High-voltage input flyback converter and power supply system
By setting up a loop suppression circuit in the flyback converter and using capacitors to uniformize the circuit, the problem of loop current to circuit stability under high voltage input is solved, and safety and efficiency are improved.
Patent Information
- Application Number
- CN202510450013.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-10
- Publication Date
- 2025-08-05
AI Technical Summary
In the switching power supply with high voltage input, the multi-overlapping flyback converter has problems that affect circuit stability, especially the circulating problem caused by uneven voltage between capacitors and inconsistent number of turns of the transformer, which harms circuit components.
A loop suppression circuit is set up between the input buffer circuit and the main power circuit, and a voltage equalization process is performed using a capacitor. By suppressing the loop current generated when the capacitor absorbs the switch tube, the voltage equalization of the main power circuit is achieved.
It effectively suppresses the generation of circulation, improves the safety, stability and efficiency of the system, and avoids heat loss of resistive devices. It is suitable for high-voltage input flyback converters and power supply systems.
Smart Images
Figure CN120433591A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of switching power supplies, and in particular to a flyback converter with a high-voltage input and a power supply system. Background Art
[0002] In switching power supplies, high voltage input is increasingly used. To address the voltage stress problem of the switch tube under high voltage, a multi-overlap topology is often used. Under an N-fold overlapping topology, the voltage stress of the switch tube can be reduced by N times.
[0003] A multi-overlap topology requires connecting input capacitors in series, and the transformer coils in the main power circuit often share a common core. When the primary switching transistor is on, the voltages across the primary windings follow the turns ratio, resulting in equal voltages across each primary winding. Ideally, the voltage across each primary winding equals the input voltage connected in parallel with it. However, due to varying leakage currents and equivalent impedances of the capacitors, the input voltage is not evenly distributed across the series capacitors. When the switching transistor is on, the circuit of the capacitor with the higher voltage is coupled through the primary winding to the circuit of the capacitor with the lower voltage. The switching transistor in this circuit then charges the capacitor, causing a circulating current. Due to the low impedance of the circuit itself, even a small voltage difference between the capacitors can cause a significant circulating current, potentially damaging circuit components (such as sampling resistors and switching transistors connected in series). In addition, when the primary windings differ greatly, for example, the actual turns ratio does not meet 1:1, even if the input capacitor is voltage-equalizing, the coil with fewer turns will reflect the voltage to the coil with more turns when the switch tube is turned on, and the above-mentioned circulating current problem will also exist. Summary of the Invention
[0004] The main purpose of the present application is to provide a flyback converter with a high voltage input and a power supply system, which can at least solve the problem in the related art that the circulating current of multiple overlapping flyback converters affects the circuit stability.
[0005] To achieve the above-mentioned objectives, the first aspect of the present application provides a flyback converter with a high-voltage input, comprising: an input buffer circuit, a circulating current suppression circuit and a main power circuit, wherein the input buffer circuit comprises a plurality of capacitors connected in series, the main power circuit comprises a plurality of main power units connected in series, and the circulating current suppression circuit comprises at least one circulating current suppression capacitor; the input buffer circuit and the main power circuit are both electrically connected to a power supply, the circulating current suppression capacitor is electrically connected to the main power circuit, or the circulating current suppression capacitor is electrically connected to the input buffer circuit and the main power circuit respectively; the circulating current suppression circuit is used to perform voltage equalization processing on the main power circuit using the circulating current suppression capacitor.
[0006] Furthermore, the input buffer circuit includes n capacitors connected in series, where n is an integer greater than or equal to 2; the first end of the series-connected capacitor unit is electrically connected to the positive electrode of the power supply, the second end of the series-connected capacitor unit is electrically connected to the negative electrode of the power supply, and the connection point of two adjacent capacitors is used as a series capacitor midpoint. The series capacitor unit has a total of n-1 series capacitor midpoints.
[0007] Furthermore, the main power circuit includes n main power units, each of which includes a switching tube and a primary winding of a transformer, and the circulating current suppression circuit includes n-1 circulating current suppression capacitors; one end of the primary winding of the transformer in the first main power unit is electrically connected to the positive pole of the power supply, and one end of the primary winding of the transformer in the remaining main power units is electrically connected to one end of the corresponding circulating current suppression capacitor, the other end of the primary winding of the transformer in each main power unit is electrically connected to the first end of the switching tube, the second end of the switching tube in the last main power unit is electrically connected to the negative pole of the power supply, and the second ends of the switching tubes in the remaining main power units are electrically connected to one end of the primary winding of the transformer in the next main power unit, the third end of the switching tube in each main power unit is used to be electrically connected to an external controller, and the other end of the circulating current suppression capacitor is electrically connected to the midpoint of the corresponding series capacitor.
[0008] Furthermore, the main power circuit includes n main power units connected in series, each of which includes a switching tube and a primary winding of a transformer, and the circulating current suppression circuit includes n circulating current suppression capacitors; one end of the primary winding of the transformer in the first main power unit is electrically connected to the corresponding circulating current suppression capacitor and the positive pole of the power supply, and one end of the primary winding of the transformer in the remaining main power units is electrically connected to the corresponding circulating current suppression capacitor, and the other end of the primary winding of the transformer in each main power unit is electrically connected to the first end of the switching tube, and the second end of the switching tube in the last main power unit is electrically connected to the corresponding circulating current suppression capacitor and the negative pole of the power supply, and the second end of the switching tube in the remaining main power units is electrically connected to one end of the primary winding of the transformer in the next main power unit, and the third end of the switching tube in each main power unit is used to be electrically connected to an external controller.
[0009] Furthermore, the main power unit further includes a clamping circuit, a first end of the clamping circuit being electrically connected to one end of the primary winding of the transformer, and a second end of the clamping circuit being electrically connected to the other end of the primary winding of the transformer.
[0010] Furthermore, the circulating current suppression capacitor is used to absorb the current generated by the switch tube during the conduction and closing process and flowing into the midpoint of the series capacitor, so as to realize voltage balancing of the output voltage of the primary winding of the transformer.
[0011] Furthermore, the capacitance of the circulating current suppression capacitor is smaller than the capacitance of the capacitor in the input buffer circuit.
[0012] A second aspect of the present application provides a power supply system, comprising the flyback converter as described in the first aspect of the present application.
[0013] From the above description, it can be seen that the present application sets a circulating current suppression circuit composed of at least one capacitor between the input buffer circuit and the main power circuit, thereby achieving circulating current suppression of the multi-overlap flyback converter through the capacitor, ensuring the safety of the device, eliminating the need to set up resistive devices, avoiding affecting the system efficiency, and effectively improving the safety and stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.
[0015] Figure 1 is a circuit schematic diagram of a first flyback converter according to an embodiment of the present application; Figure 2 is a circuit schematic diagram of a second flyback converter according to an embodiment of the present application; Figure 3 1 is a schematic diagram of a current loop of the first flyback converter according to an embodiment of the present application when the input buffer circuit has an uneven voltage; Figure 4 is a circuit schematic diagram of a third flyback converter according to an embodiment of the present application; Figure 5 Schematic diagram of the current loop of the third flyback converter according to the embodiment of the present application when the input buffer circuit has uneven voltage. DETAILED DESCRIPTION
[0016] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of this application.
[0017] In the related art, there is a problem that the circulating current of multiple overlapping flyback converters affects the stability of the circuit. Therefore, an embodiment of the present application provides a flyback converter.
[0018] like Figure 1 、 Figure 2 The figures show the circuit schematic diagrams of the first and second flyback converters provided in the embodiments of the present application, respectively. The flyback converter includes: an input buffer circuit, a circulating current suppression circuit, and a main power circuit. The input buffer circuit includes multiple capacitors connected in series, the main power circuit includes multiple main power units connected in series, and the circulating current suppression circuit includes at least one circulating current suppression capacitor. The input buffer circuit and the main power circuit are both electrically connected to a power supply, and the circulating current suppression capacitor is electrically connected to the main power circuit, or the circulating current suppression capacitor is electrically connected to the input buffer circuit and the main power circuit respectively. The circulating current suppression circuit is used to perform voltage equalization on the main power circuit using the circulating current suppression capacitor.
[0019] Specifically, in this embodiment, the input buffer circuit in the flyback converter is used to store and buffer the input voltage, while the main power circuit is used to convert the input voltage. The circulating current suppression circuit, comprised of capacitors, is connected between the input buffer circuit and the main power circuit, or to the main power circuit itself. The capacitors are used to equalize the voltage in the main power circuit to achieve circulating current suppression. Compared to related art methods that use resistive devices to reduce circulating current, this embodiment employs a capacitive suppression method to avoid losses caused by resistive device heating and the resulting impact on system efficiency, thereby effectively improving system stability.
[0020] Further, see Figure 1 and Figure 2 The input buffer circuit includes n capacitors connected in series, where n is an integer greater than or equal to 2; a first end of the series capacitor unit is electrically connected to the positive electrode of the power supply, a second end of the series capacitor unit is electrically connected to the negative electrode of the power supply, and a connection point between two adjacent capacitors is used as a series capacitor midpoint. The series capacitor unit has a total of n-1 series capacitor midpoints.
[0021] Specifically, in this embodiment, the input buffer circuit consists of multiple high-voltage, high-capacity capacitors (such as aluminum electrolytic capacitors) connected in series. This input buffer circuit helps smooth the input voltage waveform and reduce voltage fluctuations and high-frequency noise in the input power supply. Because the source voltage in a power supply system may be affected by other loads, the series combination of capacitors can provide instantaneous current and reduce power supply ripple. Furthermore, the series combination of capacitors can store a certain amount of energy at the input terminal, allowing for transient current during sudden load changes, ensuring output stability.
[0022] Further, see Figure 1The main power circuit includes n main power units, each including a switch tube and a transformer primary winding. The circulating current suppression circuit includes n-1 circulating current suppression capacitors. One end of the transformer primary winding in the first main power unit is electrically connected to the positive pole of the power supply, and one end of the transformer primary winding in the remaining main power units is electrically connected to one end of the corresponding circulating current suppression capacitor. The other end of the transformer primary winding in each main power unit is electrically connected to the first end of the switch tube. The second end of the switch tube in the last main power unit is electrically connected to the negative pole of the power supply. The second end of the switch tube in the remaining main power units is electrically connected to one end of the transformer primary winding in the next main power unit. The third end of the switch tube in each main power unit is used to be electrically connected to an external controller, and the other end of the circulating current suppression capacitor is electrically connected to the midpoint of the corresponding series capacitor. The circulating current suppression capacitor is used to absorb the current generated by the switch tube during the conduction and closing process and flowing into the midpoint of the series capacitor, so as to realize voltage equalization of the output voltage of the transformer primary winding.
[0023] Further, see Figure 1 and Figure 2 The main power unit also includes a clamping circuit, a first end of the clamping circuit is electrically connected to one end of the primary winding of the transformer, and a second end of the clamping circuit is electrically connected to the other end of the primary winding of the transformer.
[0024] Further, see Figure 1 and Figure 2 , the capacitance of the circulating current suppression capacitor is smaller than the capacitance of the capacitor in the input buffer circuit.
[0025] Specifically, the working principle of the first flyback converter provided in the embodiment of the present application is as follows: When there is a voltage difference between the input capacitors, a circulating current will be formed between the first waves of the switch tube turning on, charging the circulating current suppression capacitor Cx, for example Figure 3 The diagram shows the current loop of the first flyback converter when the input buffer circuit is not voltage-balanced. Assuming Vci1>Vci2, at the moment the switch is turned on, the voltages of the two coils are clamped, Vnp1=Vnp2=Vci1, and a voltage is generated in the circuit. Figure 3The currents Ip1 and Ip2 are shown, with Ip2 representing the circulating current. Since Cx is a small-value capacitor, the voltage across it rises rapidly, reaching half the voltage difference between the coils, that is, Vcx = 0.5*(Vci1 - Vci2). Subsequently, even if there is a voltage difference ΔV between the coils due to uneven voltage distribution between the input capacitors or inconsistent primary windings, when the switch is turned on, the voltage between the first coil, Vnp1, = Vci1 - Vcx = Vci1 - 0.5ΔV, and the voltage between the second coil, Vnp2, = Vcx + Vci2 = Vci1 - 0.5ΔV. This means that the voltages between the two coils are equal, thus preventing circulating current during normal operation. Even if the input electrolytic capacitors remain unevenly distributed or there is a large difference between the primary windings, this will not result in circulating current, and the voltage stress on the switch remains constant. During normal operation, the voltage on capacitor Cx will track and maintain a constant voltage of half the voltage difference between the input capacitors. It should be noted that the circulating current suppression capacitor Cx is a non-polar, high-frequency, small-capacitance capacitor, typically ranging from a few nanofarads to tens of nanofarads depending on the converter power level. The first flyback converter provided in the present embodiment only requires the addition of a single high-frequency, small capacitor, resulting in low cost, simple design, and high reliability.
[0026] See Figure 2 The main power circuit includes n main power units connected in series, each main power unit includes a switching tube and a primary winding of a transformer, and the circulating current suppression circuit includes n circulating current suppression capacitors; one end of the primary winding of the transformer in the first main power unit is electrically connected to the corresponding circulating current suppression capacitor and the positive pole of the power supply, and one end of the primary winding of the transformer in the remaining main power units is electrically connected to the corresponding circulating current suppression capacitor, and the other end of the primary winding of the transformer in each main power unit is electrically connected to the first end of the switching tube, and the second end of the switching tube in the last main power unit is electrically connected to the corresponding circulating current suppression capacitor and the negative pole of the power supply, and the second end of the switching tube in the remaining main power units is electrically connected to one end of the primary winding of the transformer in the next main power unit, and the third end of the switching tube in each main power unit is used to be electrically connected to an external controller.
[0027] Specifically, the working principle of the second flyback converter provided in the embodiment of the present application is as follows: Since the electrical connection points of the various capacitors in the input buffer circuit are disconnected from the main power circuit, even if the capacitors in the input buffer circuit are not voltage-equalized, it will not affect the normal operation of the main power circuit. It should be noted that the circulating current suppression capacitor Cy is a non-polar, high-frequency, small-capacitance capacitor, generally between tens and one hundred nanofarads. At the moment the switch tube is turned on, the circulating current suppression capacitor will automatically equalize the voltage. Since the capacitance of the circulating current suppression capacitor is very small, the voltage equalization process is very rapid, greatly reducing the impact of the circulating current. It should be noted that the capacitor Cy needs to be a high-voltage capacitor with a larger capacity than the capacitor Cx directly connected in series between the input capacitor and the switch tube, and the number of capacitors Cy should be one more than the capacitor Cx.
[0028] like Figure 4 The circuit diagram of the third flyback converter provided by the embodiment of the present application is shown as follows. Figure 1 The N-stacked variant of the flyback converter shown can better illustrate the role of the circulating current suppression capacitor mentioned above in this application.
[0029] See Figure 5 FIG. 1 is a schematic diagram of a current loop of a third flyback converter when the input buffer circuit is uneven. The working principle of the third flyback converter is as follows: Assuming that the voltage of the first capacitor in the input buffer circuit is the highest, Vci1>Vci2>...>Vcin, when the switch is turned on, the voltage of each primary winding is:
[0030] The voltage across each primary winding is clamped by Vci1, and the voltage across each circulating current suppression capacitor Cx can be calculated using the above equation. During normal operation, the voltage across the Cx capacitor absorbs the uneven voltage of the input buffer capacitor, making the voltage across all primary windings equal. This also ensures that all switches in the main power circuit are voltage-balanced. Therefore, the N-stacked flyback topology eliminates the circulating current problem, effectively addressing the root cause of the circulating current issue.
[0031] It's important to note that when the switches are driven inconsistently, the current in the loop of the last switch to turn off flows through capacitor Cx, generating no additional losses and only charging and discharging Cx. To avoid large voltage deviations after charge and discharge when Cx is small, which can increase stress on the switches, the capacitance of Cx should be kept small and can be slightly increased depending on the driving inconsistency.
[0032] The flyback converter provided in the embodiment of the present application uses a capacitor as a circulating current suppression circuit and is connected between the input buffer circuit and the main power circuit. When the capacitors in the input buffer circuit are not voltage-balanced or the number of transformer turns in the main power circuit is inconsistent, the generation of circulating current can be suppressed by the action of the circulating current suppression capacitor. Moreover, when the switch tubes in each main power unit are driven inconsistently, in the loop of the switch tube that is last turned off, the current will only charge and discharge the circulating current suppression capacitor, and will not generate additional losses. This avoids the heat loss caused by the use of resistive devices for circulating current suppression, which affects the system stability. It can effectively suppress the generation of circulating current and improve system efficiency. Moreover, the circulating current suppression circuit is compatible with any number of overlapping flyback topologies and is more advantageous in application scenarios with high-level input voltage.
[0033] An embodiment of the present application further provides a power supply system, which includes the above-mentioned flyback converter.
[0034] It should be noted that the various embodiments in the present application are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referenced to each other.
[0035] It should also be noted that, in the content of this application, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.
[0036] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments shown herein but is intended to be applied in the broadest manner consistent with the principles and novel features disclosed herein.
Claims
1. A flyback converter with high voltage input, characterized in that: include: An input buffer circuit, a circulating current suppression circuit, and a main power circuit, wherein the input buffer circuit includes multiple capacitors connected in series, the main power circuit includes multiple main power units connected in series, and the circulating current suppression circuit includes at least one circulating current suppression capacitor; the input buffer circuit and the main power circuit are both electrically connected to a power supply, the circulating current suppression capacitor is electrically connected to the main power circuit, or the circulating current suppression capacitor is electrically connected to the input buffer circuit and the main power circuit respectively; The circulating current suppression circuit is used to perform voltage balancing on the main power circuit using the circulating current suppression capacitor.
2. The flyback converter according to claim 1, wherein: The input buffer circuit includes n capacitors connected in series, where n is an integer greater than or equal to 2; The first end of the series-connected capacitor unit is electrically connected to the positive electrode of the power supply, and the second end of the series-connected capacitor unit is electrically connected to the negative electrode of the power supply. The connection point of two adjacent capacitors is used as a series capacitor midpoint. The series capacitor unit has a total of n-1 series capacitor midpoints.
3. The flyback converter according to claim 2, wherein: The main power circuit includes n main power units, each of which includes a switch tube and a primary winding of a transformer, and the circulating current suppression circuit includes n-1 circulating current suppression capacitors; One end of the primary winding of the transformer in the first main power unit is electrically connected to the positive pole of the power supply, one end of the primary winding of the transformer in the remaining main power units is electrically connected to one end of the corresponding circulating current suppression capacitor, the other end of the primary winding of the transformer in each main power unit is electrically connected to the first end of the switching tube, the second end of the switching tube in the last main power unit is electrically connected to the negative pole of the power supply, the second end of the switching tube in the remaining main power units is electrically connected to one end of the primary winding of the transformer in the next main power unit, the third end of the switching tube in each main power unit is used to be electrically connected to an external controller, and the other end of the circulating current suppression capacitor is electrically connected to the midpoint of the corresponding series capacitor.
4. The flyback converter according to claim 2, wherein: The main power circuit includes n main power units connected in series, each main power unit includes a switch tube and a primary winding of a transformer, and the circulating current suppression circuit includes n circulating current suppression capacitors; One end of the primary winding of the transformer in the first main power unit is electrically connected to the corresponding circulating current suppression capacitor and the positive pole of the power supply, respectively; one end of the primary winding of the transformer in the remaining main power units is electrically connected to the corresponding circulating current suppression capacitor; the other end of the primary winding of the transformer in each main power unit is electrically connected to the first end of the switching tube; the second end of the switching tube in the last main power unit is electrically connected to the corresponding circulating current suppression capacitor and the negative pole of the power supply, respectively; the second end of the switching tube in the remaining main power units is electrically connected to one end of the primary winding of the transformer in the next main power unit; and the third end of the switching tube in each main power unit is used to be electrically connected to an external controller.
5. The flyback converter according to claim 3 or 4, characterized in that: The main power unit further includes a clamping circuit, a first end of the clamping circuit being electrically connected to one end of the primary winding of the transformer, and a second end of the clamping circuit being electrically connected to the other end of the primary winding of the transformer.
6. The flyback converter according to claim 3, wherein: The circulating current suppression capacitor is used to absorb the current generated by the switch tube during the conduction and closing process and flowing into the midpoint of the series capacitor, so as to realize voltage balancing of the output voltage of the primary winding of the transformer.
7. The flyback converter according to any one of claims 1 to 6, characterized in that: The capacitance of the circulating current suppression capacitor is smaller than the capacitance of the capacitor in the input buffer circuit.
8. A power supply system, characterized in that: The flyback converter comprises the flyback converter according to any one of claims 1 to 7.