DC-DC converter and switching power supply

Abstract

A DC-DC converter (21) comprises a first switching element (S1), a second switching element (S2), an LC series resonant circuit (LC), a conductor, a first winding (LT21) and a second winding (LT22) that are magnetically coupled to each other in a positive manner, a first rectifying element (D1), and a second rectifying element (D2). The LC series resonant circuit is connected to the conductor. The conductor is connected to the first winding and the first rectifying element. The first winding is connected to the second winding. The second winding is connected to the second switching element and the second rectifying element.

Description

Technical Field

[0001] The present invention relates to a DC-DC converter and a switching power supply device.

Background Art

[0002] As an invention related to a conventional DC-DC converter, for example, the DC-DC converter described in Patent Document 1 is known. The DC-DC converter described in Patent Document 1 is supplied with 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, inductance elements 14 and 15, diodes 16 and 17, and a smoothing capacitor 18. The inductance element 14 includes a primary winding 141, a secondary winding 142, and output voltage terminals 201 and 202. The turns ratio between the primary winding 141 and the secondary winding 142 is n to 1. The inductance element 15 includes a primary winding 151 and a secondary winding 152. The turns ratio between the primary winding 151 and the secondary winding 152 is n to 1.

[0003] One end of a series circuit of the switching elements 11 and 12 is connected to the positive electrode of the DC power supply 10. The other end of the series circuit of the switching elements 11 and 12 is connected to the negative electrode of the DC power supply 10.

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

[0005] One end of the secondary winding 142 of inductance element 14 is connected to the cathode of diode 16. The other end of the secondary winding 142 of inductance element 14 is connected to one end of the secondary winding 152 of inductance element 15. The other end of the secondary winding 152 of inductance element 15 is connected to the cathode of diode 17. The connection point between the other end of the secondary winding 142 of inductance element 14 and the one end of the secondary winding 152 of inductance element 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 output voltage terminals 201 and 202. The voltage Vout output from the DC-DC converter is expressed as D × (1 - D) × Vin / n. Here, D is the ratio of the on-period of the switching element 11 to the switching period (sum of the on-period and off-period of the switching element 11). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4649299 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the above configuration, if you want to increase the step-down ratio of the DC-DC converter, you need to increase the number of turns in the primary winding. For example, if D=0.5, to make the step-down ratio 1 / 8 (Vout=1 / 8Vin), n=2. The turns ratio between primary winding 141 and secondary winding 142 becomes 2:1, and the turns ratio between primary winding 151 and secondary winding 152 also becomes 2:1. Therefore, the sum of the turns of primary windings 141 and 151 and the turns ratio between secondary windings 142 and 152 becomes 4:1:1. When the number of turns in the primary winding increases, the resistance of the primary winding increases, and thus the copper loss due to the primary winding increases.

[0008] Furthermore, when switching element 11 is on and switching element 12 is off, no current flows through the secondary winding 142 of inductance element 14 and diode 16, while current flows through the secondary winding 152 of inductance element 15 and diode 17. When switching element 11 is off and switching element 12 is on, current flows through the secondary winding 142 of inductance element 14, but no current flows through the secondary winding 152 of inductance element 15. Thus, the period during which current flows through the secondary winding 142 of inductance element 14 (first period) and the period during which current flows through the secondary winding 152 of inductance element 15 (second period) are biased towards predetermined periods. Therefore, for a predetermined output current, the effective value of the current Irec2 flowing through the secondary winding 142 of inductance element 14 becomes larger during the first period. Similarly, during the second period, the effective value of the current Irec1 flowing through the secondary winding 152 of the inductance element 15 increases. As a result, the copper loss due to the secondary winding 142 of the inductance element 14 and the copper loss due to the secondary winding 152 of the inductance element 15 increase.

[0009] Therefore, the object of the present invention is to provide a DC-DC converter and a switching power supply that can reduce copper loss. [Means for solving the problem]

[0010] A DC-DC converter according to one embodiment of the present invention is A first switching element having a first end and a second end, wherein the first end is connected to a DC power supply, A second switching element having a third end and a fourth end, wherein the third end is connected to the second end, An LC series resonant circuit having a fifth end and a sixth end, wherein the fifth end is connected to the connection point between the second end and the third end, A conductor having a seventh end and an eighth end, A first winding having a ninth end and a tenth end, A second winding having an 11th end and a 12th end, A first rectifier element having a 13th end and a 14th end, A second rectifier element having a 15th end and a 16th end, wherein the 15th end is connected to the 13th end, It is equipped with, The first winding and the second winding are magnetically positively coupled to each other. The sixth end is connected to the seventh end, The eighth end is connected to the ninth and fourteenth ends, The tenth end is connected to the eleventh end, The twelfth end is connected to the fourth end and the sixteenth end.

[0011] Since the eighth end of the conductor is connected to the ninth end of the first winding and the fourteenth end of the first rectifier element, the first winding also becomes part of the primary winding. As a result, the DC-DC converter according to one embodiment of the present invention can increase the step-down ratio of the DC-DC converter without increasing the number of turns of the primary winding. Consequently, the DC-DC converter according to one embodiment of the present invention can reduce copper loss due to the primary winding. [Effects of the Invention]

[0012] According to the DC-DC converter and switching power supply device of the present invention, copper loss can be reduced. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a circuit diagram showing a switching power supply 20 equipped with a DC-DC converter 21 and a load resistor RL1. [Figure 2] Figure 2 shows 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 excitation current im flowing through the first excitation inductance Lm1, the current iD1 flowing through the first diode D1, and the current iD2 flowing through the second diode D2. [Figure 3] FIG. 3 is a cross-sectional view schematically showing the structure of transformer TR1 and a diagram showing the connection of transformer TR1. [Figure 4] FIG. 4 is a plan view schematically showing the structure of the first core CO1. [Figure 5] FIG. 5 is an operation diagram showing the current flowing through the switching power supply device 20 and the load resistor RL1 in the first period P1. [Figure 6] FIG. 6 is an operation diagram showing the current flowing through the switching power supply device 20 and the load resistor RL1 in the second period P2. [Figure 7] FIG. 7 is a cross-sectional view schematically showing the structure of transformer TR2 and a diagram showing the connection of transformer TR2. [Figure 8] FIG. 8 is a plan view schematically showing the structure of the first core CO1. [Figure 9] FIG. 9 is a circuit diagram showing the switching power supply device 20b provided with the DC-DC converter 21b and the load resistor RL1. [Figure 10] FIG. 10 is a circuit diagram showing the switching power supply device 20c provided with the DC-DC converter 21c and the load resistors RL1 and RL2. [Figure 11] FIG. 11 is a circuit diagram showing the switching power supply device 20d provided with the DC-DC converter 21d and the load resistors RL1 and RL2. [Figure 12] FIG. 12 is a circuit diagram showing the switching power supply device 20e provided with the DC-DC converter 21e and the load resistor RL1. [Figure 13] FIG. 13 is a cross-sectional view schematically showing the structure of transformer TR4 and a diagram showing the connection of transformer TR4. [Figure 14] FIG. 14 is a plan view schematically showing the structure of the first core CO1. [Figure 15] FIG. 15 is a cross-sectional view schematically showing the structure of transformer TR6 and a diagram showing the connection of transformer TR6. [Figure 16] FIG. 16 is a plan view schematically showing the structure of the first core CO1. [Figure 17] Figure 17 is a circuit diagram showing a switching power supply unit 20g equipped with a DC-DC converter 21g and a load resistor RL1. [Figure 18] Figure 18 is a schematic cross-sectional view showing the structure of transformer TR7 and a diagram showing the wiring of transformer TR7. [Figure 19] Figure 19 is a schematic plan view showing the structure of the second core CO2. [Figure 20] Figure 20 is a schematic cross-sectional view showing the structure of transformer TR8 and a diagram showing the wiring of transformer TR8. [Figure 21] Figure 21 is a schematic plan view showing the structure of the second core CO2. [Figure 22] Figure 22 is a circuit diagram showing the switching circuit SW in the ninth modified example. [Figure 23] Figure 23 is a circuit diagram showing the switching circuit SW in the tenth modified example. [Figure 24] Figure 24 is a circuit diagram showing a modified example of the first rectifier element. [Modes for carrying out the invention]

[0014] [First Embodiment] Below, a switching power supply device 20 equipped with a DC-DC converter 21 according to a first embodiment of the present invention will be described with reference to the drawings. Figure 1 is a circuit diagram showing the switching power supply device 20 equipped with the DC-DC converter 21 and a load resistor RL1. Note that the leakage inductance of the transformer TR1 is omitted in Figure 1. Figure 2 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 excitation current im flowing through the first excitation inductance Lm1, the current iD1 flowing through the first diode D1, and the current iD2 flowing through the second diode D2. Note that the horizontal axis in Figure 2 is time t. Furthermore, the vertical axis in Figure 2 represents 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 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 excitation current im flowing through the first excitation inductance Lm1, the current iD1 flowing through the first diode D1, and the current iD2 flowing through the second diode D2. In Figure 2, the direction of current iD1 is defined as positive when it flows from the first anode A1 to the first cathode K1. Also in Figure 2, the direction of current iD2 is defined as positive when it flows from the second anode A2 to the second cathode K2. Figure 3 is a schematic cross-sectional view showing the structure of transformer TR1 and a diagram showing the connections of transformer TR1. Figure 4 is a schematic plan view showing the structure of the first core CO1.

[0015] The switching power supply unit 20 is used to supply a DC voltage to the load. As shown in Figure 1, the switching power supply unit 20 includes a DC power supply DCPS, a DC-DC converter 21, and first output terminals O1 and O2.

[0016] The first output terminals O1 and O2 are connected to both 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 earth. Note that the first output terminal O2 does not necessarily have to be connected to earth. 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 reactance component.

[0017] 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 is, for example, a battery or an electric double-layer capacitor. Note that the DC power supply DCPS only needs to output a DC voltage. Therefore, the DC power supply DCPS may be an AC-DC converter or a DC-DC converter, etc.

[0018] The DC-DC converter 21 receives a first DC voltage Vin from a DC power supply DCPS. The DC-DC converter 21 is used to supply a second DC voltage Vout, which is different from the first DC voltage Vin, to the load. The 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. Note that the smoothing capacitor SC1 is not essential.

[0019] 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.

[0020] The switching circuit SW includes a first switching element S1 and a second switching element S2. The first switching element S1 is connected to an input terminal IT, a second switching element S2, and a 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 a 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 end" of the present invention. The source S of the first switching element S1 corresponds to the "second end" of the present invention. Note that the "first switching element" of the present invention is not limited to a MOSFET, but may be a bipolar transistor or an IGBT (Insulated Gate Bipolar Transistor) or other element having a switching function.

[0021] 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 end" of the present invention. The source S of the second switching element S2 corresponds to the "fourth end" of the present invention. Note that the "second switching element" of the present invention is not limited to a MOSFET, but may be a bipolar transistor or an IGBT or other element having a switching function.

[0022] A first control signal CS1 is applied to the gate G1 of the first switching element S1 from the gate drive circuit GD. The first switching element S1 is controlled to be on / off by the first control signal CS1. As shown in Figure 2, the first switching element S1 alternates between an on state and an off state. In the on state, the first switching element S1 conducts. In the off state, the first switching element S1 does not conduct. 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 period (sum of the on period and off period of the first switching element S1) is 0.5. Note that the ratio of the on period to the off period of the first switching element S1 is not limited to 1:1.

[0023] A second control signal CS2 is applied to the gate G2 of the second switching element S2 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 alternates between the on state and the off state. In the on state, the second switching element S2 conducts. In the off state, the second switching element S2 does not conduct. However, the gate drive circuit GD generates the second control signal CS2 such that when the first switching element S1 is in the off state, the second switching element S2 is in the on state. As a result, there is a first period P1 in which the first switching element S1 conducts and the second switching element S2 does not conduct, and a second period in which the second switching element S2 conducts and the first switching element S1 It becomes non-conductive.The second period P2 is repeated periodically. In this embodiment, the ratio of the on period to the off period of the second switching element S2 is 1:1. As a result, the ratio of the first period P1 to the second period P2 is 1:1. Note that a dead time period may be provided between the first period P1 and the second period P2, not limited to the first period P1 and the second period P2. That is, during the dead time period, the gate drive circuit GD may generate the first control signal CS1 and the second control signal CS2 so that the first switching element S1 and the second switching element S2 are both in the off state. By providing 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 at the same time. Furthermore, the ratio of the on period to the off period of the second switching element S2 is not limited to 1:1.

[0024] As shown in Figure 1, the parasitic capacitor C1 is connected between the drain D and source S of the first switching element S1. The parasitic capacitor C1 suppresses ringing during the turn-on and turn-off of the first switching element S1. Furthermore, the parasitic capacitor C1 enables the first switching element S1 to perform ZVS (Zero Voltage Switching) during the dead time period.

[0025] The parasitic diode FD1 is connected between the drain D and source S of the first switching element S1. The cathode of the parasitic diode FD1 is connected to the drain D of the first switching element S1. The anode of the parasitic diode FD1 is connected to the source S of the first switching element S1. Due to the parasitic diode FD1, when the first switching element S1 is turned off, current flows back from the anode to the cathode of the parasitic diode FD1. This suppresses the flow of current from the source S to the drain D of the first switching element S1, thereby preventing the first switching element S1 from being destroyed. A separate freewheeling diode may also be provided in addition to the first switching element S1.

[0026] The parasitic capacitor C2 is connected between the drain D and source S of the second switching element S2. The parasitic capacitor C2 suppresses ringing during the turn-on and turn-off of the second switching element S2. In addition, the parasitic capacitor C2 enables the second switching element S2 to perform ZVS during the dead time period.

[0027] 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. Due to 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 flow of current from the source S to the drain D of the second switching element S2, thereby preventing the second switching element S2 from being destroyed. Note that a separate freewheeling diode may be provided in addition to the second switching element S2.

[0028] The LC series resonant circuit LC includes a reactor L and a capacitor C. The reactor L is connected to the connection point between the source S of the first switching element S1 and the drain D of the second switching element S2, and 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 perform soft switching by current resonance between the reactor L and the capacitor C. The terminal TL of the reactor L, which is connected to the connection point between 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 the present invention. The terminal TC of the capacitor C, which is connected to the transformer TR1, corresponds to the "sixth terminal" of the present invention.

[0029] In the circuit diagram shown in Figure 1, transformer TR1 includes a first excitation inductance Lm1 and windings LT11, LT21, and LT22. Windings LT11, LT21, and LT22 are magnetically coupled. The first excitation inductance Lm1 is the inductance that generates a magnetic flux φ that links with all of windings LT11, LT21, and LT22. In this embodiment, the turns ratio of windings LT11, LT21, and LT22 is n to 1 to 1. Also, n=2. However, it is not limited to n=2. Furthermore, the turns ratio of windings LT11, LT21, and LT22 does not have to be n to 1 to 1.

[0030] In the cross-sectional view shown in Figure 3, the transformer TR1 includes a first core CO1 and windings LT11, LT21, and LT22. The material of the first core CO1 is 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 each wound around the first core section CR1. As shown in Figures 3 and 4, the first core CO1 forms a magnetic path. In this embodiment, the cross-sectional area of ​​the second core section CR2 perpendicular to the magnetic path is equal to the cross-sectional area of ​​the first core section CR1 perpendicular to the magnetic path. An air gap may be provided between the first core section CR1 and the second core section CR2.

[0031] As shown in Figure 1, one end T1 of winding LT11 is connected to the end TC of capacitor C. The other end T2 of winding LT11 is connected to winding LT21 and the first diode D1. Therefore, winding LT11 and winding LT21 are not isolated from each other. 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.

[0032] 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 the present invention. One end T3 of winding LT21 corresponds to the "ninth end" of the present invention. The other end T4 of winding LT21 corresponds to the "tenth end" of the present invention.

[0033] 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 the present invention. One end T5 of winding LT22 corresponds to the "eleventh end" of the present invention. The other end T6 of winding LT22 corresponds to the "twelfth end" of the present invention.

[0034] As shown in Figure 3, in transformer TR1, the direction of the magnetic flux φ generated when current flows from one end T1 to the other end T2 of winding LT11 coincides with the direction of the magnetic flux φ generated when current flows from one end T3 to the other end T4 of winding LT21, and the direction of the magnetic flux φ generated when current flows from one end T5 to the other end T6 of winding LT22. Therefore, windings LT11, LT21, and LT22 are positively coupled to each other magnetically. In other words, the coupling coefficient between winding LT11 and winding LT21 is positive. Also, the coupling coefficient between winding LT11 and winding LT22 is positive. Also, the coupling coefficient between winding LT21 and winding LT22 is positive.

[0035] As shown in Figure 1, 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.

[0036] 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.

[0037] The smoothing capacitor SC1 is connected to the second output terminals O3 and O4. Specifically, the smoothing capacitor SC1 is connected to the connection point between the other end T4 of winding LT21 and winding LT22, and to the connection point between the first anode A1 and the second anode A2.

[0038] Next, the operation of the DC-DC converter 21 will be explained. Figure 5 is an operation diagram showing the current flowing through the switching power supply 20 and load resistor RL1 during the first period P1. Figure 6 is an operation diagram showing the current flowing through the switching power supply 20 and load resistor RL1 during the second period P2.

[0039] As shown in Figure 5, during the first period P1, current i1 flows in the following order: 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, the excitation current im flows through the first excitation inductance Lm1. At this time, due to the magnetic coupling of windings LT11 and LT22, current i2 flows through winding LT22. Current i2 flows in the following order: 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, the currents i1 and i2 flow, causing the potential at one end T3 of the winding LT21 to be different from the potential at the source S of the second switching element S2. More specifically, during the first period P1, the potential at one end T3 of the winding LT21 is higher than the potential at the source S of the second switching element S2.

[0040] As shown in Figure 2, 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.

[0041] As shown in Figure 6, during the second period P2, capacitor C discharges. Current i1 is the discharge current of capacitor C during the second period P2. During the second period P2, current i1 flows in the following order: capacitor C, second switching element S2, winding LT22, second output terminal O3, first output terminal O1, load resistor RL1, first output terminal O2, second output terminal O4, first diode D1, winding LT11, and capacitor C. When current i1 flows through winding LT11, the excitation current im flows through the first excitation inductance Lm1. At this time, due to the magnetic coupling of windings LT11 and LT21, current i2 flows through winding LT21. Current i2 flows in the following order: winding LT21, second output terminal O3, first output terminal O1, load resistor RL1, first output terminal O2, first diode D1, and winding LT21. During the second period P2, the currents i1 and i2 flow, causing the potential at one end T3 of the winding LT21 to differ from the potential at the source S of the second switching element S2. More specifically, during the second period P2, the potential at one end T3 of the winding LT21 is lower than the potential at the drain D of the first switching element S1.

[0042] As shown in Figure 2, 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.

[0043] In this embodiment, the second DC voltage Vout is expressed by the following formula 1 using the first DC voltage Vin and n.

[0044]

number

[0045] [effect] The DC-DC converter 21 can reduce copper losses. More specifically, the second DC voltage Vout is expressed by Equation 1 above, using the first DC voltage Vin and n. Therefore, when the ratio of the ON period of the first switching element S1 to the switching period is 0.5, if we want to set the step-down ratio of the DC-DC converter 21 to 1 / 8 (Vout = 1 / 8Vin), 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 and the secondary windings 142 and 152 was 4:1:1. Therefore, the number of turns of winding LT11 is reduced compared to the primary windings 141 and 151 in the DC-DC converter described in Patent Document 1. In other words, according to the DC-DC converter 21 of this embodiment, the resistance value of the winding LT11 can be reduced by reducing the number of turns of the winding LT11. As a result, according to the DC-DC converter 21 of this embodiment, copper loss due to the winding LT11 can be reduced.

[0046] Furthermore, the DC-DC converter 21 can further reduce copper losses. More specifically, in 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 as the current flowing through winding LT22 with respect to the load resistor RL1. In other words, in the first period P1, the current flowing through the load resistor RL1 is divided between the current flowing through winding LT21 and the current flowing through winding LT22. Also, in 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 as the current flowing through winding LT22 with respect to the load resistor RL1. In other words, in the second period P2 as well, the current flowing through the load resistor RL1 is divided between the current flowing through winding LT21 and the current flowing through winding LT22. Therefore, the periods during which current flows through winding LT21 and winding LT22 are not biased towards a predetermined period. As a result, the effective values ​​of the current flowing through winding LT21 and winding LT22 do not need to be unnecessarily large for a given output current. Consequently, the DC-DC converter 21 can reduce copper losses due to windings LT21 and LT22.

[0047] Furthermore, the DC-DC converter 21 can extend the lifespan of the second diode D2. More specifically, during the first period P1, no current i1 flows through the capacitor C into the second diode D2. Also, 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. As a result, the losses generated by the second diode D2 are small, and the amount of heat generated by the second diode D2 is also small. Therefore, the temperature of the second diode D2 can be kept low, and the lifespan of the second diode D2 can be extended.

[0048] [First variation] The following describes a DC-DC converter 21a and a switching power supply 20a according to the first modified example of the present invention, with reference to the drawings. Figure 7 is a schematic cross-sectional view showing the structure of transformer TR2 and a diagram showing the wiring of transformer TR2. Figure 8 is a schematic plan view showing the structure of the first core CO1. Note that for the DC-DC converter 21a and switching power supply 20a according to the first modified example, only the parts that differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment will be described, and the rest will be omitted.

[0049] The DC-DC converter 21a and switching power supply 20a according to the first modified example differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment in that they each include a transformer TR2 instead of transformer TR1.

[0050] As shown in Figure 7, the first core CO1 further has a third core CR3. That is, the first core CO1 has three core sections. The winding LT22 is wound around the third core CR3. That is, windings LT11, LT21, and LT22 are each wound around one of the three different core sections of the first core CO1. As shown in Figure 8, an air gap V is provided between the first core CR1 and the third core CR3. As shown in Figures 7 and 8, the first core CO1 forms a magnetic path. More specifically, the first core CR1 and the second core CR2 form a magnetic path through which magnetic flux φ1 flows. Also, the second core CR2 and the third core CR3 form a magnetic path through which magnetic flux φ2 flows. In this case, the relationship φ = φ1 + φ2 holds. In this modified example, the cross-sectional area of ​​the first core CR1 perpendicular to the magnetic path and the cross-sectional area of ​​the third core CR3 perpendicular to the magnetic path are each half the cross-sectional area of ​​the second core CR2 perpendicular to the magnetic path. The sum of the cross-sectional areas of the first core CR1 perpendicular to the magnetic path and the cross-sectional area of ​​the third core CR3 perpendicular to the magnetic path is equal to the cross-sectional area of ​​the second core CR2 perpendicular to the magnetic path. Therefore, the magnitude of magnetic flux φ1 and the magnitude of magnetic flux φ2 are each half the magnetic flux φ. Note that the first core CO1 may have four or more core sections.

[0051] In this modified example, the second DC voltage Vout is expressed by the following equation 2, using the first DC voltage Vin and n.

[0052]

number

[0053] The DC-DC converter 21a and switching power supply 20a described above also produce the same effects as the DC-DC converter 21 and switching power supply 20. Furthermore, the DC-DC converter 21a can reduce copper loss when the step-down ratio is the same. More specifically, the magnitude of magnetic flux φ1 and the magnitude of magnetic flux φ2 are each half of magnetic flux φ. Therefore, the induced electromotive force generated in each of the windings LT21 and LT22 of the DC-DC converter 21a is half of the induced electromotive force generated in each of the windings LT21 and LT22 of the DC-DC converter 21. In the case of the DC-DC converter 21, in order to make n=2, it was 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, in order to set n=2, the number of turns of winding LT11 should be set to 1, the number of turns of winding LT21 should be set to 1, and the number of turns of winding LT22 should be set to 1. In other words, the number of turns of winding LT11 can be half the number of turns of winding LT11 in DC-DC converter 21. Therefore, with DC-DC converter 21a, the resistance value of winding LT11 can be made smaller by further reducing the number of turns of winding LT11. As a result, copper loss due to winding LT11 can be further reduced with DC-DC converter 21a.

[0054] In other words, if the number of turns of winding LT11, winding LT21, and winding LT22 are the same for DC-DC converter 21 and DC-DC converter 21a, the step-down ratio of DC-DC converter 21a is higher than that of DC-DC converter 21. DC-DC converter 21a makes it possible to achieve a high step-down ratio without increasing the number of turns of winding LT11 and without increasing the cross-sectional area perpendicular to the magnetic path of the core.

[0055] [Second variation] Below, a DC-DC converter 21b and a switching power supply 20b according to a second modification of the present invention will be described with reference to the drawings. Figure 9 is a circuit diagram showing a switching power supply 20b equipped with a DC-DC converter 21b and a load resistor RL1. Note that for the DC-DC converter 21b and switching power supply 20b according to the second modification, only the parts that differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment will be described, and the rest will be omitted.

[0056] The DC-DC converter 21b and switching power supply 20b according to the second modified example differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment in that they each include a transformer TR3 instead of transformer TR1. As shown in Figure 9, transformer TR3 does not include winding LT11.

[0057] In this modified example, the DC-DC converter 21b includes a conductor CON. One end CON1 of conductor CON is connected to the end TC of capacitor C. The other end CON2 of conductor CON is connected to the winding LT21 and the first diode D1. In this modified example, conductor CON corresponds to the "conductor" of the present invention. One end CON1 of conductor CON corresponds to the "seventh end" of the present invention. The other end CON2 of conductor CON corresponds to the "eighth end" of the present invention.

[0058] The DC-DC converter 21b and switching power supply 20b described above also produce the same effects as the DC-DC converter 21 and switching power supply 20. Furthermore, with the DC-DC converter 21b, the step-down ratio of the DC-DC converter 21b can be set to 1 / 4 (Vout = 1 / 4Vin) even without winding LT11. More specifically, by substituting n=0 into Equation 1, Vout = 1 / 4Vin is obtained. In addition, by reducing winding LT11, the DC-DC converter can be made smaller and less expensive.

[0059] [Third variation] Below, a DC-DC converter 21c and switching power supply 20c according to a third modification of the present invention will be described with reference to the drawings. Figure 10 is a circuit diagram showing the switching power supply 20c equipped with the DC-DC converter 21c and load resistors RL1 and RL2. Note that for the DC-DC converter 21c and switching power supply 20c according to the third modification, only the parts that differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment will be described, and the rest will be omitted.

[0060] The switching power supply device 20c according to the third modified example differs from the switching power supply device 20 according to the first embodiment in that it further comprises third output terminals O5 and O6, the DC-DC converter 21c comprises a transformer TR4 instead of transformer TR1, and the DC-DC converter 21c further comprises a smoothing capacitor SC2, a third diode D3, a fourth diode D4, and fourth output terminals O7 and O8.

[0061] As shown in Figure 10, the transformer TR4 further includes windings LT23 and LT24. Windings LT11, LT21, LT22, LT23, and LT24 are magnetically coupled. The first excitation inductance Lm1 is the inductance that generates a magnetic flux φ that links with all of the windings LT11, LT21, LT22, LT23, and LT24. In the 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 of winding LT11 coincides with the direction of the magnetic flux φ 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 φ generated when current flows from one end T9 of winding LT24 to the other end T10 of winding LT24. Therefore, windings LT11, LT21, LT22, LT23, and LT24 are positively coupled to each other magnetically. In this embodiment, the turns ratio of windings LT11, LT21, LT22, LT23, and LT24 is n:1:1:1:1. However, the turns ratio of windings LT11, LT21, LT22, LT23, and LT24 does not have to be n:1:1:1:1.

[0062] The third output terminals O5 and O6 are connected across the load resistor RL2. The third output terminal O6 is connected to ground potential. The third output terminals O5 and O6 output a third DC voltage different from the first DC voltage Vin. The load resistor RL2 is a specific example of a load. The load may include a reactance component as well as a resistance component. The third DC voltage may be equal to the second DC voltage Vout, or it may be different from the second DC voltage Vout.

[0063] 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. The connections of the smoothing capacitor SC2, the third diode D3, the fourth diode D4, windings LT23, LT24, the third output terminals O5, O6 and the fourth output terminals O7, O8 are the same as the connections of the smoothing capacitor SC1, the first diode D1, the second diode D2, windings LT21, LT22, the first output terminals O1, O2 and the second output terminals O3, O4, except that the third diode D3 and winding LT23 are not connected to the other end T2 of winding LT11, and the fourth diode D4 and winding LT24 are not connected to the source S of the second switching element S2, so the explanation is omitted. The third diode D3 corresponds to the "third rectifier element" of the present invention. The third anode A3 corresponds to the "21st terminal" of the present invention. The third cathode K3 corresponds to the "22nd terminal" of the present invention. The fourth diode D4 corresponds to the "fourth rectifier element" of the present invention. The fourth anode A4 corresponds to the "23rd terminal" of the present invention. The fourth cathode K4 corresponds to the "24th terminal" of the present invention.

[0064] Winding LT23 corresponds to the "fourth winding" of the present invention. One end T7 of winding LT23 corresponds to the "seventeenth end" of the present invention. The other end T8 of winding LT23 corresponds to the "eighteenth end" of the present invention. Winding LT24 corresponds to the "fifth winding" of the present invention. One end T9 of winding LT24 corresponds to the "nineteenth end" of the present invention. The other end T10 of winding LT24 corresponds to the "twentieth end" of the present invention.

[0065] The DC-DC converter 21c and switching power supply 20c described above also achieve the same effects as the DC-DC converter 21 and switching power supply 20. Furthermore, the DC-DC converter 21c can output DC voltages in parallel.

[0066] [Fourth variation] The following describes a DC-DC converter 21d and a switching power supply 20d according to a fourth modification of the present invention, with reference to the drawings. Figure 11 is a circuit diagram showing the switching power supply 20d equipped with the DC-DC converter 21d and load resistors RL1 and RL2. Note that for the DC-DC converter 21d and switching power supply 20d according to the fourth modification, only the parts that differ from the DC-DC converter 21c and switching power supply 20c according to the third modification will be described, and the rest will be omitted.

[0067] The DC-DC converter 21d and switching power supply 20d according to the fourth modification differ from the DC-DC converter 21c and switching power supply 20c according to the third modification in that they each include a transformer TR5 instead of transformer TR4. As shown in Figure 11, transformer TR5 does not include winding LT11.

[0068] In this modified example, the DC-DC converter 21d includes a conductor CON. One end CON1 of the conductor CON is connected to the end TC of the capacitor C. The other end CON2 of the conductor CON is connected to the winding LT21 and the first diode D1. In this modified example, the conductor CON corresponds to the "conductor" of the present invention. One end CON1 of the conductor CON corresponds to the "seventh end" of the present invention. The other end CON2 of the conductor CON corresponds to the "eighth end" of the present invention.

[0069] The DC-DC converter 21d and switching power supply 20d described above also produce the same effects as the DC-DC converters 21b and 21c and switching power supplies 20b and 20c.

[0070] [Fifth variation] The following describes a DC-DC converter 21e and switching power supply 20e according to a fifth modification of the present invention, with reference to the drawings. Figure 12 is a circuit diagram showing the switching power supply 20e equipped with the DC-DC converter 21e and the load resistor RL1. Figure 13 is a schematic cross-sectional view showing the structure of the transformer TR4 and a diagram showing the wiring of the transformer TR4. Figure 14 is a schematic plan view showing the structure of the first core CO1. Note that for the DC-DC converter 21e and switching power supply 20e according to the fifth modification, only the parts that differ from the DC-DC converter 21c and switching power supply 20c according to the third modification will be described, and the rest will be omitted.

[0071] The switching power supply 20e according to the fifth modification differs from the switching power supply 20c according to the third modification in that it 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. In this modification, the third DC voltage output by the third output terminals O5 and O6 is equal to the second DC voltage Vout.

[0072] As shown in Figure 12, the connection point between 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 between the other end T8 of winding LT23 and one end T9 of winding LT24 is connected to the connection point between the other end T4 of winding LT21 and one end T5 of winding LT22. The connection point between the third anode A3 and the fourth anode A4 is connected to the second output terminal O4. That is, the connection point between the third anode A3 and the fourth anode A4 is connected to the connection point between the first anode A1 and the second anode A2.

[0073] As shown in Figure 13, the first core CO1 further has a third core CR3. Windings LT23 and LT24 are wound around the third core CR3, respectively. As shown in Figure 14, an air gap V is provided between the first core CR1 and the third core CR3. As shown in Figures 13 and 14, the first core CO1 forms a magnetic path. More specifically, the first core CR1 and the second core CR2 form a magnetic path through which magnetic flux φ1 flows. The second core CR2 and the third core CR3 also form a magnetic path through which magnetic flux φ2 flows. In this case, the relationship φ = φ1 + φ2 holds. In this modified example, the cross-sectional area of ​​the first core CR1 perpendicular to the magnetic path and the cross-sectional area of ​​the third core CR3 perpendicular to the magnetic path are each half the cross-sectional area of ​​the second core CR2 perpendicular to the magnetic path. The sum of the cross-sectional area of ​​the first core section CR1 perpendicular to the magnetic path and the cross-sectional area of ​​the third core section CR3 perpendicular to the magnetic path is equal to the cross-sectional area of ​​the second core section CR2 perpendicular to the magnetic path. Therefore, the magnitude of magnetic flux φ1 and magnetic flux φ2 are each half of magnetic flux φ. The third core section CR3 corresponds to the "second core section" of the present invention.

[0074] The DC-DC converter 21e and switching power supply 20e described above also achieve the same effects as the DC-DC converters 21 and 21a and switching power supplies 20 and 20a. In other words, the DC-DC converter 21e can further reduce copper loss due to the winding LT11. To put it another way, the DC-DC converter 21e can achieve a high step-down ratio without increasing the number of turns of the winding LT11 and without increasing the cross-sectional area perpendicular to the magnetic path of the core.

[0075] [Sixth variation] Below, a DC-DC converter 21f and a switching power supply 20f according to the sixth modification of the present invention will be described with reference to the drawings. Figure 15 is a schematic cross-sectional view showing the structure of transformer TR6 and a diagram showing the wiring of transformer TR6. Figure 16 is a schematic plan view showing the structure of the first core CO1. Note that for the DC-DC converter 21f according to the sixth modification, only the parts that differ from the DC-DC converter 21e and switching power supply 20e according to the fifth modification will be described, and the rest will be omitted.

[0076] The DC-DC converter 21f and switching power supply 20f according to the sixth modification differ from the DC-DC converter 21e and switching power supply 20e according to the fifth modification in that they each include a transformer TR6 instead of transformer TR4.

[0077] As shown in Figure 15, the first core CO1 further comprises a fourth core section CR4 and a fifth core section CR5. That is, the first core CO1 has five core sections. Winding LT22 is wound around the fourth core section CR4. Winding LT23 is wound around the fifth core section CR5. Winding LT24 is wound around the third core section CR3. That is, windings LT11, LT21, LT22, LT23, and LT24 are each wound around one of the five different core sections. As shown in Figure 16, there is an air gap V between the first core section CR1 and the fourth core section CR4. There is an air gap V between the fourth core section CR4 and the fifth core section CR5. There is an air gap V between the fifth core section CR5 and the third core section CR3. As shown in Figures 15 and 16, the first core CO1 forms a magnetic path. More specifically, the first core section CR1 and the second core section CR2 form a magnetic path through which magnetic flux φ1 flows. The second core section CR2 and the third core section CR3 form a magnetic path through which magnetic flux φ2 flows. The second core section CR2 and the fourth core section CR4 form a magnetic path through which magnetic flux φ3 flows. The second core section CR2 and the fifth core section CR5 form a magnetic path through which magnetic flux φ4 flows. In this case, the relationship φ = φ1 + φ2 + φ3 + φ4 holds. In this modified example, the cross-sectional area perpendicular to the magnetic path of the first core section CR1, the third core section CR3, the fourth core section CR4, and the fifth core section CR5 is each 1 / 4 of the cross-sectional area perpendicular to the magnetic path of the second core section CR2. The sum of the cross-sectional areas perpendicular to the magnetic path of the first core section CR1, the third core section CR3, the fourth core section CR4, and the fifth core section CR5 is equal to the cross-sectional area perpendicular to the magnetic path of the second core section CR2. Therefore, the magnitudes of magnetic flux φ1, φ2, φ3, and φ4 are each 1 / 4 of the magnetic flux φ. The number of core sections may be six or more.

[0078] The DC-DC converter 21f and switching power supply 20f described above also achieve the same effects as the DC-DC converters 21a and 21e and the switching power supplies 20a and 20e. Furthermore, the DC-DC converter 21f can reduce copper loss due to the winding LT11 compared to the DC-DC converter 21e. In other words, the DC-DC converter 21f can achieve a higher step-down ratio than the DC-DC converter 21e without increasing the number of turns of the winding LT11 or increasing the cross-sectional area perpendicular to the magnetic path of the core.

[0079] [Seventh variation] Below, a DC-DC converter 21g and a switching power supply 20g according to the seventh modification of the present invention will be described with reference to the drawings. Figure 17 is a circuit diagram showing the switching power supply 20g equipped with the DC-DC converter 21g and the load resistor RL1. Figure 18 is a schematic cross-sectional view showing the structure of the transformer TR7 and a diagram showing the wiring of the transformer TR7. Figure 19 is a schematic plan view showing the structure of the second core CO2. Note that for the DC-DC converter 21g and switching power supply 20g according to the seventh modification, only the parts that differ from the DC-DC converter 21e and switching power supply 20e according to the fifth modification will be described, and the rest will be omitted.

[0080] The DC-DC converter 21g and switching power supply 20g according to the seventh modification differ from the DC-DC converter 21e and switching power supply 20e according to the fifth modification in that they are equipped with transformers TR1 and TR7 instead of transformer TR4, respectively. The structure of transformer TR1 is the same as that of transformer TR1 according to the first embodiment, except that the cross-sectional area perpendicular to the magnetic path of the first core CO1 is half the cross-sectional area perpendicular to the magnetic path of the first core CO1 according to the first embodiment, so a description is omitted.

[0081] In the circuit diagram shown in Figure 17, transformer TR7 includes a second excitation inductance Lm2 and windings LT12, LT23, and LT24. Windings LT12, LT23, and LT24 are magnetically coupled. The second excitation inductance Lm2 is the inductance that generates a magnetic flux φ12 that links with all of 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 of winding LT12 coincides with 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 to n / 2 to 1 to 1 to 1 to 1. Also, n=2. However, it is not limited to n=2. Furthermore, the turns ratio of windings LT11, LT12, LT21, LT22, LT23, and LT24 is n / 2 vs n / 2 The relationship does not have to be 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.

[0082] 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.

[0083] In the cross-sectional view shown in Figure 18, the transformer TR7 includes a second core CO2 and windings LT12, LT23, and LT24. The material of the second core CO2 is a magnetic material. The second core CO2 has a fourth core section CR4 and a sixth core section CR6. Winding LT2 3 LT2 4These are each wound around the fourth core section CR4. Winding LT12 is wound around the sixth core section CR6. As shown in Figures 18 and 19, the second core CO2 forms a magnetic path. More specifically, the fourth core section CR4 and the sixth core section CR6 form a magnetic path through which magnetic flux φ3 flows. In this modified example, the cross-sectional area of ​​the second core CO2 perpendicular to the magnetic path is half the cross-sectional area of ​​the first core CO1 perpendicular to the magnetic path in the first embodiment. Also in this modified example, the cross-sectional area of ​​the fourth core section CR4 perpendicular to the magnetic path is equal to the cross-sectional area of ​​the sixth core section CR6 perpendicular to the magnetic path. An air gap may be provided between the fourth core section CR4 and the sixth core section CR6. In this modified example, the first core section CR1 corresponds to the "first core section" of the present invention. In this modified example, the second core section CR2 corresponds to the "second core section" of the present invention. In this modified example, the fourth core portion CR4 corresponds to the "third core portion" of the present invention. In this modified example, the sixth core portion CR6 corresponds to the "fourth core portion" of the present invention.

[0084] The DC-DC converter 21g and switching power supply 20g described above also produce the same effects as the DC-DC converter 21e and switching power supply 20e.

[0085] [Variation 8] Below, a DC-DC converter 21h and a switching power supply 20h according to the eighth modification of the present invention will be described with reference to the drawings. Figure 20 is a schematic cross-sectional view showing the structure of transformer TR8 and a diagram showing the wiring of transformer TR8. Figure 21 is a schematic plan view showing the structure of the second core CO2. Note that for the DC-DC converter 21h and switching power supply 20h according to the eighth modification, only the parts that differ from the DC-DC converter 21f and switching power supply 20f according to the seventh modification will be described, and the rest will be omitted.

[0086] The DC-DC converter 21h and switching power supply 20h according to the eighth modification differ from the DC-DC converter 21g and switching power supply 20g according to the seventh modification in that they are equipped with transformer TR2 instead of transformer TR1 and transformer TR8 instead of transformer TR7, respectively. The structure of transformer TR2 is the same as that of transformer TR2 according to the first modification, except that the cross-sectional area perpendicular to the magnetic path of the first core CO1 is half the cross-sectional area perpendicular to the magnetic path of the first core CO1 according to the first modification, so a description is omitted.

[0087] As shown in Figure 20, the second core CO2 further has a fifth core CR5. That is, the second core CO2 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 each wound around one of the three different cores of the second core CO2. As shown in Figure 21, an air gap V is provided between the fourth core CR4 and the fifth core CR5. As shown in Figures 20 and 21, the second core CO2 forms a magnetic path. More specifically, the fourth core CR4 and the sixth core CR6 form a magnetic path through which magnetic flux φ31 flows. Also, the fifth core CR5 and the sixth core CR6 form a magnetic path through which magnetic flux φ32 flows. In this case, the relationship φ3 = φ31 + φ32 holds. In this modified example, the cross-sectional area of ​​the fourth core section CR4 perpendicular to the magnetic path and the cross-sectional area of ​​the fifth core section CR5 perpendicular to the magnetic path are each half of the cross-sectional area of ​​the sixth core section CR6 perpendicular to the magnetic path. The sum of the cross-sectional areas of the fourth core section CR4 perpendicular to the magnetic path and the fifth core section CR5 perpendicular to the magnetic path is equal to the cross-sectional area of ​​the sixth core section CR6 perpendicular to the magnetic path. Therefore, the magnitudes of magnetic flux φ31 and magnetic flux φ32 are each half of magnetic flux φ3. Note that the second core CO2 may have four or more core sections.

[0088] The DC-DC converter 21h and switching power supply 20h described above also produce the same effects as the DC-DC converters 21 and 21a and switching power supplies 20 and 20a. In other words, the DC-DC converter 21h can further reduce copper loss due to the winding LT11. To put it another way, the DC-DC converter 21h can achieve a high step-down ratio without increasing the number of turns of the winding LT11 and without increasing the cross-sectional area perpendicular to the magnetic path of the core.

[0089] [9th variation] The DC-DC converter 21i and switching power supply 20i according to the ninth modified example of the present invention will be described below with reference to the drawings. Figure 22 is a circuit diagram showing the switching circuit SW in the ninth modified example. Note that only the parts of the DC-DC converter 21i and switching power supply 20i according to the ninth modified example that differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment will be described, and the rest will be omitted.

[0090] As shown in Figure 22, the switching circuit SW further 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-period of the first switching element S1 coincides with the on-period of the third switching element S3. Also, the on-period of the second switching element S2 coincides with the on-period of the fourth switching element S4. This makes it possible to increase the upper limit of the first DC voltage Vin that can be input to the DC-DC converters 21, 21a to 21h and the switching power supply units 20, 20a to 20h. The third switching element S3 may have a parasitic capacitor C3 and a parasitic diode FD3. The fourth switching element S4 may 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 end" of the present invention.

[0091] [Tenth variation] The following describes a DC-DC converter 21j and a switching power supply 20j according to the tenth modified example of the present invention, with reference to the drawings. Figure 23 is a circuit diagram showing the switching circuit SW in the tenth modified example. Note that only the parts of the DC-DC converter 21j and switching power supply 20j according to the tenth modified example that differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment will be described, and the rest will be omitted.

[0092] As shown in Figure 23, the switching circuit SW further 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-period of the first switching element S1 coincides with the on-period of the third switching element S3. Also, the on-period of the second switching element S2 coincides with the on-period of the fourth switching element S4. This makes it possible to increase 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. The third switching element S3 may have a parasitic capacitor C3 and a parasitic diode FD3. The fourth switching element S4 may 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.

[0093] [The 11th variation] The following describes a DC-DC converter 21k and a switching power supply 20k according to the 11th modified version of the present invention, with reference to the drawings. Figure 24 is a circuit diagram showing a modified version of the first rectifier element. Note that for the DC-DC converter 21k and switching power supply 20k according to the 11th modified version, only the parts that differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment will be described, and the rest will be omitted.

[0094] The DC-DC converter 21k and switching power supply 20k according to the 11th modified example differ from the DC-DC converter 21 and switching power supply 20 according to the first embodiment in that they each include a MOSFET rectifier MOSC instead of the first diode D1.

[0095] The MOSFET rectifier MOSC includes a MOSFET1, an operational amplifier OP, and a DC power supply Vcc. The 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 less than or equal to the potential of the source S of MOSFET1. The operational amplifier OP does not apply a positive voltage between the gate G and source S of MOSFET1, turning MOSFET1 off, when the potential of the drain D of MOSFET1 is greater than the potential of the source S of MOSFET1. In other words, 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 rectifying 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 rectifying element" can be reduced.

[0096] As shown in this modified example, 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 limited to diodes.

[0097] [Other embodiments] The DC-DC converter according to the present invention is not limited to DC-DC converters 21, 21a to 21k, but can be modified within the scope of its gist. Furthermore, the structures of DC-DC converters 21, 21a to 21k may be arbitrarily combined.

[0098] The switching power supply device according to the present invention is not limited to switching power supply devices 20, 20a to 20k, but can be modified within the scope of its gist. Furthermore, the structures of switching power supply devices 20, 20a to 20k may be arbitrarily combined.

[0099] Note that DC-DC converters 21, 21a~21k and switching power supplies 20, 20a~2 0kIn this context, the switching circuit SW should not be a full-bridge type. Using a full-bridge type switching circuit SW increases the number of switching elements, which complicates the circuit configuration and control, increases losses, and also makes the DC-DC converter and switching power supply larger, making heat dissipation more difficult.

[0100] The present invention has the following configuration.

[0101] (1) A first switching element having a first end and a second end, wherein the first end is connected to a DC power supply, A second switching element having a third end and a fourth end, wherein the third end is connected to the second end, An LC series resonant circuit having a fifth end and a sixth end, wherein the fifth end is connected to the connection point between the second end and the third end, A conductor having a seventh end and an eighth end, A first winding having a ninth end and a tenth end, A second winding having an 11th end and a 12th end, A first rectifier element having a 13th end and a 14th end, A second rectifier element having a 15th end and a 16th end, wherein the 15th end is connected to the 13th end, It is equipped with, The first winding and the second winding are magnetically positively coupled to each other. The sixth end is connected to the seventh end, The eighth end is connected to the ninth and fourteenth ends, The tenth end is connected to the eleventh end, The 12th end is connected to the 4th end and the 16th end, DC-DC converter.

[0102] (2) The aforementioned conductor is the third winding, The first winding, the second winding, and the third winding are magnetically positively coupled to each other. (1) The DC-DC converter described above.

[0103] (3) A fourth winding having ends 17 and 18, A fifth winding having ends 19 and 20, A third rectifier element having terminals 21 and 22, A fourth rectifier element having a 23rd end and a 24th end, wherein the 23rd end is connected to the 21st end, It also has the following features: The first winding, the second winding, the fourth winding, and the fifth winding are magnetically positively 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, (1) or (2) the DC-DC converter described above.

[0104] (4) A fourth winding having ends 17 and 18, A fifth winding having ends 19 and 20, A third rectifier element having terminals 21 and 22, A fourth rectifier element having a 23rd end and a 24th end, wherein the 23rd end is connected to the 21st end, It also has the following features: The first winding, the second winding, the fourth winding, and the fifth winding are magnetically positively 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 between the 18th end and the 19th end is connected to the connection point between the 10th end and the 11th end, and the connection point between the 21st end and the 23rd end is connected to the connection point between the 13th end and the 15th end. (1) or (2) the DC-DC converter described above.

[0105] (5) It further includes a core that forms a magnetic path, The aforementioned core is The first core section and The second core section, It has, The first winding and the second winding are each wound around the first core portion. The fourth winding and the fifth winding are each wound around the second core. (4) The DC-DC converter described above.

[0106] (6) It further includes a core that forms a magnetic path, The aforementioned core has 5 or more core sections, The first winding, the second winding, the fourth winding, and the fifth winding are each wound around one of the five or more different core sections. (4) The DC-DC converter described above.

[0107] (7) The first rectifier element and the second rectifier element are each diodes. The 13th and 15th ends are anodes, respectively. The 14th and 16th ends are cathodes, respectively. A DC-DC converter as described in any of (1) through (6).

[0108] (8) The third and fourth rectifier elements are each diodes. The 21st and 23rd ends are anodes, respectively. The 22nd and 24th ends are cathodes, respectively. (3) or (4) the DC-DC converter described above.

[0109] (9) The first switching element conducts and the second switching element does not conduct, and the second switching element conducts and the first switching element does not conduct are repeated periodically. During the first period, the potential at terminal 9 was different from the potential at terminal 4. A DC voltage is output from the connection point between the 10th terminal and the 11th terminal, and from the connection point between the 13th terminal and the 15th terminal. A DC-DC converter as described in any of (1) through (8).

[0110] (10) The ratio of the first period to the second period is 1:1. (9) The DC-DC converter described above.

[0111] (11) A first switching element having a first end and a second end, wherein the first end is connected to a DC power supply, A second switching element having a third end and a fourth end, wherein the third end is connected to the second end, An LC series resonant circuit having a fifth end and a sixth end, wherein the fifth end is connected to the connection point between the second end and the third end, A third winding having a seventh end and an eighth end, A first winding having a ninth end and a tenth end, A second winding having an 11th end and a 12th end, A first rectifier element having a 13th end and a 14th end, A second rectifier element having a 15th end and a 16th end, wherein the 15th end is connected to the 13th end. Rectifier and, A fourth winding having ends 17 and 18, A fifth winding having ends 19 and 20, A sixth winding having ends 25 and 26, A third rectifier element having terminals 21 and 22, A fourth rectifier element having a 23rd end and a 24th end, wherein the 23rd end is connected to the 21st end, It is equipped with, The sixth end is connected to the seventh end, The eighth end is connected to the 25th end, The 26th end is connected to the 9th end and the 14th end, The tenth end is connected to the eleventh 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 between the 18th end and the 19th end is connected to the connection point between the 10th end and the 11th end, and the connection point between the 21st end and the 23rd end is connected to the connection point between the 13th end and the 15th end. DC-DC converter.

[0112] (12) A first core that forms a magnetic circuit, A second core that forms a magnetic circuit, It also has the following features: The first core is, The first core section and The second core section, It has, The first winding and the second winding are each wound around the first core portion. The third winding is wound around the second core, The second core is, The third core section, The fourth core section, It has, The fourth winding and the fifth winding are each wound around the third core, The sixth winding is wound around the fourth core portion. (11) The DC-DC converter described above.

[0113] (13) A first core that forms a magnetic circuit, A second core that forms a magnetic circuit, It also has the following features: The first core has three or more core sections, The first winding, the second winding, and the third winding are each wound around one of the three or more different core portions of the first core. The second core has three or more core sections, The fourth winding, the fifth winding, and the sixth winding are each wound around one of the three or more different core portions of the second core. (11) The DC-DC converter described above.

[0114] (14) The first rectifier element, the second rectifier element, the third rectifier element, and the fourth rectifier element are each diodes. The 13th, 15th, 21st, and 23rd ends are anodes, The 14th, 16th, 22nd, and 24th ends are cathodes, respectively. A DC-DC converter as described in any of (11) to (13).

[0115] (15) The first switching element conducts and the second switching element does not conduct, and the second switching element conducts and the first switching element does not conduct are repeated periodically. During the first period, the potential at terminal 26 is different from the potential at terminal 4. A DC voltage is output from the connection point between the 10th terminal and the 11th terminal, and from the connection point between the 13th terminal and the 15th terminal. A DC-DC converter as described in any of (11) to (14).

[0116] (16) The ratio of the first period to the second period is 1:1. (15) The DC-DC converter described above.

[0117] (17) A DC-DC converter as described in any of (1) to (16), The aforementioned DC power supply, Equipped with, Switching power supply. [Explanation of Symbols]

[0118] 20, 20A~20K: Switching power supply 21,21a~21k: DC-DC converter A1: First anode A2: Second anode A3: Third Anode A4: Fourth anode C1, C2, C3, C4: Parasitic capacitors C: Capacitor CO1: First Core CO2: Second core CR1: First Core Section CR2: Second Core Unit CR3: Third Core Section CR4: Fourth Core Section CR5: Fifth Core Section CR6: 6th Core Section CS1: First control signal CS2: Second control signal FD1, FD2, FD3, FD4: Parasitic diodes D1: First diode D2: Second diode D3: Third diode D4: Fourth diode DCPS,Vcc: Direct current power supply GD: Gate Drive Circuit IT: Input terminals K1: First cathode K2: Second Cathode K3: Third Cathode K4: Fourth Cathode L: Reactor LC:LC series resonant circuit LT11, LT12, LT21, LT22, LT23, LT24: Winding Lm1: First excitation inductance Lm2: Second excitation inductance O1, O2: First output terminals O3, O4: Second output terminals O5, O6: Third output terminal O7, O8: 4th output terminal OP: Operational amplifier P1: First Period P2: Second Period RL1,RL2:Load resistance S1: First switching element S2: Second switching component S3: Third switching element S4: Fourth switching element SC1, SC2: Smoothing capacitors SW: Switching circuit TR1~TR8: Transformers V: void Vin: First DC voltage Vout: 2nd DC voltage i1,i2,iD1,iD2: Current im: excitation current φ: Magnetic flux

Claims

1. A first switching element having a first end and a second end, wherein the first end is connected to a DC power supply, A second switching element having a third end and a fourth end, wherein the third end is connected to the second end, An LC series resonant circuit having a fifth end and a sixth end, wherein the fifth end is connected to the connection point between the second end and the third end, A conductor having a seventh end and an eighth end, A first winding having a ninth end and a tenth end, A second winding having an eleventh end and a twelfth end, A first rectifier element having a 13th end and a 14th end, A second rectifier element having a 15th end and a 16th end, wherein the 15th end is connected to the 13th end, It is equipped with, The first winding and the second winding are magnetically positively coupled to each other. The sixth end is connected to the seventh end, The eighth end is connected to the ninth end and the fourteenth end, The tenth end is connected to the eleventh end, The 12th end is connected to the 4th end and the 16th end, DC-DC converter.

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

3. A fourth winding having ends 17 and 18, A fifth winding having the 19th and 20th ends, A third rectifier element having a 21st end and a 22nd end, A fourth rectifier element having a 23rd end and a 24th end, wherein the 23rd end is connected to the 21st end, It also has the following features: The first winding, the second winding, the fourth winding, and the fifth winding are magnetically positively 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. A DC-DC converter according to claim 1 or claim 2.

4. A fourth winding having ends 17 and 18, A fifth winding having the 19th and 20th ends, A third rectifier element having a 21st end and a 22nd end, A fourth rectifier element having a 23rd end and a 24th end, wherein the 23rd end is connected to the 21st end, It also has the following features: The first winding, the second winding, the fourth winding, and the fifth winding are magnetically positively 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 between the 18th end and the 19th end is connected to the connection point between the 10th end and the 11th end, and the connection point between the 21st end and the 23rd end is connected to the connection point between the 13th end and the 15th end. A DC-DC converter according to claim 1 or claim 2.

5. It further includes a core that forms a magnetic path, The aforementioned core is The first core section and The second core section, It has, The first winding and the second winding are each wound around the first core portion. The fourth winding and the fifth winding are each wound around the second core portion. The DC-DC converter according to claim 4.

6. It further includes a core that forms a magnetic path, The aforementioned core has five or more core sections, The first winding, the second winding, the fourth winding, and the fifth winding are each wound around one of the five or more different core sections. The DC-DC converter according to claim 4.

7. The first rectifier element and the second rectifier element are each diodes. The 13th and 15th ends are anodes, respectively. The 14th and 16th ends are cathodes, respectively. A DC-DC converter according to claim 1 or claim 2.

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

9. The first switching element conducts and the second switching element does not conduct, and the second switching element conducts and the first switching element does not conduct are repeated periodically. During the first period, the potential at the ninth terminal is different from the potential at the fourth terminal. A DC voltage is output from the connection point between the 10th terminal and the 11th terminal, and from the connection point between the 13th terminal and the 15th terminal. A DC-DC converter according to claim 1 or claim 2.

10. The ratio of the first period to the second period is 1:

1. The DC-DC converter according to claim 9.

11. A first switching element having a first end and a second end, wherein the first end is connected to a DC power supply, A second switching element having a third end and a fourth end, wherein the third end is connected to the second end, An LC series resonant circuit having a fifth end and a sixth end, wherein the fifth end is connected to the connection point between the second end and the third end, A third winding having a seventh end and an eighth end, A first winding having a ninth end and a tenth end, A second winding having an eleventh end and a twelfth end, A first rectifier element having a 13th end and a 14th end, A second rectifier element having a 15th end and a 16th end, wherein the 15th end is connected to the 13th end, A fourth winding having ends 17 and 18, A fifth winding having the 19th and 20th ends, A sixth winding having ends 25 and 26, A third rectifier element having a 21st end and a 22nd end, A fourth rectifier element having a 23rd end and a 24th end, wherein the 23rd end is connected to the 21st end, It is equipped with, The sixth end is connected to the seventh end, The eighth end is connected to the twenty-fifth end, The 26th end is connected to the 9th end and the 14th end, The tenth end is connected to the eleventh 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 between the 18th end and the 19th end is connected to the connection point between the 10th end and the 11th end, and the connection point between the 21st end and the 23rd end is connected to the connection point between the 13th end and the 15th end. DC-DC converter.

12. A first core that forms a magnetic path, A second core that forms a magnetic circuit, It also has the following features: The first core is, The first core section and The second core section, It has, The first winding and the second winding are each wound around the first core portion. The third winding is wound around the second core portion, The second core is, The third core section, The fourth core section, It has, The fourth winding and the fifth winding are each wound around the third core portion. The sixth winding is wound around the fourth core portion. The DC-DC converter according to claim 11.

13. A first core that forms a magnetic path, A second core that forms a magnetic circuit, It also has the following features: The first core has three or more core sections, The first winding, the second winding, and the third winding are each wound around one of the three or more different core portions of the first core. The second core has three or more core sections, The fourth winding, the fifth winding, and the sixth winding are each wound around one of the three or more different core portions of the second core. The DC-DC converter according to claim 11.

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

15. The first switching element conducts and the second switching element does not conduct, and the second switching element conducts and the first switching element does not conduct are repeated periodically. During the first period, the potential at the 26th terminal is different from the potential at the 4th terminal. A DC voltage is output from the connection point between the 10th terminal and the 11th terminal, and from the connection point between the 13th terminal and the 15th terminal. A DC-DC converter according to any one of claims 11 to 13.

16. The ratio of the first period to the second period is 1:

1. The DC-DC converter according to claim 15.

17. A DC-DC converter according to claim 1, claim 2, and any one of claims 11 to 13, The aforementioned DC power supply, Equipped with, Switching power supply.

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