Inductor devices – Coil or coil turn supports or spacers – Printed circuit-type coil
Reexamination Certificate
1998-05-11
2002-03-12
Mai, Anh (Department: 2832)
Inductor devices
Coil or coil turn supports or spacers
Printed circuit-type coil
C336S232000, C336S223000
Reexamination Certificate
active
06356181
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to laminated common-mode choke coils and, more particularly, to a structure of a laminated common-mode choke coil in which the absolute value of normal-mode impedance can be reduced.
2. Description of the Related Art
As one type of common-mode choke coil, a laminated common-mode choke coil is available having a structure in which thin metallic patterns in the form of a coil are interposed between magnetic substrates. Two examples of this type of choke coil are disclosed in, for example, Japanese Unexamined Patent Publication No. 4-364709. The choke coil disclosed in this publication is constructed to have a plurality of layers in the following manner: a primary coil conductor and a secondary coil conductor are laminated through an insulating layer in the thickness direction according to a thin-film forming process, such as photolithography. In this laminated structure, since the insulating layer is formed according to a thin-film forming process, the thickness of the resulting layer can be reduced. This makes it possible to decrease the distance between the primary coil conductor and the secondary coil conductor opposedly facing each other across the insulating layer. Thus, a high coupling coefficient can be obtained, and a high impedance in response to common-mode noise can be achieved. As a consequence, a laminated common-mode choke coil exhibiting excellent performance in eliminating common-mode noise can be obtained.
However, the choke coil disclosed and shown in
FIG. 5
in the above publication disadvantageously changes the waveform of normal-mode signals. This arises from a disturbance in magnetic balance between the primary and secondary coil conductors caused by a difference in the number of turns between the conductors.
In order to solve this problem, in the laminated common-mode choke coil disclosed and illustrated in
FIG. 1
in the above publication, the configuration of the coil is adjusted to have the same number of turns between the primary and secondary coil conductors. The outer appearance of such a choke coil is shown in FIG.
5
. In this choke coil generally indicated by
50
, the number of turns between the primary and secondary coil conductors is made equal so that external electrodes
51
and
52
used as input/output electrodes for the primary coil conductor are diagonally disposed on the chip, and so that external electrodes
53
and
54
serving as input/output electrodes for the secondary coil conductor are also diagonally placed on the chip. With this arrangement, however, when such a coil is mounted for use, it is necessary that wiring to be connected to the primary coil conductor and to the secondary coil conductor be diagonally laid, thereby resulting in a complicated wiring pattern for mounting the coil.
To further overcome the above drawback, the following type of choke coil has been invented: a laminated common-mode choke coil having the same number of turns for the primary and secondary coil electrodes in which the external electrodes for the primary coil electrode are aligned on the same side of the chip and the external electrodes for the secondary coil electrode are also aligned on the opposing side of the chip.
FIG. 6
is an exploded perspective view of an example of known laminated common-mode choke coils having the above-described construction;
FIG. 7
is a plan view illustrating the pattern configuration of the primary and secondary coil electrodes; and
FIG. 8
is a cross sectional view taken along line Y—Y of FIG.
6
.
Referring to
FIGS. 6 through 8
, a laminated common-mode choke coil generally designated by
10
is constructed by laminating a plurality of insulating layers
13
A,
13
and
15
between a pair of magnetic substrates
11
and
17
. Formed between the insulating layers
13
A and
13
is a primary coil electrode
12
a
formed of a thin metallic film. The primary coil electrode
12
a
is connected at one end to an external electrode
3
a
and at the other end to a node
22
a
between the electrode
12
a
and first through-hole electrodes
23
a
and
25
a
. Also, a secondary coil electrode
14
b
is disposed between the two insulating layers
13
and
15
. The electrode
14
b
is connected at one end to an external electrode
2
b
and at the other end to a node
24
b
between the electrode
14
b
and a second through-hole electrode
25
b.
Further, formed between the insulating layer
15
and magnetic substrate
17
are a lead electrode
16
a
for the primary coil electrode
12
a
and a lead electrode
16
b
for the secondary coil electrode
14
b
. The primary-coil lead electrode
16
a
is connected between an external electrode
4
a
and a node
26
a
between the electrode
16
a
and the first through-hole electrodes
23
a
and
25
a
, while the secondary-coil lead electrode
16
b
is connected between an external electrode
5
b
and a node
26
b
between the electrode
16
b
and the second through-hole electrode
25
b.
In this common-mode choke coil
10
, the number of turns of the primary coil electrode
12
a
and that of the secondary coil electrode
14
b
are set substantially equal to each other, and more particularly, the former is set to approximately 2T (turns), while the latter is set to 2·1/8T. Additionally, the external electrodes
3
a
and
4
a
for the primary coil electrode
12
a
are disposed to project from the same side of the rectangular-prism-shaped chip, and the external electrodes
2
b
and
5
b
for the secondary coil electrode
14
b
are also placed to project from the opposite side of the chip.
As described above, in the above type of choke coil, in order to keep the waveform of normal-mode signals from changing, it is important to maintain a magnetic balance between the primary and secondary coil electrodes. Accordingly, in the choke coil illustrated in
FIGS. 6 through 8
, the number of turns of the primary coil electrode
12
a
is set equal to that of the secondary coil electrode
14
b.
If the coil pattern is arranged so that the number of turns of the primary coil electrode
12
a
can be equal to that of the secondary coil electrode
14
b
, as illustrated in
FIG. 7
, there are disadvantageously created portions in which the primary and secondary coil electrodes
12
a
and
14
b
are not overlapped in the vicinity of the through-hole electrodes
23
a
and
25
b
. Magnetic coupling force between the coil electrodes
12
a
and
14
b
is weaker in such non-overlapping portions, thereby increasing the impedance in relation to normal-mode signals.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a laminated common-mode choke coil that can reduce the impedance in the normal mode by improving the magnetic coupling force between a pair of coil electrodes.
In order to achieve the above object, according to the present invention, there is provided a laminated common-mode choke coil comprising: a laminated structure having a plurality of layers including a pair of magnetic substrates and an insulating layer interposed between the pair of magnetic substrates; primary (first) and secondary (second) coil electrodes disposed on the different layers of the laminated structure; first through fourth external electrodes formed at the edges of the laminated structure, the first external electrode being connected to one end of the primary coil electrode, and the third external electrode being connected to one end of the secondary coil electrode; and first and second through-hole electrodes through which the second external electrode is connected to the other end of the primary coil electrode and the fourth external electrode is connected to the other end of the secondary coil electrode, wherein said primary and secondary coil electrodes are spiral in shape, and said primary coil electrode extending from a connecting portion with said first external electrode and overlapping with said secondary coil electrode except at a position between said first and second through-hole elec
Burns Doane , Swecker, Mathis LLP
Mai Anh
Murata Manufacturing Co. Ltd.
LandOfFree
Laminated common-mode choke coil does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Laminated common-mode choke coil, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laminated common-mode choke coil will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2877578