JP2009284701A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply which is integrated with an inverter circuit for miniaturization and is improved in a noise terminal voltage performance. <P>SOLUTION: The switching power supply has a shut off part 120 for shutting off electromagnetic wave between a metal fitting frame 100 for securing an AC inlet (an AC voltage input terminal) and a transformer T2, to reduce electromagnet wave noises resulting from the transformer T2 of the inverter circuit. Thus, the inverter circuit can be disposed adjacent to the power input part on a single substrate 310, allowing the switching power supply to be reduced in size. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply apparatus that includes an AC-DC converter and an inverter circuit and outputs an AC voltage.

  9A and 9B are a plan view and a front view of a metal fitting frame 200 (input portion outer frame) of a conventional AC inlet (AC voltage input terminal). The purpose of the conventional metal frame 200 is to supplement the mechanical strength of the AC connector.

  FIG. 10 is a plan view showing a switching power supply device using the metal frame 200. As shown in FIG. 10, the metal frame 200 fixes and reinforces the AC inlet 300. On the substrate 310, next to the AC inlet 300, a fuse F1, a variable resistor NR1, an across the line capacitor C1, and a line filter L1 constituting a noise filter circuit are arranged. A transformer T2 of an inverter circuit is arranged next to (on the left of the drawing) a power input unit composed of the AC inlet 300 and the noise filter circuit.

  Further, since the metal frame 200 is a part that can be touched by a person, when the material is a conductive metal, the metal frame 200 is configured to be grounded to the GND potential instead of the floating potential from the viewpoint of safety.

  However, the purpose of the metal frame 200 is to supplement the mechanical strength of the AC connector, and although it is grounded to the GND potential, it does not function as a shield that shields the external electromagnetic field mixed in the AC connector. .

  An example of an AC inlet including a noise filter device that reduces electromagnetic noise from an external electromagnetic field is disclosed in Patent Document 1. According to this document, a noise filter device that surrounds all of the line filter up to the AC connector and the noise filter portion of the across the line capacitor by the shield case and shields it from an external electromagnetic field that is disturbance noise is shown.

An example of an AC inlet provided with another noise filter device is disclosed in Patent Document 2. According to this document, a shield plate is formed below the printed circuit board to shield it from external electromagnetic fields, which are disturbance noises.
JP 10-107571 A (published April 24, 1998) Japanese Utility Model Publication 2-65090 (published May 16, 1990)

  Due to the demand for smaller and thinner switching power supply devices in recent years, there has been an increase in switching power supply devices integrated with a switching power supply circuit and an inverter circuit for lighting a cold cathode tube used as lighting for a thin liquid crystal television, for example. Yes.

  FIG. 11 is a front view of the conventional switching device shown in FIG. Since the high voltage output part of the inverter circuit emits electromagnetic waves, it is preferable to increase the distance between the edge surface of the AC power input part of the switching power supply device and the edge surface of the high voltage output part of the inverter circuit. However, because of the small and small board shape, the distance between the transformer T2 of the inverter circuit mounted on the board 310 and the AC inlet part (AC voltage input terminal) and the input filter part (noise filter circuit) of the switching power supply device. May get closer. The output voltage of the transformer T2 of this inverter circuit is, for example, an AC voltage output (AC output) of 1000 Vrms to 2000 Vrms, for example, outputs a high frequency signal of about 50 kHz, and generates an electromagnetic field like a high voltage line. Since the metal frame 200 does not cover the entire AC inlet, an electromagnetic field indicated by an arrow can be directly mixed into the AC inlet portion. As a result, unnecessary noise voltage (electromagnetic wave noise) appears in the internal circuit of the switching power supply device in the frequency band that drives the inverter circuit and in the frequency band that is a natural number multiple of the frequency. This unnecessary noise voltage degrades the noise terminal voltage performance, which is one of the required specifications of the switching power supply. The noise terminal voltage needs to be suppressed below the level of EMI standards such as VCCI standard, CISPR standard, FCC standard, etc., but the distance between the transformer of the inverter circuit and the AC inlet part and input filter part of the switching power supply unit May become a level that cannot be ignored if it approaches 5 cm or less.

  However, the configuration described in Patent Document 1 does not consider electromagnetic waves that are mixed directly into the AC inlet. In addition, since it is necessary to form a case above the line filter and line capacitor in consideration of the height, the size of the outer shape is large, for example, width × length × height: 60 × 70 × 40 mm. turn into. For this reason, when there is a demand for a low profile such that the height of the switching power supply device is desired to be 20 mm or less, it cannot be used for a configuration using a marginal part such as a maximum line filter or line capacitor of 18 mm, for example. . Furthermore, there is a problem that it is expensive to cover the whole.

  Further, in the configuration described in Patent Document 2, when the AC inlet and the transformer of the inverter circuit are juxtaposed, there is no structure for shielding electromagnetic waves from the upper surface and side surfaces of the AC inlet. Mixing is inevitable.

  As another aspect, in the case of drawing a pattern on a substrate under such a situation where a high voltage / high frequency voltage is handled, a pattern connected to a terminal to which a high voltage winding is actually soldered The pattern connected to the terminal to which the low voltage winding is soldered needs to be separated according to the potential difference. In addition, with regard to the electromagnetic field to be mixed in, signal lines may malfunction due to electromagnetic induction, so it is necessary to consider that the pattern does not pass even under the high voltage winding, even on the back side of the board. is there.

  The present invention has been made in view of the above problems, and its object is to reduce the size, height, and space of a switching power supply device when the switching power supply circuit and the inverter circuit are integrated. It is an object of the present invention to provide a switching power supply device that enables the electromagnetic wave emitted from the transformer of the inverter circuit to be mixed into the switching power supply device.

  A switching power supply device according to the present invention includes a power input unit including an AC voltage input terminal and a noise filter circuit that reduces electromagnetic noise, a converter circuit that converts an AC input from the power input unit into a DC output, An inverter circuit that converts the DC output of the converter circuit to an AC output and includes a transformer, and a shielding unit that shields electromagnetic waves generated by the transformer between the AC voltage input terminal and the transformer. It is characterized by.

  According to said structure, since the electromagnetic wave from the transformer of an inverter circuit to an alternating voltage input terminal is shielded, electromagnetic wave noise can be reduced and the noise terminal voltage performance of a switching power supply device can be improved. Therefore, since the inverter circuit and the power supply input unit can be arranged next to each other on a single substrate, the switching power supply device can be reduced in size.

  In the switching power supply according to the present invention, the converter circuit preferably includes a ringing choke converter circuit.

  According to the above configuration, a small switching power supply device can be configured at low cost.

  In the switching power supply according to the present invention, it is preferable that the shielding portion is arranged so as to shield between the power input portion excluding a noise filter circuit portion and the transformer.

  According to the above configuration, in addition to the AC voltage input terminal, the electromagnetic wave to the power input part including the noise filter circuit is also shielded, so that the electromagnetic wave noise can be further reduced and the noise terminal voltage performance of the switching power supply device can be improved. it can.

  In the switching power supply according to the present invention, the shielding portion is preferably a conductive metal.

  According to said structure, the effect which shields electromagnetic waves further is high.

  In the switching power supply according to the present invention, the conductive metal material may be copper.

  In the switching power supply according to the present invention, the conductive metal material may be iron.

  In the switching power supply according to the present invention, it is preferable that the conductive metal is connected to GND on the secondary side of the circuit of the switching power supply.

  According to said structure, since the electromagnetic wave absorbed by the shielding part is rapidly dissipated by GND, the effect which shields electromagnetic wave is further high.

  In the switching power supply according to the present invention, it is preferable that the shielding portion covers at least a part of an upper portion of the high-voltage winding portion of the transformer.

  According to said structure, since the electromagnetic wave which wraps around from the upper part of a shielding part to the power input part side can be shielded, electromagnetic noise can be reduced further and the noise terminal voltage performance of a switching power supply device can be improved. .

  In the switching power supply device according to the present invention, a portion of the shielding part that includes an upper part of the high-voltage winding part of the transformer and a part that shields between the power input part and the transformer is L It is preferably formed in a letter shape.

  According to said structure, since the electromagnetic wave which wraps around from the upper part of a shielding part to the power input part side can be shielded, electromagnetic noise can be reduced further and the noise terminal voltage performance of a switching power supply device can be improved. .

  Since the switching power supply according to the present invention includes a shielding portion that shields electromagnetic waves generated by the transformer between the AC voltage input terminal and the transformer as described above, electromagnetic noise that appears at the AC voltage input terminal. The noise terminal voltage performance of the switching power supply device can be improved. Therefore, since the inverter circuit and the power supply input unit can be arranged next to each other on a single substrate, the switching power supply device can be reduced in size.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
FIGS. 1A and 1B are a plan view and a front view showing a metal fitting frame (input portion outer frame) 100 of an AC inlet (AC voltage input terminal) of the switching power supply apparatus according to the embodiment of the present invention. FIG. 2 is a circuit diagram showing a power supply input unit and a converter circuit of the switching power supply device. In this embodiment, a ringing choke converter (RCC) circuit is used as a converter circuit that converts an AC input into a DC output.

  The power input unit 410 includes an AC inlet composed of a polarity live L and a neutral N, a fuse F1 that forms a noise filter circuit, variable registers NR1 and NR2, an arrester AR1, an across the line capacitor C1, and a line filter L1. Converter circuit 440 includes rectifier circuit 420 and RCC circuit 430. The rectifier circuit 420 includes resistors R1A and R1B, capacitors C2 and C3, a bridge diode BD1, and an electrolytic capacitor C4. The RCC circuit 430 includes resistors R2, R3, R4, R5, R6, capacitors C5, C6, a switching element (FET) Q1, a transistor Q2, a photocoupler PC1, a transformer T1, a diode D20, and an electrolytic capacitor C20. Although not shown in FIG. 2, the switching power supply device in the present embodiment further includes an inverter circuit. The inverter circuit includes a transformer.

  In the switching power supply configured as described above, an AC voltage (AC input) is first input from the outside to the AC inlet. The AC input input to the AC inlet passes through the noise filter circuit and is input to the converter circuit. It is output as a DC output through a rectifier circuit and an RCC circuit in the converter circuit. This DC output is input to the inverter circuit and output as an AC output.

  In the present embodiment, the noise of the switching power supply device is reduced by reducing the mixing of unnecessary electromagnetic fields (electromagnetic waves) from the high voltage winding of the transformer of the inverter circuit, particularly for the AC inlet of the power input unit 410 shown in FIG. It improves the terminal voltage performance. Here, except for the across-the-line capacitor C1 and the line filter L1, there is generally no role of a noise filter that reduces electromagnetic noise. Therefore, when an electromagnetic field is directly mixed into the AC inlet or the power input unit 410, a noise voltage (electromagnetic wave noise) is unintentionally output to an external wire through an external connector connected to the AC inlet, which is a problem.

  The transformer T2 of the inverter circuit according to the present embodiment will be described below with reference to FIG. This transformer T2 has one input and two outputs, and has a low-voltage winding portion N1 which is a primary side (input side) in the middle, and a secondary side (output side) at both ends thereof. It has two high-voltage winding parts N2. The voltage at each portion of the high-voltage winding portion N2 is low on the low-voltage winding portion side and high on the opposite side. Here, electromagnetic noise due to electromagnetic waves from the secondary high-voltage winding portion N2 becomes a problem.

  AC bracket metal frame 100 shown in FIGS. 1 (a) and 1 (b) includes an L-shaped shielding portion 120 for blocking the above-described electromagnetic wave as seen in FIG. 1 (b) (front view). FIG. 4 is a plan view showing a switching power supply device using the metal frame 100, and FIG. 5 is a front view thereof.

  As shown in FIG. 4, a fuse F <b> 1, a variable resistor NR <b> 1, an across-the-line capacitor C <b> 1, and a line filter L <b> 1 constituting a noise filter circuit are arranged on the substrate 310 next to the AC inlet 300. A transformer T2 of an inverter circuit is arranged next to (on the left of the drawing) a power input unit composed of the AC inlet 300 and the noise filter circuit.

  As shown in FIGS. 1A and 1B, the metal frame 100 includes an AC inlet holding portion 100a and fixing portions 100b and 100c. As shown in FIG. 1A, the AC inlet holding portion 100a has a concave shape to hold the AC inlet 300 (see FIG. 4). The fixing portions 100b and 100c are provided on both sides of the AC inlet holding portion 100a in order to fix the AC inlet holding portion 100a to the substrate 310 (see FIG. 4) by screwing or the like.

  The shielding part 120 has an upright part 120a and a roof part 120b. The upright portion 120a is formed so as to rise substantially vertically from the side of the fixing portion 100c with respect to the bottom surface of the metal frame 100 (the fixed side surface of the metal frame 100 shown in FIG. 5 to the substrate 310). The roof portion 120b is formed so as to extend from the upper end portion of the upright portion 120a to the side opposite to the metal frame 100. As shown in FIG. 4, the roof portion 120 b is also formed to extend toward the transformer T <b> 2 and cover a part of the transformer T <b> 2 in a state where the metal frame 100 is fixed to the substrate 310.

  As shown in FIG. 4, the L-shaped shielding portion 120 of the metal frame 100 covers the power input portion side on the upper side of the high-voltage winding portion N2 of the transformer T2. The shield 120 is made of a conductive metal, and is connected to the secondary side GND of the circuit of the switching power supply device via the metal frame 100. As a result, as indicated by an arrow in FIG. 5, the electromagnetic wave emitted from the transformer T2 is reflected or absorbed by the L-shaped shielding portion 120 of the metal frame 100. Electromagnetic wave noise due to the absorbed electromagnetic waves is quickly dissipated to GND through the metal frame 100. Therefore, the direct mixing of electromagnetic waves or magnetic fields into the AC inlet 300 (see FIG. 4) and the power input unit is reduced. Here, the lengths of the upright portion 120a and the roof portion 120b are determined on the basis that a high-voltage electromagnetic field is not directly mixed into the winding portion of the line filter L1 shown in FIG. A part of the high-voltage winding part N2 of the transformer T2 is not shielded by the shielding part 120. This is because the electromagnetic wave mixed into the AC inlet and the power supply input unit is sufficiently small without being shielded by the shielding unit 120 because the distance between the high-voltage winding portion N2 and the AC inlet and the power supply input unit is sufficiently large.

  In this embodiment, the shield 120 is a conductive metal, but any material that shields electromagnetic waves can be used. For example, the shielding part 120 may be made of ceramic, plastic or the like.

[Embodiment 2]
Further, as shown in FIG. 6, the shielding part 130 may not cover the upper part of the transformer T2, and may be structured to shield between the transformer T2 and the AC inlet. FIG. 6 is a front view of a switching power supply device in which the shielding part 130 includes the I-shaped bracket frame 110. Other configurations are the same as those of the first embodiment.

  In the present embodiment, it is conceivable that the electromagnetic field generated from the transformer T2 wraps around the conductive metal plate as the shield 130 and enters the AC inlet. On the other hand, the mixing of the electromagnetic field into the AC inlet can be reduced by further reducing the distance between the shield 130 and the transformer T2. Further, if the height of the wall of the shielding part 130 is increased, there is an effect of preventing the mixing of the electromagnetic field. However, when a reduction in height is required due to the small size and small space, the height is also limited. Therefore, the shielding portion preferably covers the upper portion of the transformer T2 as in the first embodiment.

  FIG. 7 and FIG. 8 show the actual measurement results of the noise terminal voltage for the present embodiment and the prior art shown in FIG. In both cases, the distance between the power input unit and the high-voltage winding of the transformer is about 3 cm, the height of the AC inlet is 1.5 cm, and the height of the transformer is 0.8 cm. The height of the shielding part 130 according to the present embodiment is 2 cm. The voltage of the high-voltage winding part of the transformer is about 900 Vrms, and the drive frequency is about 55 kHz. About this Embodiment and the prior art shown in FIG. 11, the structure and conditions other than the shielding part 130 are completely the same.

  Comparing the graphs of FIGS. 7 and 8 with the noise terminal voltage evaluation results under the above conditions, it can be seen that there is an effect of reducing the noise terminal voltage in a frequency band near about 1 MHz which is the output frequency of the inverter circuit. In the configuration of FIG. 8 without the shielding portion, the noise terminal voltage was about 45 dBμV, whereas in the configuration of FIG. 7 with the shielding portion, a reduction effect of about 8 dBμV was confirmed. The smaller the noise terminal voltage, the better, and the margin for the upper limit of the target noise terminal voltage increased from 11.4 dBμV to 19.0 dBμV. Therefore, the present invention is effective in improving the noise terminal voltage performance, and the inverter circuit and the power supply input section can be arranged adjacent to each other on a single substrate, so that the switching power supply device can be reduced in size.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  When the switching power supply unit is integrated with an inverter circuit that outputs a high voltage and is used for a printed board with a small size, a low profile, and a small space, it can be applied to improve the noise terminal voltage performance of the switching power source device.

(A) is a top view which shows the metal fitting frame of AC inlet concerning one Embodiment of this invention, (b) is a front view which shows the said metal fitting frame. It is a circuit diagram which shows the power supply input part and RCC circuit of the switching power supply which concern on this invention. It is a top view which shows the winding part of the transformer of an inverter circuit. It is a top view which shows the switching power supply device which concerns on this invention. It is a front view which shows the switching power supply device shown in FIG. It is a front view which shows the switching power supply device which concerns on this invention. It is the graph which measured the noise terminal voltage of the switching power supply concerning the present invention. It is the graph which measured the noise terminal voltage of the conventional switching power supply device. (A) is a top view which shows the metal fitting frame of the conventional AC inlet, (b) is a front view which shows the said metal fitting frame. It is a top view which shows the conventional switching power supply device. It is a front view which shows the switching power supply device shown in FIG.

Explanation of symbols

100 Bracket frame 100a AC inlet holder 100a
100b, 100c Fixed part 110 Metal frame 120 Shield part 120a Upright part 120b Roof part 130 Shield part 200 Metal frame 300 AC inlet (AC voltage input terminal)
310 Substrate 410 Power Input 420 420 Rectifier Circuit 430 Ringing Choke Converter (RCC) Circuit 440 Converter Circuit F1 Fuse R1A, R1B Resistor C1 Across The Line Capacitor C2, C3 Capacitor BD1 Bridge Diode C4 Electrolytic Capacitor R2, R3 Resistor Q1 Switching Element (FET) )
Q2 transistor C5 capacitor C6 capacitor R4 resistor R5 resistor R6 resistor T1 transformer T2 transformer D20 diode C20 electrolytic capacitor PC1 photocoupler N1 low voltage winding part N2 high voltage winding part

Claims (9)

A power input unit comprising an AC voltage input terminal and a noise filter circuit for reducing electromagnetic noise,
A converter circuit for converting an AC input from the power input unit into a DC output;
In the switching power supply device comprising: an inverter circuit provided with a transformer that converts the direct current output of the converter circuit into an alternating current output;
A switching power supply device comprising a shielding portion that shields electromagnetic waves generated by the transformer between the AC voltage input terminal and the transformer.   The switching power supply device according to claim 1, wherein the converter circuit includes a ringing choke converter circuit.   The switching power supply according to claim 1, wherein the shielding unit is arranged to shield between the power input unit excluding a noise filter circuit unit and the transformer.   The switching power supply according to any one of claims 1 to 3, wherein the shielding portion is a conductive metal.   5. The switching power supply device according to claim 4, wherein the conductive metal is made of copper.   The switching power supply according to claim 4, wherein the conductive metal is iron.   The switching power supply according to any one of claims 1 to 6, wherein the conductive metal is connected to GND on a secondary side of the circuit of the switching power supply.   The switching power supply according to any one of claims 1 to 7, wherein the shielding portion covers at least a part of an upper portion of the high-voltage winding portion of the transformer.   A portion of the shielding portion that covers an upper portion of the high-voltage winding portion of the transformer and a portion that includes a portion that shields between the power input portion and the transformer are formed in an L shape. 9. The switching power supply device according to claim 8, wherein

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