Switching power supply device

Abstract

A double resonance transformer uses a primary winding, a first secondary winding, and a second secondary winding to perform voltage conversion using an electromagnetic induction phenomenon based on a winding ratio of the primary winding, the first secondary winding, and the second secondary winding in a rectification operation period that is a conduction period of a first rectification element or a second rectification element. The double resonance transformer uses a primary-side resonance circuit and a first secondary-side resonance circuit or a second secondary-side resonance circuit to perform power transfer using an electromagnetic field resonance phenomenon based on the formation of electromagnetic field coupling between the primary-side resonance circuit and the first secondary-side resonance circuit or the second secondary-side resonance circuit in a rectification stop period in which both the first rectification element and the second rectification element are non-conductive. Due to the electromagnetic field resonance phenomenon, the double resonance transformer 30 holds, as resonance energy, electromagnetic field energy not involved in the power transfer in the primary-side resonance circuit and the first secondary-side resonance circuit or the second secondary-side resonance circuit. The first secondary-side resonance circuit and the second secondary-side resonance circuit start resonance operations at the start of the rectification stop period, end the resonance operation at the end of the rectification stop period, alternately switch the resonance operations of the first secondary-side resonance circuit and the second secondary-side resonance circuit over time, and supply the resonance energy to a load connected to a secondary-side smoothing circuit.

Description

Switching power supply device

[0001] The present disclosure relates to a switching power supply device using a multi-resonance transformer.

[0002] Patent Document 1 describes a switching power supply device using a laminated transformer. In the laminated transformer, a primary winding and a secondary winding are magnetically coupled sharing a core.

[0003] In the switching power supply device of Patent Document 1, an LC resonance circuit is configured only on the primary side, and an equivalent mutual inductance L is formed by the magnetic coupling between the primary winding and the secondary winding, and power is transmitted by magnetic field coupling.

[0004] Japanese Patent Application Laid-Open No. 2019-146359

[0005] However, in a switching power supply device using magnetic coupling such as the switching power supply device of Patent Document 1, the effect of voltage conversion in the transformer, that is, the effect of forming a desired secondary-side voltage by the winding ratio of the primary winding and the secondary winding can be obtained. Leakage magnetic flux not involved in magnetic coupling forms an equivalent leakage inductance. The primary-side leakage inductance is effective for constituting the primary-side resonance circuit, but the magnetic energy of the secondary-side leakage inductance causes power loss and switching noise in the secondary-side circuit, such as switching loss and resistance loss of the rectifier diode, and switching surge.

[0006] In particular, when the magnetic coupling is small, the leakage inductance of the secondary winding becomes large, power loss and switching surge increase, and power cannot be efficiently transmitted from the primary side to the secondary side of the transformer.

[0007] In the switching power supply device of Patent Document 2, a configuration is provided in which LC resonance circuits are connected to the primary side and the secondary side of the transformer. Thereby, power is transmitted by electromagnetic field resonance coupling, and by using the resonance phenomenon, it is possible to improve the power efficiency even when the leakage inductance of the secondary winding is large. On the other hand, by using the resonance phenomenon, the effect of voltage conversion in the transformer, that is, the effect of forming a desired secondary-side voltage by the winding ratio of the primary winding and the secondary winding cannot be obtained.

[0008] Therefore, the object of this disclosure is to provide a switching power supply that simultaneously realizes a desired voltage conversion function by winding ratio utilizing electromagnetic induction phenomena and a power conversion function for obtaining a desired voltage gain by resonance phenomena, thereby achieving high power conversion efficiency.

[0009] A switching power supply device according to one embodiment of the present invention comprises a double resonant transformer, a primary resonant capacitor, a first secondary resonant capacitor, a second secondary resonant capacitor, a primary power conversion circuit, a secondary rectifier circuit, and a secondary smoothing circuit.

[0010] The double-resonant transformer comprises a primary winding, a first secondary winding, and a second secondary winding. It forms an excitation inductor by magnetic coupling between the primary winding and the first and second secondary windings, an equivalent primary-side resonant inductor in series with the primary winding due to leakage inductance, an equivalent first secondary-side resonant inductor in series with the first secondary winding due to leakage inductance, and an equivalent second secondary-side resonant inductor in series with the second secondary winding due to leakage inductance.

[0011] The primary resonant capacitor, together with the primary resonant inductor, constitutes a primary resonant circuit. The first secondary resonant capacitor, together with the first secondary resonant inductor, constitutes a first secondary resonant circuit. The second secondary resonant capacitor, together with the second secondary resonant inductor, constitutes a second secondary resonant circuit.

[0012] The primary power conversion circuit comprises multiple switching elements. The primary power conversion circuit generates a square wave voltage with a periodic switching frequency by intermittently supplying the input DC voltage to the primary resonant circuit through a switching operation that alternately turns the multiple switching elements on and off with a dead time in between.

[0013] The secondary rectifier circuit comprises a first rectifier element formed by equivalently connecting a first secondary resonant capacitor in parallel, and a second rectifier element formed by equivalently connecting a second secondary resonant capacitor in parallel. The secondary rectifier circuit rectifies the AC current output from the first secondary resonant circuit and the second secondary resonant circuit by alternately switching the first and second rectifier elements on and off with a dead time in between. The secondary smoothing circuit smooths the rectified voltage to obtain a DC voltage.

[0014] In a double-resonant transformer, during the rectification period when the first or second rectifying element is conducting, voltage conversion is performed using the primary winding, the first secondary winding, and the second secondary winding, utilizing the electromagnetic induction phenomenon based on the turns ratio of the primary winding, the first secondary winding, and the second secondary winding.

[0015] In a double-resonant transformer, during the rectification stop period when both the first and second rectifying elements are non-conductive, power transmission is performed using the primary resonant circuit and the first or second secondary resonant circuit, utilizing the electromagnetic field resonance phenomenon based on the formation of electromagnetic field coupling between the primary resonant circuit and the first or second secondary resonant circuit.

[0016] A double-resonant transformer, through the electromagnetic field resonance phenomenon, retains electromagnetic field energy that is not involved in power transmission as resonant energy in the primary resonant circuit and the first secondary resonant circuit or the second secondary resonant circuit.

[0017] The first secondary resonant circuit and the second secondary resonant circuit begin resonant operation at the start of the rectification stop period and end resonant operation at the end of the rectification stop period, and alternately switch the resonant operation of the first secondary resonant circuit and the second secondary resonant circuit over time, supplying resonant energy to the load connected to the secondary smoothing circuit.

[0018] In this configuration, the switching power supply alternately performs voltage conversion using electromagnetic induction and power transmission using electromagnetic field resonance. This allows for the realization of a desired voltage conversion function based on the winding ratio utilizing electromagnetic induction and a power conversion function to obtain a desired voltage gain through resonance, all within one switching cycle.

[0019] According to this invention, it is possible to simultaneously realize a desired voltage conversion function using a winding ratio that utilizes electromagnetic induction and a power transmission function that obtains a desired voltage gain through resonance, thereby achieving high power conversion efficiency.

[0020] Figure 1 is an equivalent circuit diagram of a switching power supply device according to the first embodiment of the present invention. Figure 2 is a diagram showing examples of waveforms of each part during power supply operation of the switching power supply device according to the first embodiment of the present invention. Figure 3 is an equivalent circuit diagram of a switching power supply device according to the second embodiment of the present invention. Figure 4 is an equivalent circuit diagram of a switching power supply device according to the third embodiment of the present invention. Figure 5 is an equivalent circuit diagram of a switching power supply device according to the fourth embodiment of the present invention. Figure 6 is an equivalent circuit diagram of a switching power supply device according to the fifth embodiment of the present invention. Figure 7 is an equivalent circuit diagram of a switching power supply device according to the sixth embodiment of the present invention.

[0021] [First Embodiment] A switching power supply device according to the first embodiment of the present invention will be described with reference to the figures. Figure 1 is an equivalent circuit diagram of the switching power supply device according to the first embodiment of the present invention.

[0022] As shown in Figure 1, the switching power supply unit 10 includes an input capacitor Ci, a primary power conversion circuit 21, a primary resonant circuit 22, a double resonant transformer 30, a secondary resonant circuit 41, a secondary resonant circuit 42, a rectifier element Ds1, a rectifier element Ds2, and an output capacitor Co. The switching power supply unit 10 also includes a pair of power input terminals PIH and PIL, and a pair of output terminals POH and POL.

[0023] (Circuit configuration of the double-resonant transformer 30) The double-resonant transformer 30 is composed of an isolated transformer in which the primary and secondary sides are insulated. The double-resonant transformer 30 includes a primary winding np, a secondary winding ns1 (first secondary winding), and a secondary winding ns2 (second secondary winding). The secondary windings ns1 and ns2 are connected in series.

[0024] The number of turns of secondary winding ns1 and secondary winding ns2 are the same. Secondary winding ns1 corresponds to the "first secondary winding" of the present invention, and secondary winding ns2 corresponds to the "second secondary winding" of the present invention.

[0025] The primary winding np and the secondary windings ns1 and ns2 are magnetically coupled according to a predetermined coupling coefficient. The coupling coefficient between the primary winding np and the secondary winding ns1 (first coupling coefficient) and the coupling coefficient between the primary winding np and the secondary winding ns2 (second coupling coefficient) are the same.

[0026] The coupling coefficients between the primary winding np and the secondary windings ns1 and ns2 are set so that a predetermined leakage inductance is generated. For example, the coupling coefficient between the primary winding np and the secondary winding ns1 (first coupling coefficient) and the coupling coefficient between the primary winding np and the secondary winding ns2 (second coupling coefficient) are set to be between 0.5 and less than 1.0.

[0027] The secondary windings ns1 and ns2 are magnetically coupled. The coupling coefficient between secondary windings ns1 and ns2 is set higher than the coupling coefficient between primary winding np and secondary winding ns1 (first coupling coefficient), and the coupling coefficient between primary winding np and secondary winding ns2 (second coupling coefficient).

[0028] The double-resonant transformer 30 is equivalently provided with a primary-side excitation inductor Lmr, a secondary-side excitation inductor Lms1, and a secondary-side excitation inductor Lms2 as mutual inductances due to magnetic coupling between the primary winding np and the secondary windings ns1 and ns2.

[0029] The primary excitation inductor Lmr is connected in parallel to the primary winding np. The secondary excitation inductor Lms1 is connected in parallel to the secondary winding ns1. The secondary excitation inductor Lms2 is connected in parallel to the secondary winding ns2.

[0030] The double-resonant transformer 30 is equivalently equipped with a primary resonant inductor Lr, a secondary resonant inductor Ls1, and a secondary resonant inductor Ls2, based on its leakage inductance.

[0031] The primary resonant inductor Lr is composed of a first primary resonant inductor and a second primary resonant inductor. The first primary resonant inductor is composed of the primary side leakage inductance between the primary winding np and the secondary winding ns1. The second primary resonant inductor is composed of the primary side leakage inductance between the primary winding np and the secondary winding ns2. The primary resonant inductor Lr is connected in series with the primary winding np.

[0032] The secondary resonant inductor Ls1 is formed by the secondary leakage inductance between the primary winding np and the secondary winding ns1. The secondary resonant inductor Ls1 is connected in series to the terminal on the secondary winding ns1 opposite to the terminal connected to the secondary winding ns2.

[0033] The secondary resonant inductor Ls2 is formed by the secondary leakage inductance between the primary winding np and the secondary winding ns2. The secondary resonant inductor Ls2 is connected in series to the terminal on the secondary winding ns2 opposite to the terminal connected to the secondary winding ns1.

[0034] (Circuit configuration of switching power supply 10) (Primary side of double resonant transformer 30) The positive terminal of the DC power supply PSDC is connected to the power input terminal PIH. The negative terminal of the DC power supply PSDC is connected to the power input terminal PIL.

[0035] The input capacitor Ci is connected between the power input terminal PIH and the power input terminal PIL.

[0036] The primary power conversion circuit 21 includes a switching control IC 210, a switching element Q1, and a switching element Q2. Switching elements Q1 and Q2 are composed of, for example, power FETs.

[0037] The drain terminal of switching element Q2 is connected to the power input terminal PIH. The source terminal of switching element Q2 is connected to the drain terminal of switching element Q1. The source terminal of switching element Q1 is connected to the power input terminal PIL.

[0038] The gate terminal of the switching element Q1 and the gate terminal of the switching element Q2 are connected to the switching control IC210.

[0039] A primary resonance capacitor Cr is connected to the drain terminal of the switching element Q2 in the primary power conversion circuit 21. A primary resonance inductor Lr of the double resonance transformer 30 is connected in series to the primary resonance capacitor Cr.

[0040] A primary resonance circuit 22 is constituted by a series resonance circuit of the primary resonance capacitor Cr and the primary resonance inductor Lr.

[0041] A parallel circuit of the primary winding np and the primary exciting inductor Lmr is connected in series to the primary resonance inductor Lr. A connection node between the drain terminal of the switching element Q1 and the source terminal of the switching element Q2 is connected to the parallel circuit of the primary winding np and the primary exciting inductor Lmr.

[0042] (Secondary side of the double resonance transformer 30) A connection node (intermediate connection node) between the secondary winding ns1 (a parallel circuit of the secondary winding ns1 and the secondary exciting inductor Lms1) and the secondary winding ns2 (a parallel circuit of the secondary winding ns2 and the secondary exciting inductor Lms2) is connected to the output terminal POL.

[0043] A secondary resonance inductor Ls1 is connected in series to the terminal on the side opposite to the intermediate connection node in the secondary winding ns1. A rectifying element Ds1 is connected in series to the secondary resonance inductor Ls1. The rectifying element Ds1 is, for example, a diode. The anode of the rectifying element Ds1 is connected to the secondary resonance inductor Ls1.

[0044] A secondary resonance capacitor Cs1 is connected in parallel to the rectifying element Ds1. The secondary resonance capacitor Cs1 is constituted by, for example, the junction capacitance of the rectifying element Ds1. That is, the secondary resonance capacitor Cs1 is equivalently connected in parallel to the rectifying element Ds1.

[0045] With this configuration, a series resonance circuit of the secondary resonance inductor Ls1 and the secondary resonance capacitor Cs1 is constituted, and the "first secondary resonance circuit" of the present application is constituted.

[0046] The terminal on the side opposite to the intermediate connection node in the secondary winding ns2 is connected in series with the secondary-side resonance inductor Ls2. A rectifying element Ds2 is connected in series with the secondary-side resonance inductor Ls2. The rectifying element Ds2 is, for example, a diode. The anode of the rectifying element Ds2 is connected to the secondary-side resonance inductor Ls2.

[0047] A secondary-side resonance capacitor Cs2 is connected in parallel with the rectifying element Ds2. The secondary-side resonance capacitor Cs2 is constituted by, for example, the junction capacitance of the rectifying element Ds2. That is, the secondary-side resonance capacitor Cs2 is equivalently connected in parallel with the rectifying element Ds2.

[0048] With this configuration, a series resonance circuit of the secondary-side resonance inductor Ls2 and the secondary-side resonance capacitor Cs2 is formed, and the "second secondary-side resonance circuit" of the present application is formed.

[0049] The cathode of the rectifying element Ds1 and the cathode of the rectifying element Ds2 are electrically connected to each other and connected to the output terminal POH.

[0050] The rectifying element Ds1 and the rectifying element Ds2 constitute the "secondary-side rectifying circuit" of the present application.

[0051] An output capacitor Co is connected between the output terminal POH and the output terminal POL. This output capacitor Co constitutes the "secondary-side smoothing circuit" of the present invention.

[0052] Then, a load Ro to which power is supplied by the switching power supply device 10 is connected to the output terminal POH and the output terminal POL.

[0053] (Power supply operation of the switching power supply 10 to the load Ro) The switching control IC 210 is driven by power from the DC power supply PSDC. The switching control IC 210 generates a switching control signal consisting of a predetermined switching frequency fs and outputs it to switching elements Q1 and Q2. The switching control signal output to switching element Q1 and the switching control signal output to switching element Q2 have a relationship in which the High state and Low state are inverse of each other. In this case, a dead time is set in the switching control signals so that the High states of each do not overlap. As a result, switching elements Q1 and Q2 perform a switching operation in which they alternately turn on and off with the dead time in between.

[0054] Through this switching control, the switching power supply 10 performs ZVS operation (zero voltage switching operation) by commutating the current flowing through switching element Q1 and switching element Q2 during the dead time period.

[0055] As a result, the primary power conversion circuit 21 intermittently supplies the input DC voltage to the primary resonant circuit 22, generating a square wave voltage with a periodic switching frequency fs. With such a square wave voltage applied, the switching power supply device 10 performs the following power supply operation.

[0056] Figure 2 shows an example of waveforms of each part during power supply operation of a switching power supply device according to the first embodiment of the present invention. In Figure 2, Vgs1 represents the gate-source voltage of switching element Q1, and Vgs2 represents the gate-source voltage of switching element Q2. Vds1 represents the drain-source voltage of switching element Q1, and Vds2 represents the drain-source voltage of switching element Q2. ir represents the current flowing through the primary resonant inductor Lr, and im represents the induced current generated in the double resonant transformer 30. Vrcs1 represents the voltage across the rectifier element Ds1, and Vrcs2 represents the voltage across the rectifier element Ds2. is represents the current flowing through the common ground connecting the secondary winding ns1 and the intermediate connection node of the secondary winding to the output terminal POL.

[0057] ・STATE 1 (from time t1 to time t2) The rectifier element Dqs1 of the switching element Q1 is initially conducting. By turning on the switching element Q1 during the period when the rectifier element Dqs1 is conducting, ZVS operation is performed and the switching element Q1 becomes conducting. Due to mutual induction between the primary winding np and the secondary windings ns1 and ns2, equivalent primary-side excitation inductors Lmr, Lms1, and Lms2 are formed. In addition, due to the leakage inductance of the primary winding np and the secondary windings ns1 and ns2, equivalent primary-side resonant inductors Lr, Ls1, and Ls2 are formed.

[0058] This creates a double resonant circuit composed of a primary resonant capacitor Cr, a primary resonant inductor Lr, a primary excitation inductor Lmr, a secondary resonant capacitor Cs1, a secondary resonant inductor Ls1, a secondary excitation inductor Lms1, a secondary resonant capacitor Cs2, a secondary resonant inductor Ls2, and a secondary excitation inductor Lms2. This double resonant circuit causes the primary resonant circuit 22 and the secondary resonant circuits 41 and 42 to resonate, forming an electromagnetic field resonance phenomenon in which resonant currents flow through the primary excitation inductor Lmr, the secondary excitation inductor Lms1, and the secondary excitation inductor Lms2.

[0059] As a result, power is transmitted from the primary circuit to the secondary circuit of the double-resonant transformer 30. Specifically, in the primary circuit, resonant current flows through the primary resonant capacitor Cr, the primary resonant inductor Lr, and the primary excitation inductor Lmr. In the secondary circuit, resonant current flows through the secondary resonant capacitor Cs1, the secondary resonant inductor Ls1, and the secondary excitation inductor Lms1, and resonant current flows through the secondary resonant capacitor Cs2, the secondary resonant inductor Ls2, and the secondary excitation inductor Lms2.

[0060] This operation charges the secondary resonant capacitor Cs1 and discharges the secondary resonant capacitor Cs2. Then, current is supplied to the load Ro from the output capacitor Co. After this, when the voltage Vrcs1 and the output voltage Vo become equal and the voltage Vrcs2 becomes 0 [V], the rectifier element Ds1 conducts, and STATE 2 is reached.

[0061] STATE 2 (from time t2 to time t3): Equivalent primary-side excitation inductors Lmr and Lms1 are formed between the primary winding np and the secondary winding ns1 by mutual induction, and power is transmitted from the primary circuit to the secondary circuit of the double-resonant transformer 30 by electromagnetic field coupling.

[0062] In the primary circuit, resonant current flows through the primary resonant capacitor Cr, primary resonant inductor Lr, and primary excitation inductor Lmr. In the secondary circuit, resonant current flows through the secondary excitation inductor Lms1 and secondary resonant inductor Ls1, supplying current to the load Ro through the rectifier element Ds1. When the switching element Q1 turns off, STATE 3 is reached.

[0063] • STATE 3 (from time t3 to time t4) In the primary circuit, the primary resonant capacitor Cr is charged by the current ir flowing through the primary resonant inductor Lr. In the secondary circuit, the current in the secondary resonant inductor Ls1 supplies current to the load Ro through the rectifier element Ds1. When the voltage Vds1 becomes the input voltage Vi and the voltage Vds2 becomes 0 [V], the rectifier element Dqs2 of the switching element Q2 conducts, and STATE 4 is reached.

[0064] • STATE 4 (from time t4 to time t5) The rectifier element Dqs2 of the switching element Q2 is initially conducting. During the period when the rectifier element Dqs2 is conducting, the switching element Q2 is turned on, performing ZVS operation, and the switching element Q2 becomes conducting.

[0065] Mutual induction between the primary winding np and the secondary windings ns1 and ns2 forms equivalent primary excitation inductors Lmr, Lms1, and Lms2. Additionally, the leakage inductance of the primary winding np and the secondary windings ns1 and ns2 forms equivalent primary resonant inductors Lr, Ls1, and Ls2.

[0066] This creates a double resonant circuit composed of a primary resonant capacitor Cr, a primary resonant inductor Lr, a primary excitation inductor Lmr, a secondary resonant capacitor Cs1, a secondary resonant inductor Ls1, a secondary excitation inductor Lms1, a secondary resonant capacitor Cs2, a secondary resonant inductor Ls2, and a secondary excitation inductor Lms2. This double resonant circuit causes the primary resonant circuit 22 and the secondary resonant circuits 41 and 42 to resonate, forming an electromagnetic field resonance phenomenon in which resonant currents flow through the primary excitation inductor Lmr, the secondary excitation inductor Lms1, and the secondary excitation inductor Lms2.

[0067] As a result, power is transmitted from the primary circuit to the secondary circuit of the double-resonant transformer 30. Specifically, in the primary circuit, resonant current flows through the primary resonant capacitor Cr, the primary resonant inductor Lr, and the primary excitation inductor Lmr. In the secondary circuit, resonant current flows through the secondary resonant capacitor Cs1, the secondary resonant inductor Ls1, and the secondary excitation inductor Lms1, and resonant current flows through the secondary resonant capacitor Cs2, the secondary resonant inductor Ls2, and the secondary excitation inductor Lms2.

[0068] This operation discharges the secondary resonant capacitor Cs1 and charges the secondary resonant capacitor Cs2. Then, current is supplied to the load Ro from the output capacitor Co. After this, when the voltage Vrcs2 and the output voltage Vo become equal and the voltage Vrcs1 becomes 0 [V], the rectifier element Ds2 conducts, and STATE 5 is reached.

[0069] STATE 5 (from time t5 to time t6): An equivalent primary-side excitation inductor Lmr and a secondary-side excitation inductor Lms2 are formed between the primary winding np and the secondary winding ns2 by mutual induction, and power is transmitted from the primary circuit to the secondary circuit of the double-resonant transformer 30 by electromagnetic field coupling.

[0070] In the primary circuit, resonant current flows through the primary resonant capacitor Cr, primary resonant inductor Lr, and primary excitation inductor Lmr. In the secondary circuit, resonant current flows through the secondary excitation inductor Lms2 and secondary resonant inductor Ls2, supplying current to the load Ro through the rectifier element Ds2. When the switching element Q2 turns off, STATE 6 is reached.

[0071] - STATE 6 (from time t6 to time t7) In the primary circuit, the primary resonant capacitor Cr is discharged by the current ir flowing through the primary resonant inductor Lr. In the secondary circuit, the current in the secondary resonant inductor Ls2 supplies current to the load Ro through the rectifier element Ds2. When the voltage Vds2 becomes the input voltage Vi and the voltage Vds1 becomes 0 [V], the rectifier element Dqs1 of the switching element Q1 conducts, and STATE 1 is established.

[0072] From this point onward, the above steps 1 through 6 are repeated periodically.

[0073] By performing such control, the switching power supply 10 can use the double-resonant transformer 30 to perform power transmission using the electromagnetic field resonance phenomenon based on the formation of electromagnetic field coupling between the primary resonant circuit 22 and the first secondary resonant circuit or the second secondary resonant circuit during the rectification stop period when both rectifier elements Ds1 and Ds2 are non-conductive.

[0074] In this case, due to the electromagnetic field resonance phenomenon, electromagnetic field energy that is not involved in power transmission is held as resonant energy in the primary resonant circuit 22 and the secondary resonant circuit 41 or secondary resonant circuit 42 by the primary resonant capacitor Cr, the secondary resonant capacitor Cs1, and the secondary resonant capacitor Cs2.

[0075] The secondary resonant circuits 41 and 42 begin resonant operation at the start of the rectification stop period and end resonant operation at the end of the rectification stop period. The resonant operation of the secondary resonant circuits 41 and 42 is switched alternately over time, and the resonant energy held in the secondary resonant capacitors Cs1 and Cs2 is supplied to the load Ro through the output capacitor Co.

[0076] Furthermore, the switching power supply 10 can use the double-resonant transformer 30 to perform voltage conversion using the electromagnetic induction phenomenon based on the turns ratio of the primary winding np and the secondary windings ns1 and ns2 during the rectification operation period, which is the conduction period of the rectifier element Ds1 or rectifier element Ds2.

[0077] As a result, the switching power supply 10 can simultaneously realize a desired voltage conversion function using a winding ratio that utilizes electromagnetic induction and a power conversion function that obtains a desired voltage gain through resonance (electromagnetic field resonance), thereby achieving high power conversion efficiency.

[0078] Furthermore, the switching power supply unit 10 can achieve even higher power conversion efficiency by employing ZVS operation.

[0079] Furthermore, in the operation of power transmission, the switching power supply 10 preferably adjusts the element values ​​of each element of the double-resonant transformer 30 to set the input impedance viewed from the primary-side power conversion circuit 21 to the load Ro side to an impedance near the minimum at the secondary-side resonant frequency during the rectification stop period. This allows the switching power supply 10 to more reliably realize the electromagnetic field resonance phenomenon and achieve high power transmission efficiency.

[0080] Furthermore, since the switching power supply 10 utilizes the secondary leakage flux as the inductance of the secondary resonant circuit, it can suppress power losses and switching noise in the secondary circuit, such as switching losses and resistance losses of the rectifier diodes, as well as switching surges. As a result, the switching power supply 10 can achieve even higher power transmission efficiency.

[0081] Furthermore, it is preferable to set the primary resonant frequency fr1 of the primary resonant circuit 22 to be lower than the switching frequency fs, and the secondary resonant frequency fr2 using the secondary resonant circuit 41 and the secondary resonant circuit 42 to be higher than the switching frequency fs. This allows the primary resonant circuit 22 to be set to an inductive impedance in which the current waveform flowing through the primary resonant circuit 22 lags behind the phase of the square wave voltage waveform during voltage conversion. Therefore, the switching power supply 10 can perform ZVS operation more reliably.

[0082] Furthermore, the switching power supply 10 controls the switching frequency fs according to the load. More specifically, it is preferable that the switching power supply 10 controls the switching frequency fs such that there is no load around the operating frequency fc (no-load resonant frequency) when the entire switching cycle is a rectification stop period when viewed from the primary side power conversion circuit 21 towards the load Ro, and the maximum load is around the primary side resonant frequency fr1 of the primary side resonant circuit 22. In other words, it is preferable that the switching power supply 10 sets the switching frequency fs such that fr1 ≤ fs ≤ fc. This allows the switching power supply 10 to supply a desired output voltage according to the state of the load Ro.

[0083] Furthermore, the switching power supply 10 constitutes a primary resonant inductor Lr by the leakage inductance of the primary winding np, a secondary resonant inductor Ls1 by the leakage inductance of the secondary winding ns1, and a secondary resonant inductor Ls2 by the leakage inductance of the secondary winding ns2. In addition, the switching power supply 10 constitutes a primary excitation inductor Lmr, a secondary excitation inductor Lms1, and a secondary excitation inductor Lms2 by the mutual inductance due to the magnetic coupling between the primary winding np and the secondary windings ns1 and ns2. As a result, the switching power supply 10 can construct a double resonant transformer 30 with a small number of components.

[0084] [Second Embodiment] A switching power supply device according to a second embodiment of the present invention will be described with reference to the figures. Figure 3 is an equivalent circuit diagram of the switching power supply device according to the second embodiment of the present invention.

[0085] As shown in Figure 3, the switching power supply 10A according to the second embodiment differs from the switching power supply 10 according to the first embodiment in the configuration of the capacitor connected to the secondary side of the double resonant transformer 30. The other configurations of the switching power supply 10A are the same as those of the switching power supply 10, and the description of the similar parts will be omitted.

[0086] The switching power supply unit 10A includes a plurality of secondary resonant capacitors Cs1, Cs2, Cs3, and Cs4.

[0087] The secondary resonant capacitor Cs1 is connected in series with the secondary resonant inductor Ls1. More specifically, the secondary resonant capacitor Cs1 is connected in series between the secondary resonant inductor Ls1 and the rectifier element Ds1.

[0088] The secondary resonant capacitor Cs2 is connected in series with the secondary resonant inductor Ls2. More specifically, the secondary resonant capacitor Cs2 is connected in series with the secondary resonant inductor Ls2 and the rectifier element Ds2.

[0089] The secondary resonant capacitor Cs3 is connected in parallel with the output capacitor Co. More specifically, one terminal of the secondary resonant capacitor Cs3 is connected to the connection node between the secondary resonant capacitor Cs1 and the rectifier element Ds1, and the other terminal of the secondary resonant capacitor Cs3 is connected to the intermediate ground line connecting the intermediate connection node between the secondary windings ns1 and ns2 and the output terminal POL. The secondary resonant capacitor Cs3 can be configured, for example, by the winding capacitance of the secondary winding ns1.

[0090] The secondary resonant capacitor Cs4 is connected in parallel with the output capacitor Co. More specifically, one terminal of the secondary resonant capacitor Cs4 is connected to the connection node between the secondary resonant capacitor Cs2 and the rectifier element Ds2, and the other terminal of the secondary resonant capacitor Cs3 is connected to the intermediate ground line. The secondary resonant capacitor Cs4 can be constructed, for example, by the winding capacitance of the secondary winding ns2.

[0091] With this configuration, the switching power supply 10A, like the switching power supply 10, simultaneously realizes a desired voltage conversion function using a winding ratio that utilizes electromagnetic induction and a power conversion function that obtains a desired voltage gain through resonance, thereby achieving high power conversion efficiency.

[0092] Furthermore, the switching power supply 10A can more reliably set the secondary resonant frequency to the desired frequency by increasing the number of capacitors that set the secondary resonant frequency.

[0093] [Third Embodiment] A switching power supply device according to a third embodiment of the present invention will be described with reference to the figures. Figure 4 is an equivalent circuit diagram of the switching power supply device according to the third embodiment of the present invention.

[0094] As shown in Figure 4, the switching power supply 10B according to the third embodiment differs from the switching power supply 10 according to the first embodiment in the configuration of the secondary side of the double resonant transformer and the circuit configuration connected to the secondary side of the double resonant transformer. The other configurations of the switching power supply 10B are the same as those of the switching power supply 10, and the explanation of the similar parts will be omitted.

[0095] The switching power supply unit 10B comprises a double resonant transformer 30B, a plurality of secondary resonant capacitors Cs1, Cs2, Cs3, Cs4, and a plurality of rectifier elements Ds1, Ds2, Ds3, Ds4.

[0096] The double-resonant transformer 30B comprises a secondary winding ns, a secondary resonant inductor Ls, and a secondary excitation inductor Lms. That is, the double-resonant transformer 30B has one secondary winding ns, and this secondary winding ns realizes the functions of the secondary windings ns1 and ns2 according to the first embodiment.

[0097] The secondary resonant inductor Ls is effectively connected in series with the secondary winding ns. The secondary excitation inductor Lms is effectively connected in parallel with the secondary winding ns.

[0098] The anode of the rectifier element Ds1 is connected to the secondary resonant inductor Ls, and the cathode of the rectifier element Ds1 is connected to the output terminal POH. The secondary resonant capacitor Cs1 is connected in parallel to the rectifier element Ds1. The secondary resonant capacitor Cs1 is formed, for example, by the junction capacitance of the rectifier element Ds1.

[0099] Furthermore, the cathode of the rectifier element Ds4 is connected to the secondary resonant inductor Ls, and the anode of the rectifier element Ds4 is connected to the output terminal POL. The secondary resonant capacitor Cs4 is connected in parallel to the rectifier element Ds4. The secondary resonant capacitor Cs4 is formed, for example, by the junction capacitance of the rectifier element Ds4.

[0100] In the parallel circuit of the secondary winding ns and the secondary excitation inductor Lms, the anode of the rectifier element Ds2 is connected to the terminal opposite to the connection terminal of the secondary resonant inductor Ls, and the cathode of the rectifier element Ds2 is connected to the output terminal POH. The secondary resonant capacitor Cs2 is connected in parallel to the rectifier element Ds2. The secondary resonant capacitor Cs2 is formed, for example, by the junction capacitance of the rectifier element Ds2.

[0101] Furthermore, in the parallel circuit of the secondary winding ns and the secondary excitation inductor Lms, the cathode of the rectifier element Ds3 is connected to the terminal opposite to the connection terminal of the secondary resonant inductor Ls, and the anode of the rectifier element Ds3 is connected to the output terminal POL. The secondary resonant capacitor Cs3 is connected in parallel to the rectifier element Ds3. The secondary resonant capacitor Cs3 is formed, for example, by the junction capacitance of the rectifier element Ds3.

[0102] With this configuration, a secondary resonant circuit 40B is formed by a secondary resonant inductor Ls and multiple secondary resonant capacitors Cs1, Cs2, Cs3, and Cs4. In addition, a rectifier circuit 50B is formed by multiple rectifier elements Ds1, Ds2, Ds3, and Ds4. The rectifier circuit 50B constitutes a full-wave rectifier circuit.

[0103] With the above configuration, the switching power supply unit 10B, like the switching power supply unit 10, simultaneously realizes a desired voltage conversion function using a winding ratio that utilizes electromagnetic induction and a power conversion function that obtains a desired voltage gain through resonance, thereby achieving high power conversion efficiency.

[0104] Furthermore, since the switching power supply unit 10B is equipped with a full-wave rectifier circuit, the rectification function can be improved.

[0105] [Fourth Embodiment] A switching power supply device according to the fourth embodiment of the present invention will be described with reference to the figures. Figure 5 is an equivalent circuit diagram of the switching power supply device according to the fourth embodiment of the present invention.

[0106] As shown in Figure 5, the switching power supply 10C according to the fourth embodiment differs from the switching power supply 10B according to the third embodiment in the circuit configuration connected to the secondary side of the double-resonant transformer. The other configurations of the switching power supply 10C are the same as those of the switching power supply 10B, and the explanation of the similar parts will be omitted.

[0107] The switching power supply unit 10C comprises a double resonant transformer 30C, a plurality of secondary resonant capacitors Cs, Cs1, Cs2, and a plurality of rectifier elements Ds1, Ds2.

[0108] The double-resonant transformer 30C, like the double-resonant transformer 30B, is equipped with a secondary winding ns, a secondary resonant inductor Ls, and a secondary excitation inductor Lms.

[0109] The secondary resonant capacitor Cs is connected in series with the secondary resonant inductor Ls. More specifically, one terminal of the secondary resonant capacitor Cs is connected to the secondary resonant inductor Ls, and the other terminal of the secondary resonant capacitor Cs is connected to the output terminal POH.

[0110] The rectifier element Ds2 is connected between the other terminal of the secondary resonant capacitor Cs and the terminal opposite to the connection terminal of the secondary resonant inductor Ls in the parallel circuit of the secondary winding ns and the secondary excitation inductor Lms. More specifically, the cathode of the rectifier element Ds2 is connected to the other terminal of the secondary resonant capacitor Cs, and the anode of the rectifier element Ds2 is connected to the terminal opposite to the connection terminal of the secondary resonant inductor Ls in the parallel circuit of the secondary winding ns and the secondary excitation inductor Lms.

[0111] Rectifier element Ds1 is connected between rectifier element Ds2 and output terminal POL. More specifically, the cathode of rectifier element Ds1 is connected to the anode of rectifier element Ds2, and the anode of rectifier element Ds1 is connected to output terminal POL.

[0112] In this configuration, rectifier elements Ds1 and Ds2 are connected in series between output terminal POL and output terminal POH, forming a rectifier circuit 50C. With this configuration, the rectifier circuit 50C constitutes a voltage doubler rectifier circuit.

[0113] The secondary resonant capacitor Cs2 is connected in parallel to the rectifier element Ds2. The secondary resonant capacitor Cs2 is formed, for example, by the junction capacitance of the rectifier element Ds2.

[0114] The secondary resonant capacitor Cs1 is connected in parallel to the rectifier element Ds1. The secondary resonant capacitor Cs1 is formed, for example, by the junction capacitance of the rectifier element Ds1.

[0115] In this configuration, the secondary resonant inductor Ls and the multiple secondary resonant capacitors Cs, Cs1, and Cs2 constitute a secondary resonant circuit 40C.

[0116] With the above configuration, the switching power supply unit 10C, like the switching power supply unit 10B, simultaneously realizes a desired voltage conversion function using a winding ratio that utilizes electromagnetic induction and a power conversion function that obtains a desired voltage gain through resonance, thereby achieving high power conversion efficiency.

[0117] Furthermore, since the switching power supply 10C is equipped with a voltage doubler rectifier circuit, it can supply a higher output voltage to the load Ro.

[0118] [Fifth Embodiment] A switching power supply device according to the fifth embodiment of the present invention will be described with reference to the figures. Figure 6 is an equivalent circuit diagram of the switching power supply device according to the fifth embodiment of the present invention.

[0119] As shown in Figure 6, the switching power supply 10D according to the fifth embodiment differs from the switching power supply 10B according to the third embodiment in the circuit configuration connected to the primary and secondary sides of the double-resonant transformer. The other configurations of the switching power supply 10D are the same as those of the switching power supply 10B, and a description of the similar parts will be omitted.

[0120] The switching power supply unit 10D comprises a double resonant transformer 30D, a primary resonant capacitor Cr, a plurality of secondary resonant capacitors Cs, Cs1, Cs2, and a plurality of rectifier elements Qs1, Qs2.

[0121] The double-resonant transformer 30D comprises a primary winding np, a secondary winding ns, a primary resonant inductor Lr, a primary excitation inductor Lmr, a secondary resonant inductor Ls, and a secondary excitation inductor Lms.

[0122] The primary resonant inductor Lr is connected to the connection node between the drain terminal of switching element Q1 and the source terminal of switching element Q2.

[0123] A parallel circuit of the primary winding np and the primary excitation inductor Lmr is connected in series to the primary resonant inductor Lr. A primary resonant capacitor Cr is connected to the parallel circuit of the primary winding np and the primary excitation inductor Lmr.

[0124] The primary resonant capacitor Cr is connected to the source terminal of the switching element Q1 and is connected to the reference potential. In other words, the primary resonant capacitor Cr is connected in series with the reference potential line in the primary circuit.

[0125] The secondary resonant capacitor Cs is connected to the terminal opposite to the terminal to which the secondary resonant inductor Ls is connected in the parallel circuit of the secondary winding ns and the secondary excitation inductor Lms. In other words, the secondary resonant capacitor Cs is connected in series to the line on the output terminal POL side in the secondary circuit.

[0126] Rectifier elements Qs1 and Qs2 are composed of power FETs. Rectifier elements Qs1 and Qs2 constitute a rectifier circuit 50D. Rectifier elements Qs1 and Qs2 perform synchronous rectification synchronized with the switching timing of primary-side switching elements Q1 and Q2 by a secondary-side switching control IC (not shown).

[0127] The drain terminal of rectifier element Qs1 is connected to the secondary resonant inductor Ls. The source terminal of rectifier element Qs1 is connected to the output terminal POL. The source terminal of rectifier element Qs2 is connected to the drain terminal of both the secondary resonant inductor Ls and rectifier element Qs1. The drain terminal of rectifier element Qs2 is connected to the output terminal POH.

[0128] The secondary resonant capacitor Cs1 is connected between the source terminal and drain terminal of the rectifier element Qs1. The secondary resonant capacitor Cs2 is connected between the source terminal and drain terminal of the rectifier element Qs2.

[0129] With the above configuration, the switching power supply 10D, like the switching power supply 10B, simultaneously realizes a desired voltage conversion function using a winding ratio that utilizes electromagnetic induction and a power conversion function that obtains a desired voltage gain through resonance, thereby achieving high power conversion efficiency.

[0130] Furthermore, the switching power supply unit 10D allows for the appropriate arrangement of the primary resonant capacitor Cr, secondary resonant capacitor Cs, primary winding np, and secondary winding ns2, thus enabling effective utilization of the component mounting area.

[0131] Furthermore, the switching power supply unit 10D can easily measure the voltage across the primary resonant capacitor Cr by connecting the primary resonant capacitor Cr to the reference potential on the primary side (input side). As a result, the switching power supply unit 10D can supply the desired power with higher precision by detecting the voltage across the primary resonant capacitor Cr and controlling the switching of the switching elements Q1 and Q2.

[0132] Furthermore, the switching power supply unit 10D can reduce rectification losses by performing synchronous rectification using the rectifier circuit 50D.

[0133] [Sixth Embodiment] A switching power supply device according to the sixth embodiment of the present invention will be described with reference to the figures. Figure 7 is an equivalent circuit diagram of the switching power supply device according to the sixth embodiment of the present invention.

[0134] As shown in Figure 7, the switching power supply 10E according to the sixth embodiment differs from the switching power supply 10A according to the second embodiment in the configuration of the secondary resonant circuit. The other configurations of the switching power supply 10E are the same as those of the switching power supply 10A, and the explanation of the similar parts will be omitted.

[0135] The switching power supply unit 10E includes a secondary resonant circuit 41E and a secondary resonant circuit 42E. The secondary resonant circuit 41E includes a secondary resonant inductor Ls1 and a secondary resonant capacitor Cs1. The secondary resonant circuit 42E includes a secondary resonant inductor Ls2 and a secondary resonant capacitor Cs2.

[0136] The secondary resonant inductor Ls1 is connected to the anode of the rectifier element Ds1. One terminal of the secondary resonant capacitor Cs1 is connected to the connection node between the secondary resonant inductor Ls1 and the anode of the rectifier element Ds1. The other terminal of the secondary resonant capacitor Cs1 is connected to the intermediate connection node on the secondary side of the double resonant transformer 30.

[0137] The secondary resonant inductor Ls2 is connected to the anode of the rectifier element Ds2. One terminal of the secondary resonant capacitor Cs2 is connected to the connection node between the secondary resonant inductor Ls2 and the anode of the rectifier element Ds2. The other terminal of the secondary resonant capacitor Cs2 is connected to the intermediate connection node on the secondary side of the double resonant transformer 30. In other words, the secondary resonant capacitors Cs1 and Cs2 are electrically short-circuited.

[0138] With this configuration, the switching power supply unit 10E can achieve the same effects as the switching power supply unit 10A.

[0139] 10, 10A, 10B, 10C, 10D: Switching power supply 21: Primary power conversion circuit 22: Primary resonant circuit 30, 30B, 30C, 30D: Double resonant transformer 40B, 40C, 41, 42: Secondary resonant circuit 50B, 50C, 50D: Rectifier circuit 210: Switching control IC Ci: Input capacitor Co: Output capacitor Cr: Primary resonant capacitor Cs, Cs1, Cs2, Cs3, Cs4: Secondary resonant capacitor Dqs1, Dqs2, Ds1, Ds2, Ds3, Ds4, Qs1, Qs2: Rectifier element L: Mutual inductance Lmr: Primary excitation inductor Lms, Lms1, Lms2: Secondary excitation inductor Lr: Primary resonant inductor Ls, Ls1, Ls2: Secondary resonant inductor PIH, PIL: Power input terminals POH, POL: Output terminals PSDC: DC power supply Q1, Q2: Switching element Ro: Load np: Primary winding ns, ns1, ns2: Secondary winding

Claims

1. A double resonant transformer comprising a primary winding, a first secondary winding, and a second secondary winding, forming an excitation inductor by magnetic coupling between the primary winding and the first and second secondary windings, an equivalent primary resonant inductor in series with the primary winding due to leakage inductance, an equivalent first secondary resonant inductor in series with the first secondary winding due to leakage inductance, and an equivalent second secondary resonant inductor in series with the second secondary winding due to leakage inductance; a primary resonant capacitor that constitutes a primary resonant circuit together with the primary resonant inductor; a first secondary resonant capacitor that constitutes a first secondary resonant circuit together with the first secondary resonant inductor; and a second secondary resonant capacitor that constitutes a second secondary resonant circuit together with the second secondary resonant inductor. A primary power conversion circuit comprising multiple switching elements, which intermittently supplies an input DC voltage to the primary resonant circuit by switching the multiple switching elements alternately on and off with a dead time in between to generate a square wave voltage with a periodic switching frequency; a secondary rectifier circuit comprising a first rectifier element formed by equivalently connecting the first secondary resonant capacitor in parallel and a second rectifier element formed by equivalently connecting the second secondary resonant capacitor in parallel, which rectifies the AC current output from the first secondary resonant circuit and the second secondary resonant circuit by alternately switching the first rectifier element and the second rectifier element on and off with a dead time in between; and a secondary smoothing circuit which smooths the rectified voltage to obtain a DC voltage; wherein the double resonant transformer is, During the rectification operation period, which is the conduction period of the first or second rectifier element, voltage conversion is performed using the primary winding, the first secondary winding, and the second secondary winding, utilizing the electromagnetic induction phenomenon based on the turns ratio of the primary winding, the first secondary winding, and the second secondary winding, and,During the rectification stop period when both the first and second rectifier elements are non-conductive, power transmission is performed using the primary resonant circuit and the first secondary resonant circuit or the second secondary resonant circuit, utilizing the electromagnetic field resonance phenomenon based on the formation of electromagnetic field coupling between the primary resonant circuit and the first secondary resonant circuit or the second secondary resonant circuit, and, due to the electromagnetic field resonance phenomenon, the primary resonant circuit and the first secondary resonant circuit or the second secondary resonant circuit hold electromagnetic field energy that is not involved in power transmission as resonant energy, the first secondary resonant circuit and the second secondary resonant circuit start resonant operation at the start of the rectification stop period and end the resonant operation at the end of the rectification stop period, and the resonant operation of the first secondary resonant circuit and the second secondary resonant circuit are alternately switched in time, and the resonant energy is supplied to the load connected to the secondary smoothing circuit. A switching power supply device that alternately performs voltage conversion using the aforementioned electromagnetic induction phenomenon and power transmission using the aforementioned electromagnetic field resonance phenomenon in a time-dependent manner.

2. The switching power supply device according to claim 1, wherein the primary resonant circuit, the first secondary resonant circuit, and the second secondary resonant circuit constitute a double resonant circuit in electromagnetic field coupling, and the double resonant circuit, in the operation of power transmission, sets the input impedance viewed from the primary power conversion circuit to the load side to an impedance near the minimum at the secondary resonant frequency during the rectification stop period, thereby realizing the electromagnetic field resonance phenomenon.

3. The switching power supply device according to claim 1 or claim 2, wherein the primary resonant frequency of the primary resonant circuit is set lower than the switching frequency, the secondary resonant frequencies using the first secondary resonant circuit and the second secondary resonant circuit are set higher than the switching frequency, the primary resonant circuit is set to have an inductive impedance such that the current waveform flowing through the primary resonant circuit lags behind the phase of the square wave voltage waveform during the voltage conversion operation, and zero-voltage switching operation is performed in the plurality of switching elements.

4. The switching frequency is controlled such that, when viewed from the primary power conversion circuit towards the load side, there is no load near the operating frequency where the entire switching period is the rectification stop period, and there is maximum load near the primary resonance frequency, according to any one of claims 1 to 3.

5. The switching power supply device according to any one of claims 1 to 4, wherein the first rectifier element is turned on later than the first switching element on the Low side and the second switching element on the High side in the plurality of switching elements, and the second rectifier element is turned on later than the second switching element on the High side and the first switching element on the Low side in the plurality of switching elements, and the on / off control of each is performed in conjunction with each other.

6. The switching power supply device according to any one of claims 1 to 5, wherein the first rectifier element is turned off before the second switching element on the Hi side and the first switching element on the Low side in the plurality of switching elements, and the second rectifier element is turned off before the first switching element on the Low side and the second switching element on the Hi side in the plurality of switching elements, the on / off control of each is performed in conjunction with the other.

7. The switching power supply device according to any one of claims 1 to 6, wherein the coupling coefficient between the primary winding and the first secondary winding and the coupling coefficient between the primary winding and the second secondary winding are 0.5 or more and less than 1.

0.

8. The switching power supply device according to any one of claims 1 to 7, wherein the coupling coefficient between the first secondary winding and the second secondary winding is higher than the coupling coefficient between the primary winding and the first secondary winding and the coupling coefficient between the primary winding and the second secondary winding.

9. The switching power supply device according to any one of claims 1 to 8, wherein the first secondary resonant capacitor is composed of a capacitor connected in parallel with the first secondary winding, and the second secondary resonant capacitor is composed of a capacitor connected in parallel with the second secondary winding.

10. The switching power supply device according to any one of claims 1 to 8, wherein the first secondary resonant capacitor is composed of a winding capacitance connected in parallel to the first secondary winding, and the second secondary resonant capacitor is composed of a winding capacitance connected in parallel to the second secondary winding.

11. The switching power supply device according to any one of claims 1 to 8, wherein the first secondary resonant capacitor is composed of the junction capacitance of the first rectifier element, and the second secondary resonant capacitor is composed of the junction capacitance of the second rectifier element.

12. The switching power supply device according to any one of claims 1 to 11, wherein the primary side resonant inductor is composed of a first primary side resonant inductor and a second primary side resonant inductor, the first primary side resonant inductor is composed of the primary side leakage inductance between the primary winding and the first secondary winding, and the second primary side resonant inductor is composed of the primary side leakage inductance between the primary winding and the second secondary winding.

13. The switching power supply device according to any one of claims 1 to 12, wherein the first secondary resonant inductor is formed by the secondary leakage inductance between the primary winding and the first secondary winding, and the second secondary resonant inductor is formed by the secondary leakage inductance between the primary winding and the second secondary winding.

14. The switching power supply device according to any one of claims 1 to 13, wherein the plurality of switching elements are composed of power FETs.

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