DC-DC converter and switching power supply device

Abstract

A DC-DC converter (21) is provided with a first switching element (S1), a second switching element (S2), an LC series resonance circuit (LC), a conductor, a first winding (LT21) and a second winding (LT22) that are positively magnetically coupled to each other, a first rectifying element (D1), and a second rectifying element (D2), the LC series resonance circuit being connected to the conductor, the conductor being connected to the first winding and the first rectifying element, and the second winding (LT21) being connected to the second rectifying element. The first winding is connected to the second winding, and the second winding is connected to the second switching element and the second rectifying element.

Description

Technical Field

[0001] This invention relates to DC-DC converters and switching power supply devices. Background Technology

[0002] As a prior art invention related to DC-DC converters, for example, the DC-DC converter described in Patent Document 1 is known. The DC-DC converter described in Patent Document 1 receives a voltage Vin from a DC power supply 10 and outputs a voltage Vout. The DC-DC converter described in Patent Document 1 includes switching elements 11 and 12, a capacitor 13, inductors 14 and 15, diodes 16 and 17, and a smoothing capacitor 18. Inductor 14 includes a primary winding 141, a secondary winding 142, and output voltage terminals 201 and 202. The turns ratio of the primary winding 141 to the secondary winding 142 is n:1. Inductor 15 includes a primary winding 151 and a secondary winding 152. The turns ratio of the primary winding 151 to the secondary winding 152 is n:1.

[0003] The positive terminal of the DC power supply 10 is connected to one end of the series circuit of switching element 11 and switching element 12. The negative terminal of the DC power supply 10 is connected to the other end of the series circuit of switching element 11 and switching element 12.

[0004] Switching elements 11 and 12 are controlled such that when one is turned on, the other is turned off. The connection point of switching elements 11 and 12 is connected to the negative terminal of the DC power supply via a series circuit of capacitor 13, primary winding 141 of inductor 14, and primary winding 151 of inductor 15.

[0005] One end of the secondary winding 142 of inductor 14 is connected to the cathode of diode 16. The other end of the secondary winding 142 of inductor 14 is connected to one end of the secondary winding 152 of inductor 15. The other end of the secondary winding 152 of inductor 15 is connected to the cathode of diode 17. The connection point between the other end of the secondary winding 142 of inductor 14 and one end of the secondary winding 152 of inductor 15 is connected to the output voltage terminal 201. The anodes of diodes 16 and 17 are both connected to the output voltage terminal 202. A smoothing capacitor 18 is connected between the output voltage terminals 201 and 202. The voltage Vout output from the DC-DC converter can be expressed as D×(1-D)×Vin / n. Here, D is the ratio of the on-time of switching element 11 to the switching cycle (the sum of the on-time and off-time of switching element 11).

[0006] Prior art literature

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 4649299 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In the above structure, to increase the buck ratio of the DC-DC converter, the number of turns in the primary winding needs to be increased. For example, with D=0.5, if the buck ratio is to be set to 1 / 8 (Vout=1 / 8Vin), then n=2. Because the turns ratio of the primary winding 141 to the secondary winding 142 becomes 2:1, and the turns ratio of the primary winding 151 to the secondary winding 152 also becomes 2:1, the turns ratio of the total of the primary windings 141 and 151 to the secondary windings 142 and 152 becomes 4:1:1. If the number of turns in the primary winding increases, the resistance of the primary winding increases, and therefore the copper losses caused by the primary winding increase.

[0011] Furthermore, when switching element 11 is on and switching element 12 is off, no current flows through the secondary winding 142 of inductor 14 and diode 16, but current flows through the secondary winding 152 of inductor 15 and diode 17. When switching element 11 is off and switching element 12 is on, current flows through the secondary winding 142 of inductor 14, but no current flows through the secondary winding 152 of inductor 15. Thus, the periods during which current flows through the secondary winding 142 of inductor 14 (the first period) and the periods during which current flows through the secondary winding 152 of inductor 15 (the second period) are biased towards a given period. Therefore, relative to a given output current, the effective value of the current Irec2 flowing through the secondary winding 142 of inductor 14 increases during the first period. Similarly, the effective value of the current Irec1 flowing through the secondary winding 152 of inductor 15 increases during the second period. Therefore, the copper losses caused by the secondary winding 142 of inductor 14 and the copper losses caused by the secondary winding 152 of inductor 15 increase.

[0012] Therefore, the object of the present invention is to provide a DC-DC converter and a switching power supply device that can reduce copper losses.

[0013] Technical solutions for solving the problem

[0014] One aspect of the present invention relates to a DC-DC converter comprising:

[0015] The first switching element has a first terminal and a second terminal, wherein the first terminal is connected to a DC power supply;

[0016] The second switching element has a third terminal and a fourth terminal, wherein the third terminal is connected to the second terminal;

[0017] An LC series resonant circuit has a fifth terminal and a sixth terminal, wherein the fifth terminal is connected to the connection point of the second terminal and the third terminal;

[0018] A conductor having a 7th end and an 8th end;

[0019] The first winding has a 9th end and a 10th end;

[0020] The second winding has an 11th end and a 12th end;

[0021] The first rectifier element has a 13th terminal and a 14th terminal; and

[0022] The second rectifier element has a 15th terminal and a 16th terminal, wherein the 15th terminal is connected to the 13th terminal.

[0023] The first winding and the second winding are positively magnetically coupled to each other.

[0024] The sixth end is connected to the seventh end.

[0025] The 8th end is connected to the 9th end and the 14th end.

[0026] The 10th end is connected to the 11th end.

[0027] The 12th end is connected to the 4th end and the 16th end.

[0028] The 8th end of the conductor is connected to the 9th end of the first winding and the 14th end of the first rectifier element, thereby making the first winding also equivalent to part of the primary winding. Therefore, the DC-DC converter according to one aspect of the present invention can improve the buck ratio of the DC-DC converter without increasing the number of turns in the primary winding. As a result, the DC-DC converter according to one aspect of the present invention can reduce copper losses caused by the primary winding.

[0029] Invention Effects

[0030] The DC-DC converter and switching power supply device according to the present invention can reduce copper loss. Attached Figure Description

[0031] Figure 1 This is a circuit diagram showing a switching power supply device 20 equipped with a DC-DC converter 21 and a load resistor RL1.

[0032] Figure 2This is a diagram showing an example of the drain-source voltage v1 of the first switching element S1, the drain-source voltage v2 of the second switching element S2, the first control signal CS1, the second control signal CS2, the current i1 flowing through the capacitor C, the magnetizing current im flowing through the first magnetizing inductor Lm1, the current iD1 flowing through the first diode D1, and the current iD2 flowing through the second diode D2.

[0033] Figure 3 It is a schematic cross-sectional view showing the structure of transformer TR1 and a diagram showing the wiring of transformer TR1.

[0034] Figure 4 This is a schematic top view showing the construction of the first core CO1.

[0035] Figure 5 This is a diagram showing the operation of the current flowing through the switching power supply device 20 and the load resistor RL1 during the first period P1.

[0036] Figure 6 This is a diagram showing the operation of the current flowing through the switching power supply device 20 and the load resistor RL1 in the second period P2.

[0037] Figure 7 It is a schematic cross-sectional view showing the structure of transformer TR2 and a diagram showing the wiring of transformer TR2.

[0038] Figure 8 This is a schematic top view showing the construction of the first core CO1.

[0039] Figure 9 This is a circuit diagram showing a switching power supply device 20b with a DC-DC converter 21b and a load resistor RL1.

[0040] Figure 10 This is a circuit diagram showing a switching power supply device 20c equipped with a DC-DC converter 21c and load resistors RL1 and RL2.

[0041] Figure 11 This is a circuit diagram showing a switching power supply device 20d equipped with a DC-DC converter 21d and load resistors RL1 and RL2.

[0042] Figure 12 This is a circuit diagram showing a switching power supply device 20e with a DC-DC converter 21e and a load resistor RL1.

[0043] Figure 13 It is a schematic cross-sectional view showing the structure of transformer TR4 and a diagram showing the wiring of transformer TR4.

[0044] Figure 14 This is a schematic top view showing the construction of the first core CO1.

[0045] Figure 15 It is a schematic cross-sectional view showing the structure of transformer TR6 and a diagram showing the wiring of transformer TR6.

[0046] Figure 16 This is a schematic top view showing the construction of the first core CO1.

[0047] Figure 17 This is a circuit diagram showing a switching power supply device 20g equipped with a DC-DC converter 21g and a load resistor RL1.

[0048] Figure 18 It is a schematic cross-sectional view showing the structure of transformer TR7 and a diagram showing the wiring of transformer TR7.

[0049] Figure 19 This is a schematic top view showing the structure of the second CO2 core.

[0050] Figure 20 It is a schematic cross-sectional view showing the structure of transformer TR8 and a diagram showing the wiring of transformer TR8.

[0051] Figure 21 This is a schematic top view showing the structure of the second CO2 core.

[0052] Figure 22 This is a circuit diagram showing the switching circuit SW in the 9th variation.

[0053] Figure 23 This is a circuit diagram showing the switching circuit SW in the 10th variation.

[0054] Figure 24 This is a circuit diagram showing a modified example of the first rectifier element. Detailed Implementation

[0055] [First Implementation]

[0056] Hereinafter, a switching power supply device 20 having the DC-DC converter 21 according to the first embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a circuit diagram showing a switching power supply device 20 equipped with a DC-DC converter 21 and a load resistor RL1. Additionally, in Figure 1 The leakage inductance of transformer TR1 is omitted in the text. Figure 2This is a diagram illustrating an example of the drain-source voltage v1 of the first switching element S1, the drain-source voltage v2 of the second switching element S2, the first control signal CS1, the second control signal CS2, the current i1 flowing through the capacitor C, the magnetizing current im flowing through the first magnetizing inductor Lm1, the current iD1 flowing through the first diode D1, and the current iD2 flowing through the second diode D2. Additionally, Figure 2 The horizontal axis in the graph represents time t. Furthermore... Figure 2 The vertical axis represents the voltage v1 between the drain (D) and source (S) of the first switching element S1, the voltage v2 between the drain (D) and source (S) of the second switching element S2, the first control signal CS1 of the first switching element S1, the second control signal CS2 of the second switching element S2, the current i1 flowing through the capacitor C, the magnetizing current im flowing through the first magnetizing inductor Lm1, the current iD1 flowing through the first diode D1, and the current iD2 flowing through the second diode D2. Figure 2 In this context, the direction of current iD1 is defined as the direction from the first anode A1 through the first cathode K1, which is considered positive. Furthermore, in... Figure 2 In this context, the direction of current iD2 is defined as the direction from the second anode A2 through the second cathode K2 as positive. Figure 3 It is a schematic cross-sectional view showing the structure of transformer TR1 and a diagram showing the wiring of transformer TR1. Figure 4 This is a schematic top view showing the construction of the first core CO1.

[0057] The switching power supply unit 20 is used to supply DC voltage to the load. For example... Figure 1 As shown, the switching power supply device 20 includes a DC power supply DCPS, a DC-DC converter 21, and first output terminals O1 and O2.

[0058] The first output terminals O1 and O2 are connected to the two ends of the load resistor RL1. The first output terminal O2 is connected to ground potential. In this embodiment, the first output terminal O2 is connected to the ground wire. Alternatively, the first output terminal O2 may not be connected to the ground wire. Furthermore, the load resistor RL1 is a specific example of a load. The load is not limited to a resistive component and may also include a reactive component.

[0059] The DC power supply (DCPS) outputs a first DC voltage, Vin. The negative terminal of the DC power supply (DCPS) is connected to the first output terminal O2. Therefore, the negative terminal of the DC power supply (DCPS) is connected to ground potential. The positive terminal of the DC power supply (DCPS) is connected to the DC-DC converter 21. The DC power supply (DCPS) can be, for example, a battery or a double-layer capacitor. Alternatively, the DC power supply (DCPS) only needs to output a DC voltage. Therefore, the DC power supply (DCPS) can also be an AC-DC converter or a DC-DC converter, etc.

[0060] In DC-DC converter 21, a first DC voltage Vin is input from a DC power supply DCPS. DC-DC converter 21 supplies a second DC voltage Vout, different from the first DC voltage Vin, to the load. DC-DC converter 21 includes a switching circuit SW, an LC series resonant circuit LC, a smoothing capacitor SC1, a first diode D1, a second diode D2, a transformer TR1, a gate drive circuit GD, an input terminal IT, and second output terminals O3 and O4. The smoothing capacitor SC1 is not required.

[0061] The input terminal IT is connected to the positive terminal of the DC power supply DCPS. The second output terminals O3 and O4 output the second DC voltage Vout. The second output terminals O3 and O4 are connected to the first output terminals O1 and O2, respectively.

[0062] The switching circuit SW includes a first switching element S1 and a second switching element S2. The first switching element S1 is connected to the input terminal IT, the second switching element S2, and the reactor L. In this embodiment, the first switching element S1 is a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). The first switching element S1 has a parasitic capacitor C1 and a parasitic diode FD1. The drain D of the first switching element S1 is connected to the positive terminal of the DC power supply DCPS via the input terminal IT. The source S of the first switching element S1 is connected to the reactor L and the second switching element S2. The drain D of the first switching element S1 corresponds to the "first terminal" of the present invention. The source S of the first switching element S1 corresponds to the "second terminal" of the present invention. Furthermore, the "first switching element" of the present invention is not limited to a MOSFET, but can also be a bipolar transistor or an IGBT (Insulated Gate Bipolar Transistor) or other switching device.

[0063] The second switching element S2 is connected to the first switching element S1, the reactor L, the transformer TR1, and the second diode D2. In this embodiment, the second switching element S2 is a MOSFET. The second switching element S2 has a parasitic capacitor C2 and a parasitic diode FD2. The drain D of the second switching element S2 is connected to the first switching element S1 and the reactor L. The source S of the second switching element S2 is connected to the transformer TR1 and the second diode D2. The drain D of the second switching element S2 corresponds to the "third terminal" of the present invention. The source S of the second switching element S2 corresponds to the "fourth terminal" of the present invention. Furthermore, the "second switching element" of the present invention is not limited to a MOSFET, but can also be a bipolar transistor or an IGBT, or other switching device.

[0064] At the gate G1 of the first switching element S1, a first control signal CS1 is applied from the gate drive circuit GD. The first switching element S1 is controlled to be ON / OFF by the first control signal CS1. Figure 2 As shown, the first switching element S1 repeatedly enters an on state and an off state. In the on state, the first switching element S1 is turned on. In the off state, the first switching element S1 is not turned on. In this embodiment, the ratio of the on period to the off period of the first switching element S1 is 1:1. Therefore, the ratio of the on period of the first switching element S1 to the switching cycle (the sum of the on period and the off period of the first switching element S1) is 0.5. However, the ratio of the on period to the off period of the first switching element S1 is not limited to 1:1.

[0065] At the gate G2 of the second switching element S2, a second control signal CS2 is applied from the gate drive circuit GD. The second switching element S2 is controlled to be on / off by the second control signal CS2. The second switching element S2 repeatedly enters the on and off states. In the on state, the second switching element S2 is turned on. In the off state, the second switching element S2 is not turned on. However, the gate drive circuit GD generates the second control signal CS2, causing the second switching element S2 to be turned on when the first switching element S1 is off. Thus, the first period P1 in which the first switching element S1 is on and the second switching element S2 is not turned on, and the second period P2 in which the second switching element S2 is on and the first switching element S1 is on are periodically repeated. In this embodiment, the ratio of the on period to the off period of the second switching element S2 is 1:1. Therefore, the ratio of the first period P1 to the second period P2 is 1:1. Furthermore, instead of being limited to the first period P1 and the second period P2, a dead time period can also be set between the first period P1 and the second period P2. That is, during the dead time period, the gate drive circuit GD can also generate the first control signal CS1 and the second control signal CS2, causing the first switching element S1 to be in the off state and the second switching element S2 to be in the off state. By setting a dead time period, it is possible to more reliably prevent both the first switching element S1 and the second switching element S2 from being in the on state simultaneously. In addition, the ratio of the on period to the off period of the second switching element S2 is not limited to 1:1.

[0066] like Figure 1 As shown, the parasitic capacitor C1 is connected between the drain D and source S of the first switching element S1. The parasitic capacitor C1 suppresses oscillation when the first switching element S1 is switched on and off. Furthermore, the first switching element S1 can perform ZVS (Zero Voltage Switching) during the dead time period via the parasitic capacitor C1.

[0067] Parasitic diode FD1 is connected between the drain (D) and source (S) of the first switching element S1. The cathode of parasitic diode FD1 is connected to the drain (D) of the first switching element S1. The anode of parasitic diode FD1 is connected to the source (S) of the first switching element S1. Through parasitic diode FD1, when the first switching element S1 is turned off, current flows back from the anode to the cathode of parasitic diode FD1. This suppresses the current flowing from the source (S) to the drain (D) of the first switching element S1, preventing breakdown of the first switching element S1. Alternatively, the return diode can be provided independently of the first switching element S1.

[0068] A parasitic capacitor C2 is connected between the drain (D) and source (S) of the second switching element S2. The parasitic capacitor C2 suppresses oscillations when the second switching element S2 is switched on and off. Furthermore, the second switching element S2 can perform ZVS during the dead time using the parasitic capacitor C2.

[0069] The parasitic diode FD2 is connected between the drain (D) and source (S) of the second switching element S2. The cathode of the parasitic diode FD2 is connected to the drain (D) of the second switching element S2. The anode of the parasitic diode FD2 is connected to the source (S) of the second switching element S2. Through the parasitic diode FD2, when the second switching element S2 is turned off, current flows back from the anode to the cathode of the parasitic diode FD2. This suppresses the current flowing from the source (S) to the drain (D) of the second switching element S2, preventing breakdown of the second switching element S2. Alternatively, the return diode can be provided independently of the second switching element S2.

[0070] The LC series resonant circuit LC includes a reactor L and a capacitor C. The reactor L is connected to the connection point of the source S of the first switching element S1 and the drain D of the second switching element S2, as well as to the capacitor C. The capacitor C is connected to the reactor L and the transformer TR1. The capacitor C is connected in series with the reactor L. The first switching element S1 and the second switching element S2 can be soft-switched by the current resonance of the reactor L and the capacitor C. The terminal TL of the reactor L connected to the connection point of the source S of the first switching element S1 and the drain D of the second switching element S2 corresponds to the "fifth terminal" of this invention. The terminal TC of the capacitor C connected to the transformer TR1 corresponds to the "sixth terminal" of this invention.

[0071] exist Figure 1In the circuit diagram shown, transformer TR1 includes a first magnetizing inductor Lm1 and windings LT11, LT21, and LT22. Windings LT11, LT21, and LT22 are magnetically coupled. The first magnetizing inductor Lm1 is an inductor that generates a magnetic flux φ that links with all windings LT11, LT21, and LT22. In this embodiment, the turns ratio of windings LT11, LT21, and LT22 is n:1:1. Alternatively, n=2. However, it is not limited to n=2. Furthermore, the turns ratio of windings LT11, LT21, and LT22 may not be n:1:1.

[0072] exist Figure 3 In the cross-sectional view shown, transformer TR1 includes a first core CO1 and windings LT11, LT21, and LT22. The first core CO1 is made of a magnetic material. The first core CO1 has a first core section CR1 and a second core section CR2. Winding LT11 is wound around the second core section CR2. Windings LT21 and LT22 are wound around the first core section CR1. Figure 3 as well as Figure 4 As shown, the first core CO1 forms a magnetic circuit. In this embodiment, the cross-sectional area of ​​the second core CR2 orthogonal to the magnetic circuit is equal to the cross-sectional area of ​​the first core CR1 orthogonal to the magnetic circuit. Alternatively, an air gap may be provided between the first core CR1 and the second core CR2.

[0073] like Figure 1 As shown, one end T1 of winding LT11 is connected to end TC of capacitor C. The other end T2 of winding LT11 is connected to winding LT21 and the first diode D1. Therefore, windings LT11 and LT21 are not insulated. Winding LT11 corresponds to the "conductor" and "third winding" of the present invention. One end T1 of winding LT11 corresponds to the "seventh end" of the present invention. The other end T2 of winding LT11 corresponds to the "eighth end" of the present invention.

[0074] One end T3 of winding LT21 is connected to the other end T2 of winding LT11 and the first diode D1. The other end T4 of winding LT21 is connected to winding LT22 and the second output terminal O3. Winding LT21 corresponds to the "first winding" of this invention. One end T3 of winding LT21 corresponds to the "ninth end" of this invention. The other end T4 of winding LT21 corresponds to the "tenth end" of this invention.

[0075] One end T5 of winding LT22 is connected to the other end T4 of winding LT21 and the second output terminal O3. The other end T6 of winding LT22 is connected to the source S of the second switching element S2 and the second diode D2. Winding LT22 corresponds to the "second winding" of this invention. One end T5 of winding LT22 corresponds to the "eleventh end" of this invention. The other end T6 of winding LT22 corresponds to the "twelfth end" of this invention.

[0076] like Figure 3 As shown, in transformer TR1, the direction of the magnetic flux φ generated when current flows from one end T1 of winding LT11 to the other end T2 of winding LT11 is the same as the direction of the magnetic flux φ generated when current flows from one end T3 of winding LT21 to the other end T4 of winding LT21, and the direction of the magnetic flux φ generated when current flows from one end T5 of winding LT22 to the other end T6 of winding LT22. Therefore, windings LT11, LT21, and LT22 are positively magnetically coupled to each other. In other words, the coupling coefficient between windings LT11 and LT21 is positive. Furthermore, the coupling coefficient between windings LT11 and LT22 is positive. Additionally, the coupling coefficient between windings LT21 and LT22 is positive.

[0077] like Figure 1 As shown, the first diode D1 has a first anode A1 and a first cathode K1. The first cathode K1 is connected to the other end T2 of winding LT11 and one end T3 of winding LT21. The first anode A1 is connected to the second diode D2 and the second output terminal O4. The first diode D1 corresponds to the "first rectifier element" of the present invention. The first anode A1 corresponds to the "13th terminal" of the present invention. The first cathode K1 corresponds to the "14th terminal" of the present invention.

[0078] The second diode D2 has a second anode A2 and a second cathode K2. The second cathode K2 is connected to the source S of the second switching element S2 and the other end T6 of the winding LT22. The second anode A2 is connected to the first anode A1 and the second output terminal O4. The second diode D2 corresponds to the "second rectifier element" of the present invention. The second anode A2 corresponds to the "15th terminal" of the present invention. The second cathode K2 corresponds to the "16th terminal" of the present invention.

[0079] The smoothing capacitor SC1 is connected to the second output terminals O3 and O4. That is, the smoothing capacitor SC1 is connected to the other end T4 of winding LT21, the connection point of winding LT22, and the connection point of the first anode A1 and the second anode A2.

[0080] Next, the operation of the DC-DC converter 21 will be explained. Figure 5This is a diagram showing the operation of the current flowing through the switching power supply device 20 and the load resistor RL1 during the first period P1. Figure 6 This is a diagram showing the operation of the current flowing through the switching power supply device 20 and the load resistor RL1 in the second period P2.

[0081] like Figure 5 As shown, during the first period P1, current i1 flows sequentially through ground, DC power supply DCPS, input terminal IT, first switching element S1, reactor L, capacitor C, windings LT11 and LT21, second output terminal O3, first output terminal O1, load resistor RL1, and ground. During the first period P1, capacitor C is charged by current i1. That is, current i1 is the charging current of capacitor C during the first period P1. When current i1 flows through winding LT11, magnetizing current im flows through the first magnetizing inductor Lm1. At this time, due to the magnetic coupling between windings LT11 and LT22, current i2 flows through winding LT22. Current i2 flows sequentially through winding LT22, second output terminal O3, first output terminal O1, load resistor RL1, first output terminal O2, second output terminal O4, second diode D2, and winding LT22. During the first period P1, due to the flow of currents i1 and i2, the potential of one end T3 of winding LT21 is different from the potential of the source S of the second switching element S2. More specifically, during the first period P1, the potential of one end T3 of winding LT21 is higher than the potential of the source S of the second switching element S2.

[0082] like Figure 2 As shown, during the first period P1, no current flows through the first diode D1. On the other hand, during the first period P1, current flows through the second diode D2.

[0083] like Figure 6As shown, during the second period P2, capacitor C discharges. Current i1 during the second period P2 is the discharge current of capacitor C. During the second period P2, current i1 flows sequentially through capacitor C, the second switching element S2, winding LT22, the second output terminal O3, the first output terminal O1, the load resistor RL1, the first output terminal O2, the second output terminal O4, the first diode D1, winding LT11, and capacitor C. When current i1 flows through winding LT11, the magnetizing current im flows through the first magnetizing inductor Lm1. At this time, due to the magnetic coupling between windings LT11 and LT21, current i2 flows through winding LT21. Current i2 flows sequentially through winding LT21, the second output terminal O3, the first output terminal O1, the load resistor RL1, the first output terminal O2, the first diode D1, and winding LT21. During the second period P2, due to the flow of currents i1 and i2, the potential of one end T3 of winding LT21 is different from the potential of the source S of the second switching element S2. More specifically, during the second period P2, the potential of one end T3 of winding LT21 is lower than the potential of the drain D of the first switching element S1.

[0084] like Figure 2 As shown, during the second period P2, current flows through the first diode D1. On the other hand, during the second period P2, no current flows through the second diode D2.

[0085] In this embodiment, the second DC voltage Vout can be represented by the first DC voltage Vin and n through the following mathematical formula 1.

[0086] [Mathematical Expression 1]

[0087]

[0088] [Effect]

[0089] According to the DC-DC converter 21, copper losses can be reduced. More specifically, the second DC voltage Vout can be expressed using the first DC voltage Vin and n through the above-described mathematical formula 1. Therefore, when the ratio of the on-time of the first switching element S1 to the switching cycle is 0.5, if the step-down ratio of the DC-DC converter 21 is to be set to 1 / 8 (Vout = 1 / 8 Vin), then n = 2. That is, the turns ratio of windings LT11, LT21, and LT22 is 2:1:1. In the case of the DC-DC converter described in Patent Document 1 (Japanese Patent No. 4649299), the turns ratio of the total of the primary windings 141 and 151 to the secondary windings 142 and 152 is 4:1:1. Therefore, compared with the primary windings 141 and 151 in the DC-DC converter described in Patent Document 1, the number of turns of winding LT11 is reduced. That is, according to the DC-DC converter 21 of this embodiment, by reducing the number of turns of the winding LT11, the resistance value of the winding LT11 can be reduced. As a result, according to the DC-DC converter 21 of this embodiment, the copper loss caused by the winding LT11 can be reduced.

[0090] Furthermore, according to the DC-DC converter 21, copper losses can be further reduced. More specifically, during the first period P1, current flows through both windings LT21 and LT22. At this time, the current flowing through winding LT21 flows in the same direction relative to the load resistor RL1 as the current flowing through winding LT22. In other words, during the first period P1, the current flowing through the load resistor RL1 is shared between the current flowing through winding LT21 and the current flowing through winding LT22. Furthermore, during the second period P2, current flows through both windings LT21 and LT22. At this time, the current flowing through winding LT21 flows in the same direction relative to the load resistor RL1 as the current flowing through winding LT22. In other words, during the second period P2, the current flowing through the load resistor RL1 is also shared between the current flowing through winding LT21 and the current flowing through winding LT22. Therefore, the current flowing through winding LT21 and winding LT22 does not deviate from a given period. Consequently, it is not necessary to increase the effective values ​​of the current flowing through winding LT21 and winding LT22 respectively relative to a given output current. Therefore, according to the DC-DC converter 21, copper losses caused by windings LT21 and LT22 can be reduced.

[0091] Furthermore, according to the DC-DC converter 21, the lifespan of the second diode D2 can be extended. More specifically, during the first period P1, the current i1 flowing through the capacitor C does not flow through the second diode D2. Furthermore, during the second period P2, no current flows through the second diode D2. Therefore, the effective value of the current flowing through the second diode D2 is relatively small. Consequently, the losses generated by the second diode D2 are small, and the heat generated by the second diode D2 is also reduced. Therefore, the temperature of the second diode D2 can be kept low, thus extending its lifespan.

[0092] [First Variation]

[0093] Hereinafter, the DC-DC converter 21a and the switching power supply device 20a according to the first modification of the present invention will be described with reference to the accompanying drawings. Figure 7 It is a schematic cross-sectional view showing the structure of transformer TR2 and a diagram showing the wiring of transformer TR2. Figure 8 This is a schematic top view showing the structure of the first core CO1. Furthermore, regarding the DC-DC converter 21a and switching power supply device 20a involved in the first modification, only the parts that differ from the DC-DC converter 21 and switching power supply device 20 involved in the first embodiment will be described; the rest will be omitted.

[0094] The difference between the DC-DC converter 21a and the switching power supply device 20a in the first modification example and the DC-DC converter 21 and the switching power supply device 20 in the first embodiment is that a transformer TR2 is provided instead of a transformer TR1.

[0095] like Figure 7 As shown, the first core CO1 also has a third core CR3. That is, the first core CO1 has three cores. Winding LT22 is wound around the third core CR3. Specifically, windings LT11, LT21, and LT22 are wound around any one of the three cores of the first core CO1. Figure 8 As shown, a gap V is provided between the first core CR1 and the third core CR3. Figure 7 as well as Figure 8As shown, the first core CO1 forms a magnetic circuit. More specifically, the first core CR1 and the second core CR2 form a magnetic circuit through which magnetic flux φ1 flows. Furthermore, the second core CR2 and the third core CR3 form a magnetic circuit through which magnetic flux φ2 flows. In this case, the relationship φ = φ1 + φ2 holds true. In this modified example, the cross-sectional areas of the first core CR1 and the third core CR3 that are orthogonal to the magnetic circuit are each half of the cross-sectional area of ​​the second core CR2 that is orthogonal to the magnetic circuit. The sum of the cross-sectional areas of the first core CR1 and the third core CR3 that are orthogonal to the magnetic circuit is equal to the cross-sectional area of ​​the second core CR2 that is orthogonal to the magnetic circuit. Therefore, the magnitudes of magnetic flux φ1 and φ2 are each half of the magnetic flux φ. Alternatively, the first core CO1 may have more than four cores.

[0096] In this variant, the second DC voltage Vout can be represented by the first DC voltage Vin and n through the following mathematical formula 2.

[0097] [Mathematical Expression 2]

[0098]

[0099] In the DC-DC converter 21a and switching power supply device 20a as described above, the same effect as that of DC-DC converter 21 and switching power supply device 20 is achieved. Furthermore, according to DC-DC converter 21a, copper losses can be reduced while maintaining the same buck ratio. More specifically, the magnitudes of magnetic flux φ1 and magnetic flux φ2 are each half of the magnetic flux φ. Therefore, the induced electromotive force generated in windings LT21 and LT22 of DC-DC converter 21a is half of the induced electromotive force generated in windings LT21 and LT22 of DC-DC converter 21. In the case of DC-DC converter 21, to achieve n=2, for example, it is necessary to set the number of turns of winding LT11 to 2, the number of turns of winding LT21 to 1, and the number of turns of winding LT22 to 1. On the other hand, in the case of DC-DC converter 21a, to achieve n=2, it is sufficient to set the number of turns of winding LT11 to 1, the number of turns of winding LT21 to 1, and the number of turns of winding LT22 to 1. That is, the number of turns of winding LT11 can be half the number of turns of winding LT11 in DC-DC converter 21. Therefore, according to DC-DC converter 21a, by further reducing the number of turns of winding LT11, the resistance value of winding LT11 can be further reduced. As a result, according to DC-DC converter 21a, the copper loss caused by winding LT11 can be further reduced.

[0100] In other words, in DC-DC converters 21 and 21a, when the number of turns in winding LT11, winding LT21, and winding LT22 are all equal, DC-DC converter 21a has a higher buck ratio than DC-DC converter 21. According to DC-DC converter 21a, a high buck ratio can be achieved without increasing the number of turns in winding LT11 or increasing the cross-sectional area of ​​the core orthogonal to the magnetic circuit.

[0101] [Second Variation]

[0102] Hereinafter, the DC-DC converter 21b and the switching power supply device 20b according to the second modification of the present invention will be described with reference to the accompanying drawings. Figure 9 This is a circuit diagram showing a switching power supply device 20b equipped with a DC-DC converter 21b and a load resistor RL1. Furthermore, regarding the DC-DC converter 21b and switching power supply device 20b according to the second modification, only the parts that differ from the DC-DC converter 21 and switching power supply device 20 according to the first embodiment will be described; the rest will be omitted.

[0103] The difference between the DC-DC converter 21b and the switching power supply device 20b in the second modification and those in the first embodiment is that a transformer TR3 is provided instead of transformer TR1. Figure 9 As shown, transformer TR3 does not include winding LT11.

[0104] In this variation, the DC-DC converter 21b includes a conductor CON. One end CON1 of the conductor CON is connected to the terminal TC of the capacitor C. The other end CON2 of the conductor CON is connected to the winding LT21 and the first diode D1. The conductor CON in this variation corresponds to the "conductor" of the present invention. One end CON1 of the conductor CON corresponds to the "seventh terminal" of the present invention. The other end CON2 of the conductor CON corresponds to the "eighth terminal" of the present invention.

[0105] The same effect as that of DC-DC converter 21 and switching power supply device 20 is achieved in DC-DC converter 21 and switching power supply device 20 as described above. Furthermore, according to DC-DC converter 21b, even without winding LT11, the buck ratio of DC-DC converter 21b can be set to 1 / 4 (Vout = 1 / 4Vin). More specifically, by substituting n = 0 into mathematical formula 1, Vout = 1 / 4Vin is obtained. Moreover, by reducing the winding LT11, the DC-DC converter can be miniaturized and its cost reduced.

[0106] [3rd Variation]

[0107] Hereinafter, the DC-DC converter 21c and the switching power supply device 20c according to the third modification of the present invention will be described with reference to the accompanying drawings. Figure 10 This is a circuit diagram showing a switching power supply device 20c equipped with a DC-DC converter 21c and load resistors RL1 and RL2. Furthermore, regarding the DC-DC converter 21c and switching power supply device 20c according to the third modification, only the parts that differ from the DC-DC converter 21 and switching power supply device 20 according to the first embodiment will be described; the rest will be omitted.

[0108] The difference between the switching power supply device 20c in the third modification and the switching power supply device 20 in the first embodiment is that: it also has a third output terminal O5, O6; the DC-DC converter 21c has a transformer TR4 instead of a transformer TR1; and the DC-DC converter 21c also has a smoothing capacitor SC2, a third diode D3, a fourth diode D4, and a fourth output terminal O7, O8.

[0109] like Figure 10 As shown, transformer TR4 also includes windings LT23 and LT24. Windings LT11, LT21, LT22, LT23, and LT24 are magnetically coupled. The first magnetizing inductance Lm1 is the inductance that generates a magnetic flux φ that links with all windings LT11, LT21, LT22, LT23, and LT24. In transformer TR4, the direction of the magnetic flux φ generated when current flows from one end T1 of winding LT11 to the other end T2 is the same as the direction of the magnetic flux φ generated when current flows from one end T7 of winding LT23 to the other end T8, and the direction of the magnetic flux φ generated when current flows from one end T9 of winding LT24 to the other end T10. Therefore, windings LT11, LT21, LT22, LT23, and LT24 are positively magnetically coupled to each other. In this embodiment, the turns ratio of windings LT11, LT21, LT22, LT23, and LT24 is n:1:1:1:1. Alternatively, the turns ratio of windings LT11, LT21, LT22, LT23, and LT24 may not be n:1:1:1:1.

[0110] The third output terminals O5 and O6 are connected to the two ends of the load resistor RL2. Furthermore, the third output terminal O6 is connected to ground. The third output terminals O5 and O6 output a third DC voltage, different from the first DC voltage Vin. Additionally, the load resistor RL2 is a specific example of a load. The load is not limited to a resistive component; it may also include a reactive component. The third DC voltage may be equal to or different from the second DC voltage Vout.

[0111] The third diode D3 has a third anode A3 and a third cathode K3. The fourth diode D4 has a fourth anode A4 and a fourth cathode K4. Furthermore, regarding the connections of the smoothing capacitor SC2, the third diode D3, the fourth diode D4, the windings LT23 and LT24, the third output terminals O5 and O6, and the fourth output terminals O7 and O8, except that the third diode D3 and the winding LT23 are not connected to the other end T2 of the winding LT11, and the fourth diode D4 and the winding LT24 are not connected to the source S of the second switching element S2, the connections are the same as those of the smoothing capacitor SC1, the first diode D1, the second diode D2, the windings LT21 and LT22, the first output terminals O1 and O2, and the second output terminals O3 and O4, and therefore, descriptions are omitted. The third diode D3 corresponds to the "third rectifier element" of this invention. The third anode A3 corresponds to the "21st terminal" of this invention. The third cathode K3 corresponds to the "22nd terminal" of this invention. The fourth diode D4 corresponds to the "fourth rectifier element" of this invention. The fourth anode A4 corresponds to the "23rd terminal" of this invention. The fourth cathode K4 corresponds to the "24th terminal" of this invention.

[0112] Winding LT23 corresponds to the "4th winding" of the present invention. One end T7 of winding LT23 corresponds to the "17th end" of the present invention. The other end T8 of winding LT23 corresponds to the "18th end" of the present invention. Winding LT24 corresponds to the "5th winding" of the present invention. One end T9 of winding LT24 corresponds to the "19th end" of the present invention. The other end T10 of winding LT24 corresponds to the "20th end" of the present invention.

[0113] The same effect as that of DC-DC converter 21c and switching power supply device 20c, as described above, is achieved in DC-DC converter 21 and switching power supply device 20. Furthermore, DC-DC converter 21c can be used to output DC voltage in parallel.

[0114] [4th Variation]

[0115] Hereinafter, the DC-DC converter 21d and the switching power supply device 20d according to the fourth modification of the present invention will be described with reference to the accompanying drawings. Figure 11This is a circuit diagram showing a switching power supply device 20d equipped with a DC-DC converter 21d and load resistors RL1 and RL2. Furthermore, regarding the DC-DC converter 21d and switching power supply device 20d according to the fourth modification, only the parts that differ from the DC-DC converter 21c and switching power supply device 20c according to the third modification will be described; the rest will be omitted.

[0116] The difference between the DC-DC converter 21d and the switching power supply device 20d in the fourth modification and the DC-DC converter 21c and the switching power supply device 20c in the third modification is that a transformer TR5 is provided instead of a transformer TR4. Figure 11 As shown, transformer TR5 does not include winding LT11.

[0117] In this modified example, the DC-DC converter 21d includes a conductor CON. One end CON1 of the conductor CON is connected to the terminal TC of the capacitor C. The other end CON2 of the conductor CON is connected to the winding LT21 and the first diode D1. The conductor CON in this modified example corresponds to the "conductor" of the present invention. One end CON1 of the conductor CON corresponds to the "seventh terminal" of the present invention. The other end CON2 of the conductor CON corresponds to the "eighth terminal" of the present invention.

[0118] The same effect as that of DC-DC converters 21b and 21c and switching power supply devices 20b and 20c is also achieved in DC-DC converters 21d and 20d as described above.

[0119] [5th ​​Variation]

[0120] Hereinafter, the DC-DC converter 21e and the switching power supply device 20e according to the fifth modification of the present invention will be described with reference to the accompanying drawings. Figure 12 This is a circuit diagram showing a switching power supply device 20e with a DC-DC converter 21e and a load resistor RL1. Figure 13 It is a schematic cross-sectional view showing the structure of transformer TR4 and a diagram showing the wiring of transformer TR4. Figure 14 This is a schematic top view showing the structure of the first core CO1. Furthermore, regarding the DC-DC converter 21e and the switching power supply device 20e involved in the fifth modification, only the parts that differ from the DC-DC converter 21c and the switching power supply device 20c involved in the third modification will be described; the rest will be omitted.

[0121] The difference between the switching power supply device 20e in the fifth modification and the switching power supply device 20c in the third modification is that the fifth modification does not have third output terminals O5 and O6; and the DC-DC converter 21e does not have a smoothing capacitor SC2 and fourth output terminals O7 and O8. Furthermore, in this modification, the third DC voltage output from the third output terminals O5 and O6 is equal to the second DC voltage Vout.

[0122] like Figure 12 As shown, the connection point of the other end T8 of winding LT23 and one end T9 of winding LT24 is connected to the second output terminal O3. That is, the connection point of the other end T8 of winding LT23 and one end T9 of winding LT24 is connected to the connection point of the other end T4 of winding LT21 and one end T5 of winding LT22. The connection point of the third anode A3 and the fourth anode A4 is connected to the second output terminal O4. That is, the connection point of the third anode A3 and the fourth anode A4 is connected to the connection point of the first anode A1 and the second anode A2.

[0123] like Figure 13 As shown, the first core CO1 also has a third core CR3. Windings LT23 and LT24 are wound around the third core CR3. Figure 14 As shown, a gap V is provided between the first core CR1 and the third core CR3. Figure 13 as well as Figure 14 As shown, the first core CO1 forms a magnetic circuit. More specifically, the first core CR1 and the second core CR2 form a magnetic circuit through which magnetic flux φ1 flows. Furthermore, the second core CR2 and the third core CR3 form a magnetic circuit through which magnetic flux φ2 flows. In this case, the relationship φ = φ1 + φ2 holds true. In this modified example, the cross-sectional areas of the first core CR1 and the third core CR3 that are orthogonal to the magnetic circuit are each half of the cross-sectional area of ​​the second core CR2 that is orthogonal to the magnetic circuit. The sum of the cross-sectional areas of the first core CR1 and the third core CR3 that are orthogonal to the magnetic circuit is equal to the cross-sectional area of ​​the second core CR2 that is orthogonal to the magnetic circuit. Therefore, the magnitudes of magnetic flux φ1 and φ2 are each half of the magnetic flux φ. The third core CR3 corresponds to the "second core" of this invention.

[0124] The same effect as that of DC-DC converters 21e and switching power supply device 20e described above is achieved in DC-DC converters 21 and 21a and switching power supply devices 20 and 20a. That is, according to DC-DC converter 21e, copper losses caused by winding LT11 can be further reduced. In other words, according to DC-DC converter 21e, a high buck ratio can be achieved without increasing the number of turns of winding LT11 and without increasing the cross-sectional area of ​​the core orthogonal to the magnetic circuit.

[0125] [Sixth Variation]

[0126] Hereinafter, the DC-DC converter 21f and the switching power supply device 20f according to the sixth modification of the present invention will be described with reference to the accompanying drawings. Figure 15 It is a schematic cross-sectional view showing the structure of transformer TR6 and a diagram showing the wiring of transformer TR6. Figure 16 This is a schematic top view showing the structure of the first core CO1. Furthermore, regarding the DC-DC converter 21f involved in the sixth modification, only the parts that differ from the DC-DC converter 21e involved in the fifth modification and the switching power supply device 20e will be described; the rest are omitted.

[0127] The difference between the DC-DC converter 21f and the switching power supply device 20f in the sixth modification and the DC-DC converter 21e and the switching power supply device 20e in the fifth modification is that the transformer TR6 is provided instead of the transformer TR4.

[0128] like Figure 15 As shown, core CO1 also has a fourth core CR4 and a fifth core CR5. That is, core CO1 has 5 cores. Winding LT22 is wound on the fourth core CR4. Winding LT23 is wound on the fifth core CR5. Winding LT24 is wound on the third core CR3. That is, windings LT11, LT21, LT22, LT23, and LT24 are wound on any one of the five different cores. Figure 16 As shown, a gap V is provided between the first core CR1 and the fourth core CR4. A gap V is provided between the fourth core CR4 and the fifth core CR5. A gap V is provided between the fifth core CR5 and the third core CR3. Figure 15 as well as Figure 16As shown, the first core CO1 forms a magnetic circuit. More specifically, the first core CR1 and the second core CR2 form a magnetic circuit through which magnetic flux φ1 flows. Furthermore, the second core CR2 and the third core CR3 form a magnetic circuit through which magnetic flux φ2 flows. Furthermore, the second core CR2 and the fourth core CR4 form a magnetic circuit through which magnetic flux φ3 flows. Furthermore, the second core CR2 and the fifth core CR5 form a magnetic circuit through which magnetic flux φ4 flows. At this time, the relationship φ = φ1 + φ2 + φ3 + φ4 holds. In this modified example, the cross-sectional areas of the first core CR1, the third core CR3, the fourth core CR4, and the fifth core CR5 that are orthogonal to the magnetic circuit are each 1 / 4 of the cross-sectional area of ​​the second core CR2 that is orthogonal to the magnetic circuit. The combined cross-sectional areas of the first core CR1, the third core CR3, the fourth core CR4, and the fifth core CR5 (all perpendicular to the magnetic circuit) are equal to the cross-sectional area of ​​the second core CR2 (also perpendicular to the magnetic circuit). Therefore, the magnitudes of magnetic flux φ1, φ2, φ3, and φ4 are each 1 / 4 of the magnetic flux φ. Furthermore, the number of cores can be six or more.

[0129] The same effects as those of DC-DC converters 21a and 21e, and switching power supplies 20a and 20e, are achieved in DC-DC converters 21f and 20f, as in the switching power supplies 20a and 20e described above. Furthermore, according to DC-DC converter 21f, copper losses caused by winding LT11 can be reduced compared to DC-DC converter 21e. In other words, according to DC-DC converter 21f, a higher step-down ratio than DC-DC converter 21e can be achieved without increasing the number of turns in winding LT11 or increasing the cross-sectional area of ​​the core orthogonal to the magnetic circuit.

[0130] [7th Variation]

[0131] Hereinafter, the DC-DC converter 21g and the switching power supply device 20g according to the seventh modification of the present invention will be described with reference to the accompanying drawings. Figure 17 This is a circuit diagram showing a switching power supply device 20g equipped with a DC-DC converter 21g and a load resistor RL1. Figure 18 It is a schematic cross-sectional view showing the structure of transformer TR7 and a diagram showing the wiring of transformer TR7. Figure 19 This is a schematic top view showing the structure of the second CO2 core. Furthermore, regarding the DC-DC converter 21g and switching power supply device 20g involved in the 7th modification, only the parts that differ from the DC-DC converter 21e and switching power supply device 20e involved in the 5th modification will be described; the rest are omitted.

[0132] The DC-DC converter 21g and switching power supply device 20g in the seventh modification differ from the DC-DC converter 21e and switching power supply device 20e in the fifth modification in that they respectively replace transformer TR4 with transformers TR1 and TR7. Furthermore, regarding the structure of transformer TR1, except that the cross-sectional area of ​​the first core CO1 orthogonal to the magnetic circuit is half that of the first core CO1 orthogonal to the magnetic circuit in the first embodiment, the structure is the same as that of transformer TR1 in the first embodiment, and therefore description is omitted.

[0133] exist Figure 17 In the circuit diagram shown, transformer TR7 includes a second magnetizing inductor Lm2 and windings LT12, LT23, and LT24. Windings LT12, LT23, and LT24 are magnetically coupled. The second magnetizing inductor Lm2 is the inductor that generates a magnetic flux φ12 that links with all windings LT12, LT23, and LT24. In transformer TR7, the direction of the magnetic flux φ12 generated when current flows from one end T11 of winding LT12 to the other end T12 is the same as the direction of the magnetic flux φ12 generated when current flows from one end T7 of winding LT23 to the other end T8 of winding LT23, and the direction of the magnetic flux φ12 generated when current flows from one end T9 of winding LT24 to the other end T10 of winding LT24. Therefore, windings LT12, LT23, and LT24 are positively magnetically coupled to each other. In this modified example, the turns ratio of windings LT11, LT12, LT21, LT22, LT23, and LT24 is n / 2:n / 2:1:1:1:1. Furthermore, n=2. However, it is not limited to n=2. Additionally, the turns ratio of windings LT11, LT12, LT21, LT22, LT23, and LT24 may not be n:n:1:1:1:1. Winding LT12 corresponds to the "sixth winding" of the present invention. Winding LT23 corresponds to the "fourth winding" of the present invention. Winding LT24 corresponds to the "fifth winding" of the present invention.

[0134] The other end T2 of winding LT11 is connected to one end T11 of winding LT12. The other end T12 of winding LT12 is connected to one end T3 of winding LT21 and the first cathode K1. One end T11 of winding LT12 corresponds to the "25th end" of the present invention. The other end T12 of winding LT12 corresponds to the "26th end" of the present invention.

[0135] exist Figure 18In the cross-sectional view shown, transformer TR7 includes a second core CO2 and windings LT12, LT23, and LT24. The second core CO2 is made of a magnetic material. The second core CO2 has a fourth core CR4 and a sixth core CR6. Windings LT22 and LT23 are wound around the fourth core CR4. Winding LT12 is wound around the sixth core CR6. Figure 18 as well as Figure 19 As shown, the second CO2 core forms a magnetic circuit. More specifically, the fourth core CR4 and the sixth core CR6 form a magnetic circuit through which magnetic flux φ3 flows. In this modified example, the cross-sectional area of ​​the second CO2 core orthogonal to the magnetic circuit is half of the cross-sectional area of ​​the first CO1 core orthogonal to the magnetic circuit according to the first embodiment. Furthermore, in this modified example, the cross-sectional areas of the fourth core CR4 and the sixth core CR6 orthogonal to the magnetic circuit are equal. Additionally, an air gap may be provided between the fourth core CR4 and the sixth core CR6. The first core CR1 in this modified example corresponds to the "first core" of the present invention. The second core CR2 in this modified example corresponds to the "second core" of the present invention. The fourth core CR4 in this modified example corresponds to the "third core" of the present invention. The sixth core CR6 in this modified example corresponds to the "fourth core" of the present invention.

[0136] The same effect as that of DC-DC converter 21e and switching power supply device 20e is also achieved in DC-DC converter 21g and switching power supply device 20e, as described above.

[0137] [8th Variation]

[0138] Hereinafter, the DC-DC converter 21h and the switching power supply device 20h according to the eighth modification of the present invention will be described with reference to the accompanying drawings. Figure 20 It is a schematic cross-sectional view showing the structure of transformer TR8 and a diagram showing the wiring of transformer TR8. Figure 21 This is a schematic top view showing the structure of the second CO2 core. Furthermore, regarding the DC-DC converter 21h and switching power supply device 20h involved in the 8th modification, only the parts that differ from the DC-DC converter 21f and switching power supply device 20f involved in the 7th modification will be described; the rest are omitted.

[0139] The difference between the DC-DC converter 21h and the switching power supply device 20h in the 8th modification example and the DC-DC converter 21g and the switching power supply device 20g in the 7th modification example is that a transformer TR2 is provided instead of transformer TR1, and a transformer TR8 is provided instead of transformer TR7. Furthermore, regarding the construction of transformer TR2, except that the cross-sectional area of ​​the first core CO1 orthogonal to the magnetic circuit is half of the cross-sectional area of ​​the first core CO1 orthogonal to the magnetic circuit in the 1st modification example, the construction is the same as that of transformer TR2 in the 1st modification example, and therefore, the description is omitted.

[0140] like Figure 20 As shown, the second CO2 core also has a fifth core CR5. That is, the second CO2 core has three cores. Winding LT23 is wound around the fourth core CR4. Winding LT24 is wound around the fifth core CR5. That is, windings LT12, LT23, and LT24 are wound around any one of the three cores of the second CO2 core. Figure 21 As shown, a gap V is provided between the fourth core CR4 and the fifth core CR5. Figure 20 as well as Figure 21 As shown, the second CO2 core forms a magnetic circuit. More specifically, the fourth core CR4 and the sixth core CR6 form a magnetic circuit through which magnetic flux φ31 flows. Furthermore, the fifth core CR5 and the sixth core CR6 form a magnetic circuit through which magnetic flux φ32 flows. In this case, the relationship φ3 = φ31 + φ32 holds true. In this modified example, the cross-sectional areas of the fourth core CR4 and the fifth core CR5 that are orthogonal to the magnetic circuit are each half of the cross-sectional area of ​​the sixth core CR6 that is orthogonal to the magnetic circuit. The sum of the cross-sectional areas of the fourth core CR4 and the fifth core CR5 that are orthogonal to the magnetic circuit is equal to the cross-sectional area of ​​the sixth core CR6 that is orthogonal to the magnetic circuit. Therefore, the magnitudes of magnetic flux φ31 and φ32 are each half of magnetic flux φ3. Alternatively, the second CO2 core may have more than four cores.

[0141] The same effect as that of DC-DC converters 21h and switching power supply device 20h described above is achieved in DC-DC converters 21 and 21a and switching power supply devices 20 and 20a. That is, according to DC-DC converter 21h, copper losses caused by winding LT11 can be further reduced. In other words, according to DC-DC converter 21h, a high buck ratio can be achieved without increasing the number of turns of winding LT11 and without increasing the cross-sectional area of ​​the core orthogonal to the magnetic circuit.

[0142] [9th Variation]

[0143] Hereinafter, the DC-DC converter 21i and the switching power supply device 20i according to the 9th modification of the present invention will be described with reference to the accompanying drawings. Figure 22 This is a circuit diagram showing the switching circuit SW in the 9th variation. Furthermore, regarding the DC-DC converter 21i and switching power supply device 20i involved in the 9th variation, only the parts that differ from the DC-DC converter 21 and switching power supply device 20 involved in the 1st embodiment will be described; the rest will be omitted.

[0144] like Figure 22 As shown, the switching circuit SW also includes a third switching element S3 connected in series with the first switching element S1, and a fourth switching element S4 connected in series with the second switching element S2. The on-time of the first switching element S1 coincides with the on-time of the third switching element S3. Furthermore, the on-time of the second switching element S2 coincides with the on-time of the fourth switching element S4. This increases the upper limit of the first DC voltage Vin that can be input to the DC-DC converters 21, 21a-21h and the switching power supply devices 20, 20a-20h. Additionally, the third switching element S3 may also have a parasitic capacitor C3 and a parasitic diode FD3. Furthermore, the fourth switching element S4 may also have a parasitic capacitor C4 and a parasitic diode FD4. In this modified example, the first switching element S1 and the third switching element S3 correspond to the "first switching element" of the present invention. The source S of the third switching element S3 corresponds to the "second terminal" of the present invention. The second switching element S2 and the fourth switching element S4 correspond to the "second switching element" of the present invention. The source S of the fourth switching element S4 corresponds to the "fourth terminal" of the present invention.

[0145] [10th Variation]

[0146] Hereinafter, the DC-DC converter 21j and the switching power supply device 20j according to the 10th modification of the present invention will be described with reference to the accompanying drawings. Figure 23 This is a circuit diagram showing the switching circuit SW in the 10th variation. Furthermore, regarding the DC-DC converter 21j and switching power supply device 20j involved in the 10th variation, only the parts that differ from the DC-DC converter 21 and switching power supply device 20 involved in the first embodiment will be described; the rest will be omitted.

[0147] like Figure 23As shown, the switching circuit SW also includes a third switching element S3 connected in parallel with the first switching element S1, and a fourth switching element S4 connected in parallel with the second switching element S2. The on-time of the first switching element S1 coincides with the on-time of the third switching element S3. Furthermore, the on-time of the second switching element S2 coincides with the on-time of the fourth switching element S4. This increases the upper limit of the current that can be input to the DC-DC converters 21, 21a-21h and the switching power supply devices 20, 20a-20h. Additionally, the third switching element S3 may also have a parasitic capacitor C3 and a parasitic diode FD3. Furthermore, the fourth switching element S4 may also have a parasitic capacitor C4 and a parasitic diode FD4. In this modified example, the first switching element S1 and the third switching element S3 correspond to the "first switching element" of the present invention. The second switching element S2 and the fourth switching element S4 correspond to the "second switching element" of the present invention.

[0148] [Example 11]

[0149] Hereinafter, the DC-DC converter 21k and the switching power supply device 20k according to the 11th modification of the present invention will be described with reference to the accompanying drawings. Figure 24 This is a circuit diagram showing a modified example of the first rectifier element. Furthermore, regarding the DC-DC converter 21k and switching power supply device 20k involved in the 11th modification, only the parts that differ from the DC-DC converter 21 and switching power supply device 20 involved in the first embodiment will be described; the rest will be omitted.

[0150] The difference between the DC-DC converter 21k and the switching power supply device 20k in the 11th variation and the DC-DC converter 21 and the switching power supply device 20 in the first embodiment is that a MOSFET rectifier MOSC is provided instead of the first diode D1.

[0151] The MOSFET rectifier MOSC includes MOSFET1, operational amplifier OP, and DC power supply Vcc. When the potential of the drain D of MOSFET1 is below the potential of the source S of MOSFET1, operational amplifier OP applies a positive voltage between the gate G and source S of MOSFET1, turning MOSFET1 on. When the potential of the drain D of MOSFET1 is greater than the potential of the source S of MOSFET1, operational amplifier OP does not apply a positive voltage between the gate G and source S of MOSFET1, turning MOSFET1 off. That is, the MOSFET rectifier MOSC has the same function as the first diode D1. In this modified example, the MOSFET rectifier MOSC corresponds to the "first rectifier element" of the present invention. One end A11 of the MOSFET rectifier MOSC corresponds to the "13th end" of the present invention. The other end K11 of the MOSFET rectifier MOSC corresponds to the "14th end" of the present invention. By using a MOSFET with low on-resistance as MOSFET1, the conduction loss generated by the "first rectifier element" can be reduced.

[0152] As shown in this variation, the "first rectifier element" of the present invention is not limited to a diode. Similarly, the "second rectifier element," "third rectifier element," and "fourth rectifier element" of the present invention are not each limited to a diode.

[0153] [Other Implementation Methods]

[0154] The DC-DC converters involved in this invention are not limited to DC-DC converters 21, 21a to 21k, and can be modified within the scope of their intent. Furthermore, the structures of DC-DC converters 21, 21a to 21k can be arbitrarily combined.

[0155] The switching power supply device involved in this invention is not limited to switching power supply devices 20, 20a to 20k, and can be modified within its scope. Furthermore, the structures of switching power supply devices 20, 20a to 20k can be arbitrarily combined.

[0156] Furthermore, in the DC-DC converters 21, 21a to 21k and the switching power supply devices 20, 20a to 20jk, the switching circuit SW should not be configured as a full-bridge circuit. If the switching circuit SW is configured as a full-bridge circuit, the number of switching elements increases, thus making the circuit structure and control more complex. This not only increases losses but also makes the DC-DC converter and switching power supply devices larger and more difficult to dissipate heat.

[0157] The present invention has the following structure. (1)

[0159] A DC-DC converter, comprising:

[0160] The first switching element has a first terminal and a second terminal, wherein the first terminal is connected to a DC power supply;

[0161] The second switching element has a third terminal and a fourth terminal, wherein the third terminal is connected to the second terminal;

[0162] An LC series resonant circuit has a fifth terminal and a sixth terminal, wherein the fifth terminal is connected to the connection point of the second terminal and the third terminal;

[0163] A conductor having a 7th end and an 8th end;

[0164] The first winding has a 9th end and a 10th end;

[0165] The second winding has an 11th end and a 12th end;

[0166] The first rectifier element has a 13th terminal and a 14th terminal; and

[0167] The second rectifier element has a 15th terminal and a 16th terminal, wherein the 15th terminal is connected to the 13th terminal.

[0168] The first winding and the second winding are positively magnetically coupled to each other.

[0169] The sixth end is connected to the seventh end.

[0170] The 8th end is connected to the 9th end and the 14th end.

[0171] The 10th end is connected to the 11th end.

[0172] The 12th end is connected to the 4th end and the 16th end. (2)

[0174] According to the DC-DC converter described in (1), wherein,

[0175] The conductor is the third winding.

[0176] The first winding, the second winding, and the third winding are positively magnetically coupled to each other. (3)

[0178] According to the DC-DC converter described in (1) or (2), wherein,

[0179] It also has:

[0180] The fourth winding has a 17th end and an 18th end;

[0181] The fifth winding has a 19th end and a 20th end;

[0182] The third rectifier element has a 21st terminal and a 22nd terminal; and

[0183] The fourth rectifier element has a 23rd terminal and a 24th terminal, wherein the 23rd terminal is connected to the 21st terminal.

[0184] The first winding, the second winding, the fourth winding, and the fifth winding are positively magnetically coupled to each other.

[0185] The 17th end is connected to the 22nd end.

[0186] The 18th end is connected to the 19th end.

[0187] The 20th end is connected to the 24th end. (4)

[0189] According to the DC-DC converter described in (1) or (2), wherein,

[0190] It also has:

[0191] The fourth winding has a 17th end and an 18th end;

[0192] The fifth winding has a 19th end and a 20th end;

[0193] The third rectifier element has a 21st terminal and a 22nd terminal; and

[0194] The fourth rectifier element has a 23rd terminal and a 24th terminal, wherein the 23rd terminal is connected to the 21st terminal.

[0195] The first winding, the second winding, the fourth winding, and the fifth winding are positively magnetically coupled to each other.

[0196] The 17th end is connected to the 22nd end.

[0197] The 18th end is connected to the 19th end.

[0198] The 20th end is connected to the 24th end.

[0199] The connection point of the 18th end and the 19th end is connected to the connection point of the 10th end and the 11th end, and the connection point of the 21st end and the 23rd end is connected to the connection point of the 13th end and the 15th end. (5)

[0201] According to the DC-DC converter described in (4), wherein,

[0202] It also has a core that forms a magnetic circuit.

[0203] The core has a first core portion and a second core portion.

[0204] The first winding and the second winding are respectively wound around the first core.

[0205] The fourth winding and the fifth winding are respectively wound around the second core. (6)

[0207] According to the DC-DC converter described in (4), wherein,

[0208] It also has a core that forms a magnetic circuit.

[0209] The core has more than 5 core sections.

[0210] The first winding, the second winding, the fourth winding, and the fifth winding are each wound on any one of the five or more different cores. (7)

[0212] The DC-DC converter according to any one of (1) to (6), wherein,

[0213] The first rectifier element and the second rectifier element are diodes, respectively.

[0214] The 13th end and the 15th end are respectively the anodes.

[0215] The 14th end and the 16th end are cathodes, respectively. (8)

[0217] According to the DC-DC converter described in (3) or (4), wherein,

[0218] The third and fourth rectifier elements are diodes, respectively.

[0219] The 21st end and the 23rd end are respectively the anodes.

[0220] The 22nd end and the 24th end are cathodes, respectively. (9)

[0222] The DC-DC converter according to any one of (1) to (8), wherein,

[0223] The process periodically repeats a first period in which the first switching element is turned on and the second switching element is turned off, and a second period in which the second switching element is turned on and the first switching element is turned off.

[0224] During the first period, the potential of the ninth terminal is different from the potential of the fourth terminal.

[0225] A DC voltage is output from the connection point of the 10th and 11th terminals and the connection point of the 13th and 15th terminals. (10)

[0227] According to the DC-DC converter described in (9), wherein,

[0228] The ratio of the first period to the second period is 1:1. (11)

[0230] A DC-DC converter, comprising:

[0231] The first switching element has a first terminal and a second terminal, wherein the first terminal is connected to a DC power supply;

[0232] The second switching element has a third terminal and a fourth terminal, wherein the third terminal is connected to the second terminal;

[0233] An LC series resonant circuit has a fifth terminal and a sixth terminal, wherein the fifth terminal is connected to the connection point of the second terminal and the third terminal;

[0234] The third winding has a seventh end and an eighth end;

[0235] The first winding has a 9th end and a 10th end;

[0236] The second winding has an 11th end and a 12th end;

[0237] The first rectifier element has a 13th terminal and a 14th terminal; and

[0238] The second diode is a second rectifier element having a 15th terminal and a 16th terminal, wherein the 15th terminal is connected to the 13th terminal;

[0239] The fourth winding has a 17th end and an 18th end;

[0240] The fifth winding has a 19th end and a 20th end;

[0241] The 6th winding has a 25th end and a 26th end;

[0242] The third rectifier element has a 21st terminal and a 22nd terminal; and

[0243] The fourth rectifier element has a 23rd terminal and a 24th terminal, wherein the 23rd terminal is connected to the 21st terminal.

[0244] The sixth end is connected to the seventh end.

[0245] The 8th end is connected to the 25th end.

[0246] The 26th end is connected to the 9th end and the 14th end.

[0247] The 10th end is connected to the 11th end.

[0248] The 12th end is connected to the 4th end and the 16th end.

[0249] The 17th end is connected to the 22nd end.

[0250] The 18th end is connected to the 19th end.

[0251] The 20th end is connected to the 24th end.

[0252] The connection point of the 18th end and the 19th end is connected to the connection point of the 10th end and the 11th end, and the connection point of the 21st end and the 23rd end is connected to the connection point of the 13th end and the 15th end. (12)

[0254] According to the DC-DC converter described in (11), wherein,

[0255] It also has a first core for forming a magnetic circuit and a second core for forming a magnetic circuit.

[0256] The first core has a first core portion and a second core portion.

[0257] The first winding and the second winding are respectively wound around the first core.

[0258] The third winding is wound around the second core.

[0259] The second core has a third core portion and a fourth core portion.

[0260] The fourth winding and the fifth winding are respectively wound around the third core.

[0261] The sixth winding is wound around the fourth core. (13)

[0263] According to the DC-DC converter described in (11), wherein,

[0264] It also has a first core for forming a magnetic circuit and a second core for forming a magnetic circuit.

[0265] The first core has three or more core sections.

[0266] The first winding, the second winding, and the third winding are respectively wound around any one of the three or more different core portions of the first core.

[0267] The second core has more than three core sections.

[0268] The fourth winding, the fifth winding, and the sixth winding are respectively wound around any one of the three or more different cores of the second core. (14)

[0270] The DC-DC converter according to any one of (11) to (13), wherein,

[0271] The first rectifier element, the second rectifier element, the third rectifier element, and the fourth rectifier element are all diodes.

[0272] The 13th end, the 15th end, the 21st end, and the 23rd end are all anodes.

[0273] The 14th end, the 16th end, the 22nd end, and the 24th end are all cathodes. (15)

[0275] The DC-DC converter according to any one of (11) to (14), wherein,

[0276] The process periodically repeats a first period in which the first switching element is turned on and the second switching element is turned off, and a second period in which the second switching element is turned on and the first switching element is turned off.

[0277] During the first period, the potential of the 26th terminal is different from the potential of the 4th terminal.

[0278] A DC voltage is output from the connection point of the 10th and 11th terminals and the connection point of the 13th and 15th terminals. (16)

[0280] According to the DC-DC converter described in (15), wherein,

[0281] The ratio of the first period to the second period is 1:1. (17)

[0283] A switching power supply device, comprising:

[0284] The DC-DC converter described in any one of (1) to (16); and

[0285] The DC power supply.

[0286] Explanation of reference numerals in the attached figures

[0287] 20, 20a~20k: Switching power supply devices;

[0288] 21, 21a~21k: DC-DC converters;

[0289] A1: First anode;

[0290] A2: Second anode;

[0291] A3: Third anode;

[0292] A4: Fourth anode;

[0293] C1, C2, C3, C4: Parasitic capacitors;

[0294] C: Capacitor;

[0295] CO1: 1st core;

[0296] CO2: Core 2;

[0297] CR1: 1st core;

[0298] CR2: 2nd core;

[0299] CR3: The third core;

[0300] CR4: 4th core;

[0301] CR5: 5th core;

[0302] CR6: The 6th core;

[0303] CS1: First control signal;

[0304] CS2: Second control signal;

[0305] FD1, FD2, FD3, FD4: Parasitic diodes;

[0306] D1: First diode;

[0307] D2: Second diode;

[0308] D3: The third diode;

[0309] D4: The fourth diode;

[0310] DCPS, Vcc: DC power supply;

[0311] GD: Gate drive circuit;

[0312] IT: Input terminal;

[0313] K1: First cathode;

[0314] K2: Second cathode;

[0315] K3: Third cathode;

[0316] K4: Fourth cathode;

[0317] L: Reactor;

[0318] LC: LC series resonant circuit;

[0319] LT11, LT12, LT21, LT22, LT23, LT24: Windings;

[0320] Lm1: First magnetizing inductor;

[0321] Lm2: Second magnetizing inductor;

[0322] O1, O2: First output terminal;

[0323] O3, O4: Second output terminals;

[0324] O5, O6: Third output terminal;

[0325] O7, O8: Fourth output terminal;

[0326] OP: Operational amplifier;

[0327] P1: Period 1;

[0328] P2: Period 2;

[0329] RL1, RL2: Load resistors;

[0330] S1: First switching element;

[0331] S2: Second switching element;

[0332] S3: Third switching element;

[0333] S4: Fourth switching element;

[0334] SC1, SC2: Smoothing capacitors;

[0335] SW: Switching circuit;

[0336] TR1~TR8: Transformers;

[0337] V: Gap

[0338] Vin: First DC voltage;

[0339] Vоut: Second DC voltage;

[0340] i1, i2, iD1, iD2: Current;

[0341] im: excitation current;

[0342] φ: magnetic flux.

Claims

1. A DC-DC converter, comprising: The first switching element has a first terminal and a second terminal, wherein, The first terminal is connected to a DC power supply; The second switching element has a third terminal and a fourth terminal, wherein the third terminal is connected to the second terminal; An LC series resonant circuit has a fifth terminal and a sixth terminal, wherein the fifth terminal is connected to the connection point of the second terminal and the third terminal; A conductor having a 7th end and an 8th end; The first winding has a 9th end and a 10th end; The second winding has an 11th end and a 12th end; The first rectifier element has a 13th terminal and a 14th terminal; and The second rectifier element has a 15th terminal and a 16th terminal, wherein the 15th terminal is connected to the 13th terminal. The first winding and the second winding are positively magnetically coupled to each other. The sixth end is connected to the seventh end. The 8th end is connected to the 9th end and the 14th end. The 10th end is connected to the 11th end. The 12th end is connected to the 4th end and the 16th end.

2. The DC-DC converter according to claim 1, wherein, The conductor is the third winding. The first winding, the second winding, and the third winding are positively magnetically coupled to each other.

3. The DC-DC converter according to claim 1 or 2, wherein, It also has: The fourth winding has a 17th end and an 18th end; The fifth winding has a 19th end and a 20th end; The third rectifier element has a 21st terminal and a 22nd terminal; as well as The fourth rectifier element has a 23rd terminal and a 24th terminal, wherein the 23rd terminal is connected to the 21st terminal. The first winding, the second winding, the fourth winding, and the fifth winding are positively magnetically coupled to each other. The 17th end is connected to the 22nd end. The 18th end is connected to the 19th end. The 20th end is connected to the 24th end.

4. The DC-DC converter according to claim 1 or 2, wherein, It also has: The fourth winding has a 17th end and an 18th end; The fifth winding has a 19th end and a 20th end; The third rectifier element has a 21st terminal and a 22nd terminal; as well as The fourth rectifier element has a 23rd terminal and a 24th terminal, wherein the 23rd terminal is connected to the 21st terminal. The first winding, the second winding, the fourth winding, and the fifth winding are positively magnetically coupled to each other. The 17th end is connected to the 22nd end. The 18th end is connected to the 19th end. The 20th end is connected to the 24th end. The connection point of the 18th end and the 19th end is connected to the connection point of the 10th end and the 11th end, and the connection point of the 21st end and the 23rd end is connected to the connection point of the 13th end and the 15th end.

5. The DC-DC converter according to claim 4, wherein, It also has a core that forms a magnetic circuit. The core has a first core portion and a second core portion. The first winding and the second winding are respectively wound around the first core. The fourth winding and the fifth winding are respectively wound around the second core.

6. The DC-DC converter according to claim 4, wherein, It also has a core that forms a magnetic circuit. The core has more than 5 core sections. The first winding, the second winding, the fourth winding, and the fifth winding are each wound on any one of the five or more different cores.

7. The DC-DC converter according to any one of claims 1 to 6, wherein, The first rectifier element and the second rectifier element are diodes, respectively. The 13th end and the 15th end are respectively the anodes. The 14th end and the 16th end are cathodes, respectively.

8. The DC-DC converter according to claim 3 or 4, wherein, The third and fourth rectifier elements are diodes, respectively. The 21st end and the 23rd end are respectively the anodes. The 22nd end and the 24th end are cathodes, respectively.

9. The DC-DC converter according to any one of claims 1 to 8, wherein, The process periodically repeats a first period in which the first switching element is turned on and the second switching element is turned off, and a second period in which the second switching element is turned on and the first switching element is turned off. During the first period, the potential of the ninth terminal is different from the potential of the fourth terminal. A DC voltage is output from the connection point of the 10th and 11th terminals and the connection point of the 13th and 15th terminals.

10. The DC-DC converter according to claim 9, wherein, The ratio of the first period to the second period is 1:

1.

11. A DC-DC converter, comprising: The first switching element has a first terminal and a second terminal, wherein, The first terminal is connected to a DC power supply; The second switching element has a third terminal and a fourth terminal, wherein the third terminal is connected to the second terminal; An LC series resonant circuit has a fifth terminal and a sixth terminal, wherein the fifth terminal is connected to the connection point of the second terminal and the third terminal; The third winding has a seventh end and an eighth end; The first winding has a 9th end and a 10th end; The second winding has an 11th end and a 12th end; The first rectifier element has a 13th terminal and a 14th terminal; The second diode is a second rectifier element having a 15th terminal and a 16th terminal, wherein the 15th terminal is connected to the 13th terminal; The fourth winding has a 17th end and an 18th end; The fifth winding has a 19th end and a 20th end; The 6th winding has a 25th end and a 26th end; The third rectifier element has a 21st terminal and a 22nd terminal; and The fourth rectifier element has a 23rd terminal and a 24th terminal, wherein the 23rd terminal is connected to the 21st terminal. The sixth end is connected to the seventh end. The 8th end is connected to the 25th end. The 26th end is connected to the 9th end and the 14th end. The 10th end is connected to the 11th end. The 12th end is connected to the 4th end and the 16th end. The 17th end is connected to the 22nd end. The 18th end is connected to the 19th end. The 20th end is connected to the 24th end. The connection point of the 18th end and the 19th end is connected to the connection point of the 10th end and the 11th end, and the connection point of the 21st end and the 23rd end is connected to the connection point of the 13th end and the 15th end.

12. The DC-DC converter according to claim 11, wherein, It also has a first core for forming a magnetic circuit and a second core for forming a magnetic circuit. The first core has a first core portion and a second core portion. The first winding and the second winding are respectively wound around the first core. The third winding is wound around the second core. The second core has a third core portion and a fourth core portion. The fourth winding and the fifth winding are respectively wound around the third core. The sixth winding is wound around the fourth core.

13. The DC-DC converter according to claim 11, wherein, It also has a first core for forming a magnetic circuit and a second core for forming a magnetic circuit. The first core has three or more core sections. The first winding, the second winding, and the third winding are respectively wound around any one of the three or more different core portions of the first core. The second core has more than three core sections. The fourth winding, the fifth winding, and the sixth winding are respectively wound around any one of the three or more different cores of the second core.

14. The DC-DC converter according to any one of claims 11 to 13, wherein, The first rectifier element, the second rectifier element, the third rectifier element, and the fourth rectifier element are all diodes. The 13th end, the 15th end, the 21st end, and the 23rd end are all anodes. The 14th end, the 16th end, the 22nd end, and the 24th end are all cathodes.

15. The DC-DC converter according to any one of claims 11 to 14, wherein, The process periodically repeats a first period in which the first switching element is turned on and the second switching element is turned off, and a second period in which the second switching element is turned on and the first switching element is turned off. During the first period, the potential of the 26th terminal is different from the potential of the 4th terminal. A DC voltage is output from the connection point of the 10th and 11th terminals and the connection point of the 13th and 15th terminals.

16. The DC-DC converter according to claim 15, wherein, The ratio of the first period to the second period is 1:

1.

17. A switching power supply device, comprising: The DC-DC converter according to any one of claims 1 to 16; and The DC power supply.

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