Switching power supply device

Abstract

Provided is a switching power supply device including: a passive EMI filter including a capacitor connected to an output terminal thereof and a ground GND, respectively; a first soft switching converter connected with the output terminal of the passive EMI filter and connected to ground GND, the first soft switching converter including: a primary side switching circuit connected with the output terminal of the passive EMI filter; an isolation transformer having a primary winding and a secondary winding, the primary winding being connected to the primary-side switching circuit, and a rectifying circuit having a rectifying element, the rectifying circuit being respectively connected to the secondary winding and an output terminal of the switching power supply device; and a first common mode noise reduction path connected between a connection node of the capacitor and the output terminal of the passive EMI filter and a node connecting the dotted terminal of the secondary winding and the rectifying element in the rectifying circuit, where the first common mode noise reduction path includes an impedance.

Description

Technical Field

[0001] The present disclosure relates to a switching power supply device, and more particularly to a switching power supply device for reducing EMI (electromagnetic interference) in a soft switching converter. Background Art

[0002] Soft-switching converters can provide very low switching losses, which is beneficial to the high operating frequency of high power density switch mode power supply design. On the other hand, due to the high operating frequency, the fundamental frequency component and its harmonics may fall into the conducted EMI related range of 150kHz to 30MHz. Since the noise amplitude of low-order harmonics is usually higher, larger EMI filters may be required to suppress the noise level to meet EMI standards. This does not match the high power density goals of power supply design. Summary of the invention

[0003] The present disclosure provides a means to reduce common mode noise by introducing a common mode noise reduction path without relying entirely on passive filters. This suppresses noise levels without requiring larger EMI filters, retaining the high power density target of using high operating frequency converters.

[0004] An aspect of the present disclosure provides a switching power supply device, the switching power supply device comprising:

[0005] A passive EMI filter receives an AC or DC input via an input terminal of the switching power supply device, wherein the passive EMI filter includes a capacitor connected to an output terminal thereof and a ground GND, respectively;

[0006] a first soft switching converter connected to the output terminal of the passive EMI filter and to the ground GND, the first soft switching converter comprising: a primary side switching circuit connected to the output terminal of the passive EMI filter; an isolation transformer having a primary winding and a secondary winding, the primary winding being connected to the primary side switching circuit, wherein the same-name end of the primary winding is connected to a node connecting windings in the primary side switching circuit; a rectifying circuit connected to the secondary winding and the output terminal of the switching power supply device, respectively, and having a rectifying element; and

[0007] A first common-mode noise reduction path is connected between: a connection node between the capacitor and an output terminal of the passive EMI filter, and a node connecting a same-name end of the secondary winding and a rectifying element in the rectifying circuit, wherein the first common-mode noise reduction path includes an impedance.

[0008] According to an embodiment of the present disclosure, the impedance may further include a safety capacitor connected in series in the path.

[0009] According to an embodiment of the present disclosure, the capacitor in the passive EMI filter may include a first capacitor and a second capacitor, and

[0010] The first capacitor may be connected between a first output terminal of the passive EMI filter and a ground GND, and the second capacitor may be connected between a second output terminal of the passive EMI filter and a ground GND.

[0011] According to an embodiment of the present disclosure, the first common mode noise reduction path may be connected to any one of the first capacitor and the second capacitor of the passive EMI filter.

[0012] According to an embodiment of the present disclosure, the passive EMI filter may be composed of one or more stages of filters.

[0013] According to an embodiment of the present disclosure, the switching power supply device may further include at least one second soft switching converter and at least one corresponding second common-mode noise reduction path, wherein:

[0014] The second soft switching converter is connected in parallel with the first soft switching converter between the output terminal of the passive EMI filter and the output terminal of the switching power supply device and has the same configuration as the first soft switching converter, and

[0015] The second common-mode noise reduction path is connected between: a connection node of the capacitor and the output terminal of the passive EMI filter, and a node connecting the same-name end of the secondary winding of the isolation transformer included in the second soft-switching converter and a rectifying element in a rectifying circuit included in the second soft-switching converter, and the second common-mode noise reduction path has the same configuration as the first common-mode noise reduction path.

[0016] According to an embodiment of the present disclosure, the rectification circuit may be a half-bridge rectification circuit, and the secondary winding may have two windings.

[0017] According to an embodiment of the present disclosure, the rectification circuit may be a full-bridge synchronous rectification circuit, and the secondary winding may have one winding.

[0018] According to an embodiment of the present disclosure, the rectifying element in the rectifying circuit may be a diode or a field effect transistor.

[0019] According to an embodiment of the present disclosure, the primary side switching circuit may be a half-bridge configuration.

[0020] According to an embodiment of the present disclosure, the first soft switching converter may further include a filter capacitor connected between output terminals of the power supply device.

[0021] By using the embodiments of the present disclosure, the impedance in the common-mode noise reduction path can be adjusted so that the noise reduction current amplitude is similar to the common-mode noise current to minimize the resulting common-mode noise amplitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other objects, features and advantages will become apparent from the following detailed description of embodiments made with reference to the accompanying drawings.

[0023] Figure 1 An example of the configuration of a switching power supply device according to an embodiment is shown.

[0024] Figure 2 Another example of the configuration of the switching power supply device according to the embodiment is shown.

[0025] Figure 3 It shows that according to the embodiment Figure 1 The equivalent circuit of the switching power supply device shown in FIG.

[0026] Figure 4 The waveforms of a practical implementation of a switching power supply arrangement before the common mode noise reduction path is introduced are shown.

[0027] Figure 5 Waveforms of an actual implementation of a switching power supply device after introducing a common mode noise reduction path according to an embodiment are shown.

[0028] Figure 6 and Figure 7 The EMI measurement results before and after the implementation of the present invention are shown respectively.

[0029] Figure 8 Another example of the configuration of the switching power supply device according to the embodiment is shown. DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0031] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The words "a", "an (kind)" and "the" used herein should also include the meanings of "multiple" and "multiple", unless the context clearly indicates otherwise. In addition, the terms "including", "comprising" and the like used herein indicate the presence of the features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0032] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification, and should not be interpreted in an idealized or overly rigid manner.

[0033] Below, we will refer to Figure 1 The circuit structure of the switching power supply device of the present invention will be described. Figure 1 An example of the configuration of the switching power supply device 1 according to the embodiment is shown.

[0034] The switching power supply device 1 may include a passive EMI filter 101 , a PFC (power factor correction) converter 102 (which may be optional), a soft-switching DC-DC converter 103 , and a common-mode noise reduction path 108 .

[0035] Passive EMI filters are mainly used to suppress electromagnetic interference, especially electromagnetic interference (noise) in electronic and electrical equipment in the circuit. In the embodiments of the present disclosure, the passive EMI filter can be composed of one or more stages of filters. Increasing the number of stages can improve the filter performance. For example, a multi-stage filter can use multiple stages of capacitors and inductors to provide a higher level of attenuation. Figure 1 As shown, the passive EMI filter 101 may have input terminals 101_I1, 101_I2 and output terminals 101_O1, 101_O2, wherein AC or DC input is received at the input terminals 101_I1, 101_I2. The output terminals 101_O1, 101_O2 of the passive EMI filter 101 may be connected to the input terminals 102_I1, 102_I2 of the PFC converter 102, respectively. Here, since the PFC converter 102 may be optional, the output terminals 101_O1, 101_O2 of the passive EMI filter 101 may be directly connected to the input terminals 103_I1, 103_I2 of the soft-switching DC-DC converter 103, respectively.

[0036] In addition, the input terminals 101_I1 and 101_I2 of the passive EMI filter 101 may be regarded as input terminals of the switching power supply device 1 .

[0037] In addition, the passive EMI filter 101 Figure 1 In the example shown, the filter 101 may include a common mode inductor 111, an X capacitor 101C1, an X capacitor 101C2, and Y capacitors 106 and 107. In addition, the filter 101 may include other circuit elements in addition to the above-mentioned circuit elements.

[0038] The X capacitor 101C1 is connected between the input terminals 101_I1 and 101_I2, and the X capacitor 101C2 is connected between the output terminals 101_O1 and 101_O2. The Y capacitor 107 may be connected between the output terminal 101_O1 and the ground GND, and the Y capacitor 106 may be connected between the output terminal 101_O2 and the ground GND. In this embodiment, the connection to the ground GND may be a direct connection or an equivalent connection through an electronic device having a low impedance at a high frequency.

[0039] Figure 1 In the example shown, the common mode inductor 111 may have two coils, namely a first coil and a second coil. The first coil is connected between the input terminal 101_I1 and the output terminal 101_O1. In addition, the second coil is connected between the input terminal 101_I2 and the output terminal 101_O2.

[0040] In order to improve the power factor and reduce the harmonic content of the input current, a PFC converter is mostly used in power electronic equipment to adjust the waveform of the input current to make it "sinusoidal", but this is not necessary and the PFC converter can be omitted. The PFC converter 102 (which can also be called a PFC pre-regulator) has input terminals 102_I1, 102_I2 and output terminals 102_O1, 102_O2. As mentioned above, the input terminals 102_I1, 102_I2 are respectively connected to the output terminals 101_O1, 101_O2 of the passive EMI filter 101. The PFC converter 102 can receive an AC or DC input transmitted via the passive EMI filter 101 as a power input source at its input terminals 102_I1, 102_I2.

[0041] The input terminals 103_I1 and 103_I2 of the soft-switching DC-DC converter 103 are respectively connected to the output terminals 102_O1 and 102_O2 of the PFC converter 102. The soft-switching DC-DC converter 103 can convert the output of the PFC converter 102 into a desired output and simultaneously provide isolation between the input (primary side) and the output (secondary side). In addition, the input terminals 103_I1 and 103_I2 of the soft-switching DC-DC converter 103 can be directly connected to the output terminals 101_O1 and 101_O2 of the passive EMI filter 101, respectively, without passing through the PFC converter.

[0042] like Figure 1 As shown, the soft-switching DC-DC converter 103 may include a primary-side switching circuit 114 , an isolation transformer 105 , an output rectification circuit 109 , and a filter capacitor 112 .

[0043] The primary side switching circuit 114 may be a half-bridge configuration and may include a capacitor 103C1 , a capacitor 103C2 , a capacitor 103C3 , a field effect transistor 103VT1 , a field effect transistor 103VT2 , a winding 103W1 , and a winding 103W2 .

[0044] The capacitor 103C1 is connected between the input terminals 103_I1 and 103_I2 of the soft-switching DC-DC converter 103 .

[0045] The drain of the field effect transistor 103VT1 is connected to the input terminal 103_I1, the source of the field effect transistor 103VT1 is connected to the drain of the field effect transistor 103VT2, and the source of the field effect transistor 103VT2 is connected to the input terminal 103_I2. That is, the field effect transistors 103VT1 and 103VT2 connected in series and the capacitor 103C1 are connected in parallel between the input terminals 103_I1 and 103_I2.

[0046] Similarly, the capacitor 103C2 and the capacitor 103C3 connected in series are also connected in parallel with the capacitor 103C1 between the input terminals 103_I1 , 103_I2 .

[0047] The winding 103W1 and the winding 103W2 are connected in series between a node connecting the source of the field effect transistor 103VT1 and the drain of the field effect transistor 103VT2 and a node connecting the capacitor 103C2 and the capacitor 103C3 .

[0048] The isolation transformer 105 may have a primary winding 104 and a secondary winding 113 .

[0049] One end of the primary winding 104 (eg Figure 1 As shown, the same-named end) is connected to the node connecting the winding 103W1 and the winding 103W2, and the other end of the primary winding 104 is connected to the node connecting the capacitor 103C2 and the capacitor 103C3.

[0050] In this embodiment, the output rectifier circuit 109 may be, for example, a half-bridge rectifier circuit having three input terminals 109_I1 , 109_I2 , and 109_I3 , and two output terminals 109_O1 and 109_O2 .

[0051] In the case where the output rectifying circuit 109 is a half-bridge rectifying circuit, the secondary winding 113 may have two windings 113 a and 113 b , and the two windings 113 a and 113 b may be connected in series.

[0052] The end of the winding 113a not connected to the winding 113b can be connected to the input terminal 109_I1 of the output rectifier circuit 109, and the end of the winding 113b not connected to the winding 113a (such as Figure 1 As shown, the same-name terminal) can be connected to the input terminal 109_I3, and the node connecting the winding 113a and the winding 113b can be connected to the input terminal 109_I2.

[0053] In addition, the output rectifying circuit 109 may further include a rectifying element. In this embodiment, the rectifying element may be a diode, and the output rectifying circuit 109 may include two diodes (ie, a diode 109_D1 and a diode 109_D2).

[0054] The cathode of the diode 109_D1 is connected to the input terminal 109_I1 , and the anode of the diode 109_D1 is connected to the output terminal 109_O2 .

[0055] Similarly, the cathode of the diode 109_D2 is connected to the input terminal 109_I3, and the anode of the diode 109_D1 is connected to the output terminal 109_O2.

[0056] Furthermore, the input terminal 109_I2 of the output rectifying circuit 109 is connected to the output terminal 109_O1.

[0057] The output terminals 109_O1 , 109_O2 of the output rectifying circuit 109 may be connected to the output terminals 103_O1 , 103_O2 of the soft-switching DC-DC converter 103 , respectively.

[0058] Here, the output terminals 103_O1 and 103_O2 of the soft-switching DC-DC converter 103 may be regarded as output terminals of the switching power supply device 1 .

[0059] The filter capacitor 112 may be connected between the output terminals 103_O1 , 103_O2 of the soft-switching DC-DC converter 103 , and a node connecting the filter capacitor 112 and the output terminal 103_O2 may be connected to the ground GND.

[0060] Typically, one of the main sources of common-mode noise current is generated by the switching voltage on the primary winding 104 of the isolation transformer 105, which is coupled to the grounded secondary side through the winding capacitance of the transformer and then returns to the primary side through the ground connection and the Y capacitors 106 and 107 in the passive EMI filter 101. The path of this common-mode noise current will be described later. Figure 3 Shown in.

[0061] Continue to refer Figure 1, one end of the common-mode noise reduction path 108 can be connected to the connection node between the output terminal 101_O2 of the passive EMI filter 101 and the Y capacitor 106 (i.e., connected to the Y capacitor 106), and the other end of the common-mode noise reduction path 108 can be connected to the node connecting the same-name end of the secondary winding 113 of the isolation transformer 105 and the rectifying element in the output rectifying circuit 109 (i.e., connected to the node connecting the same-name end of the winding 113b and the cathode of the diode 109_D2).

[0062] In this embodiment, the common mode noise reduction path 108 may include an impedance 110 .

[0063] Therefore, through the above circuit structure, the common-mode noise reduction path 108 can be connected from the cathode of the diode 109_D2 (due to soft switching, a very good scaled replica of the switching voltage signal of the primary winding 104 is provided at the cathode of the diode 109_D2) through the impedance 110 to the Y capacitor 106, so that the current generated in this path is out of phase with the common-mode noise current.

[0064] Additionally, impedance 110 may include a safety Y capacitor in series in the path to preserve safety isolation requirements, and the impedance may be adjusted so that the noise reduction current amplitude is similar to the common mode noise current to minimize the resulting common mode noise amplitude.

[0065] It should be noted that common mode noise reduction path 108 may be connected to either of the Y capacitors 106 or 107 to provide a similar noise reduction effect.

[0066] Figure 3 FIG. 2 shows an equivalent circuit of the switching power supply device 1 according to the embodiment. Figure 3 In the figure, the clockwise arrow A1 is the common-mode noise current path generated by the primary-side switching circuit (“V primary ” represents a common mode noise current generating source), and the counterclockwise arrow A2 is the noise cancellation current generated by the cancellation source V113 (the switching voltage across the winding 113b).

[0067] Impedance Z110 (“ 110 ”) may be adjusted to control the magnitude of the noise cancellation current to offset the noise current generated by the primary switching circuit (ie, the primary side switching circuit).

[0068] C105 is the winding parasitic capacitance between the primary winding 104 and the secondary winding 113 of the isolation transformer 105. The X capacitors of the input filter and the filter capacitor 112 are considered as short circuits in the EMI relevant frequency range.

[0069] Based on Figure 1 The same concept shown, Figure 2FIG. 2 shows another example of the configuration of the switching power supply device according to the embodiment. Figure 2 As shown, the circuit structure of the switching power supply device 2 is similar to Figure 1 The circuit structure of the switching power supply device 1 is similar to that of the switching power supply device 1, but with an additional soft switching converter 211 operated in parallel for use in higher power applications.

[0070] In this embodiment, the soft switching converter 211 may have a configuration substantially the same as or similar to the structure of the soft switching converter 203 .

[0071] In addition, it should be noted that the rectifying element in the output rectifying circuit of the soft switching converter 203, 211 is not limited to a diode, and it can be any rectifying circuit, including Figure 2 Synchronous rectification elements 209 and 212 (eg, field effect transistors) are shown.

[0072] exist Figure 2 In the example, each soft-switching DC-DC converter is Figure 1 With reference to the description of the common mode noise reduction path 108 in FIG. 1 , common mode noise reduction paths 208 and 213 and impedances 214 and 210 are introduced to achieve the common mode noise reduction purpose as described above.

[0073] Based on Figure 1 and Figure 2 Although the present invention has an embodiment with a single soft-switching DC-DC converter and a dual soft-switching DC-DC converter, the present invention can be extended to any number of soft-switching DC-DC converters.

[0074] Figure 4 Figure 1 shows the waveform of the actual implementation of the switching power supply device before the common mode noise reduction path is introduced. Specifically, Figure 4 Shows Figure 2 The waveform of the switching power supply device 2 before the common mode noise reduction paths 208 and 213 are introduced.

[0075] Channel 1 (C1) is Figure 2 The waveform of the drain of 209 measured relative to ground. Channel 3 (C3) and Channel 4 (C4) are respectively Figure 2 The voltage waveform measured across the Y capacitors 206 and 207 in FIG. 1 reflects the common mode noise current amplitude and waveform.

[0076] Figure 5 1 shows the waveform of the actual implementation of the switching power supply device after the common mode noise reduction path is introduced according to the embodiment. Specifically, Figure 5 The waveforms after implementing the common mode noise reduction paths 208 and 213 are shown. The minimum noise voltage across the Y capacitors 206 and 207 can be obtained by adjusting the impedances 210 and 214. Figure 5 As can be seen, the common-mode noise voltage level is significantly reduced.

[0077] Further, Figure 6 and Figure 7 The EMI measurement results before and after the implementation of the present invention are shown respectively. Figure 6 and Figure 7 , EMI noise levels are significantly reduced, including the fundamental frequency components around 230kHz of the soft-switching converter. For example, Figure 6 The noise level of the fundamental frequency component in is about 78 (dBμV), while Figure 7 The noise level of the fundamental frequency component in is reduced to about 68 (dBμV).

[0078] Figure 8 Another example of the configuration of the switching power supply device according to the embodiment is shown.

[0079] In this embodiment, the circuit elements of the switching power supply device 3 are connected to the reference Figure 1 The circuit elements of the switching power supply device 1 described are basically the same, except that the output rectifier circuit 809 is changed to a full-bridge synchronous rectifier. Accordingly, the secondary winding 813 of the isolation transformer 805 has only one winding.

[0080] like Figure 8 As shown, the output rectifier circuit 809 may include four rectifier elements, which may be diodes or any rectifier circuits. In this embodiment, the rectifier element may be, for example, a field effect transistor.

[0081] The drain of the field effect transistor 809VT1 is connected to the output terminal 809_O1 of the output rectifying circuit 809 , the source of the field effect transistor 809VT1 is connected to the drain of the field effect transistor 809VT2 , and the source of the field effect transistor 809VT2 is connected to the output terminal 809_O2 of the output rectifying circuit 809 .

[0082] Similarly, the drain of field effect transistor 809VT3 is connected to output terminal 809_O1 of output rectification circuit 809 , the source of field effect transistor 809VT3 is connected to the drain of field effect transistor 809VT4 , and the source of field effect transistor 809VT4 is connected to output terminal 809_O2 of output rectification circuit 809 .

[0083] In addition, one end (opposite-name end) of the secondary winding 813 of the isolation transformer 805 can be connected to a node connecting the source of the field effect transistor 809VT1 and the drain of the field effect transistor 809VT2, and the other end (same-name end) of the secondary winding 813 can be connected to a node connecting the source of the field effect transistor 809VT3 and the drain of the field effect transistor 809VT4.

[0084] One end of the common mode noise reduction path 808 is connected to a node connecting the same-name end of the secondary winding 813 and the connection node of the source of the field effect transistor 809VT3 and the drain of the field effect transistor 809VT4, and the other end is connected to the output terminal of the passive EMI filter.

[0085] Similarly, although Figure 8 One soft switching converter is shown, but the present disclosure is not limited thereto, and the number of soft switching converters may be any number. In addition, the primary side switching circuit is also not limited to a half-bridge configuration, and may be any configuration capable of operating with soft switching.

[0086] The embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, but the specific structure is not limited to the above embodiments. References to "one embodiment", "embodiment", etc. in the present disclosure indicate that the described embodiment may include specific features, structures, or characteristics, but not every embodiment must include the specific features, structures, or characteristics. In addition, these phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure, or characteristic is described in conjunction with an embodiment, it should be considered that it is within the knowledge of a person skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments (whether or not explicitly described).

[0087] It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish elements from each other. For example, without departing from the scope of the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0088] Under the premise of not departing from the principle of the inventive concept basically, many changes and modifications can be made to the embodiment. All these changes and modifications are intended to be included in the scope of the inventive concept herein. Therefore, the above-mentioned subject matter should be understood as exemplary and not restrictive, and the examples of the embodiments are intended to cover all these modifications, improvements and other embodiments that fall within the spirit and scope of the inventive concept. Therefore, to the maximum extent permitted by law, the scope of the inventive concept should be determined by the widest permissible interpretation of the present disclosure including the examples of the embodiments and their equivalents, and should not be limited to or restricted to the previous specific embodiments.

Claims

1. A switching power supply device, comprising: A passive EMI filter receives an AC or DC input via an input terminal of the switching power supply device, wherein the passive EMI filter includes a capacitor connected to an output terminal thereof and a ground GND, respectively; A first soft switching converter is connected to the output terminal of the passive EMI filter and to the ground GND, and the first soft switching converter comprises: a primary-side switching circuit connected to the output terminal of the passive EMI filter, an isolation transformer having a primary winding and a secondary winding, the primary winding being connected to the primary-side switching circuit, wherein the same-name end of the primary winding is connected to a node connecting the windings in the primary-side switching circuit, a rectifier circuit connected to the secondary winding and the output terminal of the switching power supply device, respectively, and having a rectifier element; and a first common mode noise reduction path connected between: a connection node between the capacitor and an output terminal of the passive EMI filter, and a node connecting a common-name end of the secondary winding and a rectifying element in the rectifying circuit, Wherein, the first common-mode noise reduction path includes impedance.

2. The switching power supply device according to claim 1, wherein: The impedance also includes a safety capacitor connected in series in the first common-mode noise reduction path.

3. The switchgear device according to claim 1, wherein: The capacitor in the passive EMI filter includes a first capacitor and a second capacitor, and The first capacitor is connected between a first output terminal of the passive EMI filter and a ground GND, and the second capacitor is connected between a second output terminal of the passive EMI filter and a ground GND.

4. The switching power supply device according to claim 3, wherein: The first common mode noise reduction path is connected to any one of the first capacitor and the second capacitor of the passive EMI filter.

5. The switching power supply device according to claim 4, wherein: The passive EMI filter is composed of one or more stages of filters.

6. The switching power supply device according to claim 1, wherein: The first soft-switching converter is connected to an output terminal of the passive EMI filter via a PFC converter.

7. The switching power supply device according to claim 1, further comprising at least one second soft switching converter and corresponding at least one second common mode noise reduction path, wherein: The second soft switching converter is connected in parallel with the first soft switching converter between the output terminal of the passive EMI filter and the output terminal of the switching power supply device and has the same configuration as the first soft switching converter, and The second common-mode noise reduction path is connected between: a connection node of the capacitor and the output terminal of the passive EMI filter, and a node connecting the same-name end of the secondary winding of the isolation transformer included in the second soft-switching converter and a rectifying element in a rectifying circuit included in the second soft-switching converter, and the second common-mode noise reduction path has the same configuration as the first common-mode noise reduction path.

8. The switching power supply device according to claim 1, wherein: The rectification circuit is a half-bridge rectification circuit, and the secondary winding has two windings.

9. The switching power supply device according to claim 1, wherein: The rectification circuit is a full-bridge synchronous rectification, and the secondary winding has one winding.

10. The switching power supply device according to claim 1, wherein: The rectifying element in the rectifying circuit is a diode or a field effect transistor.

11. The switching power supply device according to claim 1, wherein: The primary side switching circuit is a half-bridge configuration.

12. The switching power supply device according to claim 1, wherein: The first soft-switching converter further includes a filter capacitor connected between output terminals of the power supply device.

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