Switching power supply device

Abstract

Provided is a switching power supply device that can easily suppress noise voltage from being generated due to leakage magnetic flux from a power conversion circuit acting on a lead wire of a component with a lead. Lead wires 22a, 22b of a capacitor element 18 are connected at the tip to a printed wiring board 12, and a magnetic flux passage space 24 for leakage magnetic flux φ discharged from a power conversion circuit 14 is formed between the lead wires 22a, 22b. An electromagnetic shield member 28 includes a shield portion 30 having a metal frame body 30a and a penetration region 30b inside the metal frame body 30a. The shield portion 30 is positioned so that a central axis 40 of the penetration region 30b passes through the magnetic flux passage space 24. The leakage magnetic flux φ acts on the shield portion 30, and a current flows in the circumferential direction of the frame body 30a, and thus a magnetic field is generated in a direction eliminating the leakage magnetic flux φ, and the magnetic flux density of the leakage magnetic flux φ passing through the magnetic flux passage space 24 is suppressed.

Description

Switching Power Supply

[0001] The present invention relates to a switching power supply device having a shield portion that suppresses noise caused by the release of leakage magnetic flux due to switching operations.

[0002] Conventionally, as disclosed in Patent Document 1 by the applicant of the present application, there has been a switching power supply device with a structure in which a pair of connection patterns connecting the output-side smoothing capacitor and the output terminal intersect in a three-dimensional manner. Normally, the loop formed by the smoothing capacitor and the connection pattern is large, and leakage magnetic flux from magnetic components interlinks with this loop, causing a large induced current to flow, generating a large noise voltage in the connection pattern, etc., and adversely affecting external loads, etc. However, with this switching power supply device structure, it is possible to reduce the induced current and suppress the generation of noise voltage.

[0003] Utility Model Registration No. 3142501

[0004] The structure of Patent Document 1 is an excellent structure in terms of suppressing the generation of noise voltage due to leakage magnetic flux, but if the lead wires of the smoothing capacitor are long, it cannot be expected to be effective in suppressing the generation of noise voltage in the lead wires.

[0005] For example, in a conventional switching power supply 10 shown in FIG. 6 , a power conversion circuit 14 is mounted on a printed wiring board 12, and a capacitor element 18, which is a lead-attached component, is mounted near a magnetic component 16, which is a component of the power conversion circuit 14. The capacitor element 18 has a cylindrical component body 20 arranged horizontally. A pair of lead wires 22a, 22b extend from the end of the component body 20 toward the printed wiring board 12, with the ends of the lead wires 22a, 22b connected to the wiring pattern on the printed wiring board. The long lead wires 22a, 22b allow for the mounting of circuit components (not shown) below the component body 20. The long lead wires 22a, 22b prevent the component body 20 from contacting the circuit components below. Therefore, a loop is formed by the lead wires 22a, 22b extending from the printed wiring board 12. Hereinafter, the space between the lead wires 22a, 22b will be referred to as a magnetic flux passage space 24.

[0006] The power conversion circuit 14 is a circuit that performs power conversion by switching operation. The magnetic component 16 is, for example, a switching transformer or a power inductor, and emits leakage magnetic flux φ during switching operation. Some of this leakage magnetic flux φ passes through the magnetic flux passage space 24 of the capacitor element 18, causing an induced current to flow through the lead wires 22 a and 22 b, which generates a large noise voltage in the lead wires 22 a and 22 b, which can adversely affect external loads, etc. This problem cannot be solved even by using the structure described in Patent Document 1.

[0007] The capacitor element 18 shown in FIG. 6 is a smoothing aluminum electrolytic capacitor or the like, but even in the case of a small capacitor element (ceramic capacitor or film capacitor) used in a control circuit or a resistor element with a very small resistance value, if the lead wires are long, the above-mentioned noise voltage may be generated, which may cause the control circuit to malfunction.

[0008] The present invention has been made in view of the above-mentioned background art, and has as its object to provide a switching power supply device that can easily suppress the generation of noise voltage caused by leakage magnetic flux from a power conversion circuit acting on the lead wires of lead-equipped components.

[0009] The present invention comprises a printed wiring board, a power conversion circuit mounted on the printed wiring board and performing power conversion by switching operation, a leaded component which is a component within the power conversion circuit or a component other than the power conversion circuit and has a pair of lead wires extending in the same direction from an end of a component body, and an electromagnetic shielding member having a shielding portion formed of an annular, electrically closed conductor frame body with an inner side being a penetration area through which magnetic lines can pass, wherein the lead wires of the leaded component have their tip portions connected to a wiring pattern of the printed wiring board and stand up from the printed wiring board, and the space between the pair of lead wires forms a magnetic flux passage space for leakage magnetic flux emitted from the power conversion circuit, and when the electromagnetic shielding member is mounted on the printed wiring board, the shielding portion is positioned so that the leakage magnetic flux can pass through the penetration area and the leakage magnetic flux passing through the penetration area passes through the magnetic flux passage space, The leakage magnetic flux acts on the shield portion, and current flows circumferentially around the frame body, generating a magnetic field in a direction that cancels out the leakage magnetic flux, thereby suppressing the magnetic flux density of the leakage magnetic flux passing through the magnetic flux passage space.

[0010] The shield portion is positioned so that the plane formed by the frame body and the magnetic flux passage space face each other parallel to each other, and a central axis that is perpendicular to the plane and passes through the center of the penetration area passes through the magnetic flux passage space.

[0011] At least a portion of the frame of the electromagnetic shielding member is made of a metal plate. Furthermore, the frame of the electromagnetic shielding member may be formed of a metal plate and have an integrally protruding mounting portion that is inserted into a through-hole in the printed wiring board and fixed thereto. Furthermore, the electromagnetic shielding member may have a heat dissipation portion integrally provided at an end of the shielding portion for dissipating heat from circuit components.

[0012] The frame of the electromagnetic shielding member is partially formed by the wiring pattern of the printed wiring board. Alternatively, the frame of the electromagnetic shielding member may be formed by the wiring pattern of an auxiliary printed wiring board that is separate from the printed wiring board. The auxiliary printed wiring board may have an integrally protruding mounting portion that is inserted into a through hole in the printed wiring board and fixed thereto. The lead-attached component is, for example, a capacitor element.

[0013] The switching power supply of the present invention is equipped with an electromagnetic shield member having a shield portion with a unique structure, so that when leakage magnetic flux acts on the shield portion, current flows in the circumferential direction of the electromagnetic shield member, generating a magnetic field in a direction that cancels the leakage magnetic flux. This effectively suppresses the magnetic flux density of the leakage magnetic flux passing through the magnetic flux passage space, and effectively suppresses the noise voltage generated in the lead wires.

[0014] 1 is a perspective view showing an embodiment of a switching power supply device of the present invention. It is a perspective view (a) to (c) showing three specific examples of the electromagnetic shielding member of FIG. 1. It is a circuit diagram showing the internal circuit of a prototype of the switching power supply device of this embodiment and the external connection circuit of an effectiveness confirmation experiment conducted using this prototype. It is a graph showing the results of the effectiveness confirmation experiment, with graphs (a) to (c) respectively showing the measurement results of the frequency characteristics of the noise terminal voltage of comparative examples A and B and the prototype, and line graphs (d) to (f) comparing the voltage levels of specific frequencies. It is a front view (a) showing one modified example of the electromagnetic shielding member, and a perspective view (b) showing another modified example. It is a perspective view showing one form of a conventional switching power supply device.

[0015] An embodiment of a switching power supply device according to 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 will not be described again.

[0016] As shown in FIG. 1, a switching power supply 26 of this embodiment is configured by adding an electromagnetic shielding member 28 to the switching power supply 10 described above, but other configurations are the same as those of the switching power supply 10.

[0017] Electromagnetic shield member 28 can have specific structures such as those shown in Figures 2(a) to 2(c). Electromagnetic shield member 28(1) shown in Figure 2(a) has the simplest structure, which can be manufactured by punching a flat metal plate, and has a shield portion 30 consisting of a flat, closed, annular frame body 30a and a penetration region 30b inside frame body 30a. Attachment portions 32 that are inserted into through-holes or the like in printed wiring board 12 and fixed are integrally provided at the lower end of shield portion 30 and protrude therefrom.

[0018] 2(b) is formed by punching a flat metal plate and then bending the side edges, and has a shielding portion 30 consisting of a frame body 30a that is closed into a ring shape and slightly bent into an L-shape, and a penetration region 30b inside the frame body 30a. A mounting portion 32 that is inserted into a through-hole or the like in the printed wiring board 12 and fixed thereto is integrally formed at the lower end of the shielding portion 30 and protrudes therefrom.

[0019] 2(c) is an electromagnetic shield member 28(3) in which the side end of the shield portion 30 of the electromagnetic shield member 28(2) is extended in a U-shape to provide a heat dissipation portion 34. The heat dissipation portion 34 sandwiches a heat-generating component 36 (or a heat-generating circuit module) covered with a silicon heat dissipation cap 38 from both sides, and functions to dissipate heat from the heat-generating component 36 (or heat-generating circuit module).

[0020] As shown in FIG. 1, the electromagnetic shielding member 28 is mounted on the printed wiring board 12, with the shielding portion 30 positioned near the lead wires 22 a, 22 b of the capacitor element 18, and positioned so that the plane formed by the frame body 30 a and the magnetic flux passage space 24 face each other parallel to each other, and a central axis 40 that is perpendicular to the plane and passes through the center of the penetration region 30 b passes through approximately the center of the magnetic flux passage space 24.

[0021] The electromagnetic shield member 28 functions in such a way that when the leakage magnetic flux φ emitted from the magnetic component 16 passes through the penetration region 30b inside the frame body 30a of the shield section 30, an eddy current flows in the circumferential direction of the frame body 30a. This generates a magnetic field in the shield section 30 in a direction that cancels out the leakage magnetic flux φ, suppressing the magnetic flux density of the leakage magnetic flux φ in the magnetic flux passage space 24 facing the frame body 30a and effectively suppressing the noise voltage generated in the lead wires 22a, 22b.

[0022] In order to confirm the effect of the electromagnetic shielding member 28, the inventors produced a prototype 26x of the switching power supply 26 of the present invention and conducted an experiment to measure the noise level (noise terminal voltage) returning from the prototype 26x to the input power supply 42 side using the measurement circuit shown in FIG. 3.

[0023] The internal circuit of prototype 26x is configured so that an AC input voltage output from an input power supply 42 is received by a noise filter 44, rectified and smoothed by a rectifier element 46 and a capacitor element 18, and input to a power conversion circuit 14 (DC-DC converter) that performs switching operations. The magnetic component 16 and the capacitor element 18 are positioned in such a way that a portion of the leakage magnetic flux φ emitted from the magnetic component 16 can easily pass through the magnetic flux passage space 24 of the capacitor element 18. As shown in FIG. 1, the electromagnetic shield member 28 is disposed near the lead wires 22a, 22b of the capacitor element 24. The shield portion 30 is positioned so that the central axis 40 of the penetration region 30b passes through approximately the center of the magnetic flux passage space 24.

[0024] 3, the connection between the prototype 26x of the switching power supply 26 and the measurement circuit was such that an impedance matching artificial mains network 48 was inserted between the input power supply 42 and the input terminal of the prototype 26x, and a load 50 consuming a predetermined amount of power was connected to the output terminal of the prototype 26x. A spectrum analyzer 52 was then connected to the artificial mains network 48, and the frequency characteristics of the conducted noise were measured.

[0025] For comparison, a switching power supply unit [comparison example (A)] in which the shielding portion 30 was removed from the electromagnetic shielding member 28 by modifying the electromagnetic shielding member 28 of the prototype 26x, and a switching power supply unit [comparison example (B)] in which the penetration region 30b of the shielding portion 30 was removed and made into a simple flat plate were fabricated, and similar measurements were performed.

[0026] Figures 4(a) to (c) show the frequency characteristics of the noise terminal voltage measured by spectrum analyzer 52 for Comparative Example (A), Comparative Example (B), and Prototype 26x, with Prototype 26x shown in Figure 4(c) having the best characteristics. Furthermore, when the peak voltage level of the noise terminal voltage around 210 kHz is examined, as shown in Figure 4(d), it is 72.1 dBμV for Comparative Example (A), 65.7 dBμV for Comparative Example (B), and 54.9 dBμV for Prototype 26x(C), with Prototype 26x(C) having the lowest voltage level. When the peak voltage level of the noise terminal voltage around 650 kHz is examined, as shown in Figure 4(e), it is 62.6 dBμV for Comparative Example (A), 54.8 dBμV for Comparative Example (B), and 44.9 dBμV for Prototype 26x(C), with Prototype 26x(C) having the lowest voltage level. Furthermore, looking at the peak voltage level of the noise terminal voltage around 2 MHz, as shown in FIG. 4(f), the comparative example (A) had a voltage level of 61.6 dBμV, the comparative example (B) had a voltage level of 52.7 dBμV, and the prototype 26x(C) had a voltage level of 47.7 dBμV, with the prototype 26x(C) having the lowest voltage level.

[0027] Comparing the measurement results of Comparative Example (A) and Comparative Example (B), it is clear that a certain level of shielding effect can be obtained simply by providing a shield section 30 made of a simple flat plate. This is thought to be because eddy currents flow in the shield section 30, generating a magnetic field in a direction that cancels out the leakage magnetic flux φ that attempts to pass through the magnetic flux passage space 24 of the capacitor element 18, and this canceling magnetic field suppresses to some extent the magnetic flux density of the leakage magnetic flux φ that passes through the magnetic flux passage space 24, thereby reducing the noise terminal voltage.

[0028] Comparing the measurement results of Comparative Example (B) and Prototype 26x, it can be seen that the shielding effect is further improved by providing the through-hole region 30b in the shield section 30. Because Comparative Example (B) does not have the through-hole region 30b, the eddy currents flowing in the shield section 30 are small, making it difficult to effectively generate a magnetic field in the canceling direction. In contrast, Prototype 26x provides the through-hole region 30b in the shield section 30, and positions the center axis 40 of the through-hole region 30b so that it passes through the magnetic flux passage space 24 of the capacitor element 18. This restricts the eddy currents to flow along the circumferential direction of the frame body 30a, generating a magnetic field in the shield section 30 in a direction that cancels the leakage magnetic flux φ, effectively suppressing the magnetic flux density of the leakage magnetic flux φ in the magnetic flux passage space 24. This is thought to be the result of a significant reduction in the noise terminal voltage.

[0029] As shown in FIG. 1, the prototype 26x was arranged in the order of magnetic component 16, shielding portion 30, and magnetic flux passage space 24, viewed from the side closest to the magnetic component 16. However, even if the order is changed to magnetic component 16, magnetic flux passage space 24, and shielding portion 30, substantially the same effect can be obtained based on the same principle as described above.

[0030] As described above, the switching power supply 26 is equipped with an electromagnetic shield member 28 having a uniquely structured shield section 30, which is composed of a metal frame 30a and a through region 30b formed therein. Therefore, when leakage magnetic flux φ acts on the shield section 30, eddy currents flow in the circumferential direction of the frame 30a, generating a magnetic field in a direction that cancels out the leakage magnetic flux φ, and this magnetic field can be effectively applied to the magnetic flux passage space 24. This effectively suppresses the magnetic flux density of the leakage magnetic flux φ passing through the magnetic flux passage space 24, easily solving the problem of noise voltage generation in the lead wires 22a, 22b.

[0031] The switching power supply device of the present invention is not limited to the above embodiment. For example, the structures of the electromagnetic shield members 28(1) to 28(3) shown in Figures 2(a) to 2(c) are preferred examples, and can be modified as appropriate to suit the structure of the actual power supply device.

[0032] The shielding portion of the electromagnetic shielding member is not limited to the structure of the shielding portion 30 described above, as long as it is composed of a ring-shaped, electrically closed, conductive frame body and a penetration region inside it. For example, the shapes of the frame body and the penetration region may be changed to shapes other than a rectangle. Note that the "penetration region" in this invention includes not only a space where no physical components exist, as in the above embodiment, but also a region where an insulating material exists and through which magnetic field lines can pass. This is because insulating materials are equivalent to air for electromagnetic waves and have almost no effect on the performance of the shielding portion.

[0033] Alternatively, the electromagnetic shield member may have a structure like that of electromagnetic shield member 28(4) shown in Figure 5(a). The shield portion 30 of electromagnetic shield member 28(4) has a U-shaped metal member 54 that is partially open in the circumferential direction, and both ends of the U-shaped metal member 54 are connected to and short-circuited with wiring patterns 56 on the printed wiring board 12. In this embodiment, a frame body 30a is formed by the U-shaped metal member 54 and the wiring patterns 56, and a through region 30b is formed inside this. Even if the structure is changed to this one, approximately the same effect can be obtained.

[0034] The electromagnetic shielding member can also be structured as shown in FIG. 5(b) as electromagnetic shielding member 28(5). Electromagnetic shielding member 28(5) is formed using an auxiliary printed wiring board 58 that is separate from printed wiring board 12. The base material 58a of printed wiring board 58 is an insulating material such as glass epoxy or paper phenol. The shielding section 30 has a frame 30a formed by a wiring pattern laid out in a ring shape, and the inside of this wiring pattern is the penetration region 30b. In the case of electromagnetic shielding member 28(5), the penetration region 30b is formed by the base material 58a, but because the base material 58a is an insulating material, magnetic field lines can penetrate it, which has almost no effect on shielding performance. Even with this structure, substantially the same effect can be obtained.

[0035] Furthermore, the material of the frame of the shielding section may be any conductive material such as metal, and can be selected appropriately from aluminum, copper, brass, phosphor bronze, iron, and other materials commonly used for shielding cases, etc., and generally similar effects can be obtained. Furthermore, there are no particular limitations on the type or use of leaded components that can be electromagnetically shielded, and in addition to the smoothing capacitor elements mentioned above, it can also be small capacitor elements used in control circuits, resistor elements with very low resistance, and so on. Excellent effects are particularly obtained when components with very low main impedance (the impedance of the parts other than the lead wires) in the high-frequency band are targeted.

[0036] 10, 26 Switching power supply device 12 Printed wiring board 14 Power conversion circuit 18 Capacitor element (component with leads) 20 Component body 22a, 22b Lead wire 24 Magnetic flux passage space 26x Prototype 28, 28(1) to 28(5) Electromagnetic shielding member 30 Shielding portion 30a Frame 30b Penetration area 32 Mounting portion 34 Heat dissipation portion 36 Heat-generating component 38 Heat dissipation cap 40 Central axis 42 Input power supply 44 Noise filter 46 Rectifier element 48 Pseudo power supply circuit network 50 Load 52 Spectrum analyzer 54 U-shaped metal member (frame) 56 Wiring pattern (frame) 58 Auxiliary printed wiring board 58a Base material φ Leakage magnetic flux

Claims

1. A device comprising: a printed wiring board; a power conversion circuit mounted on the printed wiring board and performing power conversion by switching operation; a leaded component which is a component within the power conversion circuit or a component other than the power conversion circuit and has a pair of lead wires extending in the same direction from an end of a component body; and an electromagnetic shielding member having a shielding portion formed in an annular shape with an inner side being a through region through which magnetic lines can pass and formed of an electrically closed conductor frame, wherein the lead wires of the leaded component have their tips connected to the wiring pattern of the printed wiring board and stand up from the printed wiring board, and the space between the pair of lead wires forms a magnetic flux passage space for leakage magnetic flux emitted from the power conversion circuit, and wherein when the electromagnetic shielding member is mounted on the printed wiring board, the shielding portion is positioned so that the leakage magnetic flux can pass through the through region and the leakage magnetic flux passing through the through region passes through the magnetic flux passage space, A switching power supply device characterized in that the leakage magnetic flux acts on the shield portion, and a magnetic field is generated in a direction that cancels out the leakage magnetic flux by a current flowing in the circumferential direction of the frame body, thereby suppressing the magnetic flux density of the leakage magnetic flux passing through the magnetic flux passage space.

2. A switching power supply unit as claimed in claim 1, wherein said shielding portion is positioned so that a plane formed by said frame and said magnetic flux passage space face each other parallel to each other, and a central axis perpendicular to said plane and passing through the centre of said penetration region passes through said magnetic flux passage space.

3. A switching power supply device according to claim 1 or 2, wherein at least a part of said frame of said electromagnetic shielding member is made of a metal plate.

4. A switching power supply device according to claim 3, wherein said frame of said electromagnetic shielding member is formed from a metal plate and has an integrally protruding mounting portion which is inserted into a through hole in said printed wiring board and fixed thereto.

5. A switching power supply device according to claim 4, wherein said electromagnetic shielding member has a heat dissipation section integrally provided at an end of said shielding section for dissipating heat from circuit components.

6. A switching power supply device according to claim 1 or 2, wherein the frame of the electromagnetic shielding member is formed in part by the wiring pattern of the printed wiring board.

7. A switching power supply unit according to claim 1 or 2, wherein said frame of said electromagnetic shielding member is formed by a wiring pattern of an auxiliary printed wiring board which is separate from said printed wiring board.

8. A switching power supply device according to claim 7, wherein said auxiliary printed wiring board is integrally provided with a protruding mounting portion which is inserted into a through hole of said printed wiring board and fixed thereto.

9. A switching power supply device according to claim 1 or 2, wherein the component with leads is a capacitor element.

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