Switching power supply circuit without y-capacitor and electronic device

Abstract

The application relates to a Y-capacitor-free switching power supply circuit and electronic equipment, the switching power supply circuit comprising an input port, an input circuit, a transformer, an output circuit and an output port connected in sequence; the input circuit comprises an input filter circuit, the input filter circuit comprising a first inductor and a second inductor, the first inductor being connected between the positive electrode of the input port and the first end of the primary winding, and the second inductor being connected between the negative electrode of the input port and the ground end of the input circuit, the inductance value of the first inductor being smaller than that of the second inductor. A big-small inductor design is adopted at the input side of the switching power supply circuit, the inductors with different inductance values have different impedances to noise of different frequencies, the noise generated by the transformer or the power switch is blocked by the inductors, the interference flowing into the LISN or the alternating current network is reduced, and the CE and RE performances can be improved.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and in particular relates to a switching power supply circuit and electronic device without Y capacitor. Background Technology

[0002] Switching power supplies transfer energy from the primary side to the secondary side by controlling the periodic switching of switching devices. The energy is then processed by the secondary filter circuit before being supplied to the user side. During the high-frequency switching of the switching devices, voltage and current spikes are generated. These high-frequency spike signals are coupled and transmitted through the parasitic parameters of the power devices, leads, and circuit board traces, causing severe electromagnetic interference (EMI) to the public power grid. Switching power supplies have requirements for conducted interference (CE) and radiated interference (RE), with frequency band requirements of 150kHz-30MHz for conducted interference and 30MHz-1GHz for radiated interference. Conducted interference can be further divided into common-mode interference and differential-mode interference based on its propagation mode. Analyzing common-mode interference is more difficult than analyzing differential-mode interference.

[0003] In switching power supplies, to reduce the impact of common-mode interference on the collector (CE) and emitter (RE), a Y capacitor is typically used to connect the primary and secondary sides. For example, the primary ground and secondary ground are connected through a Y capacitor. Compared to the parasitic capacitance of each component, the Y capacitor has a larger capacitance, effectively providing a low-impedance path to ground for common-mode interference signals. For the CE, some interference signals can directly reach ground, thus avoiding detection by the Line Impedance Stabilization Network (LISN), thereby improving the CE. For the RE, some common-mode interference signals will not be transmitted to the AC connector on the primary side or the DC bus on the secondary side, reducing the amount of radiated interference signal. This reduces the interference signal detected by the antenna, thus improving the RE. However, the Y capacitor connects the primary and secondary sides, generating leakage current. This leakage current not only introduces noise into the system but may also pose safety risks to users. For example, in voice communication equipment, leakage current can cause strong power frequency interference, resulting in a buzzing sound that can be heard in the telephone line. Therefore, the Y capacitor in the circuit needs to be removed. However, directly removing the Y capacitor will worsen the adapter's CE and RE by more than 10dB. To solve the EMI problem without increasing costs, we can only hope to optimize the circuit design and transformer design. Utility Model Content

[0004] The purpose of this application is to provide a switching power supply circuit and electronic device without Y capacitors, which aims to solve the electromagnetic interference problem of traditional switching power supplies.

[0005] In a first aspect, embodiments of this application provide a switching power supply circuit without a Y capacitor, comprising an input port, an input circuit, a transformer, an output circuit, and an output port connected in sequence;

[0006] The input circuit includes an input filter circuit connected between the input port and a first end of the primary winding of the transformer. The second end of the primary winding of the transformer is connected to a power switch of the input circuit. The input filter circuit includes a first filter capacitor, a second filter capacitor, a first inductor, and a second inductor. The first filter capacitor is connected between the positive and negative terminals of the input port. The first inductor is connected between the positive terminal of the input port and the first end of the primary winding. The second filter capacitor is connected between the first end of the primary winding and the ground terminal of the input circuit. The second inductor is connected between the negative terminal of the input port and the ground terminal of the input circuit. The inductance value of the first inductor is greater than the inductance value of the second inductor.

[0007] In some embodiments, the input filter circuit further includes a first resistor and a second resistor, wherein the first resistor is connected in parallel with the first inductor and the second resistor is connected in parallel with the second inductor.

[0008] In some embodiments, the transformer includes a magnetic core, a frame disposed on the magnetic core, and a winding wound on the magnetic core and located between the primary side and the secondary side of the frame, the winding including a primary winding, an auxiliary winding, a shielding winding and a secondary winding stacked sequentially from the magnetic core outwards.

[0009] In some embodiments, a first grounding conductor is further included, which is connected between the ground terminal of the input circuit and the magnetic core.

[0010] In some embodiments, the winding between the first and second ends of the primary winding is wound in multiple layers on the magnetic core, and the second end of the primary winding is located on the outer layer of the winding.

[0011] In some embodiments, the winding layer of the auxiliary winding is wound to fill the width of the skeleton, the winding layer of the shielding winding is wound to a portion of the width of the skeleton, and the winding layer of the shielding winding is wound close to the primary side of the skeleton.

[0012] In some embodiments, the auxiliary winding has one winding layer, and the auxiliary winding has three windings connected in parallel and wound in parallel.

[0013] In some embodiments, the winding layer of the shielding winding is a single layer, and the winding density of the winding layer of the shielding winding in the middle portion of the frame width is greater than the winding density on both sides, or the winding density of the winding layer of the shielding winding near the primary side of the frame is lower than the winding density near the secondary side.

[0014] In some embodiments, the secondary winding has one winding layer, the first end of the secondary winding is connected to the ground terminal of the output circuit, the second end of the secondary winding is connected to the positive output terminal of the output circuit, the second end of the secondary winding is directly opposite to the second end of the primary winding, and both are located close to the primary side or the secondary side of the frame.

[0015] Secondly, embodiments of this application provide an electronic device, including the Y-capacitor-free switching power supply circuit described above.

[0016] The beneficial effects of this application embodiment compared with related technologies are as follows: The switching power supply circuit without Y capacitor includes an input port, an input circuit, a transformer, an output circuit, and an output port connected in sequence; the input circuit includes an input filter circuit, which is connected between the input port and the first end of the primary winding of the transformer, and the second end of the primary winding of the transformer is connected to the power switch of the input circuit. The input filter circuit includes a first filter capacitor, a second filter capacitor, a first inductor, and a second inductor. The first filter capacitor is connected between the positive terminal and the negative terminal of the input port, the first inductor is connected between the positive terminal of the input port and the first end of the primary winding, the second filter capacitor is connected between the first end of the primary winding and the ground terminal of the input circuit, and the second inductor is connected between the negative terminal of the input port and the ground terminal of the input circuit. The inductance value of the first inductor is greater than the inductance value of the second inductor. A design using a large and a small inductor on the input side of the switching power supply circuit is employed. Inductors with different inductance values ​​have different impedances to noise at different frequencies. Noise generated by transformers or power switches is blocked by the inductors, reducing interference flowing into the LISN or AC network, and improving CE and RE performance. In addition, based on the different inductance values, the large inductor has a higher impedance at low frequencies, while the small inductor has a higher impedance at high frequencies. Therefore, using a design with a large and a small inductor can improve the bandwidth of the frequency band, thereby reducing electromagnetic interference. Attached Figure Description

[0017] Figure 1 A circuit diagram of a switching power supply circuit provided in an embodiment of this application;

[0018] Figure 2 A schematic diagram of the cross-sectional structure of the transformer in a switching power supply circuit provided in an embodiment of this application;

[0019] Figure 3This is the CE test waveform in a conventional switching power supply circuit.

[0020] Figure 4 This is the RE test waveform in a conventional switching power supply circuit;

[0021] Figure 5 CE test waveform of a switching power supply circuit provided in an embodiment of this application;

[0022] Figure 6 The RE test waveform of a switching power supply circuit provided in an embodiment of this application. Detailed Implementation

[0023] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0024] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0025] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0026] Furthermore, 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 technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0027] like Figure 1 As shown, this application provides a switching power supply circuit without a Y capacitor, which can be applied to any electronic device that requires a switching power supply, such as an adapter.

[0028] The switching power supply circuit includes an input port, an input circuit 11, a transformer 12, an output circuit 13, and an output port connected in sequence. The input port includes the positive terminal VIN+ and the negative terminal VIN-, and the output port includes the positive terminal V+ and the negative terminal V-.

[0029] In some embodiments, the input circuit 11 includes a startup circuit 110 and a switching power supply chip U1. The switching power supply chip U1 integrates a switching transistor (or power switch), such as a MOSFET. The drain of the switching transistor is connected to the SW pin (switch control pin) of the switching power supply chip U1. The positive terminal VIN+ of the input terminal VIN is connected to the SW pin through the primary winding N1 of the transformer 12. The CS (current sampling) pin of the switching power supply chip U1 is grounded through the sampling resistor R2. The FB (feedback) pin of the switching power supply chip U1 is connected to the auxiliary winding N2 through a resistor R3 and also to the primary ground GND1 through a resistor R4. A surface-mount capacitor C1 is connected in parallel across the resistor R4. The auxiliary winding N2 is connected to the VDD (power supply) pin of the switching power supply chip U1. The startup circuit 110 is connected to the positive terminal VIN+ of the input port. The startup circuit 110 generally includes a current-limiting resistor and an electrolytic capacitor C2.

[0030] In some embodiments, the flyback switching power supply generally also includes a clamping circuit 111, which is connected to both ends of the primary winding N1 and is used to absorb the peak voltage and peak current generated during the high-frequency turn-on and turn-off processes of the switching transistor. The input port may include a rectifier bridge and a filter capacitor for connecting AC voltage; the input port may also be a DC input for connecting DC power.

[0031] In some embodiments, the output circuit 13 typically includes a rectifier diode D1 and a filter capacitor C3. The rectifier diode D1 is connected between the secondary winding N4 of the transformer 12 and the positive terminal V+ of the output port, and the filter capacitor C3 is connected between the positive terminal V+ and the negative terminal V- of the output port. It is understood that the above is merely a brief description of the input circuit 11 and output circuit 13 of a flyback switching power supply in one specific embodiment. It is exemplary and used to illustrate the technical solution of this application, and not to limit it. Those skilled in the art should understand that the input circuit 11 and output circuit 13 of the flyback switching power supply can also have other equivalent embodiments.

[0032] like Figure 1As shown, in some embodiments, the input circuit 11 further includes an input filter circuit 112. The input filter circuit 112 is connected between the input port and the first terminal Pin1 of the primary winding N1 of the transformer 12. The second terminal Pin2 of the primary winding N1 of the transformer 12 is connected to the power switch of the input circuit 11. The input filter circuit 112 includes a first filter capacitor C11, a second filter capacitor C12, a first inductor L1, and a second inductor L2. The first filter capacitor C11 is connected between the positive terminal VIN+ and the negative terminal VIN- of the input port. The first inductor L1 is connected between the positive terminal VIN+ of the input port and the first terminal Pin1 of the primary winding N1. The second filter capacitor C12 is connected between the first terminal Pin1 of the primary winding N1 and the ground terminal (i.e., primary ground) GND1 of the input circuit 11. The second inductor L2 is connected between the negative terminal VIN- of the input port and the ground terminal GND1 of the input circuit 11. The inductance value of the first inductor L1 is smaller than the inductance value of the second inductor L2.

[0033] It is understandable that Pin 1, the first terminal of the primary winding N1, is the stationary pin of the transformer, and Pin 2, the second terminal of the primary winding N1 of transformer 12, is the moving pin of the transformer. The first inductor L1 and the second inductor L2 employ a design with one large and one small inductor. Inductors with different inductance values ​​have different impedances to noise at different frequencies. Noise generated by transformer 12 or the power switch is blocked by the inductors, reducing interference flowing into the LISN and the AC network, thus improving CE and RE performance. Furthermore, based on the design of the large and small inductance values ​​of the first inductor L1 and the second inductor L2, the larger inductor has a higher impedance at low frequencies, while the smaller inductor has a higher impedance at high frequencies. Therefore, using a design with one large and one small inductor can improve the bandwidth of the frequency band, thereby reducing electromagnetic interference.

[0034] In some embodiments, the first inductor L1 and the second inductor L2 are color-coded inductors; in alternative embodiments, other types of inductors may be used instead.

[0035] like Figure 1 As shown, the input filter circuit 112 also includes a first resistor R11 and a second resistor R12. The first resistor R11 is connected in parallel with the first inductor L1, and the second resistor R12 is connected in parallel with the second inductor L2. It is understood that the larger the quality factor Q of the inductor, the lower the loss of the input filter circuit 112, and the better the noise filtering effect for a specific frequency band. According to Q = wL / R, the parallel resistors reduce the equivalent resistance R, increasing the Q value and further improving the filtering effect.

[0036] like Figure 2As shown, in some embodiments, the transformer 12 includes a magnetic core 121, a frame 122 disposed on the magnetic core 121, and a winding of the frame width wound on the magnetic core 121 and located between the primary side 122A and the secondary side 122B of the frame 122. The winding includes a primary winding N1, an auxiliary winding N2, a shielding winding N3 and a secondary winding N4 stacked sequentially from the magnetic core 121 outward.

[0037] Two auxiliary windings, N2 and N3, are designed between the primary winding N1 and the secondary winding N4 to increase the distance between the primary winding N1 and the secondary winding N4, reduce the parasitic capacitance between the primary winding N1 and the secondary winding N4, and thus reduce the common-mode noise between the primary winding N1 and the secondary winding N4.

[0038] like Figure 1 As shown, in some embodiments, the flyback switching power supply further includes a first ground conductor 14, which is connected between the ground terminal GND1 of the input circuit 11 and the magnetic core 121. This bypasses some common-mode noise to the ground terminal GND1 of the input circuit 11, i.e., the primary ground, preventing it from being detected by the LISN or antenna. The first ground conductor 14 can be, for example, a wire or a copper trace laid on a circuit board.

[0039] like Figure 2 As shown, in some embodiments, the winding between the first end Pin1 and the second end Pin2 of the primary winding N1 is wound in multiple layers on the magnetic core 121, and the second end Pin2 of the primary winding N1 is located on the outer layer of the winding. Increasing the distance between the second end Pin2 of the primary winding N1, i.e., the moving pin, and the magnetic core 121 reduces parasitic capacitance, thereby reducing common-mode noise in this path. For example, the primary winding N1 is wound with a single wire, starting at the first end Pin1 of the primary winding N1, close to the primary side 122A of the magnetic core 121 and the frame 122, and wound counterclockwise for two layers, ending at the second end Pin2 of the primary winding N1, also close to the primary side 122A of the frame 122, but farther away from the magnetic core 121 than the first end Pin1 of the primary winding N1.

[0040] like Figure 2 As shown, in some embodiments, the winding layer of the auxiliary winding N2 is wound to fill the width of the skeleton, the winding layer of the shielding winding N3 is wound to a portion of the width of the skeleton, and the winding layer of the shielding winding N3 is wound close to the primary side 122A of the skeleton 122.

[0041] For example, the auxiliary winding N2 has a single winding layer, and the winding layer of the auxiliary winding N2 consists of three windings connected in parallel. Furthermore, the winding layer of the auxiliary winding N2 is tightly wound clockwise, filling the width of the bobbin. After the winding is completed, two layers of insulating tape are wound to make the surface relatively flat, thereby improving the consistency of the next layer of shielding winding N3.

[0042] like Figure 2 As shown, in some embodiments, the winding layer of the shielding winding N3 is a single layer, and the winding density of the winding layer of the shielding winding N3 in the middle portion between the primary side 122A and the secondary side 122B of the frame 122 is greater than the winding density on both sides, or the winding density of the winding layer of the shielding winding N3 near the primary side 122A of the frame 122 is lower than the winding density near the secondary side 122B.

[0043] For example, the shielding winding N3 is single-wire wound, with a clockwise close winding near the primary side 122A of the bobbin 122, resulting in good consistency. The zero-voltage Y can be adjusted by rationally designing the number of turns in the shielding winding N3 (e.g., ...). Figure 2 As shown, the voltage distribution of windings between different layers can be plotted, and the corresponding common-mode noise flow path can be drawn. By increasing or decreasing the number of turns of the shielding winding N3, the total common-mode noise flowing from the primary winding N1 to the secondary winding N4 and from the secondary winding N4 to the primary winding N1 can be changed, ultimately achieving the purpose of zeroing. This reduces the total common-mode noise between the primary winding N1 and the secondary winding N4. At the same time, the position of the shielding winding N3 relative to the width of the frame can also be finely adjusted, such as being densely wound in the center or densely wound near the secondary side, to finely adjust the Y voltage. This can help solve the problem of Y voltage deviation in transformer mass production. After winding, three layers of insulating tape are wound.

[0044] like Figure 2 As shown, in some embodiments, the secondary winding N4 has one winding layer. The first end Pin6 of the secondary winding N4 is connected to the ground terminal (i.e., secondary ground) GND2 of the output circuit 13. The second end Pin7 of the secondary winding N4 is connected to the positive output terminal V+ of the output circuit 13. The second end Pin7 of the secondary winding N4 is directly opposite to the second end Pin2 of the primary winding N1, and both are located close to the primary side 122A or the secondary side 122B of the frame 122.

[0045] The exemplary secondary winding N4 is wound with a single wire of three layers of insulation, with one layer wound counterclockwise. The starting point is the first end Pin6 of the secondary winding N4, and the ending point is the second end Pin7 of the secondary winding N4. That is, the moving point pins of the secondary winding N4 and the primary winding N1 are both placed on the same side of the frame 122. The induced voltage difference between the secondary winding N4 and the primary winding N1 becomes smaller. Under the condition that the parasitic capacitance remains unchanged, the common mode noise current between the secondary winding N4 and the primary winding N1 is reduced.

[0046] See Figures 3 to 6 Compared to conventional switching power supply circuits with Y capacitors, the present application presents a switching power supply circuit without Y capacitors. The conventional switching power supply circuit with Y capacitors has a transformer winding structure consisting of: a first primary winding, an auxiliary winding and a shielding winding in the same layer, a secondary winding, and a second primary winding.

[0047] See Figure 3 and Figure 4 CE and RE test waveforms of a conventional switching power supply circuit:

[0048] CE test waveforms: insufficient margin in the 0.5-5M frequency band, no margin or even exceeding the standard in the 6-10M frequency band.

[0049] RE test waveforms: a total of 3 frequency points at 30M, 50M and 80M, and the readings exceeded the limits.

[0050] See Figure 5 and Figure 6 The CE and RE test waveforms of the switching power supply circuit in this application embodiment are as follows:

[0051] CE test waveform: within the 0.5~30MHz frequency band, the margin is above 15dB.

[0052] RE test waveform: No reading point is needed, and the expected margin is around 10dB.

[0053] As can be seen, the CE and RE of the switching power supply circuit in this application embodiment are greatly improved.

[0054] The switching power supply circuit of this application embodiment, after removing the Y capacitor, does not add any other electronic components. Only by optimizing the circuit design and transformer winding structure design, the adapter CE and RE margins are sufficient, and the transformer scheme has good consistency, meeting the needs of large-scale mass production.

[0055] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A switching power supply circuit without a Y capacitor, characterized in that, It includes an input port, an input circuit, a transformer, an output circuit, and an output port connected in sequence; The input circuit includes an input filter circuit connected between the input port and a first end of the primary winding of the transformer. The second end of the primary winding of the transformer is connected to a power switch of the input circuit. The input filter circuit includes a first filter capacitor, a second filter capacitor, a first inductor, and a second inductor. The first filter capacitor is connected between the positive and negative terminals of the input port. The first inductor is connected between the positive terminal of the input port and the first end of the primary winding. The second filter capacitor is connected between the first end of the primary winding and the ground terminal of the input circuit. The second inductor is connected between the negative terminal of the input port and the ground terminal of the input circuit. The inductance value of the first inductor is smaller than the inductance value of the second inductor.

2. The switching power supply circuit as described in claim 1, characterized in that, The input filter circuit further includes a first resistor and a second resistor, wherein the first resistor is connected in parallel with the first inductor, and the second resistor is connected in parallel with the second inductor.

3. The switching power supply circuit as described in claim 1, characterized in that, The transformer includes a magnetic core, a frame disposed on the magnetic core, and a winding wound on the magnetic core, located between the primary side and the secondary side of the frame, with a frame width. The winding includes a primary winding, an auxiliary winding, a shielding winding, and a secondary winding stacked sequentially from the magnetic core outwards.

4. The switching power supply circuit as described in claim 3, characterized in that, It also includes a first grounding conductor, which is connected between the ground terminal of the input circuit and the magnetic core.

5. The switching power supply circuit as described in claim 3, characterized in that, The winding between the first and second ends of the primary winding is wound in multiple layers on the magnetic core, and the second end of the primary winding is located on the outer layer of the winding.

6. The switching power supply circuit as described in claim 3, characterized in that, The auxiliary winding is wound to fill the width of the skeleton, the shielding winding is wound to a portion of the width of the skeleton, and the shielding winding is wound close to the primary side of the skeleton.

7. The switching power supply circuit as described in claim 3 or 6, characterized in that, The auxiliary winding has one layer, and the auxiliary winding consists of three parallel windings connected in parallel.

8. The switching power supply circuit as described in claim 3 or 6, characterized in that, The shielding winding has one layer, and the winding density of the shielding winding in the middle part of the frame width is greater than the winding density on both sides, or the winding density of the shielding winding on the primary side near the frame is lower than the winding density on the secondary side.

9. The switching power supply circuit as described in claim 6, characterized in that, The secondary winding has one layer. The first end of the secondary winding is connected to the ground terminal of the output circuit. The second end of the secondary winding is connected to the positive output terminal of the output circuit. The second end of the secondary winding is directly opposite to the second end of the primary winding and is located close to the primary side or the secondary side of the frame.

10. An electronic device, characterized in that, Including the Y-capacitor-free switching power supply circuit as described in any one of claims 1 to 9.

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