, and
14
,
15
, and
16
provided in the cylindrical body portions
3
and
13
, respectively.
The winding
7
is formed by electrically connecting a first winding portion
7
a
and a second winding portion
7
b
in series. The first winding portion
7
a
is wound between the flange portions
4
and
6
of the bobbin
2
, and the second winding portion
7
b
is wound between the flange portions
5
and
6
. Similarly, the winding
17
is formed by electrically connecting a first winding portion
17
a
and a second winding portion
17
b
in series. The first winding portion
17
a
is wound between the flange portions
14
and
16
of the bobbin
12
, and the second winding portion
17
b
is wound between the flange portions
15
and
16
.
The bobbins
2
and
12
are arranged so that the cylindrical body portions
3
and
13
thereof are parallel to each other. Leg portions
20
b
and
21
b
of the core members
20
and
21
extend in holes
3
a
and
13
a
of the cylindrical body portions
3
and
13
, respectively. The core members
20
and
21
define one closed magnetic circuit with the leading end surfaces of the leg portions
20
b
and
21
abutting against each other inside the holes
3
a
and
13
a.
In the common-mode choke coil
1
having the above-described configuration, since the stray capacitance is substantially proportional to the winding width, when the windings
7
and
17
are divided into the two winding portions
7
a
and
7
b
and the two winding portions
17
a
and
17
b
, respectively, the stray capacitance of one winding portion is half the stray capacitance of the undivided winding.
Since the winding portions
7
a
and
7
b
, or the winding portions
17
and
17
b
are connected in series, the stray capacitance of each of the windings
7
and
17
in the two-section winding common-mode choke coil
1
is one fourth of the stray capacitance of the undivided winding (for example, approximately 4.0 pF).
Another winding structure is a so-called single-layer winding structure in which a winding is wound only in one layer. In this winding structure, the turns are adjacent only in the lateral direction, and a number of stray capacitances produced in the adjacent turns corresponding to the number of turns are connected in series, which can minimize the stray capacitance. For example, the stray capacitance (4.0 pF) in the above-described sectional winding can be reduced to approximately one-sixth or less by the single-layer winding. However, the inductance obtained in this case is low.
A so-called single-layer multiple winding structure is also known in which a plurality of single-layer windings are stacked in parallel. In order to overcome the problem of low inductance in the single-layer winding structure, in this winding structure, the diameter of the wire is decreased, and the number of turns in each layer of the winding is increased, thereby increasing the inductance. Since the direct resistance of the windings is thereby increased, a plurality of stacked layers of windings are connected in parallel. That is, the single-layer multiple winding structure has characteristics similar to those of the single-layer winding structure, and also achieves a relatively high inductance. However, the stray capacitance is higher than in the single-layer winding structure.
Table 1 shows the general differences of the stray capacitance, the direct resistance of the winding, and the inductance among the above-described winding structures when the wire diameter is not changed.
TABLE 1
Stray Capacitance
Single-layer < Single-layer Multiple < Sectional
Direct Resistance
Single-layer Multiple < Single-layer < Sectional
Inductance
Single-layer = Single-layer Multiple < Sectional
In general, the areas in which the windings
7
and
17
of the common-mode choke coil
1
can be wound are limited by, for example, the planar area of the space defined by the inner peripheries of the core members
20
and
21
that define the closed magnetic circuit, the thickness of the bobbins
2
and
12
, and the insulation distance. The known common-mode choke coil
1
is designed so that there is no wasted space, in order to achieve the maximum possible inductance in the limited winding areas. Therefore, only the minimum gaps required for assembly operation and safety standards are formed between the core members
20
and
21
and the bobbins
2
and
12
, or between the core members
20
and
21
and the windings
7
and
17
. Consequently, the stray capacitance produced by the core members
20
and
21
is relatively high. In the common-mode choke coil
1
in which the windings
7
and
17
are wound in a manner that produces less stray capacitance than the multiple winding common-mode choke coil which does not have the center flange porti

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