Common mode choke coil

Details Common mode choke coil Common mode choke coil

2001-12-27

2004-02-10

Mai, Anh (Department: 2832)

Inductor devices

Coils of special configuration

Toroidal

C336S208000, C336S198000, C336S192000

Reexamination Certificate

active

06690257

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a common mode choke coil. More specifically, the present invention relates to a structure of a common mode choke coil capable of providing improved characteristics at high frequencies.
2. Description of the Related Art
An alternating current (AC) power supply line constitutes a route through which external noises flow into an electronic apparatus or noises generated inside an electronic apparatus flow out. A choke coil is therefore inserted in series with the AC power supply line for cutting off the noises. There are two types of noises; a normal mode noise generated between lines and a common mode noise generated in both lines relating to the ground, and in general the common mode noise causes problems. It is required that a common mode choke coil for removing the common mode noise have a large inductance for the common mode noise and that magnetic fluxes cancel out each other for the AC voltage of a commercial power supply.
When a toroidal core is used as a magnetic core of the common mode choke coil, bifilar winding in which two wires are wound together generates little leakage flux. However, since insulation between the wires must be considered when a high voltage is applied therebetween and since also line capacitance between the wires must be considered in order to obtain preferable characteristics at high frequencies, the two wires must be wound apart from each other prohibiting the use of the bifilar winding. Accordingly, in general, one wire is wound around one half of the toroidal core, and another wire is wound around the other half thereof such that the both wires are wound equally so that respective magnetic fluxes cancel out each other relative to a normal mode current.
FIGS. 9 and 10
show conventional common mode choke coils.
FIG. 9
is a perspective view of a conventional toroidal common mode choke coil of vertical type.
FIG. 10
is a perspective view of a conventional toroidal common mode choke coil of horizontal type. In
FIGS. 9 and 10
, a plastic insulating partition
90
is arranged across a center opening of a plastic insulating case (hereinafter, referred to as a bobbin)
95
housing a toroidal core, and two coils
93
and
94
are wound in the same direction so as to sandwich the plastic insulating partition
90
. The magnetic core is mounted vertically on a plastic base
91
in
FIG. 9
, and horizontally in FIG.
10
. The two coils lead out from respective corresponding terminals
92
a
and
92
b,
and
92
c
and
92
d
(
92
d
not shown) via respective corresponding through-holes
93
b
and
94
b
formed in the plastic base
91
and two other holes (not shown) formed in symmetric relation thereto in the base
91
. Terminations of the coils
93
and
94
are connected to the respective corresponding terminals
92
a
and
92
b,
and
92
c
and
92
d.
To be specific, one termination of one coil wound around one half of the bobbin
95
is connected to the terminal
92
a
and the other termination thereof is connected to the terminal
92
b
. Similarly, one termination of the other coil wound around the other half of the bobbin
95
is connected to the terminal
92
d
(not shown) and the other termination thereof is connected to the terminal
92
c.
The coils are wound around the bobbin
95
which is shown in an exploded view in FIG.
11
. More specifically, the bobbin
95
is configured in such a manner that a toroidal core
113
is housed in a cylinder
114
composed of an insulating material and having an opening
112
at the center thereof and a cover
110
is fitted thereto. One of the two coils is wound around one half of the bobbin
95
having a configuration described above and the other coil is wound around the other half thereof such that the both coils are wound equally so that respective magnetic fluxes cancel out each other relative to a normal mode current.
Typically, in the bobbin
95
, a partition
90
is inserted separating the both coils in order to improve the withstand voltage therebetween. The cylinder
114
and the cover
110
have respective fitting mechanisms
115
, and
115
′ and
115
″ for fitting the partition
90
thereto.
The vertical type toroidal common mode choke coil shown in
FIG. 9
, which can save an installation area, is generally used in a circuit board,.
FIG. 12
is a sectional view for explaining problems in the vertical type toroidal common mode choke coil. In
FIG. 12
, the bobbin
95
is mounted on the base
91
and the coil
93
is wound with a regular interval around one half of the bobbin
95
. One termination of the coil
93
is connected to the terminal
92
b,
and the other termination is connected to the terminal
92
a.
Parts
12
A and
12
B of a toroidal core
12
are shown at a section of the bobbin
95
. The coil
93
is shown only at its starting and finishing ends.
In such a configuration, the coil
93
starting from the terminal
92
b
provided on the base
91
located under the bobbin
95
, that is, toward the part
12
B of the core
12
, is wound all the way around the half of the bobbin
95
. The coil
93
then passes diagonally through the center opening of the bobbin
95
from upper part of the bobbin
95
, that is, the part
12
A, toward the terminal
92
a
provided on the base
91
, when travelling from one end face of the bobbin
95
to the other end face thereof, and terminates there to be connected to the terminal
92
a.
In the aforesaid case, a starting end part A of the coil
93
is disposed in contact with or close to the bobbin
95
, and a finishing end part C is disposed in contact with or close to a portion of the bobbin
95
where the coil
93
starts (hereinafter, referred to as beginning of the coil) in order to prevent both starting and finishing end parts of the coil
93
from getting damaged by a vibration or contact. However, in such an arrangement, the following problems arise. Referring to
FIG. 13
, the problems will be described.
FIG. 13
is an electrical equivalent circuit of the arrangement of FIG.
12
. The coil
93
includes an input terminal XA and an output terminal XB, and the coil
94
includes an input terminal YA and an output terminal YB. Both the coils
93
and
94
are wound around the toroidal core
12
, and have inductances ZLX and ZLY, respectively. The stray capacitance (hereinafter, referred to as a capacitance) of each part will be defined as follows.
Reference symbol CL
1
denotes a capacitance between the inputs of the coils
93
and
94
. Reference symbol CL
2
denotes a capacitance between the outputs of the coils
93
and
94
. Reference symbols C
1
X and C
2
X denote capacitances generated due to the finishing end part C of the coil
93
disposed close to or in contact with a beginning of the coil
93
, as shown in FIG.
12
. Similarly, reference symbols C
1
Y and C
2
Y denote capacitances generated due to the finishing end part C of the coil
94
disposed close to or in contact with a beginning of the coil
94
.
Other symbols CS
1
, CS
2
, CS
3
, CS
4
, CS
5
, CS
6
and CS
7
denote line capacitances between the coils.
The common mode choke coil is inserted in series with an AC power supply line in order to cut off a noise. More specifically, the terminals XA and YA are used as input terminals and the terminals XB and YB are used as output terminals. When the terminals XA and YA are connected to each other to form a terminal XYA and the terminals XB and YB are connected to each other to form a terminal XYB, it is preferred that an impedance ZAB between the both connection terminals be large with respect to the common mode noise.
As is evident from
FIG. 13
, the impedance ZAB between the both connection terminals is not influenced by the capacitances CL
1
and CL
2
, and becomes an impedance ZAB of the circuit, which is connected in parallel with the inductance ZLX of the coil
93
and the inductance ZLY of the coil
94
, the capacitances C
1
X, C
2
X, C
1
Y and C
2
Y, and the capacitances CS
1
, CS
2
, CS
3
, CS
4
, CS
5
, CS
6
and CS
7
. In su

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