EMI filtering optimization structure for switching power supply

Abstract

The utility model relates to the technical field of electromagnetic interference (EMI) filtering, in particular to an EMI filtering optimization structure for a switching power supply. The EMI filter circuit is electrically connected with the input end of the rectifier bridge BD1, the output end of the rectifier bridge BD1 is electrically connected with the drive circuit through the filter module, the drive circuit is electrically connected with the primary side of the transformer T1, the dotted terminal of the secondary side of the transformer T1 is electrically connected with the anode of the diode D3, and the synonym terminal of the secondary side of the transformer T1 and the cathode of the capacitor EC3 are grounded. The cathode of the diode D3 is electrically connected with the anode of the capacitor EC3; the filtering module has a harmonic filtering function; the mounting position of the secondary side of the transformer T1 on the circuit board is far away from the EMI filter circuit; the problems that noise is introduced by subsequent harmonic filtering of the EMI filter circuit 1 and self EMI filtering fails due to improper layout of the circuit board are solved.

Description

Technical Field

[0001] This utility model relates to the field of electromagnetic interference (EMI) filtering technology, and in particular to an optimized EMI filtering structure for switching power supplies. Background Technology

[0002] Currently, although switching power supplies incorporate EMI filter circuits at the rectifier bridge input when connected to mains power to reduce electromagnetic interference, and based on ERP standards, harmonic filtering is required to effectively reduce harmonic pollution and ensure the stability and safety of the power system, thus necessitating the placement of an inductor between the EMI filter circuit and the positive input of the rectifier bridge, this placement generates power frequency noise. The magnetic flux distortion caused by power frequency current and electromagnetic forces result in significant noise from inductor vibration (if the inductor is before the rectifier bridge, the direction of the current flowing through it changes due to the presence of power frequency AC current, resulting in both positive and negative currents, i.e., currents with the same amplitude but opposite directions, leading to a larger peak-to-peak current and a larger rate of change of current di / dt). This necessitates the use of better materials (such as iron-silicon-aluminum), the addition of soundproof caps, or methods like soaking the inductor coils and cores in varnish to reduce noise, significantly increasing costs and yielding less than ideal results, leading to low cost-effectiveness.

[0003] More importantly, the current layout of switching power supply circuit boards does not take into account the impact of moving points (referring to high-frequency interference sources; for flyback switching power supplies, typical high-frequency interference sources are MOSFETs, secondary rectifier diodes, transformers, etc.) on EMI filter circuits. When the EMI filter circuit and the moving point are too close, the EMI filter circuit is easily affected by the moving point and fails. Utility Model Content

[0004] To address the aforementioned shortcomings, the purpose of this invention is to propose an optimized EMI filtering structure for switching power supplies, which solves the problems of noise introduced by subsequent harmonic filtering in EMI filtering circuits and EMI filtering failure due to improper circuit board layout.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] An EMI filtering optimization structure for a switching power supply includes an EMI filter circuit, a rectifier bridge BD1, a filter module, a drive circuit, a transformer T1, a diode D3, and a capacitor EC3. The EMI filter circuit is electrically connected to the input terminal of the rectifier bridge BD1, the output terminal of the rectifier bridge BD1 is electrically connected to the drive circuit via the filter module, the drive circuit is electrically connected to the primary side of the transformer T1, the same-name terminal of the secondary side of the transformer T1 is electrically connected to the anode of the diode D3, the opposite-name terminal of the secondary side of the transformer T1 is grounded to the negative terminal of the capacitor EC3, and the cathode of the diode D3 is electrically connected to the positive terminal of the capacitor EC3.

[0007] The filtering module has a harmonic filtering function;

[0008] The secondary side of the transformer T1 is located away from the EMI filter circuit at its mounting position on the circuit board.

[0009] Furthermore, the filtering module includes an RC filter and an LC filter; the output of the rectifier bridge BD1 is electrically connected to the drive circuit after passing through both the RC filter and the LC filter.

[0010] Furthermore, the filtering module includes an inductor L1, a resistor R13, a capacitor C11, and a capacitor C3; one end of the inductor L1, one end of the resistor R13, and one end of the capacitor C11 are all electrically connected to the positive output terminal of the rectifier bridge BD1, and the other end of the capacitor C11 is electrically connected to the negative output terminal of the rectifier bridge BD1.

[0011] The other end of the inductor L1, the other end of the resistor R13, and one end of the capacitor C3 are connected together and then electrically connected to the driving circuit; the other end of the capacitor C11 and the other end of the capacitor C3 are connected together and then electrically connected to the driving circuit.

[0012] Furthermore, in the circuit board, the EMI filter circuit and the rectifier bridge BD1 are centrally mounted on the primary side of the transformer T1, and the diode D3 is mounted on the secondary side of the transformer T1.

[0013] Furthermore, the EMI filter circuit includes a common-mode inductor and a safety capacitor.

[0014] The technical solution provided by this utility model can include the following beneficial effects: In the main circuit of the switching power supply, which includes an EMI filter circuit, a rectifier bridge BD1, a drive circuit, a transformer T1, a diode D3, and a capacitor EC3, the harmonic filtering between the EMI filter circuit and the rectifier bridge BD1 is integrated into the filter module located between the rectifier bridge BD1 and the drive circuit. Thus, the harmonics are removed after rectification by the rectifier bridge BD1. Since the current of the filter module is unidirectional, the peak-to-peak ripple current is smaller, the current change rate di / dt is smaller, and no noise is introduced after the EMI filter circuit, and the cost is lower. At the same time, the secondary side of the transformer T1 is mounted far away from the EMI filter circuit on the circuit board, so that the components in the EMI filter circuit are farther away from the secondary side of the transformer T1, and thus farther away from the diode D3 (moving point). The electrical air gap and creepage distance of high-frequency interference coupled to the EMI filter circuit through the air via the wires are longer, and the EMI filter circuit is less affected, avoiding EMI filter failure. Attached Figure Description

[0015] Figure 1 This is a circuit diagram of an EMI filtering optimization structure for a switching power supply, which is one embodiment of this utility model.

[0016] Figure 2 This is a circuit board layout diagram of an existing EMI filter structure.

[0017] Figure 3 Is it like this? Figure 1 The diagram shows a circuit board layout for an EMI filtering optimization structure used in switching power supplies.

[0018] The components include: EMI filter circuit 1, rectifier bridge BD1, filter module 2, drive circuit 3, transformer T1, diode D3, capacitor EC3, inductor L1, resistor R13, capacitor C11, and capacitor C3. Detailed Implementation

[0019] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0020] In the description of embodiments of this utility model, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of embodiments of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0021] In the description of the embodiments of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this utility model according to the specific circumstances.

[0022] The following is combined Figures 1 to 3 This invention describes an EMI filtering optimization structure for a switching power supply according to an embodiment of the present invention.

[0023] An EMI filtering optimization structure for a switching power supply includes an EMI filter circuit 1, a rectifier bridge BD1, a filter module 2, a drive circuit 3, a transformer T1, a diode D3, and a capacitor EC3. The EMI filter circuit 1 is electrically connected to the input terminal of the rectifier bridge BD1, the output terminal of the rectifier bridge BD1 is electrically connected to the drive circuit 3 via the filter module 2, the drive circuit 3 is electrically connected to the primary side of the transformer T1, the same-name terminal of the secondary side of the transformer T1 is electrically connected to the anode of the diode D3, the opposite-name terminal of the secondary side of the transformer T1 is grounded to the negative terminal of the capacitor EC3, and the cathode of the diode D3 is electrically connected to the positive terminal of the capacitor EC3.

[0024] Filter module 2 has harmonic filtering function;

[0025] The secondary side of transformer T1 is located far from the EMI filter circuit 1 on the circuit board.

[0026] This utility model proposes a preferred embodiment of an EMI filtering optimization structure for switching power supplies, such as... Figures 1 to 3As shown, in the main circuit of the switching power supply, which includes an EMI filter circuit 1, a rectifier bridge BD1, a drive circuit 3, a transformer T1, a diode D3, and a capacitor EC3, the harmonic filtering between the EMI filter circuit 1 and the rectifier bridge BD1 is integrated into the filter module 2 located between the rectifier bridge BD1 and the drive circuit 3. Thus, the harmonics are removed after rectification by the rectifier bridge BD1. Because the current in the filter module 2 is unidirectional, the peak-to-peak ripple current is smaller, and the current change rate di / dt is smaller, preventing the introduction of noise after the EMI filter circuit 1, and also reducing cost. Simultaneously, the secondary side of the transformer T1 is mounted on the circuit board away from the EMI filter... The wave circuit 1 makes the components in the EMI filter circuit 1 farther away from the secondary side of transformer T1, thus away from diode D3 (the moving point). The electrical air gap and creepage distance of high-frequency interference that crosses the wires and couples to the EMI filter circuit through the air are longer, and the EMI filter circuit 1 is less affected, avoiding EMI filter failure. The reason why the moving point of diode D3 is chosen to be far away in the switching power supply is that an RCD circuit (such as one composed of resistor R5, capacitor C8 and diode D3) is usually set between the output of the secondary side of transformer T1 and capacitor EC3. Before being filtered by capacitor EC3, the moving point interference will be relatively large, which is a leakage point in the filter of the switching power supply.

[0027] It should be noted that the term "drive circuit 3" generally refers to the functional circuits of the switching power supply located on the primary side of transformer T1, such as PFC circuits (e.g., PFC chips and their peripheral circuits), flyback drive circuits (e.g., flyback drive chips and their peripheral circuits), etc.

[0028] Furthermore, the filter module 2 includes an RC filter and an LC filter; the output of the rectifier bridge BD1 is electrically connected to the drive circuit 3 after passing through both the RC filter and the LC filter.

[0029] In this embodiment, the filter module 2 located at the output end of the rectifier bridge BD1 needs to have not only harmonic filtering capabilities, but also other filtering capabilities to ensure the stability of the signal output from the rectified circuit to the drive circuit 3; therefore, the filter module 2 is a composite filter module, which integrates an RC filter and an LC filter (mainly responsible for harmonic filtering).

[0030] Furthermore, the filter module 2 includes an inductor L1, a resistor R13, a capacitor C11, and a capacitor C3; one end of the inductor L1, one end of the resistor R13, and one end of the capacitor C11 are all electrically connected to the positive output terminal of the rectifier bridge BD1, and the other end of the capacitor C11 is electrically connected to the negative output terminal of the rectifier bridge BD1.

[0031] The other end of inductor L1, the other end of resistor R13, and one end of capacitor C3 are connected together and then electrically connected to drive circuit 3; the other end of capacitor C11 and the other end of capacitor C3 are connected together and then electrically connected to drive circuit 3.

[0032] In this embodiment, the filter module 2 is a composite filter module. The specific circuit preferably consists of an inductor L1, a resistor R13, a capacitor C11, and a capacitor C3. The inductor L1, capacitor C11, and capacitor C3 form a CLCΠ-type filter structure, and the resistor R13, capacitor C11, and capacitor C3 form a CRCΠ-type filter structure. By utilizing the characteristics of fast charging and slow discharging of capacitors C11 and C3, the characteristic of DC-passing and AC-blocking of inductor L1, and the characteristic of AC-blocking of resistor R13, the voltage ripple after rectifier bridge BD1 is reduced, providing a certain degree of protection against lightning strikes and surge currents during power-on and power-off. Furthermore, by using capacitor C11 and resistor R13 in parallel, in situations with high current, it avoids the large resistance loss caused by using CRC-type filtering alone. With CLC-type filtering, the inductor theoretically does not lose energy.

[0033] Furthermore, in the circuit board, the EMI filter circuit 1 and the rectifier bridge BD1 are mounted together on the primary side of the transformer T1, and the diode D3 is mounted on the secondary side of the transformer T1.

[0034] In this embodiment, to ensure that the secondary side of transformer T1 is located away from the EMI filter circuit 1 on the circuit board, and that the EMI filter circuit 1 and rectifier bridge BD1 are centrally mounted on the primary side of transformer T1, the EMI filter circuit 1 is constantly isolated by the main body of transformer T1. It must cross the main body of transformer T1 to reach the secondary side of transformer T1, thus moving it away from the diode D3 (moving point) connected to the secondary side of transformer T1, thereby lengthening the electrical air gap and creepage distance. Optional circuit board layout adjustments include directly rotating transformer T1 by 90°, such as... Figure 2 (before rotation) and Figure 3 As shown (after rotation), the dashed lines generally refer to electrical air gaps and creepage distances.

[0035] Furthermore, the EMI filter circuit 1 is equipped with a common-mode inductor and a safety capacitor.

[0036] In this embodiment, the high-frequency interference from the moving point mainly affects the EMI filter circuit 1, which is composed of a common-mode inductor and a safety capacitor, causing the common-mode inductor and safety capacitor to fail. Therefore, the EMI filter circuit 1 with the EMI filter optimization structure preferably includes a common-mode inductor and a safety capacitor (the number is not limited).

[0037] Other configurations and operations of the EMI filtering optimization structure for a switching power supply according to the embodiments of this utility model are known to those skilled in the art and will not be described in detail here.

[0038] In this specification, the terms "embodiment," "example," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An EMI filtering optimization structure for switching power supplies, characterized in that: Includes EMI filter circuit, rectifier bridge BD1, filter module, drive circuit, transformer T1, diode D3 and capacitor EC3; The EMI filter circuit is electrically connected to the input terminal of the rectifier bridge BD1. The output terminal of the rectifier bridge BD1 is electrically connected to the drive circuit via the filter module. The drive circuit is electrically connected to the primary side of the transformer T1. The same-name terminal of the secondary side of the transformer T1 is electrically connected to the anode of the diode D3. The opposite-name terminal of the secondary side of the transformer T1 is grounded to the negative terminal of the capacitor EC3. The cathode of the diode D3 is electrically connected to the positive terminal of the capacitor EC3. The filtering module has a harmonic filtering function; The secondary side of the transformer T1 is located away from the EMI filter circuit at its mounting position on the circuit board.

2. The EMI filtering optimization structure for switching power supplies according to claim 1, characterized in that: The filtering module includes an RC filter and an LC filter; the output of the rectifier bridge BD1 is electrically connected to the drive circuit after passing through both the RC filter and the LC filter.

3. The EMI filtering optimization structure for switching power supplies according to claim 1, characterized in that: The filtering module includes an inductor L1, a resistor R13, a capacitor C11, and a capacitor C3; one end of the inductor L1, one end of the resistor R13, and one end of the capacitor C11 are all electrically connected to the positive output terminal of the rectifier bridge BD1, and the other end of the capacitor C11 is electrically connected to the negative output terminal of the rectifier bridge BD1. The other end of the inductor L1, the other end of the resistor R13, and one end of the capacitor C3 are connected together and then electrically connected to the driving circuit; the other end of the capacitor C11 and the other end of the capacitor C3 are connected together and then electrically connected to the driving circuit.

4. The EMI filtering optimization structure for switching power supplies according to claim 1, characterized in that: In the circuit board, the EMI filter circuit and the rectifier bridge BD1 are mounted together on the primary side of the transformer T1, and the diode D3 is mounted on the secondary side of the transformer T1.

5. The EMI filtering optimization structure for a switching power supply according to claim 1, characterized in that: The EMI filter circuit is equipped with a common-mode inductor and a safety capacitor.

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