Switching power supply and control method thereof

Abstract

The invention provides a switching power supply and a control method thereof, and the switching power supply comprises an inductor, a main power tube and an auxiliary power tube, and also comprises a first module which is connected between a first node and the control end of the auxiliary power tube, and the common connection end of the inductor and the main power tube is the first node; the self-powered circuit comprises a power supply capacitor and a linear voltage regulator, the linear voltage regulator is connected between the power supply capacitor and the connecting end of the main power tube and the auxiliary power tube, and the voltage of the connecting end of the main power tube and the auxiliary power tube charges the power supply capacitor through the linear voltage regulator; wherein the change rate of the voltage of the first node is adjusted through the first module, so that the change rate of the voltage of the first node reaches an expected change rate, and the charging current of the power supply capacitor is within an expected range. According to the invention, the current flowing through the capacitor module can be flexibly adjusted, and the EMI performance and the charging efficiency are effectively optimized.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a switching power supply and a control method thereof. Background Art

[0002] By using normally on power devices, self-starting and self-powering can be realized more conveniently. The self-starting function can save the need for additional resistor starting or high-voltage starting circuits, and the self-powering function can save the need for auxiliary winding power supply.

[0003] like Figure 1 As shown, it is a switching power supply of the prior art. The switching power supply takes a flyback converter as an example, and includes a main power tube Q1 and an auxiliary power tube Q2 connected in series and a self-powered circuit. The self-powered circuit includes an LDO (linear regulator) and a power supply capacitor C0. One end of the LDO is connected to the common connection end of the main power tube Q1 and the auxiliary power tube Q2, and the other end is connected to the power supply capacitor C0. The power supply capacitor C0 generates a power supply voltage VCC for powering the control chip of the switching power supply. The existing working waveform of the switching power supply is shown in FIG. Figure 2 As shown, during the conduction period of the main power tube Q1 and the auxiliary power tube Q2, the excitation inductor of the flyback converter stores energy, and the excitation inductor current I LM The voltage Vsw at the connection terminal SW between the main power tube Q1 and the primary winding and the voltage drop Vds_Q2 across the auxiliary power tube Q2 are low level. The control chip is powered by the power supply voltage VCC, and the VCC voltage drops.

[0004] When the auxiliary power tube Q2 is turned on, the voltage Vsw at the node SW decreases. By controlling the decreasing slope of the voltage Vsw, the EMI of the system can be optimized. LM After the auxiliary power tube Q2 is turned on, it starts to rise from zero, so a relatively large current I4 can be used to pull it down, causing the parasitic capacitor C EQ The voltage Vsw on the capacitor decreases, and the parasitic capacitance C can be adjusted by adjusting the current I4. EQ The falling slope of the upper voltage.

[0005] By increasing the current I4 flowing through the LDO, the parasitic capacitance C is pulled down EQ This will cause the power supply voltage VCC to be too high, which will lead to the problem that the LDO cannot pull the load. In order to deal with this problem, the LDO needs to add a clamping circuit. And if the excitation inductor used in the application is small, the excitation inductor current I LM The auxiliary power tube Q2 will increase significantly during its on-time, which will lead to I4-I LMThe decrease affects the Vsw falling slope, which in turn requires a large current I4 flowing through the LDO, resulting in the need to strengthen the pull-down capability of the power supply voltage VCC, resulting in a larger device selection and affecting the cost. Based on the above analysis, the existing measures for optimizing the system EMI performance cannot achieve satisfactory results. Summary of the invention

[0006] The object of the present invention is to provide a high-efficiency switching power supply for solving the problem of unsatisfactory EMI performance in the prior art.

[0007] The present invention provides a switching power supply, comprising an inductor, a main power tube and an auxiliary power tube, wherein the inductor is connected to a first end of the main power tube, the auxiliary power tube is connected between a second end of the main power tube and a ground end, and further comprising:

[0008] A first module is connected between a first node and a control end of the auxiliary power tube, and a common connection end of the inductor and the main power tube is the first node;

[0009] A self-powered circuit, comprising a power supply capacitor and a linear regulator, wherein the linear regulator is connected between the power supply capacitor and a connection end between the main power tube and the auxiliary power tube, and the voltage at the connection end between the main power tube and the auxiliary power tube charges the power supply capacitor through the linear regulator;

[0010] The change rate of the first node voltage is adjusted by the first module so that the change rate of the first node voltage reaches an expected change rate, and the charging current of the power supply capacitor is within an expected range.

[0011] Optionally, the first module adjusts the charging current of the power supply capacitor by adjusting the current flowing through the auxiliary power tube.

[0012] Optionally, the current flowing through the first module is adjusted by adjusting the driving current of the auxiliary power tube.

[0013] Optionally, the change rate of the first node voltage is adjusted by adjusting the change rate of the first module voltage, or adjusting the current flowing through the first module.

[0014] Optionally, the first module includes a capacitor module connected between the first node and the control end of the auxiliary power tube;

[0015] The change rate of the voltage of the first node is adjusted by adjusting the change rate of the voltage of the capacitor module.

[0016] Optionally, the first module includes:

[0017] a sampling circuit connected to the first node and configured to sample a change rate of the voltage of the first node to obtain a sampling signal representing the change rate;

[0018] A controlled current source is connected between the first node and the control end of the auxiliary power tube, and the sampling signal adjusts the magnitude of the output current of the controlled current source to adjust the current of the first module.

[0019] Optionally, the capacitor module includes one capacitor or a series-parallel combination of multiple capacitors.

[0020] Optionally, the current flowing through the capacitor module is adjusted to adjust the rate of change of the voltage across the capacitor module.

[0021] Optionally, a given fixed current flows through the capacitor module, and the capacitance value of the capacitor module is adjusted to adjust the rate of change of the voltage across the capacitor module.

[0022] Optionally, a driving circuit is included, connected to the control end of the auxiliary power tube, the driving circuit receives a PWM signal and outputs a driving current, and the PWM signal is used to drive the auxiliary power tube on and off;

[0023] By adjusting the magnitude of the driving current, the magnitude of the current flowing through the capacitor module is adjusted.

[0024] Optionally, during the turning-on process of the auxiliary power tube, the linear regulator is turned on and the power supply capacitor is charged.

[0025] Optionally, the current flowing through the linear regulator is set to be less than or equal to the current flowing through the main power tube.

[0026] Optionally, the power tube is a depletion-type transistor.

[0027] The present invention also provides a control method for a switching power supply, comprising an inductor, a main power tube and an auxiliary power tube, wherein the inductor is connected to a first end of the main power tube, the auxiliary power tube is connected between a second end of the main power tube and a ground end, and a common connection end of the inductor and the main power tube is recorded as a first node;

[0028] The voltage at the connection end of the main power tube and the auxiliary power tube charges the power supply capacitor through a linear regulator;

[0029] The change rate of the first node voltage is adjusted by the first module so that the change rate of the first node voltage reaches an expected change rate and the charging current of the power supply capacitor is within an expected range.

[0030] Optionally, the first module adjusts the charging current of the power supply capacitor by adjusting the current flowing through the auxiliary power tube.

[0031] Optionally, the current flowing through the first module is adjusted by adjusting the driving current of the auxiliary power tube.

[0032] Optionally, the change rate of the first node voltage is adjusted by adjusting the change rate of the first module voltage, or adjusting the current flowing through the first module.

[0033] Compared with the prior art, the present invention has the following advantages: the present invention introduces a first module, which is connected between a first node (a common connection end of the inductor and the main power tube) and a control end of the auxiliary power tube. The change rate of the voltage of the first node can be adjusted by adjusting the change rate of the voltage of the first module or adjusting the current flowing through the first module, thereby optimizing the EMI performance of the system; there are multiple adjustment methods for adjusting the change rate of the voltage of the first module, and the adjustment method is simple; in addition, the introduced first module can be combined with the power supply circuit, which will not affect the power supply effect and EMI performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the schematic diagram of the switching power supply in the prior art;

[0035] Figure 2 It is a working waveform diagram of the switching power supply in the prior art;

[0036] Figure 3 This is a block diagram of the switching power supply of the present invention;

[0037] Figure 4 This is a schematic diagram of a first module embodiment 1 of a switching power supply of the present invention;

[0038] Figure 5 This is a schematic diagram of a first module embodiment 2 of the switching power supply of the present invention;

[0039] Figure 6 This is a schematic diagram of Embodiment 3 of the first module of the switching power supply of the present invention;

[0040] Figure 7 This is a waveform diagram of the switching power supply of the present invention in the DCM working mode. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made on the spirit and range of the present invention.

[0042] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0043] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0044] like Figure 3 As shown, a working principle diagram of the switching power supply of the present invention is illustrated. The switching power supply is explained by taking a flyback converter as an example. However, in the present invention, the switching power supply is not limited to a flyback converter, and may also be a buck converter, a boost converter, etc. The flyback converter of this embodiment rectifies the AC input voltage AC to obtain a DC input voltage Vin. The main power tube Q1 and the primary winding Np of the transformer T are connected in series, and the connection node is the first node SW. The rectifier tube D0 and the secondary winding Ns of the transformer T are connected in series. By controlling the switching state of the main power tube Q1, the DC input voltage Vin is converted into an output voltage Vo through the transformer T. The main power tube Q1 of the present invention is a depletion-type transistor, preferably a depletion-type gallium nitride transistor, and the gate of the main power tube Q1 is grounded; there is a parasitic capacitance between the gate and drain of the main power tube Q1, and the primary winding of the transformer T also has a parasitic capacitance. There is also a parasitic capacitance on the connection path between the main power tube Q1 and the primary winding of the transformer T. These parasitic capacitances in the flyback converter are equivalent to the equivalent capacitance C in the figure. EQ The flyback converter also includes an auxiliary power tube Q2 connected to the main power tube Q1 and a drive circuit 02. The drive circuit 02 receives a PWM signal to control the on / off of the auxiliary power tube Q2. When PWM changes from invalid to valid, a pull-up drive current I is generated. GS , and then generate a high-level driving voltage to control the auxiliary power tube Q2 to turn on, or control the auxiliary power tube Q2 to turn on after a short delay when the PWM signal changes from invalid to valid. In short, the auxiliary power tube Q2 is turned on during the effective period of PWM, and when the PWM signal changes from valid to invalid, a pull-down driving current I is generated. GS , and then generate a low-level driving voltage to control the auxiliary power tube Q2 to turn off. The flyback converter also includes a self-powered circuit, and the self-powered circuit 03 includes an LDO (linear regulator) and a power supply capacitor C0. The first end of the LDO is connected to the common connection end of the main power tube Q1 and the auxiliary power tube Q2, and the second end of the LDO is connected to the first end of the power supply capacitor C0. The second end of the power supply capacitor C0 is grounded. The power supply capacitor C0 generates a power supply voltage VCC for powering the drive circuit 02. The power supply capacitor C0 is usually integrated outside the control chip, and the main power tube Q1, the auxiliary power tube Q2 and the LDO are integrated inside the chip.

[0045] The switching power supply of the present invention further includes a first module 01, which is connected between the first node and the control end of the auxiliary power tube Q2. Since one end of the first module 01 is connected to the first node SW, the present invention is designed to adjust the rate of change of the voltage on the first module 01 or the current I2 flowing through the first module to adjust the rate of change of the first node voltage Vsw to reach the expected rate of change, thereby optimizing the EMI of the system. The rate of change of the first node voltage is related to the rate of change of the voltage on the first module 01 or the current I2 flowing through the first module 01, preferably positively correlated, where the positive correlation means that the absolute value of the rate of change of the first node voltage is positively correlated to the absolute value of the rate of change of the voltage on the first module 01 or the absolute value of the current I2 flowing through the first module.

[0046] When the switching power supply has a self-powered circuit 03 as shown in the present invention, while adjusting the change rate of the first node through the first module 01, the power supply loss of the self-powered circuit can also be optimized through the first module 01 to improve the power supply efficiency. Specifically, the current I4 (I4 is less than or equal to I2) flowing through the LDO is set, the change rate of the first node voltage Vsw is large, and the current of the main power tube Q1 is large I3. When the change rate of the first node voltage Vsw needs to be reduced, the current I2 flowing through the first module 01 is adjusted to decrease, that is, the current drawn from the gate of the auxiliary power tube Q2 is reduced, so that the gate drive voltage Vg2 of the auxiliary power tube increases, and then the current I5 flowing through the auxiliary power tube Q2 is adjusted to increase, while the current I4 flowing through the LDO is always maintained at the set current, so that the sum of the currents I4 and I5 is always equal to I3. According to the above analysis, the first module 01 can automatically adjust the current I5 flowing through the auxiliary power tube Q2, so that the value of the current I4 flowing through the LDO is just the charging current of the power supply capacitor, without wasting energy. The first module 01 optimizes the charging energy of the power supply capacitor C0 while optimizing the system EMI.

[0047] like Figure 4 , Figure 5 As shown, it is a schematic diagram of Embodiment 1 and Embodiment 2 of the first module of the present invention. Figure 3 The first module in the embodiment includes a capacitor module, and the capacitor module includes a capacitor or a series-parallel combination of multiple capacitors. Figure 5 In the example, the capacitor module 01 includes a capacitor C0, and the capacitor C0 is connected between the first node SW and the gate control terminal of the auxiliary power tube Q2. Since the driving voltage of the gate of the auxiliary power tube Q2 is much smaller than the voltage Vsw of the first node, the voltage Vsw of the first node can be equivalent to the voltage across the capacitor 01, and then there is formula (1): Wherein, I2 is the current flowing through the capacitor C0 (the current direction is from the gate Gate2 of the auxiliary power tube Q2 to the first node SW), and Vsw is the voltage of the first node. It can be seen from formula (1) that when the capacitance value of the capacitor C0 is fixed, the change rate of the first node voltage Vsw can be adjusted by adjusting the current I2 flowing through the capacitor C0, and the EMI of the system can be optimized by adjusting the change rate to the ideal change rate. Preferably, the larger the current I2 flowing through the capacitor C0, the larger the change rate of the first node voltage Vsw, and I2 is proportional to the change rate.

[0048] Furthermore, since the capacitor C0 is connected to the control terminal of the auxiliary power tube Q2, the current I2 flowing through the capacitor C0 and the driving current I generated by the driving circuit 02 GS The Miller platform voltage of the auxiliary power tube Q2 is jointly determined, thereby determining the falling slope of the first node voltage Vsw. Therefore, by adjusting the driving current I GS The current I2 flowing through the capacitor 01 can be adjusted to adjust the rate of change of the first node voltage Vsw and optimize the system EMI; in addition, by adjusting the current I2 flowing through the capacitor 01, the current I5 flowing through the auxiliary power tube Q2 can also be adjusted to optimize the system power supply.

[0049] Furthermore, when a given fixed current flows through the capacitor module, the capacitance value of the capacitor module can be adjusted by adjusting the number of capacitors connected in parallel / series, thereby adjusting the rate of change of the first node voltage Vsw and optimizing system EMI.

[0050] like Figure 5 As shown, the capacitor module 01 includes multiple capacitors. In the figure, three capacitors are taken as an example. The capacitor C0 is connected between the first node SW and the auxiliary power tube Q2. The capacitor C1 and the switch K1 are connected in series and connected in parallel with the capacitor C0. The capacitor C2 and the switch K2 are connected in series and connected in parallel with the capacitor C0. The capacitor C0 can be a basic capacitor with a smaller capacitance in the capacitor module 01. In this embodiment, given a fixed current flowing through the capacitor module, the capacitance of the capacitor in the capacitor module 01 is adjusted by adjusting the number of capacitors connected in parallel, thereby adjusting the rate of change of the first node voltage Vsw. For example, when the rate of change of the first node voltage Vsw needs to be reduced, the capacitance of the capacitor needs to be increased, and the number of capacitors connected in parallel with the capacitor C0 is increased on the basis of the capacitor C0; when the rate of change of the first node voltage Vsw needs to be increased, the capacitance of the capacitor in the capacitor module needs to be reduced, and the number of capacitors connected in parallel with the capacitor C0 is reduced. The capacitance of the capacitor module 01 here refers to the total capacitance of all capacitors that can flow current in parallel. Furthermore, the capacitor module may also be a plurality of capacitors connected in series (not shown in the figure). Given a fixed current flowing through the capacitor module, the rate of change of the first node voltage Vsw is adjusted by adjusting the number of capacitors connected in series in the capacitor module, thereby optimizing the system EMI.

[0051] like Figure 6 As shown, the schematic diagram of the embodiment 3 of the first module of the present invention is shown. Figure 4 As described in the embodiment, the output current of the controlled current source I2 can be equivalent to the current flowing through the capacitor module, that is, the controlled current source I2 is equivalent to a capacitor model. Therefore, the output current of the controlled current source I2 is designed to be related to the change rate of the first node, and then the size of the controlled current source output current is controlled according to the change rate of the first node to adjust the change rate of the first node. Specifically, the first module 01 includes a sampling circuit 101, a sampling and holding circuit 102 and a controlled current source I2. The sampling circuit 101 includes a resistor R101 and a capacitor C101 connected in series. The first end of the capacitor C101 is connected to the first node SW, and the second end thereof is connected to the resistor R101. The second end of the resistor R101 is grounded. The voltage at the connection end of the resistor R101 and the capacitor C101 can represent the change rate of the first node voltage Vsw. The input end of the sampling and holding circuit 102 is connected to the common connection end of the resistor R101 and the capacitor C101. When the PWM signal is valid, the voltage at the ends of the resistor R101 and the capacitor C101 is sampled and held to obtain a sampling signal V1. The control end of the controlled current source I2 receives the sampling signal V1. The sampling signal V1 controls the magnitude of the output current of the controlled current source I2. The direction of the output current of the controlled current source I2 is from the gate of the auxiliary power tube Q2. Furthermore, the greater the change rate of the first node voltage, the smaller the output current of the controlled current source I2 is adjusted. For example, when the change rate of the first node voltage Vsw is large and the current flowing through the main power tube Q1 is large, the output current of the controlled current source I2 is reduced, thereby reducing the change rate of the first node voltage Vsw to reach the expected change rate. At the same time, since the current drawn from the gate of the auxiliary power tube Q2 is reduced, the gate drive voltage of the auxiliary power tube Q2 is increased, and then the current I5 flowing through the auxiliary power tube Q2 is increased, and the current flowing through the LDO is always maintained at the expected set current. This embodiment adjusts the current flowing through the first module by detecting the change rate of the first node voltage, which can optimize the EMI and power supply efficiency of the system.

[0052] like Figure 7 As shown in the figure, the working waveform of the switching power supply of the present invention in the DCM mode is shown. LMis the excitation inductor current waveform of the flyback converter, Vsw is the first node voltage waveform, VD2 is the auxiliary power tube Q2 drain voltage waveform, VCC is the power supply voltage waveform, PWM is the pulse width modulation signal obtained by the switching power supply, and Vg2 is the auxiliary power tube gate voltage waveform. At t1, when the PWM signal changes from low level invalid to high level valid, the auxiliary power tube Q2 is turned on, the LDO is also turned on, and the auxiliary power tube Q2 drain voltage VD2 decreases; in the t1-t2 time period, it is the turn-on process stage of the auxiliary power tube Q2, that is, the incomplete conduction stage. In this stage, the auxiliary power tube Q2 gate voltage Vg2 gradually rises to the Miller platform voltage until the Miller platform stage ends, the first node voltage Vsw charges the power supply capacitor through the normally open main power tube Q1 and LDO, the power supply voltage VCC begins to rise, the first node voltage Vsw decreases, the excitation inductor is charged, and the excitation inductor current I LM At time t2, the auxiliary power tube Q2 is fully turned on, the drain voltage of the auxiliary power tube Q2 drops to a low level, the first node voltage Vsw drops to a low level, the LDO is short-circuited and turned off, the power supply capacitor stops charging, and the power supply voltage VCC stops rising; in the t2-t3 time period, as the auxiliary power tube Q2 is fully turned on, the excitation inductor continues to charge, and the excitation inductor current I LM Continue to rise, and the power supply voltage VCC gradually decreases due to the power supply to the control chip. In this working waveform, when the inductor circuit drops to the bottom, during the opening process of the auxiliary power tube Q2, the power supply capacitor is charged until the auxiliary power tube Q2 is fully turned on. In another working waveform, the auxiliary power tube Q2 is turned on after a delay of a period of time after the PWM signal changes from invalid to valid. In this working waveform, charging can also be started when the PWM signal changes from invalid to valid until the auxiliary power tube Q2 is fully turned on. In the CCM working mode, the same power supply method can also be used. Therefore, during the opening process of the auxiliary power tube, controlling the charging of the power supply capacitor can recover part of the opening loss, improve the power supply efficiency, and avoid the high loss caused by the large voltage Vsw charging the power supply capacitor when the auxiliary power tube is turned off.

[0053] The present invention can not only optimize the EMI performance of the switching power supply, but also reduce power supply loss and improve the power supply efficiency of the system.

[0054] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0055] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A switching power supply, comprising an inductor, a main power tube and an auxiliary power tube, wherein the inductor is connected to a first end of the main power tube, the auxiliary power tube is connected between a second end of the main power tube and a ground end, and further comprising: A first module is connected between a first node and a control end of the auxiliary power tube, and a common connection end of the inductor and the main power tube is the first node; A self-powered circuit, comprising a power supply capacitor and a linear regulator, wherein the linear regulator is connected between the power supply capacitor and a connection end between the main power tube and the auxiliary power tube, and the voltage at the connection end between the main power tube and the auxiliary power tube charges the power supply capacitor through the linear regulator; in, The change rate of the first node voltage is adjusted by the first module so that the change rate of the first node voltage reaches an expected change rate and the charging current of the power supply capacitor is within an expected range.

2. The switching power supply according to claim 1, characterized in that: The first module adjusts the charging current of the power supply capacitor by adjusting the current flowing through the auxiliary power tube.

3. The switching power supply according to claim 2, characterized in that: The magnitude of the current flowing through the first module is adjusted by adjusting the driving current of the auxiliary power tube.

4. The switching power supply according to claim 1, characterized in that: The change rate of the first node voltage is adjusted by adjusting the change rate of the first module voltage or adjusting the current flowing through the first module.

5. The switching power supply according to claim 1, characterized in that: The first module includes a capacitor module connected between the first node and the control end of the auxiliary power tube; The change rate of the voltage of the first node is adjusted by adjusting the change rate of the voltage of the capacitor module.

6. The switching power supply according to claim 1, characterized in that: The first module includes: a sampling circuit connected to the first node and configured to sample a change rate of the voltage of the first node to obtain a sampling signal representing the change rate; A controlled current source is connected between the first node and the control end of the auxiliary power tube, and the sampling signal adjusts the magnitude of the output current of the controlled current source to adjust the current of the first module.

7. The switching power supply according to claim 3, characterized in that: The capacitor module includes one capacitor or a series-parallel combination of multiple capacitors.

8. The switching power supply according to claim 5, characterized in that: The current flowing through the capacitor module is adjusted to adjust the rate of change of the voltage across the capacitor module.

9. The switching power supply according to claim 5, characterized in that: A fixed current is given to flow through the capacitor module, and the capacitance value of the capacitor module is adjusted to adjust the rate of change of the voltage across the capacitor module.

10. The switching power supply according to claim 3, characterized in that: It includes a driving circuit connected to the control end of the auxiliary power tube, the driving circuit receives a PWM signal and outputs a driving current, and the PWM signal is used to drive the auxiliary power tube to turn on and off; By adjusting the magnitude of the driving current, the magnitude of the current flowing through the capacitor module is adjusted.

11. The switching power supply according to claim 1, characterized in that: During the turning-on process of the auxiliary power tube, the linear regulator is turned on and the power supply capacitor is charged.

12. The switching power supply according to claim 1, characterized in that: The current flowing through the linear regulator is set to be less than or equal to the current flowing through the main power tube.

13. The switching power supply according to claim 1, characterized in that: The power tube is a depletion-type transistor.

14. A control method for a switching power supply, comprising an inductor, a main power tube and an auxiliary power tube, wherein the inductor is connected to a first end of the main power tube, and the auxiliary power tube is connected between a second end of the main power tube and a ground terminal, characterized in that: The common connection end of the inductor and the main power tube is recorded as a first node; The voltage at the connection end of the main power tube and the auxiliary power tube charges the power supply capacitor through a linear regulator; The change rate of the first node voltage is adjusted by the first module so that the change rate of the first node voltage reaches an expected change rate and the charging current of the power supply capacitor is within an expected range.

15. The control method according to claim 14, characterized in that: The first module adjusts the charging current of the power supply capacitor by adjusting the current flowing through the auxiliary power tube.

16. The control method according to claim 15, characterized in that: The magnitude of the current flowing through the first module is adjusted by adjusting the driving current of the auxiliary power tube.

17. The control method according to claim 14, characterized in that: The change rate of the first node voltage is adjusted by adjusting the change rate of the first module voltage or adjusting the current flowing through the first module.

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