Coil

Description

This invention relates to a coil that may be used, for example, as a component of a transformer or as a choke.

BACKGROUND OF THE INVENTION

The applicant of the present application filed U.S. patent application Ser. No. 10/006,478 on Dec. 6, 2001, entitled “High-Frequency Large Current Handling Transformer”, which was published on Jun. 13, 2002 under US-2002-0070836-A1. The transformer disclosed in the U.S. application includes coil sheets or planar coil members

1

,

2

,

3

,

4

,

5

and

6

of metal, e.g. copper, as shown in FIG.

1

. The metallic coil sheets

1

,

2

,

3

,

4

,

5

and

6

are formed in a rectangular shape with windows

1

a

,

2

a

,

3

a

,

4

a

,

5

a

and

6

a

in their center portions. One side of each coil sheet is cut to form a slit

1

b

,

2

b

,

3

b

,

4

b

,

5

b

,

6

b

therein. Tabs

1

c

and

1

d

extend outward from the portions facing across the slit

1

b

. Similarly, tabs

2

c

and

2

d

,

3

c

and

3

d

,

4

c

and

4

d

,

5

c

and

5

d

, and

6

c

and

6

d

extend outward from the portions of the respective sheet coils

2

,

3

,

4

,

5

and

6

facing each other across the slits

2

b

,

3

b

,

4

b

,

5

b

and

6

b

. The tabs

1

c

,

2

c

,

3

c

,

4

c

,

5

c

and

6

c

provide winding start terminals, while the tabs

1

d

,

2

d

,

3

d

,

4

d

,

5

d

and

6

d

provide winding end terminals. The coil sheets

1

,

2

and

3

are stacked, with the tabs

1

d

and

2

c

interconnected and with the tabs

2

d

and

3

c

interconnected, to thereby provide a primary winding of the transformer. Similarly, the coil sheets

4

,

5

and

6

are stacked, with the tabs

4

c

,

5

c

and

6

c

interconnected and with the tabs

4

d

,

5

d

and

6

d

interconnected, to thereby provide a secondary winding. Insulating sheets

9

,

10

,

11

and

14

are disposed in such a manner that each coil sheets

1

,

2

and

3

are sandwiched between two of the insulating sheets. An insulating sheet

17

is disposed on the stack of the coil sheets

4

,

5

and

6

so as to sandwich them between the insulating sheets

17

and

14

. The insulating sheets

9

,

10

,

11

,

14

and

17

have center windows

9

a

,

10

a

,

11

a

,

14

a

and

17

a

, respectively. Two core halves of, for example, ferrite,

18

and

19

are used. The core halves

18

and

19

have center legs

18

a

and

19

a

, respectively, with grooves

18

b

and

18

c

, and

19

b

and

19

c

located on opposite sides of the respective legs

18

a

and

19

a

. Outward of the grooves

18

b

and

18

c

are outer legs

18

d

and

18

e

, respectively, and outward of the grooves

19

b

and

19

c

are outer legs

19

d

and

19

e

, respectively. The core halves

18

and

19

are combined in such a manner that the center legs

18

a

and

19

a

can be placed to extend through the center windows

1

a

-

6

a

in the coil sheets

1

-

6

and the center windows

9

a

-

14

a

and

17

a

in the insulating sheets

9

-

14

and

17

.

In manufacturing this transformer, work for stacking the metallic coil sheets and the insulating sheets alternately is necessary, which increases the cost of the transformer. Furthermore, with this arrangement, the metallic coil sheets are exposed to air and, therefore, may be oxidized and rust after long use. In addition, in order to fulfill safety standards for transformers, it must be so arranged that a sufficient creepage distance can be kept even when the insulating sheets

9

,

10

,

11

,

14

and

17

are displaced more or less with respect to is the metallic coil sheets. For that purpose, larger insulating sheets must be used, which makes transformers larger in size.

An object of the present invention is to provide a coil that requires fewer steps in manufacturing it, is hardly oxidized and is small in size.

SUMMARY OF THE INVENTION

A coil according to one embodiment of the present invention includes a coil section having a plurality of metallic coil sheets. The coil sheets are planar and each have a window in the center portion thereof. A slit is formed in each coil sheet, which extends from a location on the periphery of the window through the sheet to the outer periphery of the sheet. Connection terminals are formed on the sheet at locations facing each other across the slit. The coil sheets are stacked, and adjacent coil sheets are electrically connected with each other by the connection terminals. A core is disposed within the windows in the coil sheets. Each of the metallic coil sheets is individually coated completely with an insulating coating before the metallic coil sheets are stacked.

With the above-described arrangement, since each of the metallic coil sheet of the coil is individually pre-coated with an insulating coating, there is no need for placing an insulating sheet between adjacent coil sheets when the metallic coils sheets are stacked, which can reduce the manufacturing steps, which, in turn, can reduce the manufacturing cost. Furthermore, by covering the entire surface of each of the metallic coil sheets with an insulating coating, the metallic coil sheets are hardly oxidized and rusted. In addition, since each of the metallic sheets is individually pre-coated with an insulating coating, there is no need to take care to keep that insulating sheets are not displaced relative to the metallic coil sheets when the metallic coil sheets are stacked. Accordingly, it is not necessary to take such displacement into account when setting a creepage distance, and, therefore, the creepage distance can be set small. Then, the size of transformers can be reduced.

A plurality of coil sections may be used. The core is disposed to extend through the windows in the metallic coil sheets of the coil sections, so that the plural coil sections are inductively coupled with each other. This arrangement provides a transformer which can be manufactured at a low cost and hardly rust, and is small in size.

The insulating coatings may be formed by applying an insulative resin directly over the metallic coil sheet. Alternatively, an insulating film may be bonded to the metallic coil sheet to cover part of or the entirety of the surface of the metallic coil sheet before stacking the metallic coil sheets. The insulating resin may be used as an adhesive to bond the pre-formed insulating film to the metallic coil sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is an exploded perspective view of a prior art transformer.

FIG. 2

is an exploded perspective view of a transformer according to a first embodiment of the present invention.

FIGS. 3

a

,

3

b

,

3

c

and

3

d

illustrate steps for manufacturing a metallic coil sheet useable in the transformer shown in FIG.

2

.

FIG. 4

a

is a plan view of a metallic coil sheet useable in the transformer of

FIG. 2

,

FIG. 4

b

is a cross-sectional view of the metallic coil sheet shown in

FIG. 4

a

along a line

4

b

—

4

b

, and

FIG. 4

c

is a cross-sectional view of the metallic coil sheet of

FIG. 4

a

along a line

4

c

—

4

c.

FIG. 5

a

is a cross-sectional view of a metallic coil sheet useable in the transformer of

FIG. 2

, and

FIG. 5

b

is a cross-sectional view of a metallic coil sheet used in a prior art transformer.

FIG. 6

is an exploded perspective view of a choke manufactured using a coil of the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention may be embodied in a high-frequency large current handling transformer, as shown in FIG.

2

. The transformer includes a plurality, two, for example, of coil sections, or windings

30

and

32

.

The winding

30

includes a plurality, three, for example, of metallic coil sheets

34

,

36

and

38

, which are formed in a rectangular shape and have the same size. The metallic coil sheets

34

,

36

and

38

have windows

34

a

,

36

a

and

38

a

, respectively, in their center areas. The windows

34

a

,

36

a

and

38

a

have the same size. The metallic coil sheets

34

,

36

and

38

are formed of metal, e.g. copper. Each of the coil sheets

34

,

36

and

38

includes a slit

34

b

,

36

b

,

38

b

in one of the four sides around the window. The sides in which the slits are formed are on the same side of the completed transformer, but the locations of the slits

34

b

,

36

b

and

38

b

are offset with respect to each other. On the portions of the coil sheet

34

facing each other across the slit

34

b

, terminals

34

c

and

34

d

are provided. Similarly, terminals

36

c

and

36

d

and terminals

38

c

and

38

d

are provided on the portions of the coil sheets

36

and

38

facing each other across the respective slits

36

b

and

38

b

. The terminals

34

c

,

36

c

and

38

c

provide winding start terminals, and the terminals

34

d

,

36

d

and

38

d

provide winding end terminals. The metallic coil sheets

34

,

36

and

38

are stacked up with the windows

34

a

,

36

a

and

38

a

therein aligned with each other. The locations of the slits

34

b

,

36

b

and

38

are determined such that, when the coil sheets are stacked, the terminals

34

d

and

36

d

are vertically aligned, and the terminals

36

d

and

38

c

are vertically aligned.

The winding

32

includes metallic coil sheets

40

,

42

and

44

configured similarly to the metallic coil sheets

34

,

36

and

38

of the winding

30

. The metallic coil sheets

40

,

42

and

44

have respective windows

40

a

,

42

a

and

44

a

, respective slits

40

b

,

42

b

and

44

b

, respective pairs of terminals

40

c

and

40

d

,

42

c

and

42

d

, and

44

c

and

44

d

. The metallic coil sheets

40

,

42

and

44

, too, are stacked in such a manner that the windows

40

a

,

42

a

and

44

a

therein are vertically aligned. The locations of the slits

40

b

,

42

b

and

44

b

are determined such that the terminals

40

d

and

42

c

can be vertically aligned and the terminals

42

d

and

44

c

can be vertically aligned when the metallic coil sheets

40

,

42

and

44

are stacked.

Each of the metallic coil sheets

34

,

36

,

38

,

40

,

42

and

44

has an insulating coating (

46

) thereon, as represented by the metallic coil sheet

38

shown in detail in

FIGS. 4

a

,

4

b

and

4

c

. The insulating coating

46

covers the entire surface of the metallic coil sheet

38

.

FIG. 4

b

is a cross-sectional view of the metallic coil sheet

38

with the insulating coating shown in

FIG. 4

a

along a line

4

b

—

4

b

, and

FIG. 4

c

is a cross-sectional view along a line

4

c

—

4

c.

The insulating coating

46

is formed of an insulating film and an epoxy resin layer, and is formed in the following manner. First, the metallic coil sheet

38

is formed by punching a copper sheet

50

along broken lines, as shown in

FIG. 3

a

. At this stage, holes

52

and

54

are also formed in the terminals

38

c

and

38

d

, respectively. Next, as shown in

FIG. 3

b

, two insulating films, e.g. polyimide films

56

with an insulating adhesive layer, e.g. an epoxy resin layer

58

, are prepared by applying epoxy resin over one surface of each polyimide film

56

. The polyimide films

56

are rectangular and larger in size than the metallic coil sheet

38

.

When the epoxy resin layers

58

are partly dried, the polyimide films

56

are joined to opposing two major surfaces of the metallic coil sheet

38

, by placing, as shown in

FIG. 3

c

, the epoxy resin layers

58

to contact with the major surfaces of the metallic coil sheet

38

. Thus, the metallic coil sheet

38

is sandwiched. As is seen from

FIG. 3

c

, the terminals

38

c

and

38

d

are not covered with the polyimide films

56

.

Then, as shown in

FIG. 3

d

, downward and upward pressures are applied to the polyimide films

56

joined to the metallic coil sheet

38

, by means of a press (not shown), e.g. a press with silicone rubber pressing surfaces, and the metallic coil sheet

38

and the polyimide films

56

are heated at a temperature between about 150° C. and about 180° C. for a time period of from three (3) hours to five (5) hours, to thereby cure the epoxy resin

58

. After that, unnecessary peripheral and center portions of the polyimide films

56

and epoixy resin layers

58

are punched and removed, which results in the metallic coil sheet

38

with the polyimide films

56

, shown in

FIG. 4

a

. The holes

52

and

54

in the terminals

38

c

and

38

d

are used in positioning the metallic coil sheet

38

for this punching step. The other metallic coil sheets are also provided with an insulating coating in the same manner as described above. It should be noted that the thickness of the polyimide films

56

and epoxy resin layers

58

is exaggerated in

FIGS. 3

a

-

3

d

and

4

a

-

4

c.

The metallic coil sheets

34

,

36

and

38

with the respective insulating coatings formed in the manner described above are stacked in such a manner that the terminal

36

c

is placed on the terminal

34

d

and the terminal

38

c

is placed on the terminal

36

d

, whereby the winding

30

is formed. Similarly, the metallic coil sheets

40

,

42

and

44

with the respective insulating coatings formed in the manner described above are stacked such that the terminal

42

c

is placed on the terminal

40

d

and the terminal

44

c

is placed on the terminal

42

d

, whereby the winding

32

is formed. The terminals

34

d

and

36

c

of the winding

30

are electrically connected together, and also, the terminals

36

d

and

38

c

are electrically connected. Similarly, the terminals

40

d

and

42

c

of the winding

32

are electrically connected together, and the terminals

42

d

and

44

c

are electrically connected together.

The two windings

30

and

32

are stacked in such a manner that the windows

34

a

,

36

a

,

38

a

,

40

a

,

42

a

and

44

a

are vertically aligned, and cores

60

and

62

of, for example, ferrite, are placed to sandwich the vertically stacked windings

30

and

32

. More specifically, the upper core

60

has a center leg

60

a

, two outer legs

60

d

and

60

e

, and grooves

60

b

and

60

c

between the center leg

60

a

and the outer leg

60

d

and between the center leg

60

a

and the outer leg

60

e

, respectively. Similarly, the lower core

62

has a center leg

62

a

, two outer legs

62

d

and

62

e

, and grooves

62

b

and

62

c

between the center leg

62

a

and the outer leg

62

d

and between the center leg

62

a

and the outer leg

62

e

, respectively. The center legs

60

a

and

62

a

are adapted to be placed into the windows

34

a

,

36

a

,

38

a

,

40

a

,

42

a

and

44

a

, and two opposing sides of each metallic coil sheet

34

,

36

,

38

,

40

,

42

and

44

are placed in the respective spaces defined by the grooves

60

b

,

60

c

,

62

b

and

62

c

, when the cores

60

and

62

are placed over the stacked windings

30

and

32

from above and below the stack.

FIG. 5

a

is a cross-sectional view of the metallic coil sheet

38

provided with the insulating coating

46

.

FIG. 5

b

is a cross-sectional view of the prior art metallic coil sheet

2

(

FIG. 1

) which does not have an insulating coating like the coating

46

, but is insulated by means of the insulating sheets

10

and

11

, for example. The metallic coil sheets

38

and

2

have the same size. As is understood from

FIG. 5

b

, the prior art metallic coil sheet

2

requires larger insulating sheets so as to provide a larger creepage distance “a” in order to secure its necessary creepage distance when the position of the coil sheet

2

relative to the insulating sheets

10

and

11

is deviates from the nominal position. In contrast, according to the present invention, as shown in

FIG. 5

a

, since the metallic coil sheet

38

is joined with the insulating coating

46

, the creepage distance “b” can be only what is required and need not be longer than required. Shorter creepage distance can make it possible to downsize the transformer. Furthermore, since the metallic coil sheets are individually covered with the insulating coatings

56

, working to place an insulating sheet between adjacent metallic coil sheets can be eliminated, which reduces the manufacturing cost. In addition, the insulating coatings

56

entirely covering the individual metallic coil sheets

38

can prevent the sheets

38

from rusting.

FIG. 6

shows a coil according to the present invention as used for forming a high-frequency choke. The structure of the high-frequency choke show is same as that of the transformer shown in

FIG. 2

from which the coil

30

is removed. Therefore, the same reference numerals as used in

FIG. 2

are used for equivalent portions, and detailed description of the choke is not given.

In place of the two windings

30

and

32

used for the transformer shown in

FIG. 2

, more windings may be used so that a transformer with one primary winding and a plurality of secondary windings may be formed. In place of polyimide and epoxy, other materials may be used for the insulating films and insulating adhesive.

Claims

1. A coil comprising:a coil section including a plurality of metallic coil sheets, each of said metallic coil sheets being planar, and having a center window and a slit extending from said window to an outer edge of said sheet, said metallic coil sheets each having connection terminals at locations facing each other across said slit, said plurality of metallic coil sheets being stacked, with adjacent ones of said stacked metallic coil sheets electrically connected with each other by means of said connection terminals; and a core disposed in said windows of said stacked metallic coil sheets; wherein each of said metallic coil sheets is individually covered with an insulating coating before said metallic coil sheets are stacked; and each of said insulating coatings is bonded to an associated one of said coil sheets with an insulating adhesive.
2. A transformer comprising a plurality of said coil sections as defined by claim 1, with said core disposed in said windows of said stacked metallic coil sheets of said plurality of coil sections.

Priority Claims (1)

Number	Date	Country	Kind
2002-152117	May 2002	JP

US Referenced Citations (3)

Number	Name	Date	Kind
5559487	Butcher et al.	Sep 1996	A
6087922	Smith	Jul 2000	A
6211767	Jitaru	Apr 2001	B1

Foreign Referenced Citations (4)

Number	Date	Country
0 608 127	Jul 1994	EP
0 767 473	Apr 1997	EP
2 369 251	May 2002	GB
2 373 640	Sep 2002	GB

Non-Patent Literature Citations (1)

Entry
Yamanobe et al [US2003/005276A1], Coil for Electrical and Electronic Equipment as Well as Process for Production Thereof, Mar. 2003.

Information

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Date Filed

Date Issued

Inventors

Original Assignees

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CPC

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