Control circuit and method for a switching power supply and switching power supply

Abstract

The application provides a control circuit and method of a switching power supply and the switching power supply, and relates to the technical field of switching power supplies. The switching power supply comprises a cascaded power factor correction circuit and an isolated conversion circuit. A feedback input end of the control circuit is used for receiving a feedback signal, the feedback signal is converted based on an output signal of the isolated conversion circuit and is used for representing load variation. A control output end of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal. The application adjusts the voltage loop response speed of the power factor correction circuit by detecting the load variation of the isolated conversion circuit in the latter stage.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and in particular to a control circuit, method, and switching power supply for a switching power supply. Background Technology

[0002] In a two-stage power supply architecture that includes a PFC (Power Factor Correction) circuit and an isolated converter, a large bus capacitor is connected in parallel at the output of the PFC. To ensure power factor (PF) and total harmonic distortion (THD), the voltage loop bandwidth of the PFC is usually designed to be very low (typically around 10Hz to 20Hz), resulting in a slow PFC response.

[0003] However, when the load downstream of the isolated converter undergoes significant changes (such as a sudden switch between full load and no load), the system's energy balance is disrupted, causing serious consequences. For example, when the load suddenly switches from full load to no load, due to loop delay in the PFC, a large amount of excess energy is channeled into the bus capacitor. The bus voltage spikes instantaneously, potentially exceeding the withstand voltage limit of the bus capacitor or the main switching transistor of the isolated converter, leading to direct device breakdown and frequent triggering of overvoltage protection. Conversely, when the load switches instantaneously from no load to full load, the bus voltage drops sharply, triggering undervoltage protection and causing the isolated converter to lose its zero-voltage switching (ZVS) capability.

[0004] Existing technologies adjust the loop response speed of the PFC based on the PFC output voltage to optimize load response. However, at this time, the PFC output voltage has already dropped or exceeded a certain range. Even if the PFC loop response speed is improved, it will still have a serious impact. For example, the PFC output voltage may exceed the withstand voltage limit of the bus capacitor and the main switch of the isolated converter, or the PFC output voltage may trigger undervoltage protection and cause the isolated converter to lose the zero-voltage switching (ZVS) condition. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a control circuit, method and switching power supply for a switching power supply, which adjusts the voltage loop response speed of the power factor correction circuit by detecting the load change of the subsequent isolated converter circuit.

[0006] In a first aspect, the present invention provides a control circuit for a switching power supply, the switching power supply including a cascaded power factor correction circuit and an isolated conversion circuit; The feedback input terminal of the control circuit is used to receive feedback signals, which are converted from the output signal of the isolation converter circuit and are used to characterize load changes. The control output terminal of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal.

[0007] In one embodiment, the control circuit includes a load change judgment unit, and the signal input terminal of the load change judgment unit is connected to the feedback input terminal. The load change judgment unit generates a change indication signal based on the feedback signal; the control circuit controls the voltage loop response speed of the power factor correction circuit based on the change indication signal.

[0008] In one embodiment, the load change determination unit is specifically used to: determine whether the load of the switching power supply has changed abruptly based on the difference between two output powers in adjacent cycles and a preset difference threshold; or, determine whether the load of the switching power supply has changed abruptly based on the rate of change of output power and a preset rate of change threshold. The output power is determined based on the feedback signal.

[0009] In one implementation, the output power is determined based on the feedback signal, the output voltage of the power factor correction circuit, and the switching frequency of the isolated converter circuit.

[0010] In one embodiment, the control circuit further includes a control unit, the signal input terminal of which is connected to the signal output terminal of the load change judgment unit, and the signal output terminal of which is connected to the control output terminal. The control unit is used to: receive a sudden change indication signal; if the sudden change indication signal indicates that a sudden change has occurred in the load, control the power factor correction circuit to adjust from the first voltage loop response speed to the second voltage loop response speed, wherein the second voltage loop response speed is higher than the first voltage loop response speed; if the sudden change indication signal indicates that no sudden change has occurred in the load, control the power factor correction circuit to maintain or restore the first voltage loop response speed.

[0011] In one embodiment, when the feedback signal is a voltage feedback signal, the control circuit further includes a power calculation unit. The signal input terminal of the power calculation unit is connected to the feedback input terminal, and the signal output terminal of the power calculation unit is connected to the signal input terminal of the load change judgment unit.

[0012] In one embodiment, when the feedback signal is a current feedback signal, the control circuit further includes a feedback conversion unit and a power calculation unit. The signal input terminal of the feedback conversion unit is connected to the feedback input terminal, the signal output terminal of the feedback conversion unit is connected to the signal input terminal of the power calculation unit, and the signal output terminal of the power calculation unit is connected to the signal input terminal of the load change judgment unit.

[0013] Secondly, the present invention provides a control method for a switching power supply, the switching power supply including a cascaded power factor correction circuit and an isolated conversion circuit; the method includes: The feedback signal is received and converted from the output signal of the isolated conversion circuit to characterize load changes. The voltage loop response speed of the power factor correction circuit is controlled based on the feedback signal.

[0014] In one implementation, controlling the voltage loop response speed of the power factor correction circuit based on a feedback signal includes: A sudden change indication signal is generated based on the feedback signal, and the voltage loop response speed of the power factor correction circuit is controlled based on the sudden change indication signal.

[0015] In one implementation, generating a mutation indication signal based on a feedback signal includes: Based on the difference between two output powers in adjacent cycles and a preset difference threshold, determine whether the load of the switching power supply has changed abruptly, and generate a change indication signal; or, based on the rate of change of output power and a preset rate of change threshold, determine whether the load of the switching power supply has changed abruptly, and generate a change indication signal. The output power is determined based on the feedback signal.

[0016] In one implementation, the output power is determined based on the feedback signal, the output voltage of the power factor correction circuit, and the switching frequency of the isolated converter circuit.

[0017] In one implementation, controlling the voltage loop response speed of the power factor correction circuit based on a sudden change indication signal includes: If the mutation indicator signal indicates that a sudden change has occurred in the load, the control power factor correction circuit adjusts from the first voltage loop response speed to the second voltage loop response speed, which is higher than the first voltage loop response speed; if the mutation indicator signal indicates that no sudden change has occurred in the load, the control power factor correction circuit maintains or reverts to the first voltage loop response speed.

[0018] Thirdly, the present invention provides a switching power supply, including a power factor correction circuit, an isolated conversion circuit, and a control circuit; The feedback input terminal of the control circuit is connected to an isolated converter circuit; The feedback input receives a feedback signal, which is converted from the output signal of the isolated converter circuit and is used to characterize load changes. The control output of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal.

[0019] This invention provides a control circuit, method, and switching power supply for a switching power supply. The switching power supply includes a cascaded power factor correction circuit and an isolated converter circuit. The feedback input terminal of the control circuit receives a feedback signal, which is converted from the output signal of the isolated converter circuit and is used to characterize load changes. The control output terminal of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal. This invention adjusts the voltage loop response speed of the power factor correction circuit by detecting load changes in the downstream isolated converter circuit. The adjustment of the response speed is completed before the output voltage of the power factor correction circuit changes drastically, thereby avoiding the bus voltage exceeding the withstand voltage limit of the bus capacitor and the main switching transistor of the isolated converter circuit due to sudden load changes. It also avoids the bus voltage triggering undervoltage protection and causing the isolated converter circuit to lose its zero-voltage switching condition.

[0020] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the control circuit of a switching power supply provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the overall structure of a control circuit for a switching power supply provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the overall structure of a control circuit for another switching power supply provided in an embodiment of the present invention; Figure 4A control circuit operating waveform diagram provided in an embodiment of the present invention; Figure 5 A flowchart illustrating a control method for a switching power supply provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the overall process of a control method for a switching power supply provided in an embodiment of the present invention.

[0024] Explanation of key component symbols: 1-Power factor correction circuit; 2-Isolation conversion circuit; 3-Control circuit; 31-Control unit; 32-Load change judgment unit; 33-Power calculation unit; 34-Feedback conversion unit; 4-Voltage feedback unit; 5-Current feedback unit. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Currently, existing technologies trigger response speed increases based on drops or over-limits in the PFC output voltage, resulting in adjustments lagging behind load changes. This fails to prevent bus voltage exceeding limits and subsequent consequences such as device overvoltage breakdown, undervoltage protection false triggering, or ZVS failure. Therefore, this invention provides a control circuit, method, and power supply for a switching power supply. By detecting load changes in the subsequent isolated converter circuit, it adjusts the voltage loop response speed of the power factor correction circuit to avoid the aforementioned problems in existing technologies.

[0027] To facilitate understanding of this embodiment, a detailed description of the control circuit of a switching power supply disclosed in this embodiment of the invention will be provided first. (See [link to relevant documentation]). Figure 1 The diagram shows a control circuit for a switching power supply, which includes a cascaded power factor correction (PFC) circuit and an isolated converter circuit 2. The output of the power factor correction circuit 1 is connected to the input of the isolated converter circuit 2. The input of the power factor correction circuit 1 receives an external input voltage, and the output of the isolated converter circuit 2 provides an output voltage to the load. The control circuit 3 can be used to control only the power factor correction circuit 1, or it can be used to control both the power factor correction circuit 1 and the isolated converter circuit 2 simultaneously.

[0028] The feedback input terminal of control circuit 3 is used to receive feedback signals, which are converted from the output signal of isolated converter circuit 2 and are used to characterize load changes, such as... Figure 1The feedback signal shown The control output terminal of the control circuit 3 is connected to the power factor correction circuit 1, and the control circuit 3 controls the voltage loop response speed of the power factor correction circuit 1 based on the feedback signal.

[0029] Specifically, control circuit 3 directly detects whether the load of the two-stage switching power supply undergoes a sudden change: when a sudden load change is detected, the response speed of the PFC voltage loop is increased, so that the power factor correction circuit 1 can follow the load change more quickly and adjust its output power; when no sudden load change is detected, the PFC voltage loop maintains or restores its original response speed to take into account the requirements of power factor and total harmonic distortion.

[0030] The voltage loop response speed refers to how quickly the voltage control loop in the power factor correction circuit 1 responds to changes in the output voltage. The voltage loop response speed can be achieved by adjusting the voltage loop bandwidth; a larger bandwidth results in a faster response. Preferably, the voltage loop response speed is achieved by adjusting the voltage loop proportional coefficient. Increasing the proportional coefficient increases the voltage loop bandwidth and improves the response speed; decreasing the proportional coefficient decreases the voltage loop bandwidth and reduces the response speed.

[0031] Furthermore, control circuit 3 receives feedback signals that characterize the output electrical parameters of the two-stage switching power supply, such as the state of the output voltage or output current. Control circuit 3 uses these feedback signals to detect whether a sudden change occurs in the load of the two-stage switching power supply.

[0032] When the load changes, the output current or output voltage of the isolated converter circuit 2 will change accordingly, so the feedback signal can reflect the load variation. There are several ways to generate the feedback signal, such as converting the output voltage of the isolated converter circuit 2 into a feedback signal through an optocoupler feedback circuit, or directly obtaining the voltage feedback signal from the output terminal of the isolated converter circuit 2 through a resistor voltage divider feedback circuit. The control output terminal of the control circuit 3 provides a control signal to the power factor correction circuit 1 to adjust the operating state of the power factor correction circuit 1.

[0033] Furthermore, the control circuit 3 adjusts the response speed of the PFC voltage loop by regulating its bandwidth. Preferably, the bandwidth of the PFC voltage loop is adjusted by regulating the voltage loop proportional coefficient.

[0034] Furthermore, the control circuit 3 detects whether the load of the two-stage switching power supply has changed abruptly, and makes a judgment based on the amplitude or rate of change of the feedback signal. Specifically, the amplitude of the feedback signal change includes comparing the difference between two feedback signals in adjacent cycles with a preset difference threshold to determine whether the load of the switching power supply has changed abruptly; the rate of change of the feedback signal includes taking the derivative of the feedback signal and comparing the derivative value with a set threshold to determine whether the load has changed abruptly.

[0035] Furthermore, a feedback circuit can be set between the feedback signal and the output, including optocoupler feedback or resistor voltage divider feedback.

[0036] The control circuit of the switching power supply provided in this embodiment of the invention directly detects whether the load of the two-stage switching power supply undergoes a sudden change, thereby adjusting the response speed of the PFC voltage loop. This accelerates the response speed of the PFC voltage loop before the PFC output voltage changes drastically, improves the PFC output voltage to meet the load change requirements, and avoids the PFC output voltage from exceeding the withstand voltage limits of the bus capacitor and the main switching transistor of the isolated converter, or the PFC output voltage triggering undervoltage protection and causing the isolated converter to lose the zero-voltage switching (ZVS) condition.

[0037] Through the above scheme, control circuit 3 directly uses the feedback signal characterizing load changes to adjust the voltage loop response speed of power factor correction circuit 1, instead of waiting for the output voltage of power factor correction circuit 1 to change before adjustment. Since the feedback signal comes directly from the output signal of isolated converter circuit 2, load changes can be sensed by control circuit 3 in a timely manner through the feedback signal. Therefore, control circuit 3 has already completed the adjustment of voltage loop response speed before the output voltage of power factor correction circuit 1 changes drastically. In this way, when the load switches from full load to no load, power factor correction circuit 1 can reduce output power in a timely manner to avoid excess energy flowing into the bus capacitor and causing the bus voltage to rise instantaneously; when the load switches from no load to full load, power factor correction circuit 1 can increase output power in a timely manner to avoid a large drop in bus voltage. As a result, the bus voltage can be kept within a safe range, avoiding exceeding the withstand voltage limit of the bus capacitor or the main switching transistor of isolated converter circuit 2, and also avoiding triggering undervoltage protection or causing isolated converter circuit 2 to lose zero-voltage switching conditions.

[0038] It should be understood that Figure 1 The control circuit 3 is shown as independent of the power factor correction circuit 1 and the isolated converter circuit 2. However, in other embodiments, the control circuit 3 may also be integrated with the power factor correction circuit 1 in the same chip, or the control circuit 3 may simultaneously perform the control functions of the power factor correction circuit 1 and the isolated converter circuit 2, as long as the control circuit 3 can receive feedback signals and control the voltage loop response speed of the power factor correction circuit 1 based on the feedback signals.

[0039] exist Figure 1 Based on this, the present invention provides a specific implementation of a control circuit for a switching power supply.

[0040] The control circuit 3 includes a load change judgment unit. The signal input terminal of the load change judgment unit is connected to the feedback input terminal. The load change judgment unit generates a change indication signal based on the feedback signal. The control circuit 3 controls the voltage loop response speed of the power factor correction circuit 1 based on the change indication signal.

[0041] Specifically, the load change judgment unit receives the feedback signal from the feedback input terminal, processes and analyzes the feedback signal, determines whether a change has occurred in the load of the switching power supply, and outputs a change indication signal that characterizes the judgment result. The change indication signal can be a level signal, such as a high level indicating a load change and a low level indicating no load change; it can also be a digitally encoded signal, with different encoding values ​​representing different load states. The control circuit 3 determines whether to adjust the voltage loop response speed of the power factor correction circuit 1 based on the change indication signal, thereby distinguishing the load change judgment function from the response speed adjustment function on the signal link, allowing the judgment logic and adjustment logic to be designed and optimized separately.

[0042] In some optional implementations, the load change detection unit can determine whether a sudden change has occurred in the load of the switching power supply based on one or more of the following: output power, output current, and output voltage. Specifically: Method 1: Determine whether the load of the switching power supply changes abruptly based on the output power.

[0043] The output power is determined based on the feedback signal and the output voltage of the power factor correction circuit 1. Specifically, the feedback signal originates from the output signal of the isolated converter circuit 2, which can be a voltage feedback signal or a current feedback signal. The output voltage of the power factor correction circuit 1 can be obtained by sampling the output of the power factor correction circuit 1, for example, through a voltage sampling circuit connected to the output of the power factor correction circuit 1.

[0044] The explanation of the feedback signal is as follows: In the first embodiment, the feedback signal is a voltage feedback signal, see [link to relevant documentation]. Figure 2 The diagram shows the overall structure of a control circuit for a switching power supply. The control circuit 3 includes a power calculation unit 33, whose signal input terminal is connected to a feedback input terminal (i.e., Figure 2 The feedback pin (LFB) of the power calculation unit 33 is connected to the output of the isolated converter circuit 2 via the voltage feedback unit 4, and the signal output of the power calculation unit 33 is connected to the signal input of the load change judgment unit 32 in the control circuit 3. Based on this circuit structure, the voltage feedback unit 4 receives the voltage output from the output terminal. And convert it into a voltage feedback signal. Transmitted to power calculation unit 33.

[0045] Optionally, the specific circuit of the voltage feedback unit 4 is not limited, as long as the voltage feedback unit 4 can convert the output signal of the isolated conversion circuit 2 into a voltage signal that characterizes the load change.

[0046] In the second embodiment, the feedback signal is a current feedback signal, see [link to relevant documentation]. Figure 3 The diagram shows the overall structure of another switching power supply control circuit. The control circuit 3 includes a power calculation unit 33 and a feedback conversion unit 34. The signal input terminal of the feedback conversion unit 34 is connected to the feedback input terminal (i.e., Figure 3 The feedback pin (LFB) is connected to the output of the isolated converter circuit 2 via the voltage feedback unit 4. The signal output of the feedback conversion unit 34 is connected to the signal input of the power calculation unit 33, and the signal output of the power calculation unit 33 is connected to the signal input of the load change judgment unit 32. Based on this circuit structure, the voltage feedback unit 4 receives the voltage output from the output terminal. And convert it into a current feedback signal. The signal is transmitted to the feedback conversion unit 34, which then converts the current feedback signal into a signal. Signal converted into voltage form The voltage form of the signal Transmitted to power calculation unit 33.

[0047] Optionally, the specific circuit of the voltage feedback unit 4 is not limited, as long as it can be converted from the output signal of the isolation conversion circuit 2 to obtain a current signal that characterizes the load change.

[0048] Optionally, the feedback conversion unit 34 can be implemented using a current-to-voltage conversion circuit, for example, by using a sampling resistor to convert the current feedback signal. Converted to current feedback signal proportional signals When the current feedback signal When the signal increases, The corresponding increase; when the current feedback signal When the signal decreases, The input current is reduced accordingly. Optionally, the feedback conversion unit 34 can also be implemented using a transimpedance amplifier. A transimpedance amplifier can convert the input current into an output voltage while providing a lower input impedance, which is beneficial for the stable operation of the optocoupler feedback circuit. Optionally, the feedback conversion unit 34 can also be implemented using a current mirror circuit, an active current-to-voltage conversion circuit, etc., as long as it can convert the current feedback signal... It can be converted into a voltage signal that can be used by the power calculation unit 33.

[0049] In this embodiment, the current feedback signal needs to be converted into a signal form by the feedback conversion unit 34 before the power calculation unit 33 performs power calculation. The introduction of this additional conversion step enables the control circuit 3 to adapt to feedback circuit types that output feedback signals in the form of current.

[0050] Regardless of whether the first or second embodiment is adopted, optionally, the voltage feedback unit can be implemented in the form of optocoupler isolation, which isolates the output side of the isolated converter circuit 2 from the primary side where the control circuit 3 is located.

[0051] Regardless of whether the first or second embodiment is used, the power calculation unit 33 can obtain the signal. And then based on the signal The output power is determined by the output voltage of the power factor correction circuit 1. Optionally, the power calculation unit 33 can be implemented using analog circuitry or digital circuitry, for example, by using an analog-to-digital converter to process the signal. After sampling, the digital processing unit calculates the output power according to the preset calculation logic. .

[0052] When the power calculation unit 33 outputs power When the load change judgment unit 32 transmits the data, the load change judgment unit 32 can determine the load change based on the output power of two adjacent cycles. The difference between the output power and a preset threshold value is used to determine whether the load of the switching power supply has changed abruptly; or, based on the output power... The rate of change and a preset rate of change threshold are used to determine whether the load of the switching power supply has changed abruptly.

[0053] In the first judgment method, the load change judgment unit 32 calculates the output power of two adjacent cycles. The difference is calculated and compared with a preset difference threshold. Adjacent cycles refer to two time-adjacent calculation cycles, which can be the same as the switching cycle of the isolated converter circuit 2, or an integer multiple of the switching cycle. The preset difference threshold can be pre-set according to the rated output power of the switching power supply, load surge definition standards, or actual application requirements.

[0054] In one example, when the output power of two adjacent cycles When the absolute value of the difference exceeds the preset difference threshold, the load change judgment unit 32 determines that a load change has occurred (including two cases: load increase and load decrease); when the output power of two adjacent cycles When the absolute value of the difference does not exceed the preset difference threshold, the load change judgment unit 32 determines that the load has not changed.

[0055] For example, the preset difference threshold can be set to 30% of the rated output power, when the output power of two adjacent cycles... When the difference changes from 5W to 40W, the load change judgment unit 32 determines that a load change has occurred.

[0056] In the second embodiment, it can also be based on the output power. The rate of change is determined. Specifically, the output power is... The rate of change is obtained by differentiation. When the rate of change is greater than a preset rate of change threshold, the load change judgment unit 32 determines that there is a sudden increase or decrease in load; when the rate of change is not greater than the preset rate of change threshold, the load change judgment unit 32 determines that no change in load has occurred. The preset rate of change threshold can be preset according to the rated output power of the switching power supply, the definition standard of load change, or actual application requirements.

[0057] It should be understood that the above-mentioned judgment methods can be used alone or in combination, and the embodiments of the present invention do not impose any restrictions on this.

[0058] Method 2: Determine whether the load of the switching power supply has changed abruptly based on the output current.

[0059] Specifically, the load change judgment unit 32 directly performs load change identification based on any or a combination of the following criteria based on the feedback signal, and the feedback signal is generated based on the output current of the switching power supply.

[0060] In the first judgment method, when the absolute value of the difference between two feedback signals in adjacent cycles exceeds the preset difference threshold, the load change judgment unit 32 determines that a load change has occurred (including two cases: load increase and load decrease); when the absolute value of the difference between two feedback signals in adjacent cycles does not exceed the preset difference threshold, the load change judgment unit 32 determines that no load change has occurred.

[0061] In the second judgment method, the judgment can also be made based on the rate of change of the feedback signal. Specifically, the rate of change of the feedback signal is obtained by taking its derivative. When the rate of change is greater than a preset rate of change threshold, the load change judgment unit 32 determines that there is a sudden increase or decrease in load; when the rate of change is not greater than the preset rate of change threshold, the load change judgment unit 32 determines that no sudden change has occurred in the load.

[0062] It should be understood that the above-mentioned judgment methods can be used alone or in combination, and the embodiments of the present invention do not impose any restrictions on this.

[0063] Method 3: Determine whether the load of the switching power supply has changed abruptly based on the output voltage.

[0064] Specifically, the load change judgment unit 32 directly performs load change identification based on any or a combination of the following criteria based on the feedback signal, and the feedback signal is generated based on the output voltage of the switching power supply.

[0065] In the first judgment method, when the absolute value of the difference between two feedback signals in adjacent cycles exceeds the preset difference threshold, the load change judgment unit 32 determines that a load change has occurred (including two cases: load increase and load decrease); when the absolute value of the difference between two feedback signals in adjacent cycles does not exceed the preset difference threshold, the load change judgment unit 32 determines that no load change has occurred.

[0066] In the second judgment method, the judgment can also be made based on the rate of change of the feedback signal. Specifically, the rate of change of the feedback signal is obtained by taking its derivative. When the rate of change is greater than a preset rate of change threshold, the load change judgment unit 32 determines that there is a sudden increase or decrease in load; when the rate of change is not greater than the preset rate of change threshold, the load change judgment unit 32 determines that no sudden change has occurred in the load.

[0067] It should be understood that the above-mentioned judgment methods can be used alone or in combination, and the embodiments of the present invention do not impose any restrictions on this.

[0068] For the aforementioned methods one through three, under the same load change conditions, methods two (based on output current) and three (based on output voltage) rely solely on changes in a single electrical parameter for identification, requiring a relatively long load change judgment time to reach the reliable judgment amplitude or change threshold, resulting in slow load change identification. In contrast, method one, based on output power... By making judgments, the time interval from the occurrence of a mutation to system confirmation can be significantly shortened, thus achieving faster load mutation identification. The principle is as follows: Output power The expression is: = , The resonant capacitor current of isolated converter circuit 2 is... The expression is: Within one switching cycle, It can be equivalent to ,in For the switching cycle of isolated converter circuit 2, The change in voltage across the resonant capacitor is the value of the output power. The expression can be rewritten as: , This refers to the switching frequency. Since the switching power supply controls the resonant capacitor voltage through feedback, the change in the resonant capacitor voltage can be considered equivalent to a voltage feedback signal. Change value. Based on this, due to capacitance... and switching frequency The value remains constant, that is, the output power. The output voltage of power factor correction circuit 1 With voltage feedback signal Together, these two voltage parameters respond synchronously and fluctuate in the same direction when a load change occurs. Their product causes the power signal to exhibit a nonlinear amplification effect, with both the amplitude and rate of change being significantly higher than either parameter alone. This allows for faster identification of whether a load change has occurred, and thus faster voltage loop adjustment of the power factor correction circuit during a load change, further preventing the deterioration of the bus voltage.

[0069] Please continue reading Figure 2 and Figure 3 The control circuit 3 also includes a control unit 31. The signal input terminal of the control unit 31 is connected to the signal output terminal of the load change judgment unit 32, and the signal output terminal of the control unit 31 is connected to the control output terminal.

[0070] The control unit 31 is used to receive a sudden change indication signal. If the sudden change indication signal indicates that a sudden change has occurred in the load, the control power factor correction circuit 1 is adjusted from the first voltage loop response speed to the second voltage loop response speed, which is higher than the first voltage loop response speed. If the sudden change indication signal indicates that no sudden change has occurred in the load, the control power factor correction circuit 1 is maintained or restored to the first voltage loop response speed.

[0071] Specifically, the first voltage loop response speed is the voltage loop response speed of the power factor correction circuit 1 under normal operating conditions. This response speed is typically designed to be low to ensure that the power factor and total harmonic distortion meet the requirements. The second voltage loop response speed is the voltage loop response speed of the power factor correction circuit 1 under load abrupt changes. This response speed is higher than the first voltage loop response speed, enabling the power factor correction circuit 1 to follow load changes more quickly. After receiving a sudden change indication signal, the control unit 31 selects the corresponding voltage loop response speed according to the content of the sudden change indication signal. When the sudden change indication signal indicates that a sudden change has occurred in the load, the control unit 31 outputs a corresponding control signal to the power factor correction circuit 1, adjusting the voltage loop response speed from the first voltage loop response speed to the second voltage loop response speed. When the sudden change indication signal indicates that no sudden change has occurred in the load, if the power factor correction circuit 1 is currently at the first voltage loop response speed, the control unit 31 maintains it at the first voltage loop response speed; if the power factor correction circuit 1 is currently at the second voltage loop response speed, the control unit 31 restores it to the first voltage loop response speed.

[0072] The voltage loop response speed can be adjusted by changing the voltage loop proportional coefficient. For example, the control unit 31 can increase the voltage loop proportional coefficient from the first proportional coefficient to the second proportional coefficient when the load changes abruptly, thereby increasing the voltage loop bandwidth and improving the response speed; when the load does not change abruptly, the voltage loop proportional coefficient can be restored to the first proportional coefficient, thereby decreasing the voltage loop bandwidth and reducing the response speed.

[0073] For ease of understanding, the embodiments of the present invention are described in detail below. Figure 3 Taking the circuit structure shown as an example, the following is provided: Figure 4 The diagram shows the waveform of a control circuit in operation. Taking an increase in load as an example: when the output signal of the isolated converter circuit 2... When the current feedback signal rises from low level to high level Consequently, it decreases; for the current feedback signal The output power is obtained after processing. Output power Increase, when the output power of two adjacent cycles Tsw is increased The difference exceeds the preset difference threshold. Post control signal Setting the voltage level from low to high improves the voltage loop response speed of power factor correction circuit 1, and the high-level duration is... The signals are aligned with each other by vertical dashed lines, showing their correspondence on the time axis.

[0074] Based on the aforementioned circuit structure, this invention provides a control method for a switching power supply, see [link to relevant documentation]. Figure 5 The flowchart illustrating a control method for a switching power supply includes the following steps S502 to S504: Step S502: Receive feedback signal. The feedback signal is based on the output signal conversion of the isolated conversion circuit and is used to characterize load changes.

[0075] Step S504: Control the voltage loop response speed of the power factor correction circuit based on the feedback signal.

[0076] After receiving the feedback signal, the control circuit directly adjusts the voltage loop response speed of the power factor correction circuit based on the load change indicated by the feedback signal. Since the feedback signal originates directly from the output signal of the isolated converter circuit, load changes can be promptly sensed by the control circuit through the feedback signal. Therefore, the control circuit has already adjusted the voltage loop response speed before the output voltage of the power factor correction circuit changes drastically. For details, please refer to the relevant content in the foregoing embodiments; further elaboration is unnecessary.

[0077] In some embodiments, step S504 above can be implemented through the following steps: (1) Generate a mutation indication signal based on the feedback signal.

[0078] The mutation indicator signal is used to characterize whether the load has undergone a mutation or not.

[0079] In a preferred embodiment, a sudden change in the load of the switching power supply is determined based on the difference between two output powers in adjacent cycles and a preset difference threshold, thereby generating a sudden change indication signal; or, a sudden change in the load of the switching power supply is determined based on the rate of change of the output power and a preset rate of change threshold, thereby generating a sudden change indication signal. The output power is determined based on a feedback signal. As an example, the output power is determined based on the feedback signal, the output voltage of the power factor correction circuit, and the switching frequency of the isolated converter circuit.

[0080] In some other embodiments, the change in load of the switching power supply can be determined based on the current or the voltage.

[0081] (2) The voltage loop response speed of the power factor correction circuit is controlled based on the mutation indication signal.

[0082] If the mutation indicator signal indicates that a sudden change has occurred in the load, the control power factor correction circuit adjusts from the first voltage loop response speed to the second voltage loop response speed, which is higher than the first voltage loop response speed; if the mutation indicator signal indicates that no sudden change has occurred in the load, the control power factor correction circuit maintains or reverts to the first voltage loop response speed.

[0083] For ease of understanding, based on Figure 3 The circuit structure shown, taking increased load as an example, provides the following embodiment of the present invention: Figure 6 The schematic diagram shown is an overall flow chart of a control method for a switching power supply, including: If the load on the two-stage switching power supply increases, the current feedback signal fed back to control circuit 3 will... Reduce; reduce the current feedback signal Converted into voltage feedback signal The voltage feedback signal Consequently, it decreases; based on voltage feedback signal and the output voltage of power factor correction circuit 1 Determine the output power If the output power of adjacent cycles If the difference between them exceeds the preset difference threshold, the control signal... Setting it high improves the voltage loop response speed of the power factor correction circuit; if the output power of adjacent cycles is high... If the difference between the values ​​is lower than a preset difference threshold, the system returns to a stable state, and the control signal... When the voltage is set low, the voltage loop of the power factor correction circuit returns to normal operating speed.

[0084] Through the above scheme, the control circuit 3 completes the adjustment of the voltage loop response speed after a load change occurs but before the output voltage of the power factor correction circuit 1 changes drastically. The load change judgment unit 32 directly generates a change indication signal based on the feedback signal, and the control circuit 3 switches the voltage loop response speed according to the change indication signal. The entire control link does not depend on the output voltage change of the power factor correction circuit 1, thus avoiding the response lag problem caused by waiting for the output voltage change.

[0085] The control method provided in this embodiment of the invention has the same implementation principle and technical effect as the aforementioned circuit embodiment. For the sake of brevity, any part not mentioned in the method embodiment can be referred to the corresponding content in the aforementioned circuit embodiment.

[0086] Based on the foregoing embodiments, this invention also provides a switching power supply, which includes a power factor correction circuit, an isolated conversion circuit, and a control circuit. The feedback input terminal of the control circuit is connected to an isolated converter circuit; The feedback input receives a feedback signal, which is converted from the output signal of the isolated converter circuit and is used to characterize load changes. The control output of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal.

[0087] The switching power supply provided in this embodiment of the invention has the same implementation principle and technical effect as the aforementioned circuit embodiment. For the sake of brevity, any parts not mentioned in the switching power supply embodiment can be referred to the corresponding content in the aforementioned circuit embodiment.

[0088] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" 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 mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0089] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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 the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0090] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, 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 the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A control circuit for a switching power supply, characterized in that, The switching power supply includes a cascaded power factor correction circuit and an isolated conversion circuit. The feedback input terminal of the control circuit is used to receive feedback signals, which are converted based on the output signal of the isolated conversion circuit and are used to characterize load changes. The control output terminal of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal.

2. The control circuit of the switching power supply according to claim 1, characterized in that, The control circuit includes a load change judgment unit, and the signal input terminal of the load change judgment unit is connected to the feedback input terminal. The load mutation judgment unit generates a mutation indication signal based on the feedback signal; wherein the control circuit controls the voltage loop response speed of the power factor correction circuit based on the mutation indication signal.

3. The control circuit of the switching power supply according to claim 2, characterized in that, The load change judgment unit is specifically used to: determine whether the load of the switching power supply has changed abruptly based on the difference between two output powers in adjacent cycles and a preset difference threshold; or, determine whether the load of the switching power supply has changed abruptly based on the rate of change of output power and a preset rate of change threshold. The output power is determined based on the feedback signal.

4. The control circuit of the switching power supply according to claim 3, characterized in that, The output power is determined based on the feedback signal, the output voltage of the power factor correction circuit, and the switching frequency of the isolated converter circuit.

5. The control circuit of the switching power supply according to any one of claims 2-4, characterized in that, The control circuit also includes a control unit, the signal input terminal of which is connected to the signal output terminal of the load change judgment unit, and the signal output terminal of which is connected to the control output terminal. The control unit is configured to: receive the mutation indication signal; if the mutation indication signal indicates that the load has undergone a mutation, control the power factor correction circuit to adjust from the first voltage loop response speed to the second voltage loop response speed, wherein the second voltage loop response speed is higher than the first voltage loop response speed; if the mutation indication signal indicates that the load has not undergone a mutation, control the power factor correction circuit to maintain or restore the first voltage loop response speed.

6. The control circuit of the switching power supply according to any one of claims 2-4, characterized in that, When the feedback signal is a voltage feedback signal, the control circuit further includes a power calculation unit; The signal input terminal of the power calculation unit is connected to the feedback input terminal, and the signal output terminal of the power calculation unit is connected to the signal input terminal of the load change judgment unit.

7. The control circuit of the switching power supply according to any one of claims 2-4, characterized in that, When the feedback signal is a current feedback signal, the control circuit further includes a feedback conversion unit and a power calculation unit; The signal input terminal of the feedback conversion unit is connected to the feedback input terminal, the signal output terminal of the feedback conversion unit is connected to the signal input terminal of the power calculation unit, and the signal output terminal of the power calculation unit is connected to the signal input terminal of the load change judgment unit.

8. A control method for a switching power supply, characterized in that, The switching power supply includes a cascaded power factor correction circuit and an isolated conversion circuit; the method includes: Receive a feedback signal, which is converted based on the output signal of the isolated conversion circuit and is used to characterize load changes; The voltage loop response speed of the power factor correction circuit is controlled based on the feedback signal.

9. The control method for a switching power supply according to claim 8, characterized in that, Controlling the voltage loop response speed of the power factor correction circuit based on the feedback signal includes: A sudden change indication signal is generated based on the feedback signal, and the voltage loop response speed of the power factor correction circuit is controlled based on the sudden change indication signal.

10. The control method for a switching power supply according to claim 9, characterized in that, Generate a mutation indication signal based on the feedback signal, including: Based on the difference between two output powers in adjacent cycles and a preset difference threshold, determine whether the load of the switching power supply has changed abruptly, and generate a change indication signal; or, based on the rate of change of output power and a preset rate of change threshold, determine whether the load of the switching power supply has changed abruptly, and generate a change indication signal. The output power is determined based on the feedback signal.

11. The control method for a switching power supply according to claim 10, characterized in that, The output power is determined based on the feedback signal, the output voltage of the power factor correction circuit, and the switching frequency of the isolated converter circuit.

12. The control method for a switching power supply according to any one of claims 9-11, characterized in that, Controlling the voltage loop response speed of the power factor correction circuit based on the mutation indication signal includes: If the mutation indication signal indicates that the load has undergone a sudden change, the power factor correction circuit is controlled to adjust from the first voltage loop response speed to the second voltage loop response speed, where the second voltage loop response speed is higher than the first voltage loop response speed; if the mutation indication signal indicates that the load has not undergone a sudden change, the power factor correction circuit is controlled to maintain or restore the first voltage loop response speed.

13. A switching power supply, characterized in that, Includes power factor correction circuit, isolated conversion circuit and control circuit; The feedback input terminal of the control circuit is connected to the isolated conversion circuit; The feedback input terminal receives a feedback signal, which is converted based on the output signal of the isolated converter circuit and is used to characterize load changes. The control output terminal of the control circuit is connected to the power factor correction circuit. The control circuit controls the voltage loop response speed of the power factor correction circuit based on the feedback signal.

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