Switching power supply controller and control method thereof

Abstract

The application provides a switching power supply controller and a control method thereof. The switching power supply controller comprises: a reference voltage generation circuit configured to generate a reference voltage signal according to a feedback voltage signal representing output power; a frequency jitter control circuit configured to generate a frequency jitter control signal according to the feedback voltage signal, so as to control the size of the reference voltage signal according to the frequency jitter control signal; and an off signal generation circuit connected with the reference voltage generation circuit and configured to generate an off control signal according to the reference voltage signal, the off control signal being used to control the off of a power switch tube in the switching power supply. The method of judging the peak current jitter enable threshold through the feedback voltage can maximize the frequency jitter caused by the peak current under the premise of meeting the requirement of maximum peak current limiting in the full range input.

Description

Technical Field

[0001] This application relates to power electronics technology, and more specifically, to a switching power supply controller and its control method. Background Technology

[0002] Quasi-resonant flyback converters are widely used in adapters for mobile phones and laptops due to their simplicity, reliability, and high efficiency. Thanks to the universal Type-C interface and PD universal protocol, all low-power consumer electronics such as mobile phones and laptops can share the same adapter. As adapter power has gradually increased from 20W, 40W, and 65W to the current 135W, the quasi-resonant flyback converter has become the most common topology for these different power levels.

[0003] Quasi-resonant flyback converters are generally categorized into PWM control, PFM control, and QR control. PFM and QR modes are both frequency modulation control modes, and to reduce switching losses, the main switch is typically controlled to turn on at the valley voltage. Therefore, at a given power level, valley-to-peak control results in a fixed switching frequency. However, with the increasing demands for small size and high power density in fast-charging devices, frequency dithering is needed to address conduction issues with minimal EMI filters. Frequency dithering can typically be achieved through frequency limiting line dithering and peak current dithering. When the quasi-resonant converter operates in PFM and QR modes, the frequency is locked by valley tracking, so peak current dithering is used to change the operating frequency. Peak dithering typically exhibits a ±5–10% peak variation over a certain period. Quasi-resonant flyback converters generally use peak current control, where the maximum peak current value is often the design limit of the transformer, a key parameter to prevent transformer saturation. Due to transformer size limitations, for 90VAC low-voltage input full-load output applications, current transformer designs operate in maximum current mode at the lowest point of the input voltage. Therefore, the tolerance for the maximum peak current becomes a limiting factor in transformer design. To meet the transformer's unsaturation requirements within a minimal core size, the tolerance for the maximum value needs to be reduced. However, fluctuations in peak current lead to an additional increase in peak current, creating a contradiction.

[0004] To address the above issues, the industry has proposed a method where the peak current does not fluctuate under low-voltage input but does fluctuate under high-voltage input. When the input voltage is less than 150VAC, the peak current does not fluctuate, utilizing the inherent characteristic of large capacitor ripple under low-voltage input to solve the frequency fluctuation problem. When the input voltage is higher than 150VAC, the frequency fluctuation is met through peak current fluctuation. However, this method of using the input voltage as a dividing line for peak current fluctuation still has the potential to exceed the saturation requirement when the converter is operating under high-voltage input, output overcurrent, or short circuit conditions. Therefore, it loses the protection capability of peak current control under high-voltage input, and thus has shortcomings.

[0005] Therefore, it is desirable to provide an improved switching power supply controller to meet the above requirements. Summary of the Invention

[0006] The content of this application is provided to introduce, in a simplified form, some concepts that will be further described in the detailed description below. This content is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0007] The purpose of this application is to provide an improved switching power supply controller to enhance protection against peak current control under high input voltage. The foregoing and other objectives are achieved through the features of the independent claims. Further embodiments will be apparent from the dependent claims, the specification, and the drawings.

[0008] A first aspect of this application provides a switching power supply controller for controlling a switching power supply, characterized by comprising: a reference voltage generation circuit configured to generate a reference voltage signal based on a feedback voltage signal characterizing output power; a frequency dithering control circuit configured to generate a frequency dithering control signal based on the feedback voltage signal to control the magnitude of the reference voltage signal according to the frequency dithering control signal; and a shutdown signal generation circuit connected to the reference voltage generation circuit, configured to generate a shutdown control signal based on the reference voltage signal, the shutdown control signal being used to control the shutdown of a power switching transistor in the switching power supply.

[0009] Optionally, the frequency dithering control circuit receives the feedback voltage signal and the first threshold voltage, and controls the reference voltage signal to change stepwise when the feedback voltage signal is less than the first threshold voltage.

[0010] Optionally, the reference voltage generation circuit is connected to the frequency dithering control circuit. When the feedback voltage signal is greater than the first threshold voltage, the frequency dithering control signal is output to control the reference voltage signal to not generate dithering. Or, when the feedback voltage signal is greater than the first threshold voltage, the frequency dithering control signal is output to control the reference voltage signal to reduce dithering until dithering is completely eliminated.

[0011] Optionally, the shutdown signal generation circuit receives the reference voltage signal and the current sampling signal, compares the reference voltage signal and the current sampling signal to output the shutdown control signal.

[0012] Optionally, the reference voltage generation circuit includes: a voltage-controlled current source configured to generate a first current based on the feedback voltage signal, wherein the first current is linearly related to the feedback voltage signal; a first current mirror configured to be connected to the voltage-controlled current source, receive the first current, and generate a second threshold current; and a variable resistor configured to be controlled by the frequency dithering control module, the resistance of which varies according to the frequency dithering control signal; the reference voltage generation circuit generates the reference voltage signal based on the second threshold current and the resistance value of the variable resistor.

[0013] Optionally, when the feedback voltage signal is less than the first threshold voltage, the resistance value of the variable resistor changes in a stepwise manner; otherwise, the resistance value of the variable resistor remains unchanged.

[0014] Optionally, the frequency dithering control circuit includes: a first comparator, configured such that a first input terminal of the first comparator receives the feedback voltage signal, a second input terminal receives the first threshold voltage, and an output terminal is connected to the reference voltage generation circuit to output a frequency dithering control signal to control the dithering of the reference voltage signal.

[0015] Optionally, the shutdown signal generation circuit includes: a second comparator, configured such that a first input terminal of the second comparator receives the current sampling signal, a second input terminal receives the reference voltage signal, and an output terminal outputs the shutdown control signal.

[0016] According to a second aspect of this application, a switching power supply control method is provided, characterized by comprising: generating a reference voltage signal based on a feedback voltage signal characterizing output power; generating a frequency dithering control signal based on the feedback voltage signal to control the magnitude of the reference voltage signal according to the frequency dithering control signal; and generating a shutdown control signal based on the reference voltage signal to control the shutdown of a power switching transistor in the switching power supply.

[0017] Optionally, generating a jitter control signal based on the feedback voltage signal to control the step change of the reference voltage signal according to the jitter control signal includes: receiving the feedback voltage signal and a first threshold voltage, wherein when the feedback voltage signal is less than the first threshold voltage, the reference voltage signal is controlled to undergo a step change to generate jitter; when the feedback voltage signal is greater than the first threshold voltage, the jitter control signal is output to control the reference voltage signal to not generate jitter, or when the feedback voltage signal is greater than the first threshold voltage, the jitter control signal is output to control the reference voltage signal to reduce jitter until jitter is completely eliminated.

[0018] Optionally, generating a shutdown control signal based on the reference voltage signal, the shutdown control signal being used to control the shutdown of the power switching transistor in the switching power supply, includes: receiving the reference voltage signal and the current sampling signal, comparing the reference voltage signal and the current sampling signal to output the shutdown control signal.

[0019] This application proposes a switching power supply controller and its control method. The controller determines the peak current jitter enable threshold using feedback voltage. Above the threshold, the current jitter function is disabled, or the peak current jitter amplitude is gradually reduced within the range from the threshold to below the maximum peak value. This not only achieves the maximum peak current limiting requirement across the entire input range but also maximizes the frequency jitter effect generated by the peak current jitter. Under low input voltage and full-load output, frequency jitter is achieved through the natural jitter of the bus capacitor voltage. Under high input voltage and full-load output, the controller can be designed so that the actual peak current operating point or feedback voltage is within the frequency jitter enable threshold, thus ensuring frequency jitter functionality under high input. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic diagram of a switching circuit in the prior art is shown;

[0022] Figure 2 A schematic diagram of the structure of a switching power supply controller according to an embodiment of this application is shown;

[0023] Figure 3 A schematic diagram of the reference voltage generation circuit of a switching power supply controller according to an embodiment of this application is shown;

[0024] Figure 4 It shows that according to Figure 3 The resistance waveform of the variable resistor in the embodiment;

[0025] Figure 5 A schematic diagram of the frequency dithering control circuit of a switching power supply controller according to an embodiment of this application is shown;

[0026] Figure 6 The diagram illustrates the waveform relationship between the primary current sampling signal and the feedback voltage signal of the switching power supply controller according to an embodiment of this application.

[0027] Figure 7 The diagram showing the relationship between the frequency dithering range of the reference voltage signal and the feedback voltage signal in an embodiment of this application is illustrated.

[0028] Figure 8 A schematic diagram of the shutdown signal generation circuit of a switching power supply controller according to an embodiment of this application is shown.

[0029] Figure 9 A flowchart of a switching power supply control method according to an embodiment of this application is shown.

[0030] In the following text, the same reference numerals denote the same or at least functionally the same features. Detailed Implementation

[0031] The technical solutions of the embodiments of this application will now be described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0032] For example, it should be understood that the disclosure of the described method applies to the corresponding apparatus or system for performing the method, and vice versa. For example, if specific method steps are described, the corresponding apparatus may include units that perform the described method steps, even if such units are not described or shown in detail in the accompanying drawings. On the other hand, for example, if a particular device is described based on functional units, the corresponding method may include steps that perform the described functions, even if such steps are not explicitly described or illustrated in the accompanying drawings. Furthermore, it should be understood that features of the various exemplary aspects described herein can be combined with each other unless otherwise specifically stated.

[0033] It should be understood that the connection / coupling of A and B in the embodiments of this application means that A and B can be connected in series or in parallel, or A and B can be connected through other devices. The embodiments of this application do not limit this.

[0034] Figure 1A schematic diagram of a conventional QR flyback converter is shown, such as... Figure 1 As shown, the flyback converter includes a primary-side rectifier circuit, a flyback switching transformer, an auxiliary winding circuit, a primary-side control circuit, and a secondary-side control circuit, wherein V bus The bus voltage is obtained by rectification by the primary-side rectifier circuit. Naux is the auxiliary winding. The primary-side control circuit includes the primary-side control chip, I. VS The current flowing out of the VS pin when the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is turned on reflects the input voltage information. In the secondary-side control circuit, the optocoupler generates different feedback voltages based on changes in output power, which are received by the FB pin of the primary-side control chip and transmitted through the F pin. MAX The pin is connected to the primary-side control chip. The frequency regulation circuit integrated in the primary-side control chip outputs the frequency to the next processing module, which then outputs the switching frequency through the DRV pin. Existing technology sets a threshold for directly judging the input voltage. For example, when the input voltage is less than 150VAC, the current peak does not jitter, utilizing the inherent characteristic of large capacitor ripple under low-voltage input to solve the frequency jitter problem. When the input voltage is higher than 150VAC, the frequency jitter requirement is met through peak current jitter. That is, no jitter under low-voltage input, and jitter under high-voltage input, this method prevents transformer oversaturation. However, for voltages of V... AC_th Using peak current jitter as a dividing line still presents a possibility that the peak current may exceed the saturation requirement when the converter is operating under high voltage input, output overcurrent, or short circuit conditions. This means that the protection capability of peak current control under high input voltage is lost, and therefore there is a defect.

[0035] Figure 2 A schematic diagram of the structure of a switching power supply controller according to an embodiment of this application is shown, as follows: Figure 2 As shown, the switching power supply controller includes a reference voltage generation circuit 101, a frequency dithering control circuit 102, and a turn-off signal generation module 103. The reference voltage generation circuit 101 receives a feedback voltage signal to generate a reference voltage signal. The frequency dithering control circuit 102 receives the feedback voltage signal to generate a frequency dithering control signal and controls the step change of the reference voltage signal. The turn-off signal generation circuit receives the reference voltage signal Vcs_ref sent by the reference voltage generation circuit 101 and the current sampling signal Vcs that detects the primary inductor current, and generates a turn-off control signal based on the two signals. The turn-off control signal is used to control the turn-off of the power switching transistor in the switching power supply.

[0036] Optionally, the switching power supply controller also includes a trigger. The set terminal S of the trigger receives a turn-on control signal that controls the primary-side switching transistor of the switching power supply to turn on. The reset terminal R receives a turn-off control signal output by the turn-off signal generation module 103. The output terminal Q outputs the drive signal of the primary-side power switching transistor.

[0037] Figure 3 A schematic diagram of the reference voltage generation circuit of a switching power supply controller according to an embodiment of this application is shown. Figure 4 It shows that according to Figure 3 The resistance waveform of the variable resistor in the embodiment.

[0038] like Figure 3 As shown, the reference voltage generation circuit 101 includes a power supply V. A The system consists of a voltage-controlled current source M0, a first current mirror M1, and a variable resistor Rp. The voltage-controlled current source M0 receives a feedback voltage signal V. FB The first current I is generated. cs_ref The first current mirror M1 replicates the first current at a certain ratio and supplies it to the upper end of the variable resistor Rp. The specific changes in the resistance value of the variable resistor Rp are as follows: Figure 4 As shown, the variable resistor Rp is controlled by the frequency dithering control signal output by the frequency dithering control circuit. When V FB >V FB_th When V, the resistance of the variable resistor Rp remains constant. FB <V FB_th At this time, the resistance value of the variable resistor Rp changes in a step manner within the frequency dithering range (Δ%). The upper end of the variable resistor Rp outputs a reference voltage signal. The reference voltage signal circuit 101 generates a reference voltage signal based on the second threshold current and the resistance value of the variable resistor Rp. That is, when V FB >V FB_th At that time, the reference voltage signal is only related to the feedback voltage signal V. FB Related, no jitter is generated, when V FB <V FB_th When the variable resistor Rp changes stepwise within the frequency dithering range (Δ%), the reference voltage signal is affected by the variable resistor Rp and also changes stepwise.

[0039] As an example, the reference voltage generation circuit 101 generates a stepped reference voltage signal based on the feedback voltage signal. The offset value Δ% is between [0, 5%]. That is, the offset between the maximum value and the average value of the variable resistor Rp is between [0, 5%], and the offset between its minimum value and the average value is between [0, 5%]. Moreover, the maximum and minimum values ​​are symmetrical about the average value.

[0040] It is understood that the offset value range Δ% in this application embodiment is only an example. Various different value ranges may exist according to different needs. This application does not limit this. The above describes an example of the reference voltage generation circuit of this application embodiment. However, the embodiments of this application are not limited to this. There may be other extensions and modifications.

[0041] For example, it should be understood that the current mirror circuit in the foregoing embodiments can be a bipolar junction transistor (BJT) current mirror or a field effect transistor (FET) current mirror, and this application does not limit it in this regard.

[0042] Figure 5 A schematic diagram of the frequency dithering control circuit of a switching power supply controller according to an embodiment of this application is shown; as follows: Figure 5 As shown, the frequency dithering control circuit 102 includes a first comparator. The first input terminal of the first comparator receives a feedback voltage signal, the second input terminal receives a first threshold voltage, and the output terminal is connected to a reference voltage generation circuit. It outputs a frequency dithering control signal to control the dithering of the reference voltage signal. In this embodiment, it controls the change in the resistance value of the variable resistor Rp. When the feedback voltage signal is less than the first threshold voltage, the reference voltage signal is controlled to change stepwise to generate dithering. When the feedback voltage signal is greater than the first threshold voltage, the frequency dithering control signal is output to control the reference voltage signal not to generate dithering. That is, when the feedback voltage signal is less than the first threshold voltage, the frequency dithering control signal is high, the resistance value of the variable resistor Rp changes stepwise, and the frequency dithering control signal controls the dithering of the reference voltage signal. Otherwise, the frequency dithering control signal is low, the resistance value of the variable resistor Rp remains unchanged, and the frequency dithering control signal controls the reference voltage signal not to generate dithering.

[0043] Figure 6 The following diagram illustrates the waveform relationship between the primary-side current sampling signal and the feedback voltage signal of the switching power supply controller according to an embodiment of this application. Figure 6 As shown in the figure, the relationship between the current sampling signal and the feedback voltage signal is as follows. As an example, when the feedback voltage signal is used as the input signal of the first comparator, the value of the first threshold voltage of the switching power supply in quasi-resonant mode is less than 3.2V. When the feedback voltage signal is within this range, the frequency dithering control circuit enables the switching power supply control circuit to perform frequency dithering to meet the requirements of no frequency dithering under low voltage, frequency dithering under high voltage full load, and ensuring that the peak current is not saturated, thus better protecting the performance of the transformer.

[0044] It should be understood that the range of the first threshold voltage can be changed according to the needs of actual application, and this application does not limit it. The above describes an example of the frequency dithering control circuit of the embodiment of this application. However, the embodiments of this application are not limited to this and there may be other extensions and modifications.

[0045] For example, when the feedback voltage signal is greater than the first threshold voltage, the output jitter control signal can control the reference voltage signal to reduce jitter until it is completely eliminated. Figure 7 The diagram showing the relationship between the frequency dithering range of the reference voltage signal and the feedback voltage signal in an embodiment of this application is illustrated. Figure 7 As shown, when the feedback voltage signal rises above the first threshold voltage, the jitter range of the reference voltage signal slowly decreases until the jitter range of the reference voltage signal is zero. It can be understood that the jitter range of the reference voltage signal and the current sampling voltage can be linear or nonlinear, as long as the reference voltage signal gradually decreases as the current sampling voltage increases. This application does not limit this.

[0046] Figure 8 A schematic diagram of the shutdown signal generation circuit of a switching power supply controller according to an embodiment of this application is shown, as follows: Figure 8 As shown, the shutdown signal generation circuit 103 includes a second comparator. The first input of the second comparator receives a current sampling signal Vcs, and the second input receives a reference voltage signal Vcs_ref. It outputs a shutdown control signal. When the resistance value of the variable resistor Rp remains unchanged, the shutdown signal generation circuit 103 compares the reference voltage signal Vcs_ref with the current sampling signal Vcs_ref. cs ref With current sampling signal V cs Output a shutdown control signal; when the resistance of the variable resistor Rp changes in a stepwise manner, receive the current sampling signal V. cs and reference voltage signal V cs_ref Compare the reference voltage signal V cs_ref and current sampling signal V cs Output a shutdown control signal, which is sent to the reset terminal R of the trigger. Due to the jitter of the reference voltage signal, the frequency jitter of the system can be controlled.

[0047] The foregoing describes an example of a switching power supply controller according to an embodiment of this application. However, the embodiments of this application are not limited thereto, and there may be other extensions and variations.

[0048] For example, it should be understood that the reference ground potential in the foregoing embodiments may be replaced in alternative embodiments with other non-zero reference potentials (with positive or negative voltage amplitudes) or a controlled-change reference signal.

[0049] For example, the resistors and capacitors provided in the embodiments of this application can be lumped-parameter capacitor elements and resistor elements, or other equivalent elements with similar functions to capacitors and resistors. The equivalent structures described herein are, for example, but not limited to, microstrip lines, varactors, conductor structures with certain patterns, etc., which can provide inductive impedance and / or capacitive impedance.

[0050] Furthermore, those skilled in the art will recognize that the structures and methods described in conjunction with the embodiments disclosed herein can be used with different configuration or adjustment methods to achieve the described functions for each structure or reasonable variations thereof, but such implementations should not be considered beyond the scope of this application. Moreover, it should be understood that the connection relationships between the various components of the amplifier in the foregoing figures in the embodiments of this application are illustrative examples and do not impose any limitations on the embodiments of this application.

[0051] Figure 9 A flowchart of a switching power supply control method according to an embodiment of this application is shown, such as... Figure 8 As shown, the control method for the switching power supply includes S901-S903, and this switching power supply control method can be used for... Figure 2 In the switching power supply controller.

[0052] In step S901, a reference voltage signal is generated based on the feedback voltage signal characterizing the output power;

[0053] In step S902, a frequency dithering control signal is generated based on the feedback voltage signal to control the step change of the reference voltage signal according to the frequency dithering control signal;

[0054] In step S903, a shutdown control signal is generated based on the reference voltage signal. The shutdown control signal is used to control the shutdown of the power switching transistor in the switching power supply.

[0055] Optionally, generating a reference voltage signal based on a feedback voltage signal characterizing the output power includes: receiving the frequency control signal and generating the reference voltage signal with a stepped variation based on the feedback voltage signal and the frequency control signal.

[0056] Optionally, generating a jitter control signal based on the feedback voltage signal to control the step change of the reference voltage signal according to the jitter control signal includes: receiving the feedback voltage signal and a first threshold voltage, wherein when the feedback voltage signal is less than the first threshold voltage, the reference voltage signal is controlled to undergo a step change to generate jitter; when the feedback voltage signal is greater than the first threshold voltage, the jitter control signal is output to control the reference voltage signal to not generate jitter, or when the feedback voltage signal is greater than the first threshold voltage, the jitter control signal is output to control the reference voltage signal to reduce jitter until jitter is completely eliminated.

[0057] Optionally, generating a shutdown control signal based on the reference voltage signal, the shutdown control signal being used to control the shutdown of the power switching transistor in the switching power supply, includes: receiving the reference voltage signal and the current sampling signal, comparing the reference voltage signal and the current sampling signal to output the shutdown control signal.

[0058] Any ranges or device values ​​given herein may be extended or modified without loss of the desired effect. Furthermore, any embodiment may be combined with another embodiment that is not expressly prohibited.

[0059] Although the subject matter has been described in language specific to structural features and / or actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as examples of implementing the claims, and other equivalent features and actions are intended to fall within the scope of the claims.

[0060] It should be understood that the above benefits and advantages may relate to one embodiment or several embodiments. The embodiments are not limited to embodiments that solve any or all of the described problems, or embodiments that have any or all of the described benefits and advantages. It should also be understood that a reference to "one" item may refer to one or more of those items.

[0061] The steps of the methods described herein can be performed in any suitable order, or simultaneously where appropriate. Furthermore, individual blocks can be removed from any method without departing from the spirit and scope of the subject matter described herein. Aspects of any of the embodiments described above can be combined with aspects of any other described embodiments to form further embodiments without loss of the desired effects.

[0062] The terms “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0063] It should be understood that the above description is given by way of example only, and various modifications can be made by those skilled in the art. The above description, examples, and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments with a certain degree of specificity have been described above, or reference has been made to one or more individual embodiments, those skilled in the art can make various changes to the disclosed embodiments without departing from the spirit or scope of this specification.

Claims

1. A switching power supply controller for controlling a switching power supply, characterized by comprising: The application relates to a switching power supply, comprising: a reference voltage generating circuit configured to generate a reference voltage signal according to a feedback voltage signal representing output power; a dithering control circuit configured to generate a dithering control signal according to the feedback voltage signal, so as to control the magnitude of the reference voltage signal according to the dithering control signal; a shutdown signal generating circuit connected with the reference voltage generating circuit and configured to generate a shutdown control signal according to the reference voltage signal, the shutdown control signal being used to control the shutdown of a power switch tube in the switching power supply; the dithering control circuit receives the feedback voltage signal and a first threshold voltage, when the feedback voltage signal is less than the first threshold voltage, the reference voltage signal is controlled to change in steps to generate dithering; the reference voltage generating circuit is connected with the dithering control circuit to receive the dithering control signal, when the feedback voltage signal is greater than the first threshold voltage, the dithering control signal is output to control the reference voltage signal to generate no dithering, or when the feedback voltage signal is greater than the first threshold voltage, the dithering control signal is output to control the reference voltage signal to reduce dithering until no dithering is generated.

2. The switching power supply controller according to claim 1, characterized in that the shutdown signal generating circuit receives the reference voltage signal and a current sampling signal, and compares the reference voltage signal and the current sampling signal to output the shutdown control signal.

3. The switching power supply controller of claim 1, wherein, The reference voltage generating circuit comprises: a voltage-controlled current source configured to generate a first current according to the feedback voltage signal, wherein the first current is in linear relationship with the feedback voltage signal; a first current mirror connected with the voltage-controlled current source and configured to receive the first current to generate a second threshold current; a variable resistor configured to be controlled by the dithering control circuit, and the resistance of the variable resistor changes according to the dithering control signal; the reference voltage generating circuit generates the reference voltage signal according to the second threshold current and the resistance of the variable resistor.

4. The switching power supply controller according to claim 3, characterized in that When the feedback voltage signal is less than the first threshold voltage, the resistance of the variable resistor changes in steps, otherwise, the resistance of the variable resistor remains unchanged.

5. The switching power supply controller of claim 1, wherein, The dithering control circuit comprises: a first comparator configured to receive the feedback voltage signal at a first input end, receive the first threshold voltage at a second input end, and output a dithering control signal at an output end connected with the reference voltage generating circuit, so as to control the dithering of the reference voltage signal.

6. The switching power supply controller of claim 2, wherein, The shutdown signal generating circuit comprises: a second comparator configured to receive the current sampling signal at a first input end, receive the reference voltage signal at a second input end, and output the shutdown control signal at an output end.

7. A switching power supply control method characterized by comprising: The application relates to a switching power supply, comprising: generating a reference voltage signal according to a feedback voltage signal representing output power; generating a dithering control signal according to the feedback voltage signal, so as to control the magnitude of the reference voltage signal according to the dithering control signal; generating a shutdown control signal according to the reference voltage signal, the shutdown control signal being used to control the shutdown of a power switch tube in the switching power supply; generating a dithering control signal according to the feedback voltage signal, to control the reference voltage signal to dither according to the dithering control signal, comprising: receiving the feedback voltage signal and a first threshold voltage, wherein when the feedback voltage signal is less than the first threshold voltage, controlling the reference voltage signal to dither; and when the feedback voltage signal is greater than the first threshold voltage, outputting the dithering control signal to control the reference voltage signal to not dither, or when the feedback voltage signal is greater than the first threshold voltage, outputting the dithering control signal to control the reference voltage signal to reduce dithering until no dithering is produced.

8. The switching power supply control method according to claim 7, wherein generating an off control signal according to the reference voltage signal, the off control signal used to control the off of a power switch in the switching power supply, comprising: receiving the reference voltage signal and a current sampling signal, and comparing the reference voltage signal and the current sampling signal to output the off control signal.

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