Forward type DC / DC converter

Abstract

To provide a forward type DC / DC converter capable of being miniaturized.SOLUTION: A converter 10 includes a core 50 around which a primary winding 21, a secondary winding 22 of a transformer 11, and a smoothing coil 43 are wound. The core 50 includes: a first base unit 51a; a second base unit 52a; a third core component 53 located between the first base unit 51a and the second base unit 52a; a first middle leg unit 51b that is located between the first base unit 51a and the third core component 53 and about which the primary winding 21 and the secondary winding 22 are wound; and a second middle leg unit 52b that is located between the second base unit 52a and the third core component 53 and about which the smoothing coil 43 is wound. A winding direction of the primary winding 21 from a first end 21a toward a second end 21b, a winding direction of the secondary winding 22 from a third end 22a toward a fourth end 22b, and a winding direction of the smoothing coil 43 from a fifth end 43a toward a sixth end 43b are the same direction.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a forward type DC-DC converter. [Background technology]

[0002] Patent Document 1 describes a forward type DC-DC converter. The forward type DC-DC converter includes a transformer and a smoothing reactor. The transformer includes a transformer core, a primary winding, and a secondary winding. The transformer core is configured with two core components. The primary winding and the secondary winding are each wound around the transformer core. The smoothing reactor includes a smoothing reactor core and a smoothing coil. The reactor core is configured with two core components. The smoothing coil is electrically connected to the secondary winding. The smoothing coil is wound around the smoothing reactor core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-131464 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for miniaturization of such forward type DC-DC converters. [Means for solving the problem]

[0005] A forward type DCDC converter for solving the above problems includes a transformer having a primary winding and a secondary winding, a switching element electrically connected to the primary winding, a rectifier circuit electrically connected to the secondary winding, a smoothing reactor having a smoothing coil electrically connected to the secondary winding, and a core around which the primary winding, the secondary winding, and the smoothing coil are wound, the core having a first base portion, a second base portion, a middle portion located between the first base portion and the second base portion, a first center leg portion located between the first base portion and the middle portion and around which the primary winding and the secondary winding are wound, a pair of first outer legs located on both sides of the first center leg portion between the first base portion and the middle portion, a second center leg portion located between the second base portion and the middle portion and around which the smoothing coil is wound, and a second outer leg portion located between the second base portion and the middle portion. a pair of second outer legs located on both sides of a middle leg, wherein a first end which is one end of the primary winding is electrically connected to a positive electrode of a DC power supply, a second end which is the other end of the primary winding is electrically connected to a negative electrode of the DC power supply, a third end which is one end of the secondary winding is electrically connected to a positive input terminal of the rectifier circuit, a fourth end which is the other end of the secondary winding is electrically connected to a negative input terminal of the rectifier circuit, a fifth end which is one end of the smoothing coil is electrically connected to a positive output terminal of the rectifier circuit, and a sixth end which is the other end of the smoothing coil is electrically connected to a negative output terminal of the rectifier circuit, and a winding direction of the primary winding from the first end to the second end, a winding direction of the secondary winding from the third end to the fourth end, and a winding direction of the smoothing coil from the fifth end to the sixth end are the same.

[0006] According to the above configuration, the magnetic flux generated by the current flowing through the primary winding passes through the first base portion, the intermediate portion, the first center leg portion, and the pair of first outer legs. That is, the first base portion, the intermediate portion, the first center leg portion, and the pair of first outer legs constitute a transformer core. Also, the magnetic flux generated by the current flowing through the smoothing coil passes through the second base portion, the intermediate portion, the second center leg portion, and the pair of second outer legs. That is, the second base portion, the intermediate portion, the second center leg portion, and the pair of second outer legs constitute a smoothing reactor core. In this way, the intermediate portion serves as a part of the transformer core and a part of the smoothing reactor core, so that the number of core components constituting the core can be reduced compared to the case where the transformer core and the smoothing reactor core are prepared separately. Therefore, the forward type DC-DC converter can be made smaller.

[0007] Furthermore, in the intermediate section, the direction of the magnetic flux generated by the current flowing through the primary winding and the direction of the magnetic flux generated by the current flowing through the smoothing coil are opposite. Therefore, in the intermediate section, the magnetic flux generated by the current flowing through the primary winding and the magnetic flux generated by the current flowing through the smoothing coil cancel each other out, allowing the magnetic flux density in the intermediate section to be reduced. As a result, the magnetic flux density in the intermediate section is less likely to exceed the upper limit of the magnetic flux density set for each core material, allowing the intermediate section to be made smaller. This also makes it possible to miniaturize the forward type DCDC converter.

[0008] Furthermore, by reducing the maximum magnetic flux density in the intermediate portion, the iron loss can be reduced compared to the total iron loss of the transformer and the smoothing reactor when the transformer and the smoothing reactor are provided separately.

[0009] The above forward type DC-DC converter may further include a first circuit board that holds the primary winding and the secondary winding, and a second circuit board that holds the smoothing coil. According to the above configuration, the primary winding and the secondary winding can be stably held by the first circuit board. Also, the smoothing coil can be stably held by the second circuit board. In this case, the primary winding, the secondary winding, and the smoothing coil can be held at low cost compared to a case where the primary winding, the secondary winding, and the smoothing coil are wound on bobbins, respectively.

[0010] In the above forward type DCDC converter, the core is composed of a first core component having the first base portion, the first center leg portion, and the pair of first outer legs, a second core component having the second base portion, the second center leg portion, and the pair of second outer legs, and a third core component constituting the intermediate portion, and the third core component may be separate from at least one of the first core component and the second core component.

[0011] For example, when the first base, the intermediate section, the first center leg, and the pair of first outer legs are integrated, in order to wind the primary winding and the secondary winding around the first center leg, it is necessary to pass the primary winding and the secondary winding between the first center leg and each of the first outer legs. In contrast, if the third core component constituting the intermediate section is separate from the first core component having the first base, the first center leg, and the pair of first outer legs, it is possible to wind the primary winding and the secondary winding, and then insert the first center leg inside the wound primary winding and secondary winding. This makes it easier to wind the primary winding and the secondary winding around the first center leg.

[0012] For example, when the second base portion, the intermediate portion, the second center leg portion, and the pair of second outer legs are integrated, in order to wind the smoothing coil around the second center leg portion, it is necessary to pass the smoothing coil between the second center leg portion and each of the second outer legs. In contrast, if the third core component constituting the intermediate portion is separate from the second core component having the second base portion, the second center leg portion, and the pair of second outer legs, it is possible to insert the second center leg portion inside the wound smoothing coil after winding the smoothing coil. This makes it easier to wind the smoothing coil around the second center leg portion.

[0013] The above forward type DCDC converter may further include an active clamp circuit connected in parallel to the primary winding. According to the above configuration, when the switching element is off, the energy stored in the primary side of the transformer while the switching element was on is released by the active clamp circuit. Therefore, even when the switching element is off, a current flows through the primary winding. Therefore, in the intermediate portion, not only when the switching element is on but also when it is off, the magnetic flux generated by the current flowing through the primary winding and the magnetic flux generated by the current flowing through the smoothing coil cancel each other out, thereby reducing losses. Effect of the Invention

[0014] According to the present invention, the forward type DC-DC converter can be made smaller. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a circuit configuration diagram of a forward type DC-DC converter according to an embodiment. [Diagram 2] Figure 2(a) is a diagram showing the state of the main switching element, Figure 2(b) is a diagram showing the state of the clamp switching element, Figure 2(c) is a graph of the current flowing in the smoothing coil, and Figure 2(d) is a graph of the current flowing in the primary winding. [Diagram 3] FIG. 3 is an exploded perspective view of a forward type DC-DC converter according to an embodiment. [Figure 4] FIG. 4 is a cross-sectional view of a forward DC-DC converter according to an embodiment. [Diagram 5] FIG. 5 is a diagram for explaining the operation of the forward type DC-DC converter in the embodiment. [Figure 6] FIG. 6 is a cross-sectional view of a forward type DC-DC converter in a modified example. [Figure 7] FIG. 7 is a cross-sectional view of a forward type DC-DC converter in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] An embodiment of a forward type DC-DC converter will be described below with reference to Figures 1 to 5. In the following description, the forward type DC-DC converter will be simply referred to as a "converter".

[0017] As shown in Fig. 1, a DC power supply 101 is connected to the input side of a converter 10. A load 102 is connected to the output side of the converter 10. The converter 10 transforms DC power from the DC power supply 101 and supplies the transformed power to the load 102. The DC power supply 101 in this embodiment is a high-voltage battery. The converter 10 in this embodiment steps down the DC power from the high-voltage battery and supplies the transformed power to the load 102.

[0018] The converter 10 includes a transformer 11, a main switching element 12 as a switching element, a rectifier circuit 13, a smoothing circuit 14, and a control circuit 15. The converter 10 of this embodiment further includes an active clamp circuit 16. Therefore, the converter 10 of this embodiment is an active clamp type forward DC-DC converter.

[0019] The transformer 11 has a primary winding 21 and a secondary winding 22. The primary winding 21 has a first end 21a and a second end 21b. The first end 21a is one end of the primary winding 21, and the second end 21b is the other end of the primary winding 21. The first end 21a of the primary winding 21 is electrically connected to the positive electrode of the DC power supply 101. The secondary winding 22 has a third end 22a and a fourth end 22b. The third end 22a is one end of the secondary winding 22, and the fourth end 22b is the other end of the secondary winding 22. In this embodiment, the number of turns of the secondary winding 22 is smaller than the number of turns of the primary winding 21. The number of turns of the primary winding 21 and the number of turns of the secondary winding 22 are appropriately set according to the required output voltage.

[0020] The main switching element 12 is electrically connected to the primary winding 21 of the transformer 11. The main switching element 12 in this embodiment is a MOSFET. The main switching element 12 may be an IGBT. One end of the main switching element 12 is electrically connected to a second end 21b of the primary winding 21, and the other end of the main switching element 12 is electrically connected to the negative electrode of the DC power supply 101. Therefore, the second end 21b of the primary winding 21 is connected to the negative electrode of the DC power supply 101 via the main switching element 12.

[0021] The rectifier circuit 13 is electrically connected to the secondary winding 22 of the transformer 11. The rectifier circuit 13 has a positive bus L1, a negative bus L2, a first diode 31, and a second diode 32. One end of the positive bus L1 constitutes a positive input end 13a, and the other end of the positive bus L1 constitutes a positive output end 13c. One end of the negative bus L2 constitutes a negative input end 13b, and the other end of the negative bus L2 constitutes a negative output end 13d. The first diode 31 is provided on the positive bus L1. The anode of the first diode 31 is located on the positive input end 13a side. The cathode of the first diode 31 is located on the positive output end 13c side. The second diode 32 is electrically connected to both the positive bus L1 and the negative bus L2. The anode of the second diode 32 is electrically connected to the negative bus L2. The cathode of the second diode 32 is electrically connected between the first diode 31 and the positive output terminal 13c in the positive bus L1.

[0022] The third end 22a of the secondary winding 22 is electrically connected to the positive input terminal 13a of the rectifier circuit 13. The fourth end 22b of the secondary winding 22 is electrically connected to the negative input terminal 13b of the rectifier circuit 13.

[0023] The smoothing circuit 14 is electrically connected to the secondary winding 22 of the transformer 11. The smoothing circuit 14 has a smoothing reactor 41 and a smoothing capacitor 42. The smoothing reactor 41 has a smoothing coil 43. The smoothing coil 43 has a fifth end 43a and a sixth end 43b. The fifth end 43a is one end of the smoothing coil 43, and the sixth end 43b is the other end of the smoothing coil 43.

[0024] The fifth end 43a of the smoothing coil 43 is electrically connected to the positive output end 13c of the rectifier circuit 13. The sixth end 43b of the smoothing coil 43 is electrically connected to one end of the smoothing capacitor 42, and the other end of the smoothing capacitor 42 is electrically connected to the negative output end 13d of the rectifier circuit 13. Therefore, the sixth end 43b of the smoothing coil 43 is electrically connected to the negative output end 13d of the rectifier circuit 13 via the smoothing capacitor 42.

[0025] The active clamp circuit 16 has a clamp capacitor 61 and a clamp switching element 62. The clamp capacitor 61 and the clamp switching element 62 are connected in series. The active clamp circuit 16 is connected in parallel with the primary winding 21. The clamp switching element 62 in this embodiment is a MOSFET. The clamp switching element 62 may be an IGBT. One end of the clamp capacitor 61 is electrically connected to the positive electrode of the DC power supply 101, and the other end of the clamp capacitor 61 is electrically connected to one end of the clamp switching element 62. The other end of the clamp switching element 62 is electrically connected to one end of the main switching element 12.

[0026] The control circuit 15 includes a processor and a storage unit. The processor is, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit includes a random access memory (RAM) and a read only memory (ROM). The storage unit stores program codes or instructions configured to cause the processor to execute processes. The storage unit, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control circuit 15 may be configured by a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control circuit 15, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0027] The control circuit 15 controls the switching operations of the main switching element 12 and the clamp switching element 62. The control circuit 15 turns the main switching element 12 and the clamp switching element 62 on and off alternately.

[0028] As shown in Figures 2(a) and 2(b), when the main switching element 12 is turned on, the control circuit 15 turns off the clamp switching element 62. When the main switching element 12 is turned off, the control circuit 15 turns on the clamp switching element 62. The duty ratios shown in Figures 2(a) and 2(b) are examples. The duty ratio is set appropriately according to the required output voltage.

[0029] <Converter operation> 1 indicates the flow of current in the converter 10 when the main switching element 12 is on. When the main switching element 12 is on, an excitation current flows from the DC power supply 101 to the primary winding 21 of the transformer 11, generating an induced electromotive force on the secondary side of the transformer 11. This induced electromotive force causes a current to flow from the secondary winding 22 of the transformer 11 to the load 102 via the first diode 31 and the smoothing reactor 41. At this time, energy is stored in the smoothing reactor 41 due to the current i43 flowing through the smoothing coil 43. In addition, energy is stored on the primary side of the transformer 11 due to the current i21 flowing through the primary winding 21.

[0030] 1 indicates the flow of current in the converter 10 when the main switching element 12 is off. When the main switching element 12 is off, the smoothing reactor 41 releases its stored energy, causing a current to flow from the smoothing reactor 41 to the load 102 via the second diode 32. The converter 10 of this embodiment includes an active clamp circuit 16. Therefore, when the main switching element 12 is off, the energy stored on the primary side of the transformer 11 is released.

[0031] 2(c), the current i43 flowing through the smoothing coil 43 gradually increases after a certain time has elapsed after the main switching element 12 is turned on. When the main switching element 12 is turned off, the current i43 flowing through the smoothing coil 43 gradually decreases.

[0032] 2(d), when the main switching element 12 is on, a current i21 flows through the primary winding 21. In addition, in this embodiment, when the main switching element 12 is off, the energy stored on the primary side of the transformer 11 is released, causing the current i21 to flow through the primary winding 21. In other words, in this embodiment, the current i21 flows through the primary winding 21 not only when the main switching element 12 is on but also when it is off.

[0033] <Converter structure> As shown in FIGS. 3 and 4, the converter 10 includes a core 50, a first circuit board 71, a second circuit board 72, a first gap sheet 81, and a second gap sheet .

[0034] The primary winding 21 of this embodiment is formed by winding a conductor. The primary winding 21 of this embodiment is wound 14 turns. However, since the primary winding 21 is illustrated in FIG. 4 only diagrammatically, the number of turns of the primary winding 21 illustrated in FIG. 4 is less than the actual number of turns. The secondary winding 22 of this embodiment is formed by winding a metal plate. The secondary winding 22 of this embodiment is wound one turn. The primary winding 21 and the secondary winding 22 are held by a first circuit board 71. The first circuit board 71 is fixed to a case (not shown). The primary winding 21 is provided on a first surface 71a of the first circuit board 71. The secondary winding 22 is provided on a second surface 71b of the first circuit board 71.

[0035] A first center leg insertion hole 71c is formed in the first circuit board 71. The first center leg insertion hole 71c penetrates the first circuit board 71 in the plate thickness direction. The primary winding 21 and the secondary winding 22 are each arranged to surround the first center leg insertion hole 71c.

[0036] The smoothing coil 43 is composed of a first winding 431 and a second winding 432. In this embodiment, the first winding 431 and the second winding 432 are each formed by winding a metal plate. The first winding 431 is wound one turn. The second winding 432 is wound two turns. The first winding 431 and the second winding 432 are held by a second circuit board 72. The second circuit board 72 is fixed to a case (not shown). The first winding 431 is provided on a first surface 72a of the second circuit board 72. The second winding 432 is provided on a second surface 72b of the second circuit board 72.

[0037] A second center leg insertion hole 72c is formed in the second circuit board 72. The second center leg insertion hole 72c penetrates the second circuit board 72 in the plate thickness direction. The first winding 431 and the second winding 432 are each disposed so as to surround the second center leg insertion hole 72c.

[0038] A through hole 72d is formed in the second circuit board 72. The through hole 72d penetrates the second circuit board 72 in the plate thickness direction. A conductive connection member 90 is inserted into the through hole 72d. A first end 431a of the first winding 431 is electrically connected to the connection member 90. A first end 432a of the second winding 432 is electrically connected to the connection member 90. The first winding 431 and the second winding 432 are electrically connected via the connection member 90. Therefore, the smoothing coil 43 of this embodiment is wound three turns. The second end 431b, which is the end opposite to the first end 431a of the first winding 431, constitutes the sixth end 43b of the smoothing coil 43. The second end 432b, which is the end opposite to the first end 432a of the second winding 432, constitutes the fifth end 43a of the smoothing coil 43.

[0039] The core 50 of this embodiment is composed of a first core constituent body 51, a second core constituent body 52, and a third core constituent body 53. The first core constituent body 51, the second core constituent body 52, and the third core constituent body 53 are each separate bodies. That is, the core 50 of this embodiment is composed of three core constituent bodies. The core 50 of this embodiment is a ferrite core.

[0040] The first core structure 51 is an E core. The first core structure 51 has a flat plate-shaped first base portion 51a, a first center leg portion 51b, and a pair of first outer legs 51c, 51d. The first center leg portion 51b and the pair of first outer legs 51c, 51d extend from the first base portion 51a. The pair of first outer legs 51c, 51d are located on both sides of the first center leg portion 51b. The first circuit board 71 is located between the pair of first outer legs 51c, 51d. The first center leg portion 51b is inserted into the first center leg insertion hole 71c of the first circuit board 71. The first center leg portion 51b and the pair of first outer legs 51c, 51d protrude from the second surface 71b of the first circuit board 71.

[0041] The primary winding 21 and the secondary winding 22 of the transformer 11 are each wound around the first center leg 51b. Therefore, the primary winding 21 and the secondary winding 22 are wound around the core 50. The winding direction of the primary winding 21 from the first end 21a to the second end 21b is the same as the winding direction of the secondary winding 22 from the third end 22a to the fourth end 22b.

[0042] The second core structure 52 is an E core. The second core structure 52 has a flat second base portion 52a, a second center leg portion 52b, and a pair of second outer legs 52c, 52d. The second center leg portion 52b and the pair of second outer legs 52c, 52d extend from the second base portion 52a. The pair of second outer legs 52c, 52d are located on both sides of the second center leg portion 52b. The second circuit board 72 is located between the pair of second outer legs 52c, 52d. The second center leg portion 52b is inserted into the second center leg insertion hole 72c of the second circuit board 72. The second center leg portion 52b and the pair of second outer legs 52c, 52d protrude from the first surface 72a of the second circuit board 72.

[0043] The first winding 431 and the second winding 432 of the smoothing coil 43 are each wound around the second center leg 52b. Therefore, the smoothing coil 43 is wound around the second center leg 52b of the core 50. The winding direction of the smoothing coil 43 from the fifth end 43a to the sixth end 43b is the same as the winding direction of the primary winding 21 from the first end 21a to the second end 21b and the winding direction of the secondary winding 22 from the third end 22a to the fourth end 22b.

[0044] The third core construct 53 is an I-core. The third core construct 53 is flat. The third core construct 53 is disposed between the first core construct 51 and the second core construct 52. Therefore, the core 50 of this embodiment is an EIE core in which the third core construct 53, which is an I-core, is disposed between the first core construct 51, which is an E-core, and the second core construct 52, which is an E-core. The third core construct 53 constitutes an intermediate portion located between the first base portion 51a and the second base portion 52a.

[0045] The first center leg 51b and the pair of first outer legs 51c, 51d extend from the first base 51a toward the third core component 53. The first center leg 51b and the pair of first outer legs 51c, 51d are located between the first base 51a and the third core component 53. The first gap sheet 81 is disposed between the first center leg 51b and the pair of first outer legs 51c, 51d and the third core component 53.

[0046] The second center leg 52b and the pair of second outer legs 52c, 52d extend from the second base 52a toward the third core construct 53. The second center leg 52b and the pair of second outer legs 52c, 52d are located between the second base 52a and the third core construct 53. The second gap sheet 82 is disposed between the second center leg 52b and the pair of second outer legs 52c, 52d and the third core construct 53. In this embodiment, the second gap sheet 82 is thicker than the first gap sheet 81. This allows the energy stored in the smoothing coil 43 to be increased.

[0047] The tip surface of the first center leg 51b faces the tip surface of the second center leg 52b via the first gap sheet 81, the third core construct 53, and the second gap sheet 82. The tip surface of one of the first outer legs 51c faces the tip surface of one of the second outer legs 52c via the first gap sheet 81, the third core construct 53, and the second gap sheet 82. The tip surface of the other of the first outer legs 51d faces the other of the second outer legs 52d via the first gap sheet 81, the third core construct 53, and the second gap sheet 82.

[0048] [Operation of this embodiment] The operation of this embodiment will now be described. The core 50 is composed of a first core component 51, a second core component 52, and a third core component 53. The first core component 51 has a first base 51a, a first center leg 51b, and a pair of first outer legs 51c, 51d. The second core component 52 has a second base 52a, a second center leg 52b, and a pair of second outer legs 52c, 52d. The third core component 53 is an intermediate portion located between the first base 51a and the second base 52a. The first center leg 51b is located between the first base 51a and the third core component 53. The primary winding 21 and the secondary winding 22 are wound around the first center leg 51b. The pair of first outer legs 51c, 51d are located on both sides of the first center leg 51b between the first base portion 51a and the third core component 53. The second center leg 52b is located between the second base portion 52a and the third core component 53. The smoothing coil 43 is wound around the second center leg 52b. The pair of second outer legs 52c, 52d are located on both sides of the second center leg 52b between the second base portion 52a and the third core component 53.

[0049] A first end 21a of the primary winding 21 is electrically connected to the positive electrode of the DC power supply 101. A second end 21b of the primary winding 21 is electrically connected to the negative electrode of the DC power supply 101. A third end 22a of the secondary winding 22 is connected to the positive input terminal 13a of the rectifier circuit 13. A fourth end 22b of the secondary winding 22 is connected to the negative input terminal 13b of the rectifier circuit 13. A fifth end 43a of the smoothing coil 43 is electrically connected to the positive output terminal 13c of the rectifier circuit 13. A sixth end 43b of the smoothing coil 43 is electrically connected to the negative output terminal 13d of the rectifier circuit 13. The winding direction of the primary winding 21 from the first end 21a to the second end 21b, the winding direction of the secondary winding 22 from the third end 22a to the fourth end 22b, and the winding direction of the smoothing coil 43 from the fifth end 43a to the sixth end 43b are the same direction.

[0050] As shown in FIG. 5, in this embodiment, the current i21 flowing through the primary winding 21 flows from the inner side of the paper to the inner side of the paper between the first center leg 51b and one of the first outer legs 51c. The current i21 flowing through the primary winding 21 flows from the inner side of the paper to the inner side of the paper between the first center leg 51b and the other first outer leg 51d. Therefore, in the core 50, a magnetic flux Φ1 that draws a loop from the first center leg 51b through the first base 51a, the first outer legs 51c and 51d, and the third core component 53 in this order and returns to the first center leg 51b flows. The first core component 51 and the third core component 53 constitute a transformer core through which the magnetic flux Φ1 generated by the current i21 flowing through the primary winding 21 flows.

[0051] The current i43 flowing through the smoothing coil 43 flows from the inner side of the drawing to the inner side of the drawing between the second center leg 52b and one of the second outer legs 52c. The current i43 flowing through the smoothing coil 43 flows from the inner side of the drawing to the inner side of the drawing between the second center leg 52b and the other of the second outer legs 52d. Therefore, in the core 50, a magnetic flux Φ2 that draws a loop from the second center leg 52b through the third core constituent 53, the second outer legs 52c and 52d, and the second base 52a in this order and returns to the second center leg 52b flows. The second core constituent 52 and the third core constituent 53 constitute a smoothing reactor core through which the magnetic flux Φ2 generated by the current i43 flowing through the smoothing coil 43 flows.

[0052] In this way, the third core component 53 serves as a part of the transformer core and a part of the smoothing reactor core, so that the number of core components constituting the core 50 can be reduced compared to the case where a transformer core and a smoothing reactor core are separately prepared, and therefore the converter 10 can be made smaller.

[0053] Furthermore, in the third core constituent 53, the direction of the magnetic flux Φ1 and the direction of the magnetic flux Φ2 are opposite to each other. Therefore, in the third core constituent 53, the magnetic flux Φ1 and the magnetic flux Φ2 cancel each other out, thereby reducing the magnetic flux density of the third core constituent 53. Therefore, the magnetic flux density of the third core constituent 53 is less likely to exceed the upper limit of the magnetic flux density determined for each material of the core 50, and the third core constituent 53 can be made smaller. This also makes it possible to make the converter 10 smaller.

[0054] [Effects of this embodiment] The effects of this embodiment will be described. (1) A magnetic flux Φ1 generated by a current i21 flowing through the primary winding 21 flows through the first base portion 51a, the first center leg portion 51b, and the pair of first outer legs 51c, 51d of the first core component 51, and the third core component 53 which is the intermediate portion. In other words, the first core component 51 and the third core component 53 constitute a transformer core. Also, a magnetic flux Φ2 generated by a current i43 flowing through the smoothing coil 43 flows through the second base portion 52a, the second center leg portion 52b, and the pair of second outer legs 52c, 52d of the second core component 52, and the third core component 53 which is the intermediate portion. In other words, the second core component 52 and the third core component 53 constitute a smoothing reactor core. In this way, the third core constituent 53, which is the intermediate portion, serves as a part of the transformer core and a part of the smoothing reactor core, so that the number of core constituents constituting the core 50 can be reduced compared to the case where a transformer core and a smoothing reactor core are separately prepared, and therefore the converter 10 can be made smaller in size.

[0055] In the third core component 53, the direction of the magnetic flux Φ1 generated by the current i21 flowing through the primary winding 21 and the direction of the magnetic flux Φ2 generated by the current i43 flowing through the smoothing coil 43 are opposite to each other. Therefore, in the third core component 53, the magnetic flux Φ1 and the magnetic flux Φ2 cancel each other out, thereby reducing the magnetic flux density of the third core component 53. As a result, the magnetic flux density of the third core component 53 is less likely to exceed the upper limit of the magnetic flux density determined for each material of the core 50, and the third core component 53 can be made smaller in size. This also makes it possible to make the converter 10 smaller in size.

[0056] Furthermore, by reducing the maximum magnetic flux density of the third core structure 53, the iron loss can be reduced compared to the sum of the iron loss of the transformer 11 and the iron loss of the smoothing reactor 41 when the transformer 11 and the smoothing reactor 41 are provided separately.

[0057] (2) The converter 10 of this embodiment includes a first circuit board 71 that holds the primary winding 21 and the secondary winding 22, and a second circuit board 72 that holds the smoothing coil 43. This allows the primary winding 21 and the secondary winding 22 to be stably held by the first circuit board 71. Also, the smoothing coil 43 can be stably held by the second circuit board 72. In this case, the primary winding 21, the secondary winding 22, and the smoothing coil 43 can be held at low cost compared to, for example, a case in which the primary winding 21, the secondary winding 22, and the smoothing coil 43 are each wound around a bobbin.

[0058] (3) For example, when the first core assembly 51 and the third core assembly 53 are integrated, in order to wind the primary winding 21 and the secondary winding 22 around the first center leg 51b, it is necessary to pass the primary winding 21 and the secondary winding 22 between the first center leg 51b and each of the first outer legs 51c and 51d. In contrast, in this embodiment, the first base 51a, the first center leg 51b, and the pair of first outer legs 51c and 51d are integrated as the first core assembly 51. On the other hand, the intermediate portion is formed by the third core assembly 53, which is separate from the first core assembly 51. Therefore, after winding the primary winding 21 and the secondary winding 22, the first center leg 51b can be inserted inside the wound primary winding 21 and secondary winding 22. This makes it easier to wind the primary winding 21 and the secondary winding 22 around the first center leg 51b.

[0059] For example, when the second core construct 52 and the third core construct 53 are integrated, in order to wind the smoothing coil 43 around the second center leg 52b, it is necessary to pass the smoothing coil 43 between the second center leg 52b and each of the second outer legs 52c and 52d. In contrast, in this embodiment, the second base 52a, the second center leg 52b, and the pair of second outer legs 52c and 52d are integrated as the second core construct 52. On the other hand, the middle part is formed by the third core construct 53 which is separate from the second core construct 52. Therefore, after winding the smoothing coil 43, the second center leg 52b can be inserted inside the wound smoothing coil 43. This makes it easier to wind the smoothing coil 43 around the second center leg 52b.

[0060] (4) The converter 10 of this embodiment includes an active clamp circuit 16 connected in parallel to the primary winding 21 of the transformer 11. As a result, when the main switching element 12 is off, the energy stored on the primary side of the transformer 11 while the main switching element 12 is on is released by the active clamp circuit 16. For this reason, even when the main switching element 12 is off, a current i21 flows through the primary winding 21. Therefore, in the third core body 53, the magnetic fluxes Φ1 and Φ2 cancel each other out not only when the main switching element 12 is on but also when it is off, thereby reducing losses.

[0061] [Example of change] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0062] The converter 10 may be configured to boost the power of the DC power supply 101 and output the boosted power to the load 102 . The converter 10 does not have to include the active clamp circuit 16.

[0063] The converter 10 does not necessarily have to include the first circuit board 71 and the second circuit board 72. In this case, the primary winding 21, the secondary winding 22, and the smoothing coil 43 are each wound around a bobbin and held by the bobbin, for example.

[0064] The first gap sheet 81 may be omitted. The first center leg 51b and the pair of first outer leg portions 51c, 51d may each abut against the third core structure 53. In this case, since the first gap sheet 81 is omitted, costs can be reduced.

[0065] 6, instead of disposing the first gap sheet 81 between the first core component 51 and the third core component 53, a gap G1 may be provided. Specifically, the length of the first center leg 51b of the first core component 51 is made shorter than the lengths of the first outer legs 51c, 51d. This provides a gap G1 between the first center leg 51b and the third core component 53. The pair of first outer legs 51c, 51d abut against the third core component 53. In this case, the first gap sheet 81 is omitted, thereby reducing costs.

[0066] As shown in FIG. 6, instead of disposing the second gap sheet 82 between the second core construct 52 and the third core construct 53, a gap G2 may be provided. Specifically, the length of the second center leg 52b of the second core construct 52 is made shorter than the lengths of the second outer legs 52c and 52d. This provides a gap G2 between the second center leg 52b and the third core construct 53. The gap G2 between the second center leg 52b and the third core construct 53 is larger than the gap G1 between the first center leg 51b and the third core construct 53. The pair of second outer legs 52c and 52d abut against the third core construct 53. In this case, the cost can be reduced by the amount that the second gap sheet 82 is omitted.

[0067] The first core structure 51 and the second core structure 52 are not limited to EE cores. The first core structure 51 and the second core structure 52 may be, for example, EER cores or PQ cores. The third core structure 53 is not limited to an I-core.

[0068] As shown in Fig. 7, the third core body 53 may be an E core. The third core body 53 has a flat third base portion 53a, a third center leg portion 53b, and a pair of third outer legs 53c, 53d. The third center leg portion 53b and the pair of third outer legs 53c, 53d extend from the third base portion 53a. The pair of third outer legs 53c, 53d are located on both sides of the third center leg portion 53b.

[0069] A first gap sheet 81 is disposed between the first core construct 51 and the third core construct 53. More specifically, the first gap sheet 81 is disposed between the first center leg 51b and the pair of first outer legs 51c, 51d of the first core construct 51 and the third base 53a of the third core construct 53. A second gap sheet 82 is not disposed between the second core construct 52 and the third core construct 53. The length of the second center leg 52b is shorter than the length of each of the second outer legs 52c, 52d. In addition, the length of the third center leg 53b is shorter than the length of each of the third outer legs 53c, 53d. As a result, a gap G is provided between the second center leg 52b of the second core construct 52 and the third center leg 53b of the third core construct 53. The pair of second outer legs 52c, 52d of the second core body 52 abuts against the pair of third outer legs 53c, 53d of the third core body 53.

[0070] In the above configuration, the third base portion 53a corresponds to the "middle portion" in the claims. The second center leg portion 52b and the third center leg portion 53b correspond to the "second center leg portion" in the claims. The pair of second outer legs 52c, 52d and the pair of third outer legs 53c, 53d correspond to the "pair of second outer legs" in the claims.

[0071] ○ The second core constituent body 52 is not limited to an E core. For example, when the third core constituent body 53 is an E core, the second core constituent body 52 may be an I core. In this case, the third base portion 53a corresponds to the "middle portion" in the claims. The third center leg portion 53b corresponds to the "second center leg portion" in the claims. The pair of third outer legs 53c, 53d correspond to the "pair of second outer legs" in the claims. The second core constituent body 52 corresponds to the "second base portion" in the claims.

[0072] The number of core components constituting the core 50 is not limited to three. For example, the third core assembly 53 may be integrally formed with the first core assembly 51 and separate from the second core assembly 52. ​​In other words, a part of the transformer core may also serve as a part of the smoothing reactor core. In this case, the number of core assemblies constituting the core 50 is two.

[0073] According to this configuration, since the third core body 53 is separate from the second core body 52, after the smoothing coil 43 is wound, the second center leg 52b can be inserted inside the wound smoothing coil 43. This makes it easier to wind the smoothing coil 43 around the second center leg 52b.

[0074] For example, the third core assembly 53 may be integrally formed with the second core assembly 52 and separate from the first core assembly 51. In other words, a part of the smoothing reactor core may also serve as a part of the transformer core. In this case, the number of core assemblies constituting the core 50 is two.

[0075] According to this configuration, since the third core body 53 is a body separate from the first core body 51, after the primary winding 21 and the secondary winding 22 are wound, the first center leg 51b can be inserted inside the wound primary winding 21 and secondary winding 22. This facilitates the winding operation of the primary winding 21 and the secondary winding 22 around the first center leg 51b.

[0076] In other words, the winding work is facilitated if the third core construct 53 is separate from at least one of the first core construct 51 and the second core construct 52. Note that "at least one of the first core construct 51 and the second core construct 52" refers to only the first core construct 51, only the second core construct 52, or both the first core construct 51 and the second core construct 52.

[0077] The primary winding 21 may be formed by winding a metal plate. The secondary winding 22 may be formed by winding a conductive wire. Each of the first winding 431 and the second winding 432 may be formed by winding a conductive wire.

[0078] The smoothing coil 43 may be formed by winding a single conductive wire or a single metal plate. The smoothing coil 43 may be formed by winding and electrically connecting three or more conductive wires or three or more metal plates.

[0079] The number of turns of the smoothing coil 43 may be changed as appropriate. The configuration of the rectifier circuit 13 may be changed as appropriate. For example, the first diode 31 may be changed to a first rectification switching element such as a MOSFET. The second diode 32 may be changed to a second rectification switching element such as a MOSFET. In this case, the control circuit 15 controls the switching operations of the first rectification switching element and the second rectification switching element. When the main switching element 12 is turned on, the control circuit 15 turns on the first rectification switching element and turns off the second rectification switching element. When the main switching element 12 is turned off, the control circuit 15 turns off the first rectification switching element and turns on the second rectification switching element.

[0080] For example, the first diode 31 may be provided on the negative bus L2. The anode of the first diode 31 is located on the negative output terminal 13d side. The cathode of the first diode 31 is located on the positive input terminal 13b side.

[0081] [Note] The technical ideas that can be understood from the above-described embodiment and modified examples will be described below. <Supplementary Note 1> A transformer having a primary winding and a secondary winding, a switching element electrically connected to the primary winding, a rectifier circuit electrically connected to the secondary winding, a smoothing reactor having a smoothing coil electrically connected to the secondary winding, and a core around which the primary winding, the secondary winding, and the smoothing coil are wound, the core having a first base, a second base, a middle section between the first base and the second base, a first center leg section between the first base and the middle section and around which the primary winding and the secondary winding are wound, a pair of first outer legs between the first base and the middle section and on both sides of the first center leg section, a second center leg section between the second base and the middle section and around which the smoothing coil is wound, and a pair of second outer legs between the second base and the middle section and on both sides of the second center leg section. a first end which is one end of the primary winding is electrically connected to a positive electrode of a DC power supply, a second end which is the other end of the primary winding is electrically connected to a negative electrode of the DC power supply, a third end which is one end of the secondary winding is electrically connected to a positive input terminal of the rectifier circuit, a fourth end which is the other end of the secondary winding is electrically connected to a negative input terminal of the rectifier circuit, a fifth end which is one end of the smoothing coil is electrically connected to a positive output terminal of the rectifier circuit, and a sixth end which is the other end of the smoothing coil is electrically connected to a negative output terminal of the rectifier circuit, and a winding direction of the primary winding from the first end to the second end, a winding direction of the secondary winding from the third end to the fourth end, and a winding direction of the smoothing coil from the fifth end to the sixth end are the same.

[0082] <Appendix 2> A forward type DC-DC converter according to <Appendix 1>, comprising: a first circuit board that holds the primary winding and the secondary winding; and a second circuit board that holds the smoothing coil.

[0083] <Appendix 3> The forward type DCDC converter according to <Appendix 1> or <Appendix 2>, wherein the core is composed of a first core component having the first base portion, the first center leg portion, and the pair of first outer legs, a second core component having the second base portion, the second center leg portion, and the pair of second outer legs, and a third core component constituting the intermediate portion, and the third core component is separate from at least one of the first core component and the second core component.

[0084] <Supplementary Note 4> The forward type DC-DC converter according to any one of <Supplementary Note 1> to <Supplementary Note 3>, further comprising an active clamp circuit connected in parallel to the primary winding. [Explanation of symbols]

[0085] 10...converter as a forward type DCDC converter, 11...transformer, 12...main switching element as a switching element, 13...rectifier circuit, 13a...positive input terminal, 13b...negative input terminal, 13c...positive output terminal, 13d...negative output terminal, 16...active clamp circuit, 21...primary winding, 21a...first end, 21b...second end, 22...secondary winding, 22a...third end, 22b...fourth end, 41...smoothing relay Reactor, 43...smoothing coil, 43a...fifth end, 43b...sixth end, 50...core, 51...first core component, 52...second core component, 53...third core component as intermediate section, 51a...first base, 51b...first center leg, 51c...first outer leg, 51d...first outer leg, 52a...second base, 52b...second center leg, 52c...second outer leg, 52d...second outer leg, 71...first circuit board, 72...second circuit board, 101...DC power supply.

Claims

1. a transformer having a primary winding and a secondary winding; a switching element electrically connected to the primary winding; a rectifier circuit electrically connected to the secondary winding; a smoothing reactor having a smoothing coil electrically connected to the secondary winding; a core around which the primary winding, the secondary winding, and the smoothing coil are wound; Equipped with The core is A first base portion; A second base portion; an intermediate portion located between the first base portion and the second base portion; a first center leg portion located between the first base portion and the intermediate portion, around which the primary winding and the secondary winding are wound; a pair of first outer legs located on both sides of the first middle leg between the first base portion and the intermediate portion; a second middle leg portion located between the second base portion and the intermediate portion and around which the smoothing coil is wound; a pair of second outer legs located on both sides of the second middle leg between the second base portion and the intermediate portion; having a first end which is one end of the primary winding is electrically connected to a positive electrode of a DC power supply, and a second end which is the other end of the primary winding is electrically connected to a negative electrode of the DC power supply; a third end which is one end of the secondary winding is electrically connected to a positive input terminal of the rectifier circuit, and a fourth end which is the other end of the secondary winding is electrically connected to a negative input terminal of the rectifier circuit; a fifth end which is one end of the smoothing coil is electrically connected to a positive output terminal of the rectifier circuit, and a sixth end which is the other end of the smoothing coil is electrically connected to a negative output terminal of the rectifier circuit; A forward type DC-DC converter, characterized in that the winding direction of the primary winding from the first end to the second end, the winding direction of the secondary winding from the third end to the fourth end, and the winding direction of the smoothing coil from the fifth end to the sixth end are the same direction.

2. a first circuit board that holds the primary winding and the secondary winding; A second circuit board that holds the smoothing coil; The forward DC-DC converter according to claim 1 .

3. The core is a first core structure having the first base portion, the first center leg portion, and the pair of first outer leg portions; a second core structure having the second base portion, the second center leg portion, and the pair of second outer leg portions; a third core structure constituting the intermediate portion; 2. The forward type DC-DC converter according to claim 1, wherein the third core assembly is separate from at least one of the first core assembly and the second core assembly.

4. The forward type DC-DC converter according to claim 1 , further comprising an active clamp circuit connected in parallel to the primary winding.

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