Magnetic device

Abstract

Coil patterns are provided in first and second outer surface layers and an inner layer of the board. First and second heat-dissipation patterns are provided in the second outer surface layer. A first thermal inter-layer connection member connects the coil pattern of the first outer surface layer and the first heat-dissipation pattern. A second thermal inter-layer connection member connects the coil pattern of the inner layer and the second heat-dissipation pattern. The coil pattern provided in the second outer surface layer and the first and second heat-dissipation patterns are separated from each other. An area of the second heat-dissipation pattern is larger than an area of the first heat-dissipation pattern.

Claims

1. A magnetic device comprising: a core which is formed of a magnetic substance; a board which is formed of an insulating substance, which has an opening portion into which the core is inserted, and which comprises first and second outer surface layers provided on both surfaces and an inner layer provided between the outer surface layers; coil patterns which are formed of a conductor, and which are provided in the first and second outer surface layers and the inner layer of the board so as to be wound around the core; a first heat-dissipation pattern which is formed of a conductor, which is provided to correspond to the coil pattern provided in the first outer surface layer of the board, and which is provided in the second outer surface layer; a second heat-dissipation pattern which is formed of a conductor, which is provided to correspond to the coil pattern provided in the inner layer of the board, and which is provided in second the outer surface layer; a first thermal inter-layer connection member which connects the coil pattern of the first outer surface layer and the first heat-dissipation pattern which correspond to each other; and a second thermal inter-layer connection member which connects the coil pattern of the inner layer and the second heat-dissipation pattern which correspond to each other, wherein the coil pattern provided in the second outer surface layer and the first and second heat-dissipation patterns are separated from each other, and wherein an area of the second heat-dissipation pattern is larger than an area of the first heat-dissipation pattern.

2. The magnetic device according to claim 1, wherein the first heat-dissipation pattern is separated from the second heat-dissipation pattern.

3. The magnetic device according to claim 1, further comprising: An electrical inter-layer connection member which connects the coil patterns provided in different layers of the board with each other.

4. The magnetic device according to claim 1, further comprising: a third heat-dissipation pattern which is formed of a conductor provided in the second outer surface layer of the board, and which is connected to the coil pattern provided in the second outer surface layer, wherein the third heat-dissipation pattern and the first and second heat-dissipation patterns are separated from each other, and wherein an area of the first heat-dissipation pattern is larger than an area of the third heat-dissipation pattern.

5. The magnetic device according to claim 1, wherein the second heat-dissipation pattern is provided in the second outer surface layer of the board, and a heat radiator is attached to the second outer surface layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a configuration diagram of a switching power supply apparatus.

(2) FIG. 2 is an exploded perspective view of a magnetic device according to an embodiment of the present invention.

(3) FIGS. 3(a) to 3(c) are plan views of layers of a board in FIG. 2.

(4) FIGS. 4(a) and 4(b) are cross-sectional views of the magnetic device in FIG. 2.

MODE FOR CARRYING OUT THE INVENTION

(5) Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In each of the drawings, the same parts or the corresponding parts are denoted by the same reference signs.

(6) FIG. 1 is a configuration diagram of a switching power supply apparatus 100. The switching power supply apparatus 100 is a DC-DC converter for an electric vehicle (or hybrid car). The switching power supply apparatus 100 performs switching so as to convert a DC high voltage into an AC voltage, and then converts the AC voltage into a DC low voltage. Details thereof will be described below.

(7) A high voltage battery 50 is connected to input terminals T1 and T2 of the switching power supply apparatus 100. A voltage of the high voltage battery 50 is, for example, in a range of DC 220 V to DC 400 V. A noise is removed from a DC voltage Vi of the high voltage battery 50 input to the input terminals T1 and T2 by a filter circuit 51, and then a result of removal is applied to a switching circuit 52.

(8) The switching circuit 52 is formed of a well-known circuit having, for example, a field effect transistor (FET). In the switching circuit 52, the FET is caused to turn ON and OFF based on a pulse width modulation (PWM) signal from a PWM driving unit 58 and a switching operation is performed on the DC voltage. Thus, the DC voltage is converted into a high-frequency pulse voltage.

(9) The converted pulse voltage is applied to a rectifier circuit 54 through a transformer 53. The rectifier circuit 54 rectifies the pulse voltage by using a pair of diodes D1 and D2. A voltage rectified by the rectifier circuit 54 is input to a smoothing circuit 55. The smoothing circuit 55 smoothes the rectified voltage by a filter action which is performed by a choke coil L and a capacitor C. The smoothed voltage is output to output terminals T3 and T4 as a low DC voltage. A low voltage battery 60 connected to the output terminals T3 and T4 is charged so as to be, for example, DC 12 V by using this DC voltage. A DC voltage of the low voltage battery 60 is supplied to various types of vehicle-mounted electric components (not illustrated).

(10) An output voltage Vo of the smoothing circuit 55 is detected by an output voltage detection circuit 59 and then is output to the PWM driving unit 58. The PWM driving unit 58 calculates a duty ratio of a PWM signal based on the output voltage Vo, and generates the PWM signal in accordance with the duty ratio. The PWM driving unit 58 outputs the generated PWM signal to a gate of the FET in the switching circuit 52. Thus, feedback control for holding the output voltage to be constant is performed.

(11) A control unit 57 controls an operation of the PWM driving unit 58. A power source 56 is connected to an output side of the filter circuit 51. The power source 56 steps down a voltage of the high voltage battery 50 and supplies a power source voltage (for example, DC 12 V) to the control unit 57.

(12) In the switching power supply apparatus 100, magnetic devices 1 which will be described later are used as the choke coil L in the smoothing circuit 55. A high current of, for example, DC 150 A flows in the choke coil L. Terminals 6i and 6o for power input and output are provided at both ends of the choke coil L.

(13) Next, a structure of a magnetic device 1 will be described with reference to FIGS. 2 to 4.

(14) FIG. 2 is an exploded perspective view of the magnetic device 1. FIGS. 3(a) to 3(c) are plan views of layers in the board 3 of the magnetic device 1. FIG. 4 is a cross-sectional view of the magnetic device 1; FIG. 4(a) illustrates an X-X cross-section in FIGS. 3(a) to 3(c), and FIG. 4(b) illustrates a Y-Y cross-section in FIGS. 3(a) to 3(c).

(15) As illustrated in FIG. 2, cores 2a and 2b are configured by a pair of two, that is, an upper core 2a and a lower core 2b. The upper core 2a has an E-shape and the lower core 2b has an I-shape. The cores 2a and 2b are formed of a magnetic substance such as ferrite and an amorphous metal.

(16) The upper core 2a has three convex portions 2m, 2L, and 2r so as to protrude downwardly. A protrusion amount of the right and left convex portions 2L and 2r is more than a protrusion amount of the center convex portion 2m.

(17) As illustrated in FIG. 4(a), lower ends of the right and left convex portions 2L and 2r of the upper core 2a adhere to an upper surface of the lower core 2b and thus the cores 2a and 2b are combined. Since DC superimposition characteristics are strengthened in this state, a gap of a predetermined size is provided between the convex portion 2m of the upper core 2a and the upper surface of the lower core 2b. Thus, even when a high current flows in the magnetic device 1 (choke coil L), it is possible to realize a predetermined inductance. The cores 2a and 2b are fixed to each other by fixation means (not illustrated) such as a screw and metal fittings.

(18) The lower core 2b is fitted into a concave portion 10k (FIG. 2) provided on an upside of the heat sink 10. A fin 10f is provided on a downside of the heat sink 10. The heat sink 10 is made of metal and is an example of a heat radiator according to the present invention.

(19) The board 3 is formed of a thick copper foil board obtained by forming a pattern on each layer of a thin plate-like base with a thick copper foil (conductor). The thin plate-like base is formed of an insulating substance. In this embodiment, other electronic components or other circuits are not provided on the board 3. However, when the magnetic device 1 is practically used in the switching power supply apparatus 100 in FIG. 1, other electronic components or other circuits are provided on the same board larger than the board 3, in addition to the magnetic device 1 and the switching power supply apparatus 100.

(20) A front-side outer surface layer L1 as illustrated in FIG. 3(a) is provided on a front surface (upper surface in FIGS. 2 and 4(a) and 4(b)) of the board 3. A back-side outer surface layer L3 as illustrated in FIG. 3(c) is provided on a back surface (lower surface in FIGS. 2 and 4(a) and 4(b)) of the board 3. As illustrated in FIGS. 4(a) and 4(b), an inner layer L2 as illustrated in FIG. 3(b) is provided between both of the outer surface layers L1 and L3. That is, the board 3 has three layers L1, L2, and L3 of the two outer surface layers L1 and L3, and the one inner layer L2.

(21) Opening portions 3m, 3L, and 3r is provided in the board 3. Each of the opening portions 3m, 3L, and 3r is formed by a rectangular through hole. As illustrated in FIGS. 2 to 4(a), the convex portions 2m, 2L, and 2r of the core 2a are respectively inserted into the opening portions 3m, 3L, and 3r.

(22) A plurality of through holes 3a having a small circular shape is provided in the board 3. As illustrated in FIGS. 2 and 4(b), screws 11 are respectively inserted into the through holes 3a. A back surface (back-side outer surface layer L3) of the board 3 is caused to face an upper surface (surface opposite to the fin 10f) of the heat sink 10. The screws 11 is respectively caused to pass through the through holes 3a from a front surface (front-side outer surface layer L1) of the board 3 and are screwed with screw holes 10a of the heat sink 10. Thus, as illustrated in FIGS. 4(a) and 4(b), the heat sink 10 is attached to the back-side outer surface layer L3 side of the board 3 in a proximity state.

(23) An insulating sheet 12 having a heat transfer property is interposed between the board 3 and the heat sink 10. Since the insulating sheet 12 has flexibility, the insulating sheet 12 adheres to the board 3 or the heat sink 10 without a gap.

(24) As illustrated in FIGS. 3(a) to 3(c), conductors of through holes 8a, 8d, 9a to 9d, pads 8b and 8c, the terminals 6i and 6o, patterns 4a to 4h, 5a.sub.1 to 5a.sub.9, and 5b.sub.1 to 5b.sub.9, and pins 7a to 7f are provided in the board 3. The through holes 8a, 8d, and 9a to 9d connect patterns 4a to 4f, 5a.sub.7 to 5a.sub.9, and 5b.sub.7 to 5b.sub.9 in different layers L1, L2, and L3 with each other.

(25) In detail, the through hole 8a connects the patterns 4a and 4b in the front-side outer surface layer L1 with other layers L2 and L3. The through hole 8d connects the front-side outer surface layer L1 with other layers L2 and L3, to connect the patterns 4a and 4b in the front-side outer surface layer L1 with the patterns 5a.sub.9 and 5b.sub.9 in the back-side outer surface layer L3, or to connect the patterns 4c and 4d in the inner layer L2 with the patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 in the back-side outer surface layer L3. The through holes 9a and 9d connect the patterns 4a and 4b in the front-side outer surface layer L1 with the patterns 4c and 4d in the inner layer L2. The through holes 9b and 9c connect the patterns 4c and 4d in the inner layer L2 with the pattern 4e in the back-side outer surface layer L3.

(26) The terminal 6i for inputting power is buried in one of a pair of through holes 8a having a large diameter, and the terminal 6o for outputting power is buried in another of the pair of through holes 8a. The terminals 6i and 6o are formed of a copper pin. Pads 8b formed of a copper foil are provided around the terminals 6i and 6o in the front-side outer surface layer L1 and the back-side outer surface layer L3. Copper plating is performed on front surfaces of the terminals 6i and 6o or the pads 8b. Lower ends of the terminals 6i and 6o come into contact with the insulating sheet 12 (not illustrated).

(27) Coil patterns 4a to 4e and heat-dissipation patterns 4g, 4h, 5a.sub.4 to 5a.sub.9 and 5b.sub.1 to 5b.sub.9 are provided in the layers L1, L2, and L3 of the board 3. The patterns 4a to 4e, 4g, 4h, 5a.sub.1 to 5a.sub.9, and 5b.sub.1 to 5b.sub.9 are formed of copper foils. Insulating processing is performed on front surfaces of the patterns 4a, 4b, 5a.sub.1 to 5a.sub.4, and 5b.sub.1 to 5b.sub.4 in the front-side outer surface layer L1.

(28) The width, the thickness, or the cross-sectional area of the coil patterns 4a to 4e is set to achieve predetermined performance of a coil and to suppress heat quantities in the coil patterns 4a to 4e up to a certain extent and enable heat dissipation even when a predetermined high current (for example, DC 150 A) flows.

(29) As illustrated in FIG. 3(a), the coil pattern 4a is wound once in four directions of surroundings of the convex portion 2L in the front-side outer surface layer L1. The coil pattern 4b is wound once in four directions of surroundings of the convex portion 2r.

(30) As illustrated in FIG. 3(b), the coil pattern 4c is wound once in the four directions of the surroundings of the convex portion 2L in the inner layer L2. The coil pattern 4d is wound once in the four directions of the surroundings of the convex portion 2r.

(31) As illustrated in FIG. 3(c), the coil pattern 4e in the back-side outer surface layer L3 is wound once in the four directions of the surroundings of the convex portion 2L, is wound once in the three directions of the surroundings of the convex portion 2m, and then is wound once in the four directions of the surroundings of the convex portion 2r.

(32) One end of the coil pattern 4a and one end of the coil pattern 4c are connected to each other by using the through hole 9a. Another end of the coil pattern 4c and one end of the coil pattern 4e are connected to each other by using the through hole 9c. Another end of the coil pattern 4e and one end of the coil pattern 4d are connected to each other by using the through hole 9b. Another end of the coil pattern 4d and one end of the coil pattern 4b are connected to each other by using the through hole group 9d.

(33) Copper plating is performed on the front surface of each of through holes 9a to 9d. Copper and the like may be buried in each of the through holes 9a to 9d. The through holes 9a to 9d are an example of electrical inter-layer connection means according to the present invention.

(34) Small patterns 4f are provided in the surrounding of the through holes 9b and 9c in the front-side outer surface layer L1 and the surrounding of the through holes 9a and 9d in the back-side outer surface layer L3 in order to easily form the through holes 9a to 9d. The through holes 9a to 9d and the small patterns 4f are respectively connected to each other. The small patterns 4f are formed of a copper foil. Insulating processing is performed on front surfaces of the small patterns 4f in the front-side outer surface layer L1.

(35) Another end of the coil pattern 4a is connected to the terminal 6i through the pad 8b. Another end of the coil pattern 4b is connected to the terminal 6o through the pad 8b.

(36) With the above descriptions, after the coil patterns 4a to 4e of the board 3 are wound firstly around the convex portion 2L from the terminal 6i which is a starting point, the coil patterns 4a to 4e of the board 3 are connected to the inner layer L2 through the through hole 9a, in the front-side outer surface layer L1. Then, after the coil patterns 4a to 4e are wound secondly around the convex portion 2L in the inner layer L2, the coil patterns 4a to 4e of the board 3 are connected to the back-side outer surface layer L3 through the through hole 9c.

(37) Then, after the coil patterns 4a to 4e are wound thirdly around the convex portion 2L and wound fourthly around the convex portion 2r through a circumference of the convex portion 2m, the coil patterns 4a to 4e are connected to the inner layer L2 through the through hole 9b, in the back-side outer surface layer L3. Then, after the coil patterns 4a to 4e are wound fifthly around the convex portion 2r in the inner layer L2, the coil patterns 4a to 4e are connected to the front-side outer surface layer L1 through the through hole 9d. After the coil patterns 4a to 4e are wound sixthly around the convex portion 2r in the front-side outer surface layer L1, the coil patterns 4a to 4e are connected to the terminal 6o which is an ending point.

(38) As described above, a current flowing in the magnetic device 1 flows in an order of the terminal 6i, the coil pattern 4a, the through hole 9a, the coil pattern 4c, the through hole 9c, the coil pattern 4e, the through hole 9b, the coil pattern 4d, the through hole 9d, the coil pattern 4b, and the terminal 6o.

(39) The heat-dissipation patterns 5a.sub.1 to 5a.sub.9 and 5b.sub.1 to 5b.sub.9 are formed in certain free spaces around the coil patterns 4a to 4e or the small patterns 4f in the layers L1 to L3, so as to be separate from the patterns 4a to 4e and 4f. The heat-dissipation patterns 5a.sub.1 to 5a.sub.9 and 5a.sub.i to 5a.sub.9 are separated from each other. That is, each of the heat-dissipation patterns 5a.sub.1 to 5a.sub.9 and 5b.sub.1 to 5b.sub.9 is separated from the coil patterns 4a to 4e, the small pattern 4f, and other heat-dissipation patterns 5a.sub.1 to 5a.sub.9 and 5b.sub.1 to 5b.sub.9.

(40) As illustrated in FIG. 3(c), in the back-side outer surface layer L3, the heat-dissipation patterns 4g and 4h are provided so as to be integrated with the coil pattern 4e in the back-side outer surface layer L3. That is, the heat-dissipation patterns 4g and 4h are connected to the coil pattern 4e. The heat-dissipation patterns 4g and 4h are separated from the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9.

(41) As illustrated in FIGS. 3(a) to 3(c), the pads 8b, the terminals 6i and 6o, the through hole 3a, and the screws 11 are insulated from the heat-dissipation patterns 5a.sub.1 to 5a.sub.9, 5b.sub.1 to 5b.sub.9, 4g, and 4h. An insulating area R1 around the through hole 3a in the front-side outer surface layer L1 is wider than an insulating area R2 (area of no conductor) around the through hole 3a in the inner layer L2 or the back-side outer surface layer L3, in order to cause a head portion 11a of the screw 11 having a diameter larger than that of a shaft portion 11b thereof to be disposed on the front surface side of the board 3.

(42) Heat-dissipation pins 7a to 7f are respectively buried into a plurality of through holes 8d having a large diameter. The heat-dissipation pins 7a to 7f are formed of copper pins. The pads 8c formed of a copper foil are provided around the heat-dissipation pins 7a to 7f in the front-side outer surface layer L1 and the back-side outer surface layer L3. Copper plating is performed on front surfaces of the heat-dissipation pins 7a to 7f or the pads 8c. Lower ends of the heat-dissipation pins 7a to 7f come into contact with the insulating sheet 12 (see FIG. 4(b)).

(43) As illustrated in FIG. 3(a), the heat-dissipation pin 7a, the pad 8c around the heat-dissipation pin 7a, and the through hole 8d are connected to the coil pattern 4a in the front-side outer surface layer L1. The heat-dissipation pin 7b, the pad 8c around the heat-dissipation pin 7b, and the through hole 8d are connected to the coil pattern 4b. Other heat-dissipation pins 7c to 7f, the pads 8c around the heat-dissipation pins 7c to 7f, and the through holes 8d are insulated from the heat-dissipation patterns 5a.sub.1 to 5a.sub.4 and 5b.sub.1 to 5b.sub.4, the coil patterns 4a and 4b, and the small patterns 4f. The coil patterns 4a and 4b and the small pattern 4f are insulated from the heat-dissipation patterns 5a.sub.1 to 5a.sub.4 and 5b.sub.1 to 5b.sub.4.

(44) As illustrated in FIG. 3(b), the heat-dissipation pins 7c and 7e, and the through holes 8d around the heat-dissipation pins 7c and 7e are connected to the coil pattern 4c in the inner layer L2. The heat-dissipation pins 7d and 7f, and the through holes 8d around the heat-dissipation pins 7d and 7f are connected to the coil pattern 4d. Other heat-dissipation pins 7a and 7b, and the through holes 8d around the heat-dissipation pins 7a and 7b are insulated from the heat-dissipation patterns 5a.sub.5, 5a.sub.6, 5b.sub.5, and 5b.sub.6, and the coil patterns 4c and 4d. The coil patterns 4c and 4d are insulated from the heat-dissipation patterns 5a.sub.5, 5a.sub.6, 5b.sub.5, and 5b.sub.6.

(45) As illustrated in FIG. 3(c), a heat-dissipation pattern 5a.sub.9 is provided in the back-side outer surface layer L3 so as to correspond to the coil pattern 4a in the front-side outer surface layer L1. A heat-dissipation pattern 5b.sub.9 is provided in the back-side outer surface layer L3 so as to correspond to the coil pattern 4b. Heat-dissipation patterns 5a.sub.7 and 5a.sub.8 are provided so as to correspond to the coil pattern 4c in the inner layer L2. Heat-dissipation patterns 5b.sub.7 and 5b.sub.8 are provided so as to correspond to the coil pattern 4d. The heat-dissipation patterns 5a.sub.9 and 5b.sub.9 are an example of the first heat-dissipation pattern according to the present invention. The heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7 and 5b.sub.8 are an example of the second heat-dissipation pattern according to the present invention.

(46) The heat-dissipation pin 7c, the pad 8c around the heat-dissipation pin 7c, and the through hole 8d are connected to the heat-dissipation pattern 5a.sub.7 in the back-side outer surface layer L3. The heat-dissipation pin 7e, the pad 8c around the heat-dissipation pin 7e, and the through hole 8d are connected to the heat-dissipation pattern 5a.sub.8. The heat-dissipation pin 7a, the pad 8c around the heat-dissipation pin 7a, and the through hole 8d are connected to the heat-dissipation pattern 5a.sub.9.

(47) The heat-dissipation pin 7d, the pad 8c around the heat-dissipation pin 7d, and the through hole 8d are connected to the heat-dissipation pattern 5b.sub.7 in the back-side outer surface layer L3. The heat-dissipation pin 7f, the pad 8c around the heat-dissipation pin 7f, and the through hole 8d are connected to the heat-dissipation pattern 5b.sub.8. The heat-dissipation pin 7b, the pad 8c around the heat-dissipation pin 7b, and the through hole 8d are connected to the heat-dissipation pattern 5b.sub.9.

(48) The coil pattern 4e and the small pattern 4f are insulated from the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9 in the back-side outer surface layer L3. The coil pattern 4e and the small pattern 4f are insulated from the heat-dissipation pins 7a to 7f, the pads 8c, and the through holes 8d.

(49) With the above descriptions, the coil pattern 4a in the front-side outer surface layer L1 and the heat-dissipation pattern 5a.sub.9 in the back-side outer surface layer L3 are connected to each other by using the heat-dissipation pin 7a, the pad 8c around the heat-dissipation pin 7a, and the through hole 8d. The coil pattern 4b in the front-side outer surface layer L1 and the heat-dissipation pattern 5b.sub.9 in the back-side outer surface layer L3 are connected to each other by using the heat-dissipation pin 7b, the pad 8c around the heat-dissipation pin 7b, and the through hole 8d. That is, the coil patterns 4a and 4b in the front-side outer surface layer L1 are respectively connected to the corresponding heat-dissipation patterns 5a.sub.9 and 5b.sub.9 at one place in the back-side outer surface layer L3. The heat-dissipation pins 7a and 7b, the pads 8c around the heat-dissipation pins 7a and 7b, and the through holes 8d are an example of first thermal inter-layer connection means according to the present invention.

(50) The coil pattern 4c in the inner layer L2 and the heat-dissipation patterns 5a.sub.7 and 5a.sub.8 in the back-side outer surface layer L3 are connected to each other by using the heat-dissipation pins 7c and 7e, the pads 8c around the heat-dissipation pins 7c and 7e, and the through holes 8d. The coil pattern 4d in the inner layer L2 and the heat-dissipation patterns 5b.sub.7 and 5b.sub.8 in the back-side outer surface layer L3 are connected to each other by using the heat-dissipation pins 7d and 7f, the pads 8c around the heat-dissipation pins 7d and 7f, and the through holes 8d. That is, the coil patterns 4c and 4d in the inner layer L2 are respectively connected to the corresponding heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 at two places in the back-side outer surface layer L3. The heat-dissipation pins 7c to 7f, the pads 8c around the heat-dissipation pins 7c to 7f, and the through holes 8d are an example of second thermal inter-layer connection means according to the present invention.

(51) The total area of the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 in the back-side outer surface layer L3, which are connected to the coil patterns 4c and 4d in the inner layer L2 is larger than the total area of the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 in the back-side outer surface layer L3, which are connected to the coil patterns 4a and 4b in the front-side outer surface layer L1.

(52) The total area of the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 in the back-side outer surface layer L3 is larger than the total area of the heat-dissipation patterns 4g and 4h connected to the coil pattern 4e in the back-side outer surface layer L3.

(53) Since a high current flows in the coil patterns 4a to 4e, the coil patterns 4a to 4e function as a heat generation source, and thus the temperature of the board 3 increases.

(54) In the front-side outer surface layer L1, heat of the board 3 is diffused to the heat-dissipation patterns 5a.sub.1 to 5a.sub.4 and 5b.sub.1 to 5b.sub.4, and is dissipated on the front surfaces of the conductors such as the patterns 4a, 4b, 4f, 5a.sub.1 to 5a.sub.4, and 5b.sub.1 to 5b.sub.4. Heat of the board 3 is transferred to the conductors passing through the board 3, such as the heat-dissipation pins 7a to 7f, the through holes 8d, 8a, and 9a to 9d, and thus is dissipated through the insulating sheet 12 by the heat sink 10. The through holes 9a to 9d function as thermal vias. Particularly, heat generated by the coil patterns 4a and 4b is transferred to the heat-dissipation pins 7a and 7b and the like and is diffused to the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 in the back-side outer surface layer L3. Thus, the heat is dissipated from front surfaces of the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 or lower surfaces of the heat-dissipation pins 7a and 7b, through the insulating sheet 12 by the heat sink 10.

(55) In the inner layer L2, heat of the board 3 is diffused to the heat-dissipation patterns 5a.sub.5, 5a.sub.6, 5b.sub.5, and 5b.sub.6, is transferred to the conductors passing through the board 3, such as the heat-dissipation pins 7a to 7f, the through holes 8d, and 9a to 9d, and thus the heat is dissipated through the insulating sheet 12 by the heat sink 10. Particularly, heat generated by the coil patterns 4c and 4d is transferred to the heat-dissipation pins 7c to 7f and the like and is diffused to the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 in the back-side outer surface layer L3. Thus, the heat is dissipated from front surfaces of the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 or lower surfaces of the heat-dissipation pins 7c to 7f, through the insulating sheet 12 by the heat sink 10.

(56) In the back-side outer surface layer L3, heat of the board 3 is diffused to the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9, and is dissipated from front surfaces of the conductors such as the patterns 4e, 4f, 5a.sub.7 to 5a.sub.9, and 5b.sub.7 to 5b.sub.9, through the insulating sheet 12 by the heat sink 10. Particularly, heat generated by the coil pattern 4e is dissipated from the front surface of the coil pattern 4e through the insulating sheet 12 by the heat sink 10.

(57) According to the embodiment, it is possible to dissipate heat generated by the coil patterns 4a and 4b in the front-side outer surface layer L1 of the board 3 from the front surfaces of the patterns 4a and 4b. In addition, the heat generated by the coil patterns 4a and 4b in the front-side outer surface layer L1 of the board 3 is transferred to the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 in the back-side outer surface layer L3 by using the heat-dissipation pins 7a and 7b, and thus it is possible to dissipate the heat from the front surfaces of the patterns 5a.sub.9 and 5b.sub.9 through the insulating sheet 12 by the heat sink 10. The heat generated by the coil pattern 4e in the back-side outer surface layer L3 is diffused to the heat-dissipation patterns 4g and 4h, and thus it is possible to dissipate the heat from the front surface of the patterns 4e, 4g, and 4h through the insulating sheet 12 by the heat sink 10.

(58) Heat generated by the coil patterns 4c and 4d in the inner layer L2 is transferred to the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 in the back-side outer surface layer L3 by using the heat-dissipation pins 7c to 7f and the like, and thus it is possible to dissipate the heat from the front surface of the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 through the insulating sheet 12 by the heat sink 10. In the back-side outer surface layer L3, since the total area of the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 is larger than the total area of the heat-dissipation patterns 5a.sub.9 and 5b.sub.9, it is possible to easily dissipate heat generated by the coil patterns 4c and 4d in the inner layer L2 from the front surfaces of the heat-dissipation patterns 5a.sub.7, 5a.sub.8, 5b.sub.7, and 5b.sub.8 through the insulating sheet 12 by the heat sink 10.

(59) Accordingly, heat in the inner layer L2 can be easily dissipated in the board 3 in which the coil patterns 4a to 4e are provided in the outer surface layers L1 and L3, and the inner layer L2, and heat dissipation performance can be improved.

(60) In the back-side outer surface layer L3, the heat-dissipation patterns 5a.sub.7 to 5a.sub.9, 5b.sub.7 to 5b.sub.9, 4g, and 4h are separated from each other. The heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9 are separated from the coil pattern 4e. The coil patterns 4a to 4e in the different layers L1 to L3 are connected to each other by using the through holes 9a to 9d. The coil patterns 4a to 4d are connected with the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9 by using the heat-dissipation pins 7a to 7f, and the like. For this reason, it is possible to ensure a heat-dissipation path of heat generated by the patterns 4a to 4e without an influence on an electrification path of the coil patterns 4a to 4e.

(61) Heat generated by the coil patterns 4a to 4d in the front-side outer surface layer L1 and the inner layer L2 of the board 3 is transferred to the heat sink 10 through a different heat-dissipation path of the heat-dissipation pins 7a to 7f, or the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9 in the back-side outer surface layer L3, and thus it is possible to dissipate the heat with high efficiency.

(62) Since the total area of the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 is larger than the total area of the heat-dissipation patterns 4g and 4h, heat generated by the coil patterns 4a and 4b in the front-side outer surface layer L1 is transferred by using the heat-dissipation pins 7a and 7b, and thus it is possible to easily dissipate the heat from the front surfaces of the heat-dissipation patterns 5a.sub.9 and 5b.sub.9 through the insulating sheet 12 by the heat sink 10.

(63) In the present invention, various embodiments can be employed in addition to the above descriptions. For example, in the above embodiments, an example in which the coil patterns coil patterns 4a to 4e are formed in the layers L1 to L3 of the board 3 having the two outer surface layers L1 and L3, and the one inner layer L2 is described. However, the present invention is not limited to only this example. In a board having two outer surface layers and inner layers of two or more, coil patterns may be formed in each of the outer surface layers, and at least one inner layer.

(64) In the above embodiment, an example in which the coil patterns 4a to 4e are formed in the board 3 so as to be wound around the three convex portions 2m, 2L, and 2r of the core 2a is described. However, the present invention is not limited to only this example. The coil patterns may be wound around at least one convex portion of the core.

(65) In the above embodiment, an example in which the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9 are provided in the back-side outer surface layer L3 of the board 3 so as to correspond to the coil patterns 4a to 4d in other layers L1 and L2 is described. However, the present invention is not limited to only this example. In addition, heat-dissipation patterns may be provided in the front-side outer surface layer so as to correspond to coil patterns in the back-side outer surface layer of a board. A heat-dissipation pattern corresponding to a coil pattern in the inner layer may be provided in the front-side outer surface layer or may be provided in both of the front-side outer surface layer and the back-side outer surface layer.

(66) In the above embodiment, an example in which the heat-dissipation patterns 4g and 4h connected to the coil pattern 4e are provided in the back-side outer surface layer L3 of the board is described. However, the present invention is not limited to only this example. In addition, the heat-dissipation patterns 4g and 4h in the back-side outer surface layer L3 may be omitted and other heat-dissipation patterns 5a.sub.8, 5a.sub.9, 5b.sub.8, and 5b.sub.9 may be expanded. A heat-dissipation pattern connected to a coil pattern in the layer may be provided in the front-side outer surface layer of the board or a heat-dissipation pattern connected to a coil pattern in the layer may be provided in the inner layer of the board.

(67) In the above embodiment, an example in which the coil patterns 4a to 4d and the heat-dissipation patterns 5a.sub.7 to 5a.sub.9 and 5b.sub.7 to 5b.sub.9 which correspond to each other in different layers L1 to L3 are connected by using the heat-dissipation pins 7a to 7f, the pads 8c, and the through holes 8d is described. However, the present invention is not limited to only this example. In addition, the coil patterns and the heat-dissipation patterns which correspond to each other in different layers may be connected to each other by at least one thermal inter-layer connection means of, for example, the terminals, the pins, and the through holes, and the like.

(68) In the above embodiment, an example in which the coil patterns 4a to 4e in the different layers L1 to L3 are connected to each other by using the through holes 9a to 9d is described. However, the present invention is not limited to only this example. In addition, the coil patterns in the different layers may be connected to each other by, for example, using another electrical inter-layer connection means such as the terminal and the pin.

(69) In the above embodiments, an example of using the heat sink 10 as a heat radiator is described. However, the present invention is not limited to only this example. In addition, an air-cooled heat radiator, a water-cooled heat radiator, a heat radiator using a coolant, and the like may be used. For example, a heat radiator formed of resin having high thermal conductivity may be used in addition to a metallic heat radiator. In this case, the insulating sheet 12 is not necessarily provided between the heat radiator and the board, and thus it is possible to omit the insulating sheet 12. Heat radiators may be respectively provided in both of the outer surface layers of the board, or a heat radiator may be omitted.

(70) In the above embodiments, an example of using a thick copper foil board is described. However, the present invention is not limited to only this example. Other boards such as a printed board manufactured by using general resin, and a metallic board may be used. In a case of the metallic board, an insulating substance may be provided between a base and each of the patterns.

(71) In the above embodiments, an example in which the I-shaped lower core 2b is combined with the E-shaped upper core 2a is described. However, the present invention may be also applied to a magnetic device having two E-shaped cores which are combined with each other.

(72) In the above embodiments, an example in which the present invention is applied to the magnetic devices 1 used as the choke coil L of the smoothing circuit 55 in the vehicle switching power supply apparatus 100 is described. However, the present invention may be also applied to a magnetic device used as the transformer 53 (FIG. 1). The present invention may be also applied to a magnetic device used in a switching power supply apparatus for, for example, electronic equipment in addition to a vehicle.

DESCRIPTION OF REFERENCE SIGN(S)

(73) 1 MAGNETIC DEVICE

(74) 2a UPPER CORE

(75) 2b LOWER CORE

(76) 3 BOARD

(77) 3L, 3m, 3r OPENING PORTION

(78) 4a TO 4e COIL PATTERN

(79) 4g, 4h HEAT-DISSIPATION PATTERN

(80) 5a.sub.7 TO 5a.sub.9, 5b.sub.7 to 5b.sub.9 HEAT-DISSIPATION PATTERN

(81) 7a TO 7f HEAT-DISSIPATION PIN

(82) 8d THROUGH HOLE

(83) 8c PAD

(84) 9a TO 9d THROUGH HOLE

(85) 10 HEAT SINK

(86) L1 FRONT-SIDE OUTER SURFACE LAYER

(87) L2 INNER LAYER

(88) L3 BACK-SIDE OUTER SURFACE LAYER