Switching power supply

Abstract

To provide a switching power supply device capable of easily preventing a leakage magnetic flux from a power conversion circuit from acting on a lead wire of a component having the lead to generate a noise voltage.SOLUTION: Lead wires 22a, 22b of a capacitor element 18 stand up with their tips connected to a printed wiring board 12. Between lead wires 22a and 22b, a magnetic flux passage space 24 is formed, which is a path for a leakage magnetic flux φ emitted from a power conversion circuit 14. An electromagnetic shielding member 28 has a shielding unit 30 composed of a metal frame 30a and a through-hole space 30b inside the frame and is mounted on the printed wiring board 12. The shielding unit 30 is positioned so that a central axis 40 of the through-hole space 30b passes through the magnetic flux passage space 24. The leakage magnetic flux φ acts on the shielding unit 30. A magnetic flux in an opposite direction to the leakage magnetic flux φ is generated by a current flowing in a circumferential direction of the frame 30a, which suppresses magnetic flux density of the leakage magnetic flux φ passing through the magnetic flux passage space 24.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a switching power supply device having a shielding portion that suppresses noise caused by leakage magnetic flux released by a switching operation.

Background Art

[0002] Conventionally, for example, as disclosed in Patent Document 1 by the applicant of the present application, there has been a switching power supply device having a structure in which a pair of connection patterns connecting a smoothing capacitor on the output side and an output terminal are three-dimensionally crossed. Normally, the loop formed by the smoothing capacitor and the connection pattern becomes large, and leakage magnetic flux from magnetic components intersects this loop, causing a large induced current to flow, generating a large noise voltage in the connection pattern, etc., and having an adverse effect on an external load, etc. However, by applying the structure of this switching power supply device, the above-mentioned induced current can be reduced, and the generation of the noise voltage can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The structure of Patent Document 1 is a very excellent structure in terms of suppressing the generation of noise voltage due to leakage magnetic flux. However, when the lead wire of the smoothing capacitor is long, the effect of suppressing the generation of noise voltage in the lead wire cannot be expected.

[0005] For example, in the conventional switching power supply unit 10 shown in Figure 6, a power conversion circuit 14 is mounted on a printed circuit board 12, and a capacitor element 18, which is a leaded component, is mounted near a magnetic component 16, which is a part of the power conversion circuit 14. The capacitor element 18 has a cylindrical component body 20 arranged horizontally, and a pair of lead wires 22a and 22b extend from the end of the component body 20 toward the printed circuit board 12, with the tips of the lead wires 22a and 22b connected to the wiring pattern of the printed circuit board. The lead wires 22a and 22b are long in order to mount circuit components (not shown) below the component body 20, and by making the lead wires 22a and 22b long, the component body 20 is prevented from coming into contact with the circuit components below. As a result, a loop of a predetermined area is formed by the lead wires 22a and 22b rising from the printed circuit board 12. Hereinafter, the space between the lead wires 22a and 22b will be referred to as the 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 when it performs switching operation it emits leakage magnetic flux φ. A portion of this leakage magnetic flux φ passes through the magnetic flux passage space 24 of the capacitor element 18, inducing a current to flow in the lead wires 22a and 22b, generating a large noise voltage in the lead wires 22a and 22b, which adversely affects external loads, etc. This problem cannot be solved even by using the structure of Patent Document 1.

[0007] Although the capacitor element 18 shown in Figure 6 is an aluminum electrolytic capacitor for smoothing, even with small capacitor elements used in control circuits (ceramic capacitors, film capacitors) or resistor elements with very low resistance values, the above-mentioned noise voltage may be generated when the lead wires are long, potentially causing the control circuit to malfunction.

[0008] The present invention has been made in view of the above-mentioned background art, and aims 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 a leaded component. [Means for solving the problem]

[0009] The present invention comprises a printed circuit board, a power conversion circuit mounted on the printed circuit board and performing power conversion by switching operation, a leaded component which is a part of 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 the end of the component body, and an electromagnetic shielding member which has a shielding portion consisting of a closed annular conductive frame and a through space inside the frame. The lead wires of the leaded component are connected at their tips to the wiring patterns of the printed circuit board and stand upright, and a magnetic flux passage space is formed between the pair of lead wires, which serves as a path for the leakage magnetic flux emitted from the power conversion circuit. The electromagnetic shielding member is mounted on the printed circuit board, and the shielding portion is positioned such that the central axis of the through-space passes through the magnetic flux passage space. This switching power supply device is characterized in that the leakage magnetic flux acts on the shield portion, causing a current to flow in the circumferential direction of the frame, thereby generating a magnetic flux opposite to the leakage magnetic flux, and suppressing the magnetic flux density of the leakage magnetic flux passing through the magnetic flux passage space.

[0010] The frame of the electromagnetic shielding member may have a portion of its circumferential direction formed by the wiring pattern of the printed circuit board. Furthermore, at least a portion of the frame of the electromagnetic shielding member may be made of a metal plate, and the portion other than the wiring pattern may be made of a metal plate or the like. The electromagnetic shielding member may have a heat dissipation section extending from the end of the shielding portion for dissipating heat from circuit components.

[0011] Alternatively, the frame of the electromagnetic shielding member may be formed by the wiring pattern of an auxiliary printed circuit board separate from the printed circuit board. The leaded component is, for example, a capacitor element. [Effects of the Invention]

[0012] The switching power supply device of the present invention is equipped with an electromagnetic shielding member having a shielding section with a unique structure, the shielding section consisting of a conductive frame and a through-space inside it. Therefore, when leakage flux acts on the shielding section, eddy currents flow in the circumferential direction of the frame, generating a magnetic flux (cancellation flux) in the opposite direction to the leakage flux. Furthermore, since the shielding section is positioned so that the central axis of the through-space passes through the magnetic flux passage space of the leaded component, the cancellation flux can be precisely concentrated in the direction of the magnetic flux passage space. This effectively suppresses the magnetic flux density of the leakage flux passing through the magnetic flux passage space, easily solving the problem of noise voltage generation in the lead wires. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view showing one embodiment of the switching power supply device of the present invention. [Figure 2] Figure 1 shows three specific examples of electromagnetic shielding members, as shown in perspective views (a) to (c). [Figure 3] This is a circuit diagram showing the internal circuit of a prototype switching power supply according to this embodiment, and the external connection circuit used in an effectiveness verification experiment conducted with this prototype. [Figure 4] These graphs show the results of the effectiveness verification experiment, with graphs (a) to (c) representing the measurement results of the frequency characteristics of the noise terminal voltage of Comparative Examples 1 and 2 and the prototype, respectively, and line graphs (d) to (f) comparing the voltage levels at specific frequencies. [Figure 5] (a) is a front view showing one modified example of an electromagnetic shielding member, and (b) is a perspective view showing another modified example. [Figure 6] This is a perspective view showing one form of a conventional switching power supply. [Modes for carrying out the invention]

[0014] Hereinafter, one embodiment of the switching power supply device of the present invention will be described with reference to Figures 1 to 4. Components similar to those in the conventional switching power supply device 10 are denoted by the same reference numerals and their description is omitted.

[0015] As shown in FIG. 1, the switching power supply device 26 of this embodiment is obtained by additionally mounting an electromagnetic shielding member 28 on the above-described switching power supply device 10, and other configurations are the same as those of the switching power supply device 10.

[0016] Although the electromagnetic shielding member 28 is depicted in a simplified manner in FIG. 1, specifically, it can have a structure as shown in FIGS. 2(a) to (c). The electromagnetic shielding member 28(1) shown in FIG. 2(a) has the simplest structure that can be fabricated by punching a flat metal plate, and has a shield portion 30 composed of a flat frame body 30a closed in a ring shape and a through space 30b inside the frame body 30a. At the lower end portion of the shield portion 30, a mounting portion 32 that is inserted into and fixed to through holes or the like of the printed wiring board 12 protrudes.

[0017] The electromagnetic shielding member 28(2) shown in FIG. 2(b) has a structure that can be fabricated by punching a flat metal plate and then performing bending on the side end portions. It has a shield portion 30 composed of a frame body 30a that is closed in a ring shape and slightly bent in an L shape and a through space 30b inside the frame body 30a. At the lower end portion of the shield portion 30, a mounting portion 32 that is inserted into and fixed to through holes or the like of the printed wiring board 12 protrudes.

[0018] The electromagnetic shielding member 28(3) shown in FIG. 2(c) is obtained by extending the side end portions of the shield portion 30 of the electromagnetic shielding member 28(2) in a U shape to provide a heat dissipation portion 34. The heat dissipation portion 34 sandwiches, from both sides, a heat generating component 36 (or a heat generating circuit module 36) covered with a silicon heat dissipation cap 38, and functions to release the heat of the heat generating component 36 (or the heat generating circuit module 36).

[0019] As shown in FIG. 1, the electromagnetic shielding member 28 is mounted on the printed wiring board 12, and the shield portion 30 is arranged in the vicinity of the lead wires 22a and 22b of the capacitor element 18, and is positioned such that the central axis 40 of the through space 30b passes through substantially the center of the magnetic flux passage space 24.

[0020] To briefly explain the operation of the electromagnetic shielding member 28, when leakage magnetic flux φ is emitted from the magnetic component 16, the leakage magnetic flux φ attempting to pass through the magnetic flux passing space 24 of the capacitor element 18 acts on the shielding portion 30, and a current flows in the circumferential direction of the frame body 30a, generating a magnetic flux opposite to the leakage magnetic flux φ, thereby suppressing the magnetic flux density of the leakage magnetic flux φ passing through the magnetic flux passing space 24. This can solve the problem of a large noise voltage being generated in the lead wires 22a and 22b.

[0021] To confirm the effect of the electromagnetic shielding member 28, the inventor fabricated a prototype 26x of the switching power supply device 26 and conducted an experiment to measure the noise level (noise terminal voltage) fed back to the input power supply 42 side from the switching power supply device 26x in the measurement environment shown in FIG. 3.

[0022] The internal circuit of the prototype 26x is configured such that the AC input voltage output from the input power supply 42 is received by the noise filter 44, rectified and smoothed by the rectifying element 46 and the capacitor element 18, and input to the power conversion circuit 14 (DC-DC converter) that performs the switching operation. The magnetic component 16 and the capacitor element 18 are in a positional relationship where a part of the leakage magnetic flux φ emitted by the magnetic component 16 easily passes through the magnetic flux passing space 24 of the capacitor element 18. As shown in FIG. 1, the electromagnetic shielding member 28 is arranged near the lead wires 22a and 22b of the capacitor element 24, and the shielding portion 30 is positioned such that the central axis 40 of the through space 30b passes through substantially the center of the magnetic flux passing space 24.

[0023] To explain the external connection of the switching power supply device 26, a pseudo power supply circuit network 48 for impedance matching was inserted between the input power supply 42 and the input terminal of the prototype 26x, and a load 50 that consumes a predetermined power was connected to the output terminal of the prototype 26x. Then, a spectrum analyzer 52 was connected to the pseudo power supply circuit network 48 to measure the frequency characteristics of the noise terminal voltage.

[0024] In addition, by modifying the electromagnetic shielding member 28 of prototype 26x, a prototype [Comparative Example 1] was manufactured in which the shielding portion 30 was removed from the electromagnetic shielding member 28, and a prototype [Comparative Example 2] was manufactured in which the through-space 30b of the shielding portion 30 was eliminated, resulting in a simple flat plate, and similar measurements were performed on both prototypes.

[0025] Figures 4(a) and 4(b) show the frequency characteristics of the noise terminal voltage measured with the spectrum analyzer 52, with prototype 26x exhibiting the best characteristics. For example, looking at the peak voltage level around 210 kHz, as shown in Figure 4(d), comparative example 1 is 72.1 dBμV, comparative example 2 is 65.7 dBμV, and prototype 26x is 54.9 dBμV, with prototype 26x having the lowest voltage level. Similarly, looking at the peak voltage level around 650 kHz, as shown in Figure 4(e), comparative example 1 is 62.6 dBμV, comparative example 2 is 54.8 dBμV, and prototype 26x is 44.9 dBμV, with prototype 26x having the lowest voltage level. Furthermore, looking at the peak voltage levels around 2MHz, as shown in Figure 4(f), Comparative Example 1 is 61.6dBμV, Comparative Example 2 is 52.7dBμV, and Prototype 26x is 47.7dBμV, with Prototype 26x having the lowest voltage level.

[0026] Comparing the measurement results of Comparative Example 1 and Comparative Example 2, it can be seen that a certain shielding effect can be obtained even by simply providing a shielding section 30 made of a flat plate. This is thought to be because eddy currents flow in the shielding section 30, generating a magnetic flux (cancellation flux) that tries to cancel out the leakage magnetic flux φ that is trying to pass through the magnetic flux passage space 24 of the capacitor element 18. This cancellation flux suppresses the magnetic flux density of the leakage magnetic flux φ passing through the magnetic flux passage space 24 to some extent, thereby reducing the noise terminal voltage.

[0027] Comparing the measurement results of Comparative Example 2 and Prototype 26x, it can be seen that the shielding effect is further improved by providing a through-space 30b in the shielding section 30. In Comparative Example 2, since there is no through-space 30b, the distribution of eddy currents flowing through the shielding section 30 is easily disturbed, making it difficult to concentrate the canceling magnetic flux in the desired direction. In contrast, Prototype 26x has a through-space 30b in the shielding section 30, and the central axis 40 of the through-space 30b is positioned to pass through the magnetic flux passage space 24 of the capacitor element 18. As a result, the eddy currents are controlled to flow in the circumferential direction of the frame 30a, and the canceling magnetic flux can be accurately concentrated in the direction of the magnetic flux passage space 24. Therefore, it is thought that the magnetic flux density of the leakage magnetic flux φ passing through the magnetic flux passage space 24 is effectively suppressed by this canceling magnetic flux, and the noise terminal voltage is significantly reduced.

[0028] In prototype 26x, as shown in Figure 1, the magnetic component 16, shielding section 30, and magnetic flux passage space 24 are arranged in that order when viewed from the side closest to the magnetic component 16. However, it is believed that almost the same effect can be obtained by changing the order to magnetic component 16, magnetic flux passage space 24, and shielding section 30, based on the same principle as described above.

[0029] As described above, the switching power supply 26 is equipped with an electromagnetic shielding member 28 having a shielding section 30 with a unique structure. The shielding section 30 is not a simple metal plate, but is composed of a metal frame 30a and a through-space 30b inside it. Therefore, when leakage flux φ acts on the shielding section 30, eddy currents flow in the circumferential direction of the frame 30a, generating a canceling flux. This canceling flux can be precisely concentrated in the direction of the magnetic flux passage space 24, thereby effectively suppressing the magnetic flux density of the leakage flux φ passing through the magnetic flux passage space 24 and easily solving the problem of noise voltage generation in the lead wires 22a and 22b.

[0030] It should be noted that the switching power supply device of the present invention is not limited to the embodiments described above. For example, the structures of the electromagnetic shielding members 28(1) to 28(3) shown in Figures 2(a) to (c) are merely preferred examples and can be modified as appropriate to suit the structure of the actual power supply device.

[0031] Furthermore, the shield portion of the electromagnetic shielding member is not limited to the structure of the shield portion 30 described above, and may consist of a closed, annular conductive frame and a through-space inside it. For example, the shape of the frame and the through-space may be changed to a shape other than a rectangle. Note that the "through-space" in this invention includes not only a "space without a structure" as in the above embodiment, but also a "space with an insulating structure." This is because an insulating structure is equivalent to air to electromagnetic waves and has little effect on the performance of the shield portion.

[0032] In addition, the electromagnetic shielding member can have a structure like the electromagnetic shielding member 28(4) shown in Figure 5(a). The shield portion 30 of the electromagnetic shielding member 28(4) is made by preparing a U-shaped metal member 54 with a part of its circumference open, and connecting both ends of the U-shaped metal member 54 to the wiring pattern 56 of the printed circuit board 12 to short-circuit it. The frame 30a is formed by the U-shaped metal member 54 and the wiring pattern 56, and a through space 30b is formed inside it. Even if the structure is changed to this, almost the same effect can be obtained.

[0033] Furthermore, the electromagnetic shielding member can also have a structure like the electromagnetic shielding member 28(5) shown in Figure 5(b). The electromagnetic shielding member 28(5) is formed using an auxiliary printed circuit board 58 that is separate from the printed circuit board 12. The base material 58a of the printed circuit board 58 is an insulator such as glass epoxy or paper phenol. The shielding portion 30 is formed by a frame 30a created by a wiring pattern arranged in an annular shape, and the inside of this wiring pattern becomes a through space 30b. In the case of the electromagnetic shielding member 28(5), one end of the through space 30b is closed by the base material 58a, but since the base material 58a is an insulator, it has almost no effect on the shielding performance. Even if the structure is changed to this type, almost the same effect can be obtained.

[0034] Furthermore, the material of the shield frame can be any conductive material such as metal, and can be appropriately selected from aluminum, copper, brass, phosphor bronze, iron, etc., which are widely used as shielding cases, and generally the same effect can be obtained. In addition, there are no particular limitations on the type or application of the leaded components that are the target of electromagnetic shielding. Besides the smoothing capacitor elements mentioned above, it can also target small capacitor elements used in control circuits, or resistor elements with very low resistance values. In particular, excellent effects can be obtained when targeting elements in which the main impedance (impedance of the part other than the lead wires) in the high-frequency band is very low. [Explanation of symbols]

[0035] 10,26 Switching power supply 12 Printed circuit boards 14 Power Conversion Circuit 18 Capacitor elements (components with leads) 20 Main body parts 22a, 22b Lead wires 24 Magnetic flux passage space 28,28(1)~28(5) Electromagnetic shielding material 30 Shield section 30a frame 30b Penetration space 34 Heat radiation part 40 Central axis of the through space 54 U-shaped metal component (frame) 56 Wiring Pattern (Frame) 58 Auxiliary Printed Circuit Board φ Leakage flux

Claims

1. The device comprises a printed circuit board, a power conversion circuit mounted on the printed circuit board and performing power conversion by switching operation, a leaded component which is a part of 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 the end of the component body, and an electromagnetic shielding member which has a shielding portion consisting of a closed annular conductive frame and a through space inside the frame, The lead wires of the leaded component are connected at their tips to the wiring patterns of the printed circuit board and stand upright, and a magnetic flux passage space is formed between the pair of lead wires, which serves as a path for the leakage magnetic flux emitted from the power conversion circuit. The electromagnetic shielding member is mounted on the printed circuit board, and the shielding portion is positioned such that the central axis of the through-space passes through the magnetic flux passage space. A switching power supply device characterized in that the leakage magnetic flux acts on the shield portion, causing a current to flow in the circumferential direction of the frame, thereby generating a magnetic flux in the opposite direction to the leakage magnetic flux, and suppressing the magnetic flux density of the leakage magnetic flux passing through the magnetic flux passage space.

2. The switching power supply device according to claim 1, wherein a portion of the frame of the electromagnetic shielding member is formed by the wiring pattern of the printed circuit board in the circumferential direction.

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

4. The switching power supply device according to claim 1 or 3, wherein the electromagnetic shielding member has a heat dissipation portion extending from the end of the shield portion for dissipating heat from circuit components.

5. The switching power supply device according to claim 1, wherein the frame of the electromagnetic shielding member is formed by the wiring pattern of an auxiliary printed circuit board separate from the printed circuit board.

6. The switching power supply device according to claim 1, 2, 3, or 5, wherein the leaded component is a capacitor element.

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