Secondary output voltage soft start circuit and switching power supply

Abstract

The utility model discloses a secondary output voltage soft start circuit and a switching power supply, and relates to the technical field of switching power supplies. The technical problem that in the prior art, falling or pit falling is likely to happen in the connection process from primary soft start to secondary soft start is solved. The circuit comprises an operational amplification module, a secondary soft start module, a voltage following pre-bias module, a reference voltage module and a secondary loop control module, wherein the output end and the input negative end of the operational amplification module are connected to the two ends of the secondary loop control module; the input positive end of the operational amplification module is connected with the voltage following pre-bias module and the reference voltage module through the secondary soft start module, and the reference voltage module is connected with the voltage following pre-bias module. According to the secondary output voltage soft start circuit, monotonous rising of output voltage waveform is realized through the voltage following pre-bias module, so that the output voltage of the secondary output voltage soft start circuit does not drop or drop pits in the rising process.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply technology, and in particular to a secondary output voltage soft-start circuit and a switching power supply. Background Technology

[0002] Existing switching power supplies include primary and secondary soft-start circuits. During the output voltage rise process after power-on, a voltage drop or dip can easily occur during the transition from the primary to the secondary soft-start circuit. For example, ... Figure 1 As shown, the output voltage gradually increases from 2V. During the increase, the output voltage experiences a sudden drop before rising again (a voltage dip or dip). This is because the power supply is provided to the operational amplifier via the winding or output voltage after a step-down process. When the power supply reaches the operational amplifier's operating voltage, the positive input terminal of the operational amplifier is lower than its negative input terminal. The secondary loop regulation limits the duty cycle of the primary switch, resulting in primary energy supply being less than secondary energy loss. This easily causes the output voltage to dip or dip, making it difficult to adjust the output voltage to a monotonically increasing state when a dip or dip occurs. Utility Model Content

[0003] The purpose of this invention is to provide a secondary output voltage soft-start circuit and a switching power supply to solve the technical problem in the prior art where the connection between the primary and secondary soft-start stages is prone to drops or pitting. The various technical effects of the preferred solutions among the many technical solutions provided by this invention are detailed below.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] According to a first aspect of this utility model, a secondary output voltage soft-start circuit is provided, comprising an operational amplifier module, a secondary soft-start module, a voltage follower pre-bias module, a reference voltage module, and a secondary loop control module; the output terminal and the negative input terminal of the operational amplifier module are connected to the two ends of the secondary loop control module, and the positive input terminal of the operational amplifier module is connected to the voltage follower pre-bias module and the reference voltage module through the secondary soft-start module, wherein the reference voltage module is connected to the voltage follower pre-bias module.

[0006] In some embodiments, the secondary soft-start module includes a first resistor R1 and a first capacitor C1, with one end of the first resistor R1 and one plate of the first capacitor C1 connected to the positive input terminal of the operational amplifier module.

[0007] Furthermore, the voltage follower pre-bias module includes a first operational amplifier U1, a second resistor R2, a third resistor R3, and a first diode D1; one end of the second resistor R2 and one end of the third resistor R3 are connected to the positive input terminal of the first operational amplifier U1, and the output terminal of the first operational amplifier U1 is connected to the anode of the first diode D1; the negative input terminal of the first operational amplifier U1 and the cathode of the first diode D1 are connected between one plate of the first capacitor C1 and the positive input terminal of the operational amplifier module, and are located on the branch of the parallel first resistor R1 and the first capacitor C1.

[0008] Furthermore, the reference voltage module includes a fourth resistor R4, a fifth resistor R5, a second capacitor C2, and a second diode D2; the other end of the first resistor R1, the cathode of the second diode D2, one plate of the second capacitor C2, one end of the fourth resistor R4, and the other end of the third resistor R3 are all connected to the power supply through the fifth resistor R5; the other end of the first capacitor C1, the anode of the second diode D2, the other plate of the second capacitor C2, the other end of the fourth resistor R4, and the other end of the second resistor R2 are all connected to signal ground; and the anode of the second diode D2 is also connected to the power supply through the fifth resistor R5.

[0009] In some embodiments, the operational amplifier module includes a second operational amplifier U2, which is powered by a winding or connected to a power supply.

[0010] Furthermore, the end of the secondary loop control module connected to the output terminal of the operational amplifier module serves as the input terminal of the secondary output voltage soft-start circuit, and is used to connect the primary soft-start circuit corresponding to the secondary output voltage soft-start circuit.

[0011] Furthermore, the secondary output voltage soft-start circuit further includes a voltage output module, which has a positive voltage output port and a negative voltage output port. The input terminal of the positive voltage output port is connected to the end of the secondary loop control module connected to the negative input terminal of the operational amplifier module, and the input terminal of the negative voltage output port is connected to signal ground.

[0012] In some embodiments, the secondary loop control module includes a fourth capacitor C4 and a ninth resistor R9. One plate of the fourth capacitor C4 and one end of the ninth resistor R9 are connected to each other. The other end of the ninth resistor R9 is connected to the negative input terminal of the operational amplifier module. The other plate of the fourth capacitor C4 is connected to the output terminal of the operational amplifier module. One plate of the fourth capacitor C4 connected to the output terminal of the operational amplifier module is the input terminal of the secondary output voltage soft-start circuit.

[0013] In some embodiments, the voltage output module further includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a third capacitor C3; one plate of the third capacitor C3, one end of the seventh resistor R7, and one end of the eighth resistor R8 are connected to the extension line of the contact point connecting the negative input terminal of the operational amplifier module and one end of the ninth resistor R9; the other plate of the third capacitor C3 is connected to one end of the sixth resistor R6; the other ends of the sixth resistor R6 and the seventh resistor R7 are connected to the input terminal of the positive voltage output port; and the other end of the eighth resistor R8 is connected to signal ground.

[0014] According to another aspect of this utility model, a switching power supply is also provided, including a secondary output voltage soft-start circuit, a primary soft-start circuit, and an isolation circuit as described above. The primary soft-start circuit and the secondary output voltage soft-start circuit are both connected to the isolation circuit, and interstage isolation between the primary soft-start circuit and the secondary output voltage soft-start circuit is achieved through the isolation circuit.

[0015] In some embodiments, the primary soft-start circuit includes a power management chip U3 and a fifth capacitor C5. The soft-start pin of the power management chip U3 is connected to one plate of the fifth capacitor C5, and the other plate of the fifth capacitor C5 is grounded.

[0016] In some embodiments, the isolation circuit is an optocoupler U4. The collector of the input side of the optocoupler U4 is connected to the error compensation pin of the power management chip U3, the emitter of the input side of the optocoupler U4 is connected to the feedback pin of the power management chip U3, the positive terminal of the output side of the optocoupler U4 is connected to the power supply, and the negative terminal of the output side of the optocoupler U4 is connected to the input terminal of the secondary output voltage soft-start circuit.

[0017] Implementing one of the above-described technical solutions of this utility model has the following advantages or beneficial effects:

[0018] The reference voltage module of this stage output voltage soft-start circuit provides a reference voltage. The voltage follower pre-bias module generates a pre-bias voltage based on the reference voltage and quickly charges the voltage at the positive input terminal of the operational amplifier module to the pre-bias voltage. Furthermore, it charges the pre-bias voltage at the positive input terminal of the operational amplifier module higher than the voltage transmitted to the negative input terminal of the operational amplifier module through the secondary loop control module. Therefore, this invention achieves a monotonically rising output voltage waveform through the voltage follower pre-bias module, preventing the output voltage of the secondary output voltage soft-start circuit from dropping or experiencing a dip during the rise. Consequently, the output voltage of the switching power supply in this stage output voltage soft-start circuit does not drop or experience a dip during the rise, providing a dip-prevention function. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0020] Figure 1 This is a schematic diagram illustrating the voltage drop or dip that occurs during the voltage build-up process of an existing switching power supply.

[0021] Figure 2 A schematic diagram of a secondary output voltage soft-start circuit according to an embodiment of this utility model;

[0022] Figure 3 A schematic diagram of a winding power supply circuit for an operational amplifier module (second operational amplifier) ​​according to an embodiment of this utility model;

[0023] Figure 4 A schematic diagram of a switching power supply circuit structure according to an embodiment of this utility model.

[0024] In the picture:

[0025] 1. Secondary output voltage soft-start circuit; 11. Operational amplifier module; 12. Secondary soft-start module; 13. Voltage follower pre-bias module; 14. Reference voltage module; 15. Secondary loop control module; 16. Voltage output module; 2. Primary soft-start circuit; 3. Isolation circuit. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this utility model clearer, various exemplary embodiments described below will be referenced to the accompanying drawings, which form part of the exemplary embodiments, illustrating various exemplary embodiments that may be adopted to implement this utility model. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. It should be understood that they are merely examples of processes, methods, and apparatuses consistent with some aspects of this utility model disclosed as detailed in the appended claims, and other embodiments may be used, or structural and functional modifications may be made to the embodiments listed herein without departing from the scope and spirit of this utility model.

[0027] In the description of this utility model, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. The terms "connected" and "linked" should be interpreted broadly, for example, they can refer to fixed connections, detachable connections, integral connections, mechanical connections, electrical connections, communication connections, direct connections, indirect connections via an intermediate medium, or connections within two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0028] To illustrate the technical solution described in this utility model, specific embodiments are described below, showing only the parts related to the embodiments of this utility model.

[0029] Example 1:

[0030] like Figure 2 As shown, this embodiment provides a secondary output voltage soft-start circuit, including an operational amplifier module 11, a secondary soft-start module 12, a voltage follower pre-bias module 13, a reference voltage module 14, and a secondary loop control module 15. Specifically, the output terminal and the negative input terminal of the operational amplifier module 11 are connected to the two ends of the secondary loop control module 15. The positive input terminal of the operational amplifier module 11 is connected to the voltage follower pre-bias module 13 and the reference voltage module 14 through the secondary soft-start module 12. The reference voltage module 14 is connected to the voltage follower pre-bias module 13.

[0031] It should be noted that the soft-start principle of the secondary soft-start module is as follows: When the operational amplifier module is powered normally (e.g., the power supply reaches 5V), and the voltage at the positive input terminal of the operational amplifier module is lower than that at its negative input terminal, the secondary output voltage soft-start circuit starts working. When the secondary output voltage soft-start circuit starts working, the output voltage gradually rises until the voltage at the positive input terminal of the operational amplifier module reaches the reference voltage provided by the reference voltage module, at which point the soft-start of the secondary soft-start module ends. The rate of increase of the output voltage is controlled by the secondary soft-start module (e.g., by controlling the rate of increase of the output voltage through the parameters of a resistor R1 and a first capacitor C1, as described below).

[0032] In this embodiment, the voltage follower pre-bias module generates a pre-bias voltage based on the reference voltage provided by the reference voltage module, and quickly charges the voltage at the positive input terminal of the operational amplifier module to the pre-bias voltage. Furthermore, it charges the pre-bias voltage at the positive input terminal of the operational amplifier module higher than the voltage transmitted to the negative input terminal of the operational amplifier module through the secondary loop control module. Consequently, no voltage drop or dip occurs during the output voltage rise, achieving a monotonic increase in the output voltage waveform.

[0033] In some embodiments, the secondary soft-start module 12 includes a first resistor R1 and a first capacitor C1. One end of the first resistor R1 and one plate of the first capacitor C1 are connected to the positive input terminal of the operational amplifier module 11. The voltage rise rate at the positive input terminal of the operational amplifier module 11 can be determined by the resistance value of the first resistor R1 and the capacitance value of the first capacitor C1, thereby determining the voltage rise rate of the entire circuit output voltage.

[0034] Furthermore, the voltage follower pre-bias module 13 includes a first operational amplifier U1, a second resistor R2, a third resistor R3, and a first diode D1. Specifically, one end of the second resistor R2 and one end of the third resistor R3 are connected to the positive input terminal of the first operational amplifier U1, and the output terminal of the first operational amplifier U1 is connected to the anode of the first diode D1; the negative input terminal of the first operational amplifier U1 and the cathode of the first diode D1 are connected between one plate of the first capacitor C1 and the positive input terminal of the operational amplifier module 11, and are located on the branch of the parallel first resistor R1 and the first capacitor C1.

[0035] Furthermore, the reference voltage module 14 includes a fourth resistor R4, a fifth resistor R5, a second capacitor C2, and a second diode D2. Specifically, the other end of the first resistor R1, the cathode of the second diode D2, one plate of the second capacitor C2, one end of the fourth resistor R4, and the other end of the third resistor R3 are all connected to the power supply SVDD through the fifth resistor R5. The other end of the first capacitor C1, the anode of the second diode D2, the other plate of the second capacitor C2, the other end of the fourth resistor R4, and the other end of the second resistor R2 are all connected to signal ground (SGND). The anode of the second diode D2 is also connected to the power supply SVDD through the fifth resistor R5.

[0036] It should be noted that the aforementioned pre-bias voltage can be set using the second resistor R2 and the third resistor R3 of the voltage follower pre-bias module. Specifically, the pre-bias voltage calculation formula is as follows:

[0037] V 偏置 =Vref*R2 / (R2+R3);

[0038] Wherein, Vref is the reference voltage provided by the reference voltage module.

[0039] In some embodiments, the operational amplifier module 11 includes a second operational amplifier U2. The positive power input terminal (pin 5 of U2) and the negative power input terminal (pin 4 of U2) of the second operational amplifier U2 are powered by windings or connected to a power supply. When the connected power supply is the output voltage of the secondary output voltage soft-start circuit of this embodiment, the voltage needs to be stepped down to meet the operating voltage of the second operational amplifier U2. It should be noted that the output terminal of the operational amplifier module 11 is the output terminal of the second operational amplifier U2 (pin 1 of U2), the positive input terminal of the operational amplifier module is the positive input terminal of the second operational amplifier U2 (pin 3 of U2), the negative input terminal of the operational amplifier module is the negative input terminal of the second operational amplifier U2 (pin 2 of U2), the positive power input terminal of the operational amplifier module is the positive power input terminal of the second operational amplifier U2 (pin 5 of U2), and the negative power input terminal of the operational amplifier module is the negative power input terminal of the second operational amplifier U2 (pin 5 of U2).

[0040] In some embodiments, the end of the secondary loop control module 15 connected to the output terminal of the operational amplifier module 11 serves as the input terminal of the secondary output voltage soft-start circuit, which is used to connect to the primary soft-start circuit corresponding to the secondary output voltage soft-start circuit.

[0041] Furthermore, the secondary output voltage soft-start circuit of this embodiment also includes a voltage output module 16. The voltage output module 16 is provided with a positive voltage output port Vout+ and a negative voltage output port Vout-. The access terminal of the positive voltage output port is connected to one end of the secondary loop control module 15, and the connection terminal is also connected to the negative input terminal of the operational amplifier module 11. The access terminal of the negative voltage output port is connected to the signal ground.

[0042] In some embodiments, the secondary loop control module 15 includes a fourth capacitor C4 and a ninth resistor R9. One plate of the fourth capacitor C4 and one end of the ninth resistor R9 are connected to each other. The other end of the ninth resistor R9 is connected to the negative input terminal of the operational amplifier module 11. The other plate of the fourth capacitor C4 is connected to the output terminal of the operational amplifier module 11. One plate of the fourth capacitor C4 connected to the output terminal of the operational amplifier module 11 is the input terminal of the secondary output voltage soft-start circuit.

[0043] In some embodiments, the voltage output module 16 further includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a third capacitor C3. Specifically, one plate of the third capacitor C3, one end of the seventh resistor R7, and one end of the eighth resistor R8 are connected to the extension line of the contact point connecting the negative input terminal of the operational amplifier module 11 and one end of the ninth resistor R9. The other plate of the third capacitor C3 is connected to one end of the sixth resistor R6. The other ends of the sixth resistor R6 and the seventh resistor R7 are connected to the input terminal of the positive voltage output port, and the other end of the eighth resistor R8 is connected to signal ground.

[0044] like Figure 3 As shown, in this embodiment, the second operational amplifier U2 is powered by a winding and includes:

[0045] Transformer winding T (with iron core inductor coil), third diode D3, tenth resistor R10, eleventh resistor R11, eighth capacitor C8, ninth capacitor C9, Zener diode Z, transistor Q, tenth capacitor C10. Specifically, one end of transformer winding T is connected to the anode of the third diode D3. The cathode of the third diode D3 is connected to one end of the tenth resistor R10, one plate of the eighth capacitor C8, one end of the eleventh resistor R11, and the collector of transistor Q. The other end of the tenth resistor R10 serves as the positive terminal of the output voltage and is connected to the positive input terminal of the second operational amplifier U2 (pin 5 of U2). The emitter of transistor Q and one plate of the tenth capacitor C10 are connected to the power supply SVDD. The base of transistor Q is connected to the cathode of the Zener diode Z, the other end of the eleventh resistor R11, and one plate of the ninth capacitor. The other end of transformer winding T, the other plate of the eighth capacitor C8, the other plate of the ninth capacitor C9, the anode of the Zener diode Z, and the other plate of the tenth capacitor C10 serve as the negative terminal of the output voltage and are connected to signal ground. The negative terminal of the output voltage is connected to the negative input terminal of the second operational amplifier U2 (pin 4 of U2). Furthermore, the positive input terminal of the second operational amplifier U2 (pin 5) is connected to signal ground through capacitor C6.

[0046] Example 2:

[0047] like Figure 4 As shown, this embodiment provides a switching power supply, including a secondary output voltage soft-start circuit 1, a primary soft-start circuit 2, and an isolation circuit 3 as described in Embodiment 1 above. The primary soft-start circuit 2 and the secondary output voltage soft-start circuit 1 are both connected to the isolation circuit 3, and the isolation circuit 3 achieves interstage isolation between the primary soft-start circuit 2 and the secondary output voltage soft-start circuit 1.

[0048] In some embodiments, the primary soft-start circuit 2 includes a power management chip U3 and a fifth capacitor C5. The soft-start pin SS (pin 10) of the power management chip U3 is connected to one plate of the fifth capacitor C5, and the other plate of the fifth capacitor C5 is grounded. It should be noted that primary soft-start mainly includes SS soft-start (such as the power management chip model LM5022 in this embodiment) and COMP soft-start (such as the power management chip model UCC2843). It is understood that the power management chip U3 in this embodiment can also be UCC2843.

[0049] In some embodiments, the isolation circuit 3 is an optocoupler U4. The collector (pin 4) of the input side of the optocoupler U4 is connected to the error compensation pin COMP (pin 3) of the power management chip U3. The emitter (pin 3) of the input side of the optocoupler U4 is connected to the feedback pin FB (pin 2) of the power management chip U3. The positive terminal (pin 1) of the output side of the optocoupler U4 is connected to the power supply SVDD. The negative terminal (pin 2) of the output side of the optocoupler U4 is connected to the input terminal of the secondary output voltage soft-start circuit 1.

[0050] Furthermore, a capacitor C7 connects the collector (pin 4) on the input side of optocoupler U4 to ground between the error compensation pin COMP (pin 3) of power management chip U3. The emitter (pin 3) on the input side of optocoupler U4 is connected to ground between the feedback pin FB (pin 2) of power management chip U3.

[0051] It should be noted that after the switching power supply is turned on, if the secondary output voltage soft-start circuit cannot be powered, that is, the power supply SVDD does not reach the operating voltage of the operational amplifier module (e.g., 5V), or the voltage at pin 3 of the operational amplifier module is higher than the voltage at pin 2, the output voltage rise rate of the secondary output voltage soft-start circuit is controlled by the primary soft-start circuit. When the secondary output voltage soft-start circuit is powered normally, and at the same time, the voltage at pin 3 of the operational amplifier module is lower than the voltage at pin 2, the secondary output voltage soft-start circuit starts to work, and its output voltage rise rate is controlled by the secondary soft-start module until the voltage at pin 3 of the operational amplifier module reaches the reference voltage, at which point the soft start ends.

[0052] It should be further explained that the secondary output voltage soft-start circuit adds a voltage follower pre-bias module. The pre-bias voltage is set through the second resistor R2 and the third resistor R3. The calculation formula for the pre-bias voltage is shown in Example 1. When the switching power supply is powered on, the power supply reaches the operating voltage of the operational amplifier module. The voltage follower circuit quickly charges the voltage at the positive input signal terminal of the operational amplifier (pin 3 of U2) to the pre-bias voltage. The pre-bias voltage at the positive input terminal of the operational amplifier module (pin 3 of U2) is further charged to a level higher than the negative input terminal of the operational amplifier module (pin 2 of U) when the primary soft-start circuit is connected. When the primary soft-start circuit is connected, the secondary output voltage soft-start circuit does not (or to a limited extent) restrict the gradual opening of the duty cycle of the primary soft-start circuit, and there is no drop (or dip) in the output voltage during the rise, achieving a monotonically rising waveform during power-on. Therefore, throughout the entire power-on process of the switching power supply, the duty cycle of the primary switching transistor gradually increases, solving the problem of easy drops or dips in the output voltage during the rise after power-on, and achieving the goal of a monotonically rising output voltage.

[0053] The above embodiments are merely specific examples and do not indicate that this utility model is implemented in only one way. The above descriptions are only preferred embodiments of this utility model. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this utility model. Furthermore, under the teachings of this utility model, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this utility model.

Claims

1. A soft-start circuit for secondary output voltage, characterized in that, It includes an operational amplifier module, a secondary soft-start module, a voltage follower pre-bias module, a reference voltage module, and a secondary loop control module; The output terminal and negative input terminal of the operational amplifier module are connected to the two ends of the secondary loop control module. The positive input terminal of the operational amplifier module is connected to the voltage follower pre-bias module and the reference voltage module through the secondary soft-start module. The reference voltage module is connected to the voltage follower pre-bias module.

2. The secondary output voltage soft-start circuit according to claim 1, characterized in that, The secondary soft-start module includes a first resistor R1 and a first capacitor C1. One end of the first resistor R1 and one plate of the first capacitor C1 are connected to the positive input terminal of the operational amplifier module.

3. The secondary output voltage soft-start circuit according to claim 2, characterized in that, The voltage follower pre-bias module includes a first operational amplifier U1, a second resistor R2, a third resistor R3, and a first diode D1; One end of the second resistor R2 and one end of the third resistor R3 are connected to the positive input terminal of the first operational amplifier U1, and the output terminal of the first operational amplifier U1 is connected to the anode of the first diode D1; the negative input terminal of the first operational amplifier U1 and the cathode of the first diode D1 are connected between one plate of the first capacitor C1 and the positive input terminal of the operational amplifier module, and are located on the branch of the parallel first resistor R1 and the first capacitor C1.

4. The secondary output voltage soft-start circuit according to claim 3, characterized in that, The reference voltage module includes a fourth resistor R4, a fifth resistor R5, a second capacitor C2, and a second diode D2; The other end of the first resistor R1, the cathode of the second diode D2, one plate of the second capacitor C2, one end of the fourth resistor R4, and the other end of the third resistor R3 are all connected to the power supply through the fifth resistor R5. The other end of the first capacitor C1, the anode of the second diode D2, the other plate of the second capacitor C2, the other end of the fourth resistor R4, and the other end of the second resistor R2 are all connected to the signal ground. The anode of the second diode D2 is also connected to the power supply through the fifth resistor R5.

5. A secondary output voltage soft-start circuit according to any one of claims 1-4, characterized in that, The operational amplifier module includes a second operational amplifier U2, which is powered by windings or connected to a power supply.

6. The secondary output voltage soft-start circuit according to claim 1, characterized in that, One end of the secondary loop control module connected to the output of the operational amplifier module serves as the input of the secondary output voltage soft-start circuit, and is used to connect to the primary soft-start circuit corresponding to the secondary output voltage soft-start circuit. It also includes a voltage output module, which has a positive voltage output port and a negative voltage output port. The input terminal of the positive voltage output port is connected to the end of the secondary loop control module that is connected to the negative input terminal of the operational amplifier module, and the input terminal of the negative voltage output port is connected to the signal ground.

7. A secondary output voltage soft-start circuit according to claim 6, characterized in that, The secondary loop control module includes a fourth capacitor C4 and a ninth resistor R9. One plate of the fourth capacitor C4 and one end of the ninth resistor R9 are connected to each other. The other end of the ninth resistor R9 is connected to the negative input terminal of the operational amplifier module. The other plate of the fourth capacitor C4 is connected to the output terminal of the operational amplifier module. One plate of the fourth capacitor C4 connected to the output terminal of the operational amplifier module is the input terminal of the secondary output voltage soft-start circuit.

8. The secondary output voltage soft-start circuit according to claim 7, characterized in that, The voltage output module also includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a third capacitor C3; One plate of the third capacitor C3, one end of the seventh resistor R7, and one end of the eighth resistor R8 are connected to the extension line of the contact point connecting the negative input terminal of the operational amplifier module and one end of the ninth resistor R9. The other plate of the third capacitor C3 is connected to one end of the sixth resistor R6. The other ends of the sixth resistor R6 and the seventh resistor R7 are connected to the input terminal of the positive voltage output port. The other end of the eighth resistor R8 is connected to signal ground.

9. A switching power supply, characterized in that, The invention includes a secondary output voltage soft-start circuit, a primary soft-start circuit, and an isolation circuit as described in any one of claims 1-8, wherein the primary soft-start circuit and the secondary output voltage soft-start circuit are both connected to the isolation circuit, and interstage isolation between the primary soft-start circuit and the secondary output voltage soft-start circuit is achieved through the isolation circuit.

10. A switching power supply according to claim 9, characterized in that, The primary soft-start circuit includes a power management chip U3 and a fifth capacitor C5. The soft-start pin of the power management chip U3 is connected to one plate of the fifth capacitor C5, and the other plate of the fifth capacitor C5 is grounded. The isolation circuit is an optocoupler U4. The collector of the input side of the optocoupler U4 is connected to the error compensation pin of the power management chip U3, the emitter of the input side of the optocoupler U4 is connected to the feedback pin of the power management chip U3, the positive terminal of the output side of the optocoupler U4 is connected to the power supply, and the negative terminal of the output side of the optocoupler U4 is connected to the input terminal of the secondary output voltage soft-start circuit.

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