Switching power supply control circuit and chip

Abstract

The embodiment of the utility model discloses a switching power supply control circuit and a chip, which are applied to a switching power supply with a power tube, and comprise a first comparison module of which the first input end is connected with a first voltage end and the second input end is connected with an output voltage feedback end; the voltage selection module is connected with the output end of the first comparison module, the output voltage feedback end and the first voltage end, and the output end of the voltage selection module outputs the output voltage feedback end voltage or the first voltage end voltage corresponding to the output end signal of the first comparison module; the first input end of the second comparison module is connected with the sampling end, and the second input end of the second comparison module is connected with the output end of the voltage selection module; the input end of the control module is connected with the output end of the second comparison module, the control module generates a grid driving signal according to the output end signal of the second comparison module, and the output end of the control module is used for being connected with the grid of the power tube. Compared with the prior art, the circuit redundancy is less, and the power consumption of the switching power supply control circuit is effectively reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of integrated circuits, and in particular to a switching power supply control circuit and a chip. Background Art

[0002] With the continuous development of science and technology, various electronic devices have long been popularized in human life. At present, many devices require DC power supply. However, the mains power is usually AC. Therefore, it is necessary to convert AC into DC before supplying power to the load. For this reason, AC / DC switching power supplies have been widely used. For switching power supplies that drive higher power, they usually have a constant power mode to stably drive the load. However, the switching power supplies in the prior art have voltage and current control defects, resulting in high power consumption of the switching power supply control circuit. Utility Model Content

[0003] The purpose of the embodiment of the utility model is to provide a switch power supply control circuit and chip to solve the above problems. The embodiment of the utility model achieves the above purpose through the following technical solutions.

[0004] The embodiment of the utility model provides a switching power supply control circuit, which is applied to a switching power supply with a power tube, including: a first comparison module, whose first input terminal is connected to the first voltage terminal, and whose second input terminal is connected to the output voltage feedback terminal; a voltage selection module, which is respectively connected to the output terminal, the output voltage feedback terminal, and the first voltage terminal of the first comparison module, and whose output terminal outputs the output voltage feedback terminal voltage or the first voltage terminal voltage corresponding to the output terminal signal of the first comparison module; a second comparison module, whose first input terminal is connected to the sampling terminal, and whose second input terminal is connected to the output terminal of the voltage selection module; a control module, whose input terminal is connected to the output terminal of the second comparison module, the control module generates a gate drive signal according to the output terminal signal of the second comparison module, and the output terminal of the control module is used to be connected to the gate of the power tube.

[0005] In some embodiments, the voltage selection module is configured to select a lower voltage between the output voltage feedback terminal voltage and the first voltage terminal voltage based on the output terminal signal of the first comparison module to output through the output terminal of the voltage selection module.

[0006] In some embodiments, the voltage selection module includes: a first switch tube, a first end of which is connected to the second input end of the second comparison module, a second end of which is connected to the output end of the first comparison module, and a third end of which is connected to the first voltage end; a reverse unit, an input end of which is connected to the output end of the first comparison module; a second switch tube, a first end of which is connected to the second input end of the second comparison module, a second end of which is connected to the output end of the reverse unit, and a third end of which is connected to the output voltage feedback end.

[0007] In some embodiments, the first input terminal of the first comparison module is a non-inverting input terminal, the second input terminal of the first comparison module is an inverting input terminal, the second terminal of the first switch tube is a gate, and the second terminal of the second switch tube is a gate.

[0008] In some embodiments, the switching power supply control circuit provided in this embodiment also includes: a third comparison module, whose first input terminal is connected to the sampling terminal, whose second input terminal is connected to the second voltage terminal, whose output terminal and the output terminal of the first comparison module are respectively connected to the control module, and the control module is configured to determine whether the switching power supply is overcurrent through the output terminal signal of the third comparison module when the output terminal signal of the first comparison module indicates that the switching power supply is in a constant power state.

[0009] In some embodiments, the control module includes: an overcurrent protection counter, one end of which is connected to the output end of the third comparison module, and the other end of which is connected to the output end of the first comparison module; an overcurrent trigger unit, which is connected to the overcurrent protection counter and triggers the overcurrent protection processing when the output end signal of the third comparison module meets the overcurrent counting condition.

[0010] In some embodiments, the control module includes a pulse width modulation unit and an oscillator. The pulse width modulation unit is connected to the oscillator and the second comparison module respectively. The pulse width modulation unit is configured to generate a gate drive signal by performing logic operations on signals output by the oscillator and the second comparison module respectively.

[0011] In some embodiments, the switching power supply includes a forward switching power supply and a flyback switching power supply.

[0012] In some embodiments, the switching power supply control circuit includes: a reference current source, one end of which is connected to a third voltage terminal; a resistor, connected between the other end of the reference current source and a reference ground terminal; a feedback branch, connected between the other end of the reference current source and the reference ground terminal, the feedback branch generates a current signal representing the magnitude of the output voltage of the switching power supply, and the other end of the reference current source serves as an output voltage feedback terminal.

[0013] An embodiment of the utility model further provides a switching power supply control chip, and the switching power supply control chip includes the switching power supply control circuit provided by any of the above embodiments.

[0014] The switching power supply control circuit and chip provided in this embodiment are applied to a switching power supply with a power tube, and include: a first comparison module, a voltage selection module, a second comparison module and a control module. Compared with the prior art, in the switching power supply control circuit provided in this embodiment, the comparison process of the second comparison module is performed after the working output of the first comparison module, and the PWM signals output by the first comparison module and the second comparison module will not be lost. The control module only needs to perform signal modulation on the signal output by the second comparison module, and can directly perform corresponding logic processing on the PWM signal output by the second comparison module. Therefore, there is no need to specially adjust the output signals of the first comparison module and the second comparison module, and there is no need to specially design a circuit to reasonably adjust the corresponding time of the output of the first comparison module and the second comparison module. The circuit part has less redundancy, which effectively reduces the power consumption of the switching power supply control circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the description of the embodiments of the utility model will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 The invention is a circuit structure diagram of a switching power supply in the prior art.

[0017] Figure 2 It is a structural schematic diagram of a switching power supply control circuit provided by an embodiment of the utility model.

[0018] Figure 3 It is another structural schematic diagram of the switching power supply control circuit provided by an embodiment of the utility model.

[0019] Figure 4 This is another structural schematic diagram of the switching power supply control circuit provided by an embodiment of the utility model.

[0020] Figure 5 It is a waveform diagram of pulse width modulation of a control module in a switching power supply control circuit provided by an embodiment of the utility model.

[0021] Figure 6 It is a circuit diagram of a switching power supply control circuit provided by an embodiment of the utility model. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0023] In order to more clearly understand the technical solution of the embodiment of the utility model, the prior art described in the background technology is further explained below. Figure 1 The figure shows a common forward switching power supply circuit structure on the market. The alternating current is converted into direct current through the rectifier module, and the primary side electric energy is transmitted to the secondary side through the mutual inductance of the transformer. In the process of controlling the switching power supply, it is necessary to generate a gate drive signal based on the voltage of the sampling resistor R1 on the primary side and the output voltage of the secondary side, so as to control the on-off state of the power tube M. In the prior art, the voltage of the sampling resistor R1 is usually compared with the output voltage of the secondary side, and the voltage of the sampling resistor R1 and the output voltage of the secondary side are respectively compared with a plurality of preset voltages. In theory, this method can limit the voltage and current of the switching power supply within the preset value. However, the inventor of the utility model has found that in the comparison process in the prior art, it is necessary to pay special attention to the mismatch of the corresponding time of the output of each comparator in the switching of each comparator, which causes the PWM signal output by each comparator to disappear, and the PWM signal output by each comparator cannot be processed in time. The corresponding logic processing is then required, and a specially designed circuit is required to reasonably allocate the corresponding time of the output of each comparator, resulting in excessive redundancy of the circuit part and excessive power consumption of the switching power supply control circuit. Based on this, the inventor of the present invention proposes a switching power supply control circuit and chip in the embodiment of the present invention to solve the problems existing in the switching power supply in the prior art. The following is a detailed description of a switching power supply control circuit and chip provided by the present invention.

[0024] like Figure 2As shown, the switching power supply control circuit provided in this embodiment is applied to a switching power supply having a power tube M, and the switching power supply control circuit includes a first comparison module 10, a voltage selection module 11, a second comparison module 12 and a control module 13. Among them, the first input end of the first comparison module 10 is connected to the first voltage end, and the second input end of the first comparison module 10 is connected to the output voltage feedback end. The voltage selection module 11 is respectively connected to the output end, the output voltage feedback end, and the first voltage end of the first comparison module 10, and the output end of the voltage selection module 11 outputs the output voltage feedback end voltage V1 or the first voltage end voltage Vth1 corresponding to the output end signal of the first comparison module 10. The first input end of the second comparison module 12 is connected to the sampling end, and the second input end of the second comparison module 12 is connected to the output end of the voltage selection module 11. The input end of the control module 13 is connected to the output end of the second comparison module 12, and the control module 13 generates a gate drive signal Gate according to the output end signal of the second comparison module 12, and the output end of the control module 13 is used to connect to the gate of the power tube M.

[0025] In this embodiment, the switching power supply can be Figure 1 The forward switching power supply shown in FIG. 1 can also be a flyback switching power supply. Figure 1 Taking the circuit structure shown as an example, the power tube M can be connected in series with the primary coil of the transformer, and the alternating current is rectified by the rectifier module to output direct current. When the power tube M is turned on, the inductor stores electrical energy. When the power tube M is turned off, the inductor transfers the stored electrical energy to the load. When the power tube M is in the on state and the off state, the current of the power tube M and the primary coil of the transformer can be reflected by the current obtained from the sampling resistor R1.

[0026] It should be noted that the output voltage feedback terminal in the present embodiment can be any endpoint in the switching power supply and the switching power supply control circuit that can characterize the magnitude of the output voltage of the switching power supply. That is, the output voltage feedback terminal can be located in the primary side circuit or the secondary side circuit of the switching power supply. For example, the output voltage feedback terminal can be directly or indirectly connected to the secondary side output port OUT of the switching power supply on the secondary side of the switching power supply, or it can be a port located on the primary side of the switching power supply and directly or indirectly connected to a circuit that can indirectly detect the output voltage of the switching power supply. Therefore, no specific restrictions are made here on the specific position of the output voltage feedback terminal, nor are specific restrictions made on obtaining the voltage of the output voltage feedback terminal.

[0027] In this embodiment, the first voltage terminal can provide a first preset voltage. The voltage Vth1 of the first voltage terminal can limit the maximum charging time of the switching power supply, and further limit the corresponding maximum current in the constant voltage mode.

[0028] In this embodiment, the sampling end can be any end point in the switching power supply and the switching power supply control circuit that can represent the current magnitude of the primary coil of the transformer in the switching power supply. Usually, the sampling end, the sampling resistor R1, the power tube M, and the primary coil are in the same loop. Figure 1 As shown, the sampling end can be directly or indirectly connected to the common connection formed by the power tube M and the sampling resistor R1.

[0029] In this embodiment, the first comparison module 10 can compare the output voltage feedback terminal voltage V1 with the first voltage terminal voltage Vth1, the voltage selection module 11 can obtain the output terminal signal of the first comparison module 10, and output the first voltage terminal voltage Vth1 or the output voltage feedback terminal voltage V1 according to the output terminal signal, the second comparison module 12 compares the first voltage terminal voltage Vth1 or the output voltage feedback terminal voltage V1 with the sampling terminal voltage V2, and outputs a signal through the output terminal of the second comparison module 12, and the control module 13 generates a gate drive signal Gate according to the output terminal signal of the second comparison module 12, thereby controlling the on-off state of the power tube M in the switching power supply.

[0030] In this embodiment, the comparison process of the second comparison module 12 is performed after the working output of the first comparison module 10, and the PWM signals output by the first comparison module 10 and the second comparison module 12 will not be lost. The control module 13 only needs to perform signal modulation on the signal output by the second comparison module 12, and can directly perform corresponding logic processing on the PWM signal output by the second comparison module 12. Therefore, there is no need to specially adjust the output signals of the first comparison module 10 and the second comparison module 12, and there is no need to specially design a circuit to reasonably adjust the corresponding time of the output of the first comparison module 10 and the second comparison module 12. The circuit has less redundancy, which effectively reduces the power consumption of the switching power supply control circuit.

[0031] In some embodiments, the voltage selection module 11 in the switching power supply control circuit can be configured to select the lower voltage between the output voltage feedback terminal voltage V1 and the first voltage terminal voltage Vth1 based on the output terminal signal of the first comparison module 10 and output it through the output terminal of the voltage selection module 11.

[0032] Specifically, when the output signal of the first comparison module 10 indicates that the output voltage feedback terminal voltage V1 is greater than the first voltage terminal voltage Vth1, the output end of the voltage selection module 11 can output the first voltage terminal voltage Vth1; when the output signal of the first comparison module 10 indicates that the output voltage feedback terminal voltage V1 is less than the first voltage terminal voltage Vth1, the output end of the voltage selection module 11 can output the output voltage feedback terminal voltage V1.

[0033] In this embodiment, the on-off state of the power tube M can be controlled by the real-time feedback output voltage feedback terminal voltage V1 and the output voltage feedback terminal voltage V1 in the constant power state.

[0034] In some embodiments, Figure 3 As shown, the voltage selection module 11 in the switch power supply control circuit may include a first switch tube Q1, a second switch tube Q2 and an inverting unit INV. Among them, the first end of the first switch tube Q1 is connected to the second input end of the second comparison module 12, the second end of the first switch tube Q1 is connected to the output end of the first comparison module 10, and the third end of the first switch tube Q1 is connected to the first voltage end. The input end of the inverting unit INV is connected to the output end of the first comparison module 10. The first end of the second switch tube Q2 is connected to the second input end of the second comparison module 12, the second end of the second switch tube Q2 is connected to the output end of the inverting unit INV, and the third end of the second switch tube Q2 is connected to the output voltage feedback end.

[0035] In this embodiment, the first switch tube Q1 and the second switch tube Q2 can be various types of switches, such as P-type metal oxide semiconductor field effect transistor, N-type metal oxide semiconductor field effect transistor, P-channel junction field effect transistor, N-channel junction field effect transistor, etc., and there is no specific restriction on the specific types of the first switch tube Q1 and the second switch tube Q2.

[0036] like Figure 3 As shown, the first comparison module 10 may be a comparator Comp1, and the second comparison module 12 may be a comparator Comp2.

[0037] In some embodiments, the first input terminal of the first comparison module 10 may be a non-inverting input terminal, the second input terminal of the first comparison module 10 may be an inverting input terminal, the second terminal of the first switch tube Q1 may be a gate, and the second terminal of the second switch tube Q2 may be a gate.

[0038] In this embodiment, when the comparator Cmop1 outputs a high level, it indicates that the first voltage terminal voltage Vth1 is greater than the output voltage feedback terminal voltage V1. At this time, the first switch tube Q1 and the second switch tube Q2 can be N-type metal oxide semi-conductor field effect transistors, the first switch tube Q1 is turned on, the second switch tube Q2 is turned off, the second input terminal voltage of the comparator Comp2 is the first voltage terminal voltage Vth1, and the comparator Comp2 transmits the comparison result of the second voltage terminal voltage Vth2 and the sampling terminal voltage V2 to the control module 13. When the comparator Cmop1 outputs a low level, it indicates that the first voltage terminal voltage Vth1 is less than the output voltage feedback terminal voltage V1. At this time, the first switch tube Q1 and the second switch tube Q2 can be N-type metal oxide semi-conductor field effect transistors, the first switch tube Q1 is turned off, the second switch tube Q2 is turned on, the second input terminal voltage of the comparator Comp2 is the output voltage feedback terminal voltage V1, and the comparator Comp2 transmits the comparison result of the output voltage feedback terminal voltage V1 and the sampling terminal voltage V2 to the control module 13.

[0039] It should be noted that the connection method between the positive input terminal and the negative input terminal of the first comparison module 10 and the output voltage feedback terminal, the first voltage terminal, the connection method between the positive input terminal and the negative input terminal of the second comparison module 12 and the sampling terminal, the output terminal of the voltage selection module 11, and the switching type of the first switch tube Q1 and the second switch tube Q2 can also be set based on actual needs.

[0040] In some embodiments, Figure 4 As shown, the switch power supply control circuit may further include a third comparison module. A first input terminal of the third comparison module is connected to the sampling terminal, a second input terminal of the third comparison module is connected to the second voltage terminal, an output terminal of the third comparison module and an output terminal of the first comparison module 10 are respectively connected to the control module 13, and the control module 13 is configured to determine whether the switch power supply is overcurrent through the output terminal signal of the third comparison module when the output terminal signal of the first comparison module 10 indicates that the switch power supply is in a constant power state.

[0041] In this embodiment, the second voltage terminal can provide a second preset voltage, and the second voltage terminal voltage Vth2 can limit the maximum output current allowed by the switching power supply. The second voltage terminal voltage Vth2 is less than the first voltage terminal voltage Vth1.

[0042] In this embodiment, when the output terminal signal of the first comparison module 10 indicates that the output voltage feedback terminal voltage V1 is greater than the first voltage terminal voltage Vth1, it indicates that the switching power supply is in a constant power state, and the switching power supply can operate in a continuous conduction mode. If the output terminal signal of the third comparison module indicates that the sampling terminal voltage V2 is greater than the second voltage terminal voltage Vth2, it indicates that the switching power supply is overcurrent.

[0043] It should be noted that the maximum output current of the switching power supply described in the embodiments of the present invention and the maximum current flowing through the power tube M in the switching power supply can both be regarded as average currents.

[0044] In this embodiment, the voltage at the sampling end can be detected, and the maximum output current allowed by the switching power supply can be displayed by presetting the second voltage end voltage Vth2, thereby limiting the maximum current of the switching power supply, avoiding excessive primary and secondary currents of the switching power supply, and reducing the risk of overcurrent in the switching power supply and the system circuit used by the switching power supply.

[0045] In some embodiments, the control module 13 in the switch power supply control circuit may include an overcurrent protection counter and an overcurrent trigger unit. One end of the overcurrent protection counter is connected to the output end of the third comparison module, and the other end of the overcurrent protection counter is connected to the output end of the first comparison module 10. The overcurrent trigger unit is connected to the overcurrent protection counter, and triggers the overcurrent protection process when the output end signal of the third comparison module meets the overcurrent counting condition.

[0046] In this embodiment, if the signal outputted from the output terminal of the first comparison module 10 can indicate that the switching power supply currently enters the constant power state, the overcurrent protection counter and the overcurrent trigger unit can determine whether overcurrent protection processing is required by counting. That is, if the signal at the output terminal of the first comparison module 10 is that the output voltage feedback terminal voltage V1 is greater than the first voltage terminal voltage Vth1, the overcurrent protection counter can obtain the signal and perform corresponding counting processing.

[0047] In this embodiment, the overcurrent protection counter can calculate the preset number of pulses of the output terminal signal of the third comparison module through the clock signal, and then calculate the duration of the sampling terminal voltage V2 greater than the second voltage terminal voltage Vth2. If the overcurrent trigger unit determines that the duration is greater than the preset duration, the overcurrent protection process is triggered. The overcurrent protection counter can also calculate the preset number of pulses of the output terminal signal of the third comparison module within a specified counting cycle through the clock signal, and then calculate the proportion of the time when the sampling terminal voltage V2 is greater than the second voltage terminal voltage Vth2 in the specified counting cycle. If the overcurrent trigger unit determines that the proportion is greater than the preset proportion, the overcurrent protection process is triggered. Among them, the preset pulse can be a pulse in which the sampling terminal voltage V2 is greater than the second voltage terminal voltage Vth2. There is no specific restriction on the overcurrent counting conditions here.

[0048] In this embodiment, by providing an overcurrent protection counter and an overcurrent trigger unit, it is possible to effectively prevent the overcurrent protection from being falsely triggered, thereby maintaining the normal operation of the switching power supply.

[0049] In some embodiments, the control module 13 in the switch power supply control circuit may include a pulse width modulation unit and an oscillator. The pulse width modulation unit is connected to the oscillator and the second comparison module 12 respectively, and the pulse width modulation unit is configured to generate a gate drive signal Gate by performing a logic operation on the signals outputted by the oscillator and the second comparison module 12 respectively.

[0050] like Figure 5 As shown, the oscillator can continuously output a clock signal CLK of a specified frequency, the output signal of the second comparison module 12 is COMP, and the pulse width modulation unit can perform a logic operation on the clock signal CLK and the output signal COMP of the second comparison module 12 to generate a gate drive signal Gate.

[0051] In some embodiments, the switching power supply may include a forward switching power supply and a flyback switching power supply.

[0052] In some embodiments, Figure 6 As shown, the switching power supply control circuit may further include a reference current source Iref, a resistor R2 and a feedback branch 15. One end of the reference current source Iref is connected to the third voltage terminal. The resistor R2 is connected between the other end of the reference current source Iref and the reference ground terminal GND. The feedback branch 15 is connected between the other end of the reference current source Iref and the reference ground terminal GND, and the feedback branch 15 generates a current signal representing the magnitude of the output voltage of the switching power supply, and the other end of the reference current source Iref serves as an output voltage feedback terminal.

[0053] In this embodiment, the feedback branch may include a feedback current I1. When the output voltage of the switching power supply increases or decreases, the feedback current I1 may change accordingly, so that the voltage at the common point formed by the feedback branch 15, the reference current source Iref, and the resistor R2 changes accordingly, and the common point formed by the feedback branch 15, the reference current source Iref, and the resistor R2 is used as the output voltage feedback terminal. In addition, the third voltage terminal voltage V3 may be a power supply voltage.

[0054] It should be noted that the specific method of generating the feedback current I1 is not specifically limited here.

[0055] An embodiment of the utility model further provides a switching power supply control chip, and the switching power supply control chip includes the switching power supply control circuit provided by any of the above embodiments.

[0056] Since the circuit structure and working mode of the switching power supply control circuit in the switching power supply control chip in this embodiment are the same as those of the switching power supply control circuit in the previous embodiment, they will not be described in detail here.

[0057] In this embodiment, one or more of the first voltage terminal, the second voltage terminal, the sampling terminal, and the output voltage feedback terminal can be built into the switching power supply control chip. There is no specific restriction on the locations of the first voltage terminal, the second voltage terminal, the sampling terminal, and the output voltage feedback terminal.

[0058] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A switching power supply control circuit, characterized in that: Applicable to switching power supplies with power tubes, including: A first comparison module, a first input terminal of which is connected to the first voltage terminal, and a second input terminal of which is connected to the output voltage feedback terminal; a voltage selection module, which is connected to the output terminal of the first comparison module, the output voltage feedback terminal, and the first voltage terminal respectively, and whose output terminal outputs the output voltage feedback terminal voltage or the first voltage terminal voltage corresponding to the output terminal signal of the first comparison module; A second comparison module, a first input terminal of which is connected to the sampling terminal, and a second input terminal of which is connected to the output terminal of the voltage selection module; A control module, whose input end is connected to the output end of the second comparison module, the control module generates a gate drive signal according to the output end signal of the second comparison module, and the output end of the control module is used to be connected to the gate of the power tube.

2. The switching power supply control circuit according to claim 1, characterized in that: The voltage selection module is configured to select a lower voltage between the output voltage feedback terminal voltage and the first voltage terminal voltage based on the output terminal signal of the first comparison module and output it through the output terminal of the voltage selection module.

3. The switching power supply control circuit according to claim 1, characterized in that: The voltage selection module comprises: A first switch tube, a first end of which is connected to the second input end of the second comparison module, a second end of which is connected to the output end of the first comparison module, and a third end of which is connected to the first voltage end; a reverse unit, whose input terminal is connected to the output terminal of the first comparison module; A second switch tube has a first end connected to the second input end of the second comparison module, a second end connected to the output end of the inverting unit, and a third end connected to the output voltage feedback end.

4. The switching power supply control circuit according to claim 3, characterized in that: The first input end of the first comparison module is a non-inverting input end, the second input end of the first comparison module is an inverting input end, the second end of the first switch tube is a gate, and the second end of the second switch tube is a gate.

5. The switching power supply control circuit according to claim 1, characterized in that: Also includes: A third comparison module, wherein a first input terminal is connected to the sampling terminal, a second input terminal is connected to the second voltage terminal, an output terminal and an output terminal of the first comparison module are respectively connected to the control module, and the control module is configured to determine whether the switching power supply is overcurrent through an output terminal signal of the third comparison module when an output terminal signal of the first comparison module indicates that the switching power supply is in a constant power state.

6. The switching power supply control circuit according to claim 5, characterized in that: The control module comprises: an overcurrent protection counter, one end of which is connected to the output end of the third comparison module, and the other end of which is connected to the output end of the first comparison module; An overcurrent trigger unit is connected to the overcurrent protection counter and triggers overcurrent protection processing when the output terminal signal of the third comparison module meets the overcurrent counting condition.

7. The switching power supply control circuit according to claim 1, characterized in that: The control module includes a pulse width modulation unit and an oscillator. The pulse width modulation unit is connected to the oscillator and the second comparison module respectively. The pulse width modulation unit is configured to generate the gate driving signal by performing logic operations on signals outputted by the oscillator and the second comparison module respectively.

8. The switching power supply control circuit according to any one of claims 1 to 7, characterized in that: The switching power supply includes a forward switching power supply and a flyback switching power supply.

9. The switching power supply control circuit according to claim 8, characterized in that: include: A reference current source, one end of which is connected to the third voltage terminal; A resistor connected between the other end of the reference current source and a reference ground end; A feedback branch is connected between the other end of the reference current source and the reference ground end. The feedback branch generates a current signal representing the magnitude of the output voltage of the switching power supply. The other end of the reference current source serves as the output voltage feedback end.

10. A switching power supply control chip, characterized in that: The invention comprises a switching power supply control circuit as claimed in any one of claims 1 to 9.

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