Power supply device

Abstract

To reduce a switching loss by performing soft switching without enlarging a power supply device.SOLUTION: A power supply device comprises: a first switch element and a second switch element which is connected in series to the first switch element; a first auxiliary switch element which is connected in parallel to the first switch element; a second auxiliary switch element which is connected in parallel to the second switch element and connected in series to the first auxiliary switch element; a transformer which has a primary coil and a secondary coil; and a control section which controls switching operations of the first switch element, the second switch element, the first auxiliary switch element and the second auxiliary switch element. The control section controls the switching operations of the first switch element, the second switch element, the first auxiliary switch element and the second auxiliary switch element by utilizing leakage inductance of the secondary coil in such a manner that currents flowing to the primary coil and the secondary coil flow in a direction in which magnetic fluxes are cancelled with each other.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a power supply device. [Background technology]

[0002] Patent Document 1 describes a power conversion device that can achieve ZVS (Zero Voltage Switching) operation by using a switching circuit and an auxiliary switching circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-147850 A Summary of the Invention [Problem to be solved by the invention]

[0004] Synchronous rectification DC / DC converters are controlled by hard switching, which can lead to large switching losses. Also, adding an auxiliary circuit to perform soft switching can lead to an increase in the size of the entire device.

[0005] An object of the present disclosure is to perform soft switching and reduce switching losses without increasing the size. [Means for solving the problem]

[0006] The power supply device of the present disclosure includes a first switch element on a high side and a second switch element on a low side connected in series to the first switch element, a first auxiliary switch element connected in parallel to the first switch element, a second auxiliary switch element connected in parallel to the second switch element and connected in series to the first auxiliary switch element, a primary winding having one end electrically connected to a node between the first switch element and the second switch element and the other end electrically connected to a load, and a first auxiliary switch element having one end electrically connected to the node between the first switch element and the second switch element and the other end electrically connected to the first auxiliary switch element. the first auxiliary switch element and the second auxiliary switch element; and a control unit that controls switching operations of the first switch element, the second switch element, the first auxiliary switch element, and the second auxiliary switch element, wherein the control unit utilizes leakage inductance of the secondary winding to control the switching operations of the first switch element, the second switch element, the first auxiliary switch element, and the second auxiliary switch element so that currents flowing through the primary winding and the secondary winding, respectively, flow in directions that cancel each other's magnetic flux.

[0007] In the power supply device of the present disclosure, the control unit controls the first auxiliary switch element to an on state while keeping the first switch element and the second switch element off.

[0008] In the power supply device of the present disclosure, the control unit controls the first switch element to an on state and the first auxiliary switch element to an off state.

[0009] In the power supply device of the present disclosure, the control unit controls the second auxiliary switch element to an on state while keeping the first switch element and the second switch element off.

[0010] In the power supply device of the present disclosure, the control unit controls the second switch element to an on state and the second auxiliary switch element to an off state.

[0011] The power supply device of the present disclosure includes a transformer having a first switch element on a high side and a second switch element on a low side connected in series to the first switch element, a first auxiliary switch element connected in parallel to the first switch element, a primary winding having one end electrically connected to a node between the first switch element and the second switch element and the other end electrically connected to a load, and a secondary winding having one end electrically connected to the node between the first switch element and the second switch element and the other end connected to a source terminal of the first auxiliary switch element, and a control unit that controls switching operations of the first switch element, the second switch element, and the first auxiliary switch element, wherein the control unit uses leakage inductance of the secondary winding to control the switching operations of the first switch element, the second switch element, and the first auxiliary switch element so that currents flowing through the primary winding and the secondary winding, respectively, flow in directions that cancel each other's magnetic fluxes.

[0012] The power supply device of the present disclosure includes a transformer having a first switch element on a high side and a second switch element on a low side connected in series to the first switch element, a second auxiliary switch element connected in parallel to the second switch element, a primary winding having one end electrically connected to a node between the first switch element and the second switch element and the other end electrically connected to a load, and a secondary winding having one end electrically connected to the node between the first switch element and the second switch element and the other end connected to a drain terminal of the second auxiliary switch element, and a control unit that controls switching operations of the first switch element, the second switch element, and the second auxiliary switch element, wherein the control unit uses leakage inductance of the secondary winding to control the switching operations of the first switch element, the second switch element, and the second auxiliary switch element so that currents flowing through the primary winding and the secondary winding, respectively, flow in directions that cancel each other's magnetic fluxes. Effect of the Invention

[0013] According to the present disclosure, soft switching can be performed without increasing the size, and switching losses can be reduced. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a power supply device according to a comparative example. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of the power supply device according to the first embodiment. [Diagram 3] FIG. 3 is a timing chart for explaining the voltage step-down operation according to the first embodiment. [Figure 4] FIG. 4 is a timing chart for explaining the voltage step-down operation according to the first embodiment. [Diagram 5] FIG. 5 is a timing chart for explaining the voltage step-down operation according to the first embodiment. [Figure 6] FIG. 6 is a diagram for explaining the operation of the power supply device according to the first embodiment in the first mode. [Figure 7] FIG. 7 is a diagram for explaining the operation of the power supply device according to the first embodiment in the second mode. [Figure 8] FIG. 8 is a diagram for explaining the operation of the power supply device according to the first embodiment in the third mode. [Figure 9] FIG. 9 is a diagram for explaining the operation of the power supply device according to the first embodiment in the fourth mode. [Figure 10] FIG. 10 is a diagram for explaining the operation of the power supply device according to the first embodiment in the fifth mode. [Figure 11] FIG. 11 is a diagram for explaining the operation in the sixth mode of the power supply device according to the first embodiment. [Figure 12] FIG. 12 is a diagram for explaining the operation of the seventh mode of the power supply device according to the first embodiment. [Figure 13] FIG. 13 is a diagram for explaining the operation of the power supply device according to the first embodiment in the eighth mode. [Figure 14] FIG. 14 is a diagram for explaining the operation of the ninth mode of the power supply device according to the first embodiment. [Figure 15] FIG. 15 is a diagram for explaining the operation of the power supply device according to the first embodiment in the tenth mode. [Figure 16] FIG. 16 is a diagram for explaining the operation of the 11th mode of the power supply device according to the first embodiment. [Figure 17] FIG. 17 is a diagram for explaining the boost operation of the power supply device according to the first embodiment. [Figure 18] FIG. 18 is a diagram illustrating an example of the configuration of a power supply device according to the second embodiment. [Figure 19] FIG. 19 is a diagram illustrating an example of the configuration of a power supply device according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present disclosure is not limited to this embodiment, and in the following embodiments, the same components are designated by the same reference numerals, and duplicated descriptions will be omitted.

[0016] [Comparative Example] Before describing the embodiment, a comparative example will be described with reference to Fig. 1. Fig. 1 is a diagram showing an example of the configuration of a power supply device according to the comparative example.

[0017] As shown in FIG. 1, the power supply device 1a includes a first switch element 11, a second switch element 12, and an inductor .

[0018] The power supply device 1a receives an input voltage Vin which is a DC voltage output from a power supply 2 and smoothed by a capacitor 3. The DC voltage output from the power supply device 1a is smoothed by a capacitor 4 and connected to a load 5 as an output voltage Vout.

[0019] The high potential side of the capacitor 3 is electrically connected to the drain of the first switch element 11. The low potential side of the capacitor 3 is electrically connected to the source of the second switch element 12.

[0020] The secondary side has a power supply 8 that outputs a DC voltage. Also, between the power supply 2 and the capacitor 3, there is a load 7 having one end electrically connected to the high potential side of the capacitor 3 and the other end connected to the low potential side of the capacitor 3.

[0021] The first switch element 11 and the second switch element 12 are, for example, but not limited to, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The first switch element 11 and the second switch element 12 may be silicon power devices, GaN power devices, SiC power devices, IGBTs (Insulated Gate Bipolar Transistors), etc.

[0022] The first switch element 11 and the second switch element 12 have parasitic diodes (body diode 11-1 and body diode 12-1). A parasitic diode is a pn junction between the back gate and the source and drain of a MOSFET. The parasitic diode can be used as a freewheel diode for dissipating a transient back electromotive force when the transistor is turned off. In addition to the parasitic diode, a diode element may be added between the drain and source of each transistor.

[0023] The source of the first switch element 11 is electrically connected to the drain of the second switch element 12 .

[0024] One end of the inductor 21 is electrically connected to the source of the first switch element 11 and the drain of the second switch element 12. The other end of the inductor 21 is electrically connected to the high potential side of the capacitor 4.

[0025] The high potential side of the capacitor 4 is electrically connected to the other end of the inductor 21 and one end of the load 5. The low potential side of the capacitor 4 is electrically connected to the source of the second switch element 12 and the other end of the load 5.

[0026] The power supply device 1a is a synchronous rectification type DC / DC converter using hard switching. The power supply device 1a has a problem that switching loss increases due to hard switching between the first switch element 11 and the second switch element 12. In particular, the power supply device 1a may have large switching losses in the first switch element 11 during discharging operation and in the second switch element 12 during charging operation. If an auxiliary circuit is provided to realize soft switching between the first switch element 11 and the second switch element 12, the power supply device 1a may become large in size.

[0027] [First embodiment] An example of the configuration of the power supply device according to the first embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of the configuration of the power supply device according to the first embodiment.

[0028] As shown in FIG. 2, the power supply device 1 includes a first switch element 11, a second switch element 12, a first auxiliary switch element 31, a second auxiliary switch element 32, a diode 41, a diode 42, a transformer 50, and a control unit 100.

[0029] The drain of the first switch element 11 is electrically connected to the anode of the diode 41. The source of the first switch element 11 is electrically connected to the drain of the second switch element 12.

[0030] The source of the second switching element 12 is electrically connected to the source of the second auxiliary switching element 32 , the low potential side of the capacitor 3 , and the low potential side of the capacitor 4 .

[0031] The drain of the first auxiliary switching element 31 is electrically connected to the cathode of the diode 41. The source of the first auxiliary switching element 31 is electrically connected to the anode of the diode .

[0032] The drain of the second auxiliary switching element 32 is electrically connected to the cathode of the diode 42 .

[0033] The first auxiliary switching element 31 and the second auxiliary switching element 32 are, for example, but not limited to, MOSFETs. The first auxiliary switching element 31 and the second auxiliary switching element 32 may be silicon power devices, GaN power devices, SiC power devices, IGBTs, etc.

[0034] The first auxiliary switching element 31 and the second auxiliary switching element 32 have parasitic diodes (body diodes 31-1 and 32-1). A parasitic diode is a pn junction between the back gate of a MOSFET and the source and drain of the MOSFET. The parasitic diode can be used as a freewheel diode for dissipating a transient back electromotive force when the transistor is turned off. In addition to the parasitic diode, a diode element may be added between the drain and source of each transistor.

[0035] The anode of the diode 41 is electrically connected to the high potential side of the capacitor 3 and the drain of the first auxiliary switching element 31 .

[0036] The transformer 50 includes an inductor 51, a primary winding 52, a secondary winding 53, and a leakage inductor 54.

[0037] One end of the inductor 51 and one end of the primary winding 52 are electrically connected to each other. The other end of the inductor 51 and the other end of the primary winding 52 are electrically connected to each other.

[0038] One end of the inductor 51 and one end of the primary winding 52 are electrically connected to the high potential side of the capacitor 4. The other end of the inductor 51 and the other end of the primary winding 52 are electrically connected to the source of the first switch element 11 and the drain of the second switch element 12.

[0039] One end of the secondary winding 53 is electrically connected to the source of the first switch element 11 and the drain of the second switch element 12. The other end of the secondary winding 53 is electrically connected to one end of the leakage inductor .

[0040] The leakage inductor 54 is the leakage inductance of the secondary winding 53. The other end of the leakage inductance is electrically connected to the source of the first auxiliary switching element 31 and the anode of the diode 42.

[0041] The control unit 100 controls the switching operations of the first switch element 11, the second switch element 12, the first auxiliary switch element 31, and the second auxiliary switch element 32. The control unit 100 controls the on and off of the first switch element 11, the second switch element 12, the first auxiliary switch element 31, and the second auxiliary switch element 32. The control unit 100 includes an information processing device such as a DSP (Digital Signal Processor) with a built-in digital PWM (Pulse Width Modulation) circuit, a CPU (Central Processing Unit), or an MPU (Micro Processing Unit), and a storage device such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The control unit 100 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 100 may be realized by a combination of hardware and software.

[0042] The control unit 100 utilizes the leakage inductor 54 of the secondary winding 53 to control the switching operations of the first switch element 11, the second switch element 12, the first auxiliary switch element 31, and the second auxiliary switch element 32 so that the currents flowing through the primary winding 52 and the secondary winding 53 respectively flow in directions that cancel each other's magnetic flux.

[0043] (Power supply operation) The operation of the power supply device 1 will be described. The step-down operation of the power supply device 1 will be described below. Figs. 3, 4, and 5 are timing charts for explaining the step-down operation according to the first embodiment. In the power supply device 1, the step-down operation can be performed by controlling the first switch element 11, the second switch element 12, and the first auxiliary switch element 31. In the step-down operation, the second auxiliary switch element 32 is always off. Specifically, in the step-down operation, the first switch element 11 and the first auxiliary switch element 31 are the switch elements to be controlled, and the second switch element 12 is the switch element for synchronous rectification.

[0044] In FIG. 3, the horizontal axis represents time. Waveform 201 represents the gate voltage of the first switch element 11. Waveform 202 represents the gate voltage of the second switch element 12. Waveform 203 represents the gate voltage of the first auxiliary switch element 31. Waveform 204 represents the current flowing between the drain and source of the first switch element 11. Waveform 205 represents the voltage between the drain and source of the first switch element 11. Waveform 206 represents the current flowing between the drain and source of the second switch element 12. Waveform 207 represents the voltage between the drain and source of the second switch element 12. Waveform 208 represents the current flowing through the body diode 12-1 of the second switch element 12.

[0045] 4, the horizontal axis represents time. Waveform 209 represents the current flowing between the drain and source of the first auxiliary switching element 31. Waveform 210 represents the voltage between the drain and source of the first auxiliary switching element 31. Waveform 211 represents the current flowing through the second auxiliary switching element 32. Waveform 212 represents the voltage between the drain and source of the second auxiliary switching element 32. Waveform 213 represents the voltage across the leakage inductor 54.

[0046] 5, the horizontal axis represents time. Waveform 214 represents the current flowing through inductor 51. Waveform 215 represents the voltage across primary winding 52. Waveform 216 represents the voltage across secondary winding 53. Waveform 217 represents the current flowing through load 5. Waveform 218 represents the voltage across the anode and cathode of diode 41.

[0047] The operation of the power supply device according to the first embodiment will be described with reference to Figs. 6 to 16. Figs. 6 to 16 show circuit diagrams of the power supply device according to the first embodiment. In the circuit diagrams shown in Figs. 6 to 16, operating parts are indicated by solid lines, and non-operating parts are indicated by dotted lines. Fig. 6 is a diagram for explaining the operation of the first mode of the power supply device according to the first embodiment. The first mode is the operation at timing t1. Timing t1 is the operation of the power supply device 1 in its initial state. At timing t1, the first switch element 11 is in an off state, and the second switch element 12 is in an on state. When the second switch element 12 is turned on, a current flows through a path such as the load 5 → the second switch element 12 → the inductor 51, as shown by the arrow.

[0048] FIG. 7 is a diagram for explaining the operation of the second mode of the power supply device according to the first embodiment. The second mode is an operation at timing t2. At timing t2, the control unit 100 controls the second switching element 12 to be in the on state and the first auxiliary switching element 31 to be in the on state, as shown in waveforms 202 and 203 in FIG. 3. When the first auxiliary switching element 31 is in the on state, as shown in waveform 209 in FIG. 4, the current flowing through the inductor 51 is commutated to the first auxiliary switching element 31, and a current starts to flow between the drain and source of the first auxiliary switching element 31. Specifically, a current flows through a path such as the inductor 51 → the load 5 → the capacitor 3 → the diode 41 → the first auxiliary switching element 31 → the leakage inductor 54 → the secondary winding 53 → the inductor 51. At this time, the magnitude of the current flowing through the inductor 51 is I_Lo, the number of turns of the primary winding 52 is N1, the number of turns of the secondary winding 53 is N2, the input voltage from the capacitor 3 is Vin, the output voltage from the capacitor 4 is Vo, and the voltage between the anode and cathode of the diode 41 is Vf_D1. A current of I_Lo×N2 / (N1+N2) flows through the primary winding 52 in the direction from positive to negative polarity, and a current of I_Lo×N1 / (N1+N2) flows through the secondary winding 53 from negative to positive polarity. That is, currents flow through the primary winding 52 and the secondary winding 53 in directions that cancel out the magnetic fluxes generated by each other. A voltage of 0-Vo=-Vo is applied across the primary winding 52. A voltage of -Vo×(N2 / N1) is applied across the secondary winding 53. A voltage of (Vin-Vf_D1)+Vo×(N2 / N1) is applied across the leakage inductor 54.

[0049] FIG. 8 is a diagram for explaining the operation of the third mode of the power supply device according to the first embodiment. The third mode is the operation at timing t3. At timing t3, the control unit 100 controls the first auxiliary switching element 31 to be in the on state and the second switching element 12 to be in the off state, as shown in the waveforms 202 and 203 in FIG. 3. Since the first auxiliary switching element 31 is in the on state, a current continues to flow through the path of the load 5 → the capacitor 3 → the diode 41 → the first auxiliary switching element 31 → the leakage inductor 54 → the secondary winding 53 → the inductor 51. In addition, since the second switching element 12 is in the off state, a current flows through the path of the inductor 51 → the load 5 → the body diode 12-1 → the inductor 51, as shown in the waveform 208 in FIG. 3. Here, the voltage between the anode and the cathode of the body diode 12-1 is Vf_DQ2. At this time, a voltage of 0-Vf_DQ2-Vo=-(Vf_DQ2+Vo) is applied across primary winding 52. A voltage of -(Vf_DQ2+Vo) x (N2 / N1) is applied across secondary winding 53. A voltage of (Vin-Vf_D1)+(Vf_DQ2+Vo) x (N2 / N1) is applied across leakage inductor 54. When the current through body diode 12-1 stops flowing, the process at timing t3 ends.

[0050] FIG. 9 is a diagram for explaining the operation of the fourth mode of the power supply device according to the first embodiment. The fourth mode is the operation at timing t4. As shown in waveforms 201, 202, and 203 in FIG. 3, timing t4 indicates the operation during a dead time period in which the first auxiliary switch element 31 is in an ON state and the first switch element 11 and the second switch element 12 are in an OFF state. At this time, the charge is discharged from the parasitic capacitance 11-2 of the first switch element 11, and a current flows through a path such as the parasitic capacitance 11-2 → the diode 41 → the first auxiliary switch element 31 → the leakage inductor 54 → the secondary winding 53. In addition, a current flows through the parasitic capacitance 12-2 to charge the parasitic capacitance 12-2 through a path such as the parasitic capacitance 12-2 → the capacitor 3 → the diode 41 → the first auxiliary switch element 31 → the leakage inductor 54 → the secondary winding 53 → the parasitic capacitance 12-2. At this time, a resonant current flows through the parasitic capacitance 11-2 and the parasitic capacitance 12-2 according to the inductance of the leakage inductor 54 and the capacitance of the parasitic capacitance 11-2 and the parasitic capacitance 12-2. The resonant current flowing through the parasitic capacitance 11-2 is I_CQ1, the resonant current flowing through the parasitic capacitance 12-2 is I_CQ, the capacitance of the parasitic capacitance 11-2 is CQ1, the capacitance of the parasitic capacitance 12-2 is CQ2, and the inductance of the leakage inductor 54 is Llk. At this time, the resonant current flowing through the parasitic capacitance 11-2 and the parasitic capacitance 12-2 is I_CQ1=I_CQ2=|Vin / √(Llk / (CQ1+CQ2)) / 2|. When the resonant current stops flowing through the parasitic capacitance 11-2 and the parasitic capacitance 12-2, the process at timing t4 ends. When the resonant current finishes flowing through the parasitic capacitances 11-2 and 12-2, Vds_Q1=0 and Vds_Q2=Vin. Vds_Q1 is the drain-source voltage of the first switch element 11. Vds_Q2 is the drain-source voltage of the second switch element 12. Note that the peak value I_CQ1_pk of the resonant current flowing through the parasitic capacitance 11-2 and the peak value I_CQ2_pk of the resonant current flowing through the parasitic capacitance 12-2 are expressed as I_CQ1_pk=I_CQ2_pk=(Vin / Zo) / . Here, Zo is √(Llk / (CQ1+CQ2)).Furthermore, the drain-source voltage of the first switch element 11 and the drain-source voltage of the second switch element 12 change at a resonance frequency fs of the leakage inductor 54 and the parasitic capacitances 11-2 and 12-2. The resonance frequency fs can be expressed as fs=1 / (2π√(Llk×(CQ1+CQ2))). This voltage change occurs after the current of the body diode 12-1 stops flowing at timing t3, so the voltage does not fluctuate due to the recovery current and no surge voltage occurs. The resonance frequency may be controlled by connecting a capacitor to the first switch element 11 and the second switch element 12, in addition to the parasitic capacitances 11-2 and 12-2.

[0051] FIG. 10 is a diagram for explaining the operation of the fifth mode of the power supply device according to the first embodiment. The fifth mode is the operation at timing t5. As shown in the waveforms 201, 202, and 203 of FIG. 3, the timing t5 indicates the operation when the first auxiliary switching element 31 is in the ON state and the current flows through the body diode 11-1 during the dead time period when the first switching element 11 and the second switching element 12 are in the OFF state. As described in the operation of the fourth mode, since the parasitic capacitance 12-2 is charged to Vin, no current flows through the parasitic capacitance 12-2 and the body diode 11-1 is conductive. In this case, the current flows through the path of the load 5 → the capacitor 3 → the diode 41 → the first auxiliary switching element 31 → the leakage inductor 54 → the secondary winding 53 → the inductor 51. Also, a current flows through the following path: load 5 → capacitor 3 → diode 41 → first auxiliary switching element 31 → leakage inductor 54 → secondary winding 53 → body diode 11-1 → diode 41 → first auxiliary switching element 31 → leakage inductor 54 → secondary winding 53. That is, the current flowing through the inductor 51 is commutated to the first auxiliary switching element 31. At this time, a current of I_Lo×N2 / (N1+N2) flows through the primary winding 52 in the direction from negative polarity to positive polarity, and a current of I_Lo×N1 / (N1+N2) flows through the secondary winding 53 in the direction from positive polarity to negative polarity. That is, a current flows through the primary winding 52 and the secondary winding 53 in the direction that cancels out the magnetic flux generated by each other. A voltage of (Vin+Vf_DQ1-Vo) is applied to both ends of the primary winding 52. A voltage of (Vin+Vf_DQ1-Vo)×(N2 / N1) is applied across the secondary winding 53. The polarities of the primary winding 52 and the secondary winding 53 are changed from the second mode. A voltage of (Vin+Vf_DQ1-Vo)×(N2 / N1)+Vf_DQ1+Vf_D1 is applied across the leakage inductor 54. At timing t5, as shown by the waveform 205 in FIG. 3, the body diode 11-1 is made conductive in a state where V_Q1=0V, thereby allowing the first switch element 11 to perform ZVS operation. This makes it possible to reduce switching loss.

[0052] FIG. 11 is a diagram for explaining the operation of the sixth mode of the power supply device according to the first embodiment. The sixth mode is the operation at timing t6. At timing t6, the control unit 100 controls the first auxiliary switching element 31 to be in the on state and the first switching element 11 to be in the on state, as shown in the waveforms 201 and 203 in FIG. 3. At this time, a current flows through a path of →load 5→capacitor 3→diode 41→first auxiliary switching element 31→leakage inductor 54→secondary winding 53→inductor 51. Also, a current flows through a path of →load 5→capacitor 3→first switching element 11→inductor 51. That is, as shown in the waveform 204 in FIG. 3, a forward current flows through the first switching element 11, so that the current flowing through the inductor 51 increases. At this time, the current flowing through the first auxiliary switching element 31 becomes I_Lo×N1 / (N1+N2). In the fifth mode shown in Fig. 10, the voltage polarity of the leakage inductor 54 is switched, so that the current flowing through the leakage inductor 54 starts to decrease. If the inductor 51 is regarded as a current source, as shown by the waveform 214 in Fig. 5, a constant current flows through the inductor 51, and therefore a current that is the difference between the current flowing through the load 5 and the current flowing through the first auxiliary switching element 31 flows through the first switching element 11. Therefore, as shown by the waveform 204 in Fig. 3, a current with a slope corresponding to a positive current change flows through the first switching element 11.

[0053] FIG. 12 is a diagram for explaining the operation of the seventh mode of the power supply device according to the first embodiment. The seventh mode is the operation at timing t7. At timing t7, the current flowing between the drain and source of the first auxiliary switching element 31 becomes zero as shown by the waveform 209 in FIG. 4, and therefore the voltage applied to the leakage inductor 54 becomes zero as shown by the waveform 213 in FIG. 4. In the seventh mode, a current flows through a path such as →load 5→capacitor 3→first switching element 11→inductor 51. A voltage of Vin-Vo is applied to both ends of the primary winding 52. In addition, a voltage of (Vin-Vo)×(N2 / N1) is applied to both ends of the secondary winding 53. Since the first auxiliary switching element 31 is in an on state, no current flows between the drain and source, but the first auxiliary switching element 31 is conductive. At this time, a voltage of (Vin-Vaux) is applied between the anode and cathode of the diode 41. Vaux is a voltage that is charged to the parasitic capacitance 32-2 of the second auxiliary switching element 32 when the voltage of the leakage inductor 54 changes. The diode 41 prevents a current from flowing backward when Vaux becomes larger than Vin.

[0054] FIG. 13 is a diagram for explaining the operation of the eighth mode of the power supply device according to the first embodiment. The eighth mode is an operation at a timing t8. At the timing t8, the control unit 100 controls the first auxiliary switching element 31 to be in an off state, as shown by a waveform 203 in FIG. 3. As shown by a waveform 213 in FIG. 4, the voltage applied to the leakage inductor 54 is zero. Also, as in the seventh mode, a current flows through a path such as →load 5→capacitor 3→first switching element 11→inductor 51. As shown by a waveform 215 in FIG. 5, a positive voltage of Vin-Vo is applied to both ends of the primary winding 52. Also, as shown by a waveform 216 in FIG. 5, a positive voltage of (Vin-Vo)×(N2 / N1) is applied to both ends of the secondary winding 53. Although the first auxiliary switching element 31 is in an off state, a voltage of (Vin-Vaux) is applied to the diode 41. When Vaux is higher than Vin, the diode 41 is in a reverse biased state, and therefore the voltage applied between the drain and source of the first auxiliary switching element 31 becomes zero, as shown by a waveform 210 in Fig. 4. In the eighth mode, as shown by waveforms 209 and 210 in Fig. 4, the current between the drain and source of the first auxiliary switching element 31 is zero, and the voltage is also zero, so that the first auxiliary switching element 31 can be operated in ZCS (Zero Current Switching). This makes it possible to reduce switching loss.

[0055] FIG. 14 is a diagram for explaining the operation of the ninth mode of the power supply device according to the first embodiment. The ninth mode is an operation at a timing t9. At the timing t9, the control unit 100 turns off the first switch element 11 as shown by the waveform 201 in FIG. 3. At this time, a current flows through a path such as the load 5 → the capacitor 3 → the parasitic capacitance 11-2 → the inductor 51. Also, a current flows through a path such as the load 5 → the parasitic capacitance 12-2 → the inductor 51. That is, in the ninth mode, a current flows to charge the parasitic capacitance 11-2 and to discharge the parasitic capacitance 12-2. At this time, in order to forcibly turn off the current flowing through the first switch element 11, if the wiring inductor 60 exists, the voltage between the drain and source of the first switch element 11 oscillates as shown by the waveform 205 in FIG. 3 according to the inductance of the wiring inductor 60 and the capacitances of the parasitic capacitance 11-2 and the parasitic capacitance 12-2. When the voltage of the parasitic capacitance 11-2 changes to Vin due to charging and discharging of the parasitic capacitance 11-2 and the parasitic capacitance 12-2, the voltage polarity of the primary winding 52 and the secondary winding 53 is reversed.

[0056] FIG. 15 is a diagram for explaining the operation of the power supply device according to the first embodiment in the tenth mode. The tenth mode is an operation at a timing t10. As shown by the waveforms 201 and 202 in FIG. 3, the tenth mode shows an operation during a dead time period in which the first switch element 11 and the second switch element 12 are in an off state. At this time, a current flows through a path such as the load 5 → the capacitor 3 → the parasitic capacitance 11-2 → the inductor 51. Also, a current flows through a path such as the load 5 → the body diode 12-1 → the inductor 51. When the voltage of the parasitic capacitance 11-2 changes to Vin, a negative voltage of 0-Vf_DQ2-Vo=-(Vf_DQ2+Vo) is applied to both ends of the primary winding 52, as shown by the waveform 215 in FIG. 5. Also, a negative voltage of -(Vf_DQ2+Vo)×(N2 / N1) is applied to both ends of the secondary winding 53, as shown by the waveform 216 in FIG. 5. During the dead time, the body diode 12-1 is conductive, and the voltage Vds_Q1 between the drain and source of the first switch element 11 oscillates as shown by the waveform 205 in FIG. 3. Vds_Q1 is expressed as Vds_Q1=Vin+Id_Q1×Zosinωt. Here, Id_Q1 is the value of the current that flows through the first switch element 11 when the first switch element 11 is turned off. Zo is √(Ls / CQ1). Ls is the inductance of the wiring inductor 60. ω represents the angular frequency, and t represents the time. The magnitude of the peak of Vds_Q1 is determined by the magnitude of Id_Q1 and the magnitude of Zo. The resonant frequency fs at that time is 1 / (2π×√(Ls×CQ1)).

[0057] FIG. 16 is a diagram for explaining the operation of the 11th mode of the power supply device according to the first embodiment. The 11th mode is the operation at timing t11. At timing t11, the control unit 100 controls the second switch element 12 to be in the on state, as shown by the waveform 202 in FIG. 3. At this time, a current flows through a path such as the load 5 → the capacitor 3 → the parasitic capacitance 11-2 → the inductor 51. Also, a current flows through a path such as the load 5 → the second switch element 12 → the inductor 51. When the second switch element 12 is in the on state, the current flow is commutated from the body diode 12-1 to the second switch element 12. As shown by the waveform 205 in FIG. 3, the oscillation of the voltage Vds_Q1 between the drain and source of the first switch element 11 continues. This oscillation continues until Vds_Q1 changes to Vin. After the operation of the first mode ends, the operation returns to the first mode.

[0058] 6 to 16, the step-down operation of the power supply device 1 has been described, but the present disclosure is not limited to this. The present disclosure can also be applied to the step-up operation of the power supply device 1.

[0059] 17 is a diagram for explaining the boost operation of the power supply device according to the first embodiment. In the boost operation, the power supply device 1 receives an input voltage Vin which is a DC voltage output from a power supply 2 provided on the secondary side and smoothed by a capacitor 4. The DC voltage output from the power supply device 1 is smoothed by a capacitor 3 and input to a load 5 provided on the primary side as an output voltage Vout.

[0060] When the power supply device 1 performs a boost operation, the power supply device 1 can perform the boost operation by controlling the first switch element 11, the second switch element 12, and the second auxiliary switch element 32. In the boost operation, the first auxiliary switch element 31 is always off. Specifically, in the boost operation, the second switch element 12 and the second auxiliary switch element 32 are switch elements to be controlled, and the first switch element 11 is a switch element for synchronous rectification.

[0061] The control unit 100 controls the first switch element 11, the second switch element 12, and the second auxiliary switch element 32. The control unit 100 can realize ZVS operation and ZCS operation during the boost operation of the power supply device 1 by controlling the first switch element 11, the second switch element 12, and the second auxiliary switch element 32. A specific control method is simply to change the switch elements to be controlled from the first switch element 11 and the first auxiliary switch element 31 to the second switch element 12 and the second auxiliary switch element 32 in the examples shown in Fig. 6 to Fig. 16, and therefore a specific description thereof will be omitted.

[0062] As described above, the first embodiment can perform ZVS operation and ZCS operation during step-down operation and step-up operation. As a result, the first embodiment can realize soft switching, and therefore can reduce switching loss. In addition, in the first embodiment, when the inductor 51 is configured as a transformer, the excitation inductance of the primary winding 52 is the inductor 51, and can be realized by simply adding the secondary winding 53, so that the size can be reduced.

[0063] [Second embodiment] An example of the configuration of the power supply device according to the second embodiment will be described with reference to Fig. 18. Fig. 18 is a diagram showing an example of the configuration of the power supply device according to the second embodiment.

[0064] As shown in FIG. 18, the power supply device 1A differs from the power supply device 1 shown in FIG. 2 in that it does not include the second auxiliary switch element 32 and the diode 42. The power supply device 1A receives an input voltage Vin which is a DC voltage output from a power supply 2 provided on the primary side and smoothed by a capacitor 3. The DC voltage output from the power supply device 1A is smoothed by a capacitor 4 and input as an output voltage Vout to a load 5 provided on the secondary side. The power supply device 1A is a power supply device that supports only a step-down operation. In the power supply device 1A, the first switch element 11 and the first auxiliary switch element 31 are switch elements to be controlled, and the second switch element 12 is a switch element for synchronous rectification.

[0065] In the second embodiment, the control unit 100 controls the first switch element 11 and the first auxiliary switch element 31 in the power supply device 1A, thereby making it possible to realize the ZVS operation and the ZCS operation during the step-down operation.

[0066] [Third embodiment] An example of the configuration of the power supply device according to the third embodiment will be described with reference to Fig. 19. Fig. 19 is a diagram showing an example of the configuration of the power supply device according to the third embodiment.

[0067] As shown in FIG. 19, the power supply device 1B differs from the power supply device 1 shown in FIG. 2 in that it does not include a first auxiliary switch element 31 and a diode 41. The power supply device 1B receives an input voltage Vin, which is a DC voltage output from a power supply 2 provided on the secondary side and smoothed by a capacitor 4. The DC voltage output from the power supply device 1B is smoothed by a capacitor 3 and input as an output voltage Vout to a load 5 provided on the primary side. The power supply device 1B is a power supply device that supports only a boost operation. In the power supply device 1B, the second switch element 12 and the second auxiliary switch element 32 are switch elements to be controlled, and the first switch element 11 is a switch element for synchronous rectification.

[0068] In the third embodiment, the control unit 100 controls the second switch element 12 and the second auxiliary switch element 32 in the power supply device 1B, thereby enabling the ZVS operation and the ZCS operation to be realized during the boost operation.

[0069] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the contents of these embodiments. The above-mentioned components include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-mentioned components can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the gist of the above-mentioned embodiments. [Explanation of symbols]

[0070] 1,1A,1B power supply 2 power supply 3,4 Capacitor 5. Load 11 First switch element 11-1,12-1 Body diode 11-2,12-2 Parasitic capacitance 12 Second switch element 21,51 Inductor 31 First auxiliary switch element 32 Second auxiliary switch element 41,42 Diode 50 Transformer 52 Primary winding 53 Secondary Winding 54 Leakage Inductor 60 Wiring inductor

Claims

1. a first switch element on a high side and a second switch element on a low side connected in series to the first switch element; a first auxiliary switch element connected in parallel to the first switch element; a second auxiliary switch element connected in parallel to the second switch element and in series to the first auxiliary switch element; a transformer having a primary winding, one end of which is electrically connected to a node between the first switch element and the second switch element and the other end of which is electrically connected to a load, and a secondary winding, one end of which is electrically connected to the node between the first switch element and the second switch element and the other end of which is electrically connected to a node between the first auxiliary switch element and the second auxiliary switch element; a control unit that controls switching operations of the first switch element, the second switch element, the first auxiliary switch element, and the second auxiliary switch element, the control unit controls switching operations of the first switch element, the second switch element, the first auxiliary switch element, and the second auxiliary switch element by utilizing leakage inductance of the secondary winding so that currents flowing through the primary winding and the secondary winding respectively flow in directions that cancel each other's magnetic fluxes. power supply.

2. The control unit controls the first auxiliary switch element to an on state while keeping the first switch element and the second switch element off.

2. The power supply device of claim 1.

3. The control unit controls the first switch element to an on state and the first auxiliary switch element to an off state.

3. The power supply device of claim 2.

4. The control unit controls the second auxiliary switch element to an on state while keeping the first switch element and the second switch element off.

2. The power supply device of claim 1.

5. The control unit controls the second switch element to an on state and the second auxiliary switch element to an off state.

5. The power supply device according to claim 4.

6. a first switch element on a high side and a second switch element on a low side connected in series to the first switch element; a first auxiliary switch element connected in parallel to the first switch element; a transformer having a primary winding, one end of which is electrically connected to a node between the first switch element and the second switch element and the other end of which is electrically connected to a load, and a secondary winding, one end of which is electrically connected to the node between the first switch element and the second switch element and the other end of which is connected to a source terminal of the first auxiliary switch element; a control unit that controls switching operations of the first switch element, the second switch element, and the first auxiliary switch element, the control unit controls switching operations of the first switch element, the second switch element, and the first auxiliary switch element by utilizing leakage inductance of the secondary winding so that currents flowing through the primary winding and the secondary winding respectively flow in directions that cancel each other's magnetic fluxes. power supply.

7. a first switch element on a high side and a second switch element on a low side connected in series to the first switch element; a second auxiliary switch element connected in parallel to the second switch element; a transformer having a primary winding, one end of which is electrically connected to a node between the first switch element and the second switch element and the other end of which is electrically connected to a load, and a secondary winding, one end of which is electrically connected to the node between the first switch element and the second switch element and the other end of which is connected to a drain terminal of the second auxiliary switch element; a control unit that controls switching operations of the first switch element, the second switch element, and the second auxiliary switch element, the control unit controls switching operations of the first switch element, the second switch element, and the second auxiliary switch element by utilizing leakage inductance of the secondary winding so that currents flowing through the primary winding and the secondary winding respectively flow in directions that cancel each other's magnetic fluxes. power supply.

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