Switching Power Supply Unit

Abstract

To provide a switching power source device in which generation of high-frequency noise due to leakage of a high-frequency common mode current through stray capacitances in respective sections, can be easily and effectively suppressed.SOLUTION: A first inductor element 50a (L50a) is disposed on an output-side power source line 18 side. A second inductor element 50b (L50b) is disposed on an output-side ground line 50b side. Wiring lines of two terminals of an input winding 28a are electrostatically coupled with a frame ground 12 through identical-valued stray capacitances 54a, 54b, respectively. A wiring line of the first inductor element 50a-side input end of an output smoothing circuit 36 is electrostatically coupled with the frame ground 12 through a first stray capacitance 52a (C52a). A wiring line of the second inductor element 50b-side input end of the output smoothing circuit 36 is electrostatically coupled with the frame ground 12 through a second stray capacitance 52b(C52b). C52a L50a≒C52b L50b is established.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a full-bridge switching power supply device. [Background technology]

[0002] Conventionally, there has been a full-bridge switching power supply device 10 as shown in Fig. 8. The switching power supply device 10 has a frame, which is a metal housing or the like. ground The inverter circuit includes an input side power supply line 12, an input side ground line 14 and an input side ground line 16 through which an input voltage Vi is input between the respective phases, and an output side power supply line 18 and an output side ground line 20 through which an output voltage Vo is generated between the respective phases.

[0003] An input interphase capacitor 22, a first arm 24, and a second arm 26 are connected in parallel between the input power supply line 14 and the input ground line 16. The first arm 24 is made up of first and second switching elements 24a and 24b connected in series with each other, with one end of the first switching element 24a connected to the input power supply line 14 and one end of the second switching element 24b connected to the input ground line 16. The second arm 26 is made up of third and fourth switching elements 26a and 26b connected in series with each other, with one end of the third switching element 26a connected to the input power supply line 14 and one end of the fourth switching element 26b connected to the input ground line 16.

[0004] A transformer 28, which isolates the input side circuit from the output side circuit, has an input winding 28a and an output winding 28b, and the input winding 28a is connected between the midpoint of the first arm 24 and the midpoint of the second arm 26.

[0005] An output rectifier circuit 30 that full-wave rectifies the AC voltage generated in the output winding 28b and outputs the rectified voltage is connected to both ends of the output winding 28b of the transformer 28. This output rectifier circuit 30 is a bridge-type rectifier circuit composed of four rectifier elements.

[0006] An output smoothing circuit 36 ​​configured as a low-pass filter including a smoothing inductor 32 and a smoothing capacitor 34 is provided at the output end of the output rectifier circuit 30. The smoothing capacitor 34 is connected between the output power supply line 18 and the output ground line 20, and the smoothing inductor 32 is disposed on the side of the output power supply line 18. The output smoothing circuit 36 ​​smoothes the rectified voltage output by the output rectifier circuit 30, and generates an output voltage Vo across the smoothing capacitor 34.

[0007] The input power line 14 is protectively grounded to the frame ground 12 by an input ground capacitor 38, and the input ground line 16 is protectively grounded to the frame ground 12 by an input ground capacitor 40. Similarly, the output power line 18 is protectively grounded to the frame ground 12 by an output ground capacitor 42, and the output ground line 20 is protectively grounded to the frame ground 12 by an output ground capacitor 44.

[0008] 8 also shows a stray capacitance 46, which is not an actual circuit component. The stray capacitance 46 is a capacitance between a wiring line to which one input end of the output smoothing circuit 36 ​​(one end of the smoothing inductor 32) is connected and a frame. ground 12 is a capacitance formed by electrostatic coupling.

[0009] Furthermore, as a prior art partially related to the present invention, there is a half-bridge type switching power supply disclosed in FIG. 9 of Patent Document 1. This switching power supply is different from the switching power supply device 10 in the configuration of the main switching element and the input winding on the input side and the configuration of the protective ground, but the configurations of the output rectifier circuit and the output smoothing circuit connected to the output winding are almost the same. A characteristic point is that a common mode choke coil (a pair of inductor elements having the same number of turns and magnetically coupled to the same polarity) is inserted between the output rectifier circuit and the output smoothing circuit. This common mode choke coil is intended to suppress the common mode current caused by the recovery current of the diode of the output rectifier circuit, and does not function as a smoothing inductor for smoothing the rectified voltage output by the output rectifier circuit to generate the output voltage Vo. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 7-23562 Summary of the Invention [Problem to be solved by the invention]

[0011] In the conventional switching power supply device 10, the output side circuit is connected to the frame through the stray capacitance 46. ground 12, there is a problem in that a high frequency common mode current leaks into the input power supply, generating large high frequency noise such as input feedback noise that feeds back to the input power supply and output ripple noise that is transmitted to the load together with the output voltage Vo.

[0012] 9(a) and (b) are high-frequency equivalent circuits showing the flow of common-mode current. The capacitance C46 of the stray capacitance 46 is, for example, several tens of pF to several hundreds of pF, which is sufficiently smaller than the capacitance C34 of the smoothing capacitor 34 and the capacitances C42, C44 of the output-side grounded capacitors 42, 44. Therefore, in the high-frequency band, the voltages across the smoothing capacitor 34 and the output-side grounded capacitors 42, 44 can be considered to be almost zero volts, and the voltages across the output-side power supply line 18 and the output-side ground Line 20 is essentially the frame ground It becomes the same potential as 12 (stable potential).

[0013] The noise source that generates the common mode current Is is the voltage Vs generated across the smoothing inductor 32. The waveform of the voltage Vs shown in Fig. 9(c) is a waveform drawn based on the stable potential side, and this voltage Vs causes positive and negative common mode currents Is (Is ≒ ω·C46·Vs) to flow from the output side circuit to the frame through the stray capacitance 46, as shown in Figs. 9(a) and 9(b). ground Leaked on 12.

[0014] This common mode current Is cannot be suppressed much even if the common mode choke coil of Patent Document 1 is added to the α section between the output rectifier circuit 30 and the output smoothing circuit 36. This is because inserting a common mode choke coil in the α section does not increase the impedance of the path through which the common mode current Is flows.

[0015] In order to make the explanation easier to understand, in Fig. 9(a) and (b), the common mode current Is flowing through the stray capacitance 46 is depicted as flowing entirely into the output-side grounded capacitor 42, but in reality, it is considered that the common mode current Is also flows into the output-side grounded capacitor 44 and the input-side grounded capacitors 38 and 40. ground If a common mode current Is leaks into 12, input feedback noise, output ripple noise, and the like will occur through a complex mechanism.

[0016] Furthermore, in the input side circuit of the switching power supply device 10, the voltages across the main switches 24a, 24b, 26a, and 26b serve as a noise source, and a large common mode current may leak through a floating capacitance other than the floating capacitance 46, causing further increase in high frequency noise, so some kind of measure was required.

[0017] The present invention has been made in view of the above-mentioned background art, and has an object to provide a switching power supply device that can easily and effectively suppress the generation of high-frequency noise caused by leakage of high-frequency common mode current through stray capacitance of each component. [Means for solving the problem]

[0018] The present invention relates to a frame groundan input side power supply line and an input side ground line through which an input voltage is input between the phases, an output side power supply line and an output side ground line through which an output voltage is generated between the phases, an input interphase capacitor connected between the input side power supply line and the input side ground line, a first arm consisting of first and second switching elements connected in series with each other, one end of the first switching element connected to the input side power supply line and one end of the second switching element connected to the input side ground line, a second arm consisting of third and fourth switching elements connected in series with each other, one end of the third switching element connected to the input side power supply line and one end of the fourth switching element connected to the input side ground line, input windings insulated from each other, an output rectifier circuit that full-wave rectifies an AC voltage generated in the output winding and outputs a rectified voltage; an output smoothing circuit that is a low-pass filter composed of a smoothing inductor and a smoothing capacitor connected to an output end of the output rectifier circuit, both ends of the smoothing capacitor are connected between the output side power supply line and the output side ground line, and that smooths the rectified voltage to generate the output voltage; an input side grounding capacitor that protectively grounds at least one of the input side power supply line and the input side ground line to the frame ground; and an output side grounding capacitor that protectively grounds at least one of the output side power supply line and the output side ground line to the frame ground, the smoothing inductor is composed of first and second inductor elements, the first inductor element being disposed on the output power supply line side, and the second inductor element being disposed on the output ground line side, The wiring line to which the two terminals of the input winding are connected is Third and fourth to ground They are electrostatically coupled through stray capacitance, the capacitance values ​​of the third and fourth stray capacitances are set to be equal to each other based on a positional relationship between the wiring line serving as one electrode of the stray capacitance and the frame ground serving as the other electrode of the stray capacitance, The wiring line to which the input end of the output smoothing circuit on the side of the first inductor element is connected is groundthrough a first stray capacitance, The wiring line to which the input end of the output smoothing circuit on the side of the second inductor element is connected is ground through a second stray capacitance, a capacitance value of the first and second stray capacitances is set by a positional relationship between the wiring line serving as one electrode of the stray capacitance and the frame ground serving as the other electrode of the stray capacitance; This is a full-bridge type switching power supply device in which the product of the inductance value of the first inductor element and the capacitance value of the first stray capacitance is set to be equal to the product of the inductance value of the second inductor element and the capacitance value of the second stray capacitance.

[0019] The first and second inductor elements may be formed by a pair of windings magnetically coupled via one magnetic core, and the pair of windings may have the same number of turns and be magnetically coupled with opposite polarity. The output rectifier circuit is preferably a bridge-type rectifier circuit composed of four rectifier elements. In addition, an input rectifier / smoothing circuit that rectifies and smoothes a commercial AC voltage to generate the input voltage may be provided in front of the input power line and the input ground line, and the input ground capacitor may be configured to protectively ground at least one of the input power line and the input ground line to the frame ground via the input rectifier / smoothing circuit. Effect of the Invention

[0020] The switching power supply device of the present invention is a full-bridge switching power supply device, and a common mode current (a common mode current generated by a voltage across both ends of a smoothing inductor or a switching element as a noise source) flows through the frame via a floating capacitance. ground Therefore, the high-frequency current leaking into the output terminals (high-frequency current leaking into the output terminals) can be made very small in appearance, and the generation of high-frequency noise such as input feedback noise and output ripple noise can be easily and effectively suppressed. [Brief description of the drawings]

[0021] [Figure 1] 1 is a circuit diagram showing an embodiment of a switching power supply device of the present invention; [Diagram 2]4 is a high-frequency equivalent circuit showing the flow of a common-mode current caused by an output side circuit in the switching power supply device of this embodiment. [Diagram 3] 4A and 4B are high-frequency equivalent circuits showing the flow of common-mode current caused by an input-side circuit in the switching power supply device of this embodiment. [Figure 4] 4 is a time chart showing voltage waveforms of noise sources in each portion of the switching power supply device of this embodiment. [Diagram 5] FIG. 2 is a circuit diagram showing a first modified example of the switching power supply device of the embodiment. [Figure 6] FIG. 11 is a circuit diagram showing a second modified example of the switching power supply device of the embodiment. [Figure 7] FIG. 11 is a circuit diagram showing a third modified example of the switching power supply device of the embodiment. [Figure 8] FIG. 1 is a circuit diagram showing a conventional switching power supply device. [Figure 9] 1A and 1B are high-frequency equivalent circuits showing the flow of common-mode current caused by an output-side circuit in a conventional switching power supply device, and FIG. 1C is a time chart showing the voltage waveform of a noise source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] An embodiment of a switching power supply device of the present invention will now be described with reference to Figures 1 to 4. Here, components similar to those of the conventional switching power supply device 10 are given the same reference numerals and descriptions thereof will be omitted.

[0023] 1, a switching power supply 48 of this embodiment is a full-bridge switching power supply. It has many things in common with the conventional switching power supply 10, but what is distinctive is that the conventional smoothing inductor 32 of the output smoothing circuit 36 ​​is replaced with a smoothing inductor 50 composed of first and second inductor elements 50a and 50b, with the first inductor element 50a being arranged on the output side power supply line 18 side and the second inductor element 50b being arranged on the output side ground line 20 side.

[0024] The first and second inductor elements 50a, 50b are formed by a pair of windings that are magnetically coupled to each other via one magnetic core, and the pair of windings have the same number of turns and are magnetically coupled to each other with opposite polarity. Therefore, the inductance values ​​L50a, L50b of the first and second inductor elements 50a, 50b, that is, the effective inductance values ​​L50a, L50b when smoothing the rectified voltage output by the output rectifier circuit 30, are equal to each other (L50a ≈ L50b).

[0025] 1 also shows four stray capacitances 52a, 52b, 54a, and 54b that are not actual circuit components. The first stray capacitance 52a is a capacitance formed by electrostatic coupling between the wiring line to which the input end of the output smoothing circuit 36 ​​on the side of the first inductor element 50a is connected and the frame ground 12. The second stray capacitance 52b is a capacitance formed by electrostatic coupling between the wiring line to which the input end of the output smoothing circuit 36 ​​on the side of the second inductor element 50b is connected and the frame ground 12. The capacitance values ​​C52a and C52b of the first and second stray capacitances 52a and 52b are set to be equal to each other (C52a ≈ C52b) by devising a structural design.

[0026] The third stray capacitance 54a is formed between the wiring line to which one end of the input winding 28a of the transformer 28 on the side of the first arm 24 is connected and the frame. ground The fourth stray capacitance 54b is a capacitance formed by electrostatic coupling between the wiring line to which one end of the input winding 28a of the transformer 28 on the second arm 24 side is connected and the frame 12. ground 12. The capacitance values ​​C54a and C54b of the third and fourth stray capacitances 54a and 54b are set to be equal to each other (C54a≈C54b) by devising a structural design.

[0027] The stray capacitances 52a, 52b, 54a, and 54b serve as paths through which unnecessary current leaks from the power supply circuit toward the frame ground 12, that is, paths through which common mode current flows that can cause input feedback noise and output ripple noise.

[0028] First, the common mode current caused by the output side circuit will be described based on the high frequency equivalent circuit in Figure 2 (a) and (b). The capacitance values ​​C52a, C52b of the first and second stray capacitances 52a, 52b are, for example, several tens of pF to several hundreds of pF, which is sufficiently smaller than the capacitance value C34 of the smoothing capacitor 34 and the capacitance values ​​C42, C44 of the output side ground capacitors 42, 44. Therefore, in the high frequency band, the voltages across the smoothing capacitor 34 and the output side ground capacitors 42, 44 can be considered to be almost zero volts, and the output side power supply lines 18, 20 are substantially frame ground It becomes the same potential as 12 (stable potential).

[0029] In the case of the output side circuit, the noise source that generates the common mode current is the voltages Vs1 and Vs2 that are generated at both ends of the first and second inductor elements 50a and 50b, respectively. The waveforms of the voltages Vs1 and Vs2 shown in Fig. 4 are waveforms drawn based on the stable potential side, and since L50a ≒ L50b in this case, the waveforms have the same wave shape but are inverted in positive and negative directions.

[0030] A common mode current Is1 (Is1 ≈ ω·C52a·Vs1) with the voltage Vs1 as a noise source flows from the output side circuit to the frame through the first stray capacitance 52a as shown in FIGS. 2(a) and 2(b). ground In addition, a common mode current Is2 (Is2 ≒ ω·C52b·Vs2) caused by the voltage Vs2 as a noise source flows from the power supply circuit side through the second stray capacitance 52b to the frame 12 in the positive and negative directions. ground12 flows in the negative and positive directions.

[0031] The characteristic here is that C52a ≒ C52b and Vs1 ≒ -Vs2, so the relationship between the common mode currents Is1 and Is2 is Is1 ≒ -Is2, and they cancel each other out. In other words, although common mode currents Is1 and Is2 are generated due to the voltages Vs1 and Vs2, they flow in the opposite directions and cancel each other out, and there is no apparent frame current. ground Since there is no common mode current leaking to 12, high frequency noise caused by the voltages Vs1 and Vs2 is effectively suppressed.

[0032] Next, the common mode current caused by the input side circuit will be described based on the high frequency equivalent circuit of Figures 3(a) and (b). The capacitance values ​​C54a, C54b of the third and fourth stray capacitances 54a, 54b are, for example, several tens of pF to several hundreds of pF, which is sufficiently smaller than the capacitance value C22 of the input interphase capacitor 22 and the capacitance values ​​C38, C40 of the input side ground capacitors 38, 40. Therefore, in the high frequency band, the voltages across the input interphase capacitor 22 and the input side ground capacitors 38, 40 can be considered to be almost zero volts, and the input side power supply lines 14, 16 are substantially frame ground It becomes the same potential as 12 (stable potential).

[0033] In the case of the input side circuit, the noise sources that generate the common mode current are the voltages Vp1, Vp2, Vp3, and Vp4 that are generated at both ends of the first to fourth switching elements 24a, 24b, 26a, and 26b, respectively. The waveforms of the voltages Vp1, Vp2, Vp3, and Vp4 shown in Fig. 4 are waveforms drawn based on the stable potential side, and the voltages Vp1 and Vp4 have the same wave shape but with the positive and negative polarities reversed to each other, and the voltages Vp2 and Vp3 also have the same wave shape but with the positive and negative polarities reversed to each other.

[0034] The operation of the noise sources Vp1 and Vp4 can be explained by the diagram of switch SW being flipped to contact A, as shown in Fig. 3(a). The common mode current Ip1 (Ip1 ≒ ω·C54a·Vp1) with the noise source voltage Vp1 flows through the frame. groundA common mode current Ip4 (Ip4≒ω·C54b·Vp4) having a voltage Vp4 as a noise source flows from the input circuit to the frame through the fourth stray capacitance 54b. ground It flows in the direction towards 12.

[0035] The characteristic here is that C54a ≒ C54b and Vp1 ≒ -Vp4, so the relationship between the common mode currents Ip1 and Ip4 is Ip1 ≒ -Ip4, and they cancel each other out. In other words, although the common mode currents Ip1 and Ip4 are generated due to the voltages Vp1 and Vp4, they flow in the opposite directions and cancel each other out, and there is no apparent frame current. ground Since there is no common mode current leaking to 12, high frequency noise caused by the voltages Vp1 and Vp4 is effectively suppressed.

[0036] In addition, the operation of the noise sources Vp2 and Vp3 can be explained by the diagram in which the switch SW is set to contact B, as shown in Fig. 3(b). The common mode current Ip3 (Ip3 ≒ ω·C54b·Vp3) with the noise source Vp3 flows through the frame. ground A common mode current Ip2 (Ip2≈ω·C54a·Vp2) having a voltage Vp2 as a noise source flows from the input circuit to the frame through the third stray capacitance 54a. ground It flows in the direction towards 12.

[0037] The characteristic here is that C54a ≒ C54b and Vp2 ≒ -Vp3, so the relationship between the common mode currents Ip2 and Ip3 is Ip2 ≒ -Ip3, and they cancel each other out. In other words, although the common mode currents Ip2 and Ip3 are generated due to the voltages Vp2 and Vp3, they flow in the opposite directions and cancel each other out, and there is no apparent frame current. ground Since there is no common mode current leaking to 12, the generation of high frequency noise due to the voltages Vp2 and Vp3 is effectively suppressed.

[0038] As described above, according to the switching power supply device 48, the common mode current (which flows through the frame via stray capacitance) caused by the voltages across the smoothing inductor 50 and the switching elements 24a, 24b, 26a, and 26b as noise sources is ground This makes it possible to make the apparent high-frequency current (high-frequency current leaking into the input) very small, and effectively suppresses high-frequency noise such as input feedback noise and output ripple noise.

[0039] The switching power supply device of the present invention is not limited to the above embodiment. For example, a switching power supply device 48 is provided with two output side ground capacitors 42 and 44, and both the output side power supply line 18 and the output side ground line 20 are frame-connected. ground However, it may be possible to change to a configuration in which only one of the output side power supply line 18 and the output side ground line 20 is protectively grounded, and substantially the same effects can be obtained.

[0040] The switching power supply device 48 described above is provided with two input-side ground capacitors 38 and 40, and both the input-side power supply line 14 and the input-side ground line 16 are frame-coupled. ground However, it may be possible to change to a configuration in which only one of the input side power supply line 14 and the input side ground line 16 is protectively grounded, and substantially the same effects can be obtained.

[0041] In the explanation of the output side circuit of the switching power supply device 48, it was stated that the capacitance values ​​of the first and second stray capacitances 52a, 52b are equal (C52a ≒ C52b) and the inductance values ​​of the first and second inductor elements 50a, 50b are equal (L50a ≒ L50b), but "equal" does not mean that the values ​​are strictly the same. When the switching power supply device 48 is actually mass-produced, variations will occur due to various factors, but it is possible to manage the width of each variation within a range of about ±10 to 15%, which makes it possible to cancel out most of the common mode currents Is1 and Is2 and significantly reduce high frequency noise.

[0042] In the explanation of the input side circuit of the switching power supply device 48, it was stated that the capacitance values ​​of the third and fourth stray capacitances 54a and 54b are equal (C54a≒C54b), the voltages across the first and fourth switching elements 24a and 26b have the same waveform (Vp1≒Vp4), and the voltages across the second and third switching elements 24b and 26a have the same waveform (Vp2≒Vp3), but "equal" and "same" do not mean that the values ​​are strictly the same. In this respect, it is possible to manage the width of each variation within a range of about ±10 to 15%, as described above, and this allows most of the common mode currents Ip1 and Ip4 to be offset, and also allows most of the common mode currents Ip2 and Ip3 to be offset, thereby significantly reducing high frequency noise.

[0043] The above switching power supply 48 can be modified to a configuration like a switching power supply 48(1) shown in Fig. 5. In the switching power supply 48(1), a capacitor 60 for preventing biased magnetism of the transformer 28 and an inductor 62 for soft switching of the switching elements 24a, 24b, 26a, and 26b are inserted in a position midway along the wiring pattern connecting one end of the input winding 28a and the second arm 26. The capacitor 60 and the inductor 62 may be inserted on the side of the wiring pattern connecting the input winding 28a and the first arm 24. This type of capacitor 60 and inductor 62 are set to values ​​that can be ignored in the above-mentioned high-frequency equivalent circuit (values ​​at which the voltage across both ends can be considered to be almost zero volts), and therefore do not interfere with the operation aimed at by the present invention.

[0044] The above switching power supply 48 can be modified to have a configuration like that of a switching power supply 48(2) shown in Fig. 6. The switching power supply 48 is a DC input power supply, whereas the switching power supply 48(2) is an AC input power supply, and an input rectifying and smoothing circuit 64 that rectifies and smoothes a commercial AC voltage to generate an input voltage Vi is provided in front of the input power line 14 and the input ground line 16. The input rectifying and smoothing circuit 64 can be composed of, for example, a bridge-type input rectifying circuit 64a composed of four diodes, and an input smoothing circuit 64b (which also serves as the above-mentioned input interphase capacitor 22) composed of a capacitor. The input smoothing circuit 64b may be replaced with a known chopper circuit for improving power factor.

[0045] Another difference with the switching power supply 48(2) is that the input-side ground capacitors 38, 40 are connected upstream of the input rectifying and smoothing circuit 64, and the input-side power supply line 14 and the input-side ground line 16 are protectively grounded to the frame ground 12 via the input rectifying and smoothing circuit 64 (input rectifying circuit 64a). However, even with this configuration, substantially the same effects can be obtained.

[0046] The above switching power supply device 48 can be modified to a configuration like a switching power supply device 48(3) shown in FIG. 7. In the case of the switching power supply device 48 of the above embodiment, the first and second inductor elements 50a, 50b constituting the smoothing inductor 50 are formed by a pair of windings magnetically coupled via one magnetic core, and the pair of windings have the same number of turns and are magnetically coupled with opposite polarity. In other words, the first and second inductor elements 50a, 50b are provided as one circuit component on the condition that the inductance values ​​L50a, L50b are set to the same value. In contrast, in the case of the switching power supply device 48(3), the first and second inductor elements 50a, 50b are provided as two independent circuit components, and each inductance value L50a, L50b can be freely set.

[0047] In the switching power supply 48, in order to neatly cancel out the common mode current Is1 (Is1≈ω·C52a·Vs1) and the common mode current Is2 (Is2≈ω·C52b·Vs2) of the output side circuit, the structure is designed to set C52a≈C52b under the condition of Vs1≈-Vs2 (L50a≈L50b). For example, the output rectifier circuit 30 is a bridge-type rectifier circuit in order to make it easier to set C52a≈C52b, that is, to make it easier to arrange the wiring lines and surrounding structures connected to the first and second inductor elements 50a and 50b in a balanced manner. However, if it is difficult to set C52a≈C52b for some reason, it is preferable to change to the configuration of the switching power supply 48(3) shown in FIG. 7.

[0048] In the switching power supply device 48(3), L50a and L50b can be set to different values, so that the amplitude ratio of Vs1 and Vs2 can be changed to match the ratio of C52a and C52b by utilizing the relationship Vs1 / Vs2≒L50a / L50b. Specifically, by adjusting L50a and L50b to satisfy the relationship C52a·L50a≒C52b·L50b, the common mode currents Is1 and Is2 can be cancelled out neatly. Even if there is a variation of about ±10 to 15% between C52a·L50a and C52b·L50b, most of the common mode currents Is1 and Is2 can be cancelled out, and high frequency noise can be significantly reduced. [Explanation of symbols]

[0049] 10,48,48(1)~48(3) Switching power supply 12 Frames ground 14 Input power line 16 Input ground line 18 Output power line 20 Output ground line 22 Input interphase capacitor 24 First Arm 24a First switching element 24b Second switching element 26 Second Arm 26a Third switching element 26b Fourth switching element 28 Trans 28a Input Winding 28b Output winding 30 Output rectifier circuit (bridge type rectifier circuit) 34 Smoothing capacitor 36 Output smoothing circuit 38,40 Input side ground capacitor 42,44 Output ground capacitor 50 Smoothing inductor 50a First inductor element 50b Second inductor element 52a First stray capacitance 52b Secondary stray capacitance 54a Third stray capacitance 54b Fourth stray capacitance 64 Input rectifier / smoothing circuit Vi input voltage Vo output voltage

Claims

1. a frame ground, an input side power supply line and an input side ground line through which an input voltage is input between the phases, an output side power supply line and an output side ground line through which an output voltage is generated between the phases, an input interphase capacitor connected between the input side power supply line and the input side ground line, a first arm consisting of first and second switching elements connected in series with each other, one end of the first switching element connected to the input side power supply line and one end of the second switching element connected to the input side ground line, a second arm consisting of third and fourth switching elements connected in series with each other, one end of the third switching element connected to the input side power supply line and one end of the fourth switching element connected to the input side ground line, and an output rectifier circuit that full-wave rectifies an AC voltage generated in the output winding to output a rectified voltage; an output smoothing circuit that is a low-pass filter composed of a smoothing inductor and a smoothing capacitor connected to an output end of the output rectifier circuit, both ends of the smoothing capacitor are connected between the output power supply line and the output ground line, and that smooths the rectified voltage to generate the output voltage; an input grounding capacitor that protectively grounds at least one of the input power supply line and the input ground line to the frame ground; and an output grounding capacitor that protectively grounds at least one of the output power supply line and the output ground line to the frame ground, the smoothing inductor is composed of first and second inductor elements, the first inductor element being disposed on the output power supply line side, and the second inductor element being disposed on the output ground line side, a wiring line to which two terminals of the input winding are connected is electrostatically coupled to the frame ground through third and fourth stray capacitances, the capacitance values ​​of the third and fourth stray capacitances are set to be equal to each other based on a positional relationship between the wiring line serving as one electrode of the stray capacitance and the frame ground serving as the other electrode of the stray capacitance, a wiring line to which an input end of the output smoothing circuit on the side of the first inductor element is connected is electrostatically coupled to the frame ground through a first stray capacitance; a wiring line to which an input end of the output smoothing circuit on the side of the second inductor element is connected is electrostatically coupled to the frame ground through a second stray capacitance; A full-bridge type switching power supply device characterized in that the capacitance values ​​of the first and second stray capacitances are set by the positional relationship between the wiring line which is one electrode of the stray capacitance and the frame ground which is the other electrode, and the product of the inductance value of the first inductor element and the capacitance value of the first stray capacitance is set to be equal to the product of the inductance value of the second inductor element and the capacitance value of the second stray capacitance.

2. 2. The switching power supply device according to claim 1, wherein the first and second inductor elements are formed by a pair of windings magnetically coupled via a single magnetic core, the pair of windings having an equal number of turns and magnetically coupled with opposite polarity.

3. 3. The switching power supply according to claim 1, wherein the output rectifier circuit is a bridge-type rectifier circuit formed of four rectifier elements.

4. an input rectifying and smoothing circuit that rectifies and smoothes a commercial AC voltage to generate the input voltage, the input rectifying and smoothing circuit being provided in front of the input power supply line and the input ground line; 3. The switching power supply device according to claim 1, wherein the input-side grounding capacitor protectively grounds at least one of the input-side power supply line and the input-side ground line to the frame ground via the input rectifying and smoothing circuit.

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