Switching power supply and control circuit and control method thereof

Abstract

The application discloses a control circuit of a switching power supply, comprising: a frequency control module for generating a frequency control signal; a switching control module for generating a switching control signal according to a second compensation voltage, the frequency control signal, a current sampling signal representing an inductor current and a preset frequency value; wherein the frequency control signal is used for controlling the frequency of the switching control signal; when the frequency control signal is an effective level, the frequency of the switching control signal is a first preset frequency; when the frequency control signal is an ineffective level, the frequency of the switching control signal is a second preset frequency, wherein the first preset frequency is N times of the second preset frequency, and N is a positive integer greater than 1. The application can ensure that the switching power supply has a long enough time to make the inductor current drop in a switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a switching power supply and its control circuit and control method. Background Technology

[0002] Power over Ethernet (PoE) technology refers to the technology of providing DC power to terminal devices in a network via network cables, building upon existing Ethernet cabling infrastructure. In PoE, the network cable serves both as a data signal transmitter and a source of DC power. This technology eliminates the need for external power adapters for terminal devices, thus saving on power adapters, cables, and plugs, and reducing cabling and hardware costs.

[0003] Power over Ethernet (PoE) systems consist of power sourcing equipment (PSEs) and powered devices (PDs). The PSE connects to the PD via an Ethernet cable, which can be a twisted-pair cable. Each Ethernet twisted-pair cable typically consists of four pairs of wires. When using PoE, the PSE can power the PD using only two pairs of wires.

[0004] After the PD device is confirmed as legitimate during the detection phase, the PSE device will classify it according to the maximum power required for the PD device to work normally through a classification mechanism, and then supply power to the PD device after the classification is completed.

[0005] After receiving voltage from the power supply, a PD device typically needs to convert the voltage to a lower voltage using its internal switching power supply to provide it to the load. During startup, the switching power supply within the PD device may experience output voltage overshoot, input current exceeding the steady-state full-load current threshold, or a sudden increase in load current causing the output voltage to drop due to the specific characteristics of the load. Summary of the Invention

[0006] In view of the above, the purpose of this invention is to provide a switching power supply for power receiving equipment, and its control circuit and control method, to enhance the dynamic response capability of the switching power supply to sudden load changes.

[0007] According to a first aspect of the present invention, a control circuit for a switching power supply is provided, comprising: a frequency control module for generating a frequency control signal; and a switching control module for generating a switching control signal based on a second compensation voltage, the frequency control signal, a current sampling signal characterizing an inductor current, and a preset frequency value; wherein the frequency control signal is used to control the frequency of the switching control signal; when the frequency control signal is at an active level, the frequency of the switching control signal is a first preset frequency; and when the frequency control signal is at an inactive level, the frequency of the switching control signal is a second preset frequency, wherein the first preset frequency is N times the second preset frequency, and N is a positive integer greater than 1.

[0008] Preferably, the control circuit further includes: a compensation circuit for generating a first compensation voltage based on a voltage feedback signal characterizing the output voltage and a reference voltage; a power supply module for providing a pull-down voltage; and a pull-down module connected to the power supply module for generating a second compensation voltage based on the first compensation voltage and the pull-down voltage; wherein the frequency control module is further configured to generate a soft-start signal based on the second compensation voltage and the pull-down voltage.

[0009] Preferably, the frequency control module generates the frequency control signal based on the second compensation voltage and the soft-start signal.

[0010] Preferably, when at least one of the soft-start signal and the compensation voltage meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

[0011] Preferably, when neither the soft-start signal nor the compensation voltage meets the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to a second preset frequency.

[0012] Preferably, the preset conditions are that the soft-start signal is at an effective level and the compensation voltage is greater than or equal to a voltage threshold.

[0013] Preferably, the frequency control module generates the frequency control signal based on the soft-start signal, the second compensation voltage, the current sampling signal, and the switch control signal.

[0014] Preferably, when at least one of the soft-start signal, the compensation voltage and the current sampling signal meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

[0015] Preferably, when the soft-start signal, the compensation voltage and the current sampling signal do not meet the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to a second preset frequency.

[0016] Preferably, the preset conditions are when the soft-start signal is at an effective level, the compensation voltage is greater than or equal to a voltage threshold, and the current sampling signal is less than a current threshold for more than m cycles of the switch control signal, where m is a positive integer.

[0017] Preferably, the soft-start signal is active when the pull-down voltage is greater than the sum of the second compensation voltage and the hysteresis voltage; and is inactive when the pull-down voltage is less than the sum of the second compensation voltage and the hysteresis voltage.

[0018] Preferably, the power supply module includes: a first voltage source for providing a first voltage; a second voltage source for providing a second voltage, wherein the second voltage dynamically changes and the first voltage is greater than the second voltage; and a switch, wherein a first terminal and a second terminal are respectively connected to the first voltage source and the second voltage source, and a third terminal outputs a pull-down voltage; wherein the switch connects its third terminal to one of its first and second terminals according to a soft-start signal to achieve switching between the pull-down module and the first and second voltage sources.

[0019] Preferably, the second compensation voltage changes dynamically according to the soft-start signal and the magnitude relationship between the first voltage, the second voltage and the first compensation voltage.

[0020] Preferably, when the soft-start signal is at an invalid level, the switch switches to the second voltage source, and the pull-down module is connected to the second voltage source; when the soft-start signal is at an valid level, the switch switches to the first voltage source, and the pull-down module is connected to the first voltage source.

[0021] Preferably, when the pull-down module is connected to the second voltage source, the second compensation voltage is pulled down to the second voltage and rises dynamically following the second voltage; when the second voltage is greater than the first compensation voltage, the second compensation voltage is equal to the first compensation voltage; when the pull-down module is connected to the first voltage source, the second compensation voltage is equal to the first compensation voltage.

[0022] Preferably, the power supply module includes: a second voltage source for providing a second voltage, the second voltage being dynamically variable; wherein the second compensation voltage dynamically increases following the second voltage.

[0023] Preferably, the frequency control module includes a first comparator, a second comparator, an adder, and an OR gate; wherein, the first input terminal of the first comparator receives a second compensation voltage, the second input terminal receives a voltage threshold, and the output terminal outputs a first comparison signal; the first input terminal and the second input terminal of the adder respectively receive the second compensation voltage and the hysteresis voltage, and the output terminal outputs the sum of the second compensation voltage and the hysteresis voltage; the first input terminal of the second comparator receives a pull-down voltage, the second input terminal receives the sum of the second compensation voltage and the hysteresis voltage, and the output terminal outputs a soft-start signal; the OR gate receives the first comparison signal and the second comparison signal at its input terminals respectively, and the output terminal outputs a frequency control signal.

[0024] Preferably, the frequency control module further includes a third comparator and a counter; wherein, the first input terminal of the third comparator receives a current threshold, the second input terminal receives a current sampling signal, and the output terminal outputs a third comparison signal; the counter is used to determine whether the third comparison signal is always at an invalid level within m consecutive cycles of the switch control signal and outputs the determination result, where m is a positive integer; the input terminal of the OR gate also receives the determination result.

[0025] Preferably, when the second compensation voltage is less than the voltage threshold, the first comparison signal is at an invalid level; when the second compensation voltage is greater than or equal to the voltage threshold, the first comparison signal is at an active level.

[0026] Preferably, when the current sampling signal is less than the current threshold, the third comparison signal is at an invalid level; when the current sampling signal is greater than or equal to the current threshold, the third comparison signal is at an active level.

[0027] Preferably, when the third comparison signal is at an invalid level for m consecutive cycles of the switch control signal, the judgment result is at an valid level; when the third comparison signal is at a valid level, the judgment result is at an invalid level.

[0028] Preferably, the control circuit is used for soft-start of the continuous current mode switching power supply.

[0029] According to a second aspect of the present invention, a switching power supply is provided, comprising: a switching circuit for converting an input voltage into an output voltage; and the aforementioned control circuit; wherein the switching circuit includes a drive circuit, a switching bridge arm, and an inductor; the switching bridge arm includes a first power switch and a second power switch, wherein the first power switch and the second power switch are connected in series between the input voltage and a ground terminal; and the inductor is connected between a node between the first power switch and the second power switch and the output voltage.

[0030] Preferably, the driving circuit generates a driving signal according to the switch control signal. The driving signal includes a first driving signal and a second driving signal that are completely opposite to each other. The first driving signal is used to turn on and off the first power switch, and the second driving signal is used to turn on and off the second power switch.

[0031] Preferably, when the switch control signal is at an active level, the first power switch of the corresponding switch circuit is turned on and the second power switch is turned off; when the switch control signal is at an inactive level, the first power switch is turned off and the second power switch is turned on.

[0032] According to a third aspect of the present invention, a control method for a switching power supply is provided, comprising: generating a frequency control signal based on a second compensation voltage and a soft-start signal; generating a switching control signal based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing an inductor current, and a preset frequency value; wherein the frequency control signal is used to control the frequency of the switching control signal; when the frequency control signal is at an active level, the frequency of the switching control signal is a first preset frequency; when the frequency control signal is at an inactive level, the frequency of the switching control signal is a second preset frequency, wherein the first preset frequency is N times the second preset frequency, and N is a positive integer greater than 1.

[0033] Preferably, the control method further includes: generating a first compensation voltage based on a voltage feedback signal characterizing the output voltage and a reference voltage; generating a second compensation voltage based on the first compensation voltage and a pull-down voltage; and generating a soft-start signal based on the second compensation voltage and the pull-down voltage.

[0034] Preferably, when at least one of the soft-start signal and the compensation voltage meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

[0035] Preferably, when neither the soft-start signal nor the compensation voltage meets the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to a second preset frequency.

[0036] Preferably, the preset conditions are that the soft-start signal is at an effective level and the compensation voltage is greater than or equal to a voltage threshold.

[0037] Preferably, the control method further includes: generating a frequency control signal based on the soft-start signal, the second compensation voltage, the current sampling signal, and the switch control signal.

[0038] Preferably, when at least one of the soft-start signal, the compensation voltage and the current sampling signal meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

[0039] Preferably, when the soft-start signal, the compensation voltage and the current sampling signal do not meet the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to a second preset frequency.

[0040] Preferably, the preset conditions are when the soft-start signal is at an effective level, the compensation voltage is greater than or equal to a voltage threshold, and the current sampling signal is less than a current threshold for more than m cycles of the switch control signal, where m is a positive integer.

[0041] Preferably, the soft-start signal is active when the pull-down voltage is greater than the sum of the second compensation voltage and the hysteresis voltage; and is inactive when the pull-down voltage is less than the sum of the second compensation voltage and the hysteresis voltage.

[0042] Preferably, the control method further includes: switching the pull-down voltage between a first voltage and a second voltage according to a soft-start signal; wherein the first voltage is greater than the second voltage, and the second voltage changes dynamically.

[0043] Preferably, the second compensation voltage changes dynamically according to the soft-start signal and the magnitude relationship between the first voltage, the second voltage and the first compensation voltage.

[0044] Preferably, when the soft-start signal is at an invalid level, the pull-down voltage switches to a second voltage, and the second compensation voltage is pulled down to the second voltage and dynamically rises following the second voltage; when the soft-start signal is at an valid level, the pull-down voltage switches to a first voltage, and the second compensation voltage is equal to the first compensation voltage.

[0045] Preferably, the control method further includes: connecting the pull-down voltage to a second voltage, the second voltage changing dynamically; wherein the second compensation voltage increases dynamically following the second voltage.

[0046] The switching power supply and its control circuit and control method provided in this embodiment of the invention dynamically change the second compensation voltage during startup through a pull-down module and a second voltage that rises according to a preset curve. A frequency control signal is generated based on the second compensation voltage and a soft-start signal. A switching control signal is generated based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing the inductor current, and a preset frequency value. The frequency control signal is used to control the switching frequency of the switching control signal. Specifically, controlling the switching frequency to increase or decrease can ensure that the switching power supply has a sufficiently long time to reduce the inductor current within one switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

[0047] Furthermore, during startup, the second voltage rises according to a preset curve, and the second compensation voltage dynamically changes through the pull-down module and the second voltage, thereby ensuring that no output voltage overshoot occurs during startup; and ensuring that even if the load current suddenly increases during startup, the output voltage can still rise monotonically. Attached Figure Description

[0048] The above and other objects, features and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings.

[0049] Figure 1 A schematic circuit diagram of a Power over Ethernet (PoE) system is shown.

[0050] Figure 2 A schematic circuit diagram of a PD switching power supply provided according to a first embodiment of the present invention is shown;

[0051] Figure 3 A schematic circuit diagram of a frequency control module provided according to an embodiment of the present invention is shown;

[0052] Figure 4 A schematic circuit diagram of a PD switching power supply according to a second embodiment of the present invention is shown;

[0053] Figure 5 A schematic circuit diagram of a PD switching power supply according to a third embodiment of the present invention is shown;

[0054] Figure 6 A schematic circuit diagram of a PD switching power supply according to a fourth embodiment of the present invention is shown;

[0055] Figure 7 The waveforms of various signals in a prior art PD switching power supply are shown when the power conversion circuit operates in a continuous inductor current state.

[0056] Figure 8The diagram shows the waveforms of various signals of the PD switching power supply provided in the embodiment of the present invention when the power conversion circuit is operating in a continuous inductor current state.

[0057] Figure 9 A flowchart illustrating a control method for a switching power supply according to an embodiment of the present invention is shown. Detailed Implementation

[0058] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0059] Figure 1 A simplified structural diagram of a Power over Ethernet (PoE) system is shown. Figure 1 The diagram illustrates a Power over Ethernet (PoE) system, which may include a power supply device (PSE) 100 and a powered device (PD) 200. The PSE 100 may be a network device such as a switch, router, firewall, or hub. The PD 200 may be an Internet Protocol (IP) phone, a wireless LAN access point, a micro base station, or a network camera.

[0060] refer to Figure 1 Both the power supply device 100 and the powered device 200 can be equipped with multiple Ethernet interfaces. Each Ethernet interface of the power supply device 100 can be connected to one Ethernet interface of the powered device 200 via an Ethernet twisted-pair cable. While transmitting data signals to the powered device 200 via the Ethernet twisted-pair cable, the power supply device 100 can also transmit power signals to the powered device 200, thereby supplying power to the powered device 200. The powered device 200 includes a PD switching power supply 210 and load circuits, etc. The power controller is connected to the Ethernet interface of the powered device 200, and can receive the power signals provided by the power supply device 100 and supply power to the downstream load circuits.

[0061] The operating mode of the power supply device 100 can be controlled by a control circuit, such as an MCU controller 300 or a power supply controller. The operating modes of the power supply device 100 include, for example, normally supplying power to the powered device 200, providing MPS current to the powered device 200, or stopping supplying power to the powered device 200.

[0062] Figure 2 A schematic circuit diagram of a PD switching power supply provided in an embodiment of the present invention is shown. See also... Figure 2 The PD switching power supply includes a switching circuit 211, a control circuit 212, an output capacitor Co, and a load Rload.

[0063] The input terminal of the switching circuit 211 receives the input voltage Vin and the switching control signal PWM. Under the control of the switching control signal PWM, it outputs a voltage Vout at the output terminal and provides a current sampling signal Is representing the inductor current IL to the control circuit 212. The switching circuit 2123 can adopt any DC / DC or AC / DC conversion topology, such as synchronous or asynchronous boost and buck converters, as well as forward and flyback converters.

[0064] The control circuit 212 receives the voltage feedback signal VFB, which represents the output voltage, and the current sampling signal Is, which represents the inductor current IL, and generates the switching control signal PWM.

[0065] The control circuit 212 includes a compensation circuit 2121, a power supply module 2122, a pull-down module 2123, a frequency control module 2124, and a switch control circuit 2125.

[0066] The compensation circuit 2121 obtains the feedback signal VFB of the output voltage Vout from the positive terminal of the output capacitor Co, i.e. the output terminal of the switching circuit 211, and compares it with the reference voltage Vref to generate the first compensation voltage Vc1.

[0067] Power module 2122 is used to provide pull-down voltage Vd.

[0068] In this embodiment, the power module 2122 includes a switch K, a first voltage source, and a second voltage source. The first voltage source outputs a first voltage V1, and the second voltage source outputs a second voltage V2. The first voltage V1 is a fixed voltage, while the second voltage V2 changes dynamically. The first voltage V1 is significantly larger than the second voltage V2. The switch K includes a first terminal, a second terminal, and a third terminal. The first and second terminals are connected to the first and second voltage sources, respectively. The third terminal outputs a pull-down voltage. The switch K connects the third terminal to one of the first and second terminals according to a soft-start signal SS, thereby switching the connection between the pull-down module 2123 and the first and second voltage sources. The pull-down voltage Vd output by the power module 2122 is either the first voltage V1 or the second voltage V2.

[0069] The pull-down module 2123 is connected to the power module 2122 and generates a second compensation voltage Vc2 based on the first compensation voltage V1 and the pull-down voltage Vd.

[0070] In this embodiment, the second compensation voltage Vc2 dynamically changes according to the soft-start signal SS and the magnitude relationship between the first voltage V1, the second voltage V2, and the first compensation voltage Vc1. Specifically, when the soft-start signal SS is at an invalid level, the switch K switches to the second voltage source, and the pull-down module 2123 is connected to the second voltage source; when the soft-start signal SS is at an active level, the switch K switches to the first voltage source, and the pull-down module 2123 is connected to the first voltage source.

[0071] When the pull-down module 2123 is connected to the second voltage source, the second compensation voltage Vc2 is pulled down to the second voltage V2 and rises dynamically with the second voltage V2; when the second voltage V2 is greater than the first compensation voltage Vc1, the second compensation voltage Vc2 is equal to the first compensation voltage Vc1.

[0072] When the pull-down module 2123 is connected to the first voltage source, the second compensation voltage Vc2 is equal to the first compensation voltage Vc1.

[0073] The frequency control module 2124 is used to generate a soft-start signal SS based on the second compensation voltage Vc2 and the pull-down voltage Vd, and to generate a frequency control signal Ctrl_fre based on the soft-start signal SS and the second compensation voltage Vc2.

[0074] In this embodiment, the frequency control signal Ctrl_fre is active when at least one of the second compensation voltage Vc2 and the soft-start signal SS meets a preset condition. The preset condition is that the soft-start signal SS is active and the second compensation voltage Vc2 is greater than or equal to a voltage threshold Vth. When neither the second compensation voltage Vc2 nor the soft-start signal SS meets the preset condition, the frequency control signal Ctrl_fre is inactive.

[0075] Specifically, when the pull-down voltage Vd is greater than the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, the soft-start signal SS is at an active level; when the pull-down voltage Vd is less than the sum of the second compensation voltage Vcc and the hysteresis voltage Vhys, the soft-start signal SS is at an inactive level.

[0076] The switch control module 2125 is used to generate a switch control signal based on the second compensation voltage Vc2, the frequency control signal Ctrl_fre, the current sampling signal Is representing the inductor current, and a preset frequency value. The frequency control signal Ctrl_fre is used to control the frequency of the switch control signal PWM.

[0077] In this embodiment, when the frequency control signal Ctrl_fre is at an active level (e.g., high level), the frequency of the switch control signal PWM is a first preset frequency F1; when the frequency control signal Ctrl_fre is at an inactive level (e.g., low level), the frequency of the switch control signal PWM is a second preset frequency F2, wherein the first preset frequency F1 is N times the second preset frequency F2, and N is a positive integer greater than 1.

[0078] The switch control signal PWM is used to control the switching circuit 211 to turn on and off. When the switch control signal PWM is at an active level (e.g., high level), the switch circuit 211 is turned on; when the switch control signal is at an inactive level (e.g., low level), the switch circuit 211 is turned off.

[0079] See Figure 3 The frequency control module 2124 includes a first comparator U1, a second comparator U2, an adder Adder, and an OR gate.

[0080] The first comparator U1 receives a second compensation voltage Vc2 at its first input terminal, a voltage threshold voltage Vth at its second input terminal, and outputs a first comparison signal at its output terminal.

[0081] When the second compensation voltage Vc2 is less than the voltage threshold Vth, the first comparison signal is invalid; when the second compensation voltage Vc2 is greater than or equal to the voltage threshold Vth, the first comparison signal is valid.

[0082] The first and second input terminals of the adder receive the second compensation voltage Vc2 and the hysteresis voltage Vhys, respectively, and the output terminal outputs the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys.

[0083] The first input of the second comparator U2 receives the pull-down voltage Vd, the second input receives the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, and the output outputs the soft-start signal SS.

[0084] When the pull-down voltage Vd is greater than the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, the soft-start signal SS is at an active level, indicating that the soft-start process has ended; when the pull-down voltage Vd is less than the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, the soft-start signal SS is at an inactive level, indicating that the soft-start process has not ended.

[0085] The OR gate receives a first comparison signal and a soft-start signal SS at its input terminals, and outputs a frequency control signal at its output terminal.

[0086] See Figure 7In the initial startup phase of a switching power supply, before the output voltage Vout is established, the inductor current IL decreases slowly during the turn-off period of the switching transistor. If the PWM control signal controls the switching transistor's on and off at the normal operating frequency, the inductor current IL will continuously increase due to the high frequency, which can easily lead to inductor saturation and input current overshoot.

[0087] See Figure 8 The switching power supply operates in continuous current mode (CCM). During the initial startup phase, power module 2122 connects pull-down module 2123 to the second voltage source based on the soft-start signal SS. As the second voltage V2 dynamically increases, the second compensation voltage Vc2 also dynamically increases from an initial value. At this time, Vc2 < Vth, the first comparator U1 outputs an invalid level, and when the soft-start signal SS is also invalid, the frequency control signal Ctrl_fre is also invalid, meaning that during startup, the frequency of the switching control signal PWM is reduced to the second preset frequency F2.

[0088] When the second compensation voltage Vc2 ≥ Vth, the first comparison signal is at an effective level; or when the soft start signal SS is at an effective level, the frequency control signal Ctrl-fre output by the frequency control module is at an effective level, restoring the frequency of the switch control signal to the first preset frequency F1.

[0089] In a preferred embodiment, the frequency control module 2124 further generates a frequency control signal based on the soft-start signal SS, the second compensation voltage Vc2, the current sampling signal Is, and the switch control signal PWM.

[0090] In this embodiment, when at least one of the soft-start signal SS, the compensation voltage Vc, and the current sampling signal Is satisfies a preset condition, the frequency control signal Ctrl_fre is at an effective level.

[0091] The preset conditions are that the soft-start signal is at an effective level, the second compensation voltage Vc2 is greater than or equal to the voltage threshold Vth, and the current sampling signal Is is less than the current threshold Ith for more than m cycles of the switch control signal PWM, where m is a positive integer.

[0092] When the soft-start signal SS, the compensation voltage Vc, and the current sampling signal Is all fail to meet the preset conditions, the frequency control signal Ctrl_fre is at an invalid level. That is, when the second compensation voltage Vc2 < Vth, the time for the current sampling signal Is < Ith does not exceed m cycles of the switching control signal PWM, and the soft-start signal SS is at an invalid level.

[0093] In this embodiment, the frequency control module 2124 includes a first comparator U1, a second comparator U2, a third comparator U3, an adder Adder, a counter CNTR, and an OR gate.

[0094] The first comparator U1 receives a second compensation voltage Vc2 at its first input terminal, a voltage threshold voltage Vth at its second input terminal, and outputs a first comparison signal at its output terminal.

[0095] When the second compensation voltage Vc2 is less than the voltage threshold Vth, the first comparison signal is invalid; when the second compensation voltage Vc2 is greater than or equal to the voltage threshold Vth, the first comparison signal is valid.

[0096] The first and second input terminals of the adder receive the second compensation voltage Vc2 and the hysteresis voltage Vhys, respectively, and the output terminal outputs the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys.

[0097] The first input of the second comparator U2 receives the second voltage V2, the second input receives the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, and the output outputs the soft-start signal SS.

[0098] When the second voltage V2 is greater than the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, the soft start signal SS is at an active level, indicating that the soft start process has ended; when the second voltage V2 is less than the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, the soft start signal SS is at an inactive level, indicating that the soft start process has not ended.

[0099] The first input of the third comparator U3 receives the current threshold Ith, the second input receives the current sampling signal Is, and the output outputs the third comparison signal.

[0100] When the current sampling signal Is is less than the current threshold Ith, the third comparison signal is invalid; when the current sampling signal Is is greater than or equal to the current threshold Ith, the third comparison signal is valid.

[0101] The counter CNTR is used to determine whether the third comparison signal has been invalid for m consecutive cycles of the switching control signal PWM and outputs the judgment result.

[0102] When the third comparison signal is at an invalid level for m consecutive cycles of the switch control signal, the judgment result is at an valid level; when the third comparison signal is at a valid level, the judgment result is at an invalid level.

[0103] The OR gate receives a first comparison signal, a soft-start signal SS, and a judgment result at its input terminals, and outputs a frequency control signal at its output terminal.

[0104] See Figure 8 The switching power supply operates in continuous current mode (CCM). During the initial startup phase, power module 2122 connects pull-down module 2123 to the second voltage source based on the soft-start signal SS. As the second voltage V2 dynamically increases, the second compensation voltage Vc22 also dynamically increases from an initial value. At this time, Vc2 < Vth, the first comparator U1 outputs an invalid level, and simultaneously compares the current sampling signal Is with the current threshold Ith. When Is < Ith, the RST terminal of counter CNTR remains invalid, and the counting terminal begins counting the cycles of the switching control signal PWM. If m cycles are not counted, the output of counter CNTR outputs an invalid level. Simultaneously, when the soft-start signal is also invalid, the frequency control signal Ctrl_fre is invalid, meaning that the frequency of the switching control signal PWM is reduced to the second preset frequency F2 during startup.

[0105] When the current sampling signal Is is always less than the current threshold Vth for m consecutive cycles, the output of the counter CNTR is a valid level; or the second compensation voltage Vc2 ≥ Vth, the first comparison signal is a valid level; or when the soft start signal is a valid level, the frequency control signal Ctrl-fre output by the frequency control module is a valid level, and the frequency of the switch control signal is restored to the first preset frequency F1.

[0106] The control circuit of the switching power supply provided in this embodiment of the invention dynamically changes the second compensation voltage during startup through a pull-down module and a second voltage that rises according to a preset curve. A frequency control signal is generated based on the second compensation voltage and a soft-start signal. A switching control signal is generated based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing the inductor current, and a preset frequency value. The frequency control signal is used to control the switching frequency of the switching control signal. Specifically, controlling the switching frequency to increase or decrease can ensure that the switching power supply has a sufficiently long time to reduce the inductor current within one switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

[0107] Furthermore, during startup, the second voltage rises according to a preset curve, and the second compensation voltage dynamically changes through the pull-down module and the second voltage, thereby ensuring that no output voltage overshoot occurs during startup; and ensuring that even if the load current suddenly increases during startup, the output voltage can still rise monotonically.

[0108] Figure 4A schematic circuit diagram of a PD switching power supply according to a second embodiment of the present invention is shown. Compared with the first embodiment, the power supply module 2122 includes only a second voltage source.

[0109] The second voltage source outputs a second voltage V2, which changes dynamically. The second compensation voltage Vc2 increases dynamically in line with the second voltage V2.

[0110] The rest of the content is the same as in the first embodiment, and will not be repeated here.

[0111] The control circuit of the switching power supply provided in this embodiment of the invention dynamically changes the second compensation voltage during startup through a pull-down module and a second voltage that rises according to a preset curve. A frequency control signal is generated based on the second compensation voltage and a soft-start signal. A switching control signal is generated based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing the inductor current, and a preset frequency value. The frequency control signal is used to control the switching frequency of the switching control signal. Specifically, controlling the switching frequency to increase or decrease can ensure that the switching power supply has a sufficiently long time to reduce the inductor current within one switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

[0112] Furthermore, during startup, the second voltage rises according to a preset curve, and the second compensation voltage dynamically changes through the pull-down module and the second voltage, thereby ensuring that no output voltage overshoot occurs during startup; and ensuring that even if the load current suddenly increases during startup, the output voltage can still rise monotonically.

[0113] Figure 5 A schematic circuit diagram of a PD switching power supply according to a third embodiment of the present invention is shown. Compared with the first embodiment, the switching circuit 110 includes a first power switch QH and a second power switch QL, an inductor L, and an output capacitor Co.

[0114] In this circuit, a first power switch QH and a second power switch QL are connected in series between the input voltage Vin and ground to form a switching bridge arm. An inductor L and an output capacitor Co are connected in series between a first node between the first power switch QH and the second power switch QL and ground. A second node between the inductor L and the output capacitor Co provides the output voltage Vout. A load is connected between the second node between the inductor L and the output capacitor Co and ground. The output capacitor Co is coupled between the output terminal of the switching circuit 110 and a reference ground, and the load 130 is connected in parallel with the output capacitor Co.

[0115] The rest of the content is the same as in the first embodiment, and will not be repeated here.

[0116] The control circuit of the switching power supply provided in this embodiment of the invention dynamically changes the second compensation voltage during startup through a pull-down module and a second voltage that rises according to a preset curve. A frequency control signal is generated based on the second compensation voltage and a soft-start signal. A switching control signal is generated based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing the inductor current, and a preset frequency value. The frequency control signal is used to control the switching frequency of the switching control signal. Specifically, controlling the switching frequency to increase or decrease can ensure that the switching power supply has a sufficiently long time to reduce the inductor current within one switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

[0117] Furthermore, during startup, the second voltage rises according to a preset curve, and the second compensation voltage Vc dynamically changes through the pull-down module and the second voltage, thereby ensuring that no output voltage overshoot occurs during startup; and ensuring that even if the load current suddenly increases during startup, the output voltage can still rise monotonically.

[0118] Figure 6 A schematic circuit diagram of a PD switching power supply according to a fourth embodiment of the present invention is shown. Compared with the second embodiment, the switching circuit 110 includes a first power switch QH and a second power switch QL, an inductor L, and an output capacitor Co.

[0119] In this circuit, a first power switch QH and a second power switch QL are connected in series between the input voltage Vin and ground to form a switching bridge arm. An inductor L and an output capacitor Co are connected in series between a first node between the first power switch QH and the second power switch QL and ground. A second node between the inductor L and the output capacitor Co provides the output voltage Vout. A load is connected between the second node between the inductor L and the output capacitor Co and ground. The output capacitor Co is coupled between the output terminal of the switching circuit 110 and a reference ground, and the load 130 is connected in parallel with the output capacitor Co.

[0120] The rest of the content is the same as in the second embodiment, and will not be repeated here.

[0121] The control circuit of the switching power supply provided in this embodiment of the invention dynamically changes the second compensation voltage during startup through a pull-down module and a second voltage that rises according to a preset curve. A frequency control signal is generated based on the second compensation voltage and a soft-start signal. A switching control signal is generated based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing the inductor current, and a preset frequency value. The frequency control signal is used to control the switching frequency of the switching control signal. Specifically, controlling the switching frequency to increase or decrease can ensure that the switching power supply has a sufficiently long time to reduce the inductor current within one switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

[0122] Furthermore, during startup, the second voltage rises according to a preset curve, and the second compensation voltage Vc dynamically changes through the pull-down module and the second voltage, thereby ensuring that no output voltage overshoot occurs during startup; and ensuring that even if the load current suddenly increases during startup, the output voltage can still rise monotonically.

[0123] Figure 9 A flowchart illustrating a control method for a switching power supply according to an embodiment of the present invention is shown. See also... Figure 9 The control method for the switching power supply includes the following steps.

[0124] In step S110, a frequency control signal is generated based on the second compensation voltage and the soft-start signal.

[0125] In this embodiment, the frequency control signal Ctrl_fre is active when at least one of the second compensation voltage Vc2 and the soft-start signal SS meets a preset condition. The preset condition is that the soft-start signal SS is active and the second compensation voltage Vc2 is greater than or equal to a voltage threshold Vth. When neither the second compensation voltage Vc2 nor the soft-start signal SS meets the preset condition, the frequency control signal Ctrl_fre is inactive.

[0126] In step S120, a switching control signal is generated based on the second compensation voltage, the frequency control signal, the current sampling signal characterizing the inductor current, and the preset frequency value.

[0127] In this embodiment, when the frequency control signal Ctrl_fre is at an active level (e.g., high level), the frequency of the switch control signal PWM is a first preset frequency F1; when the frequency control signal Ctrl_fre is at an inactive level (e.g., low level), the frequency of the switch control signal PWM is a second preset frequency F2, wherein the first preset frequency F1 is N times the second preset frequency F2, and N is a positive integer greater than 1.

[0128] The switch control signal PWM is used to control the switching circuit 211 to turn on and off. When the switch control signal PWM is at an active level (e.g., high level), the switch circuit 211 is turned on; when the switch control signal is at an inactive level (e.g., low level), the switch circuit 211 is turned off.

[0129] In a preferred embodiment, the control method further includes steps S102-S106.

[0130] In step S101, a first compensation voltage is generated based on the voltage feedback signal characterizing the output voltage and the reference voltage.

[0131] In this embodiment, the feedback signal VFB of the output voltage Vout is obtained from the positive terminal of the output capacitor Co, i.e. the output terminal of the switching circuit 211, and compared with the reference voltage Vref to generate the first compensation voltage Vc1.

[0132] In step S102, the pull-down voltage is switched between the first voltage and the second voltage according to the soft-start signal.

[0133] In this embodiment, the first voltage V1 is greater than the second voltage V2, and the second voltage V2 changes dynamically.

[0134] The second compensation voltage Vc2 changes dynamically according to the soft start signal SS and the magnitude relationship between the first voltage V1, the second voltage V2 and the first compensation voltage Vc1.

[0135] In a preferred embodiment, step 102 may further be: connecting the pull-down voltage Vd to a second voltage V2, wherein the second voltage V2 changes dynamically; wherein the second compensation voltage Vc2 increases dynamically following the second voltage V2.

[0136] In step S103, a second compensation voltage is generated based on the first compensation voltage and the pull-down voltage.

[0137] In this embodiment, when the soft-start signal SS is at an invalid level, the pull-down voltage Vd switches to the second voltage V2, and the second compensation voltage Vc2 is pulled down to the second voltage V2 and dynamically rises with the second voltage V2; when the soft-start signal SS is at an valid level, the pull-down voltage Vd switches to the first voltage V1, and the second compensation voltage Vc2 is equal to the first compensation voltage Vc1.

[0138] In step S104, a soft-start signal is generated based on the second compensation voltage and the pull-down voltage.

[0139] Specifically, when the pull-down voltage Vd is greater than the sum of the second compensation voltage Vc2 and the hysteresis voltage Vhys, the soft-start signal SS is at an active level; when the pull-down voltage Vd is less than the sum of the second compensation voltage Vcc and the hysteresis voltage Vhys, the soft-start signal SS is at an inactive level.

[0140] See Figure 8The switching power supply operates in continuous current mode (CCM). During the initial startup phase, power module 2122 connects pull-down module 2123 to the second voltage source based on the soft-start signal SS. As the second voltage V2 dynamically increases, the second compensation voltage Vc2 also dynamically increases from an initial value. At this time, Vc2 < Vth, the first comparator U1 outputs an invalid level, and when the soft-start signal SS is also invalid, the frequency control signal Ctrl_fre is also invalid, meaning that during startup, the frequency of the switching control signal PWM is reduced to the second preset frequency F2.

[0141] When the second compensation voltage Vc2 ≥ Vth, the first comparison signal is at an effective level; or when the soft start signal SS is at an effective level, the frequency control signal Ctrl-fre output by the frequency control module is at an effective level, restoring the frequency of the switch control signal to the first preset frequency F1.

[0142] In a preferred embodiment, step S110 is: generating a frequency control signal Ctrl_fre based on the soft-start signal SS, the second compensation voltage Vc2, the current sampling signal Is, and the switch control signal PWM.

[0143] In this embodiment, when at least one of the soft-start signal SS, the compensation voltage Vc, and the current sampling signal Is satisfies a preset condition, the frequency control signal Ctrl_fre is at an effective level.

[0144] The preset conditions are that the soft-start signal is at an effective level, the second compensation voltage Vc2 is greater than or equal to the voltage threshold Vth, and the current sampling signal Is is less than the current threshold Ith for more than m cycles of the switch control signal PWM, where m is a positive integer.

[0145] When the soft-start signal SS, the compensation voltage Vc, and the current sampling signal Is all fail to meet the preset conditions, the frequency control signal Ctrl_fre is at an invalid level. That is, when the second compensation voltage Vc2 < Vth, the time for the current sampling signal Is < Ith does not exceed m cycles of the switching control signal PWM, and the soft-start signal SS is at an invalid level.

[0146] See Figure 8The switching power supply operates in continuous current mode (CCM). During the initial startup phase, power module 2122 connects pull-down module 2123 to the second voltage source based on the soft-start signal SS. As the second voltage V2 dynamically increases, the second compensation voltage Vc22 also dynamically increases from an initial value. At this time, Vc2 < Vth, the first comparator U1 outputs an invalid level, and simultaneously compares the current sampling signal Is with the current threshold Ith. When Is < Ith, the RST terminal of counter CNTR remains invalid, and the counting terminal begins counting the cycles of the switching control signal PWM. If m cycles are not counted, the output of counter CNTR outputs an invalid level. Simultaneously, when the soft-start signal is also invalid, the frequency control signal Ctrl_fre is invalid, meaning that the frequency of the switching control signal PWM is reduced to the second preset frequency F2 during startup.

[0147] When the current sampling signal Is is always less than the current threshold Vth for m consecutive cycles, the output of the counter CNTR is a valid level; or the second compensation voltage Vc2 ≥ Vth, the first comparison signal is a valid level; or when the soft start signal is a valid level, the frequency control signal Ctrl-fre output by the frequency control module is a valid level, and the frequency of the switch control signal is restored to the first preset frequency F1.

[0148] from Figure 8 As can be seen, during the soft-start process of a continuous current-mode switching power supply, the frequency of the switching control signal is first reduced to a second preset frequency, allowing sufficient time for the inductor current to decrease within one switching cycle, ensuring that the inductor current does not exceed the current threshold Ith, for example, 110% of the load current under steady-state full load, thus preventing output voltage overshoot. Then, when at least one of the soft-start signal, the second compensation voltage, and the inductor current meets a preset condition, the frequency of the switching control signal is increased to a first preset frequency, thereby ensuring that even if the load current suddenly increases during startup, the output voltage continues to rise monotonically.

[0149] The control method for a switching power supply provided in this embodiment of the invention dynamically changes the second compensation voltage during startup through a pull-down module and a second voltage that rises according to a preset curve. A frequency control signal is generated based on the second compensation voltage and a soft-start signal. A switching control signal is generated based on the second compensation voltage, the frequency control signal, a current sampling signal characterizing the inductor current, and a preset frequency value. The frequency control signal is used to control the switching frequency of the switching control signal. Specifically, controlling the switching frequency to increase or decrease can ensure that the switching power supply has a sufficiently long time to reduce the inductor current within one switching cycle, so that the inductor current does not exceed 110% of the load current under steady-state full load.

[0150] Furthermore, during startup, the second voltage rises according to a preset curve, and the second compensation voltage dynamically changes through the pull-down module and the second voltage, thereby ensuring that no output voltage overshoot occurs during startup; and ensuring that even if the load current suddenly increases during startup, the output voltage can still rise monotonically.

[0151] The embodiments of the present invention are as described above. These embodiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to make good use of the present invention and modifications based on it. The scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A control circuit for a switching power supply, characterized in that, include: The frequency control module generates the frequency control signal based on the second compensation voltage and the soft-start signal; The switching control module is used to generate a switching control signal based on the second compensation voltage, the frequency control signal, the current sampling signal characterizing the inductor current, and a preset frequency value. The pull-down module generates a second compensation voltage based on the first compensation voltage and the pull-down voltage. The frequency control signal is used to control the frequency of the switch control signal; When the frequency control signal is at an active level, the frequency of the switch control signal is a first preset frequency; when the frequency control signal is at an inactive level, the frequency of the switch control signal is a second preset frequency, wherein the first preset frequency is N times the second preset frequency, and N is a positive integer greater than 1.

2. The control circuit according to claim 1, characterized in that, Also includes: A compensation circuit is used to generate a first compensation voltage based on a voltage feedback signal characterizing the output voltage and a reference voltage. A power module is used to provide a pull-down voltage, and a pull-down module is connected to the power module; The frequency control module is further configured to generate a soft-start signal based on the second compensation voltage and the pull-down voltage.

3. The control circuit according to claim 1, characterized in that, When at least one of the soft-start signal and the compensation voltage meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

4. The control circuit according to claim 3, characterized in that, When neither the soft-start signal nor the compensation voltage meets the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to the second preset frequency.

5. The control circuit according to claim 4, characterized in that, The preset conditions are that the soft-start signal is at an effective level and the compensation voltage is greater than or equal to the voltage threshold.

6. The control circuit according to claim 1 or 2, characterized in that, The frequency control module also generates the frequency control signal based on the soft-start signal, the second compensation voltage, the current sampling signal, and the switch control signal.

7. The control circuit according to claim 6, characterized in that, When at least one of the soft-start signal, the compensation voltage and the current sampling signal meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

8. The control circuit according to claim 7, characterized in that, When the soft-start signal, the compensation voltage and the current sampling signal do not meet the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to the second preset frequency.

9. The control circuit according to claim 8, characterized in that, The preset conditions are that the soft-start signal is at an effective level, the compensation voltage is greater than or equal to the voltage threshold, and the current sampling signal is less than the current threshold for more than m cycles of the switch control signal, where m is a positive integer.

10. The control circuit according to claim 1, characterized in that, When the pull-down voltage is greater than the sum of the second compensation voltage and the hysteresis voltage, the soft-start signal is at an active level; When the pull-down voltage is less than the sum of the second compensation voltage and the hysteresis voltage, the soft-start signal is invalid.

11. The control circuit according to claim 2, characterized in that, The power module includes: A first voltage source is used to provide a first voltage; A second voltage source is used to provide a second voltage, which changes dynamically, and the first voltage is greater than the second voltage. A switch, whose first and second terminals are connected to a first voltage source and a second voltage source respectively, and whose third terminal outputs a pull-down voltage; The switch connects its third terminal to one of its first and second terminals according to a soft-start signal, thereby switching the connection of the pull-down module to the first voltage source and the second voltage source.

12. The control circuit according to claim 11, characterized in that, The second compensation voltage changes dynamically based on the soft-start signal and the magnitude relationship between the first voltage, the second voltage, and the first compensation voltage.

13. The control circuit according to claim 12, characterized in that, When the soft-start signal is invalid, the switch switches to the second voltage source, and the pull-down module is connected to the second voltage source; When the soft-start signal is at an active level, the switch switches to the first voltage source, and the pull-down module is connected to the first voltage source.

14. The control circuit according to claim 13, characterized in that, When the pull-down module is connected to the second voltage source, the second compensation voltage is pulled down to the second voltage and rises dynamically following the second voltage; when the second voltage is greater than the first compensation voltage, the second compensation voltage is equal to the first compensation voltage. When the pull-down module is connected to the first voltage source, the second compensation voltage is equal to the first compensation voltage.

15. The control circuit according to claim 2, characterized in that, The power module includes: A second voltage source is used to provide a second voltage, which changes dynamically. The second compensation voltage rises dynamically following the second voltage.

16. The control circuit according to claim 1, characterized in that, The frequency control module includes a first comparator, a second comparator, an adder, and an OR gate; The first input terminal of the first comparator receives the second compensation voltage, the second input terminal receives the voltage threshold, and the output terminal outputs the first comparison signal. The first and second input terminals of the adder receive the second compensation voltage and the hysteresis voltage, respectively, and the output terminal outputs the sum of the second compensation voltage and the hysteresis voltage. The first input of the second comparator receives the pull-down voltage, the second input receives the sum of the second compensation voltage and the hysteresis voltage, and the output outputs a soft-start signal. The OR gate receives a first comparison signal and a second comparison signal at its input terminals and outputs a frequency control signal at its output terminal.

17. The control circuit according to claim 16, characterized in that, The frequency control module also includes a third comparator and a counter; The third comparator receives the current threshold at its first input terminal, receives the current sampling signal at its second input terminal, and outputs the third comparison signal at its output terminal. The counter is used to determine whether the third comparison signal has been invalid for m consecutive cycles of the switch control signal and outputs the judgment result, where m is a positive integer; The input of the OR gate also receives the judgment result.

18. The control circuit according to claim 16 or 17, characterized in that, When the second compensation voltage is less than the voltage threshold, the first comparison signal is invalid; when the second compensation voltage is greater than or equal to the voltage threshold, the first comparison signal is valid.

19. The control circuit according to claim 17, characterized in that, When the current sampling signal is less than the current threshold, the third comparison signal is invalid; when the current sampling signal is greater than or equal to the current threshold, the third comparison signal is valid.

20. The control circuit according to claim 19, characterized in that, When the third comparison signal is at an invalid level for m consecutive cycles of the switch control signal, the judgment result is at an valid level; when the third comparison signal is at a valid level, the judgment result is at an invalid level.

21. The control circuit according to claim 1, characterized in that, The control circuit is used for soft-start of the continuous current mode switching power supply.

22. A switching power supply, characterized in that, include: A switching circuit is used to convert input voltage into output voltage. The control circuit as described in any one of claims 1-21; The switching circuit includes a drive circuit, a switch bridge arm, and an inductor. The switching bridge arm includes a first power switch and a second power switch, wherein the first power switch and the second power switch are connected in series between the input voltage and the ground terminal; The inductor is connected between the node between the first power switch and the second power switch and the output voltage.

23. The switching power supply according to claim 22, characterized in that, The driving circuit generates a driving signal according to the switch control signal. The driving signal includes a first driving signal and a second driving signal that are completely opposite to each other. The first driving signal is used to turn on and off the first power switch, and the second driving signal is used to turn on and off the second power switch.

24. The switching power supply according to claim 23, characterized in that, When the switch control signal is at an active level, the first power switch of the corresponding switch circuit is turned on and the second power switch is turned off; when the switch control signal is at an inactive level, the first power switch is turned off and the second power switch is turned on.

25. A control method for a switching power supply, characterized in that, include: The second compensation voltage is generated based on the first compensation voltage and the pull-down voltage; A frequency control signal is generated based on the second compensation voltage and the soft-start signal; A switching control signal is generated based on the second compensation voltage, the frequency control signal, the current sampling signal characterizing the inductor current, and the preset frequency value; The frequency control signal is used to control the frequency of the switch control signal; When the frequency control signal is at an active level, the frequency of the switch control signal is a first preset frequency; when the frequency control signal is at an inactive level, the frequency of the switch control signal is a second preset frequency, wherein the first preset frequency is N times the second preset frequency, and N is a positive integer greater than 1.

26. The control method according to claim 25, characterized in that, Also includes: The first compensation voltage is generated based on the voltage feedback signal characterizing the output voltage and the reference voltage; A soft-start signal is generated based on the second compensation voltage and the pull-down voltage.

27. The control method according to claim 25 or 26, characterized in that, When at least one of the soft-start signal and the compensation voltage meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

28. The control method according to claim 27, characterized in that, When neither the soft-start signal nor the compensation voltage meets the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to the second preset frequency.

29. The control method according to claim 28, characterized in that, The preset conditions are that the soft-start signal is at an effective level and the compensation voltage is greater than or equal to the voltage threshold.

30. The control method according to claim 25 or 26, characterized in that, Also includes: A frequency control signal is generated based on the soft-start signal, the second compensation voltage, the current sampling signal, and the switch control signal.

31. The control method according to claim 30, characterized in that, When at least one of the soft-start signal, the compensation voltage and the current sampling signal meets a preset condition, the frequency control signal is at an effective level, and the frequency of the switch control signal is restored to the first preset frequency.

32. The control method according to claim 31, characterized in that, When the soft-start signal, the compensation voltage and the current sampling signal do not meet the preset conditions, the frequency control signal is at an invalid level, and the frequency of the switch control signal drops to the second preset frequency.

33. The control method according to claim 32, characterized in that, The preset conditions are that the soft-start signal is at an effective level, the compensation voltage is greater than or equal to the voltage threshold, and the current sampling signal is less than the current threshold for more than m cycles of the switch control signal, where m is a positive integer.

34. The control method according to claim 25, characterized in that, When the pull-down voltage is greater than the sum of the second compensation voltage and the hysteresis voltage, the soft-start signal is at an active level; When the pull-down voltage is less than the sum of the second compensation voltage and the hysteresis voltage, the soft-start signal is invalid.

35. The control method according to claim 26, characterized in that, Also includes: The pull-down voltage is switched between the first voltage and the second voltage based on the soft-start signal; The first voltage is greater than the second voltage, and the second voltage changes dynamically.

36. The control method according to claim 35, characterized in that, The second compensation voltage changes dynamically based on the soft-start signal and the magnitude relationship between the first voltage, the second voltage, and the first compensation voltage.

37. The control method according to claim 36, characterized in that, When the soft-start signal is at an invalid level, the pull-down voltage switches to the second voltage, and the second compensation voltage is pulled down to the second voltage and rises dynamically following the second voltage; When the soft-start signal is at an active level, the pull-down voltage switches to the first voltage, and the second compensation voltage is equal to the first compensation voltage.

38. The control method according to claim 26, characterized in that, Also includes: The pull-down voltage is connected to a second voltage, which changes dynamically. The second compensation voltage rises dynamically following the second voltage.

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