Power circuit device

Provided is a highly reliable power circuit device. The power circuit device includes a printed substrate, a power circuit, and a housing. The power circuit is formed on the printed substrate. The housing is connected with the printed substrate. The power circuit includes secondary-side switching elements, at least one smoothing choke coil, and smoothing capacitors. Portions of a smoothing choke coil core serving as a core of the smoothing choke coil are inserted in opening portions formed in the printed substrate. A winding of the smoothing choke coil is formed on the printed substrate. The smoothing choke coil is located between a region C in which the smoothing capacitors are arranged and regions A and B serving as a second region in which primary-side switching elements and the secondary-side switching elements serving as electric elements are arranged.

TECHNICAL FIELD

The present invention relates to a power circuit device, and more particularly to a power circuit device which dissipates heat generated from a power circuit to the outside.

BACKGROUND ART

In recent years, power circuit devices used for vehicle-mounted or vehicular large-capacity industrial apparatuses have been required to have more functions, a higher output, and a thinner size. Accordingly, electronic components mounted in a power circuit device have been required to have higher heat resistance and higher heat dissipation.

An exemplary configuration of such an electronic component having higher heat resistance and higher heat dissipation is disclosed for example in Japanese Patent Laying-Open No. 2011-139602 (hereafter referred to as PTD 1). In a power supply device disclosed in PTD 1, switching elements constituting the power supply device and generating a large heat are directly fixed to a housing. Heat dissipation property is improved by directly fixing the switching elements to the housing as described above. In the power circuit device, since a large current flows to a winding of a choke coil constituting a smoothing circuit, the winding is thickened to reduce heat generation in the winding. In the power circuit device, a component in which a core and the winding of the choke coil are integrated is connected to a circuit substrate.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

In the power supply device disclosed in PTD 1, the switching elements are directly fixed to the housing as described above, and the choke coil is connected as a separate component to a printed substrate. Accordingly, the number of assembly steps is increased, resulting in an increase in the manufacturing cost of the device. To deal with such a problem of the increase in manufacturing cost, it is conceivable to mount electronic components such as switching elements on a circuit substrate to simplify a mounting process.

Here, a power circuit device includes a smoothing capacitor as one of electronic components constituting a smoothing circuit. In a case where components such as a switching element and a transformer generate heat and the temperature thereof is increased, the smoothing capacitor having a low heat-resistance temperature receives heat through a wiring pattern of a circuit substrate and the air in a housing of the power circuit device. As a result, the smoothing capacitor may be broken by the heat, and it is difficult to secure the reliability of the power circuit device.

The present invention has been made to solve the aforementioned problem, and an object of the present invention is to provide a highly reliable power circuit device.

Solution to Problem

A power circuit device in accordance with the present invention includes a circuit substrate, a power circuit, and a housing. The power circuit is formed on the circuit substrate. The housing is connected with the circuit substrate. The power circuit includes an electric element, at least one coil, and a capacitor. The coil smoothes a current flowing through the power circuit. The capacitor smoothes a current output from the coil. A portion of a core of the coil is inserted in an opening portion formed in the circuit substrate. A winding of the coil is formed on the circuit substrate. The coil is located between a first region in which the capacitor is arranged and a second region in which the electric element is arranged.

Advantageous Effects of Invention

According to the power circuit device in accordance with the present invention, an increase in the temperature of the capacitor of the power circuit can be mitigated. Accordingly, a highly reliable power circuit device which can be used for a long time can be obtained.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings, in which identical or corresponding parts will be designated by the same reference numerals, and the description thereof will not be repeated.

First Embodiment

<Circuit Configuration of Power Circuit Device>

FIG. 1is a circuit diagram of a power circuit device in accordance with a first embodiment of the present invention. Referring toFIG. 1, a circuit configuration of the power circuit device in accordance with the present embodiment will be described.

As shown inFIG. 1, the power circuit device in accordance with the first embodiment of the present invention is a DC/DC converter, as an example.

InFIG. 1, a circuit of the DC/DC converter constituting the power circuit device mainly includes an inverter circuit and a rectification circuit. The inverter circuit includes primary-side switching elements2a,2b,2c,2dand transformers4a,4b. The rectification circuit includes secondary-side switching elements3a,3b,3c,3d. The DC/DC converter constituting the power circuit device further includes smoothing choke coils5a,5b, a smoothing capacitor6, an input capacitor16, a filter coil15, and a resonance coil14. An input terminal7to which a high-voltage direct current (DC) is input and an output terminal8which draws a flat DC voltage are each connected to the DC/DC converter. For output terminal8, a screw terminal for mounting a printed substrate, or a terminal block can be used.

Transformers4a,4bare constituted by magnetically connecting primary-side coil conductors (high voltage-side windings), which are connected to primary-side switching elements2a,2b,2c,2d, with secondary-side coil conductors (low voltage-side windings) by means of cores.

The power circuit device in the present embodiment converts, for example, a DC voltage of about 100 V to about 600 V input to input terminal7into a DC voltage of about 12 V to about 16 V, and outputs the DC voltage from output terminal8. Specifically, a high DC voltage input to input terminal7is converted by the inverter circuit into a first alternating current (AC) voltage. The first AC voltage is converted by transformers4a,4binto a second AC voltage lower than the first AC voltage. The second AC voltage is rectified by the rectification circuit including secondary-side switching elements3a,3b,3c,3d. Smoothing choke coils5a,5bsmooth the voltage output from the rectification circuit, and output a low DC voltage to the output terminal. Although two transformers4a,4band two smoothing choke coils5a,5bare mounted in the present embodiment, the number thereof may be more than two. For example, the power circuit device may include three or more transformers. The power circuit device may include three or more smoothing choke coils.

<Configuration of Power Circuit Device>

FIG. 2is a schematic perspective view of the power circuit device in accordance with the first embodiment of the present invention.FIG. 3is a schematic top view of the power circuit device in accordance with the first embodiment of the present invention.FIG. 4is an exploded schematic perspective view of the power circuit device in accordance with the first embodiment of the present invention.FIG. 5is a schematic cross sectional view along a line segment V-V inFIG. 2.FIG. 6is a schematic cross sectional view along a line segment VI-VI inFIG. 2. A configuration of the power circuit device in accordance with the present embodiment will be described with reference toFIGS. 2 to 6. InFIGS. 2 to 6, main components are shown, and wirings and some components are not shown.

FIG. 2shows an appearance of a portion of or an entire DC/DC converter101as an example of the power circuit device in the present embodiment. That is, in a case whereFIG. 2shows a portion of DC/DC converter101,FIG. 2shows only a portion cut away from the entire DC/DC converter. In DC/DC converter101, electric components such as primary-side switching elements2a,2b,2c,2d, a transformer4(transformers4a,4b), secondary-side switching elements3a,3b,3c,3d, a smoothing choke coil5(smoothing choke coils5a,5b), and smoothing capacitors6are connected to a printed substrate1serving as a circuit substrate. Printed substrate1is housed in a housing10. Although the present embodiment shows an example in which resonance coil14, filter coil15, and input capacitor16shown in an electric circuit ofFIG. 1are not mounted on printed substrate1or housing10, these electric components may be mounted on printed substrate1. As shown inFIG. 2, in the present embodiment, a region in which input terminal7and primary-side switching elements2a,2b,2c,2dare mounted is referred to as a region A, a region in which secondary-side switching elements3a,3b,3c,3dare mounted is referred to as a region B, and a region in which smoothing capacitors6are mounted is referred to as a region C.

As shown inFIG. 2, the electric components to be mounted on printed substrate1are mainly arranged in an order according to the order in the electric circuit diagram shown inFIG. 1. Specifically, input terminal7is arranged in the vicinity of one side of printed substrate1. Output terminal8is arranged in the vicinity of one side opposite to the one side adjacent to input terminal7. Primary-side switching elements2a,2b,2c,2dare linearly arranged in a line along an X-axis direction in the vicinity of input terminal7. Transformers4a,4bare arranged in a direction in which a longitudinal direction of transformer cores is substantially parallel to the line formed by primary-side switching elements2a,2b,2c,2d, that is, are arranged to be parallel to the X-axis direction. Secondary-side switching elements3a,3b,3c,3dare also linearly arranged in a line along the X-axis direction. Smoothing capacitors6are mounted at positions adjacent to output terminal8.

Smoothing choke coils5a,5bare arranged between smoothing capacitors6and the line formed by secondary-side switching elements3a,3b,3c,3dmounted on printed substrate1, in a direction in which a longitudinal direction of smoothing choke coil cores is substantially parallel to the line formed by secondary-side switching elements3a,3b,3c,3d, that is, are arranged to be parallel to the X-axis direction. Specifically, region C in which smoothing capacitors6are mounted and region B on printed substrate1in which secondary-side switching elements3a,3b,3c, and3dare mounted shown inFIG. 2are separated by smoothing choke coils5a,5b.

From a different viewpoint, the power circuit device includes printed substrate1serving as a circuit substrate, a power circuit, and housing10. The power circuit is formed on printed substrate1. Housing10is connected with printed substrate1. The power circuit includes electric elements (primary-side switching elements2a,2b,2c,2d, secondary-side switching elements3a,3b,3c,3d), at least one coil (smoothing choke coils5a,5b), and capacitors (smoothing capacitors6). Portions of each smoothing choke coil core5aE,5aI,5bE,5bI serving as a core of smoothing choke coil5a,5bserving as the coil are inserted in opening portions22formed in printed substrate1. Windings of smoothing choke coils5a,5bare formed on printed substrate1. Smoothing choke coils5a,5bare located between region C serving as a first region in which smoothing capacitors6are arranged and regions A and B serving as a second region in which primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dserving as the electric elements are arranged.

In addition, from a different viewpoint, smoothing choke coils5a,5bsmooth a current flowing through the power circuit. Smoothing capacitors6smooth currents output from smoothing choke coils5a,5b. In the circuit substrate, smoothing choke coils5a,5bare arranged between smoothing capacitors6and the electric elements (primary-side switching elements2a,2b,2c,2d, secondary-side switching elements3a,3b,3c,3d). In printed substrate1, at least one opening portion22is formed in a region between smoothing capacitors6and the electric elements. Smoothing choke coils5a,5binclude cores (smoothing choke coil cores5aE,5aI,5bE,5bI), and windings surrounding the peripheries of the cores. Portions of each core (portions of smoothing choke coil core5aE,5bE) are inserted in opening portions22of printed substrate1.

Although only one coil can constitute smoothing choke coil5in the power circuit device described above, two advantages described below are achieved by dividing smoothing choke coil5into two smoothing choke coils5a,5b. The first advantage is that, since the currents can flow in parallel, loss caused when the currents flow can be reduced in the windings. Since the temperature of printed substrate1can be thereby decreased, an increase in the temperature of smoothing capacitors6can be mitigated. The second advantage is that smoothing choke coil core5aE,5aI,5bE,5bI can have a reduced height and can be formed in a flat shape. Thereby, smoothing choke coils5a,5barranged to be aligned can separate region B and region C.

When the above configuration is described from a different viewpoint, opening portions22formed in printed substrate1include first openings (some of a plurality of opening portions22) and second openings (the others of the plurality of opening portions22). Smoothing choke coil5includes smoothing choke coil5aserving as a first coil and smoothing choke coil5bserving a second coil. The cores include smoothing choke coil cores5aE,5aI serving as first coil cores and smoothing choke coil cores5bE,5bI serving as second coil cores, corresponding to the first coil and the second coil. Portions of smoothing choke coil core5aE are inserted in some of the plurality of opening portions22serving as the first openings in printed substrate1. Portions of smoothing choke coil core5bE serving as a second coil core are inserted in the others of the plurality of opening portions22serving as the second openings in printed substrate1. Smoothing choke coil core5aE and smoothing choke coil core5bE are arranged in a line when printed substrate1is viewed from a main surface. Smoothing choke coil cores5aE,5aI and smoothing choke coil cores5bE,5bI are arranged to traverse between region C and regions A and B.

In addition, from a different viewpoint, in the power circuit device described above, smoothing choke coil5includes the first coil (smoothing choke coil5a) and the second coil (smoothing choke coil5b). Opening portions22formed in printed substrate1include the first openings (opening portions22located in a region overlapping with smoothing choke coil5a) and the second openings (opening portions22located in a region overlapping with smoothing choke coil5b). Portions of the core of the first coil (smoothing choke coil5a) (i.e., portions of smoothing choke coil core5aE) are inserted in the first openings (opening portions22) in printed substrate1. Portions of the core of the second coil (smoothing choke coil5b) (i.e., portions of smoothing choke coil core5bE) are inserted in the second openings (opening portions22) in printed substrate1.

Transformer4is arranged between region A and region B. Specifically, opening portions21are provided in a region between region A and region B in printed substrate1, and transformer cores4aE,4bE are fitted into opening portions21. Transformer cores4aE,4bE are arranged in the direction in which the longitudinal direction of transformer cores4aE,4bE is parallel to the line formed by a plurality of primary-side switching elements2a,2b,2c,2d. Conversely, region A and region B are separated by transformer4.

In addition, smoothing choke coil5is arranged between region B and region C. Specifically, opening portions22are provided in a region between region B and region C in printed substrate1, and smoothing choke coil cores5aE,5bE are fitted into opening portions22. Smoothing choke coil cores5aE,5bE are arranged in the direction in which the longitudinal direction of smoothing choke coil cores5aE,5bE is parallel to the line formed by a plurality of secondary-side switching elements3a,3b,3c,3d. Conversely, region B and region C are separated by smoothing choke coil5. In addition, when viewed from region C, region C is separated from region A by smoothing choke coil5, region B, and transformer4.

In the power circuit device shown inFIG. 2, an assembly process can be simplified because all of the electric components can be mounted on printed substrate1. Specifically, primary-side switching elements2a,2b,2c,2d, secondary-side switching elements3a,3b,3c,3d, and smoothing capacitors6can be collectively fixed to printed substrate1by a reflow soldering method, for example. Further, by forming windings beforehand on printed substrate1using a wiring pattern, transformers4a,4band smoothing choke coils5a,5bfunction merely by attaching cores on printed substrate1. Accordingly, the power circuit device shown inFIG. 2is assembled extremely easily.

In a conventional power circuit device, a separate component formed by assembling a core and a wiring is mounted as each of a transformer and a smoothing choke coil. However, in the present embodiment, since the windings are formed using the wiring pattern of printed substrate1, the transformers and the smoothing choke coils can be formed merely by placing the cores on printed substrate1. Further, since the windings formed on a front surface of printed substrate1using the wiring pattern are formed simultaneously with formation of another wiring pattern, the manufacturing cost for the windings can be reduced as a result, when compared with a conventional case where the transformer and the like are mounted as separate components. Thereby, DC/DC converter101can be manufactured at a lower cost than that of the conventional power circuit device.

Housing10is a member in the shape of a rectangular flat plate made of a metal material having a good heat conductivity. Specifically, housing10is preferably composed of aluminum, for example. Housing10may be composed of another material such as copper, an aluminum alloy, or a magnesium alloy. Housing10may be formed in a box shape to cover printed substrate1, as described later. An insulating member9is arranged above housing10. Insulating member9connects housing10and printed substrate1. That is, housing10is thermally connected with printed substrate1through insulating member9. Housing10is set at a GND potential on the secondary side of the circuit shown inFIG. 1. Housing10is electrically connected with the wiring pattern having the GND potential of printed substrate1through fastening members12(seeFIG. 8). In the present embodiment, housing10does not have to be a completely flat plate, and asperities may be formed in order to secure an electric insulation distance from printed substrate1.

Insulating member9is preferably composed of a material having electric insulation property and having a good heat conductivity. For example, a member formed by dispersing particles of an insulator having heat conductivity in a resin can be used as insulating member9. Specifically, a sheet formed by mixing particles of aluminum oxide, aluminum nitride, or the like for improving heat conductivity into a silicone resin can be used as insulating member9. Aluminum oxide or aluminum nitride has a good heat conductivity and has electric insulation property. It should be noted that, instead of the sheet described above, a grease or an adhesive may be used as insulating member9.

Referring toFIGS. 4 and 5, transformers4a,4bmounted in DC/DC converter101include transformer cores4aE,4aI,4bE,4bI, and windings (not shown) made of the wiring pattern formed on printed substrate1.

Transformer core4aE,4aI,4bE,4bI may include, for example, a ferrite core made of a Mn—Zn ferrite, a Ni—Zn ferrite, or the like, an amorphous core, or an iron dust core. As shown inFIG. 4, I-shaped transformer cores4aI,4bI are arranged on a back surface side of printed substrate1. I-shaped transformer cores4aI,4bI are arranged inside opening portions24formed in insulating member9. As shown inFIG. 5, lower surfaces of I-shaped transformer cores4aI,4bI are in contact with a front surface of housing10. In addition, E-shaped transformer cores4aE,4bE are fitted into opening portions21provided in printed substrate1, from a front surface side of printed substrate1, and are arranged to come into contact with front surfaces of I-shaped transformer cores4aI,4bI. On this occasion, it is preferable to press E-shaped transformer cores4aE,4bE toward housing10by means of springs or the like in order to reduce contact heat resistance between E-shaped transformer cores4aE,4bE and I-shaped transformer cores4aI,4bI. It should be noted that, although E-shaped transformer cores4aE,4bE are fitted from the front surface of printed substrate1in the present embodiment, E-shaped transformer cores4aE,4bE may be fitted from the back side of printed substrate1.

Transformer cores4aE,4aI,4bE,4bI generate heat due to a periodic change in magnetic flux. In particular, since a change in magnetic flux may occur in a frequency in the kHz range when DC/DC converter101is driven, transformer cores4aE,4aI,4bE, and4bI generate an extremely large amount of heat. In the present embodiment, since the transformer constituting the inverter circuit is constituted of two transformers4aand4b, a height from the front surface of printed substrate1to a top of each transformer can be reduced, and the size of the transformers in a planar direction can be increased, when compared with a case where the transformer is constituted of one transformer. Thereby, the contact area between I-shaped transformer cores4aI,4bI and housing10is increased. As a result, the heat generated by transformer cores4aE,4aI,4bE,4bI can be efficiently dissipated to housing10.

Further, referring toFIGS. 4 and 6, smoothing choke coils5a,5bmounted in DC/DC converter101include smoothing choke coil cores5aE,5aI,5bE,5bI, and windings (not shown) made of the wiring pattern formed on printed substrate1. Smoothing choke coil core5aE,5aI,5bE,5bI includes, for example, a ferrite core made of a Mn—Zn ferrite, a Ni—Zn ferrite, or the like, an amorphous core, or an iron dust core. I-shaped smoothing choke coil cores5aI,5bI are arranged on the back surface side of printed substrate1. I-shaped smoothing choke coil cores5aI,5bI are arranged inside opening portions25formed in insulating member9. Lower surfaces of I-shaped smoothing choke coil cores5aI,5bI are in contact with the front surface of housing10. In addition, E-shaped smoothing choke coil cores5aE,5bE are fitted into opening portions22provided in printed substrate1, from the front surface side of printed substrate1, and are arranged to come into contact with front surfaces of I-shaped smoothing choke coil cores5aI,5bI. On this occasion, E-shaped smoothing choke coil cores5aE,5bE may be pressed toward housing10by means of pressing members such as springs or the like in order to increase a magnetic coupling strength between the E-shaped smoothing choke coil cores and the I-shaped smoothing choke coil cores. It should be noted that, although E-shaped smoothing choke coil cores5aE,5bE are fitted from the front surface of printed substrate1in the present embodiment, E-shaped smoothing choke coil cores5aE,5bE may be fitted from the back side thereof.

Since the amount of heat generated by smoothing choke coil cores5aE,5bE,5bI is smaller than that generated by transformer cores4aE,4aI,4bE,4bI, the air surrounding smoothing choke coil cores5aE,5aI,5bE,5bI has a lower temperature as a result. In the present embodiment, since the smoothing choke coil is constituted of two smoothing choke coils5aand5b, a height from the front surface of printed substrate1to a top of each smoothing choke coil can be reduced, and the size of the smoothing choke coils in the planar direction can be increased, when compared with a case where the smoothing choke coil is constituted of one smoothing choke coil. Although a structure constituted of transformer cores4aE and4aI, a structure constituted of transformer cores4bE and4bI, a structure constituted of smoothing choke coil cores5aE and5aI, and a structure constituted of smoothing choke coil cores5bE and5bI have an equal size in the present embodiment, the size of the transformer cores may be different from the size of the smoothing choke coil cores.

Smoothing capacitor6may include, for example, a ceramic capacitor, a film capacitor, or an electrolytic capacitor. Smoothing capacitors6are mounted on printed substrate1by means of a bonding member11. Although solder is preferably used as bonding member11, for example, a material having a good heat conductivity other than solder, such as an electrically conductive adhesive or a nano-silver paste, may be used as bonding member11.

The amount of heat generated by smoothing capacitors6is smaller than those generated by switching elements2ato2d,3ato3d, the wiring pattern, transformer cores4aE,4aI,4bE,4bI, and the like. However, smoothing capacitors6may receive heat from the switching elements and the like described above through the wiring pattern or the air, and may cause an increase in temperature. In the present embodiment, by arranging fastening members12(seeFIG. 8) in the vicinity of smoothing capacitors6, a heat dissipation path for smoothing capacitors6can be secured, and the increase in the temperature of smoothing capacitors6can be mitigated.

FIG. 7is a partial schematic cross sectional view of printed substrate1serving as the circuit substrate of the power circuit device shown inFIG. 2.FIG. 8is a partial schematic top view of the printed substrate of the power circuit device shown inFIG. 2.FIGS. 9 to 11are partial schematic plan views of a second-layer wiring pattern to a fourth-layer wiring pattern of the printed substrate of the power circuit device shown inFIG. 2. A configuration of printed substrate1will be described with reference toFIGS. 7 to 11.

FIG. 7shows a partial schematic cross sectional view of wiring layers in a region for mounting secondary-side switching elements3a,3b,3c,3d, smoothing choke coils5a,5b, and smoothing capacitors6, of printed substrate1used for the power circuit device shown inFIGS. 1 to 6.FIGS. 8 to 11show planar patterns in the respective layers, that is, a first-layer wiring pattern1bto a fourth-layer wiring pattern1e, in the region for mounting secondary-side switching elements3a,3b,3c,3d, smoothing choke coils5a,5b, and smoothing capacitors6, in printed substrate1. Printed substrate1, which is a constituent of DC/DC converter101, includes a four-layer wiring pattern.

As shown inFIG. 7, printed substrate1includes insulating layers1a, and first-layer wiring pattern1b, a second-layer wiring pattern1c, a third-layer wiring pattern1d, and fourth-layer wiring pattern1e. Insulating layers1aare formed between these wiring patterns. Insulating layer1ais preferably composed of glass fibers and an epoxy resin, for example. It should be noted that the composition of insulating layer1ais not limited to the composition described above, and insulating layer1amay be composed of an aramid resin and an epoxy resin, for example. In addition, a so-called metal substrate or ceramic substrate may be used as printed substrate1. Although first-layer wiring pattern1b, second-layer wiring pattern1c, third-layer wiring pattern1d, and fourth-layer wiring pattern1eare composed of copper, they may be composed of another material. For example, first-layer wiring pattern1bto fourth-layer wiring pattern1emay be formed of an electrically conductive material, for example, a metal such as gold (Au), a copper (Cu) alloy, a nickel (Ni) alloy, a gold (Au) alloy, a silver (Ag) alloy, or the like.

A large current of 100 A or more at maximum may flow through first-layer wiring pattern1bto fourth-layer wiring pattern1e. In this case, loss is caused in the wiring patterns described above, resulting in extremely large heat generation. As shown inFIGS. 8 to 11, in printed substrate1, heat generated in first-layer wiring pattern1bto fourth-layer wiring pattern1eis transferred to housing10, through heat dissipation vias1fpenetrating the wiring patterns from the front surface to the back surface of printed substrate1, and fastening members12fastening printed substrate1and housing10and penetrating the wiring patterns. As a result, an increase in the temperature of the wiring patterns can be mitigated. In addition, not only heat is generated in the wiring patterns, but also heat generated by secondary-side switching elements3a,3b,3c,3dis conducted to the wiring patterns. Accordingly, heat dissipation vias1fand fastening members12also contribute to heat dissipation of secondary-side switching elements3a,3b,3c,3d.

In the present embodiment, the thickness from first-layer wiring pattern1bto fourth-layer wiring pattern1eis set to about 100 μm. As a result, electric resistance is reduced by about 70% in the wiring pattern of the power circuit device in accordance with the present embodiment, when compared with a 35 μm-thick wiring pattern which has been commonly used. Accordingly, the amount of heat generation can be reduced by 70% in first-layer wiring pattern1bto fourth-layer wiring pattern1e, when compared with the conventional 35 μm-thick wiring pattern. Further, by setting the thickness of the wiring pattern to 100 μm, heat resistance in the planar direction of printed substrate1can be reduced by 70%. As a result, in each of first-layer wiring pattern1bto fourth-layer wiring pattern1eshown inFIGS. 8 to 11, heat can be efficiently transferred to heat dissipation vias if and fastening members12serving as cooling points, as indicated by arrows41inFIG. 8, for example. Thereby, an increase in the temperature of the front surface of printed substrate1can be suppressed, and the temperature around printed substrate1can be decreased as a result. That is, the increase in the temperature of heat-sensitive smoothing capacitors6can be suppressed.

FIG. 12is a partial schematic cross sectional view of the power circuit device in accordance with the first embodiment of the present invention.FIG. 12is a schematic view for illustrating a heat dissipation path from a switching element having a large amount of heat generation, used in the power circuit device in accordance with the first embodiment of the present invention. It should be noted that, althoughFIG. 12shows primary-side switching element2aas an exemplary switching element, secondary-side switching element3a,3b,3c,3dalso has the same heat dissipation path.

Primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dare each a package having a semiconductor chip sealed with a resin. As the semiconductor chip, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), or the like can be used. These semiconductor chips have an extremely large amount of heat generation. In addition, silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or the like may be used for the semiconductor chip embedded in each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3d. Primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dare fixed to the front surface of printed substrate1by means of bonding member11. Solder is preferably used as bonding member11, for example. It should be noted that a material having a good heat conductivity other than solder, such as an electrically conductive adhesive or a nano-silver paste, for example, may be used as bonding member11.

In printed substrate1, a plurality of heat dissipation vias if penetrating printed substrate1to extend from one main surface of printed substrate1to reach the other main surface thereof are formed. As also shown inFIGS. 8 to 11, the plurality of heat dissipation vias if are arranged immediately below primary-side switching element2a,2b,2c,2dor secondary-side switching element3a,3b,3c,3dand around the periphery thereof. It should be noted that the positions for arranging vias if are not limited to the positions shown inFIGS. 8 to 11. In addition, heat dissipation via if is also arranged at a position for establishing electrical conduction between at least two of first-layer wiring pattern1b, second-layer wiring pattern1c, third-layer wiring pattern1d, and fourth-layer wiring pattern1e, in order to constitute an electric circuit. Heat dissipation via if may have any planar shape, and may have a circular shape, for example. Preferably, the same material as that for the wiring patterns is plated inside heat dissipation via1f. In this case, a plating layer inside heat dissipation via if is thermally connected with the wiring patterns. Therefore, heat can be efficiently diffused from the front surface to the back surface of printed substrate1, through heat dissipation vias1f.

In the power circuit device in the present embodiment, heat generated by each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dis eventually transferred to housing10, and is dissipated to the outside through housing10. In this case, a heat dissipation path to housing10can be classified into first to fifth heat dissipation paths described below.

As the first heat dissipation path, a path as described below is conceivable. Specifically, the heat generated by each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dis transferred, through bonding member11immediately below each switching element, to heat dissipation vias if formed in a region below each switching element on printed substrate1, and in a region around the periphery thereof, as indicated by arrows43. The heat transferred to heat dissipation vias if is conducted through heat dissipation vias1f, further conducted to insulating member9, and eventually conducted to housing10.

As the second heat dissipation path, a path as described below is conceivable. Specifically, the heat generated by each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dis conducted to a lead13provided to each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3d. This heat is transferred to heat dissipation vias if through lead13and first-layer wiring pattern1b. Then, the heat is conducted to housing10through heat dissipation vias if and insulating member9, as with the first heat dissipation path.

As the third heat dissipation path, a path as described below is conceivable. Specifically, the heat generated by each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dis conducted through bonding member11to heat dissipation vias if immediately below each switching element. After passing through heat dissipation vias1f, the heat is diffused in second-layer wiring pattern1cand third-layer wiring pattern1d, in the planar direction of printed substrate1. Further, the heat is transferred to first-layer wiring pattern1b, through insulating layer1alocated between second-layer wiring pattern1cand first-layer wiring pattern1b. In addition, the heat is transferred to fourth-layer wiring pattern1e, through insulating layer1alocated between third-layer wiring pattern1dand fourth-layer wiring pattern1e. Then, the heat is transferred to fastening member12electrically connected to first-layer wiring pattern1band fourth-layer wiring pattern1e. The heat is dissipated to housing10through fastening member12. On this occasion, first-layer wiring pattern1band fourth-layer wiring pattern1eestablishing electrical conduction with fastening member12are electrically insulated from second-layer wiring pattern1cand third-layer wiring pattern1destablishing electrical conduction with primary-side switching element2a,2b,2c,2dor secondary-side switching element3a,3b,3c,3d. Regarding the third heat dissipation path, the relation between a pair of first-layer wiring pattern1band fourth-layer wiring pattern1eand a pair of second-layer wiring pattern1cand third-layer wiring pattern1dmay be reversed. That is, the heat may be conducted in first-layer wiring pattern1band fourth-layer wiring pattern1e, in the planar direction of printed substrate1, and then the heat may be transferred to fastening member12through second-layer wiring pattern1cand third-layer wiring pattern1d.

As the fourth heat dissipation path, a path as described below is conceivable. Specifically, the heat generated by each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dis conducted through wiring patterns1b,1c,1d,1e. The heat is conducted to an electric component thermally connected with wiring patterns1b,1c,1d,1e. Then, the heat is diffused from the electric component to housing10through heat dissipation vias if and insulating member9. The “electric component thermally connected with wiring patterns1b,1c,1d,1e” used herein does not have to be electrically connected with wiring patterns1b,1c,1d,1e, and also includes an electric component adjacent to wiring patterns1b,1c,1d,1e. Smoothing capacitor6is an example of such an electric component.

As the fifth heat dissipation path, a path as described below is conceivable. Specifically, the fifth heat dissipation path is a path through which the heat generated by each of primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3dis directly thermally transferred to the air and dissipated, as indicated by arrows42inFIG. 12. In this case, the temperature of the air around printed substrate1is increased by the heat dissipated to the air. Then, with an increase in the temperature of the air, convection of the air within housing10occurs. Thereby, when the air having an increased temperature comes into contact with a component having a temperature lower than that of the air within housing10, for example, smoothing capacitor6, heat is transferred from the air to smoothing capacitor6. Then, the heat is eventually dissipated to housing10.

In addition, although a space above printed substrate1is filled with the air in the present embodiment, the space may be filled with a resin material composed by containing a thermally conductive filler in an epoxy resin, a silicone resin, or the like. In this case, the heat generated by each switching element is conducted to a solid resin material, conducted to smoothing capacitor6, and eventually dissipated to housing10. It should be noted that the resin material is not limited to a solid but may also be a liquid.

<Function/Effect of Power Circuit Device>

As can be seen fromFIGS. 2 to 6, by arranging two smoothing choke coils5a,5bin the X-axis direction, opening portions22for fitting E-shaped smoothing choke coil cores5aE,5bE into printed substrate1can be provided between secondary-side switching elements3a,3b,3c,3dand smoothing capacitors6. Due to the presence of opening portions22, the cross sectional area of printed substrate1in a ZX plane view between region B and region C shown inFIG. 2can be reduced to about 30 percent of those of other regions. Thereby, the amount of heat flowing from region B into region C through printed substrate1can be reduced. That is, since the area of wiring patterns1b,1c,1d,1eand insulating layers1acan be reduced as a result in a region between region B and region C (i.e., in a region in which smoothing choke coils5a,5bare formed), heat resistance in the fourth heat dissipation path described above in the region can be increased. Thus, the amount of heat flowing into smoothing capacitors6is reduced, and thereby the increase in the temperature of smoothing capacitors6can be mitigated.

Further, in addition to separation between region B and region C by E-shaped smoothing choke coil cores5aE,5bE, as shown in the schematic cross sectional view ofFIG. 6, tops of secondary-side switching element3a,3b,3c,3dand smoothing capacitor6are at positions lower than a top of E-shaped smoothing choke coil core5aE,5bE in a thickness direction (that is, a Z direction) of printed substrate1. From a different viewpoint, of a first height L1from the front surface of printed substrate1serving as the circuit substrate to the top of secondary-side switching element3a,3b,3c,3dserving as the electric element, a second height L2from the front surface of printed substrate1to the top of smoothing capacitor6, and a third height L3from the front surface of printed substrate1to the top of E-shaped smoothing choke coil core5aE,5bE, third height L3is highest. Accordingly, even when a space above region B is filled with the air surrounding secondary-side switching elements3a,3b,3c,3dwhich is heated by high-temperature secondary-side switching elements3a,3b,3c,3d, the amount of the heated air flowing from the space above region B into a space above region C is extremely small due to the presence of smoothing choke coil cores5aE,5bE. That is, the fifth heat dissipation path described above can be blocked by smoothing choke coil cores5aE,5bE. Accordingly, the increase in the temperature of smoothing capacitors6can be mitigated. Thereby, the probability that smoothing capacitors6may be broken by the increase in the temperature of smoothing capacitors6can be reduced, and thus the reliability of the power circuit device can be significantly improved.

Further, when the temperature of primary-side switching elements2a,2b,2c,2dis higher than the temperature of secondary-side switching elements3a,3b,3c,3d, it is preferable to provide opening portions21for fitting E-shaped transformer cores4aE,4bE into printed substrate1between primary-side switching elements2a,2b,2c,2dand secondary-side switching elements3a,3b,3c,3d, and constitute transformers4a,4bby arranging two transformers4a,4bin the X-axis direction, as can be seen fromFIGS. 2 to 6.

From a different viewpoint, in the power circuit device described above, the electric elements include first elements (primary-side switching elements2a,2b,2c,2d) and second elements (secondary-side switching elements3a,3b,3c,3d). The power circuit includes at least one transformer4. Transformer4has transformer cores4aE,4aI,4bE,4bI, and windings surrounding the peripheries of the transformer cores. At least one transformer opening portion (opening portion21) is formed in a region between the first elements (primary-side switching elements2a,2b,2c,2d) and the second elements (secondary-side switching elements3a,3b,3c,3d) in printed substrate1. Portions of transformer core4aE,4bE are inserted in opening portions21of printed substrate1.

In addition, transformer4includes a first transformer (transformer4a) and a second transformer (transformer4b). The transformer opening portions (opening portions21) formed in printed substrate1include first transformer openings (opening portions21formed at positions overlapping with transformer4a) and second transformer openings (opening portions21formed at positions overlapping with transformer4b). Portions of transformer core4aE of transformer4aare inserted in the first transformer openings of printed substrate1. Portions of transformer core4bE of transformer4bare inserted in the second transformer openings of printed substrate1.

In addition, as shown inFIG. 6, of a fourth height (a height L5) from the front surface of printed substrate1to a top of the first element (primary-side switching element2a,2b,2c,2d), a fifth height (height L1) from the front surface of printed substrate1to a top of the second element (secondary-side switching element3a,3b,3c,3d), and a sixth height (a height L4) from the front surface of printed substrate1to a top of transformer core4aE,4bE, the sixth height (height L4) is highest.

Since heat transfer from region A to region B through printed substrate1and the space described above can be thereby limited, the temperature of region B can be decreased. That is, the temperature of the air flowing into the space above region C can be decreased, and thus the increase in the temperature of smoothing capacitors6can be mitigated.

In addition, since smoothing capacitors6are thermally shielded from secondary-side switching elements3a,3b,3c,3dwith the above arrangement, the increase in the temperature of smoothing capacitors6is hardly influenced by the temperature of secondary-side switching elements3a,3b,3c,3d. Accordingly, secondary-side switching elements3a,3b,3c,3dcan be driven in a higher temperature state than that in a conventional case, to operate the power circuit device. As a result, two effects described below can be expected. First, since the amount of current which can flow to secondary-side switching elements3a,3b,3c,3dcan be increased when compared to that in the conventional case, the power circuit device can provide a higher output. Second, since the heat dissipation area of secondary-side switching elements3a,3b,3c,3dcan be reduced, a region occupied by secondary-side switching elements3a,3b,3c,3din the front surface of printed substrate1can be reduced, for example, by narrowing a spacing for mounting secondary-side switching elements3a,3b,3c,3d. That is, the power circuit device can be downsized.

<Configuration and Function/Effect of Variation of Power Circuit Device>

FIG. 13is a schematic cross sectional view showing a variation of the power circuit device in accordance with the first embodiment of the present invention. Although the power circuit device shown inFIG. 13basically has the same configuration as that of the power circuit device shown inFIGS. 1 to 12, the shape of housing10thereof is different from that of the power circuit device shown inFIGS. 1 to 11. That is, in the power circuit device shown inFIG. 13, housing10has a box shape. Printed substrate1is arranged inside box-shaped housing10. Housing10includes a box-shaped housing portion31having an upper opening, and a lid32closing the upper opening. The power circuit device having such a configuration can also obtain the same effect as that of the power circuit device shown inFIGS. 1 to 12.

Second Embodiment

<Configuration and Function/Effect of Power Circuit Device>

FIG. 14is a schematic cross sectional view of a power circuit device in accordance with a second embodiment of the present invention.FIG. 14is a schematic cross sectional view identical toFIG. 6in the first embodiment, in the power circuit device in the second embodiment of the present invention. A DC/DC converter102in the present embodiment basically has the same configuration as that of DC/DC converter101shown inFIGS. 1 to 13. However, as shown inFIG. 14, DC/DC converter102in the present embodiment is different from DC/DC converter101in the first embodiment in that it includes a heat shield plate17serving as a shield member in a space above at least one of smoothing choke coils5a,5band smoothing capacitor6mounted on printed substrate1. It should be noted that, inFIG. 14, heat shield plate17is formed to extend from above a smoothing choke coil core to above smoothing capacitor6. Heat shield plate17may be formed only above the smoothing choke coil core of smoothing choke coil5a, or may be formed only above smoothing capacitor6.

Referring toFIG. 14, heat shield plate17is plate-shaped. Heat shield plate17is fixed by means of a post (not shown) connected with housing10. In the present embodiment, heat shield plate17is composed of a resin having a low heat conductivity in order to shield heat. For example, heat shield plate17may be composed of an epoxy resin, a PTFE resin, or the like. Alternatively, a plate made of a highly heat conductive metal such as stainless steel (SUS) or aluminum may be used for heat shield plate17. Also with such a configuration, the presence of heat shield plate17can suppress the air heated by heat from secondary-side switching elements3a,3b,3c,3dfrom flowing into the vicinity of smoothing capacitors6. That is, the effect of mitigating the increase in the temperature of smoothing capacitors6can be fully obtained.

In addition, heat shield plate17may be a portion of housing10, and may also function as lid32of housing10shown inFIG. 13, for example. In this case, heat shield plate17is preferably composed of the same member as that for housing10. Further, heat shield plate17may also be a control circuit substrate equipped with a control circuit which includes elements60(seeFIG. 14) and drives DC/DC converter102. From a different viewpoint, heat shield plate17includes the control circuit substrate, and the control circuit having elements60. The control circuit is formed on the control circuit substrate, and controls DC/DC converter102serving as a power circuit. In this case, since the space within housing10can be used effectively, the power circuit device can be downsized.

In the present embodiment, a gap (a distance L) between the top (top surface) of E-shaped smoothing choke coil core5aE,5bE and heat shield plate17is small, and thus the air heated by the switching elements located in region B does not flow into the space above region C. Accordingly, the temperature of the air around smoothing capacitors6can be maintained low. Therefore, the increase in the temperature of smoothing capacitors6can be mitigated. That is, since the amount of heat flowing into smoothing capacitors6through the fourth heat dissipation path of each switching element described in the first embodiment can be reduced, the increase in the temperature of smoothing capacitors6can be mitigated.

As described above, by arranging heat shield plate17, the probability that smoothing capacitors6may be broken due to the increase in the temperature of smoothing capacitors6can be reduced. As a result, the reliability of the power circuit device can be significantly improved. In addition, since smoothing capacitors6are thermally shielded from secondary-side switching elements3a,3b,3c,3dby heat shield plate17, the increase in the temperature of smoothing capacitors6is hardly influenced by the temperature of secondary-side switching elements3a,3b,3c,3d. Accordingly, secondary-side switching elements3a,3b,3c,3dcan be driven in a higher temperature state to operate the power circuit device, and thus two effects described below can be expected. First, since the amount of current which can flow to secondary-side switching elements3a,3b,3c,3dcan be increased, the power circuit device can provide a higher output. Second, since the heat dissipation area of secondary-side switching elements3a,3b,3c,3dcan be reduced, the region occupied by secondary-side switching elements3a,3b,3c,3din the front surface of printed substrate1can be reduced, for example, by narrowing the spacing for mounting secondary-side switching elements3a,3b,3c,3d. That is, the power circuit device can be downsized.

<Configuration and Function/Effect of Variation of Power Circuit Device>

FIG. 15is a schematic cross sectional view of a variation of the power circuit device in accordance with the second embodiment of the present invention. Although the power circuit device shown inFIG. 15basically has the same configuration as that of the power circuit device shown inFIG. 14, it is different from the power circuit device shown inFIG. 14in that heat shield plate17serving as a shield member is in contact with at least one of E-shaped smoothing choke coil cores5aE,5bE. Thereby, the space above region B and the space above region C can be separated by heat shield plate17. Accordingly, the amount of air flowing from the space above region B into the space above region C can be further reduced. As a result, the increase in the temperature of smoothing capacitors6can be further mitigated.

In addition, in this case, when an inclined portion17b(a portion having an angle) which is inclined with respect to the front surface of printed substrate1is formed in heat shield plate17as shown inFIG. 15, heat shield plate17can have spring property. For example, heat shield plate17includes a fixed portion17aconnected with any of smoothing choke coil cores5aE,5bE, inclined portion17bconnected to fixed portion17a, and a leading end portion17cconnected to an end of inclined portion17bopposite to an end thereof connected to fixed portion17a. Then, when leading end portion17cis pressed toward printed substrate1by another member50, for example, E-shaped smoothing choke coil core5aE,5bE can be pressed by heat shield plate17. As a result, an additional effect of improving magnetic property of smoothing choke coils5a,5bcan also be expected.

FIG. 16is a schematic cross sectional view of another variation of the power circuit device in accordance with the second embodiment of the present invention. Although the power circuit device shown inFIG. 16basically has the same configuration as that of the power circuit device shown inFIG. 14, it is different from the power circuit device shown inFIG. 14in that heat shield plate17is configured to include fixed portion17aand a fin portion17dformed to protrude from fixed portion17a. Fixed portion17ais fixed to a top surface (top) of at least one of E-shaped smoothing choke coil cores5aE,5bE. In this case, as shown inFIG. 16, heat shield plate17can absorb heat of the air heated by the switching elements, and diffuse the heat to housing10through smoothing choke coil cores5aE,5aI,5bE,5bI.

Here, fin portion17dof heat shield plate17may be plate-shaped or pin-shaped. In a case where fin portion17dis plate-shaped, fin portion17dis arranged such that a direction in which fin portion17dextends is substantially parallel to the longitudinal direction of smoothing choke coil cores5aE,5aI,5bE,5bI. Thereby, the space above region B and the space above region C can be reliably separated by fin portion17d. Accordingly, the increase in the temperature of smoothing capacitors6located in region C can be further mitigated.

Third Embodiment

<Configuration and Function/Effect of Power Circuit Device>

FIG. 17is a partial schematic top view of printed substrate1serving as a circuit substrate of a power circuit device in accordance with a third embodiment of the present invention.FIG. 17corresponds toFIG. 8in the first embodiment of the present invention.

Although a DC/DC converter103in the present embodiment shown inFIG. 17basically has the same configuration as that of DC/DC converter101in the first embodiment of the present invention, arrangement of fastening members12,12aset at the GND potential is different from that in the first embodiment of the present invention. Specifically, in the present embodiment, DC/DC converter103further includes fastening members12aserving as connection members which connect printed substrate1and housing10, as shown inFIG. 17. Fastening members12aconnect housing10and a region located between secondary-side switching elements3a,3b,3c,3dserving as the electric elements and smoothing capacitors6serving as the capacitors in printed substrate1. Thereby, heat from secondary-side switching elements3a,3b,3c,3dcan be transferred to housing10through fastening members12a, and thus the heat can be suppressed from being transferred to smoothing capacitors6. Accordingly, the increase in the temperature of smoothing capacitors6can be suppressed.

For example, in the first embodiment of the present invention, the heat generated by secondary-side switching elements3a,3b,3c,3dreaches smoothing capacitors6through insulating layers1aand wiring patterns1bto1eof printed substrate1. However, in the present embodiment, the heat generated by secondary-side switching elements3a,3b,3c,3dis first conducted to fastening members12athrough insulating layers1aand wiring patterns1bto1eof printed substrate1. Then, the heat is diffused to housing10through fastening members12a.

That is, in the present embodiment, heat transfer to smoothing capacitors6can be suppressed in the fourth heat dissipation path of the heat dissipation paths of each switching element described above. Thereby, the amount of heat which reaches smoothing capacitors6can be further reduced, when compared with that in the first embodiment of the present invention. Accordingly, the increase in the temperature of smoothing capacitors6can be mitigated. As a result, the probability that smoothing capacitors6may be broken due to temperature increase is reduced, and the reliability of the power circuit device can be significantly improved.

In addition, with the above configuration, smoothing capacitors6are thermally shielded from secondary-side switching elements3a,3b,3c,3d. Accordingly, the temperature of smoothing capacitors6is hardly influenced by the temperature of secondary-side switching elements3a,3b,3c,3d. Therefore, secondary-side switching elements3a,3b,3c,3dcan be driven in a higher temperature state to operate the power circuit device. Accordingly, as in the second embodiment of the present invention, the power circuit device can provide a higher output, and the power circuit device can be downsized. It should be noted that, although fastening members12aare arranged at the positions described above in the present embodiment, an equal effect can also be obtained by providing a plurality of heat dissipation vias if at the same positions.

Fourth Embodiment

<Configuration and Function/Effect of Power Circuit Device>

FIG. 18is a partial schematic top view of printed substrate1serving as a circuit substrate of a power circuit device in accordance with a fourth embodiment of the present invention.FIG. 18corresponds toFIG. 8in the first embodiment of the present invention.

Although a DC/DC converter104in the present embodiment shown inFIG. 18basically has the same configuration as that of DC/DC converter103shown inFIG. 17, it is different from DC/DC converter103shown inFIG. 17in that heat diffusion members18are fixed to the front surface of printed substrate1using bonding member11. Specifically, DC/DC converter104serving as a power circuit device further includes heat diffusion members18arranged in a region located between fastening members12,12aserving as the connection members and smoothing capacitors6serving as the capacitors in printed substrate1. In the present embodiment, the material constituting heat diffusion members18may be copper (Cu). Heat diffusion members18are mounted on printed substrate1using solder serving as bonding member11. The material for heat diffusion members18may also be a sheet-like material which uses a metal such as gold (Au), a copper (Cu) alloy, a nickel (Ni) alloy, a gold (Au) alloy, a silver (Ag) alloy, or the like, or graphite, as a main material. In addition, since the effect of heat diffusion is reduced when heat diffusion members18are too thick, heat diffusion members18preferably have a thickness of more than or equal to about 0.5 mm and less than or equal to about 2.0 mm. In addition, each heat diffusion member18does not have to have a simple rectangular shape as shown inFIG. 18, and the effect of heat diffusion can also be further enhanced by providing an L-shaped or U-shaped heat diffusion member18so as to follow the shape of a pattern on printed substrate1.

In the third embodiment, the heat generated by secondary-side switching elements3a,3b,3c,3dis conducted to fastening members12,12athrough wiring patterns1bto1e, and is diffused to housing10. In the present embodiment, in addition to heat diffusion through wiring patterns1bto1edescribed above, heat diffusion members18are mounted on the front surface of printed substrate1. Since heat diffusion members18can conduct heat generated by wiring pattern1bto fastening members12,12amore effectively, the amount of heat transferred to smoothing capacitors6can be further reduced. This is because heat diffusion members18are utilized to control directions in which the heat is conducted. That is, in the present embodiment, as shown inFIG. 18, rectangular heat diffusion members18are mounted to extend from first-layer wiring pattern1btoward heat dissipation vias1fand fastening members12,12aserving as cooling points which are apart from heat-sensitive smoothing capacitors6. As a result, heat can be efficiently conducted from first-layer wiring pattern1btoward heat dissipation vias1fand fastening members12,12a. Accordingly, the amount of heat conducted to smoothing capacitors6can be reduced. In addition, when an electrically conductive material is used as the material for heat diffusion members18, a portion of a current flowing through first-layer wiring pattern1balso flows through heat diffusion members18. Accordingly, the amount of heat generated in first-layer wiring pattern1bcan be reduced. Also in this respect, the effect of reducing the amount of heat conducted to smoothing capacitors6can be obtained. Therefore, the probability that smoothing capacitors6may be broken due to temperature increase can be reduced, and the reliability of the power circuit device can be significantly improved.

In addition, by arranging heat diffusion members18as described above, smoothing capacitors6are thermally shielded from secondary-side switching elements3a,3b,3c,3d. Accordingly, the temperature of smoothing capacitors6is hardly influenced by the temperature of secondary-side switching elements3a,3b,3c,3d. Therefore, secondary-side switching elements3a,3b,3c,3dcan be driven in a higher temperature state to operate the power circuit device. As a result, as in the second embodiment of the present invention, the power circuit device can provide a higher output, and the power circuit device can be downsized.

Fifth Embodiment

<Configuration and Function/Effect of Power Circuit Device>

FIG. 19is a schematic cross sectional view of a power circuit device in accordance with a fifth embodiment of the present invention.FIG. 19corresponds toFIG. 6in the first embodiment of the present invention.

Although a DC/DC converter105in the present embodiment shown inFIG. 19basically has the same configuration as that of DC/DC converter101shown inFIG. 6, it is different from DC/DC converter101shown inFIG. 6in that a recessed portion10ais formed in a region of housing10located below at least one of I-shaped smoothing choke coil cores5aI,5bI. Specifically, in DC/DC converter105serving as the power circuit device shown inFIG. 19, housing10includes a first housing region (a region E) located below smoothing capacitors6, a second housing region (a region D) located below secondary-side switching elements3a,3b,3c,3dserving as the electric elements, and a third housing region (the region of housing10located below at least one of I-shaped smoothing choke coil cores5aI,5bI) located between the first housing region and the second housing region. The third housing region includes a portion which has a thickness smaller than a thickness of the first housing region (region E) and a thickness of the second housing region (region D) (i.e., a portion of housing10facing the bottom of recessed portion10a). Recessed portion10ashown inFIG. 19has an opening portion on a side close to I-shaped smoothing choke coil core5aI,5bI. That is, recessed portion10afaces any of I-shaped smoothing choke coil cores5aI,5bI.

Here, in the first embodiment of the present invention, smoothing capacitors6dissipate heat to housing10through printed substrate1, insulating member9, and fastening members12. However, when the temperature of entire housing10is increased by heat generation at primary-side switching elements2a,2b,2c,2dserving as the electric elements, transformers4a,4b, and secondary-side switching elements3a,3b,3c,3d, heat dissipation property of smoothing capacitors6may be reduced. Thus, in the present embodiment, as shown inFIG. 19, recessed portion10ais provided between region D of housing10located below regions A and B and region E located below region C in printed substrate1. By forming such a recessed portion10a, a region having a relatively small cross sectional area is formed between region D and region E of housing10, to suppress heat transfer from region D to region E. Thereby, an increase in the temperature of region E in housing10can be suppressed even in a case where the temperature of region D is increased due to heat generation from the switching elements and the like. Accordingly, deterioration of the heat dissipation property of smoothing capacitors6can be suppressed, and thus the temperature of smoothing capacitors6can be maintained low.

<Configuration and Function/Effect of Variation of Power Circuit Device>

FIG. 20is a schematic cross sectional view of a variation of the power circuit device in accordance with the fifth embodiment of the present invention.FIG. 20corresponds toFIG. 19.

Although DC/DC converter105in the present embodiment shown inFIG. 20basically has the same configuration as that of DC/DC converter105shown inFIG. 19, arrangement of recessed portion10ain the region of housing10located below I-shaped smoothing choke coil core5aI,5bI is different from that in DC/DC converter105shown inFIG. 19. Specifically, in DC/DC converter105shown inFIG. 20, recessed portion10ais formed in a surface of housing10on a side which is not in contact with insulating member9. Also with such a configuration, the same effect as that of DC/DC converter105shown inFIG. 19can be obtained. Further, in the configuration shown inFIG. 20, the contact area between I-shaped smoothing choke coil core5aI,5bI and housing10is larger than that in the configuration shown inFIG. 19. Accordingly, heat dissipation property from I-shaped smoothing choke coil core5aI,5bI to housing10is improved.

As described above, by providing recessed portion10ain housing10, reduction of the heat dissipation property of smoothing capacitors6can be suppressed. Therefore, the probability that smoothing capacitors6may be broken due to temperature increase is reduced, and the reliability of the power circuit device can be significantly improved. In addition, since the amount of current flowing to secondary-side switching elements3a,3b,3c,3dcan be increased, the power circuit device can provide a higher output.

In addition, with the above configuration, smoothing capacitors6are thermally shielded from secondary-side switching elements3a,3b,3c,3d, and thus the temperature of smoothing capacitors6is hardly influenced by the temperature of secondary-side switching elements3a,3b,3c,3d. Therefore, secondary-side switching elements3a,3b,3c,3dcan be driven in a higher temperature state to operate the power circuit device. As a result, as in the second embodiment of the present invention, the power circuit device can provide a higher output, and the power circuit device can be downsized.

Sixth Embodiment

<Configuration and Function/Effect of Power Circuit Device>

FIG. 21is a schematic top view of a power circuit device in accordance with a sixth embodiment of the present invention.FIG. 22is a schematic top view of a variation of the power circuit device shown inFIG. 21.FIGS. 21 and 22correspond toFIG. 3in the first embodiment of the present invention.

Although a DC/DC converter106in the present embodiment shown inFIG. 21basically has the same configuration as that of DC/DC converter101in the first embodiment of the present invention, arrangement of output terminal8is different therefrom. In the sixth embodiment, output terminal8is arranged between smoothing choke coil5aand smoothing choke coil5b. Smoothing choke coil5aincludes smoothing choke coil cores5aE,5aI, as shown inFIG. 4. Smoothing choke coil5bincludes smoothing choke coil cores5bE,5bI, as shown inFIG. 4. Output terminal8is arranged between smoothing choke coil cores5aE,5aI serving as the first coil cores and smoothing choke coil cores5bE,5bI serving as the second coil cores.

That is, in this case, output terminal8is not arranged in region C, and functions together with smoothing choke coils5a,5bto separate region B and region C. Thereby, output terminal8can close a gap produced between smoothing choke coil5aand smoothing choke coil5b. As a result, heat transfer from region B to region C through the air can be reduced. Here, output terminal8may have a height (a height from the front surface of printed substrate1) which is more than or equal to that of smoothing choke coils5a,5b, in order to effectively close the gap described above.

In addition, as a variation of the sixth embodiment, DC/DC converter106may be configured as shown inFIG. 22. In DC/DC converter106shown inFIG. 22, smoothing choke coil5aand smoothing choke coil5bare arranged adjacent to each other. Output terminal8is arranged on an end side of printed substrate1to be aligned with smoothing choke coils5a,5b. That is, output terminal8is not arranged in region C, and functions together with smoothing choke coil5to separate region B and region C, as with the configuration shown inFIG. 21. Thereby, DC/DC converter106has an effect of providing enhanced heat shield between region B and region C, as with the power circuit device shown inFIG. 21.

With the above configuration, smoothing capacitors6are thermally shielded from secondary-side switching elements3a,3b,3c,3d, and thus the temperature of smoothing capacitors6is hardly influenced by the temperature of secondary-side switching elements3a,3b,3c,3d. Therefore, secondary-side switching elements3a,3b,3c,3dcan be driven in a higher temperature state to operate the power circuit device. As a result, as in the second embodiment of the present invention, the power circuit device can provide a higher output, and the power circuit device can be downsized.

Although the embodiments of the present invention have been described above, the above embodiments can also be modified in various manners. In addition, the scope of the present invention is not limited to the above embodiments. The scope of the present invention is defined by the scope of the claims, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

INDUSTRIAL APPLICABILITY

The present invention is particularly advantageously applicable to a power circuit device which transfers heat to a housing for cooling.

REFERENCE SIGNS LIST