Coil device

A coil device includes first and second coils and a package for sealing the first and second coil. The first coil has a first winding including a first conductor wire wound about a first winding axis, and first and second ends which are both ends of the first conductor wire. The second coil has a second winding including a second conductor wire wound about a second winding axis, and third and fourth ends which are both ends of the second conductor wire. The second winding axis is arranged with the first winding axis. The second end of the first coil is connected with the third end of the second coil. The first end of the first coil and the fourth end of the second coil are adapted to be connected to an outside of the package. This coil device reduces magnetic flux leakage to outside of the package.

TECHNICAL FIELD

The present invention relates to a coil device for use in various electrical circuits.

BACKGROUND ART

FIG. 16is a perspective view of conventional coil device1.FIGS. 17 and 18are sectional views of coil device1. Coil device1includes winding3, package2A for sealing winding3, and external terminals4A electrically connected to winding3. Respective portions of external terminals4A are exposed to the outside of package2A.

In coil device1, upon having a current supplied, winding3generates magnetic flux5, which may leak outside package2A, i.e., coil device1while being emitted from winding3. In the case that coil device1is mounted with other devices highly-densely, effects of coil device1on the devices are considered. Patent Documents 1 and 2 disclose conventional coil devices preventing the leakage of magnetic flux.

Package2A may be made of magnetic material to reduce the effects. In order to increase the reduction of the leakage of the magnetic flux with the magnetic material, package2A is generally made of magnetic material having a high magnetic permeability, has a large size, or includes shields6A having a magnetic shielding effect.

These approaches, however, have the following problems. Package2A made of the magnetic material having the high magnetic permeability can hardly be molded, thus having its cost increase. More specifically, package2A can hardly be molded with a high-pressure pressing machine, which increases the density of the magnetic material of package2A. In addition, the magnetic material having the high magnetic permeability containing amorphous magnetic powder or Ni is expensive. Package2A having a large size increases the size of coil device1, and accordingly causes other devices to be arranged less densely. Further, shields6A attached to package2A causes energy loss due to eddy currents generated in shields6A and increases material cost.

SUMMARY OF THE INVENTION

A coil device includes first and second coils and a package for sealing the first and second coil. The first coil has a first winding including a first conductor wire wound about a first winding axis, and first and second ends which are both ends of the first conductor wire. The second coil has a second winding including a second conductor wire wound about a second winding axis, and third and fourth ends which are both ends of the second conductor wire. The second winding axis is arranged with the first winding axis. The second end of the first coil is connected with the third end of the second coil. The first end of the first coil and the fourth end of the second coil are adapted to be connected to an outside of the package.

This coil device reduces magnetic flux leakage to outside of the package.

REFERENCE NUMERALS

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1is a perspective view of coil device7according to Exemplary Embodiment1of the present invention. Coil device7includes cylindrical solenoid coils12and13and package14for sealing coils12and13. Coil12includes winding8having conductor wire8A helically wound about winding axis17, and ends10A and10B, both ends of conductor wire8A. Coil13includes winding9having conductor wire9A helically wound about winding axis18, and ends11A and11B, both ends of conductor wire9A. Ends10A and10B of coils12and13are connected to external terminals15and16, respectively, and are exposed to an outside of package14. Ends10B and11B of coils12and13are connected to each other inside package14. Windings8and9are adjacently arranged in predetermined direction17A such that coils12and13, i.e., winding axes17and18, are substantially parallel to each other. More specifically, winding axes17and18are arranged in direction17A, and hence, coils12and13(windings8and9) are arranged in direction17A. Package14is made of magnetic material. External terminal15includes fixed portion15A and connecting portion15B. Fixed portion15A is embedded in package14so as to fix external terminal15to package14. Connecting portion15B is exposed from package14to be adapted to be connected to an outside of coil device7(package14). External terminal16includes fixed portion16A and connecting portion16B. Fixed portion16A is embedded in package14so as to fix external terminal16to package14. Connecting portion16B is exposed from package14and is adapted to be connected to an outside of coil device7(package14). Thus, ends10A and10B of coils12and13are adapted to be connected to the outside of package14.

FIG. 2is a sectional view of coil device7at line2-2shown inFIG. 1for illustrating a cross section of coil device7on a plane including winding axes17and18. As shown inFIG. 2, windings8and9are adjacently arranged so that winding axes17and18are parallel to each other. Package14includes portion14B located in winding8, portion14D located in winding9, portion14C located between windings8and9, portion14A located opposite to portion14C with respect to winding8, and portion14E located opposite to portion14C with respect to winding9. In other words, portions14A and14E are located outside windings8and9. Winding8generates magnetic flux M8in winding8. Winding9generates magnetic flux M9in winding9. Magnetic fluxes M8and M9flow in directions opposite to each other. Magnetic flux M8flows out of winding8and is divided into magnetic fluxes M81and M82. Magnetic flux M81flows from winding8into winding9, whereas magnetic flux M82flows through portion14A of package14. Magnetic flux M81is a most part of magnetic flux M8and is larger than magnetic flux M82. Magnetic flux M9flowing out of winding9is divided into magnetic fluxes M91and M92. Magnetic flux M91flows from winding9into winding8, whereas magnetic flux M92flows through portion14E of package14. Magnetic flux M91is a most part of magnetic flux M9and is larger than magnetic flux M92. In portion14C of package14, the magnetic fluxes generated by windings8and9offset each other, thus producing substantially no magnetic flux. Coils12and13are connected to each other, and conductor wires8A and9A are wound so that magnetic fluxes M81and M91flow in a loop shape through windings8and9. This arrangement allows portions14B and14C of package14to substantially function as a toroidal core so as to form an inner-core magnetic circuit, thereby increasing magnetic efficiency of coil device7.

Portions14A and14E of package14having magnetic fluxes M82and M92flowing therethrough prevent magnetic flux from leaking to an outside of package14, and also maintain mechanical strength of package14.

As shown inFIG. 1, fixed portions15A and16A of external terminals15and16are located in portions14A and14E of package14which are outside windings8and9. Magnetic fluxes M81and M91which are the most parts of the magnetic fluxes flow in the loop, and package14approximates a toroidal core. This structure prevent comparatively large magnetic fluxes M81and M91from crossing fixed portions15A and16A, hence preventing the sizes or shapes of fixed portions15A and16A from affecting magnetic fluxes M81and M91. This enables external terminals15and16to be securely fixed to package14, thereby improving a mounting reliability of coil device7.

Coils12and13(windings8and9) are symmetrical with respect to center line19A of package14. Canter line19A extends between windings8and9substantially parallel to winding axes17and18. Windings8and9are symmetrical with respect to a plane located between windings8and9. This structure balances magnetic fluxes M81and M91, and hence, balances a magnetroresistance between windings8and9in package14, thereby preventing magnetic flux from leaking locally. Coils12and13(windings8and9) are located at the center of package14in the direction along center line19A. This allows magnetic fluxes M81and M91to flow through the most efficient area having a low magnetroresistance, thereby reducing magnetic flux leakage and reducing a direct-current (DC) resistance.

Winding axes17and18may not be necessarily exactly parallel to each other, but may be substantially parallel to each other geometrically to increase magnetic efficiency.

FIG. 3is a perspective view of coil device57according to Exemplary Embodiment 2.FIG. 4is a sectional view of coil device57at line4-4shown inFIG. 3. InFIGS. 3 and 4, components identical to those of coil device7according Embodiment 1 shown inFIGS. 1 and 2are denoted by the same reference numerals, and their description will be omitted. Coil device57includes coils112and113having windings20and21instead of coils12and13of coil device7shown inFIG. 1. Windings20and21are adjacently arranged so that winding axes17and18are parallel to each other. In coil device7according to Embodiment 1 shown inFIG. 1, coils12and13are common cylindrical solenoid coils and have circular cross sections in a direction perpendicular to winding axes17and18of coils12and13(windings8and9). On the other hand, as shown inFIGS. 3 and 4, winding20has a partial circular cross section perpendicular to winding axis17. The partial circular shape is formed of linear portion22and arcuate portion24which is an outer periphery of winding20. Winding21has a partial circular cross section perpendicular to winding axis18. The partial circular shape is formed of linear portion23and arcuate portion25which is an outer periphery of winding21. Arcuate portions24and25are located outside linear portions22and23. Windings20and21are sealed with package14.FIG. 4shows cross sections of windings20and21in a direction perpendicular to winding axes17and18. Windings20and21are symmetrical to each other with respect to center line19A of package14. Center line19A extends between windings20and21and in parallel to winding axes17and18. Windings20and21are symmetrical to each other with respect to center line19B of package14. Center line19B extends between windings20and21and perpendicularly to winding axes17and18. Linear portions22and23face each other across portion14C located between windings20and21of package14. This structure allows the magnetic fluxes generate by windings20and21to flow along a magnetic circuit having a short flux path. The partial circular shape of windings20and21provide windings20and21with have large cross sectional areas. This structure provides coil device57with a large inductance to an alternating-current (AC) current, a small DC resistance, and prevents the magnetic flux from leaking.

As shown inFIG. 4, package14includes side portions26which are located in directions in which linear portions22and23of windings20and21extend, and four corners27. Although side portions26are thin, four corners27have large cross sectional areas, accordingly providing package14with large strength. Package14may be formed by pressure-molding composite magnetic material made of magnetic material and resin. In this case, in spite of thin side portions26, the large cross sectional areas at corners27prevent package14from having cracks produced due to elastic deformation of windings20and21made of conductive material, such as metal.

Windings20and21have the partial circular cross sections consisting of linear portions22and23and arcuate portions24and25, however, may have other shapes.FIGS. 5A to 5Dshow sectional views of other windings20A to20D and21A to21D of coil device57according to Embodiment 2. InFIGS. 5A to 5D, components identical to those of the device shown inFIG. 4are denoted by the same reference numerals, and their description will be omitted. Windings20A to20D and21A to21D are sealed with package14.

As shown inFIG. 5A, winding20A has a partial circular cross section perpendicular to winding axis17. The cross section is formed of linear portion22A and arcuate portion24A. Winding21A has a partial circular cross section perpendicular to winding axis18. The cross section is formed of linear portion23A and arcuate portion25A. Linear portions22A and23A are located outside arcuate portions24A and25A. Arcuate portions24A and25A face each other across portion14C of package14located between windings20A and21A.

As shown inFIG. 5B, winding20B has a rectangular cross section perpendicular to winding axis17. The cross section is formed of long sides22B and short sides24B. Winding21B has a rectangular cross section perpendicular to winding axis18. The cross section is formed of long sides23B and short sides25B. Long sides22B and23B are longer than short sides24B and25B. Long sides22B and24B face each other across portion14C of package14located between windings20B and21B. Long sides22B and23B are parallel to each other. More specifically, the cross sections of windings20B and21B in the direction perpendicular to winding axes17and18have longitudinal directions120B and121B parallel to long sides22B and23B, respectively. Longitudinal directions120B and121B are parallel to each other.

As shown inFIG. 5C, winding20C has a rhombic cross section perpendicular to winding axis17. This cross section has diagonals22C and24C. Winding21C has a rhombic cross section perpendicular to winding axis18. This cross section has diagonals23C and25C. Diagonals22C and23C are longer than diagonals24C and25C, and are parallel to each other. More specifically, the cross sections of windings20C and21C in the direction perpendicular to winding axes17and18have diagonals22C and23C parallel to longitudinal directions120C and121C which are parallel to each other.

As shown inFIG. 5D, winding20D has an oval cross section perpendicular to winding axis17. This cross section is formed of linear portions22D and arcuate portions24D. Winding21D has an oval cross section perpendicular to winding axis18. This cross section is formed of linear portions23D and arcuate portions25D. Linear portions22D and23D face each other across portion14C of package14located between windings20D and21D. Linear portions22D and23D are parallel to each other. More specifically, the cross sections of windings20D and21D in the direction perpendicular to winding axes17and18have linear portions22D and24D which are parallel to longitudinal directions120D and121D which are parallel to each other.

Samples of Examples 1 to 5 of coil device57according to Embodiment 2 were. The sample of Example 1 includes windings20and21shown inFIG. 4. The sample of Example 2 includes windings20A and21A shown inFIG. 5A. The sample of Example 3 includes windings20B and21B shown inFIG. 5B. The sample of Example 4 includes windings20C and21C shown inFIG. 5C. The sample of Example 5 includes windings20D and21D shown inFIG. 5D. A sample of Comparative Example of conventional coil device1shown inFIGS. 16 to 18was produced. As shown inFIGS. 1,3, and16, packages2A and14had substantially rectangular parallelepiped shapes.FIG. 6is a sectional view of coil device57at line6-6shown inFIG. 3for illustrating the cross section of coil device57on a plane including winding axes17and18.

Package14of Examples 1 to 5 has upper surface30, lower surface32, and side surfaces34A and34B. Upper surface30is perpendicular to winding axes17and18and faces upper end29of each of windings20,20A to20D,21, and21A to21D. Lower surface32is perpendicular to winding axes17and18and faces lower end31of each of windings20,20A to20D,21, and21A to21D. Side surfaces34A and34B are opposite to each other and are perpendicular to direction17A in which winding axes17and18are arranged. Side surface34A faces each of windings20and20A to20D. Side surface34B faces each of windings21and21A to21D. Each of coil devices1and57(packages2A and14) has a volume of about 1900 mm3, and an inductance of about 7.7 μH. A center width LM, a predetermined distance between windings20and21, between windings20A and21A, between windings20B and21B, between windings20C and21C, and between windings20D and21D was 1.0 mm. A top width LH, a predetermined distance between upper surface30and upper end of each of windings20,20A to20D,21, and21A to21D was 3.4 mm. A bottom width LB, a predetermined distance between lower surface32and lower end31of each of windings20,20A to20D,21, and21A to21D was 3.4 mm. An outer width LE, a predetermined distance between side surface34A and each of windings20and20A to20D was 1.8 mm. An outer width LF, a predetermined distance between side surface34B and each of windings21and21A to21D was 1.8 mm. Similarly, in the sample of Comparative Example of conventional coil device1shown inFIG. 17, top width LH was 3.4 mm, bottom width LB was 3.4 mm, outer widths LE and LF were 1.8 mm, as shown inFIG. 18. A current of11A having a frequency of 100 kHz was supplied to the samples of Examples 1 to 5 and Comparative Example so as to measure leakage magnetic flux densities at positions P1to P4. Positions P1, P2, P3, and P4were located away by a distance of 1 mm from surfaces30,32,34A, and34B of package14, respectively. Positions P1and P2were located on center line19A, and positions P3and P4were located on a straight line connecting upper end29of winding20(20A to20D) and upper end29of winding21(21A to21D).FIG. 7shows measured leakage magnetic flux densities of the samples of Examples 1 to 5 and Comparative Example.

As shown inFIG. 7, coil device57of Examples 1 to 5 in which winding axes17and18are parallel to each other and coils12,13,112, and113sealed by package14made of magnetic body forms a inner-core magnetic circuit reduces magnetic flux leaking to an outside of package14significantly more than coil device1of Comparative Example.

Example 1 shown inFIG. 4has a smaller leakage magnetic flux than Examples 2 to 5 shown inFIGS. 5A to 5D. More specifically, leakage magnetic flux can be reduced by arranging windings20and21such that linear portions22and23of windings20and21face each other and that arcuate portions24and25are located outside linear portions22and23.

Linear portions22and23shown inFIG. 4may not be necessarily exactly linear, but may be substantially linear to sufficiently reduce the leakage magnetic flux.

Arcuate portions24and25located outside linear portions22and23as the outer peripheries of windings20and21may not necessarily have the exactly arcuate-shapes. A similar effect can be obtained by decreasing the region surrounded by windings20and21as the distance from linear portions22and23toward the outer surface of package14decreases.

The top width LH and the bottom width LB are preferably equal to each other. This arrangement allows magnetic fluxes M81and M91to flow efficiently in a loop in package14shown inFIG. 2.

As shown inFIG. 3, windings20and21have ends10A and10B connected to external terminals15and16and led out to the outside of package14, respectively. Ends10A and10B extend substantially linearly in a direction in which linear portions22and23extend. This arrangement reduces effects of ends10A and10B on the magnetic flux flowing in windings20and21. As a result, coil device57has a low leakage magnetic flux, and has inductances of windings20and21with a small loss.

Other samples of coil device57ofFIG. 3having windings20and21and various sizes of package14were produced.

Examples 6 to 8 commonly have top width LH of 3.4 mm, bottom width LB of 3.4 mm, and outer widths LE and LF of 1.8 mm. Examples 6, 7, and 8 have center widths LM of 0.1 mm, 1 mm, and 3 mm, respectively. A current of11A having a frequency of 100 kHz was supplied to the samples of Examples 6 to 8 so as to measure leakage magnetic flux densities at positions P1to P4shown inFIG. 6.FIG. 8shows the leakage magnetic flux densities of the samples Examples 6 to 8 and Comparative Example.

Examples 9 to 12 commonly have top width LH of 3.4 mm, bottom width LB of 3.4 mm, and center width LM of 1.0 mm. Examples 9, 10, 11, and 12 have outer widths LE and LF of 1 mm, 1.8 mm, 2.8 mm, and 3.7 mm, respectively. A current of11A having a frequency of 100 kHz was supplied to the samples of Examples 9 to 12 so as to measure leakage magnetic flux densities at positions P1to P4shown inFIG. 6.FIG. 9shows the leakage magnetic flux densities of the samples of Examples 9 to 12 and Comparative Example.

Examples 13 to 17 commonly have center width LM of 1.0 mm and outer widths LE and LF of 1.8 mm. Examples 13, 14, 15, 16, and 17 have top width LH of 1 mm, 2 mm, 3.4 mm, 4 mm, and 5 mm and bottom width LB of 1 mm, 2 mm, 3.4 mm, 4 mm, and 5 mm, respectively. A current of1A having a frequency of 100 kHz was supplied to the samples of Examples 13 to 17 so as to measure leakage magnetic flux densities at positions P1to P4shown inFIG. 6.FIG. 10shows the leakage magnetic flux densities of Examples 13 to 17 and Comparative Example.

Examples 6 to 8 shown inFIG. 8which are different only in center width LM out of top width LH, bottom width LB, center width LM, and outer widths LE and LF are not very different from each other in the leakage magnetic field density. Examples 9 to 12 shown inFIG. 9which are different only in outer widths LE and LF out of top width LH, bottom width LB, center width LM, and outer widths LE and LF are not very different from each other in the leakage magnetic field density. Examples 13 to 17 which are different only in top width LH and bottom width LB out of top width, bottom width LB, center width LM, and outer widths LE and LF are very different from each other in the leakage magnetic field density. Thus, large top width LH and large bottom width LB reduce the leakage magnetic flux density.

As described above, top width LH and bottom width LB are larger than outer widths LE and LF and center width LM to significantly reduce the leakage magnetic flux density. In particular, top width LH and bottom width LB are twice larger than outer widths LE and LF and center width LM to significantly reduce the leakage magnetic flux density.

In the above-mentioned Examples, as shown inFIG. 1, ends10A and10B of coils12and13are electrically connected to external terminals15and16provided on package14, respectively. Alternatively, ends10A and10B of coils12and13may extend to the outside of package14so as to function as external terminals instead of external terminals15and16. This structure eliminates the joint between end10A and external terminal15and the joint between end10B and external terminal16, thereby improving joint reliability.

External terminals15and16fixed to package14can be arranged more arbitrarily since coil devices7and57according to Embodiments 1 and 2 have low leakage magnetic flux densities. That is, magnetic flux emitted from the surface of package14to the outside is suppressed. Therefore, even if external terminals15and16are made of conductive material which shielding magnetic flux, fixed portions15A and16A embedded in package14are prevented from shielding magnetic flux flowing in windings8,9,20,20A to20D,21, and21A to21D. Thus, regardless of the locations of external terminals15and16, coils12,13,112, and113having windings8,9,20,20A to20D,21, and21A to21D can provide stable inductance.

Fixed portions15A and16A of external terminals15and16do not reach inner peripheries of windings8,9,20,20A to20D,21, and21A to21D. In the case that fixed portions15A and16A (external terminals15and16) are made of conductive material which shields magnetic flux, magnetic fluxes M82and M92shown inFIG. 2can be reduce by changing the sizes of fixed portions15A and16A embedded in package14, thereby controlling the magnetroresistance of fixed portions15A and16A. This structure allows the magnetic flux flowing in coil device7to approximate the magnetic flux flowing in the internal magnet-type magnetic circuit forming a loop of magnetic fluxes M81and M91generated by coils12and13. As a result, package14made of magnetic material can function as a toroidal core having a high magnetic efficiency. Magnetic fluxes M82and M92flow through portions14A and14E of package14outside coils12and13. Package14prevents small magnetic fluxes M82and M92from leaking to an outside, thereby reducing leakage magnetic field.

In coil device7(57) according to Embodiment 1 shown inFIG. 1, end10B of coil12(112) and end11B of coil13(113) are connected to each other.

Conductor wire8A of coil12(112) and conductor wire9A of coil13(113) may be made of a single conductor wire. In this case, coil12(112) and coil13(113) may be formed by folding the solenoid coil at the center so as to face the windings of both sides. This structure eliminates the joint between coil12(112) and coil13(113), thereby improving reliability of coil device7(57).

In this case, coil12(112) and coil13(113) have substantially the same shape and be arranged symmetrically to each other with respect to center line19A by forming the solenoid coil to a uniform shape. This structure allows magnetic flux M81generated by coil12(112) and magnetic flux M91generated by coil13(113) to have the same magnitude and to flow in directions opposite to each other, thereby reducing magnetic flux leaking from package14.

In the case that coils12and13(112and113) are formed by folding the single solenoid coil, and the solenoid coil which is folded is accommodated in package14, so that the folded coil provides package14with a spring back force. The spring back force produces the largest moment at four corners27in package14. Package14has large cross sectional areas at four corners27, hence dispersing the moment. Thus, package14maintains its strength to reduce cracks, thereby preventing magnetic property from deteriorating.

Alternatively, ends10B and11B of coils12(112) and13(113) may be connected to each other outside package14. In this case, the connection among ends10A,10B,11A, and11B of coils12and13(112and113) can be changed. This structure can change the directions of the magnetic fluxes generated by coils12and13(112and113), allowing coil device7(57) to function as selectively an inductor and a noise filter.

FIG. 11Ais an exploded perspective view of another coil device67according to Embodiment 2.FIG. 11Bis a sectional view of coil device67. InFIGS. 11A and 11B, components identical to coil device57shown inFIGS. 3 and 4are denoted by the same reference numerals, and their description will be omitted. Coil device67ofFIGS. 11A and 11Bincludes package114made of magnetic material instead of package14of coil device57shown inFIGS. 3 and 4. In coil device57shown inFIG. 3, windings20and21face each other across portion14C of package14. In coil device67shown inFIG. 11A, on the other hand, windings20and21have hollow portion114A between windings20and21, so that linear portions22and23of windings20and21face each other by the center width LM without any portion of package114between windings20and21. Package114includes cores36A and36B which are formed by molding magnetic material, such as ferrite or powder containing magnetic powder and bonding material. Cores36A and36B have recess136provided therein for accommodating windings20and21therein.

A sample of Example 18 of coil device67was produced. Example 18 was identical to Example 1 of coil device57in top width LH, bottom width LB, center width LM, and outer widths LE and LF. A current of11A having a frequency of 100 kHz was supplied to the sample of Example 18 so as to measure leakage magnetic flux densities at positions P1to P4shown inFIG. 6.FIG. 12shows the leakage magnetic flux densities of the samples of Examples 1 and 18 and Comparative Example.

As shown inFIG. 12, Examples 1 and 18 have the same leakage magnetic flux density, and nearly the same inductances. More specifically, the magnetic flux leaking from packages14and114and the inductances are almost identical to each other between coil device67in which windings20and21face each other directly and coil device57in which windings20and21face each other across portion14C of package14made of magnetic material. Portions of the magnetic fluxes generated by windings20and21flowing through portion14C of package14made of magnetic material offset each other. Portion14C of package14does not influence to the magnetic fluxes, and hence, does not influence to characteristics of coil device57. Hollow portion114A provided in cores36A and16B simplifies the design of the molds for shaping cores36A and36B shown inFIGS. 11A and 11B, and reduces the amount of the magnetic material used for cores36A and36B.

In this case, top width LH and bottom width LB are preferably equal to each other. This structure allows magnetic fluxes M81and M91to flow efficiently in a loop in package14shown inFIG. 2.

FIG. 13is a sectional view of another coil device77according to Embodiment 2. InFIG. 13, components identical to those of coil device57shown inFIG. 6are denoted by the same reference numerals, and their description will be omitted. In coil device57shown inFIG. 6, winding axes17and18of windings20and21are parallel to side surfaces34A and34B of package14. In coil device77shown inFIG. 13, winding axes17and18incline by angle T1with respect to side surfaces34A and34B. Therefore, the outer width, the distance between upper end29of winding20and side surface34A is LE−D1, while the outer width, the distance between lower end31of winding20and side surface34A is LE+D1. Similarly, the outer width, the distance between upper end29of winding21and side surface34B is LF+D1, while the outer width, the distance between lower end31of winding21and side surface34B is LF−D1. As shown inFIGS. 8 to 10, top width LH and bottom width LB influence significantly to the leakage magnetic field than the outer widths do. Winding axes17and18inclining with respect to side surfaces34A and34B reduce width LT of side surfaces34A and34B along winding axes17and18, while maintaining length LC of windings20and21along winding axes17and18, top width LH, and the bottom width LB. This structure increases the inductance of coil device57if package14has a predetermined size, or this structure reduces the size of package14if coil device57has a predetermined inductance.

Center width LM shown inFIG. 13does not influence significantly to the magnetic fluxes generated by windings20and21if center width LM is half or less than half the top width LH and the bottom width LB. Therefore, windings20and21may not necessarily be parallel to each other. In this case, the largest distance between windings20and21is preferably half or less than half the top width LH and the bottom width LB.

FIG. 14is a sectional view of coil device77for illustrating a method of manufacturing coil device77. In the case that windings20and21(winding axes17and18) incline with respect to side surfaces34A and34B of package14, respectively, as shown inFIG. 14, package14shown inFIG. 13is formed as follows. First, windings20and21are covered with semi-cured magnetic core37which is not completely molded, and then, semi-cured magnetic core37is cured by being pressed with upper and lower molds38. Semi-cured magnetic core37may be powder of the magnetic material or an aggregate formed by temporarily molding powder of the magnetic material. The powder of the magnetic body of semi-cured magnetic core37is partially collapsed while being pressure-molded with molds38. Therefore, direction39in which molds38press semi-cured magnetic core37is not parallel to winding axes17and18of windings20and21. Even in this case, as shown inFIG. 14, the powder of the magnetic material covers windings20and21, and entering into insides of windings20and21so as to form package14. Semi-cured magnetic core37is preferably made of mixture of magnetic powder and bonding material so as to be pressure-molded with molds38.

FIG. 15is a sectional view of coil device77for illustrating another method of manufacturing coil device77. As shown inFIG. 15, while winding axes17and18of windings20and21are parallel with direction39in which molds38press semi-cured magnetic core37, semi-rigid magnetic core37is pressure-molded. Windings20and21(winding axes17and18) may incline with respect to side surfaces34A and34B of package14by the pressure applied during the pressure-molding, as shown inFIG. 13.

Terms indicating directions, such as “upper end”, “lower end”, “upper surface, “lower surface”, and “side surface” do not indicate absolute directions, such as vertical directions, and do indicate relative directions depending on the positions of component parts, such as coils12,13,112, and113and packages14and114, of coil devices7,57,67, and77

INDUSTRIAL APPLICABILITY

A coil device according to the present invention reduces the amount of magnetic flux leaking to an outside of a package and is useful in various electronic apparatuses.