Buck converter

Abstract

A buck converter that reduces the number of components. The buck converter includes: a buck transformer (20) having a primary side coil (21) and a secondary side coil (22); a resin molded body (40) integrally formed with the primary side coil and the secondary side coil using a non-conductive resin; and a rectifier element (30a1) which is surface-mount type. The resin molded body (40) has a mounting surface (41a) for mounting the rectifier element (30a1), and the secondary side coil (22) has a first plate-shaped terminal (23a). The first plate-shaped terminal (23a) protrudes from the resin molded body (40) in the mounting surface (41a). A second plate-shaped terminal (42a) is provided on the mounting surface (41a) with a gap (43a) between it and the first plate-shaped terminal. The rectifier element (30a1) is joined to both the first plate-shaped terminal (23a) and the second plate-shaped terminal (42a) by solder connection. The non-conductive resin has a melting point higher than that of the solder.

Description

Technical Field

[0001] This disclosure relates to a step-down converter including a step-down transformer and a resin molded body integrally formed with the step-down transformer. Background Technology

[0002] In electric vehicles such as hybrid vehicles and electric vehicles, buck converters can be used to reduce the voltage of high-voltage batteries to a low voltage of 12V. Patent Document 1 describes an on-board DC / DC converter including an AC / DC conversion module substrate. The AC / DC conversion module substrate includes: a transformer having a primary winding and a secondary winding; a surface-mount rectifier element; and a metal substrate for mounting the transformer and the rectifier element. Multiple conductor patterns, insulated from the metal substrate by an insulating layer, are formed on the metal substrate. The ends of the secondary winding and the rectifier element are each soldered to any one of the multiple conductor patterns. The metal substrate is threadedly fastened to a heat-dissipating base plate.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-221919

[0006] In the aforementioned automotive DC / DC converter, it is conceivable to integrate the primary and secondary coils using a resin molded body made of non-conductive resin to reduce assembly time. However, the melting point of non-conductive resin is generally lower than that of solder. Therefore, in the process of mounting surface-mount rectifier elements, it is usually impossible to place the primary and secondary coils integrated by the resin molded body into the oven. Thus, in the automotive DC / DC converter of Patent Document 1, even if the primary and secondary coils are integrated by the resin molded body, a metal substrate is still required for mounting the rectifier element by reverse-flow soldering. Consequently, in the automotive DC / DC converter of Patent Document 1, there is a technical problem that it is difficult to reduce the number of components. Summary of the Invention

[0007] This disclosure was made to solve the above-mentioned technical problems, and its purpose is to provide a buck converter that can reduce the number of components.

[0008] The disclosed step-down converter includes: a step-down transformer having a primary winding and a secondary winding; a resin molded body integrally formed from a non-conductive resin and the primary winding and the secondary winding; and a rectifier element that rectifies the induced voltage of the secondary winding, the rectifier element being surface-mount, the resin molded body having a mounting surface for mounting the rectifier element, the secondary winding having a first plate-shaped terminal exposed in the mounting surface from the resin molded body, a second plate-shaped terminal spaced apart and arranged alongside the first plate-shaped terminal on the mounting surface, the rectifier element being joined to both the first plate-shaped terminal and the second plate-shaped terminal by soldering, the non-conductive resin having a melting point higher than that of the solder.

[0009] According to this disclosure, the number of components in a buck converter can be reduced. Attached Figure Description

[0010] Figure 1 This is a circuit diagram showing the circuit structure of the buck converter in Implementation Method 1.

[0011] Figure 2 This is a perspective view showing the main structural components of the buck converter in Embodiment 1.

[0012] Figure 3 This is an exploded view showing the main structural components of the buck converter in Embodiment 1.

[0013] Figure 4 This is a top view showing the main structural components of the buck converter in Embodiment 1.

[0014] Figure 5 This is a cross-sectional view showing the structure of the mounting surface of the resin molded body of the step-down converter in Embodiment 1.

[0015] Figure 6 This is a top view showing the structure of the buck converter in Embodiment 1.

[0016] Figure 7 This is a cross-sectional view showing the structure of the mounting surface of the resin molded body of the buck converter in Embodiment 2.

[0017] Figure 8 This is a perspective view showing the main structural components of the buck converter in Embodiment 3.

[0018] Figure 9 This is a top view showing the main structural components of the buck converter in Embodiment 3.

[0019] (Symbol Explanation)

[0020] 10. Switching Circuit Section;

[0021] 11a positive extreme particle;

[0022] 11b negative extreme particle;

[0023] Switching elements 12a, 12b, 12c, and 12d;

[0024] Connection points 13a and 13b;

[0025] 20 step-down transformers;

[0026] 21. Primary side coil;

[0027] 22 secondary side coils;

[0028] 22a First Coil;

[0029] 22b Second Coil;

[0030] 23a, 23b first plate terminals;

[0031] 24a, 24b terminals;

[0032] 30a, 30a1, 30a2, 30b, 30b1, 30b2 rectifier components;

[0033] 31. Smoothing reactor;

[0034] 32 smoothing capacitor;

[0035] 33 output terminals;

[0036] 34 anode terminals;

[0037] 35 Cathode terminal;

[0038] 40 resin molded body;

[0039] Mounting surfaces 41a and 41b;

[0040] 42a, 42b second plate terminals;

[0041] Gap between 43a and 43b;

[0042] 44 convex part;

[0043] 45. Fixing part;

[0044] 46. ​​Liner section;

[0045] 47. Cavity section;

[0046] 48 concavity;

[0047] 49 grooves;

[0048] 50 frame;

[0049] 51 screws. Detailed Implementation

[0050] Implementation Method 1

[0051] The buck converter of Embodiment 1 will be described. Figure 1 This is a circuit diagram showing the circuit structure of the buck converter in this embodiment. For example... Figure 1 As shown, the buck converter has a switching circuit section 10, a buck transformer 20, and multiple rectifier elements 30a and 30b.

[0052] The switching circuit section 10 is connected to the positive terminal 11a and the negative terminal 11b. The positive terminal 11a is connected to the positive terminal of the high-voltage battery. The negative terminal 11b is connected to the negative terminal of the high-voltage battery. The switching circuit section 10 has four switching elements 12a, 12b, 12c, and 12d. Each of the switching elements 12a, 12b, 12c, and 12d is controlled by a control circuit (not shown).

[0053] Switching elements 12a and 12b are connected in series between the positive terminal 11a and the negative terminal 11b. Switching elements 12c and 12d are connected in series between the positive terminal 11a and the negative terminal 11b. Switching elements 12a and 12b are connected in parallel with switching elements 12c and 12d.

[0054] The step-down transformer 20 has a primary winding 21 and a secondary winding 22. One end of the primary winding 21 is connected to the connection point 13a between switching elements 12a and 12b. The other end of the primary winding 21 is connected to the connection point 13b between switching elements 12c and 12d.

[0055] The secondary coil 22 has a first coil 22a and a second coil 22b. One end of the first coil 22a is connected to the anode of the rectifier element 30a. One end of the second coil 22b is connected to the anode of the rectifier element 30b. The other ends of the first coil 22a and the second coil 22b are maintained at a reference potential.

[0056] Rectifier element 30a and rectifier element 30b are each components that rectify the induced voltage of the secondary side coil 22. Rectifier element 30a, as described later, has two rectifier elements 30a1 and 30a2 connected in parallel (in... Figure 1 (Not shown in the figure). Similarly, as described below, rectifier element 30b has two rectifier elements 30b1 and 30b2 connected in parallel (in... Figure 1 (Not shown in the image).

[0057] The cathodes of rectifier element 30a and rectifier element 30b are connected to one end of smoothing reactor 31. The other end of smoothing reactor 31 is connected to output terminal 33 and to one electrode of smoothing capacitor 32. The other electrode of smoothing capacitor 32 is maintained at a reference potential.

[0058] Next, the physical structure of the buck converter in this embodiment will be described. Figure 2 This is a perspective view showing the main structural components of the buck converter in this embodiment. Figure 3 This is an exploded view showing the main structural components of the buck converter in this embodiment. Figure 4 This is a top view showing the main structural components of the buck converter in this embodiment. Figures 2-4 It shows Figure 1 The circuit structure of the buck converter shown mainly consists of the primary side coil 21 and secondary side coil 22 of the buck transformer 20, and rectifier elements 30a1, 30a2, 30b1, and 30b2. Figure 5 This is a cross-sectional view showing the structure of the mounting surface of the resin molded body in the buck converter of this embodiment. Figure 5 The diagram of the cured solder layer is omitted.

[0059] like Figures 2-5 As shown, the buck converter includes: a resin molded body 40, which covers the primary side coil 21 and the secondary side coil 22 of the buck transformer 20; and rectifier elements 30a1, 30a2, 30b1, and 30b2. The primary side coil 21 and the secondary side coil 22 of the buck transformer 20, except for the portions where the rectifier elements 30a1, 30a2, 30b1, and 30b2 are mounted, are covered by the resin molded body 40. Ideally, both the primary side coil 21 and the secondary side coil 22 should be made of copper to improve the conversion efficiency of the buck converter.

[0060] The resin molded body 40 is integrally molded from non-conductive resin with the primary side coil 21 and the secondary side coil 22 of the step-down transformer 20. Furthermore, the resin molded body 40 is integrally molded with the second plate-shaped terminal 42a, the second plate-shaped terminal 42b, and the plurality of bushing portions 46, which will be described later. That is, the primary side coil 21, the secondary side coil 22, the second plate-shaped terminal 42a, the second plate-shaped terminal 42b, and the plurality of bushing portions 46 are insertable components inserted into the mold during the molding of the resin molded body 40.

[0061] Terminal 24a at one end of the primary side coil 21 protrudes from a portion of the resin molded body 40. Terminal 24b at the other end of the primary side coil 21 protrudes from another portion of the resin molded body 40. Both terminals 24a and 24b are connected to... Figure 1 The switch circuit section 10 shown.

[0062] The resin molded body 40 has: a mounting surface 41a for mounting rectifier elements 30a1 and 30a2; and a mounting surface 41b for mounting rectifier elements 30b1 and 30b2. Rectifier elements 30a1, 30a2, 30b1, and 30b2 are each surface-mount type.

[0063] The secondary coil 22 has: a first plate-shaped terminal 23a, which is a terminal on one end of the first coil 22a; and a first plate-shaped terminal 23b, which is a terminal on one end of the second coil 22b. The first plate-shaped terminal 23a protrudes from the resin molded body 40 in the mounting surface 41a. The first plate-shaped terminal 23a is formed as a plate along the mounting surface 41a. The first plate-shaped terminal 23b protrudes from the resin molded body 40 in the mounting surface 41b. The first plate-shaped terminal 23b is formed as a plate along the mounting surface 41b.

[0064] A second plate-shaped terminal 42a is provided on the mounting surface 41a. The second plate-shaped terminal 42a is formed as a plate along the mounting surface 41a. The second plate-shaped terminal 42a is arranged side by side with the first plate-shaped terminal 23a across a gap 43a. A second plate-shaped terminal 42b is formed on the mounting surface 41b. The second plate-shaped terminal 42b is formed as a plate along the mounting surface 41b. The second plate-shaped terminal 42b is arranged side by side with the first plate-shaped terminal 23b across a gap 43b. Both the second plate-shaped terminal 42a and the second plate-shaped terminal 42b are electrically connected to... Figure 1 One end of the smoothing reactor 31 shown.

[0065] The second plate-shaped terminal 42a has a plurality of protrusions 44. In this embodiment, three protrusions 44 are formed on the mating surface of the second plate-shaped terminal 42a that engages with the rectifier element 30a1, and three protrusions 44 are also formed on the mating surface that engages with the rectifier element 30a2. Each protrusion 44 protrudes from the surface of the second plate-shaped terminal 42a along the normal direction of the surface. Each protrusion 44 is conductive. The second plate-shaped terminal 42a is engaged with the rectifier element 30a1 and the rectifier element 30a2 at least at the protrusions 44.

[0066] Similarly, the second plate-shaped terminal 42b has a plurality of protrusions 44. In this embodiment, three protrusions 44 are formed on the mating surface of the second plate-shaped terminal 42b that engages with the rectifier element 30b1, and three protrusions 44 are also formed on the mating surface that engages with the rectifier element 30b2. The second plate-shaped terminal 42b is engaged with the rectifier element 30b1 and the rectifier element 30b2 at least at the protrusions 44.

[0067] By forming protrusions 44 on both the second plate-shaped terminal 42a and the second plate-shaped terminal 42b, when the solder melts during the remelting process, the remaining solder accumulates on the flat surfaces other than the protrusions 44 on both the second plate-shaped terminal 42a and the second plate-shaped terminal 42b. Therefore, the thickness of the solidified solder layer can be suppressed.

[0068] In this embodiment, a protrusion 44 is formed in both the second plate terminal 42a and the second plate terminal 42b, but a protrusion may also be formed in both the first plate terminal 23a and the first plate terminal 23b.

[0069] Rectifier elements 30a1 and 30a2 are mounted on mounting surface 41a. Rectifier element 30a1 is connected to both the first plate terminal 23a and the second plate terminal 42a via a solder joint spanning gap 43a. The anode terminal 34 of rectifier element 30a1 is connected to the first plate terminal 23a via a solder joint. The cathode terminal 35 of rectifier element 30a1 is connected to the second plate terminal 42a via a solder joint. Similarly, rectifier element 30a2 is connected to both the first plate terminal 23a and the second plate terminal 42a via a solder joint spanning gap 43a.

[0070] Rectifier elements 30b1 and 30b2 are mounted on mounting surface 41b. Similar to rectifier elements 30a1 and 30a2, rectifier elements 30b1 and 30b2 each span gap 43b and are joined to the first plate terminal 23b and the second plate terminal 42b by solder connection using solder.

[0071] The non-conductive resin used as the forming material of the resin molded body 40 can be a resin with a melting point higher than that of solder. Resins with melting points higher than those of solder include PPS (Polyphenylene Sulfide) and LCP (Liquid Crystal Polymer). For example, the melting point of lead-free solder is around 220°C, while the melting point of PPS is around 280°C, and the melting point of LCP is around 280–370°C.

[0072] Therefore, in the process of installing rectifier components 30a1, 30a2, 30b1, and 30b2, the resin molded body 40 can be placed in the furnace together with the rectifier components 30a1, 30a2, 30b1, and 30b2. Thus, reflow soldering can be performed without the need for a separate metal substrate or the like for mounting the rectifier components.

[0073] Alternatively, the first plate-shaped terminal 23a and the second plate-shaped terminal 42a can be pre-plated with Ni, Au, Ti, or the like. This improves the bonding strength achieved by soldering. When the first plate-shaped terminal 23a and the second plate-shaped terminal 42a are formed first with a plating material, it is ideal to select a plating material that can withstand the molding temperature of the resin molded body 40.

[0074] Ideally, the coefficients of thermal expansion of the materials forming the primary coil 21 and the secondary coil 22 are equal to those of the non-conductive resin. With these equal coefficients of thermal expansion, even if the temperature of the primary coil 21 and the secondary coil 22 rises, peeling or cracking on the resin molded body 40 can be prevented.

[0075] Figure 6 This is a top view showing the structure of the buck converter according to this embodiment. Figure 6 In addition to Figure 4 In addition to the structure shown, the frame 50 included in the buck converter is also shown. A plurality of fixing portions 45 are formed on the resin molded body 40. The plurality of fixing portions 45 are provided for fixing the resin molded body 40 to the frame 50 that houses the resin molded body 40. Each fixing portion 45 has a cylindrical metal bushing portion 46 formed thereon. The bushing portion 46 is integrally formed with the resin molded body 40.

[0076] The resin molded body 40 is fixed to the frame 50 by screws 51 inserted into the bushing portion 46. As a result, the vibration resistance of the buck converter is improved, so that even when the buck converter is installed in an automobile, it can withstand the vibration of the automobile.

[0077] The frame 50 also functions as a heat dissipation component to release heat to the outside of the buck converter. With the resin molded body 40 fixed to the frame 50, the bottom of the resin molded body 40 faces the frame 50. A heat-conducting member (not shown) is provided between the bottom of the resin molded body 40 and the frame 50. Thus, the resin molded body 40 and the frame 50 are thermally connected via the heat-conducting member. The heat generated by the primary-side coil 21 and the secondary-side coil 22 is transferred to the frame 50 via the resin molded body 40 and the heat-conducting member, and is efficiently released from the frame 50 to the outside of the buck converter.

[0078] In this embodiment, the rectifier elements 30a1, 30a2, 30b1, and 30b2, which generate a large amount of heat, are directly connected to the first plate-shaped terminal 23a or the first plate-shaped terminal 23b of the secondary-side coil 22. Therefore, the heat generated by the rectifier elements 30a1, 30a2, 30b1, and 30b2 is transferred to the frame 50 via the secondary-side coil 22, the resin molded body 40, and the heat-conducting member, and is released from the frame 50 to the outside of the buck converter. In this way, the heat dissipation path of the rectifier elements 30a1, 30a2, 30b1, and 30b2 is shared with the heat dissipation path of the secondary-side coil 22.

[0079] Cooling fins or similar materials can also be provided on the heat dissipation surface of the frame 50. When cooling fins are provided on the heat dissipation surface of the frame 50, the heat dissipation efficiency from the frame 50 to the outside is improved. The cooling method for the frame 50 is not limited to water cooling; air cooling can also be used.

[0080] As described above, the buck converter of this embodiment includes a buck transformer 20, a resin molded body 40, and rectifier elements 30a1, 30a2, 30b1, and 30b2. The buck transformer 20 has a primary side coil 21 and a secondary side coil 22. The resin molded body 40 is integrally molded with the primary side coil 21 and the secondary side coil 22 using a non-conductive resin. The rectifier elements 30a1, 30a2, 30b1, and 30b2 are each configured to rectify the induced voltage of the secondary side coil 22. The rectifier elements 30a1, 30a2, 30b1, and 30b2 are each surface-mount type. The resin molded body 40 has: a mounting surface 41a for mounting the rectifier elements 30a1 and 30a2; and a mounting surface 41b for mounting the rectifier elements 30b1 and 30b2. The secondary coil 22 has first plate-shaped terminals 23a and 23b. The first plate-shaped terminal 23a protrudes from the resin molded body 40 in the mounting surface 41a. The first plate-shaped terminal 23b protrudes from the resin molded body 40 in the mounting surface 41b. A second plate-shaped terminal 42a is provided in the mounting surface 41a, spaced apart from the first plate-shaped terminal 23a. A second plate-shaped terminal 42b is provided in the mounting surface 41b, spaced apart from the first plate-shaped terminal 23b. Rectifying elements 30a1 and 30a2 are each joined to the first plate-shaped terminal 23a and the second plate-shaped terminal 42a by soldering. Rectifying elements 30b1 and 30b2 are each joined to the first plate-shaped terminal 23b and the second plate-shaped terminal 42b by soldering. The aforementioned non-conductive resin has a melting point higher than that of the solder.

[0081] According to the above structure, rectifier elements 30a1 and 30a2 can be mounted on the mounting surface 41a of the resin molded body 40, and rectifier elements 30b1 and 30b2 can be mounted on the mounting surface 41b of the resin molded body 40. Furthermore, in the process of mounting rectifier elements 30a1, 30a2, 30b1, and 30b2, the resin molded body 40 and the rectifier elements 30a1, 30a2, 30b1, and 30b2 can be placed together in the furnace. Therefore, even without using a metal substrate for mounting rectifier elements 30a1, 30a2, 30a1, and 30b2, the rectifier elements 30a1, 30a2, 30b1, and 30b2 can be mounted by soldering in a reflow manner. Therefore, the type of metal substrate described in Patent Document 1 can be omitted, thus reducing the number of components in the buck converter.

[0082] In the buck converter of this embodiment, each of the second plate-shaped terminals 42a and 42b has a protrusion 44 that is joined to the rectifier element. According to this structure, excess solder can be accumulated in the portion of each of the second plate-shaped terminals 42a and 42b other than the protrusion 44. Therefore, the thickness of the cured solder layer can be suppressed. The first plate-shaped terminals 23a and 23b may also each have a protrusion 44.

[0083] The buck converter of this embodiment also includes a frame 50 that houses the resin molded body 40. A cylindrical metal bushing portion 46 is formed on the resin molded body 40. The resin molded body 40 is fixed to the frame 50 by screws 51 inserted into the bushing portion 46. According to the above structure, the vibration resistance of the buck converter can be improved.

[0084] In the buck converter of this embodiment, a heat-conducting member is provided between the resin molded body 40 and the frame 50. According to the above structure, the heat generated by the primary side coil 21 and the secondary side coil 22 can be efficiently released to the outside via the resin molded body 40, the heat-conducting member and the frame 50.

[0085] Implementation Method 2

[0086] The buck converter of Embodiment 2 will be described. Figure 7 This is a cross-sectional view showing the structure of the mounting surface of the resin molded body in the buck converter of this embodiment. Furthermore, structural elements having the same function and effect as in Embodiment 1 are labeled with the same symbols, and their descriptions are omitted.

[0087] In the event of an unexpectedly large current surge that damages the rectifier element and causes a short circuit, the outer casing of the rectifier element may ignite. In this situation, the current continues to flow, and therefore, combustion may continue until the flammable components on both the rectifier element and the resin molded body are extinguished. Although the resin molded body is made of flame-retardant material, it is not necessarily non-combustible. Therefore, when the resin molded body chars and burns between the first and second plate-shaped terminals, the first and second plate-shaped terminals may become conductive through the charred resin molded body.

[0088] like Figure 7 As shown, in the resin molded body 40 of this embodiment, a cavity 47 is formed on the mounting surface 41a located between the first plate-shaped terminal 23a and the second plate-shaped terminal 42a. The cavity 47 penetrates the resin molded body 40 along its thickness direction. Ideally, the cavity 47 is formed entirely in the portion sandwiched between the first plate-shaped terminal 23a and the second plate-shaped terminal 42a when viewed from above on the mounting surface 41a. Although not shown in the figure, a cavity 47 is also formed on the mounting surface 41b located between the first plate-shaped terminal 23b and the second plate-shaped terminal 42b. If the strength of the resin molded body 40 is insufficient due to the formation of the cavity 47, the cavity 47 can be filled with a resin that has a higher flame retardancy than the forming material of the resin molded body 40.

[0089] As explained above, in the buck converter of this embodiment, a cavity 47 is formed on the mounting surface 41a located between the first plate-shaped terminal 23a and the second plate-shaped terminal 42a. Similarly, a cavity 47 is formed on the mounting surface 41b located between the first plate-shaped terminal 23b and the second plate-shaped terminal 42b.

[0090] According to the above structure, even if the outer material of rectifier element 30a1 or rectifier element 30a2 burns, the continuity between the first plate-shaped terminal 23a and the second plate-shaped terminal 42a caused by the carbonized resin molded body 40 can be prevented. Similarly, even if the outer material of rectifier element 30b1 or rectifier element 30b2 burns, the continuity between the first plate-shaped terminal 23b and the second plate-shaped terminal 42b caused by the carbonized resin molded body 40 can be prevented.

[0091] Implementation Method 3

[0092] The buck converter of Embodiment 3 will be described. Figure 8 This is a perspective view showing the main structural components of the buck converter in this embodiment. Figure 9 This is a top view showing the main structural components of the buck converter in this embodiment. Furthermore, structural elements having the same function and effect as in Embodiment 1 or 2 are labeled with the same symbols, and their descriptions are omitted.

[0093] like Figure 8 and Figure 9 As shown, the first plate-shaped terminal 23a has a recess 48. A recess 48 is formed on both the mating surface of the first plate-shaped terminal 23a that engages with the rectifier element 30a and the mating surface that engages with the rectifier element 30a2. The first plate-shaped terminal 23b also has a recess 48, similar to the first plate-shaped terminal 23a.

[0094] The second plate-shaped terminal 42a has a groove 49. A groove 49 surrounding three protrusions 44 is formed on the mating surface of the second plate-shaped terminal 42a that engages with the rectifier element 30a1. The same groove 49 is also formed on the mating surface that engages with the rectifier element 30a2. The second plate-shaped terminal 42b similarly has a groove 49 as the second plate-shaped terminal 42a.

[0095] In this embodiment, recesses 48 are formed in each of the first plate-shaped terminals 23a and 23b, allowing molten solder to accumulate in the recesses 48 during the remelting process. This suppresses solder wetting and diffusion, and consequently, prevents solder from sinking into the gaps 43a and 43b.

[0096] Furthermore, in this embodiment, grooves 49 are formed in each of the second plate-shaped terminals 42a and 42b. Therefore, molten solder can flow into the grooves 49 during the remelting process, and solder can be prevented from spreading across the grooves 49. As a result, solder wetting and diffusion can be suppressed, and the range of solder wetting and diffusion can be managed. Therefore, heat trapping of solder into the gaps 43a and 43b can be suppressed.

[0097] In this embodiment, recesses 48 are formed in each of the first plate-shaped terminals 23a and 23b, but grooves may also be formed in each of the first plate-shaped terminals 23a and 23b. Furthermore, in this embodiment, grooves 49 are formed in each of the second plate-shaped terminals 42a and 42b, but recesses may also be formed in each of the second plate-shaped terminals 42a and 42b.

[0098] Alternatively, solder resist can be applied to the surfaces of the first plate terminals 23a and 23b and the second plate terminals 42a and 42b. Applying solder resist can also suppress the wetting and diffusion of solder.

[0099] As explained above, in the buck converter of this embodiment, a recess 48 or a groove 49 is formed on the mating surface of at least one of the first plate-shaped terminal 23a and the second plate-shaped terminal 42a that engages with the rectifier elements 30a1 and 30a2. Furthermore, a recess 48 or a groove 49 is formed on the mating surface of at least one of the first plate-shaped terminal 23b and the second plate-shaped terminal 42b that engages with the rectifier elements 30b1 and 30b2. According to the above structure, solder wetting and diffusion can be suppressed, and therefore, heat trapping of solder into the gaps 43a and 43b can be suppressed.

[0100] The present application specification describes illustrative embodiments, but the various features, forms and functions described in each embodiment are not only applicable to the above embodiments, but can also be applied to other embodiments individually or in various combinations.

Claims

1. A buck converter, characterized in that, include: A step-down transformer, the step-down transformer having a primary winding and a secondary winding; A resin molded body, wherein the resin molded body is integrally molded with the primary side coil and the secondary side coil using a non-conductive resin; and A rectifier element that rectifies the induced voltage of the secondary coil. The rectifier element is surface-mount type. The resin molded body has a mounting surface for mounting the rectifier element. The secondary coil has a first plate-shaped terminal. The first plate-shaped terminal protrudes from the resin molded body in the mounting surface. A second plate-shaped terminal is provided on the mounting surface, spaced apart from the first plate-shaped terminal and arranged side by side. The rectifier element is joined to both the first plate terminal and the second plate terminal by means of solder joints. The non-conductive resin has a higher melting point than the solder. A cavity is formed on the mounting surface located between the first plate-shaped terminal and the second plate-shaped terminal. The cavity penetrates the resin molded body below the gap, and the width of the cavity is the same as the width of the gap.

2. The buck converter as described in claim 1, characterized in that, The second plate-shaped terminal has a protrusion that engages with the rectifier element. The second plate-shaped terminal has a groove formed on the mating surface that engages with the rectifier element and surrounds the protrusion.

3. The buck converter as described in claim 2, characterized in that, The first plate-shaped terminal has a protrusion that engages with the rectifier element.

4. The buck converter as described in any one of claims 1 to 3, characterized in that, It also includes a frame that houses the resin molded body. A cylindrical metal bushing portion is formed on the resin molded body. The resin molded body is fixed to the frame by screws inserted into the bushing portion.

5. The buck converter as described in any one of claims 1 to 3, characterized in that, It also includes a frame that houses the resin molded body. A heat-conducting component is provided between the resin molded body and the frame.

6. The buck converter as described in any one of claims 1 to 3, characterized in that, A recess or groove is formed on the mating surface of the first plate-shaped terminal that engages with the rectifier element.

7. The buck converter as described in claim 4, characterized in that, A recess or groove is formed on the mating surface of the first plate-shaped terminal that engages with the rectifier element.

8. The buck converter as described in claim 5, characterized in that, A recess or groove is formed on the mating surface of the first plate-shaped terminal that engages with the rectifier element.

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