Control method and device of switching power supply system and switching power supply system

Abstract

The invention discloses a control method of a switching power supply system, and belongs to the technical field of switching power supplies. The control method of the switching power supply system comprises the following steps: in an advanced pull-down stage, obtaining the bending times of a driving voltage signal corresponding to a current switching period of a secondary power tube; adjusting a gear control signal corresponding to the switching power supply system based on the bending times of the driving voltage signal in the current switching period; and under the condition of entering the next switching period, adjusting the pull-down current corresponding to the secondary side power tube based on the gear control signal, returning to execute the advanced pull-down stage, obtaining the bending times of the driving voltage signal corresponding to the current switching period of the secondary side power tube, and outputting the bending times of the driving voltage signal corresponding to the current switching period of the secondary side power tube. Stopping adjusting the pull-down current until the number of bending times of the latest acquired driving voltage signal is the target number of times; and under the condition that the bending frequency of the driving voltage signal is the target frequency, controlling the control gear of the pull-down current to be unchanged.

Description

Technical Field

[0001] The present application belongs to the technical field of switching power supplies, and in particular, relates to a control method and device for a switching power supply system and a switching power supply system. Background Art

[0002] In the flyback converter system, in order to reduce the conduction loss, the gate voltage of the secondary MOS power tube (SR tube) will be driven to the overdrive voltage, but due to the influence of the transmission delay, the SR tube cannot be turned off in time, resulting in reverse power injection to the secondary coil, reducing efficiency, and even causing the primary and secondary sides to be penetrated. In the related art, an early pull-down scheme is often used, that is, before the primary switch tube is turned on, the secondary gate voltage is reduced to near the gate-source threshold voltage to reduce the shutdown delay, but the traditional early pull-down scheme is based on the drain-source voltage of the secondary SR tube to adjust the pull-down current in real time. During the adjustment stage, the drain-source voltage is always maintained near the threshold voltage set inside the chip, resulting in a faster drop in the gate voltage of the SR tube, a lower average voltage in the early pull-down stage, and a larger increase in the on-resistance, that is, a larger sacrifice in the conduction loss. Summary of the invention

[0003] The present application aims to solve at least one of the technical problems existing in the related art. To this end, the present application proposes a control method, device and switching power supply system of a switching power supply system, which improves the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system.

[0004] In a first aspect, the present application provides a control method for a switching power supply system, wherein the switching power supply system includes a secondary power tube; the method includes:

[0005] In the early pull-down stage, the number of bends of the driving voltage signal of the secondary power tube corresponding to the current switching cycle is obtained; the early pull-down stage is the period from the moment when the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube is greater than the early pull-down start threshold for the first time to the moment when the secondary power tube is turned off;

[0006] Adjusting the gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle;

[0007] In the case of entering the next switching cycle of the current switching cycle, adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal, and returning to execute the step of obtaining the bending times of the driving voltage signal corresponding to the secondary power tube in the current switching cycle in the early pull-down stage, until the bending times of the driving voltage signal obtained most recently reaches the target times, then stopping adjusting the pull-down current;

[0008] When the number of bends of the driving voltage signal is the target number, the control gear of the pull-down current remains unchanged; the pull-down current is used to reduce the gate voltage of the secondary power tube at the shutdown moment.

[0009] According to the control method of the switching power supply system provided in the embodiment of the present application, in the early pull-down stage, according to the number of bends of the driving voltage signal in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, thereby reducing the gate voltage at the moment when the secondary power tube is turned off, and improving the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current of the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can operate stably.

[0010] A control method for a switching power supply system according to an embodiment of the present application, wherein the step of adjusting a gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle comprises:

[0011] When the number of bending times of the driving voltage signal in the current switching cycle is less than the target number, controlling the gear control signal corresponding to the switching power supply system to increase by one;

[0012] When the number of bending times of the driving voltage signal in the current switching cycle is greater than the target number, the gear control signal is controlled to decrease by one.

[0013] In a control method for a switching power supply system according to an embodiment of the present application, obtaining the number of bends of the driving voltage signal corresponding to the secondary power tube in the current switching cycle includes:

[0014] In the early pull-down stage, when it is detected that the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube changes from being greater than the early pull-down start threshold to being less than the early pull-down start threshold, the number of bends of the drive voltage signal is added by one.

[0015] A control method for a switching power supply system according to an embodiment of the present application, wherein the pull-down current corresponding to the secondary power tube is adjusted based on the gear control signal, comprises:

[0016] Acquire a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal;

[0017] Based on the gear control signal and the reference signal, obtaining a first current corresponding to the secondary power tube;

[0018] Based on the first current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

[0019] A control method for a switching power supply system according to an embodiment of the present application, wherein the pull-down current corresponding to the secondary power tube is adjusted based on the gear control signal, comprises:

[0020] Acquire a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal;

[0021] When it is determined that the switching power supply system is in a continuous conduction mode, obtaining a maximum current corresponding to the secondary power tube based on the gear control signal and the reference signal;

[0022] Based on the maximum current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

[0023] In a second aspect, the present application provides a switching power supply system based on the control method of the switching power supply system according to the first aspect, comprising:

[0024] Secondary side power tube;

[0025] A threshold comparator, one input end of the threshold comparator is connected to the drain of the secondary power tube, and the other input end of the threshold comparator is used to receive an early pull-down start threshold;

[0026] A first pull-down control circuit, wherein the first pull-down control circuit is respectively connected to the output end of the threshold comparator and the gate of the secondary power tube; the first pull-down control circuit comprises: an inflection point counting feedback circuit and a pull-down circuit, wherein the inflection point counting feedback circuit is connected to the output end of the threshold comparator, and the inflection point counting feedback circuit is used to output a gear control signal; the pull-down circuit is respectively connected to the output end of the threshold comparator and the output end of the inflection point counting feedback circuit, and the output end of the pull-down circuit is used to output the magnitude of the pull-down current corresponding to the next switching cycle of the secondary power tube in the current switching cycle.

[0027] According to the switching power supply system provided in the embodiment of the present application, in the early pull-down stage, according to the number of bends of the driving voltage signal in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, thereby reducing the gate voltage at the moment when the secondary power tube is turned off, and improving the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current of the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can operate stably.

[0028] In a switching power supply system according to an embodiment of the present application, the inflection point counting feedback circuit comprises:

[0029] An inflection point signal generating circuit, wherein the inflection point signal generating circuit is connected to an output end of the threshold comparator;

[0030] An inflection point holding circuit, the inflection point holding circuit being connected to an output end of the inflection point signal generating circuit;

[0031] A bidirectional counting module is connected to the output end of the inflection point signal generating circuit and the output end of the inflection point holding circuit respectively, and the output end of the bidirectional counting module is used to output the gear control signal.

[0032] In a switching power supply system according to an embodiment of the present application, the pull-down circuit comprises:

[0033] A pull-down current adjustment circuit, the pull-down current adjustment circuit comprising: a reference module and a plurality of first current source modules connected in parallel, the reference module being used to output a reference signal, the reference signal comprising a fixed current signal or an output voltage signal;

[0034] One end of each of the first current source modules is connected to one end of the reference module, and the other end of each of the first current source modules is connected to the other end of the reference module, the first current source module comprises a first current source and a first switch connected in series, the first current source is used to mirror the current in the reference module, and the first switch is configured to be closed based on the gear control signal;

[0035] a minimum pull-down current circuit, one end of which is connected to the pull-down current adjustment circuit, and the minimum pull-down current circuit is used to provide a fixed minimum current;

[0036] A second pull-down control circuit, wherein the second pull-down control circuit is respectively connected to the other end of the pull-down current adjustment circuit and the minimum pull-down current circuit, and the output end of the second pull-down control circuit is used to output the size of the pull-down current corresponding to the secondary power tube in the next switching cycle.

[0037] In a switching power supply system according to an embodiment of the present application, the reference module includes:

[0038] a voltage-controlled current source, the voltage-controlled current source being configured to output a second current based on the output voltage signal;

[0039] A second current source and an enabling switch connected in series, wherein one end of the second current source away from the enabling switch is respectively connected to the output end of the voltage-controlled current source and the other end of the plurality of first current sources, one end of the enabling switch away from the second current source is connected to one end of the plurality of first current source modules, and the second current source is used to mirror the second current.

[0040] In a switching power supply system according to an embodiment of the present application, the reference module includes:

[0041] A third current source and an enabling switch connected in series, wherein one end of the third current source away from the enabling switch is connected to one end of the plurality of first current source modules, and one end of the enabling switch away from the third current source is connected to the other end of the plurality of first current source modules, and the third current source is used to provide the fixed current signal.

[0042] The switching power supply system of one embodiment of the present application further includes:

[0043] A conduction control circuit connected to the drain of the secondary power tube;

[0044] A shutdown control circuit connected to the drain of the secondary power tube;

[0045] A logic control circuit, wherein the logic control circuit is respectively connected to an output end of the conduction control circuit and an output end of the shutdown control circuit;

[0046] A driving circuit, wherein the driving circuit is connected to the output end of the logic control circuit, and the output end of the driving circuit is connected to the gate of the secondary power tube.

[0047] In a third aspect, the present application provides a control device for a switching power supply system, wherein the switching power supply system includes a secondary power tube; the control device includes:

[0048] The first processing module is used to obtain the number of bends of the driving voltage signal of the secondary power tube corresponding to the current switching cycle in the early pull-down stage; the early pull-down stage is the period from the moment when the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube is greater than the early pull-down start threshold for the first time to the moment when the secondary power tube is turned off;

[0049] A second processing module, configured to adjust a gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle;

[0050] A third processing module is used for adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal when entering the next switching cycle of the current switching cycle, and returning to execute the step of obtaining the bending number of the driving voltage signal corresponding to the secondary power tube in the current switching cycle in the early pull-down stage, until the bending number of the driving voltage signal obtained most recently reaches the target number, and then stopping adjusting the pull-down current;

[0051] The fourth processing module is used to control the control gear of the pull-down current to remain unchanged when the number of bending times of the driving voltage signal is the target number; the pull-down current is used to reduce the gate voltage of the secondary power tube at the shutdown moment.

[0052] According to the control device of the switching power supply system provided in the embodiment of the present application, in the early pull-down stage, according to the number of bends of the driving voltage signal in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, thereby reducing the gate voltage at the moment when the secondary power tube is turned off, and improving the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current of the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can operate stably.

[0053] In a fourth aspect, the present application provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the control method of the switching power supply system as described in the first aspect above is implemented.

[0054] In a fifth aspect, the present application provides a chip, comprising a processor and a communication interface, wherein the communication interface is coupled to the processor, and the processor is used to run a program or instruction to implement the control method of the switching power supply system as described in the first aspect.

[0055] The above one or more technical solutions in the embodiments of the present application have at least one of the following technical effects:

[0056] By adaptively adjusting the pull-down current of the secondary power tube in the next switching cycle according to the number of bends of the driving voltage signal in the current switching cycle in the early pull-down stage, the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage is improved on the basis of reducing the gate voltage at the time of the secondary power tube being turned off, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current in the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can work stably.

[0057] Furthermore, by controlling the pull-down current of the next switching cycle to reach a maximum when the switching power supply system is in the continuous conduction mode, the risk of primary-secondary side punch-through in the continuous conduction mode is reduced.

[0058] Furthermore, by obtaining feedback information of the output voltage, the size of the pull-down current can be better controlled according to the different output voltages and the different characteristics of the demagnetization current falling slope, so as to avoid the problem of excessive pull-down current, the driving voltage signal being pulled too low, and the secondary power tube being shut down in advance and the current being continued through the body diode, which leads to increased conduction loss.

[0059] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0061] Figure 1 This is one of the structural schematic diagrams of the switching power supply system provided in the embodiment of the present application;

[0062] Figure 2 This is the second structural schematic diagram of the switching power supply system provided in the embodiment of the present application;

[0063] Figure 3 This is the third structural diagram of the switching power supply system provided in the embodiment of the present application;

[0064] Figure 4 This is the fourth structural diagram of the switching power supply system provided in the embodiment of the present application;

[0065] Figure 5 This is the fifth structural diagram of the switching power supply system provided in the embodiment of the present application;

[0066] Figure 6 This is one of the principle schematic diagrams of the control method of the switching power supply system provided in the embodiment of the present application;

[0067] Figure 7 This is the second principle schematic diagram of the control method of the switching power supply system provided in the embodiment of the present application;

[0068] Figure 8 This is the third principle schematic diagram of the control method of the switching power supply system provided in the embodiment of the present application;

[0069] Fig. 9 This is the sixth structural diagram of the switching power supply system provided in the embodiment of the present application;

[0070] Fig.10 This is the fourth principle schematic diagram of the control method of the switching power supply system provided in the embodiment of the present application;

[0071] Fig.11 This is one of the flow charts of the control method of the switching power supply system provided in the embodiment of the present application;

[0072] Fig.12 This is the seventh structural diagram of the switching power supply system provided in the embodiment of the present application;

[0073] Fig.13 This is the fifth principle schematic diagram of the control method of the switching power supply system provided in the embodiment of the present application;

[0074] Fig.14 This is a second flow chart of a control method for a switching power supply system provided in an embodiment of the present application;

[0075] Fig.15 is a schematic diagram of the structure of a control device for a switching power supply system provided in an embodiment of the present application;

[0076] Fig.16 It is a schematic diagram of the structure of an electronic device provided in an embodiment of the present application.

[0077] Reference numerals:

[0078] Secondary side power tube SR; early pull-down control circuit 100; first pull-down control circuit 110;

[0079] Inflection point counting feedback circuit 120; pull-down circuit 130; inflection point signal generating circuit 140; inflection point holding circuit 150;

[0080] Bidirectional counting module 160; pull-down current adjustment circuit 170; minimum pull-down current circuit 180;

[0081] Second pull-down control circuit 190; voltage-controlled current source 200; on-control circuit 210; off-control circuit 220;

[0082] Logic control circuit 230 ; driving circuit 240 ; threshold comparator 250 . DETAILED DESCRIPTION

[0083] The following will be combined with the drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0084] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0085] In the following, in combination with the accompanying drawings, the control method of the switching power supply system, the control device of the switching power supply system, the electronic device and the readable storage medium provided in the embodiments of the present application are described in detail through specific embodiments and their application scenarios.

[0086] The control method of the switching power supply system may be applied to a terminal, and may be specifically executed by hardware or software in the terminal.

[0087] The terminal includes, but is not limited to, a portable communication device such as a mobile phone or tablet computer with a touch-sensitive surface (e.g., a touch screen display and / or a touch pad). It should also be understood that in some embodiments, the terminal may not be a portable communication device, but a desktop computer with a touch-sensitive surface (e.g., a touch screen display and / or a touch pad).

[0088] In the following various embodiments, a terminal including a display and a touch-sensitive surface is described. However, it should be understood that the terminal may include one or more other physical user interface devices such as a physical keyboard, a mouse and a joystick.

[0089] The control method of the switching power system provided in the embodiment of the present application, the execution subject of the control method of the switching power system can be an electronic device or a functional module or functional entity in the electronic device that can implement the control method of the switching power system. The electronic devices mentioned in the embodiment of the present application include but are not limited to mobile phones, tablet computers, computers, cameras and wearable devices, etc. The control method of the switching power system provided in the embodiment of the present application is described below using the electronic device as an example of the execution subject.

[0090] like Fig.14 As shown, the control method of the switching power supply system includes: step S1, step S2, step S3 and step S4.

[0091] It should be noted that the control method of the switching power supply system can be applied to a switching power supply system.

[0092] A switching power supply is a high-frequency electric energy conversion device and a type of power supply.

[0093] Switching power supplies are used to convert a voltage level into the voltage or current required by the user through different forms of architecture.

[0094] Switching power supplies can be used in areas such as fast charging, adapters and chargers.

[0095] The switching power supply system can include a primary circuit and a secondary circuit, such as Figure 1 As shown, the secondary side circuit includes a secondary side power tube (SR tube), and the secondary side power tube can be connected to the secondary side control chip.

[0096] The secondary side power tube may be a MOS power tube, which includes a gate, a source and a drain.

[0097] Step S1, in the early pull-down stage, obtaining the bending times of the driving voltage signal of the secondary power tube corresponding to the current switching cycle;

[0098] In this step, when the secondary power tube is turned on, the switching power supply system enters the current switching cycle. During the current switching cycle, it can be determined whether the switching power supply system enters the early pull-down stage based on the voltage formed by the secondary demagnetization current on the on-impedance of the secondary power tube (i.e., the drain voltage of the secondary power tube).

[0099] When the voltage formed by the secondary side demagnetization current on the conduction impedance of the secondary side power tube is greater than the early pull-down turn-on threshold for the first time, such as Figure 6 As shown at point A in the middle, the early pull-down enable signal is flipped to a high level, and the early pull-down is enabled.

[0100] When the driving voltage signal is at a high level, the secondary power tube is in an on state, and when the driving voltage signal is at a low level, the secondary power tube is in an off state.

[0101] The early pull-down stage is the period from the moment when the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube is greater than the early pull-down start threshold for the first time to the moment when the secondary power tube is turned off, that is, the period from point A to the moment when the drive voltage signal changes from a high level to a low level in the current switching cycle.

[0102] Among them, the size of the early pull-down activation threshold can be based on user customization, and the early pull-down activation threshold can be a value less than 0, which is not limited in this application.

[0103] The switching cycle may include the excitation time and the demagnetization time, or may also include the free resonance time. The switching cycle is the duration from the current turn-on moment to the next turn-on moment of the secondary power tube.

[0104] The driving voltage signal is a voltage signal that controls the secondary side power tube to turn on or off.

[0105] During the early pull-down stage within a switching cycle, the driving voltage signal may have a bend. When the drain voltage crosses the early pull-down start-up threshold (i.e., the drain voltage changes from being greater than the early pull-down start-up threshold to being less than the early pull-down start-up threshold), it can be determined that the driving voltage signal has a bend, and the number of bends in the driving voltage signal can be obtained based on the number of times the drain voltage crosses the early pull-down start-up threshold.

[0106] Step S2: adjusting the gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle;

[0107] In this step, when the number of bending times of the driving voltage signal in the current switching cycle is not the target number, the gear control signal can be adjusted according to the number of bending times of the driving voltage signal in the current switching cycle.

[0108] The gear control signal is used to control the size of the pull-down current of the secondary power tube corresponding to the next switching cycle.

[0109] The gear control signal is a counting signal. When the gear control signal is larger, the pull-down current of the next switching cycle is larger.

[0110] For example, the gear control signal can be set to Q<0:n>, where n determines the bit width of the gear control signal and n can be used to characterize the number of pull-down current gears. When there are more gears, the pull-down control is more precise and the feedback control is more accurate.

[0111] Adjusting the gear control signal may include adding one to the gear control signal, i.e. increasing the pull-down current by one gear, or subtracting one from the gear control signal, i.e. decreasing the pull-down current by one gear. In the actual implementation process, the gear control signal may be adjusted step by step to adjust the pull-down current step by step.

[0112] Step S3, when entering the next switching cycle of the current switching cycle, adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal, and returning to the early pull-down stage to obtain the bending number of the driving voltage signal corresponding to the secondary power tube in the current switching cycle, until the bending number of the driving voltage signal obtained most recently reaches the target number, then stop adjusting the pull-down current;

[0113] In this step, after the current switching cycle ends, the secondary power tube is turned on again, that is, it is determined that the secondary power tube has entered the next switching cycle.

[0114] The pull-down current corresponding to the secondary power tube in the next switching cycle is used to pull down the driving voltage signal of the secondary power tube, that is, to reduce the gate voltage of the secondary power tube at the shutdown moment in the next switching cycle, so as to reduce the shutdown delay, reduce the degree of overlapping conduction of the original and secondary sides, and optimize the stress of the secondary power tube.

[0115] After controlling the secondary power tube to turn on again, the switching power supply system starts the next switching cycle, the next switching cycle can be determined as the current switching cycle, and the number of bending times of the driving voltage signal in the new current switching cycle can be detected.

[0116] When the number of bending times of the driving voltage signal in the new current switching cycle reaches the target number, the switching power supply system can be controlled to exit the feedback regulation stage, that is, stop regulating the pull-down current.

[0117] The target number can be customized according to user needs. Generally, the target number can be set to 1, and this application does not limit it.

[0118] Step S4: When the bending times of the driving voltage signal are the target times, the control gear of the pull-down current remains unchanged.

[0119] In this step, when the number of bends of the driving voltage signal is the target number, the subsequent switching cycle can pull down the gate voltage of the secondary power tube according to the pull-down current corresponding to the current switching cycle, that is, the pull-down current in the subsequent switching cycle can be consistent with the pull-down current of the current switching cycle, until the number of bends of the driving voltage signal is not the target number, and the feedback regulation stage will be entered again.

[0120] For example, when the pull-down current is small (case A), the driving voltage signal has no inflection point in the early pull-down stage, and the falling slope of the driving voltage signal is K_A, then the gear control signal will be controlled to increase by one, and after multiple adjustment processes, the pull-down current will be adjusted to a larger value. When the pull-down current is large (case B), the number of inflection points of the driving voltage signal in the early pull-down stage exceeds the target number, and the falling slope of the driving voltage signal is K_B, then the gear control signal will be controlled to decrease by one, and the pull-down current will be adjusted to an appropriate value (case C), so that the number of inflection points of the driving voltage signal in the early pull-down stage is the target number, and the falling slope of the driving voltage signal DRV in the early pull-down stage is K_C, where K_A <K_C<K_B。

[0121] In case (C), the rate at which the driving voltage signal decreases is slower than that in case (B) as a whole, and the rate at which the on-resistance of the secondary power tube changes is smaller than that in case (B). After appropriate current multiple design, there is only one case in the current switching cycle where the rate at which the on-resistance increases is greater than the rate at which the demagnetization current decreases, that is, the drain voltage of the secondary power tube is only pulled down to less than the early pull-down start threshold once, the early pull-down enable signal becomes a low level, the early pull-down is not enabled, and the driving voltage signal remains unchanged. At this time, the demagnetization current is already low, the drain voltage is quickly pulled to 0V, the secondary power tube is turned off, the number of bends of the driving voltage signal is 1, and the inflection point holding circuit starts to work. Figure 8 As shown in (c), the hold signal corresponding to the bidirectional counter will shield the clock of the bidirectional counter, and the output of the bidirectional counter will remain unchanged, that is, the pull-down current of the next cycle will remain unchanged. This situation indicates that the pull-down current is in a steady-state stage and the pull-down current adjustment stage will end until it is detected that the number of bending times of the driving voltage signal is not the target number, and then the pull-down current adjustment stage will be entered again.

[0122] like Fig.13 As shown, the inventors found in the research and development process that, when the early pull-down threshold is the same and the parameters of the secondary power tube are the same, the early pull-down method used in the related art is real-time feedback adjustment, and the drain-source voltage of the secondary power tube in the early pull-down stage is always maintained near the threshold voltage set inside the chip (equivalent to bending countless times), and the final effect of the related art is shown in curve A;

[0123] In the present application, in the early pull-down stage, according to the number of bends of the driving voltage signal in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, which can not only reduce the gate voltage at the time of the secondary power tube being turned off, thereby reducing the turn-off delay, reducing the degree of overlapping conduction of the original and secondary sides, and optimizing the stress of the secondary power tube, but also can change the drop rate of the driving voltage signal (or gate voltage) by feedback adjustment of the pull-down current to regulate the increase rate of the on-resistance between the drain and source of the secondary power tube, thereby reducing the amplitude of the increase of the on-resistance. The final effect of the present application is shown in curve B. The average voltage of the driving voltage signal in the pull-down time in the present application will be higher than the average voltage of the driving voltage signal in the related art. It can be seen that the increase in the on-resistance Rdson of the present application is smaller than the increase in the on-high resistance in the related art. The present application can reduce the conduction loss in the early pull-down stage and improve the efficiency of the switching power supply system.

[0124] According to the control method of the switching power supply system provided in the embodiment of the present application, in the early pull-down stage, according to the number of bends of the driving voltage signal in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, thereby reducing the gate voltage at the moment when the secondary power tube is turned off, and improving the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current of the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can operate stably.

[0125] In some embodiments, obtaining the number of bending times of the driving voltage signal corresponding to the secondary power tube in the current switching cycle may include:

[0126] In the early pull-down stage, when it is detected that the voltage formed by the secondary demagnetization current on the conduction impedance of the secondary power tube changes from greater than the early pull-down start threshold to less than the early pull-down start threshold, the number of bends of the driving voltage signal is increased by one.

[0127] In this embodiment, the number of bends of the driving voltage signal can be counted according to the magnitude relationship between the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube (i.e., the drain voltage of the secondary power tube) and the early pull-down threshold.

[0128] In the early pull-down stage in the current switching cycle, when the drain voltage changes from being greater than the early pull-down start threshold to being less than the early pull-down start threshold, that is, the drain voltage crosses the early pull-down start threshold, it can be determined that the driving voltage signal has a bend.

[0129] For example, the target number is set to 1. In the early pull-down stage, when the pull-down current in the current switching cycle is small, the drain voltage will continue to rise to 0V after being greater than the early pull-down start threshold, and it can be determined that there is no bend in the driving voltage signal.

[0130] In the early pull-down stage, when the pull-down current in the current switching cycle is large, the drain voltage will cross the early pull-down turn-on threshold twice after being greater than the early pull-down turn-on threshold, that is, the driving voltage signal has two bends.

[0131] In the early pull-down stage, when the pull-down current in the current switching cycle is appropriate, the drain voltage will cross the early pull-down turn-on threshold once after being greater than the early pull-down turn-on threshold, and then be pulled to 0V, that is, the driving voltage signal has one bend.

[0132] In some embodiments, obtaining the number of bending times of the driving voltage signal corresponding to the early pull-down phase of the secondary power tube in the current switching cycle may include:

[0133] Based on the magnitude relationship between the drain voltage and the early pull-down turn-on threshold, an inflection point signal is obtained;

[0134] Based on the number of pulses of the inflection point signal, the number of bends of the driving voltage signal corresponding to the secondary power tube in the current switching cycle is obtained.

[0135] In this embodiment, if Figure 6 As shown, the inflection point signal is a pulse signal.

[0136] In the early pull-down stage, when the drain voltage is less than the early pull-down start threshold, the inflection point signal is a high level, and when the drain voltage is greater than the early pull-down start threshold, the inflection point signal is a low level.

[0137] In the actual implementation process, Figure 4 As shown, the switching power supply system may include a threshold comparator, the positive input terminal of the threshold comparator may be used to receive the drain voltage of the secondary power tube, the negative input terminal of the threshold comparator is used to receive the early pull-down start threshold, the threshold comparator is used to output an early pull-down enable signal, and the early pull-down enable signal is used to characterize the comparison information between the drain voltage of the secondary power tube and the early pull-down start threshold.

[0138] When the early pull-down enable signal is at a high level, it indicates that the drain voltage is greater than the early pull-down start threshold, and the early pull-down start is enabled.

[0139] The switching power supply system may include an inflection point counting feedback circuit, which is used to output a gear control signal based on the early pull-down enable signal.

[0140] like Figure 5 As shown, the inflection point counting feedback circuit may include an inflection point signal generating circuit, which may input an early pull-down enable signal to the S terminal (set) of the RS trigger 1, and input the driving voltage signal to the R terminal (reset) of the RS trigger 1 after passing through the inverter INV0; the early pull-down enable signal is input to the first input terminal of the AND gate AND0 through the inverter INV1, and the output terminal Q of the RS trigger 1 is input to the second input terminal of the AND gate AND0, and the AND gate AND0 outputs an inflection point signal.

[0141] like Figure 6As shown, when the drain voltage crosses the early pull-down start threshold, that is, point A in the figure, the early pull-down enable signal flips to a high level, indicating that the early pull-down current is turned on, the gate voltage of the secondary power tube drops, and the voltage between the gate and the source of the secondary power tube VGS∝1 / Rdson (Rdson is the resistance between the drain and the source, that is, the on-resistance of the secondary power tube). When the gate-source voltage of the secondary power tube drops, the on-resistance will increase, and the drain voltage of the secondary power tube VD=Isec*Rdson, Isec represents the demagnetization current flowing through the secondary power tube. When the pull-down current is large, the gate voltage of the secondary power tube drops faster, that is, the speed at which the on-resistance increases is greater than the speed at which the demagnetization current decreases, and the drain voltage will rise and fall from A to B in the figure.

[0142] When the drain voltage crosses the early pull-down turn-on threshold, the early pull-down enable signal flips to a low level, the early pull-down current is turned off, the gate voltage of the secondary power tube stops decreasing, the demagnetization current continues to decrease, and the drain voltage crosses the early pull-down turn-on threshold again, that is, position C in the figure, the early pull-down enable signal flips to a high level, the early pull-down current is turned on, and the gate voltage continues to decrease. When the rate of increase of the on-resistance is greater than the rate of decrease of the demagnetization current again, the drain voltage will cross the early pull-down turn-on threshold again, that is, position D in the figure, the early pull-down enable signal flips to a low level again, stops pulling down, and the gate voltage is maintained. As the demagnetization current gradually decreases to 0, the drain voltage also rises to near the early pull-down turn-on threshold, controlling the secondary power tube to turn off.

[0143] In the early pull-down stage, the pulse signal of the early pull-down enable signal being a low level is the inflection point signal. When the inflection point signal is a high level, it finally appears as an inflection point on the driving voltage signal. The inflection point signal generating circuit can obtain a pulse signal that stops the pull-down in a switching cycle for feedback to the subsequent circuit.

[0144] Continue to refer Figure 5 The inflection point counting feedback circuit may include an inflection point holding circuit, and the inflection point holding circuit is used to receive the inflection point signal output by the inflection point signal generating circuit.

[0145] like Figure 7 As shown, the falling edge of the driving voltage signal is delayed for a period of time to generate a delayed driving signal, and the delayed driving signal can be input to the reset rst terminal of the counter. The reset signal is valid at a low level. The inflection point signal is input to the clock clk terminal of the counter. The rising edge of the clock signal is valid. The counter outputs q2, q1 and q0, that is, when the delayed driving signal is at a high level, the counter starts working and counts the number of rising edges of the inflection point signal.

[0146] q2 and q1 are output to the first and second input terminals of AND gate AND1 through inverters INV2 and INV3, q0 is input to the third input terminal of AND1, and the AND gate outputs a v1 signal to the input D terminal of D flip-flop 1, the delayed driving signal is input to the reset Reset terminal of D flip-flop 1, the reset signal is valid at a low level, the driving voltage signal is input to the clock clk terminal, the falling edge of the clock signal is valid, and D flip-flop 1 outputs p1 to the bidirectional counting module, that is, D flip-flop 1 starts working when the delayed driving signal is at a high level, reads the information in the input D terminal at the falling edge of the driving voltage signal, and resets when the delayed driving signal is at a low level;

[0147] The inflection point holding circuit is used to count the inflection point signals, the number of inflection point signals is equal to the number of bends of the driving voltage signal, and the optimal number of bends is the target number k (k preferably takes the value 1, or can also be other values, which are not limited in this application), that is, the outputs of counters q2, q1 and q0 are 001, and the output v1 of AND gate AND1 is high level, and then the output of D flip-flop 1 is high level;

[0148] like Figure 7 As shown, the counter counts the inflection point signals and outputs q2~q0. In the first switching cycle, the inflection point signal has two pulses, that is, q2q1q0=010 is read at the falling edge of the driving voltage signal, indicating that there are two inflection point signals. At this time, v1=0, that is, p1=0;

[0149] In the second switching cycle, the inflection point signal has only one pulse, that is, q2q1q0=001 is read at the falling edge of the driving voltage signal. At this time, v1=1, p1=1, indicating that there is an inflection point signal (where "0" represents a low level and "1" represents a high level).

[0150] In some embodiments, step S2 may include:

[0151] When the number of bending times of the driving voltage signal in the current switching cycle is less than the target number, the gear control signal is increased by one;

[0152] When the number of bending times of the driving voltage signal in the current switching cycle is greater than the target number, the gear control signal is controlled to decrease by one.

[0153] In this embodiment, the voltage difference between the gate and source of the secondary power tube is inversely proportional to the resistance (on-resistance) between the drain and source of the secondary power tube.

[0154] When the pull-down current of the current switching cycle is small, the driving voltage signal decreases slowly and has a small slope. The rate of increase of the on-resistance is less than the rate of decrease of the demagnetization current. After the drain voltage of the secondary power tube crosses the early pull-down turn-on threshold, it will no longer cross the early pull-down turn-on threshold. The drain voltage will continue to rise to 0V, and then the secondary power tube will be turned off. The driving voltage signal has no inflection point, that is, the number of bends of the driving voltage signal in the current switching cycle is 0, which is less than the target number (assuming it is 1), and the driving voltage signal is directly pulled down to shutdown in the early pull-down stage.

[0155] When the pull-down current in the current switching cycle is small, the bidirectional counter does not detect the inflection point of the driving voltage signal, and the bidirectional counter will count upward and control the gear control signal to increase by one to control the pull-down current in the output feedback current to increase.

[0156] When the pull-down current of the current switching cycle is large, the driving voltage signal will be pulled down quickly. When the increase rate of the on-resistance is multiple times greater than the decrease rate of the demagnetization circuit of the secondary power tube flowing through the secondary side, the drain voltage of the secondary power tube will be pulled down multiple times to exceed the early pull-down start threshold, that is, the driving voltage signal will bend multiple times in the current switching cycle (the number of bends is 2 in this embodiment), and the number of bends of the driving voltage signal in the current switching cycle will be greater than the target number (assuming it is 1). The bidirectional counter detects the inflection point, and the bidirectional counter counts downward, which will control the gear control signal to decrease by one, so as to control the pull-down current in the output feedback current to decrease.

[0157] In some embodiments, adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal may include:

[0158] Obtaining a reference signal corresponding to the switching power supply system;

[0159] Based on the gear control signal and the reference signal, obtaining a first current corresponding to the secondary power tube;

[0160] Based on the first current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

[0161] In this embodiment, the reference signal includes a fixed current signal or an output voltage signal.

[0162] Among them, a fixed current signal can be provided based on a current source; and an output voltage signal of the switching power supply system can be obtained through a feedback loop.

[0163] For example, an output voltage signal may be obtained according to an output voltage pin of a switching power supply system, where the output voltage signal is a DC voltage between output terminals of the switching power supply.

[0164] like Figure 2As shown, in the case where the switching power supply system includes an output voltage pin VO, the output voltage signal of the switching power supply system can be directly obtained by sampling the voltage information of the VO pin; Figure 3 As shown, when the switching power supply system does not include an output voltage pin, the output voltage sampling information of the switching power supply system can be indirectly obtained by sampling the voltage information of the VD pin (the drain voltage of the secondary power tube).

[0165] The pull-down current of the secondary power tube can be adjusted based on the gear control signal and the reference signal.

[0166] For example, a first current may be generated according to a gear control signal and a reference signal, and then the pull-down current of the secondary power tube in the next switching cycle may be determined according to a magnitude relationship between the first current and a fixed minimum current.

[0167] In some embodiments, adjusting the pull-down current corresponding to the secondary power tube based on the first current and the fixed minimum current corresponding to the switching power supply system may include:

[0168] When the first current is greater than or equal to the fixed minimum current, adjusting the pull-down current of the secondary power tube in the next switching cycle to the first current;

[0169] When the first current is less than the fixed minimum current, the pull-down current of the secondary power tube in the next switching cycle is adjusted to the fixed minimum current.

[0170] In this embodiment, the size of the fixed minimum current can be customized by the user, or can be set based on the properties of the secondary power tube. The fixed minimum current is used to provide a minimum branch pull-down current, which is used in the case of output short circuit and low output voltage, such as when the first current is less than the fixed minimum current, to ensure that there is a pull-down current in the circuit to reduce the secondary side stress.

[0171] like Fig. 9 and Fig.12 As shown, when the drain voltage of the secondary power tube crosses the early pull-down start threshold, the early pull-down enable signal is high, the switch connected to the minimum pull-down current circuit is closed, and the minimum pull-down current circuit can output a fixed minimum current.

[0172] In some embodiments, obtaining a first current corresponding to a secondary power tube based on a gear control signal and a reference signal may include:

[0173] Based on the gear control signal, a target first switch among the plurality of first switches is controlled to be closed, so that the pull-down current adjustment circuit outputs a first current corresponding to the target first switch based on the output voltage.

[0174] In this embodiment, the switching power supply system includes a pull-down current adjustment circuit, which includes a reference module and a plurality of first current source modules connected in parallel.

[0175] The reference module is used to output a reference signal.

[0176] The first current source module includes a first current source and a first switch connected in series.

[0177] The first current source is used to mirror the current in the reference module, and the first switch is configured to be closed based on the gear control signal.

[0178] When a target first switch among the plurality of first switches is closed, the current mirror corresponding to the target first switch can mirror the current in the reference module, thereby outputting the first current.

[0179] The gear control signal may be Q<0:n>, where the value of n may be user-defined. In this application, n may be set to 4, such as Fig. 9 As shown, each first switch can be controlled based on the gear control signal Q0~Q4. For example, when the gear control signal is 10000, the first switch corresponding to Q0 can be controlled to be closed; when the gear control signal is 01000, the first switch corresponding to Q1 can be controlled to be closed, ..., when the gear control signal is 00...01, the first switch corresponding to Qn can be controlled to be closed, and when the gear control signal is 11111, multiple first switches can be controlled to be closed.

[0180] like Fig. 9 As shown, in some embodiments, the reference module may include: a voltage-controlled current source, a second current source connected in series, and an enabling switch.

[0181] In this embodiment, the reference signal may include an output voltage signal.

[0182] The current output by the output voltage signal through the voltage-controlled current source is positively correlated with the output voltage signal, and forms a current mirror with the second current source, and the mirror multiple can be 1:k1.

[0183] When the early pull-down enable signal is at a high level, the enable switch is closed, and the current flowing through the second current source is Ivo_sam. The first current source can form a current mirror with the second current source, and the first current source can mirror the current in the second current source, and multiple first current sources I0, I1, I2, I3 and I4 form a binary weight relationship, that is, the mirror multiple of the current mirror formed by the first current source I0 and the second current source can be 1:20, the mirror multiple of the current mirror formed by the first current source I1 and the second current source can be 1:21, the mirror multiple of the current mirror formed by the first current source I2 and the second current source can be 1:22, the mirror multiple of the current mirror formed by the first current source I3 and the second current source can be 1:23, and the mirror multiple of the current mirror formed by the first current source I4 and the second current source can be 1:24.

[0184] The pull-down current adjustment circuit can generate a current I positively correlated with the output voltage signal based on the received output voltage signal, and then mirror the current I by k1 times to generate a current Ivo_sam, thereby mirroring Ivo_sam based on the current mirror corresponding to the target first switch to generate a first current Ivo.

[0185] Based on T_REG=Ls*vref / (Rdson*Vout) (where T_REG is the pull-down adjustment time, Ls is the secondary inductance, vref is the early pull-down start threshold, Rdson is the resistance between the drain and source of the secondary power tube, and Vout is the output voltage), it can be seen that different output voltage signals correspond to different pull-down adjustment times, such as Fig.10 As shown, the output voltage signal VO1>VO2, when the early pull-down threshold and the parameters of the secondary power tube remain unchanged, the demagnetization current when different output voltage signals are turned on for early pull-down is the same, such as Fig.10 As shown in Is0 , the time required for the demagnetization current of the output voltage signal VO1 to decrease to 0 is shorter than the time required for the demagnetization current of the output voltage signal VO2 to decrease to 0, that is, t1 < t2 .

[0186] Based on CU=Isink*T (where CU is the voltage change of the gate capacitance in the pull-down stage, Isink is the pull-down current, and T is the time required for the demagnetization current to decrease to 0), it can be known that, when the voltage change of the gate capacitance in the pull-down stage remains unchanged, the smaller the output voltage signal is, the longer the time required for the demagnetization current to decrease to 0 is, and the smaller the pull-down current is, that is, the size of the output voltage signal is positively correlated with the size of the pull-down current.

[0187] According to the control method of the switching power supply system provided in the embodiment of the present application, by obtaining feedback information of the output voltage, the size of the pull-down current is better controlled according to the characteristics of different output voltages and different falling slopes of the demagnetization current, so as to avoid the problem of excessive pull-down current, the driving voltage signal being pulled too low, the secondary power tube being shut down in advance, and the current being continued through the body diode, resulting in increased conduction loss.

[0188] like Fig.12 As shown, in some embodiments, the reference module may include: a third current source and an enabling switch connected in series.

[0189] In this embodiment, the third current source is used to provide a fixed current signal.

[0190] The third current source and each first current source form a current mirror, each first current source can mirror the current in the third current source, and a binary weight relationship is formed between I0-I4.

[0191] Q0~Q4 control a first switch respectively. A high level closes the first switch. The pull-down circuit can be controlled through feedback regulation to adjust the current output by the circuit, thereby adjusting the overall pull-down current.

[0192] In the actual implementation process, Fig. 9 and Fig.12 As shown, when the drain voltage of the secondary power tube crosses the early pull-down start threshold, the early pull-down enable signal is at a high level, and the first switch corresponding to Qn can be controlled to close according to the gear control signal. The pull-down current adjustment circuit can output a first current based on the reference signal, and the first current can be amplified k2 times by the current mirror to obtain the current Isink_vo=k2*Ivo (where Ivo is the first current). This current branch is related to the feedback of the reference signal and the number of bending times of the drive voltage, and is the main discharge path for early pull-down.

[0193] When the early pull-down enable signal is at a high level, the switch is closed, and the minimum pull-down current circuit can output a fixed minimum current to provide a minimum branch pull-down current.

[0194] The second pull-down control circuit is connected to the external PIN pin DRV and can pull down the gate voltage of the secondary power tube through two pull-down current branches.

[0195] like Fig.11 As shown, when the driving voltage signal starts to wave, the drain voltage of the secondary power tube can be detected, and then it is determined whether the drain voltage is greater than the early pull-down start threshold. If not, the drain voltage continues to be detected.

[0196] If so, the pull-down enable is turned on, the system enters the early pull-down stage, and starts feedback adjustment.

[0197] The number of bends of the driving voltage signal can be obtained, and the relationship between the number of bends and the target number (generally 1) can be determined. The bidirectional counter can adjust the gear control signal according to the number of bends of the driving voltage signal.

[0198] When the number of bends of the driving voltage signal is equal to 0, the bidirectional counter counts upward, that is, the gear control signal is increased by one, to control the increase of the pull-down current of the secondary power tube in the next switching cycle. When entering the next switching cycle, the next switching cycle is the current switching cycle, and the number of bends of the driving voltage signal in the early pull-down stage of the current switching cycle can continue to be determined.

[0199] When the number of bends of the driving voltage signal is greater than 1, the bidirectional counter counts downward, that is, the gear control signal is reduced by one, so as to control the reduction of the pull-down current of the secondary power tube in the next switching cycle, and continue to judge the number of bends of the driving voltage signal in the early pull-down stage in the current switching cycle.

[0200] When the number of bends of the driving voltage signal is equal to 1, the output of the bidirectional counter remains consistent with the previous switching cycle, that is, the gear control signal is not adjusted to keep the pull-down current of the secondary power tube in the next switching cycle consistent with the pull-down current of the current switching cycle.

[0201] In some embodiments, adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal may include:

[0202] Obtaining a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal;

[0203] When it is determined that the switching power supply system is in a continuous conduction mode, the maximum current corresponding to the secondary power tube is obtained based on the gear control signal and the reference signal;

[0204] Based on the maximum current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

[0205] In this embodiment, the continuous conduction mode is a working mode in which the secondary power tube is demagnetized after the primary power tube in the switching power supply system is turned off, and the primary power tube is turned on again before the secondary power tube is demagnetized.

[0206] When the plurality of first switches are all closed, the pull-down current adjustment circuit can output the maximum current, and then adjust the pull-down current corresponding to the secondary power tube in the next switching cycle based on the maximum current and the fixed minimum current.

[0207] According to the control method of the switching power supply system provided in the embodiment of the present application, by controlling the pull-down current of the next switching cycle to reach the maximum when the switching power supply system is in the continuous conduction mode, the risk of primary-secondary side penetration in the continuous conduction mode is reduced.

[0208] In the actual implementation process, Figure 5 As shown, the inflection point counting feedback circuit may include a bidirectional counter, a reset RST terminal of the bidirectional counter is connected to an enable signal for normal operation of the chip, the reset signal is effective at a low level, and when the enable signal is at a high level, the bidirectional counter starts to work;

[0209] The bidirectional counter can output a gear control signal Q<0:n>, where n represents the number of current gears. The more gears there are, the finer the pull-down is and the more accurate the feedback control is. In the present application, n can be determined to be 4, that is, it is divided into 32 gears to control the size of the pull-down current; the gear control signal and the external clock signal are input to the anti-overflow circuit, and the anti-overflow circuit is output to the CLK end of the bidirectional counter. The external clock signal is between the falling edge of the driving voltage signal and the falling edge of the delayed driving signal corresponding to the driving voltage signal, so as to realize the function of reading first, writing later, and then resetting;

[0210] The driving voltage signal can be used as a set signal, and the inflection point signal can be used as a reset signal to be input into the bidirectional control signal generating circuit. The bidirectional control signal generating circuit can output an upward counting signal to the UP terminal of the bidirectional counter. In a switching cycle, if the reset signal is always at a low level, the upward counting signal is always at a high level, and the bidirectional counter counts upward. If a reset signal is encountered, the upward counting signal is reset and flipped to a low level, and the bidirectional counter counts downward.

[0211] The input end of the holding control signal generating circuit is used to receive the driving voltage signal, the inflection point signal, the detection signal corresponding to the continuous conduction mode and the p1 signal output by the inflection point holding circuit. When the detection is a high level, it indicates the CCM mode. The holding control signal generating circuit outputs a holding signal to the HOLD end of the bidirectional counter.

[0212] In each switching cycle, when the up-counting signal flips, the bidirectional counter will be held for a period of time to prevent the bidirectional counter from counting incorrectly when the up-counting signal flips;

[0213] In the continuous conduction mode, the bidirectional counter will be held and the count value will remain unchanged, but the outputs of the bidirectional counter are all high level;

[0214] When the driving voltage signal bends only once, that is, when the signal p1 output by the inflection point holding circuit is 1, the bidirectional counter will be held, the count value remains unchanged, and its output is consistent with the previous cycle.

[0215] like Figure 8 As shown in (a), when the driving voltage signal has no inflection point (i.e., the inflection point signal is always at a low level), when the driving voltage signal turns from low to high, the upward counting signal turns to a high level after a delay of a period of time (the delay time is at the ns level), and when the reset signal (i.e., the inflection point signal) is not detected, the upward counting signal is always at a high level, the counter counts up, the output of the bidirectional counter is +1, and the pull-down current is increased by one gear;

[0216] like Figure 8 As shown in (b), when the driving voltage signal has multiple inflection points, when the inflection point signal turns from low to high for the first time, the upward counting signal is delayed for a period of time and reset to a low level (it can be seen from the figure that the flip edge of the upward counting signal falls during the high level period of the holding signal to prevent the bidirectional counter from counting incorrectly when the holding signal turns over). When the rising edge of the clock clk1 arrives, the holding signal is detected to be a low level, the counter counts downward, and the output of the bidirectional counter is -1, reducing the pull-down current by one gear;

[0217] like Figure 8 As shown in (c), when the driving voltage signal has only one inflection point, the inflection point holding circuit output p1 is high level, the holding signal is also high level, shielding the bidirectional counter clock clk1, and the output of the bidirectional counter is consistent with the previous cycle;

[0218] like Figure 8 As shown in (d), when the switching power supply system enters the continuous conduction mode, the signal shielding clock signal clk1 is maintained, and the count value of the bidirectional counter remains unchanged, but the output of the gear control signal Q<0:n> is all high level, and the control pull-down current gear is all opened.

[0219] The embodiment of the present application also provides a switching power supply system.

[0220] like Figure 4 As shown, the switching power supply system includes: a secondary side power tube SR and an early pull-down control circuit 100.

[0221] In this embodiment, the early pull-down control circuit 100 may include: a threshold comparator 250 and a first pull-down control circuit 110 .

[0222] One input terminal of the threshold comparator 250 is connected to the drain of the secondary power tube SR and is used to receive the drain voltage of the secondary power tube SR.

[0223] Another input terminal of the threshold comparator 250 is used to receive the early pull-down start threshold.

[0224] The first pull-down control circuit 110 is connected to the output terminal of the threshold comparator 250 , and is used to receive the early pull-down enable signal output by the threshold comparator 250 .

[0225] The first pull-down control circuit 110 may also be connected to the gate of the secondary power tube SR, for example, may be connected to the gate of the secondary power tube SR via a DRV pin, so as to obtain the gate voltage of the secondary power tube SR.

[0226] The first pull-down control circuit 110 is used to adjust the pull-down current of the secondary power tube SR corresponding to the next switching cycle of the current switching cycle based on the bending times of the driving voltage signal in the current switching cycle.

[0227] According to the switching power supply system provided in the embodiment of the present application, during the conduction period of the secondary power tube SR, according to the number of bends of the driving voltage signal in the early pull-down stage in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, thereby reducing the gate voltage at the turn-off moment of the secondary power tube SR, and improving the average driving voltage signal of the gate of the secondary power tube SR in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current of the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can operate stably.

[0228] like Figure 4 As shown, in some embodiments, the first pull-down control circuit 110 may include: an inflection point count feedback circuit 120 and a pull-down circuit 130 .

[0229] In this embodiment, the inflection point counting feedback circuit 120 is connected to the output end of the threshold comparator 250 , and the inflection point counting feedback circuit 120 is used to output a gear control signal.

[0230] The pull-down circuit 130 is connected to the output end of the threshold comparator 250 and the output end of the inflection point counting feedback circuit 120 respectively. The output end of the pull-down circuit 130 is used to output the magnitude of the pull-down current corresponding to the secondary power tube SR in the next switching cycle.

[0231] like Figure 5 As shown, in some embodiments, the inflection point counting feedback circuit 120 may include: an inflection point signal generating circuit 140 , an inflection point holding circuit 150 and a bidirectional counting module 160 .

[0232] In this embodiment, the inflection point signal generating circuit 140 is connected to the output terminal of the threshold comparator 250 .

[0233] The inflection point holding circuit 150 is connected to the output terminal of the inflection point signal generating circuit 140 .

[0234] The bidirectional counting module 160 is respectively connected to the output end of the inflection point signal generating circuit 140 and the output end of the inflection point holding circuit 150 , and the output end of the bidirectional counting module 160 is used to output a gear control signal.

[0235] The inflection point signal generating circuit 140 includes an inverter INV0 , an RS flip-flop 1 , an inverter INV1 , and an AND gate AND0 .

[0236] The driving voltage signal passes through inverter INV0 and is input to the R terminal (reset) of RS trigger 1. The early pull-down enable signal passes through inverter INV1 and is input to the first input terminal of AND gate AND0. The output terminal Q of RS trigger 1 is input to the second input terminal of AND gate AND0, and AND gate AND0 outputs an inflection point signal.

[0237] The inflection point holding circuit 150 includes a counter, an inverter INV2 , an inverter INV3 , an AND gate AND1 , and a D flip-flop 1 .

[0238] By delaying the falling edge of the driving voltage signal for a period of time, a delayed driving signal can be generated, and the delayed driving signal can be input into the reset rst terminal of the counter. The counter outputs q2, q1 and q0. q2 and q1 are output to the first and second input terminals of the AND gate AND1 through inverters INV2 and INV3. q0 is input to the third input terminal of AND1. The AND gate outputs a v1 signal to the input D terminal of the D flip-flop 1. The delayed driving signal is input into the reset Reset terminal of the D flip-flop 1. The driving voltage signal is input into the clock clk terminal. The D flip-flop 1 outputs p1 to the bidirectional counting module 160.

[0239] The bidirectional counting module 160 includes: a bidirectional control signal generating circuit, a holding control signal generating circuit, a bidirectional counter and an anti-overflow circuit.

[0240] The reset RST terminal of the bidirectional counter is connected to the en signal, the output Q<0:n> of the bidirectional counter and the external clock signal clk1 are input into the anti-overflow circuit, the anti-overflow circuit outputs to the CLK terminal of the bidirectional counter, the driving voltage signal is used as the set signal, the inflection point signal is used as the reset signal input into the bidirectional control signal generating circuit, the up-counting signal is output to the UP terminal of the bidirectional counter, the hold control signal generating circuit is used to receive the driving voltage signal, the inflection point signal, the detection signal and the p1 signal, the hold control signal generating circuit outputs the hold signal to the HOLD terminal of the bidirectional counter.

[0241] like Fig. 9 As shown, in some embodiments, the pull-down circuit 130 may include: a pull-down current adjustment circuit 170 , a minimum pull-down current circuit 180 , and a second pull-down control circuit 190 .

[0242] In this embodiment, the input terminal of the pull-down current adjustment circuit 170 is used to receive the output voltage, and the output terminal of the pull-down current adjustment circuit 170 is used to output the first current.

[0243] One end of the minimum pull-down current circuit 180 is connected to the pull-down current adjustment circuit 170 , and the minimum pull-down current circuit 180 is used to provide a fixed minimum current.

[0244] The second pull-down control circuit 190 is connected to the other end of the pull-down current adjustment circuit 170 and the minimum pull-down current circuit 180 respectively, and the output end of the second pull-down control circuit 190 is used to output the size of the pull-down current corresponding to the secondary power tube SR in the next switching cycle.

[0245] In some embodiments, the pull-down current adjustment circuit may include: a reference module and a plurality of first current source modules connected in parallel.

[0246] In this embodiment, the reference module is used to output a reference signal, and the reference signal includes a fixed current signal or an output voltage signal.

[0247] One end of each first current source module is connected to one end of the reference module, and the other end of each first current source module is connected to the other end of the reference module.

[0248] The first current source module includes a first current source and a first switch connected in series.

[0249] The first current source is used to mirror the current in the reference module, and the plurality of first current sources I0 , I1 , I2 , I3 and I4 form a binary weight relationship.

[0250] The first switch is configured to be closed based on the gear control signal.

[0251] like Fig. 9 As shown, in some embodiments, the reference module may include: a voltage-controlled current source 200, a second current source connected in series, and an enabling switch.

[0252] In this embodiment, the voltage-controlled current source 200 is used to output a second current based on the output voltage signal.

[0253] One end of the second current source away from the enabling switch is respectively connected to the output end of the voltage-controlled current source 200 and the other ends of the plurality of first current sources.

[0254] One end of the enabling switch away from the second current source is connected to one end of the plurality of first current source modules, and one end of the enabling switch away from the second current source is used to receive the voltage VDD.

[0255] The second current source is used for mirroring the second current.

[0256] like Fig.12As shown, in some embodiments, the reference module may include: a third current source and an enabling switch connected in series.

[0257] In this embodiment, one end of the third current source away from the enabling switch is connected to one end of the plurality of first current source modules.

[0258] One end of the enabling switch away from the third current source is connected to the other ends of the plurality of first current source modules.

[0259] The third current source is used to provide a fixed current signal.

[0260] The third current source and the plurality of first current sources form a current mirror, wherein the first current source mirrors the current in the third current source, and a binary weight relationship is formed between the plurality of first current sources.

[0261] The first current Ivo generated by the plurality of first current sources after being controlled by the corresponding first switches can form a current Isink_vo after being mirrored, and Isink_vo=k2*Ivo.

[0262] like Figure 2 As shown, in some embodiments, the switching power supply system may further include: a conduction control circuit 210 , a shutdown control circuit 220 , a logic control circuit 230 and a drive circuit 240 .

[0263] In this embodiment, the conduction control circuit 210 is connected to the drain of the secondary power transistor SR.

[0264] The shutdown control circuit 220 is connected to the drain of the secondary power tube SR.

[0265] The logic control circuit 230 is connected to the output terminal of the on control circuit 210 and the output terminal of the off control circuit 220 respectively.

[0266] The driving circuit 240 is connected to the output end of the logic control circuit 230 , and the output end of the driving circuit 240 is connected to the gate of the secondary power tube SR.

[0267] like Figure 3 As shown, in some embodiments, the switching power supply system may further include: an output voltage sampling and filtering circuit.

[0268] In this embodiment, the input end of the output voltage sampling and filtering circuit is connected to the drain of the secondary power tube SR, and the output end of the output voltage sampling and filtering circuit is connected to the early pull-down control circuit 100 .

[0269] The control device of the switching power supply system provided in the present application is described below. The control device of the switching power supply system described below and the control method of the switching power supply system described above can be referred to each other.

[0270] The control method of the switching power system provided in the embodiment of the present application can be executed by a control device of the switching power system. In the embodiment of the present application, the control device of the switching power system executing the control method of the switching power system is taken as an example to illustrate the control device of the switching power system provided in the embodiment of the present application.

[0271] An embodiment of the present application also provides a control device for a switching power supply system.

[0272] like Fig.15 As shown, the control device of the switching power supply system includes a secondary side power tube; the control device includes: a first processing module 1510, a second processing module 1520, a third processing module 1530 and a fourth processing module 1540.

[0273] The first processing module 1510 is used to obtain the number of bending times of the driving voltage signal of the secondary power tube corresponding to the current switching cycle in the early pull-down stage; the early pull-down stage is the period from the moment when the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube is greater than the early pull-down start threshold for the first time to the moment when the secondary power tube is turned off;

[0274] A second processing module 1520, configured to adjust a gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle;

[0275] The third processing module 1530 is used to adjust the pull-down current corresponding to the secondary power tube based on the gear control signal when entering the next switching cycle of the current switching cycle, and return to the early pull-down stage to obtain the bending number of the driving voltage signal corresponding to the secondary power tube in the current switching cycle, until the bending number of the driving voltage signal obtained most recently reaches the target number, and then stop adjusting the pull-down current;

[0276] The fourth processing module 1540 is used to control the control gear of the pull-down current to remain unchanged when the bending number of the driving voltage signal is the target number; the pull-down current is used to reduce the gate voltage of the secondary power tube at the shutdown time.

[0277] According to the control device of the switching power supply system provided in the embodiment of the present application, in the early pull-down stage, according to the number of bends of the driving voltage signal in the current switching cycle, the pull-down current of the secondary power tube in the next switching cycle is adaptively adjusted, thereby reducing the gate voltage at the moment when the secondary power tube is turned off, and improving the average driving voltage signal of the gate of the secondary power tube in the early pull-down stage, thereby reducing the conduction loss in the early pull-down stage and improving the efficiency of the switching power supply system; and by adjusting the pull-down current of the next switching cycle, the number of bends of the driving voltage signal can be maintained at the target number, so that the switching power supply system can operate stably.

[0278] In some embodiments, the second processing module 1520 may also be used to:

[0279] When the number of bending times of the driving voltage signal in the current switching cycle is less than the target number, the gear control signal corresponding to the control switching power supply system is increased by one;

[0280] When the number of bending times of the driving voltage signal in the current switching cycle is greater than the target number, the gear control signal is controlled to decrease by one.

[0281] In some embodiments, the first processing module 1510 may also be used to:

[0282] In the early pull-down stage, when it is detected that the voltage formed by the secondary demagnetization current on the conduction impedance of the secondary power tube changes from greater than the early pull-down start threshold to less than the early pull-down start threshold, the number of bends of the driving voltage signal is increased by one.

[0283] In some embodiments, the third processing module 1530 may also be used to:

[0284] Obtaining a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal;

[0285] Based on the gear control signal and the reference signal, obtaining a first current corresponding to the secondary power tube;

[0286] Based on the first current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

[0287] In some embodiments, the third processing module 1530 may also be used to:

[0288] Obtaining a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal;

[0289] When it is determined that the switching power supply system is in a continuous conduction mode, the maximum current corresponding to the secondary power tube is obtained based on the gear control signal and the reference signal;

[0290] Based on the maximum current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

[0291] The control device of the switching power supply system in the embodiment of the present application can be an electronic device, or a component in the electronic device, such as an integrated circuit or a chip. The electronic device can be a terminal, or other devices other than a terminal. Exemplarily, the electronic device can be a mobile phone, a tablet computer, a laptop computer, a PDA, a vehicle-mounted electronic device, a mobile Internet device (Mobile Internet Device, MID), an augmented reality (augmented reality, AR) / virtual reality (virtual reality, VR) device, a robot, a wearable device, an ultra-mobile personal computer (ultra-mobile personal computer, UMPC), a netbook or a personal digital assistant (personal digital assistant, PDA), etc., and can also be a server, a network attached storage (Network Attached Storage, NAS), a personal computer (personal computer, PC), a television (television, TV), a teller machine or a self-service machine, etc., which is not specifically limited in the embodiment of the present application.

[0292] The control device of the switching power supply system in the embodiment of the present application may be a device having an operating system. The operating system may be an Android operating system, an IOS operating system, or other possible operating systems, which are not specifically limited in the embodiment of the present application.

[0293] The control device of the switching power supply system provided in the embodiment of the present application can achieve Figures 1 to 14 To avoid repetition, the various processes implemented by the method embodiment are not described here.

[0294] In some embodiments, Fig.16 As shown, an embodiment of the present application also provides an electronic device 1600, including a processor 1601, a memory 1602, and a computer program stored in the memory 1602 and executable on the processor 1601. When the program is executed by the processor 1601, each process of the control method embodiment of the above-mentioned switching power supply system is implemented, and the same technical effect can be achieved. To avoid repetition, it will not be repeated here.

[0295] It should be noted that the electronic devices in the embodiments of the present application include the mobile electronic devices and non-mobile electronic devices mentioned above.

[0296] On the other hand, the present application also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the various processes of the above-mentioned control method embodiment of the switching power supply system and can achieve the same technical effect. To avoid repetition, it will not be repeated here.

[0297] On the other hand, the present application also provides a non-transitory computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the various processes of the control method embodiment of the above-mentioned switching power supply system and can achieve the same technical effect. To avoid repetition, it will not be repeated here.

[0298] On the other hand, an embodiment of the present application further provides a chip, which includes a processor and a communication interface, wherein the communication interface is coupled to the processor, and the processor is used to run programs or instructions to implement the various processes of the above-mentioned control method embodiment of the switching power supply system, and can achieve the same technical effect. To avoid repetition, it will not be repeated here.

[0299] It should be understood that the chip mentioned in the embodiments of the present application can also be called a system-level chip, a system chip, a chip system or a system-on-chip chip, etc.

[0300] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0301] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, by hardware. Based on this understanding, the above technical solution can be essentially or in other words, the part that contributes to the relevant technology can be embodied in the form of a software product, which can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiment.

[0302] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A control method for a switching power supply system, characterized in that: The switching power supply system includes a secondary side power tube; the control method includes: In the early pull-down stage, the number of bends of the driving voltage signal of the secondary power tube corresponding to the current switching cycle is obtained; the early pull-down stage is the period from the moment when the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube is greater than the early pull-down start threshold for the first time to the moment when the secondary power tube is turned off; Adjusting the gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle; In the case of entering the next switching cycle of the current switching cycle, adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal, and returning to execute the step of obtaining the bending times of the driving voltage signal corresponding to the secondary power tube in the current switching cycle in the early pull-down stage, until the bending times of the driving voltage signal obtained most recently reaches the target times, then stopping adjusting the pull-down current; When the number of bends of the driving voltage signal is the target number, the control gear of the pull-down current remains unchanged; the pull-down current is used to reduce the gate voltage of the secondary power tube at the shutdown moment.

2. The control method of the switching power supply system according to claim 1, characterized in that: The adjusting the gear control signal corresponding to the switching power supply system based on the number of bending times of the driving voltage signal in the current switching cycle includes: When the number of bending times of the driving voltage signal in the current switching cycle is less than the target number, controlling the gear control signal corresponding to the switching power supply system to increase by one; When the number of bending times of the driving voltage signal in the current switching cycle is greater than the target number, the gear control signal is controlled to decrease by one.

3. The control method of the switching power supply system according to claim 1, characterized in that: The obtaining of the bending times of the driving voltage signal corresponding to the secondary power tube in the current switching cycle includes: In the early pull-down stage, when it is detected that the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube changes from being greater than the early pull-down start threshold to being less than the early pull-down start threshold, the number of bends of the drive voltage signal is added by one.

4. The control method of the switching power supply system according to any one of claims 1 to 3, characterized in that: The step of adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal includes: Acquire a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal; Based on the gear control signal and the reference signal, obtaining a first current corresponding to the secondary power tube; Based on the first current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

5. The control method of the switching power supply system according to any one of claims 1 to 3, characterized in that: The step of adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal includes: Acquire a reference signal corresponding to the switching power supply system; the reference signal includes a fixed current signal or an output voltage signal; When it is determined that the switching power supply system is in a continuous conduction mode, obtaining a maximum current corresponding to the secondary power tube based on the gear control signal and the reference signal; Based on the maximum current and the fixed minimum current corresponding to the switching power supply system, the pull-down current corresponding to the secondary power tube is adjusted.

6. A switching power supply system based on the control method of the switching power supply system according to any one of claims 1 to 5, characterized in that: include: Secondary side power tube; A threshold comparator, one input end of the threshold comparator is connected to the drain of the secondary power tube, and the other input end of the threshold comparator is used to receive an early pull-down start threshold; A first pull-down control circuit, wherein the first pull-down control circuit is respectively connected to the output end of the threshold comparator and the gate of the secondary power tube; The first pull-down control circuit includes: an inflection point counting feedback circuit and a pull-down circuit, the inflection point counting feedback circuit is connected to the output end of the threshold comparator, and the inflection point counting feedback circuit is used to output a gear control signal; the pull-down circuit is respectively connected to the output end of the threshold comparator and the output end of the inflection point counting feedback circuit, and the output end of the pull-down circuit is used to output the size of the pull-down current corresponding to the next switching cycle of the secondary side power tube in the current switching cycle.

7. The switching power supply system according to claim 6, characterized in that: The inflection point counting feedback circuit comprises: An inflection point signal generating circuit, wherein the inflection point signal generating circuit is connected to an output end of the threshold comparator; An inflection point holding circuit, the inflection point holding circuit being connected to an output end of the inflection point signal generating circuit; A bidirectional counting module is connected to the output end of the inflection point signal generating circuit and the output end of the inflection point holding circuit respectively, and the output end of the bidirectional counting module is used to output the gear control signal.

8. The switching power supply system according to claim 6, characterized in that: The pull-down circuit comprises: A pull-down current adjustment circuit, the pull-down current adjustment circuit comprising: a reference module and a plurality of first current source modules connected in parallel, the reference module being used to output a reference signal, the reference signal comprising a fixed current signal or an output voltage signal; One end of each of the first current source modules is connected to one end of the reference module, and the other end of each of the first current source modules is connected to the other end of the reference module, the first current source module comprises a first current source and a first switch connected in series, the first current source is used to mirror the current in the reference module, and the first switch is configured to be closed based on the gear control signal; a minimum pull-down current circuit, one end of which is connected to the pull-down current adjustment circuit, and the minimum pull-down current circuit is used to provide a fixed minimum current; A second pull-down control circuit, wherein the second pull-down control circuit is respectively connected to the other end of the pull-down current adjustment circuit and the minimum pull-down current circuit, and the output end of the second pull-down control circuit is used to output the size of the pull-down current corresponding to the secondary power tube in the next switching cycle.

9. The switching power supply system according to claim 8, characterized in that: The reference module comprises: a voltage-controlled current source, the voltage-controlled current source being configured to output a second current based on the output voltage signal; A second current source and an enabling switch connected in series, wherein one end of the second current source away from the enabling switch is respectively connected to the output end of the voltage-controlled current source and the other end of the plurality of first current sources, one end of the enabling switch away from the second current source is connected to one end of the plurality of first current source modules, and the second current source is used to mirror the second current.

10. The switching power supply system according to claim 8, characterized in that: The reference module comprises: A third current source and an enabling switch connected in series, wherein one end of the third current source away from the enabling switch is connected to one end of the plurality of first current source modules, and one end of the enabling switch away from the third current source is connected to the other end of the plurality of first current source modules, and the third current source is used to provide the fixed current signal.

11. The switching power supply system according to any one of claims 6 to 10, characterized in that: Also includes: A conduction control circuit connected to the drain of the secondary power tube; A shutdown control circuit connected to the drain of the secondary power tube; A logic control circuit, wherein the logic control circuit is respectively connected to an output end of the conduction control circuit and an output end of the shutdown control circuit; A driving circuit, wherein the driving circuit is connected to the output end of the logic control circuit, and the output end of the driving circuit is connected to the gate of the secondary power tube.

12. A control device for a switching power supply system, characterized in that: The switching power supply system includes a secondary power tube; the control device includes: The first processing module is used to obtain the number of bends of the driving voltage signal of the secondary power tube corresponding to the current switching cycle in the early pull-down stage; the early pull-down stage is the period from the moment when the voltage formed by the secondary demagnetization current on the on-resistance of the secondary power tube is greater than the early pull-down start threshold for the first time to the moment when the secondary power tube is turned off; A second processing module, configured to adjust a gear control signal corresponding to the switching power supply system based on the number of bends of the driving voltage signal in the current switching cycle; A third processing module is used for adjusting the pull-down current corresponding to the secondary power tube based on the gear control signal when entering the next switching cycle of the current switching cycle, and returning to execute the step of obtaining the bending number of the driving voltage signal corresponding to the secondary power tube in the current switching cycle in the early pull-down stage, until the bending number of the driving voltage signal obtained most recently reaches the target number, and then stopping adjusting the pull-down current; The fourth processing module is used to control the control gear of the pull-down current to remain unchanged when the number of bending times of the driving voltage signal is the target number; the pull-down current is used to reduce the gate voltage of the secondary power tube at the shutdown moment.

13. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the control method of the switching power supply system according to any one of claims 1 to 5 is implemented.

14. A chip, comprising a processor and a communication interface, wherein the communication interface is coupled to the processor, characterized in that: The processor is used to run a program or an instruction, and when the processor executes the program or the instruction, the control method of the switching power supply system according to any one of claims 1 to 5 is implemented.

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