Ac / DC converter

Abstract

An AC / DC converter (10) is provided with a power conversion circuit (30), an insulating transformer (50), and rectifying circuits (61, 62). The power conversion circuit (30) generates a primary-side current having a predetermined frequency from input power from a three-phase AC power supply. The insulating transformer (50) is provided with a primary-side first coil (5011) and a primary-side second coil (5021) which are connected in series to an output side of the power conversion circuit (30), a secondary-side first coil (5012) which is coupled to the primary-side first coil (5011), and a secondary-side second coil (5022) which is coupled to the primary-side second coil (5021). The insulating transformer (50) outputs a secondary-side first current and a secondary-side second current using the primary-side current as an input. The rectifying circuit (61) connects to the secondary-side first coil (5012) and rectifies the secondary-side first current. The rectifying circuit (62) connects to the secondary-side second coil (5022) and rectifies the secondary-side second current. The rectifying circuit (61) and the rectifying circuit (62) are connected in parallel. The rectifying circuit (61) is provided with a first switching element, and an inductor (691L) is connected to the first switching element. The second rectifying circuit (62) is provided with a second switching element, and an inductor (692L) is connected to the second switching element.

Description

AC-DC converter

[0001] The present invention relates to an AC-DC converter.

[0002] Patent Document 1 describes a charging device that includes a non-insulated converter with a power factor correction function and an insulating converter.

[0003] The input terminal of the non-isolated converter with power factor correction is connected to the AC power source. The output terminal of the non-isolated converter with power factor correction is connected to the isolated converter. The output of the isolated converter is connected to the battery.

[0004] A non-isolated converter with a power factor correction function generates a specified output voltage while correcting the power factor of the input current. An isolated transformer isolated converter receives DC power from the non-isolated converter and converts the voltage using a transformer.

[0005] A rectifier circuit is connected to the secondary winding of the transformer. The rectifier circuit is made up of multiple diodes and rectifies the output of the secondary winding of the transformer.

[0006] JP 2014-53992 A

[0007] However, in a conventional configuration such as that shown in Patent Document 1, when a three-phase AC input power supply is used, the output current becomes large, which may result in large loss occurring in the rectifier elements of the rectifier circuit in the secondary circuit of the transformer of the isolated converter.

[0008] Therefore, an object of the present invention is to provide an AC-DC converter that can suppress losses even when the output current is large.

[0009] The AC-DC converter of the present invention includes a power conversion circuit, an isolation transformer, a first rectifier circuit, a second rectifier circuit, and a smoothing capacitor. The power conversion circuit is connected to a three-phase AC power supply and outputs a primary current. The isolation transformer includes a first primary coil and a second primary coil connected in series on the output side of the power conversion circuit, and a first secondary coil coupled to the first primary coil and a second secondary coil coupled to the second primary coil. The isolation transformer receives the primary current as an input and outputs a first secondary current and a second secondary current. The first rectifier circuit is connected to the first secondary coil and rectifies the first secondary current. The second rectifier circuit is connected to the second secondary coil and rectifies the second secondary current. The smoothing capacitor is connected to output terminals of the first rectifier circuit and the second rectifier circuit. The isolation transformer includes a first isolation transformer and a second isolation transformer whose magnetic coupling with each other is suppressed. The primary-side first coil and the primary-side second coil are connected in series. The first isolation transformer includes a primary-side first coil and a secondary-side first coil. The second isolation transformer includes a primary-side second coil and a secondary-side first coil. The first rectifier circuit and the second rectifier circuit are connected in parallel. The first rectifier circuit includes a first switching element, and a first inductor is connected to the first switching element. The second rectifier circuit includes a second switching element, and a second inductor is connected to the second switching element.

[0010] In this configuration, the output current is the sum of the first secondary-side current and the second secondary-side current. Therefore, the first secondary-side current and the second secondary-side current are smaller than when only one rectifier circuit is provided, to obtain the desired output current. This reduces loss in the rectifier circuit. In particular, when a large output current is required, such as when a three-phase AC power supply is used as input, the current flowing through the rectifier circuit becomes large. Therefore, loss in the rectifier circuit is likely to be large, but this configuration effectively reduces this loss.

[0011] The AC-DC converter of the present invention can suppress losses even when the output current is large.

[0012] FIG. 1 is a circuit diagram of an AC-DC converter according to a first embodiment. FIG. 2 is a circuit diagram of an AC-DC converter according to a second embodiment. FIG. 3 is a circuit diagram of a rectifier circuit on the secondary side of an isolation transformer in the AC-DC converter according to the second embodiment. FIGS. 4A and 4B are diagrams showing the configuration of a circuit module realizing a circuit from the isolation transformer to the output terminal side in the AC-DC converter according to the second embodiment. FIG. 5 is a diagram showing an example of a wiring pattern of each rectifier circuit. FIG. 6 is a circuit diagram of an AC-DC converter according to a third embodiment. FIG. 7 is a circuit diagram of a rectifier circuit portion of an AC-DC converter according to a fourth embodiment. FIG. 8 is a circuit diagram of a rectifier circuit portion of an AC-DC converter according to a fifth embodiment. FIG. 9 is a circuit diagram of an AC-DC converter according to a sixth embodiment. FIG. 10 is a circuit diagram of an AC-DC converter according to a seventh embodiment. FIG. 11 is a circuit diagram of an AC-DC converter according to an eighth embodiment. FIGS. 12A, 12B, and 12C are cross-sectional views showing schematic configurations of DC inductors. FIG. 13A is a waveform diagram showing an example of the waveform of an inductor current when the DC inductor of the present application is used, and FIG. 13B is a waveform diagram showing an example of the waveform of an inductor current of a comparative example.

[0013] [First Embodiment] An AC-DC converter according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a circuit diagram of the AC-DC converter according to the first embodiment. Note that in each embodiment including this embodiment, "same" includes manufacturing errors and characteristic errors.

[0014] 1, the AC-DC converter 10 includes an input filter circuit 20, a power conversion circuit 30, a resonant inductor 40, an isolation transformer 50, rectifier circuits 61 and 62, and a smoothing capacitor Co. The rectifier circuit 61 corresponds to the "first rectifier circuit," and the rectifier circuit 62 corresponds to the "second rectifier circuit."

[0015] (General Configuration of AC-DC Converter 10) The input terminals of the input filter circuit 20 are connected to the output terminals of the three-phase AC power supply. The output terminals of the input filter circuit 20 are connected to the input terminals of the power conversion circuit 30. The output terminals of the power conversion circuit 30 are connected to a series circuit of the resonant inductor 40 and the primary coil 51 of the isolation transformer 50.

[0016] The isolation transformer 50 includes a secondary coil 521 and a secondary coil 522. The secondary coil 521 and the secondary coil 522 are coupled to the primary coil 51 with the same degree of coupling and the same turns ratio. The secondary coil 521 corresponds to the "secondary first coil," and the secondary coil 522 corresponds to the "secondary second coil."

[0017] An output terminal of the secondary coil 521 is connected to a rectifier circuit 61. An output terminal of the secondary coil 522 is connected to a rectifier circuit 62. The rectifier circuits 61 and 62 are connected in parallel. The rectifier circuit 61 corresponds to the "first rectifier circuit," and the rectifier circuit 62 corresponds to the "second rectifier circuit."

[0018] The output terminals of the rectifier circuit 61 and the rectifier circuit 62 are connected to a smoothing capacitor Co. One terminal of the smoothing capacitor Co is the high-side output terminal PoH of the AC-DC converter 10, and the other terminal of the smoothing capacitor Co is the low-side output terminal PoL of the AC-DC converter 10. A load LD is connected between the high-side output terminal PoH and the low-side output terminal PoL.

[0019] (Specific Circuit Configuration of AC-DC Converter 10 ) (Input Filter Circuit 20 ) The input filter circuit 20 includes an inductor 211 , an inductor 221 , an inductor 231 , a capacitor 212 , a capacitor 222 , and a capacitor 232 .

[0020] One terminal of the inductor 211 is connected to a first output terminal of the three-phase AC power supply 80. The other terminal of the inductor 211 is connected to one terminal of the capacitor 212. This node serves as a first output terminal of the input filter circuit 20.

[0021] One terminal of the inductor 221 is connected to the second output terminal of the three-phase AC power supply 80. The other terminal of the inductor 221 is connected to one terminal of the capacitor 222. This node serves as the second output terminal of the input filter circuit 20.

[0022] One terminal of the inductor 231 is connected to the third output terminal of the three-phase AC power supply 80. The other terminal of the inductor 231 is connected to one terminal of the capacitor 232. This node serves as the third output terminal of the input filter circuit 20.

[0023] The other terminal of the capacitor 212, the other terminal of the capacitor 222, and the other terminal of the capacitor 232 are connected together. In this embodiment, the plurality of capacitors 212, 222, and 232 are star-connected, as shown in Fig. 1 for example. However, the plurality of capacitors 212, 222, and 232 may also be delta-connected.

[0024] As a result, inductor 211 and capacitor 212 form a low-pass filter circuit for the output current of the first phase of the three-phase AC. Inductor 221 and capacitor 222 form a low-pass filter circuit for the output current of the second phase of the three-phase AC. Inductor 231 and capacitor 232 form a low-pass filter circuit for the output current of the third phase of the three-phase AC.

[0025] (Power conversion circuit 30) The power conversion circuit 30 includes a switching circuit 311, a switching circuit 312, a switching circuit 321, a switching circuit 322, a switching circuit 331, and a switching circuit 332. Each of the switching circuits 311, 312, 321, 322, 331, and 332 is configured with a plurality of power switching elements and has the same electrical characteristics.

[0026] The switching circuit 311 and the switching circuit 312 are connected in series. A node between the switching circuit 311 and the switching circuit 312 is connected to the first output terminal of the input filter circuit 20.

[0027] The switching circuit 321 and the switching circuit 322 are connected in series. A node between the switching circuit 321 and the switching circuit 322 is connected to the second output terminal of the input filter circuit 20.

[0028] The switching circuit 331 and the switching circuit 332 are connected in series. A node between the switching circuit 331 and the switching circuit 332 is connected to the third output terminal of the input filter circuit 20.

[0029] The terminal of switching circuit 311 opposite to the node side with respect to switching circuit 312, the terminal of switching circuit 321 opposite to the node side with respect to switching circuit 322, and the terminal of switching circuit 331 opposite to the node side with respect to switching circuit 332 are connected. This node serves as a first output terminal of power conversion circuit 30.

[0030] The terminal of switching circuit 312 opposite to the node side relative to switching circuit 311, the terminal of switching circuit 322 opposite to the node side relative to switching circuit 321, and the terminal of switching circuit 332 opposite to the node side relative to switching circuit 331 are connected together. This node serves as a second output terminal of power conversion circuit 30.

[0031] (Isolation Transformer 50) The isolation transformer 50 includes a primary coil 51, a secondary coil 521, and a secondary coil 522. The secondary coil 521 and the secondary coil 522 are magnetically coupled to the primary coil 51.

[0032] The primary coil 51 and the secondary coil 521 form a first transformer. The primary coil 51 and the secondary coil 522 may form a second transformer. In this configuration, the first transformer and the second transformer are configured to suppress magnetic coupling with each other. A configuration in which magnetic coupling is suppressed refers to, for example, a configuration in which each transformer is configured to include a separate magnetic core, and the magnetic cores are arranged apart from each other.

[0033] The degree of coupling between the primary coil 51 and the secondary coil 521 (the degree of coupling of the first transformer) is the same as the degree of coupling between the primary coil 51 and the secondary coil 522 (the degree of coupling of the second transformer). The turns ratio between the primary coil 51 and the secondary coil 521 (the turns ratio of the first transformer) is the same as the turns ratio between the primary coil 51 and the secondary coil 522 (the turns ratio of the second transformer).

[0034] A first terminal PA of the primary coil 51 is connected to a first output terminal of the power conversion circuit 30 through the resonant inductor 40. A second terminal PB of the primary coil 51 is connected to a second output terminal of the power conversion circuit 30. In this embodiment, the resonant inductor 40 is provided separately from the isolation transformer 50, but the leakage inductance of the isolation transformer 50 may be used as the resonant inductor 40.

[0035] The first terminal PC1 and the second terminal PD1 of the secondary coil 521 are connected to the rectifier circuit 61. The first terminal PC2 and the second terminal PD2 of the secondary coil 522 are connected to the rectifier circuit 62.

[0036] (Rectifier Circuit 61, Rectifier Circuit 62) The rectifier circuit 61 and the rectifier circuit 62 are current doubler rectifier circuits (current doubler rectifier circuits) and are connected in parallel.

[0037] The rectifier circuit 61 includes an inductor 611L, an inductor 613L, a switching element 612Q, and a switching element 614Q. The switching elements 612Q and 614Q are power semiconductor switching elements. The inductor 611L and the inductor 613L have the same characteristics. The switching elements 612Q and 614Q have the same characteristics.

[0038] The inductor 611L and the switching element 612Q are connected in series. The inductor 613L and the switching element 614Q are connected in series. The series circuit of the inductor 611L and the switching element 612Q and the series circuit of the inductor 613L and the switching element 614Q are connected in parallel.

[0039] A node ND611 between the inductor 611L and the switching element 612Q (drain terminal) is connected to a first terminal PC1 of the secondary coil 521. A node ND612 between the inductor 613L and the switching element 614Q (drain terminal) is connected to a second terminal PD1 of the secondary coil 521.

[0040] The rectifier circuit 62 includes an inductor 621L, an inductor 623L, a switching element 622Q, and a switching element 624Q. The switching elements 622Q and 624Q are power semiconductor switching elements. The inductors 621L and 623L have the same characteristics, and are the same as the inductors 611L and 613L of the rectifier circuit 61. The switching elements 622Q and 624Q have the same characteristics, and are the same as the switching elements 612Q and 614Q of the rectifier circuit 62.

[0041] The inductor 621L and the switching element 622Q are connected in series. The inductor 623L and the switching element 624Q are connected in series. The series circuit of the inductor 621L and the switching element 622Q and the series circuit of the inductor 623L and the switching element 624Q are connected in parallel.

[0042] A node ND621 between the inductor 621L and the switching element 622Q (drain terminal) is connected to a first terminal PC2 of the secondary coil 522. A node ND622 between the inductor 623L and the switching element 624Q (drain terminal) is connected to a second terminal PD2 of the secondary coil 522.

[0043] The terminal of inductor 611L opposite node ND611, the terminal of inductor 613L opposite node ND612, the terminal of inductor 621L opposite node ND621, and the terminal of inductor 622L opposite node ND622 are connected to each other and to the Hi-side output terminal PoH of the AC-DC converter 10.

[0044] The terminal (source terminal) of switching element 612Q opposite node ND611, the terminal (source terminal) of switching element 614Q opposite node ND612, the terminal (source terminal) of switching element 622Q opposite node ND621, and the terminal (source terminal) of switching element 624Q opposite node ND622 are connected to each other and to the low-side output terminal PoL of the AC-DC converter 10.

[0045] (Smoothing Capacitor Co) The smoothing capacitor Co is connected between the high-side output terminal PoH and the low-side output terminal PoL.

[0046] (Operation of AC-DC Converter 10) The input filter circuit 20 filters the three-phase AC current input from the three-phase AC power supply 80 and outputs the filtered current to the power conversion circuit 30. This removes high-frequency noise and the like contained in the three-phase AC current.

[0047] The power conversion circuit 30 converts the three-phase AC current into a single-phase AC current (primary current) of a predetermined frequency and outputs the converted current. The single-phase AC current is supplied to a primary coil 51 of an isolation transformer 50 via a resonant inductor 40.

[0048] The secondary coil 521 of the isolation transformer 50 is excited by the single-phase AC current (primary current) flowing through the primary coil 51 to output a secondary first current of a predetermined frequency (the same frequency as the primary current).

[0049] The secondary coil 522 of the isolation transformer 50 is excited by the single-phase AC current (primary current) flowing through the primary coil 51 to output a second secondary current of a predetermined frequency (the same frequency as the primary current).

[0050] In this case, the isolation transformer 50 performs voltage conversion according to the turns ratio. The current values ​​of the first secondary current and the second secondary current are determined by the current value of the primary current and the degree of coupling. The first secondary current and the second secondary current have the same polarity and approximately the same current value.

[0051] The rectifier circuit 61 rectifies the secondary-side first current to generate a substantially DC first rectified current I61. The rectifier circuit 62 rectifies the secondary-side second current to generate a substantially DC second rectified current I62.

[0052] Since the rectifier circuit 61 and the rectifier circuit 62 are connected in parallel, a combined current (I61 + I62) of the first rectified current I61 and the second rectified current I62 flows through the load LD connected between the Hi-side output terminal PoH and the Low-side output terminal PoL.

[0053] In this way, the AC-DC converter 10 includes two secondary coils 521 and 522 that are independently coupled to the primary coil 51 of the isolation transformer 50. Furthermore, the AC-DC converter 10 includes a rectifier circuit 61 for the output current of the secondary coil 521 and a rectifier circuit 62 for the output current of the secondary coil 522, and the rectifier circuits 61 and 62 are connected in parallel.

[0054] As a result, when the current supplied to the load ZD from the high-side output terminal PoH and the low-side output terminal PoL (the output current of the AC-DC converter 10) is to be a desired current value, the current value flowing through the rectifier circuit 61 and the current value flowing through the rectifier circuit 62 can be made smaller (specifically, half the output current value) compared to when there is only one rectifier circuit. Therefore, the AC-DC converter 10 can reduce losses in the rectifier circuit 61 and the rectifier circuit 62.

[0055] In particular, AC-DC converter 10 is a large-current AC-DC converter that receives power from a three-phase AC power supply, and in such large-current AC-DC converters, the current value flowing on the secondary side of isolation transformer 50 is large, and losses are likely to be large. However, even when AC-DC converter 10 is designed for large currents, it can suppress the current flowing through rectifier circuits 61 and 62. In other words, AC-DC converter 10 can suppress losses in large output currents and achieve high efficiency.

[0056] In this embodiment, a large current refers to, as an example, a case where the output current (current supplied to the load ZD) of the AC-DC converter 10 is 100 A or more. Although the configuration of the AC-DC converter 10 is applicable even when the output current is less than 100 A, the configuration of the AC-DC converter 10 works more effectively when the output current is 100 A. The output voltage is 100 V or less, for example, 12 V or 48 V. However, for voltages of 48 V or more, the configuration of the second embodiment described below is more effective.

[0057] Furthermore, the AC-DC converter 10 uses current doubler rectifier circuits as the rectifier circuits 61 and 62. This makes it easier to handle a larger current and suppress losses.

[0058] [Second Embodiment] An AC-DC converter according to a second embodiment of the present invention will be described with reference to the drawings. Fig. 2 is a circuit diagram of the AC-DC converter according to the second embodiment. Fig. 3 is a circuit diagram of a rectifier circuit on the secondary side of an isolation transformer of the AC-DC converter according to the second embodiment.

[0059] 2 and 3, the AC-DC converter 10A according to the second embodiment differs from the AC-DC converter 10 according to the first embodiment in that it includes multiple isolation transformers 501-504 and a rectifier circuit 61A and a rectifier circuit 62A. The other configuration of the AC-DC converter 10A is the same as that of the AC-DC converter 10, and descriptions of similar parts will be omitted as appropriate.

[0060] The AC-DC converter 10A includes an input filter circuit 20, a power conversion circuit 30, a resonant inductor 40, a plurality of isolation transformers 501-504, a rectifier circuit 61A, a rectifier circuit 62A, and a smoothing capacitor Co.

[0061] (Multiple isolation transformers 501-504) The isolation transformer 501 includes a primary coil 5011 and a secondary coil 5012. The primary coil 5011 and the secondary coil 5012 are coupled with a predetermined degree of coupling and turns ratio. The isolation transformer 501 corresponds to the "first isolation transformer," the primary coil 5011 corresponds to the "primary first coil," and the secondary coil 5012 corresponds to the "secondary first coil."

[0062] The isolation transformer 502 includes a primary coil 5021 and a secondary coil 5022. The primary coil 5021 and the secondary coil 5022 are coupled with a predetermined degree of coupling and turns ratio. The isolation transformer 502 corresponds to the "third isolation transformer," the primary coil 5021 corresponds to the "primary third coil," and the secondary coil 5022 corresponds to the "secondary third coil."

[0063] The isolation transformer 503 includes a primary coil 5031 and a secondary coil 5032. The primary coil 5031 and the secondary coil 5032 are coupled with a predetermined degree of coupling and turns ratio. The isolation transformer 503 corresponds to the "second isolation transformer," the primary coil 5031 corresponds to the "primary second coil," and the secondary coil 5032 corresponds to the "secondary second coil."

[0064] The isolation transformer 504 includes a primary coil 5041 and a secondary coil 5042. The primary coil 5041 and the secondary coil 5042 are coupled with a predetermined degree of coupling and turns ratio. The isolation transformer 504 corresponds to the "fourth isolation transformer," the primary coil 5041 corresponds to the "fourth primary coil," and the secondary coil 5042 corresponds to the "fourth secondary coil."

[0065] The isolation transformers 501-504 have the same degree of coupling, the isolation transformers 501-504 have the same turns ratio, and the isolation transformers 501-504 have the same coupling polarity.

[0066] Isolation transformer 501, isolation transformer 502, isolation transformer 503, and isolation transformer 504 each include one primary coil and one secondary coil, and are formed using independent magnetic cores. Isolation transformer 501, isolation transformer 502, isolation transformer 503, and isolation transformer 504 are arranged so as not to be coupled to each other.

[0067] A primary coil 5011 of the isolation transformer 501, a primary coil 5021 of the isolation transformer 502, a primary coil 5031 of the isolation transformer 503, and a primary coil 5041 of the isolation transformer 504 are connected in series. More specifically, a first terminal PA1 of the primary coil 5011 is connected to a first output terminal of the power conversion circuit 30 via the resonant inductor 40. A second terminal PB1 of the primary coil 5011 is connected to a first terminal PA2 of the primary coil 5021. A second terminal PB2 of the primary coil 5021 is connected to a first terminal PA3 of the primary coil 5031. A second terminal PB3 of the primary coil 5031 is connected to a first terminal PA4 of the primary coil 5041. A second terminal PB4 of the primary coil 5041 is connected to a second output terminal of the power conversion circuit 30.

[0068] (Rectifier circuit 61A, rectifier circuit 62A) (Rectifier circuit 61A) As shown in Fig. 3, the rectifier circuit 61A includes a high-side rectifier circuit 61H and a low-side rectifier circuit 61L. The high-side rectifier circuit 61H and the low-side rectifier circuit 61L are connected in series. The high-side rectifier circuit 61H and the low-side rectifier circuit 61L are both current doubler rectifier circuits and have the same circuit configuration. The high-side rectifier circuit 61H corresponds to the "first rectifier circuit," and the low-side rectifier circuit 61L corresponds to the "third rectifier circuit."

[0069] (Hi-side rectifier circuit 61H) The Hi-side rectifier circuit 61H includes an inductor 611LH, an inductor 613LH, a switching element 612QH, and a switching element 614QH. The switching elements 612QH and 614QH are power semiconductor switching elements. The inductor 611LH and the inductor 613LH have the same characteristics. The switching elements 612QH and the switching elements 614QH have the same characteristics. The inductor 611LH and the inductor 613LH correspond to a "first inductor," and the switching elements 612QH and the switching elements 614QH correspond to a "first switching element."

[0070] The inductor 611LH and the switching element 612QH are connected in series. The inductor 613LH and the switching element 614QH are connected in series. The series circuit of the inductor 611LH and the switching element 612QH and the series circuit of the inductor 613LH and the switching element 614QH are connected in parallel.

[0071] A node ND6111 between the inductor 611LH and the switching element 612QH (drain terminal) is connected to a first terminal PC1 of the secondary coil 5012. A node ND6121 between the inductor 613LH and the switching element 614QH (drain terminal) is connected to a second terminal PD1 of the secondary coil 5012.

[0072] Smoothing capacitors may be provided between the inductor 611LH and the source terminal of the switching element 612QH and between the inductor 613LH and the source terminal of the switching element 614QH.

[0073] (Low-side rectifier circuit 61L) The low-side rectifier circuit 61L includes an inductor 611LL, an inductor 613LL, a switching element 612QL, and a switching element 614QL. The switching elements 612QL and 614QL are power semiconductor switching elements. The inductor 611LL and the inductor 613LL have the same characteristics. The switching elements 612QL and the switching elements 614QL have the same characteristics. The inductor 611LL and the inductor 613LL correspond to a "third inductor," and the switching elements 612QL and 614QL correspond to a "third switching element."

[0074] The inductor 611LL and the switching element 612QL are connected in series. The inductor 613LL and the switching element 614QL are connected in series. The series circuit of the inductor 611LL and the switching element 612QL and the series circuit of the inductor 613LL and the switching element 614QL are connected in parallel.

[0075] A node ND6112 between the inductor 611LL and the switching element 612QL (drain terminal) is connected to a first terminal PC2 of the secondary coil 5022. A node ND6122 between the inductor 613LL and the switching element 614QL (drain terminal) is connected to a second terminal PD2 of the secondary coil 5022.

[0076] Smoothing capacitors may be provided between the inductor 611LL and the source terminal of the switching element 612QL and between the inductor 613LL and the source terminal of the switching element 614QL.

[0077] (Rectifier Circuit 62A) As shown in Fig. 3, the rectifier circuit 62A includes a high-side rectifier circuit 62H and a low-side rectifier circuit 62L. The high-side rectifier circuit 62H and the low-side rectifier circuit 62L are connected in series. The high-side rectifier circuit 62H and the low-side rectifier circuit 62L are both current doubler rectifier circuits and have the same circuit configuration as the high-side rectifier circuit 61H and the low-side rectifier circuit 62L. The high-side rectifier circuit 62H corresponds to the "second rectifier circuit," and the low-side rectifier circuit 62L corresponds to the "fourth rectifier circuit."

[0078] (Hi-side rectifier circuit 62H) The Hi-side rectifier circuit 62H includes an inductor 621LH, an inductor 623LH, a switching element 622QH, and a switching element 624QH. The switching elements 622QH and 624QH are power semiconductor switching elements. The inductor 621LH and the inductor 623LH have the same characteristics. The switching elements 622QH and the switching elements 624QH have the same characteristics. The inductor 621LH and the inductor 623LH correspond to a "second inductor," and the switching elements 622QH and the switching elements 624QH correspond to a "second switching element."

[0079] The inductor 621LH and the switching element 622QH are connected in series. The inductor 623LH and the switching element 624QH are connected in series. The series circuit of the inductor 621LH and the switching element 622QH and the series circuit of the inductor 623LH and the switching element 624QH are connected in parallel.

[0080] A node ND6211 between the inductor 621LH and the switching element 622QH (drain terminal) is connected to a first terminal PC3 of the secondary coil 5032. A node ND6221 between the inductor 623LH and the switching element 624QH (drain terminal) is connected to a second terminal PD3 of the secondary coil 5032.

[0081] Smoothing capacitors may be provided between the inductor 621LH and the source terminal of the switching element 622QH and between the inductor 623LH and the source terminal of the switching element 624QH.

[0082] (Low-side rectifier circuit 62L) The low-side rectifier circuit 62L includes an inductor 621LL, an inductor 623LL, a switching element 622QL, and a switching element 624QL. The switching elements 622QL and 624QL are power semiconductor switching elements. The inductor 621LL and the inductor 623LL have the same characteristics. The switching elements 622QL and the switching element 624QL have the same characteristics. The inductor 621LL and the inductor 623LL correspond to a "fourth inductor," and the switching elements 622QL and the switching element 624QL correspond to a "fourth switching element."

[0083] The inductor 621LL and the switching element 622QL are connected in series. The inductor 623LL and the switching element 624QL are connected in series. The series circuit of the inductor 621LL and the switching element 622QL and the series circuit of the inductor 623LL and the switching element 624QL are connected in parallel.

[0084] A node ND6212 between the inductor 621LL and the switching element 622QL (drain terminal) is connected to a first terminal PC4 of the secondary coil 5042. A node ND6222 between the inductor 623LL and the switching element 624QL (drain terminal) is connected to a second terminal PD4 of the secondary coil 5042.

[0085] Smoothing capacitors may be provided between the inductor 621LL and the source terminal of the switching element 622QL and between the inductor 623LL and the source terminal of the switching element 624QL.

[0086] (Connection between the rectifier circuit 61A and the rectifier circuit 62A) The rectifier circuit 61A and the rectifier circuit 62A are connected in parallel. Specifically, one terminal (the terminal opposite the node ND6111) of the inductor 611LH of the high-side rectifier circuit 61H of the rectifier circuit 61A, one terminal (the terminal opposite the node ND6121) of the inductor 613LH of the high-side rectifier circuit 61H of the rectifier circuit 61A, one terminal (the terminal opposite the node ND6211) of the inductor 621LH of the high-side rectifier circuit 62H of the rectifier circuit 62A, and one terminal (the terminal opposite the node ND6221) of the inductor 623LH of the high-side rectifier circuit 62H of the rectifier circuit 62A are connected to each other and to the high-side output terminal PoH of the AC-DC converter 10A.

[0087] The terminal (source terminal) of the switching element 612QL of the low-side rectifier circuit 61L of the rectifier circuit 61A opposite to node ND6112, the terminal (source terminal) of the switching element 614QL of the low-side rectifier circuit 61L of the rectifier circuit 61A opposite to node ND6122, the terminal (source terminal) of the switching element 622QL of the low-side rectifier circuit 62L of the rectifier circuit 62A opposite to node ND6212, and the terminal (source terminal) of the switching element 624QL of the low-side rectifier circuit 62L of the rectifier circuit 62A opposite to node ND6222 are connected to each other and to the low-side output terminal PoL of the ACDC converter 10A.

[0088] With this configuration, when the current supplied to the load ZD from the high-side output terminal PoH and the low-side output terminal PoL (the output current of the ACDC converter 10A) is to be a desired current value, the current value flowing through the rectifier circuit 61A and the current value flowing through the rectifier circuit 62A can be made smaller (specifically, half the output current value) compared to when there is only one rectifier circuit. Therefore, the ACDC converter 10A can reduce losses in the rectifier circuit 61A and the rectifier circuit 62A.

[0089] Furthermore, with this configuration, the voltage V61A applied to the rectifier circuit 61A is a composite voltage obtained by adding the voltage V61H applied to the high-side rectifier circuit 61H and the voltage V61L applied to the low-side rectifier circuit 61L. Therefore, the voltages applied to the switching elements 612QL and 614QL of the low-side rectifier circuit 61L and the voltages applied to the switching elements 612QH and 614QH of the high-side rectifier circuit 61H can be lowered relative to the desired output voltage of the AC-DC converter 10A. A low voltage refers to a voltage of 100 V or less, for example.

[0090] This allows the withstand voltage of the switching elements 612QL, 614QL of the low-side rectifier circuit 61L and the switching elements 612QH, 614QH of the high-side rectifier circuit 61H to be lowered. Here, the higher the withstand voltage of the switching elements, the higher the on-resistance value. Therefore, by lowering the withstand voltage, the conduction loss of the switching elements 612QL, 614QL, 612QH, and 614QH can be suppressed.

[0091] Similarly, the voltage V62A applied to the rectifier circuit 62A is a composite voltage obtained by adding the voltage V62H applied to the high-side rectifier circuit 62H and the voltage V62L applied to the low-side rectifier circuit 62L. Therefore, the voltages applied to the switching elements 622QL and 624QL of the low-side rectifier circuit 62L and the voltages applied to the switching elements 622QH and 624QH of the high-side rectifier circuit 62H can be reduced relative to the desired output voltage of the AC-DC converter 10A.

[0092] This allows the withstand voltage of the switching elements 622QL, 624QL of the low-side rectifier circuit 62L and the switching elements 622QH, 624QH of the high-side rectifier circuit 62H to be lowered. Here, the higher the withstand voltage of the switching elements, the higher the on-resistance value. Therefore, by lowering the withstand voltage, the conduction loss of the switching elements 622QL, 624QL, 622QH, and 624QH can be suppressed.

[0093] As a result, the AC-DC converter 10A can suppress losses even when the output current is large, and can also suppress losses even when the output voltage is large, thereby achieving even higher efficiency.

[0094] In this embodiment, the high voltage is, for example, a case where the output voltage of the AC-DC converter 10 is about 48V.

[0095] Furthermore, the AC-DC converter 10A uses multiple transformers in which the primary coil and secondary coil are coupled 1:1 and each is individually formed. This reduces the difference in the degree of coupling between the primary coil and multiple secondary coils, which occurs in a transformer that couples multiple secondary coils to a single primary coil. This reduces the difference in current flowing through the multiple rectifier circuits 61A, 62A, and reduces losses in the rectifier circuits through which relatively large currents flow.

[0096] The term "individually formed" refers to a configuration in which a plurality of transformers are arranged separately from each other, for example.

[0097] In this embodiment, the multiple isolation transformers 501-504 are formed using independent magnetic cores. However, it is also possible to form multiple isolation transformers with reduced magnetic coupling using a single magnetic core, for example, by using an EI core.

[0098] 4A and 4B are diagrams showing the configuration of a circuit module that realizes a circuit from the isolation transformer to the output terminal side in the AC-DC converter according to the second embodiment. Fig. 4A is a plan view looking at the first surface side, and Fig. 4B is a plan view looking at the second surface side.

[0099] As shown in Figures 4A and 4B, the AC-DC converter 10A includes a circuit board 90. The circuit board 90 includes a first surface 91, a second surface 92, and multiple side surfaces 931, 932, 933, and 934. The first surface 91 is a surface at one end of the circuit board 90 in the thickness direction, and the second surface 92 is a surface at the other end of the circuit board 90 in the thickness direction. The side surfaces 931 and 932 are located at both ends of the first surface 91 and the second surface 92 in the first direction (DIR1) and run parallel to each other. The side surfaces 933 and 934 are located at both ends of the first surface 91 and the second surface 92 in the second direction (DIR2) and run parallel to each other.

[0100] (Mounting Mode of First Surface 91) A plurality of isolation transformers 501, 502, 503, and 504, a plurality of inductors 611LH, 613LH, 611LL, 613LL, 621LH, 623LH, 621LL, and 623LL, and a plurality of capacitors Co1, Co2, Co3, and Co4 are mounted on the first surface 91. The plurality of capacitors Co1, Co2, Co3, and Co4 are capacitors that constitute a smoothing capacitor Co.

[0101] The first surface 91 has a first region RE61, a second region RE62, a third region RE63, and a fourth region RE64. The first region RE61 and the second region RE62 are arranged side by side in a first direction (DIR1), and the third region RE63 and the fourth region RE64 are arranged side by side in the first direction (DIR1). The first region RE61 and the third region RE63 are arranged side by side in a second direction (DIR2), and the second region RE62 and the fourth region RE64 are arranged side by side in the second direction (DIR2). That is, the first region RE61, the second region RE62, the third region RE63, and the fourth region RE64 are arranged in a two-dimensional matrix on the first surface 91.

[0102] More specifically, the first region RE61 and the second region RE62 are adjacent to each other in the first direction (DIR1), and are arranged in the order of the second region RE62 and the first region RE61 from the side surface 931 toward the side surface 932. The third region RE63 and the fourth region RE64 are adjacent to each other in the first direction (DIR1), and are arranged in the order of the fourth region RE64 and the third region RE63 from the side surface 931 toward the side surface 932.

[0103] The first region RE61 and the third region RE63 are adjacent to each other in the second direction (DIR2), and are arranged in the order of the first region RE61 and the third region RE63 from the side surface 933 toward the side surface 934. The second region RE62 and the fourth region RE64 are adjacent to each other in the second direction (DIR2), and are arranged in the order of the second region RE62 and the fourth region RE64 from the side surface 933 toward the side surface 934.

[0104] The smoothing capacitor Co (plurality of capacitors Co1, Co2, Co3, and Co4) is arranged between the first region RE61 and the third region RE63 and the side surface 932 in the first direction DIR1.

[0105] An isolation transformer 501, an inductor 611LH, and an inductor 613LH are mounted in the first region RE61. The isolation transformer 501, the inductor 611LH, and the inductor 613LH are mounted side by side in the first direction. The isolation transformer 501 is mounted closer to the side surface 931 than the inductors 611LH and 613LH. The inductors 611LH and 613LH are mounted side by side in the second direction. The inductor 613LH is mounted closer to the side surface 933 than the inductor 611LH.

[0106] The isolation transformer 502, inductor 611LL, and inductor 613LL are mounted in the second region RE62. The isolation transformer 502, inductor 611LL, and inductor 613LL are mounted side by side in the first direction. The isolation transformer 502 is mounted closer to the side surface 931 than the inductors 611LL and 613LL. The inductors 611LL and 613LL are mounted side by side in the second direction. The inductor 613LL is mounted closer to the side surface 933 than the inductor 611LL.

[0107] The third region RE63 is equipped with an isolation transformer 503, an inductor 621LH, and an inductor 623LH. The isolation transformer 503, the inductor 621LH, and the inductor 623LH are mounted side by side in the first direction. The isolation transformer 503 is mounted closer to the side surface 931 than the inductors 621LH and 623LH. The inductors 621LH and 623LH are mounted side by side in the second direction. The inductor 623LH is mounted closer to the side surface 934 than the inductor 621LH.

[0108] The isolation transformer 504, inductor 621LL, and inductor 623LL are mounted in the fourth region RE64. The isolation transformer 504, inductor 621LL, and inductor 623LL are mounted side by side in the first direction. The isolation transformer 504 is mounted closer to the side surface 931 than the inductors 621LL and 623LL. The inductors 621LL and 623LL are mounted side by side in the second direction. The inductor 623LL is mounted closer to the side surface 934 than the inductor 621LL.

[0109] (Mounting Mode of Second Surface 92) The multiple switching elements 612QH, 614QH, 612QL, 614QL, 622QH, 624QH, 622QL, and 624QL are mounted on the second surface 92.

[0110] The switching element 612QH and the switching element 614QH are mounted in a region corresponding to the first region RE61 on the second surface 92. The switching element 614QH is mounted closer to the side surface 933 than the switching element 612QH.

[0111] The switching element 612QL and the switching element 614QL are mounted in a region corresponding to the second region RE62 on the second surface 92. The switching element 614QL is mounted closer to the side surface 933 than the switching element 612QL.

[0112] The switching element 622QH and the switching element 624QH are mounted in a region corresponding to the third region RE63 on the second surface 92. The switching element 624QH is mounted closer to the side surface 934 than the switching element 622QH.

[0113] The switching element 622QL and the switching element 624QL are mounted in a region corresponding to the fourth region RE64 on the second surface 92. The switching element 624QL is mounted closer to the side surface 934 than the switching element 622QL.

[0114] With this configuration, the AC-DC converter 10A forms a circuit consisting of the isolation transformer 501 and the high-side rectifier circuit 61H in the first region RE61, and a circuit consisting of the isolation transformer 502 and the low-side rectifier circuit 61L in the second region RE62. The AC-DC converter 10A forms a circuit consisting of the isolation transformer 503 and the high-side rectifier circuit 62H in the third region RE63, and a circuit consisting of the isolation transformer 504 and the low-side rectifier circuit 62L in the fourth region RE64.

[0115] As a result, in the AC-DC converter 10A, the circuit consisting of the isolation transformer 501 and the high-side rectifier circuit 61H, the circuit consisting of the isolation transformer 502 and the low-side rectifier circuit 61L, the circuit consisting of the isolation transformer 503 and the high-side rectifier circuit 62H, and the circuit consisting of the isolation transformer 504 and the low-side rectifier circuit 62L can be formed with shorter and simpler wiring patterns. Therefore, the AC-DC converter 10A can suppress loss due to the wiring patterns.

[0116] Furthermore, in the AC-DC converter 10A, the isolation transformers and the inductors in each rectifier circuit are mounted on the first surface 91, and the switching elements of each rectifier circuit are mounted on the second surface 92. This allows the wiring patterns of each rectifier circuit to be further simplified and shortened by using wiring patterns (not shown) of interlayer connecting conductors provided on the circuit board 90. Therefore, the AC-DC converter 10A can further reduce losses due to the wiring patterns.

[0117] Furthermore, the multiple high-side rectifier circuits 61H, 62H and low-side rectifier circuits 61L, 62L are formed together in separate regions on the circuit board 90. Therefore, the AC-DC converter 10A can suppress undesired coupling between the high-side rectifier circuits 61H, 62H and the low-side rectifier circuits 61L, 62L.

[0118] Furthermore, the high-side rectifier circuit 61H and the low-side rectifier circuit 61L that constitute the rectifier circuit 61A are aligned in the first direction DIR1 of the circuit board 90, and the high-side rectifier circuit 62H and the low-side rectifier circuit 62L that constitute the rectifier circuit 62A are aligned in the first direction of the circuit board 90. This allows the wiring pattern of the circuit conductor pattern of the rectifier circuit 61A, which is formed on the circuit board 90, to be separated from the wiring pattern of the rectifier circuit 62A.

[0119] Additionally, along the first direction DIR1, the rectifier circuit 61A is arranged in the order of the low-side rectifier circuit 61L and the high-side rectifier circuit 61H, and the rectifier circuit 62A is arranged in the order of the low-side rectifier circuit 62L and the high-side rectifier circuit 62H. This makes it easier to shorten and simplify the wiring pattern. Furthermore, multiple capacitors Co1, Co2, Co3, and Co4 are mounted in a position closest to the side surface 932 in the first direction DIR1. This makes it easier to shorten and simplify the wiring pattern, including the smoothing capacitor Co (multiple capacitors Co1, Co2, Co3, and Co4).

[0120] The low-side rectifier circuit 61L, the high-side rectifier circuit 61H, the low-side rectifier circuit 62L, and the high-side rectifier circuit 62H are connected by a wiring pattern as shown in Fig. 5. Fig. 5 is a diagram showing an example of the wiring pattern of each rectifier circuit. Fig. 5 is a diagram viewed from the first surface 91 side. The thick solid lines in Fig. 5 indicate wiring patterns (conductor patterns), which are formed by linear conductor patterns formed on the first surface 91 or the second surface 92 or interlayer connection conductors extending in the thickness direction of the circuit board 90.

[0121] (Low-side rectifier circuit 61L and Hi-side rectifier circuit 61H) The low-side rectifier circuit 61L and the Hi-side rectifier circuit 61H are arranged on the first surface 91 of the circuit board 90 along the first direction DIR1 in the following order: isolation transformer 502, inductor 611LL and inductor 613LL, isolation transformer 501, inductor 611LH and inductor 613LH, and smoothing capacitor Co (plurality of capacitors Co1, Co2, Co3, Co4).

[0122] In the high-side rectifier circuit 61H, the inductor 611LH and the drain terminal of the switching element 612QH are connected by a wiring pattern 9911. The inductor 613LH and the drain terminal of the switching element 614QH are connected by a wiring pattern 9912.

[0123] The isolation transformer 501 is disposed between the wiring pattern 9911 and the wiring pattern 9912 , with the first terminal PC 1 connected to the wiring pattern 9911 and the second terminal PD 1 connected to the wiring pattern 9912 .

[0124] The inductor 611LH and the inductor 613LH are connected by a wiring pattern 9913. The source terminal of the switching element 612QH and the source terminal of the switching element 614QH are connected by a wiring pattern 9914.

[0125] The positive electrode of the smoothing capacitor Co is connected to the wiring pattern 9913. The wiring pattern 9914 is connected to the wiring pattern 9923 that constitutes the low-side rectifier circuit 61L.

[0126] In the low-side rectifier circuit 61L, the inductor 611LL and the drain terminal of the switching element 612QL are connected by a wiring pattern 9921. The inductor 613LL and the drain terminal of the switching element 614QL are connected by a wiring pattern 9922.

[0127] The isolation transformer 502 is disposed between the wiring pattern 9921 and the wiring pattern 9922 , with the first terminal PC 2 connected to the wiring pattern 9921 and the second terminal PD 2 connected to the wiring pattern 9922 .

[0128] The inductor 611LL and the inductor 613LL are connected by a wiring pattern 9923. The source terminal of the switching element 612QL and the source terminal of the switching element 614QL are connected by a wiring pattern 9924.

[0129] The negative electrode of the smoothing capacitor Co is connected via an inner layer of the substrate to a wiring pattern 9924. The wiring pattern 9923 is connected to a wiring pattern 9914 that constitutes the Hi-side rectifier circuit 61H.

[0130] In this configuration, the wiring pattern consisting of multiple wiring patterns 9911, 9912, 9913, and 9914 in the high-side rectifier circuit 61H is the same as the wiring pattern consisting of multiple wiring patterns 9921, 9922, 9923, and 9924 in the low-side rectifier circuit 61L.

[0131] Therefore, the line lengths of the current loops Ri61L and Ri61H of the low-side rectifier circuit 61L and the high-side rectifier circuit 61H can be made the same. With this configuration, the parasitic inductance formed in each current loop can be made to be approximately the same, and therefore the surge voltages generated in the switching elements can be made to be approximately the same.

[0132] (Low-side rectifier circuit 62L and Hi-side rectifier circuit 62H) The low-side rectifier circuit 62L and the Hi-side rectifier circuit 62H are arranged on the first surface 91 of the circuit board 90 along the first direction DIR1 in the following order: isolation transformer 504, inductor 621LL and inductor 623LL, isolation transformer 503, inductor 621LH and inductor 623LH, and smoothing capacitor Co (plurality of capacitors Co1, Co2, Co3, Co4).

[0133] In the high-side rectifier circuit 62H, the inductor 621LH and the drain terminal of the switching element 622QH are connected by a wiring pattern 9931. The inductor 623LH and the drain terminal of the switching element 624QH are connected by a wiring pattern 9932.

[0134] The isolation transformer 503 is disposed between the wiring pattern 9931 and the wiring pattern 9932 , with the first terminal PC 3 connected to the wiring pattern 9931 and the second terminal PD 3 connected to the wiring pattern 9932 .

[0135] The inductor 621LH and the inductor 623LH are connected by a wiring pattern 9933. The source terminal of the switching element 622QH and the source terminal of the switching element 624QH are connected by a wiring pattern 9934.

[0136] The positive electrode of the smoothing capacitor Co is connected to the wiring pattern 9933. The wiring pattern 9934 is connected to a wiring pattern 9943 that constitutes the low-side rectifier circuit 62L.

[0137] In the low-side rectifier circuit 62L, the inductor 621LL and the drain terminal of the switching element 622QL are connected by a wiring pattern 9941. The inductor 623LL and the drain terminal of the switching element 624QL are connected by a wiring pattern 9942.

[0138] The isolation transformer 504 is disposed between the wiring pattern 9941 and the wiring pattern 9942 , with the first terminal PC 4 connected to the wiring pattern 9941 and the second terminal PD 4 connected to the wiring pattern 9942 .

[0139] The inductor 621LL and the inductor 623LL are connected by a wiring pattern 9943. The source terminal of the switching element 622QL and the source terminal of the switching element 624QL are connected by a wiring pattern 9944.

[0140] The negative electrode of the smoothing capacitor Co is connected via an inner layer of the substrate to a wiring pattern 9944. The wiring pattern 9943 is connected to a wiring pattern 9934 that constitutes the Hi-side rectifier circuit 62H.

[0141] In this configuration, the wiring pattern consisting of multiple wiring patterns 9931, 9932, 9933, and 9934 in the high-side rectifier circuit 62H is the same as the wiring pattern consisting of multiple wiring patterns 9941, 9942, 9943, and 9944 in the low-side rectifier circuit 62L.

[0142] Therefore, the line lengths of the current loops Ri62L and Ri62H in the low-side rectifier circuit 62L and the high-side rectifier circuit 62H can be made the same. With this configuration, the parasitic inductance formed in each current loop can be made to be approximately the same, and therefore the surge voltages generated in the switching elements can be made to be approximately the same.

[0143] Furthermore, the line lengths of the current loops Ri61L in the low-side rectifier circuit 61L, the current loops Ri61H in the high-side rectifier circuit 61H, the current loops Ri62L in the low-side rectifier circuit 62L, and the current loops Ri62H in the high-side rectifier circuit 62H are all the same, which makes it possible to make the surge voltages generated in the switching elements in all of the matching circuits approximately the same.

[0144] Furthermore, the isolation transformers 501-504 are arranged at a distance from each other, which makes it possible to prevent undesirable mutual coupling between the isolation transformers 501-504.

[0145] In addition, by distributing the isolation transformers, inductors, and switching elements to multiple parts, the power loss per component is reduced, and heat distribution is also achieved.

[0146] Furthermore, the plurality of isolation transformers, inductors, and capacitors, which are tall components, are mounted on the first surface 91, and the switching elements, which are low-profile components, are mounted on the second surface 92. This makes it possible to prevent the height of the circuit module from increasing.

[0147] [Third Embodiment] An AC-DC converter according to a third embodiment of the present invention will be described with reference to the drawings. Fig. 6 is a circuit diagram of the AC-DC converter according to the third embodiment.

[0148] 6, the AC-DC converter 10B according to the third embodiment differs from the AC-DC converter 10A according to the second embodiment in the connection pattern of the multiple isolation transformers 501-504. The other configuration of the AC-DC converter 10B is the same as that of the AC-DC converter 10A, and a description of similar parts will be omitted.

[0149] Isolation transformers 501 and 502 are connected in series. Isolation transformers 503 and 504 are connected in series. The series circuit of isolation transformers 501 and 502 and the series circuit of isolation transformers 503 and 504 are connected in parallel.

[0150] With this configuration, the AC-DC converter 10B can achieve the same effects as the AC-DC converter 10A. Furthermore, in the AC-DC converter 10B, the current flowing through the primary coils of the multiple isolation transformers 501-504 is reduced. As a result, especially when the primary current is large, the AC-DC converter 10B can suppress iron loss generated in the isolation transformers 501-504, achieving even higher efficiency.

[0151] [Fourth Embodiment] An AC-DC converter according to a fourth embodiment of the present invention will be described with reference to the drawings. Fig. 7 is a circuit diagram of a rectifier circuit portion of the AC-DC converter according to the fourth embodiment.

[0152] 7, the AC-DC converter 10C according to the fourth embodiment differs from the AC-DC converter 10A according to the second embodiment in that the intermediate potential between the rectifier circuit 61C and the rectifier circuit 62C is short-circuited. The other configuration of the AC-DC converter 10C is the same as that of the AC-DC converter 10A, and therefore a description of the same parts will be omitted.

[0153] The rectifier circuit 61C has a configuration similar to that of the rectifier circuit 61A, and the rectifier circuit 62C has a configuration similar to that of the rectifier circuit 62A.

[0154] A node ND61C between the high-side rectifier circuit 61H and the low-side rectifier circuit 61L in the rectifier circuit 61C and a node ND62C between the high-side rectifier circuit 62H and the low-side rectifier circuit 62L in the rectifier circuit 62C are electrically connected.

[0155] With this configuration, the AC-DC converter 10C can achieve the same effects as the AC-DC converter 10A while matching the source potential of the switching elements constituting the high-side rectifier circuit 61H with the source potential of the switching elements constituting the high-side rectifier circuit 62H. This allows the AC-DC converter 10C to simplify the drive circuits for the switching elements of the high-side rectifier circuits 61H and 62H.

[0156] Fifth Embodiment An AC-DC converter according to a fifth embodiment of the present invention will be described with reference to the drawings. Fig. 8 is a circuit diagram of a rectifier circuit portion of the AC-DC converter according to the fifth embodiment.

[0157] 8, the AC-DC converter 10D according to the fifth embodiment differs from the AC-DC converter 10 according to the first embodiment in that it includes a rectifier circuit 61D and a rectifier circuit 62D. The other configuration of the AC-DC converter 10D is the same as that of the AC-DC converter 10, and a description of similar parts will be omitted.

[0158] The AC-DC converter 10D includes a rectifier circuit 61D and a rectifier circuit 62D.

[0159] The rectifier circuit 61D is a full-wave rectifier circuit (full-bridge type rectifier circuit) that uses four switching elements 611Q, 612Q, 613Q, and 614Q. The rectifier circuit 61D is connected to the secondary coil 521.

[0160] The rectifier circuit 62D is a full-wave rectifier circuit (full-bridge type rectifier circuit) that uses four switching elements 621Q, 622Q, 623Q, and 624Q. The rectifier circuit 62D is connected to the secondary coil 522.

[0161] The rectifier circuit 61D and the rectifier circuit 62D are connected in parallel.

[0162] With this configuration, the AC-DC converter 10D can achieve the same effects as the AC-DC converter 10.

[0163] [Sixth Embodiment] An AC-DC converter according to a sixth embodiment of the present invention will be described with reference to the drawings. Fig. 9 is a circuit diagram of the AC-DC converter according to the sixth embodiment.

[0164] 9, the AC-DC converter 10E according to the sixth embodiment differs from the AC-DC converter 10 according to the first embodiment in that it includes eight isolation transformers 501-508 and four rectifier circuits 61E-64E. The other configuration of the AC-DC converter 10E is the same as that of the AC-DC converter 10, and a description of similar parts will be omitted.

[0165] The AC-DC converter 10E includes a plurality of (eight) isolation transformers 501-508 and a plurality of (four) rectifier circuits 61E-64E.

[0166] Each of the plurality of isolation transformers 501-508 includes a primary coil and a secondary coil, and is formed using an independent magnetic core.

[0167] The primary coils of the multiple isolation transformers 501-504 are connected in series. The primary coils of the multiple isolation transformers 505-508 are connected in series. The series circuit of the primary coils of the multiple isolation transformers 501-504 and the series circuit of the primary coils of the multiple isolation transformers 505-508 are connected in parallel. Note that the primary coils of the multiple isolation transformers 501-508 may be connected in series, or the primary coils of two isolation transformers may be connected in series, and the four series circuits may be connected in parallel.

[0168] The multiple rectifier circuits 61E-64E are connected in parallel. The rectifier circuit 61E is configured from a series circuit of a high-side rectifier circuit 61HE and a low-side rectifier circuit 61LE. The rectifier circuit 62E is configured from a series circuit of a high-side rectifier circuit 62HE and a low-side rectifier circuit 62LE. The rectifier circuit 63E is configured from a series circuit of a high-side rectifier circuit 63HE and a low-side rectifier circuit 63LE. The rectifier circuit 64E is configured from a series circuit of a high-side rectifier circuit 64HE and a low-side rectifier circuit 64LE.

[0169] The multiple high-side rectifier circuits 61HE, 62HE, 63HE, and 64HE have the same circuit configuration as the high-side rectifier circuit 61H according to the second embodiment. The multiple low-side rectifier circuits 61LE, 62LE, 63LE, and 64LE have the same circuit configuration as the low-side rectifier circuit 61L according to the second embodiment.

[0170] With this configuration, the AC-DC converter 10E can reduce the current flowing through each of the rectifier circuits 61E-64E to 1 / 4 of the output current value in order to obtain the desired output current. Also, the AC-DC converter 10E can reduce the voltage applied to the switching elements of the high-side rectifier circuit and the low-side rectifier circuit that make up each of the rectifier circuits 61E-64E to 1 / 2 of the output voltage value.

[0171] As a result, the AC-DC converter 10E can suppress losses even with a larger current. Furthermore, the AC-DC converter 10E can suppress losses even when the voltage becomes relatively high.

[0172] The number of rectifier circuits connected in parallel is not limited to 4. The number of series-connected rectifier circuits constituting each parallel-connected rectifier circuit is also not limited to 2. These can be set appropriately based on the electrical specifications (output current value, output voltage value) required by the AC-DC converter.

[0173] Seventh Embodiment An AC-DC converter according to a seventh embodiment of the present invention will be described with reference to the drawings. Fig. 10 is a circuit diagram of the AC-DC converter according to the seventh embodiment.

[0174] 10 , the AC-DC converter 10F according to the seventh embodiment differs from the AC-DC converter 10 according to the first embodiment in the configuration of the isolation transformer. Other configurations of the AC-DC converter 10F are similar to those of the AC-DC converter 10, and a description of similar parts will be omitted.

[0175] The AC-DC converter 10F includes an isolation transformer 501 and an isolation transformer 502 .

[0176] The isolation transformer 501 includes a primary coil 5011 and a secondary coil 5012. The primary coil 5011 and the secondary coil 5012 are coupled with a predetermined degree of coupling and turns ratio. The primary coil 5011 corresponds to the "primary first coil," and the secondary coil 5012 corresponds to the "secondary first coil."

[0177] The isolation transformer 502 includes a primary coil 5021 and a secondary coil 5022. The primary coil 5021 and the secondary coil 5022 are coupled with a predetermined degree of coupling and turns ratio. The primary coil 5021 corresponds to the "primary second coil," and the secondary coil 5022 corresponds to the "secondary second coil."

[0178] The degree of coupling of isolation transformer 501 is the same as the degree of coupling of isolation transformer 502. The turns ratio between the primary and secondary sides of isolation transformer 501 is the same as the turns ratio between the primary and secondary sides of isolation transformer 502.

[0179] Isolation transformer 501 and isolation transformer 502 are each formed using an independent magnetic core. Isolation transformer 501 and isolation transformer 502 are arranged so as not to be coupled to each other. Isolation transformer 501 corresponds to the "first transformer," and isolation transformer 502 corresponds to the "second transformer."

[0180] A primary coil 5011 of the isolation transformer 501 and a primary coil 5021 of the isolation transformer 502 are connected in series. More specifically, a first terminal PA1 of the primary coil 5011 is connected to a first output terminal of the power conversion circuit 30 via the resonant inductor 40. A second terminal PB1 of the primary coil 5011 is connected to a first terminal PA2 of the primary coil 5021. A second terminal PB2 of the primary coil 5021 is connected to a second output terminal of the power conversion circuit 30.

[0181] A secondary coil 5012 of the isolation transformer 501 is connected to a rectifier circuit 61. A secondary coil 5022 of the isolation transformer 502 is connected to a rectifier circuit 62.

[0182] With this configuration, the AC-DC converter 10F can achieve the same effects as the AC-DC converter 10 according to the first embodiment.

[0183] Furthermore, in AC-DC converter 10F, primary coil 5011 of isolation transformer 501 and primary coil 5021 of isolation transformer 502 are connected in series, so the value of the current flowing through primary coil 5011 is the same as the value of the current flowing through primary coil 5021. The degree of coupling and turns ratio between primary coil 5011 and secondary coil 5012 in isolation transformer 501 are the same as the degree of coupling and turns ratio between primary coil 5021 and secondary coil 5022 in isolation transformer 502.

[0184] Therefore, the current flowing through the secondary coil 5012 (input current to the rectifier circuit 61) and the current flowing through the secondary coil 5022 (input current to the rectifier circuit 62) become the same. As a result, the current value of the first rectified current I61 output from the rectifier circuit 61 becomes the same as the current value of the second rectified current I62 output from the rectifier circuit 62. As a result, the AC-DC converter 10F can output stable DC current and DC voltage.

[0185] Furthermore, the AC-DC converter 10F can suppress undesired magnetic coupling between the isolation transformer 501 and the isolation transformer 502. This can suppress adverse effects on the DC output voltage and DC output current that would otherwise be caused by undesired magnetic coupling between the isolation transformer 501 and the isolation transformer 502. Therefore, the AC-DC converter 10F can output even more stable DC current and DC voltage.

[0186] Eighth Embodiment An AC-DC converter according to an eighth embodiment of the present invention will be described with reference to the drawings. Fig. 11 is a circuit diagram of the AC-DC converter according to the eighth embodiment.

[0187] 11 , the AC-DC converter 10G according to the eighth embodiment differs from the AC-DC converter 10F according to the seventh embodiment in the configuration of the secondary side of the isolation transformer. The other configurations of the AC-DC converter 10G are the same as those of the AC-DC converter 10F, and a description of the same parts will be omitted.

[0188] The AC-DC converter 10G includes a rectifier circuit 61X, a rectifier circuit 62X, a DC inductor 691L, and a DC inductor 692L.

[0189] The rectifier circuit 61X is a full-wave rectifier circuit (full-bridge type rectifier circuit) that uses four switching elements 611Q, 612Q, 613Q, and 614Q. The rectifier circuit 61X is connected to the secondary coil 5012.

[0190] More specifically, the drain terminal of switching element 611Q is connected to the drain terminal of switching element 613. The source terminal of switching element 611Q is connected to the drain terminal of switching element 612Q. The source terminal of switching element 613Q is connected to the drain terminal of switching element 614Q. The source terminal of switching element 612Q is connected to the source terminal of switching element 614Q.

[0191] A node between the source terminal of the switching element 611Q and the drain terminal of the switching element 612Q is connected to a first terminal PC1 of the secondary coil 5012. A node between the source terminal of the switching element 613Q and the drain terminal of the switching element 614Q is connected to a second terminal PD1 of the secondary coil 5012.

[0192] The node between the drain terminal of switching element 611Q and the drain terminal of switching element 613Q is connected to one terminal of series inductor 691L. The other terminal of series inductor 691L is connected to high-side output terminal PoH. The node between the source terminal of switching element 612Q and the source terminal of switching element 614Q is connected to low-side output terminal PoH.

[0193] The rectifier circuit 62X is a full-wave rectifier circuit (full-bridge type rectifier circuit) that uses four switching elements 621Q, 622Q, 623Q, and 624Q. The rectifier circuit 62D is connected to the secondary coil 5022.

[0194] More specifically, the drain terminal of switching element 621Q is connected to the drain terminal of switching element 623. The source terminal of switching element 621Q is connected to the drain terminal of switching element 622Q. The source terminal of switching element 623Q is connected to the drain terminal of switching element 624Q. The source terminal of switching element 622Q is connected to the source terminal of switching element 624Q.

[0195] A node between the source terminal of the switching element 621Q and the drain terminal of the switching element 622Q is connected to a first terminal PC2 of the secondary coil 5022. A node between the source terminal of the switching element 623Q and the drain terminal of the switching element 624Q is connected to a second terminal PD2 of the secondary coil 5022.

[0196] The node between the drain terminal of switching element 621Q and the drain terminal of switching element 623Q is connected to one terminal of series inductor 692L. The other terminal of series inductor 692L is connected to high-side output terminal PoH. The node between the source terminal of switching element 622Q and the source terminal of switching element 624Q is connected to low-side output terminal PoH.

[0197] The DC inductors 691L and 692L have the same configuration, that is, the DC inductors 691L and 692L have the same inductance and the same inductance characteristics.

[0198] With this configuration, the AC-DC converter 10G can achieve the same effects as the AC-DC converter 10F. Furthermore, the AC-DC converter 10G uses a full-wave rectifier circuit and a DC inductor for rectification on the secondary side of the isolation transformer, thereby achieving more stable rectification that is closer to a DC waveform.

[0199] In such a configuration, it is preferable to use inductors having the following configuration for the DC inductors 691L and 692L.

[0200] 12(A), 12(B), and 12(C) are cross-sectional views showing the schematic configuration of a DC inductor. In FIGS. 12(A), 12(B), and 12(C), external connection terminals, wiring conductor patterns to the external connection terminals, and the like are omitted to clearly show characteristic features. Furthermore, in FIGS. 12(A), 12(B), and 12(C), due to differences in structure, the inductors are denoted as DC inductors 69A, 69B, and 69C. For example, when the configuration of DC inductor 69A in FIG. 12(A) is adopted, DC inductors 61 and 62 both have the configuration of DC inductor 69A.

[0201] 12A, a DC inductor 69A includes a magnetic core 690 and a winding conductor 691. The material of the magnetic core 690 is Mn-Zn ferrite or a powder magnetic core. The material of the magnetic core 690 is not limited to these, but is preferably Mn-Zn ferrite or a powder magnetic core. The winding conductor 691 is made of a metal with high conductivity.

[0202] The winding conductor 691 is spiral-shaped and has a central opening OP69.

[0203] The magnetic core 690 houses a winding conductor 691. The magnetic core 690 has a gap GAP69A. The gap GAP69A means a space inside the magnetic core 690 where no magnetic material exists.

[0204] The gap GAP69A is composed of one gap GAPC.

[0205] The gap GAPC is formed in a central opening OP69 of the winding conductor 691. The gap GAPC is flat and is formed so that the flat surface is perpendicular to the axial direction of the winding conductor 691. In other words, the gap GAPC is formed so as to cross the central opening OP69.

[0206] With this configuration, the DC inductor 69A has an air gap GAPC that crosses the central opening OP69 where the magnetic flux density is high. This reduces the effect of manufacturing errors in the magnetic core on the inductance of the DC inductor 69A. In other words, it is possible to reduce the difference in inductance between two DC inductors manufactured in the same way.

[0207] As a result, the inductance difference between the two DC inductors connected to the two rectifier circuits in the secondary circuit of the isolation transformer of the AC-DC converter can be reduced, thereby suppressing current ripple and voltage ripple caused by the inductance difference in the closed loop of the secondary circuit.

[0208] As shown in FIG. 12B, the DC inductor 69B differs from the DC inductor 69A shown in FIG. 12A in that it includes an air gap GAP69B that is composed of three air gaps GAPC.

[0209] The three gaps GAPC are formed in a central opening OP69 of the winding conductor 691. The three gaps GAPC are formed at intervals along the axial direction.

[0210] With this configuration, the DC inductor 69B has an air gap GAP1 near the winding conductor 691 through which current flows, and an air gap GAPC across the central opening OP69 where the magnetic flux density is high, thereby enabling the DC inductor 69B to achieve the same effects as the DC inductor 69A.

[0211] As shown in FIG. 12C, a DC inductor 69C differs from the DC inductor 69A shown in FIG. 12A in that it includes an air gap GAP69C that is composed of two air gaps GAPC.

[0212] One gap GAPC is formed in the central opening OP69 of the winding conductor 691. One gap GAPC is formed in one opening of the winding conductor 691, and the other gap GAPC is formed in the other opening of the winding conductor 691.

[0213] With this configuration, the DC inductor 69C has an air gap GAPC that crosses the central opening OP69 where the magnetic flux density is high, thereby allowing the DC inductor 69C to achieve the same effects as the DC inductor 69A.

[0214] The number of gaps GAPC formed in the central opening OP69 may be four or more.

[0215] The magnetic core can be formed by sintering magnetic powder, and can also be formed by appropriately using an E-type magnetic core or the like.

[0216] FIG. 13A is a waveform diagram showing an example of the waveform of an inductor current when the DC inductor of the present application is used, and FIG. 13B is a waveform diagram showing an example of the waveform of an inductor current of a comparative example.

[0217] The solid line in Fig. 13(A) shows the current value I61L when DC inductor 691L in the circuit shown in Fig. 11 is realized with any one of the structures shown in Fig. 12(A), 12(B), and 12(C). The dotted line in Fig. 13(A) shows the current value I62L when DC inductor 692L in the circuit shown in Fig. 11 is realized with any one of the structures shown in Fig. 12(A), 12(B), and 12(C).

[0218] The solid line in Fig. 13B indicates the current value I61LP when the DC inductor 691L in the circuit shown in Fig. 11 is realized with a gap-free structure. The dotted line in Fig. 13A indicates the current value I62LP when the DC inductor 692L in the circuit shown in Fig. 11 is realized with a gap-free structure.

[0219] The waveforms shown in Figures 13(A) and 13(B) show waveforms when the primary side voltage of the isolation transformer is higher than 500 V, the frequency is about 70 kHz, and the output voltage of the AC-DC converter is set to 50 V.

[0220] 13(A) and 13(B), the use of a DC inductor having the above-described air gap can suppress low-frequency ripple in the current waveform. Although not shown, the voltage ripple of the DC inductor, the drain voltage ripple of the rectifier circuit, and the voltage ripple of the isolation transformer are also suppressed.

[0221] These ripples depend on the difference in inductance between the DC inductors connected to the parallel-connected rectifier circuits in the secondary circuit of the isolation transformer of the AC-DC converter. Specifically, as the difference in inductance between the parallel-connected DC inductors increases, the ripple (voltage ripple) also increases.

[0222] However, by using the DC inductor having the air gap as described above, the inductance difference can be reduced as described above, and the ripple can be suppressed.

[0223] Furthermore, because ripples can be suppressed, there is no need to increase the withstand voltage of the DC inductors 691L and 692L, and it is sufficient to set the withstand voltage required purely for the DC conversion function. As a result, the AC-DC converter including the DC inductors with the above-described air gaps can suppress the conduction loss of the DC inductors 691L and 692L.

[0224] Furthermore, it is not necessary to increase the withstand voltage of each switching element of the rectifier circuits 61 and 62, but rather it is sufficient to set the withstand voltage required purely for the rectification function. As a result, the AC-DC converter equipped with the DC inductor having the air gap described above can suppress the conduction loss of the switching elements of the rectifier circuits 61 and 62.

[0225] Furthermore, the AC-DC converter including the DC inductor having the air gap described above does not require the withstand voltage of the isolation transformer to be undesirably high, and loss occurring in the isolation transformer can also be suppressed.

[0226] It should be noted that the configurations of the above-described embodiments can be combined in part as appropriate, and effects according to each combination can be achieved.

[0227] <1> A power conversion circuit connected to a three-phase AC power supply and outputting a primary current; an isolation transformer including a first primary coil and a second primary coil connected in series to an output side of the power conversion circuit, and a first secondary coil coupled to the first primary coil and a second secondary coil coupled to the second primary coil, the isolation transformer receiving the primary current as an input and outputting a first secondary current and a second secondary current; a first rectifier circuit connected to the first secondary coil and rectifying the first secondary current; a second rectifier circuit connected to the second secondary coil and rectifying the second secondary current; and a smoothing capacitor connected to output terminals of the first rectifier circuit and the second rectifier circuit, wherein the isolation transformer is composed of a first isolation transformer and a second isolation transformer whose magnetic coupling with each other is suppressed, the first primary coil and the second primary coil are connected in series, an AC-DC converter, wherein the first isolation transformer is provided with the primary-side first coil and the secondary-side first coil; the second isolation transformer is provided with the primary-side second coil and the secondary-side second coil; the first rectifier circuit and the second rectifier circuit are connected in parallel; the first rectifier circuit is provided with a first switching element, and a first inductor is connected to the first switching element; and the second rectifier circuit is provided with a second switching element, and a second inductor is connected to the second switching element.

[0228] <2> The AC-DC converter of <1>, further comprising: a third isolation transformer and a fourth isolation transformer separate from the first isolation transformer and the second isolation transformer, the third isolation transformer having suppressed magnetic coupling with each other; the third isolation transformer having a third primary-side coil and a third secondary-side coil; the fourth isolation transformer having a fourth primary-side coil and a fourth secondary-side coil; a third rectifier circuit connected to the third secondary-side coil; and a fourth rectifier circuit connected to the fourth secondary-side coil.

[0229] <3> The AC-DC converter according to <2>, wherein the first rectifier circuit and the third rectifier circuit are connected in series, and the second rectifier circuit and the fourth rectifier circuit are connected in series.

[0230] <4> The AC-DC converter according to <2> or <3>, wherein the first rectifier circuit, the second rectifier circuit, the third rectifier circuit, and the fourth rectifier circuit are each configured as a current doubler rectifier circuit.

[0231] <5> The AC-DC converter according to any one of <2> to <4>, wherein a first node between the first rectifier circuit and the third rectifier circuit and a second node between the second rectifier circuit and the fourth rectifier circuit are electrically connected.

[0232] <6> The AC-DC converter according to any one of <2> to <5>, wherein the primary-side first coil, the primary-side second coil, the primary-side third coil, and the primary-side fourth coil are connected in series.

[0233] <7> The AC-DC converter according to any one of <2> to <5>, wherein the primary-side first coil and the primary-side third coil are connected in series; the primary-side second coil and the primary-side fourth coil are connected in series; and a series circuit of the primary-side first coil and the primary-side third coil and a series circuit of the primary-side second coil and the primary-side fourth coil are connected in parallel.

[0234] <8> The AC-DC converter according to any one of <2> to <7>, comprising: a circuit board having a first surface at one end in a thickness direction and a second surface at the other end in the thickness direction, wherein the first transformer, the second transformer, the third transformer, the fourth transformer, a first inductor of the first rectifier circuit, a second inductor of the second rectifier circuit, a third inductor of the third rectifier circuit, and a fourth inductor of the fourth rectifier circuit are mounted on the first surface, and a first switching element of the first rectifier circuit, a second switching element of the second rectifier circuit, a third switching element of the third rectifier circuit, and a fourth switching element of the fourth rectifier circuit are mounted on the second surface.

[0235] <9> The AC-DC converter of <8>, wherein regions on the circuit board aligned in a first direction parallel to the first surface are defined as a first region and a second region; a region on the board aligned with the first region in a second direction orthogonal to the first direction is defined as a third region, and a region on the board aligned with the second region is defined as a fourth region; the first isolation transformer and the first inductor are mounted on the first surface of the first region; the third isolation transformer and the third inductor are mounted on the first surface of the second region; the second isolation transformer and the second inductor are mounted on the first surface of the third region; the fourth isolation transformer and the fourth inductor are mounted on the first surface of the fourth region; the first switching element is mounted on the second surface of the first region; the third switching element is mounted on the second surface of the second region; the second switching element is mounted on the second surface of the third region; and the fourth switching element is mounted on the second surface of the fourth region.

[0236] <10> The AC-DC converter according to <9>, wherein the third isolation transformer, the third inductor, the first isolation transformer, and the first inductor are arranged in this order on the first surface in the first direction, and the fourth isolation transformer, the fourth inductor, the second isolation transformer, and the second inductor are arranged in this order on the first surface in the first direction.

[0237] <11> The AC-DC converter of <10>, further comprising one or more smoothing capacitors, wherein the third isolation transformer, the third inductor, the first isolation transformer, the first inductor, and the smoothing capacitor are arranged in this order on the first surface of the substrate in the first direction, or the fourth isolation transformer, the fourth inductor, the second isolation transformer, the second inductor, and the smoothing capacitor are arranged in this order on the first surface of the substrate in the first direction.

[0238] <12> The AC-DC converter according to any one of <1> to <11>, wherein the first rectifier circuit and the second rectifier circuit are each configured as a full-bridge rectifier circuit.

[0239] <13> The AC-DC converter according to any one of <1> to <12>, wherein the first inductor and the second inductor include a magnetic core, and the magnetic core contains Mn—Zn ferrite or a powder magnetic core as a material and has an air gap.

[0240] <14> The AC-DC converter according to <13>, wherein the gap is shaped to cross a central opening of the winding conductor.

[0241] <15> The AC-DC converter according to <14>, wherein the portion of the gap that crosses the central opening is provided at a plurality of locations along the axial direction of the winding conductor.

[0242] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G: AC-DC converter 20: Input filter circuit 30: Power conversion circuit 40: Resonant inductor 50: Isolation transformer 51, 5011, 5021, 5031, 5041: Primary coil 61, 61A, 61C, 61D, 61E, 61X, 62, 62A, 62C, 62D, 62E, 62X, 63E, 64E: Rectifier circuit 61H, 61HE, 62H, 62HE, 63HE, 64HE: High-side rectifier circuit 61L, 61LE, 62L, 62LE, 63LE, 64LE: Low-side rectifier circuit 90: Circuit board 91: First surface 92: Second surface 931, 932, 933, 934: Side surfaces 211, 221, 231: Inductors 212, 222, 232: Capacitors 311, 312, 321, 322, 331, 332: Switching circuits 501-508: Isolation transformers 521, 522, 5012, 5022, 5032, 5042: Secondary coils 611L, 611LH, 611LL, 613L, 613LH, 613LL, 621L, 621LH, 621LL, 622L, 623L, 623LH, 623LL: Inductors 691L, 692L: DC inductors 612Q, 612QH, 612QL, 614Q, 614QH, 614QL, 622Q, 622QH, 622QL, 624Q, 624QH, 624QL: Switching elements 9911-9914, 9921-9924, 9931-9934, 9941-9944: Wiring patterns Co: Smoothing capacitor Co1, Co2, Co3, Co4: Capacitors DIR1: First direction DIR2: Second direction I61: First rectified current I62: Second rectified current LD: Load ND611, ND6111, ND6112, ND612, ND6121, ND6122, ND61C, ND621, ND6211, ND6212, ND622, ND6221, ND6222, ND62C: Nodes PA, PA1, PA2, PA3, PA4, PC1, PC2, PC3, PC4: First terminals PB, PB1, PB2, PB3, PB4, PD1, PD2, PD3, PD4: Second terminals PoH: Hi-side output terminal PoL: Low-side output terminal RE61: First region RE62: Second region RE63: Third region RE64: Fourth region Ri61L, Ri61H, Ri62L, Ri62H: Current loopV61A, V61H, V61L, V62A, V62H, V62L: Voltage ZD: Load

Claims

1. a power conversion circuit connected to a three-phase AC power supply and outputting a primary current; an isolation transformer including a primary-side first coil and a primary-side second coil connected in series to an output side of the power conversion circuit, a secondary-side first coil coupled to the primary-side first coil, and a secondary-side second coil coupled to the primary-side second coil, the isolation transformer receiving the primary-side current as an input and outputting a secondary-side first current and a secondary-side second current; a first rectifier circuit connected to the secondary-side first coil and rectifying the secondary-side first current; a second rectifier circuit connected to the secondary-side second coil and rectifying the secondary-side second current; a smoothing capacitor connected to an output terminal of the first rectifier circuit and the second rectifier circuit; Equipped with the isolation transformer is composed of a first isolation transformer and a second isolation transformer whose magnetic coupling with each other is suppressed; the primary side first coil and the primary side second coil are connected in series, the first isolation transformer includes the primary side first coil and the secondary side first coil, the second isolation transformer is provided with the primary side second coil and the secondary side second coil, the first rectifier circuit and the second rectifier circuit are connected in parallel, the first rectifier circuit includes a first switching element, and a first inductor is connected to the first switching element; the second rectifier circuit includes a second switching element, and a second inductor is connected to the second switching element; AC-DC converter.

2. a third isolation transformer and a fourth isolation transformer, which are separate from the first isolation transformer and the second isolation transformer, and which have reduced magnetic coupling with each other; the third isolation transformer includes a primary-side third coil and a secondary-side third coil, the fourth isolation transformer includes a fourth primary coil and a fourth secondary coil, a third rectifier circuit connected to the secondary-side third coil; a fourth rectifier circuit connected to the fourth secondary coil; The AC-DC converter of claim 1 further comprising:

3. the first rectifier circuit and the third rectifier circuit are connected in series; the second rectifier circuit and the fourth rectifier circuit are connected in series; The AC-DC converter according to claim 2 .

4. the first rectifier circuit, the second rectifier circuit, the third rectifier circuit, and the fourth rectifier circuit are each configured as a current doubler rectifier circuit. The AC-DC converter according to claim 2 or 3.

5. a first node between the first rectifier circuit and the third rectifier circuit and a second node between the second rectifier circuit and the fourth rectifier circuit are electrically connected to each other; The AC-DC converter according to claim 2 or 3.

6. the primary-side first coil, the primary-side second coil, the primary-side third coil, and the primary-side fourth coil are connected in series; The AC-DC converter according to claim 2 or 3.

7. the primary-side first coil and the primary-side third coil are connected in series, the primary-side second coil and the primary-side fourth coil are connected in series, a series circuit of the primary-side first coil and the primary-side third coil and a series circuit of the primary-side second coil and the primary-side fourth coil are connected in parallel; The AC-DC converter according to claim 2 or 3.

8. a circuit board having a first surface at one end in a thickness direction and a second surface at the other end in the thickness direction; the first isolation transformer, the second isolation transformer, the third isolation transformer, the fourth isolation transformer, the first inductor of the first rectifier circuit, the second inductor of the second rectifier circuit, the third inductor of the third rectifier circuit, and the fourth inductor of the fourth rectifier circuit are mounted on the first surface; a first switching element of the first rectifier circuit, a second switching element of the second rectifier circuit, a third switching element of the third rectifier circuit, and a fourth switching element of the fourth rectifier circuit are mounted on the second surface; The AC-DC converter according to claim 2 or 3.

9. regions located on the circuit board side by side in a first direction parallel to the first surface are defined as a first region and a second region; In a second direction orthogonal to the first direction, when a region located on the substrate alongside the first region is defined as a third region and a region located on the substrate alongside the second region is defined as a fourth region, the first isolation transformer and the first inductor are mounted on the first surface of the first region; the third isolation transformer and the third inductor are mounted on the first surface of the second region; the second isolation transformer and the second inductor are mounted on the first surface of the third region; the fourth isolation transformer and the fourth inductor are mounted on the first surface of the fourth region; the first switching element is mounted on the second surface of the first region; the third switching element is mounted on the second surface of the second region, the second switching element is mounted on the second surface of the third region, the fourth switching element is mounted on the second surface of the fourth region; 9. The AC-DC converter according to claim 8.

10. the third isolation transformer, the third inductor, the first isolation transformer, and the first inductor are mounted on the first surface in this order in the first direction; the fourth isolation transformer, the fourth inductor, the second isolation transformer, and the second inductor are mounted on the first surface in this order in the first direction; 10. The AC-DC converter according to claim 9.

11. further comprising one or more smoothing capacitors; the third isolation transformer, the third inductor, the first isolation transformer, the first inductor, and the smoothing capacitor are arranged in this order on the first surface of the substrate in the first direction; or the fourth isolation transformer, the fourth inductor, the second isolation transformer, the second inductor, and the smoothing capacitor are arranged in this order on the first surface of the substrate in the first direction; The AC-DC converter according to claim 10.

12. the first rectifier circuit and the second rectifier circuit are each configured as a full-bridge rectifier circuit.

2. The AC-DC converter according to claim 1.

13. the first inductor and the second inductor each include a magnetic core; The magnetic core contains Mn-Zn ferrite or a powder magnetic core as a material and has a gap.

2. The AC-DC converter according to claim 1.

14. the air gap is shaped to cross central openings of the winding conductors of the first inductor and the second inductor; 14. The AC-DC converter according to claim 13.

15. the portion of the gap that crosses the central opening is provided at a plurality of locations along the axial direction of the winding conductor; 15. The AC-DC converter of claim 14.