A low spike voltage flyback power supply circuit for a switching power supply

Abstract

The application provides a low peak voltage flyback power supply circuit for a switching power supply, which comprises an active dynamic buffer network composed of an auxiliary switch tube, a dynamic adjustment resistor and a DC blocking capacitor added on the secondary side, a transient feedforward detection unit introduced in a control unit to obtain an output voltage change rate signal in real time, a driving strength adjustment unit arranged to adjust the turn-off speed of the main switch tube, a triple coordinated control strategy based on the calculation of a prediction compensation coefficient based on the output voltage change rate, dynamic buffer duty cycle exponential decay control based on the prediction compensation coefficient and adaptive adjustment of the gate pull-down resistor based on the prediction compensation coefficient and the peak primary current, active suppression of the transient peak voltage through the feedforward mode, significant reduction of the peak voltage amplitude under adverse transient conditions such as load jump and short circuit recovery while maintaining the original steady-state high efficiency, and effective improvement of the dynamic response performance and reliability of the system.

Description

Technical Field

[0001] This invention relates to the field of power supply control, and in particular to a low-peak-voltage flyback power supply circuit for switching power supplies. Background Technology

[0002] Flyback switching power supplies, as a common isolated switching power supply topology, are widely used in various electronic devices due to their simple structure, low cost, and ability to provide electrical isolation. During the operation of a flyback power supply, when the main switch is turned off, the energy stored in the transformer leakage inductance cannot be fully transferred to the secondary side. This energy, along with the parasitic capacitance of the switch, forms an LC oscillation circuit, generating high-frequency oscillations and resulting in significant voltage spikes across the switch. These voltage spikes not only increase the voltage stress on the switch, affecting system reliability, but also generate severe electromagnetic interference, adversely affecting the overall performance of the power supply system. In existing technologies, the voltage spike problem in flyback power supplies is mainly related to the energy release from the transformer leakage inductance and magnetizing inductance, the parasitic parameters of the switch, and the design of the absorption circuit. Specifically, the transformer leakage inductance is the most significant factor in generating voltage spikes. When the switch is turned off, the energy stored in the leakage inductance cannot be transferred to the secondary side and can only be released through the parasitic capacitance of the switch, forming LC oscillations and directly generating high-frequency, high-voltage spikes. In addition, the junction capacitance and leakage inductance of the switching transistor together determine the oscillation frequency and peak amplitude, while the turn-off speed of the switching transistor also affects the rate of change of current and voltage, and thus affects the amplitude of the peak voltage.

[0003] Currently, the industry typically uses RC snubber circuits, RCD snubber circuits, or active clamping circuits to suppress voltage spikes in flyback power supplies. However, these traditional methods have significant limitations: while RC and RCD snubber circuits are simple in structure, they suffer from high energy loss, reducing the overall efficiency of the power supply; active clamping circuits, although able to recover some leakage inductance energy and improve efficiency, are complex to control and costly. More importantly, these methods address the already generated voltage spikes from the primary side, representing a "post-event treatment" approach, and fail to fundamentally solve the mechanism of voltage spike generation. In recent years, some solutions have attempted to disperse voltage stress by cascading secondary coils in series, which has reduced peak voltage levels under steady-state operation to some extent. However, the fixed-parameter buffer network and voltage deviation-based proportional-integral (PI) equalization control used in these solutions have significant drawbacks under transient conditions such as drastic load changes and short-circuit recovery: the PI controller can only adjust after the voltage deviation occurs, resulting in a delayed response to peak voltage spikes on the microsecond timescale, failing to effectively suppress them; the fixed RC buffer network cannot adapt to the dynamic changes in high-frequency oscillation components and energy levels under transient conditions, leading to a sharp increase in peak voltage during short-circuit recovery or startup; furthermore, existing solutions only detect voltage amplitude, not the rate of voltage change, making it impossible to predict load change trends and take preventative measures in advance. In addition, with the widespread application of third-generation wide-bandgap semiconductor power devices such as gallium nitride (GaN), while the increased switching speed helps improve efficiency, it also exacerbates the rate of voltage and current changes, making peak voltage problems under transient conditions more prominent, and traditional fixed-parameter suppression methods are insufficient.

[0004] Therefore, how to effectively suppress voltage spikes under transient conditions and improve the dynamic response performance of the system while maintaining the advantages of simple structure and low cost of flyback power supplies, and at the same time take into account low loss operation under steady state, has become an urgent technical problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a low-peak-voltage flyback power supply circuit for switching power supplies to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: This invention provides a low-peak-voltage flyback power supply circuit for switching power supplies, comprising: Input power; An input filter capacitor is connected to both ends of the input power supply; A transformer includes a primary coil and N independent secondary coils, wherein the N secondary coils are connected in series in sequence. The main switch is connected in series in the circuit of the primary coil; An active clamping circuit is connected in parallel across the two ends of the main switching transistor; The rectifier module includes a rectifier diode disposed corresponding to each of the secondary coils; A fixed buffer module includes a fixed buffer capacitor and a fixed buffer resistor corresponding to each of the secondary coils. The fixed buffer capacitor and the fixed buffer resistor are connected in series and then in parallel across the corresponding rectifier diode. An active dynamic buffer network includes an auxiliary switching transistor, a dynamically adjustable resistor, and a DC blocking capacitor corresponding to each of the secondary coils. The auxiliary switching transistor, the dynamically adjustable resistor, and the DC blocking capacitor are connected in series and then in parallel across the corresponding rectifier diode. An output filter capacitor is connected to the total output terminal of the secondary coil connected in series. A transient feedforward detection unit is connected across the output filter capacitor to detect the rate of change signal of the output voltage in real time. A drive intensity adjustment unit is connected to the gate terminal of the main switch transistor and is used to adjust the turn-off speed of the main switch transistor. The control unit includes a voltage detection module, a current detection module, and a digital signal processor. The voltage detection module detects the voltage of each of the secondary coils and the total output voltage. The current detection module detects the current value of the primary coil. The digital signal processor outputs a PWM control signal to the main switch, the active clamping circuit, and the auxiliary switch of the active dynamic buffer network based on the detected voltage and current values ​​and the rate of change signal output by the transient feedforward detection unit. It also outputs a drive adjustment signal to the drive intensity adjustment unit.

[0007] Preferably, the active clamping circuit includes a clamping capacitor and a clamping switch. The clamping capacitor and the clamping switch are connected in series, with one end connected to the connection point between the primary coil and the main switch, and the other end connected to the positive terminal of the input power supply.

[0008] Preferably, the anode of each rectifier diode in the rectifier module is connected to the non-grounded terminal of the corresponding secondary coil, and the cathode is connected to the grounded terminal of the next secondary coil or the positive terminal of the output filter capacitor.

[0009] Preferably, the transient feedforward detection unit includes a differentiating circuit or a digital differential circuit for extracting the rate of change signal of the output voltage.

[0010] Preferably, the drive intensity adjustment unit includes a variable pull-down resistor network connected to the gate terminal of the main switch, and the equivalent resistance value of the variable pull-down resistor network is controlled by the drive adjustment signal output by the digital signal processor.

[0011] Preferably, the main switch and the auxiliary switch are third-generation wide-bandgap semiconductor gallium nitride power devices.

[0012] The present invention also provides a control method for a low-peak-voltage flyback power supply circuit for a switching power supply, comprising the following steps: S1. System Initialization: The digital signal processor reads system parameters, including transformer leakage inductance L_k, switch output capacitance, parasitic capacitance, rated output voltage, and rated peak primary current, and initializes the controller parameters. S2. Steady-state operation: The control unit shuts down all auxiliary switching transistors of the active dynamic buffer network, the fixed buffer module works independently, and the digital signal processor performs voltage equalization control; S3. Transient Detection: The transient feedforward detection unit calculates the output voltage change rate in real time. ,when When the preset threshold is exceeded, the system is determined to enter transient mode, and based on... The sign determines the direction of the load mutation; S4. Calculate the prediction compensation coefficient: Calculate the prediction compensation coefficient based on the output voltage change rate. The calculation formula is as follows: ; in, The dimension conversion coefficient is determined experimentally. This is the rated output voltage; S5. Dynamic Buffer Control: The digital signal processor calculates the PWM duty cycle of the auxiliary switching transistor based on the prediction compensation coefficient. The calculation formula is as follows: ; in, Based on duty cycle, This is the damping adjustment coefficient. This is the elapsed time since the transient trigger moment. As the transient decay time constant, the digital signal processor outputs the calculated PWM duty cycle to the auxiliary switching transistor; S6. Turn-off speed adjustment: The digital signal processor calculates the equivalent pull-down resistance of the gate of the main switch transistor based on the prediction compensation coefficient. The calculation formula is as follows: ; in, This is the gate pull-down resistor in steady state. To drive the adjustment of the sensitivity coefficient, The peak primary current detected in the current switching cycle. The digital signal processor adjusts the gate equivalent pull-down resistance to the rated peak primary current via the drive strength adjustment unit. ; S7. Transient recovery judgment: When When the voltage drops below the preset threshold and the output voltage stabilizes, the control unit turns off the auxiliary switch, and the system switches back to steady-state operation mode.

[0013] Preferably, the voltage equalization control in step S2 includes: calculating the average value of the voltage of each secondary coil, calculating the deviation of each coil voltage from the average value, determining the maximum deviation value, and calculating the duty cycle adjustment amount through a PI controller. ; in, This is the duty cycle adjustment amount. This is the proportional gain coefficient. For the maximum voltage deviation, This is the integral gain coefficient, which is added to the main duty cycle signal as an adjustment.

[0014] Preferably, in step S3, when When <0, it is determined to be a loading transient. When the value is greater than 0, it is determined to be a load reduction transient.

[0015] Preferably, the preset threshold value ranges from 0.3V / ms to 0.8V / ms, the dimension conversion coefficient ranges from 0.05 to 0.15, the damping adjustment coefficient ranges from 0.3 to 0.8, the transient decay time constant ranges from 100μs to 500μs, and the drive adjustment sensitivity coefficient ranges from 0.1 to 0.3.

[0016] The present invention achieves the following beneficial technical effects compared to the prior art: This invention provides a low-peak-voltage flyback power supply circuit for switching power supplies. By adding an active dynamic buffer network consisting of an auxiliary switch, a dynamically adjustable resistor, and a DC-blocking capacitor on the secondary side, and introducing a transient feedforward detection unit in the control unit to acquire the output voltage change rate signal in real time, while simultaneously setting a drive strength adjustment unit to adjust the turn-off speed of the main switch, and combining this with a triple collaborative control strategy—calculating a predictive compensation coefficient based on the output voltage change rate, controlling the exponential decay of the dynamic buffer duty cycle based on the predictive compensation coefficient, and adaptively adjusting the gate pull-down resistor based on the predictive compensation coefficient and the peak primary current—it achieves feedforward active suppression of transient peak voltages. Overcoming the physical limitations of traditional PI controller response lag, the active dynamic buffer network remains off in steady state, with only the fixed buffer module operating to maintain low losses. In transient conditions, it adjusts the PWM duty cycle of the auxiliary switch in real time according to the predicted compensation coefficient, so that the buffer absorption strength dynamically matches the transient energy and decays exponentially with the transient decay. The drive strength adjustment unit actively adjusts the turn-off speed of the main switch according to the transient prediction result to match the transient energy level. The synergistic effect of the three components enables the circuit to maintain the original steady-state high efficiency while significantly reducing the peak voltage amplitude under severe transient conditions such as load jumps and short-circuit recovery, effectively improving the dynamic response performance and reliability of the system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. 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 creative effort.

[0018] Figure 1 A schematic diagram of a low-peak-voltage flyback power supply circuit for a switching power supply provided by the present invention. Figure 2 The flowchart illustrates the operation method of a low-peak-voltage flyback power supply circuit for a switching power supply provided by this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0020] The purpose of this invention is to provide a low-peak-voltage flyback power supply circuit for switching power supplies. Its core innovation lies in the synergistic cooperation between the secondary coil hierarchical series structure and the active dynamic buffer network, combined with a specially designed transient feedforward predictive control and turn-off speed adaptive adjustment algorithm, which fundamentally solves the problem of peak voltage runaway of flyback power supplies under transient conditions.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Example 1: In terms of hardware topology, this invention adds an active dynamic buffer network and a transient feedforward detection unit to the existing secondary coil hierarchical series architecture. Taking a 180W water purifier power supply project from a home appliance company as an example, the power supply has an input voltage range of 176V-264V AC and an output specification of 36V / 5A DC. The input filter capacitor is a 100μF / 450V electrolytic capacitor used to smooth the input voltage and suppress high-frequency noise. The transformer uses PQ32 magnetic core material, with 56 turns in the primary coil and 4 turns in each of the three secondary coils, employing a sandwich winding method to optimize the coupling coefficient and reduce leakage inductance. The main switching transistor is a 650V gallium nitride high electron mobility transistor, whose gate is connected to the pulse width modulation output of the digital signal processor via a drive circuit. The active clamping circuit consists of a clamping capacitor and a clamping switch. The clamping capacitor is a 22nF / 400V thin film capacitor, and the clamping switch is also a 650V gallium nitride device, forming a complementary working mode with the main switch.

[0023] The three coils on the secondary side are connected in series. One end of the first secondary coil is grounded, and one end of the last secondary coil is connected to the positive terminal of the output filter capacitor. Each secondary coil is equipped with a corresponding rectifier diode, preferably a fast recovery diode, whose withstand voltage can be reduced from 400V in the traditional solution to 150V, significantly reducing device cost and size. A fixed buffer module consisting of a fixed buffer capacitor and a fixed buffer resistor is connected in parallel across each rectifier diode to absorb local voltage spikes. Based on this, the present invention adds an active dynamic buffer network. Each active dynamic buffer network consists of an auxiliary switch, a dynamic adjustment resistor, and a DC blocking capacitor connected in series, and the entire network is connected in parallel with the corresponding fixed buffer module across the rectifier diode. The auxiliary switch also uses a gallium nitride device, and its gate receives the pulse width modulation control signal from the digital signal processor. The output filter capacitor is a 470μF / 25V electrolytic capacitor to provide a stable DC voltage to the load.

[0024] The transient feedforward detection unit is connected across the output filter capacitor. This unit, implemented using a differentiating circuit or a digital differential, is used to extract the rate of change signal of the output voltage in real time. The drive intensity adjustment unit is connected to the gate of the main switch transistor. This unit includes a variable pull-down resistor network connected to the gate of the main switch transistor, and its equivalent resistance value is controlled by the drive adjustment signal output by the digital signal processor.

[0025] The control unit is the core intelligent hub of the entire circuit, employing a digital signal processor based on the ARM Cortex-M4 core. Its built-in high-resolution timer generates precise pulse width modulation (PWM) control signals. The control unit integrates voltage and current detection modules. The voltage detection module acquires the voltage values ​​of each secondary coil and the total output voltage in real time through a voltage divider resistor network and an analog-to-digital converter channel. The current detection module uses a Hall effect current sensor or a current sensing resistor to monitor the current value of the primary coil in real time. All sensor data is sent to the PWM processor for processing at a sampling frequency of 100kHz. Based on the detected voltage and current values, as well as the rate of change signal output by the transient feedforward detection unit, the PWM control processor outputs PWM control signals to the main switch, the clamping switch of the active clamping circuit, and the auxiliary switches of the active dynamic buffer network, and also outputs drive adjustment signals to the drive intensity adjustment unit.

[0026] Regarding control parameters, the proportional gain coefficient is set to 0.05, the integral gain coefficient to 0.1, and both are tuned using the Ziegler-Nichols method. The dimension conversion coefficient is set to 0.1, the damping adjustment coefficient to 0.5, the transient decay time constant to 300 μs, and the drive adjustment sensitivity coefficient to 0.2. The preset threshold for transient detection is set to 0.5 V / ms. The specific values ​​of the above parameters can be adjusted appropriately according to the actual circuit characteristics and application requirements.

[0027] In the specific implementation of the control method, this invention adopts a hierarchical control strategy, including voltage equalization control in steady-state operation mode and feedforward predictive control in transient mode. The control process begins in the system initialization phase, where the digital signal processor reads system parameters, including transformer leakage inductance, switch output capacitance, parasitic capacitance, rated output voltage, and rated peak primary current, and initializes the controller parameters. Subsequently, a real-time control loop is entered, with each control cycle lasting 10 μs.

[0028] In steady-state operation mode, the control unit shuts down all auxiliary switches of the active dynamic buffer network, and the active dynamic buffer network does not engage; only the fixed buffer module maintains the basic spike absorption function. The digital signal processor performs voltage equalization control, the specific process of which is as follows: first, the average value of each secondary coil voltage is calculated; then, the deviation of each coil voltage from the average value is calculated, the maximum deviation value is determined, and finally, the duty cycle adjustment is calculated through the PI controller. ; in, This is the proportional gain coefficient. For the maximum voltage deviation, The integral gain coefficient is added to the main duty cycle signal to achieve closed-loop control that balances the voltages of the three secondary coils.

[0029] During the transient detection phase, the transient feedforward detection unit calculates the output voltage change rate in real time. ,when When the preset threshold is exceeded, the system is determined to have entered transient mode. At this time, the digital signal processor further determines... The sign of the load mutation determines the direction: when When <0, it is determined to be a loading transient. When the value is greater than 0, it is determined to be a load reduction transient.

[0030] Upon entering transient mode, the digital signal processor first calculates the prediction compensation coefficients. Based on the real-time acquired output voltage change rate, according to the formula: ; in, The dimension conversion coefficient is determined experimentally. This is the rated output voltage.

[0031] Dynamic buffer control is then executed. The digital signal processor calculates the pulse width modulation duty cycle of each auxiliary switch based on the prediction compensation coefficient. The calculation formula is as follows: ; in, Based on duty cycle, This is the damping adjustment coefficient. This is the elapsed time since the transient trigger moment. This is the transient decay time constant. The physical meaning of this formula is: at the initial moment of transient triggering, i.e., t=0, =1, the buffer strength reaches its maximum; as the transient process gradually decays, i.e., t increases... The buffer strength decreases exponentially, achieving real-time matching between the buffer absorption strength and the severity of the transient. The digital signal processor outputs the calculated pulse width modulation duty cycle to the gate drive circuits of each auxiliary switch.

[0032] Simultaneously, the digital signal processor performs turn-off speed adjustment. The equivalent gate pull-down resistance of the main switch is calculated based on the prediction compensation coefficient, using the following formula: ; in, This is the gate pull-down resistor in steady state. To drive the adjustment of the sensitivity coefficient, The peak primary current detected in the current switching cycle. The digital signal processor adjusts the gate equivalent pull-down resistance to the rated peak primary current via the drive strength adjustment unit. The physical meaning of this formula is that when a strong transient is predicted and the primary current is large, Increasing the gate pull-down resistance is equivalent to increasing the gate pull-down resistance and slowing down the discharge rate, thus appropriately slowing down the turn-off speed of the main switch and suppressing extreme voltage spikes caused by the ultrafast turn-off of gallium nitride devices and the resonance of transformer leakage inductance; conversely, under steady-state or weak transient conditions, Approaching Maintain normal rapid switching to achieve high efficiency.

[0033] During the transient recovery judgment phase, the digital signal processor continuously monitors the rate of change of the output voltage. When the voltage drops below the preset threshold and the output voltage stabilizes, the control unit shuts down all auxiliary switches, and the system switches back to steady-state operation mode.

[0034] In practical implementation, multiple protection mechanisms need to be considered. Overcurrent protection is achieved by monitoring the primary current; when the current exceeds a set threshold, the main switch is immediately shut down. Overvoltage protection is achieved by monitoring the voltage of each secondary coil; when the voltage of any coil rises abnormally, the control strategy is automatically adjusted. Temperature protection monitors the temperature of critical components using built-in temperature sensors to prevent overheating damage.

[0035] The software implementation of this invention is developed using embedded C language, and the control algorithm is executed at 10μs intervals. The program flow includes system initialization, data acquisition and state estimation, steady-state voltage equalization control, transient detection and mode judgment, predictive compensation coefficient calculation, dynamic buffer duty cycle calculation, turn-off speed adjustment calculation, pulse width modulation signal generation, and protection and fault handling steps. All control parameters are stored in non-volatile memory, supporting online debugging and parameter tuning.

[0036] Through the above specific implementation methods, this invention effectively suppresses voltage spikes in flyback power supplies under transient operating conditions. Experimental results show that under full load conditions, the maximum voltage stress on the primary side main switch is 619V, and the maximum voltage stress on the secondary side is 176.2V, both meeting the requirement of a margin of more than 10% of the rated withstand voltage of power devices. The system efficiency averages 92.708% under 180V AC input, 92.743% under 230V AC input, and 93.042% under 264V AC input. The output voltage ripple is less than 222.4mV under 176V, 220V, and 264V AC input conditions, meeting the 1% ripple noise requirement of the output voltage. Standby power consumption is as low as 0.16W under 230V AC input, meeting the requirement of 0.21W. The startup time is 45.557ms under 176V AC input no-load conditions and 42.807ms under full load conditions, both meeting the requirement of less than 50ms. The shutdown time is 30.544ms under full load conditions of 176V AC input, which meets the requirement of greater than 8ms. The output overcurrent protection point is between 5.8A and 6.1A, which is within the range of 1.16 to 1.22 times the rated current of 5A, meeting the requirement of 1.1 to 1.5 times the rated current.

[0037] The experimental data above fully verify the superiority of this invention in both steady-state and transient performance. Compared with existing technologies, this invention effectively solves the problem of peak voltage runaway under transient conditions while maintaining the advantages of simple structure and low cost of flyback power supplies, providing strong technical support for the promotion of flyback power supplies in high-frequency and high-efficiency application scenarios.

[0038] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0039] It should be noted that the components mentioned in the above embodiments are all general standard parts or components known to those skilled in the art. Their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0040] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and its core ideas; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the principles of this invention. Therefore, the content of this specification should not be construed as limiting the invention.

Claims

1. A low-peak-voltage flyback power supply circuit for switching power supplies, characterized in that, include: Input power; An input filter capacitor is connected to both ends of the input power supply; A transformer includes a primary coil and N independent secondary coils, wherein the N secondary coils are connected in series in sequence. The main switch is connected in series in the circuit of the primary coil; An active clamping circuit is connected in parallel across the two ends of the main switching transistor; The rectifier module includes a rectifier diode disposed corresponding to each of the secondary coils; A fixed buffer module includes a fixed buffer capacitor and a fixed buffer resistor corresponding to each of the secondary coils. The fixed buffer capacitor and the fixed buffer resistor are connected in series and then in parallel across the corresponding rectifier diode. An active dynamic buffer network includes an auxiliary switching transistor, a dynamically adjustable resistor, and a DC blocking capacitor corresponding to each of the secondary coils. The auxiliary switching transistor, the dynamically adjustable resistor, and the DC blocking capacitor are connected in series and then in parallel across the corresponding rectifier diode. An output filter capacitor is connected to the total output terminal of the secondary coil connected in series. A transient feedforward detection unit is connected across the output filter capacitor to detect the rate of change signal of the output voltage in real time. A drive intensity adjustment unit is connected to the gate terminal of the main switch transistor and is used to adjust the turn-off speed of the main switch transistor. The control unit includes a voltage detection module, a current detection module, and a digital signal processor. The voltage detection module detects the voltage of each of the secondary coils and the total output voltage. The current detection module detects the current value of the primary coil. The digital signal processor outputs a PWM control signal to the main switch, the active clamping circuit, and the auxiliary switch of the active dynamic buffer network based on the detected voltage and current values ​​and the rate of change signal output by the transient feedforward detection unit. It also outputs a drive adjustment signal to the drive intensity adjustment unit.

2. The low-peak-voltage flyback power supply circuit for switching power supplies according to claim 1, characterized in that, The active clamping circuit includes a clamping capacitor and a clamping switch. The clamping capacitor and the clamping switch are connected in series, with one end connected to the connection point between the primary coil and the main switch, and the other end connected to the positive terminal of the input power supply.

3. The low-peak-voltage flyback power supply circuit for switching power supplies according to claim 1, characterized in that, The anode of each rectifier diode in the rectifier module is connected to the non-grounded terminal of the corresponding secondary coil, and the cathode is connected to the grounded terminal of the next secondary coil or the positive terminal of the output filter capacitor.

4. The low-peak-voltage flyback power supply circuit for switching power supplies according to claim 1, characterized in that, The transient feedforward detection unit includes a differentiating circuit or a digital differential circuit, used to extract the rate of change signal of the output voltage.

5. The low-peak-voltage flyback power supply circuit for a switching power supply according to claim 1, characterized in that, The drive intensity adjustment unit includes a variable pull-down resistor network connected to the gate terminal of the main switch transistor. The equivalent resistance value of the variable pull-down resistor network is controlled by the drive adjustment signal output by the digital signal processor.

6. The low-peak-voltage flyback power supply circuit for a switching power supply according to claim 1, characterized in that, The main switch and the auxiliary switch are third-generation wide-bandgap semiconductor gallium nitride power devices.

7. A control method for a low-peak-voltage flyback power supply circuit for a switching power supply, characterized in that, Includes the following steps: S1. System Initialization: The digital signal processor reads system parameters, including transformer leakage inductance L_k, switch output capacitance, parasitic capacitance, rated output voltage, and rated peak primary current, and initializes the controller parameters. S2. Steady-state operation: The control unit shuts down all auxiliary switching transistors of the active dynamic buffer network, the fixed buffer module works independently, and the digital signal processor performs voltage equalization control; S3. Transient Detection: The transient feedforward detection unit calculates the output voltage change rate in real time. ,when When the preset threshold is exceeded, the system is determined to enter transient mode, and based on... The sign determines the direction of the load mutation; S4. Calculate the prediction compensation coefficient: Calculate the prediction compensation coefficient based on the output voltage change rate. The calculation formula is as follows: ； in, The dimension conversion coefficient is determined experimentally. This is the rated output voltage; S5. Dynamic Buffer Control: The digital signal processor calculates the PWM duty cycle of the auxiliary switching transistor based on the prediction compensation coefficient. The calculation formula is as follows: ； in, Based on duty cycle, This is the damping adjustment coefficient. This is the elapsed time since the transient trigger moment. As the transient decay time constant, the digital signal processor outputs the calculated PWM duty cycle to the auxiliary switching transistor; S6. Turn-off speed adjustment: The digital signal processor calculates the equivalent pull-down resistance of the gate of the main switch transistor based on the prediction compensation coefficient. The calculation formula is as follows: ； in, This is the gate pull-down resistor in steady state. To drive the adjustment of the sensitivity coefficient, The peak primary current detected in the current switching cycle. The digital signal processor adjusts the gate equivalent pull-down resistance to the rated peak primary current via the drive strength adjustment unit. ; S7. Transient recovery judgment: When When the voltage drops below the preset threshold and the output voltage stabilizes, the control unit turns off the auxiliary switch, and the system switches back to steady-state operation mode.

8. The control method for a low-peak voltage flyback power supply circuit for a switching power supply according to claim 7, characterized in that, The voltage equalization control in step S2 includes: calculating the average value of the voltage of each secondary coil, calculating the deviation of each coil voltage from the average value, determining the maximum deviation value, and calculating the duty cycle adjustment amount through a PI controller. ； in, This is the proportional gain coefficient. For the maximum voltage deviation, This is the integral gain coefficient, which is added to the main duty cycle signal.

9. The control method for a low-peak-voltage flyback power supply circuit for a switching power supply according to claim 7, characterized in that, In step S3, when When <0, it is determined to be a loading transient. When the value is greater than 0, it is determined to be a load reduction transient.

10. The control method for a low-peak-voltage flyback power supply circuit for a switching power supply according to claim 7, characterized in that, The preset threshold value ranges from 0.3V / ms to 0.8V / ms, the dimension conversion coefficient ranges from 0.05 to 0.15, the damping adjustment coefficient ranges from 0.3 to 0.8, the transient decay time constant ranges from 100μs to 500μs, and the drive adjustment sensitivity coefficient ranges from 0.1 to 0.3.

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