Switching power supply

Abstract

The utility model discloses a switching power supply. The switching power supply comprises a main transformer, a time delay module and at least one driving transformer, a primary coil of the main transformer is connected with the control switch in series and used for being connected with a power source. The time delay module is connected with the secondary side coil of the main transformer and the primary side coil of the driving transformer. The time delay module is used for outputting the output voltage of the main transformer to the driving transformer in a time delay mode. According to the utility model, the instantaneous starting current of the main transformer can be reduced, so that the main transformer normally outputs voltage.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to a switching power supply. Background Art

[0002] A switching power supply is a power supply that directly controls the inductive element (inductor or transformer) connected to it by a switching tube, and realizes voltage or current conversion through the energy storage and release process of the inductive element.

[0003] The existing switching power supply includes a main transformer and a drive transformer. There is a problem that the instantaneous starting current of the main transformer is too large and the output voltage cannot be normal. Utility Model Content

[0004] The utility model provides a switching power supply, which can reduce the instantaneous starting current of a main transformer and make the main transformer output voltage normally.

[0005] The utility model provides a switching power supply, comprising: a main transformer, a delay module and at least one driving transformer; the primary coil of the main transformer is connected in series with a control switch for accessing a power supply; the delay module is respectively connected with the secondary coil of the main transformer and the primary coil of the driving transformer, and the delay module is used to delay the output voltage of the main transformer to the driving transformer.

[0006] Optionally, the switching power supply further includes a PWM control module, the PWM control module is connected to the delay module, and the PWM control module is used to generate a PWM control signal to control the operation of the delay module.

[0007] Optionally, the delay module includes a first switch unit and a second switch unit, and the PWM control signal includes an alternating first level voltage and a second level voltage; the control end of the first switch unit is connected to the output end of the PWM control module, the first end of the first switch unit is connected to the first end of the secondary coil of the main transformer, and the second end of the first switch unit is connected to the second end of the secondary coil of the main transformer, and the first switch unit is used to be turned off according to the first level voltage and turned on according to the second level voltage; the control end of the second switch unit is connected to the third end of the first switch unit, the first end of the second switch unit is connected to the first end of the first switch unit, and the second end of the second switch unit is connected to the second end of the secondary coil of the main transformer, and the second switch unit is turned off when the first switch unit is turned off, and is turned on when the first switch unit is turned on.

[0008] Optionally, the delay module also includes a sampling unit; the first end of the sampling unit is respectively connected to the second end of the first switch unit and the current detection input end of the PWM control module, the second end of the sampling unit is connected to the second end of the secondary coil of the main transformer, and the sampling unit is used to convert the current flowing through the first switch unit into a voltage and input it into the PWM control module; the PWM control module is also used to stop outputting the PWM control signal when the voltage at both ends of the sampling unit is greater than a set value.

[0009] Optionally, the first switching unit includes a first transistor, a first diode and a first current limiting resistor; the first end of the first current limiting resistor serves as the control end of the first switching unit, and the second end of the first current limiting resistor is connected to the gate of the first transistor; the first electrode of the first transistor is connected to the anode of the first diode, the cathode of the first diode serves as the first end of the first switching unit, the second electrode of the first transistor serves as the second end of the first switching unit, and the anode of the first diode serves as the third end of the first switching unit.

[0010] Optionally, the first switch unit further includes a pull-down resistor; a first end of the pull-down resistor is connected to the gate of the first transistor, and a second end of the pull-down resistor is connected to the first electrode of the first transistor.

[0011] Optionally, the second switching unit includes a second transistor, a second diode and a second current limiting resistor; the first end of the second current limiting resistor is connected to the second end of the primary coil of the driving transformer and serves as the control end of the second switching unit, and the second end of the first current limiting resistor is connected to the gate of the second transistor; the first electrode of the second transistor serves as the first end of the second switching unit, the second electrode of the second transistor is respectively connected to the cathode of the second diode and the first end of the primary coil of the driving transformer, and the anode of the second diode serves as the second end of the second switching unit; wherein the channel types of the first transistor and the second transistor are different.

[0012] Optionally, the second switch unit further includes a pull-up resistor; a first end of the pull-up resistor is connected to the first electrode of the second transistor, and a second end of the pull-up resistor is connected to the gate of the second transistor.

[0013] Optionally, the switching power supply further includes a filtering module; the filtering module is connected to the secondary coil of the main transformer and is used to filter out voltage noise input from the main transformer to the delay module.

[0014] Optionally, the filtering module includes a first capacitor and a second capacitor; the first end of the first capacitor is connected to the first end of the secondary coil of the main transformer, and the second end of the first capacitor is connected to the second end of the secondary coil of the main transformer; the second capacitor is connected in parallel with the first capacitor.

[0015] The switching power supply of the embodiment of the utility model includes a transformer, a delay module and at least one driving transformer. The delay module is respectively connected to the secondary coil of the main transformer and the primary coil of the driving transformer. After the power supply output voltage of the main transformer is established, the driving transformer will receive the driving signal and start to operate, thereby reducing the instantaneous starting current of the main transformer, allowing the switch tube to be normally turned on, thereby allowing the main transformer to output voltage normally.

[0016] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present utility model, nor are they intended to limit the scope of the present utility model. Other features of the present utility model will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 It is a structural schematic diagram of a switching power supply provided by the relevant technology;

[0019] Figure 2 It is a structural schematic diagram of a switching power supply provided by an embodiment of the utility model;

[0020] Figure 3 This is a structural schematic diagram of another switching power supply provided by an embodiment of the utility model;

[0021] Figure 4 This is a structural schematic diagram of another switching power supply provided by an embodiment of the utility model;

[0022] Figure 5 This is a structural schematic diagram of another switching power supply provided by an embodiment of the utility model;

[0023] Figure 6 This is a structural schematic diagram of another switching power supply provided by an embodiment of the utility model. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solution of the utility model, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is only a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0026] As mentioned in the background technology, the existing switching power supply has the problem that the instantaneous starting current of the main transformer is too large and the output voltage cannot be normal. After careful research, the inventor found that the reason for this technical problem is:

[0027] Figure 1 It is a structural diagram of a switching power supply provided by the related technology, such as Figure 1 As shown, the switching power supply includes a switch tube K1, a PWM control circuit 10, a main transformer T1 and a plurality of drive transformers T2. Since the primary input of the drive transformer T2 is directly provided by the secondary coil of the main transformer, when the load connected to the drive transformer T2 needs to be powered, the main transformer T1 needs to drive all the drive transformers T2 to start at the same time, so that the instantaneous starting current of the main transformer T1 is too large. At this time, the PWM control circuit 10 connected to the switch tube K1 stops outputting the PWM control signal, and the switch tube K1 cannot be turned on and off normally, which causes the main transformer T1 to be unable to output voltage normally.

[0028] In view of the above research findings of the inventor, in order to solve the problems in the prior art, an embodiment of the utility model provides a switching power supply. Figure 2 Schematic diagram of a switching power supply provided by an embodiment of the utility model. Figure 2 As shown, the switching power supply includes: a main transformer M1, a delay module 11 and at least one driving transformer M2.

[0029] The primary coil of the main transformer M1 is connected in series with the control switch 12 for accessing the power source V1.

[0030] The delay module 11 is connected to the secondary coil of the main transformer M1 and the primary coil of the driving transformer M2 respectively. The delay module 11 is used for delaying the output voltage of the main transformer M1 and outputting it to the driving transformer M2.

[0031] Specifically, the switching power supply is a DC switching power supply, and its function is to convert the power supply V1, such as a battery power supply, into a DC voltage power supply that meets the load requirements. The load may be, for example, a frequency converter, a servo motor, and an inverter. When the load is an inverter, the switching power supply of the utility model can output a driving voltage to control the operation of the power tube of the inverter.

[0032] The control switch 12 controls the voltage of the secondary coil by controlling the voltage of the primary coil of the main transformer M1. Specifically, when the control switch 12 is turned on, the primary inductor of the main transformer M1 begins to store energy, generating an induced voltage that is positive at the top and negative at the bottom, and the inductor current gradually increases. Since the induced voltage of the primary coil of the main transformer is positive at the top and negative at the bottom, and the induced voltage of the secondary coil is negative at the top and positive at the bottom, the output diode is in a cut-off state, and at this time, the delay module 11 is provided with energy by the output capacitor. When the control switch 12 is turned off, the primary coil of the main transformer M1 begins to transfer energy to the secondary coil, and the induced voltage of the primary coil of the main transformer M1 is negative at the top and positive at the bottom, and the induced voltage of the secondary coil is positive at the top and negative at the bottom. At this time, the output diode is turned on, and the energy in the main transformer M1 is supplied to the delay module 11 via the output diode, and at the same time, the output capacitor is charged to replenish the lost energy.

[0033] In some embodiments, the control switch 12 includes a switch tube S1. In the embodiment of the present utility model, the switch tube S1 is taken as an N-type MOS tube for example. In addition, the switch tube S1 can also use any other suitable switch, for example, the switch tube S1 can be a P-type MOS tube, an NPN-type triode, a PNP-type triode, an insulated gate bipolar transistor (IGBT) device, etc.

[0034] The delay module 11 can be any circuit or module with a delay function. The implementation of the utility model connects the delay module 11 to the secondary coil of the main transformer M1 and the primary coil of the drive transformer M2 respectively, so that the drive transformer M2 will receive the drive signal and start to operate only after the power supply output voltage of the main transformer M1 is established, thereby reducing the instantaneous starting current of the main transformer M1, so that the switch tube S1 is normally turned on and off, so that the main transformer M1 outputs voltage normally. In addition, compared with replacing a transformer with a larger rated current to make the transformer output voltage normally, the embodiment of the utility model can reduce costs.

[0035] Optionally, the switching power supply further includes a PWM control circuit, which is connected to the switch tube S1 and is used to output a PWM signal to control the on and off of the switch tube S1. The PWM control circuit is also used to detect whether the current flowing through the switch tube S1 is greater than a set current value, and stop outputting the PWM signal when the current flowing through the switch tube S1 is greater than the set current value. In some embodiments, the PWM control circuit includes a control device such as a microcontroller unit (MCU), a digital signal processor (DSP), or a field programmable gate array (FPGA).

[0036] The switching power supply of the embodiment of the utility model includes a transformer, a delay module and at least one driving transformer. The delay module is respectively connected to the secondary coil of the main transformer and the primary coil of the driving transformer. After the power supply output voltage of the main transformer is established, the driving transformer will receive the driving signal and start to operate, thereby reducing the instantaneous starting current of the main transformer, allowing the switch tube to be normally turned on and off, thereby allowing the main transformer to output voltage normally.

[0037] Figure 3 This is a schematic diagram of the structure of another switching power supply provided by the embodiment of the utility model. Figure 3 As shown, based on the above embodiment, optionally, the switching power supply further includes a PWM control module 13, the PWM control module 13 is connected to the delay module 11, and the PWM control module 13 is used to generate a PWM control signal to control the operation of the delay module 11.

[0038] The present utility model embodiment does not specifically limit the specific implementation method of the PWM control module, as long as it can generate a PWM control signal. As an optional implementation method provided by this embodiment, Figure 4 1 is a schematic diagram of the structure of another switching power supply provided by an embodiment of the utility model, wherein the PWM control module 13 includes a switching power supply control chip U1 and its peripheral circuits. Exemplarily, the switching power supply control chip U1 may be UC2845. The UC2845 chip includes a first pin COMP, a second pin VEB, a third pin ISENSEE, a fourth pin RT / CT, a fifth pin GND, a sixth pin OUT, a seventh pin VCC, and an eighth pin VREF.

[0039] In some embodiments, the PWM control module 13 includes a microcontroller unit (MCU), a digital signal processor (DSP) or a field programmable gate array (FPGA) and other control devices. In practical applications, these control devices can execute computer programs to generate PWM control signals.

[0040] Optionally, based on the above embodiment, continue to refer to Figure 4 The delay module 11 includes a first switch unit 111 and a second switch unit 112, and the PWM control signal includes an alternating first level voltage and a second level voltage.

[0041] The control end of the first switch unit 111 is connected to the output end of the PWM control module 13, the first end of the first switch unit 111 is connected to the first end of the secondary coil of the main transformer M1, the second end of the first switch unit 111 is connected to the second end of the secondary coil of the main transformer T1, and the first switch unit 111 is used to shut down according to a first level voltage and turn on according to a second level voltage.

[0042] The control end of the second switch unit 112 is connected to the third end of the first switch unit 111, the first end of the second switch unit 112 is connected to the first end of the first switch unit 111, the second end of the second switch unit 112 is connected to the second end of the secondary coil of the main transformer T1, and the second switch unit 112 is turned off when the first switch unit 111 is turned off, and is turned on when the first switch unit 111 is turned on.

[0043] Specifically, when the PWM control module 13 includes a switch power control chip U1 , and the switch power control chip U1 is UC2845, the sixth pin OUT of the UC2845 chip serves as the output end of the PWM control module 13 .

[0044] The first switch unit 111 and the second switch unit 112 refer to switches that can realize on-off control through electrical signals or realize on-off control according to the characteristics of the components themselves. The first switch unit 111 and the second switch unit 112 can be either unidirectional switches, such as a unidirectionally conductive switch composed of a bidirectional switch and a diode in series, or bidirectional switches, such as a metal oxide semiconductor field effect transistor (Metal Oxide Semiconductor Field Effect Transistor, MOSFET) or an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT) with an anti-parallel freewheeling diode. It can be understood that the specific types of the first switch unit 111 and the second switch unit 112 can be selected and set according to the actual application scenario, etc., and the utility model is not limited here.

[0045] The first level voltage may be a high level or a low level. Exemplarily, if the transistor included in the first switch unit 111 is a P-type transistor, the first level voltage may be a high level, the second level voltage may be a low level, and the first switch unit 111 is turned off at a high level and turned on at a low level; if the transistor included in the first switch unit 111 is an N-type transistor, the first level voltage may be a low level, the second level voltage may be a high level, and the first switch unit 111 is turned on at a high level and turned off at a low level. This embodiment and the following embodiments are all described by taking the first level voltage as a low level and the second level voltage as a high level as an example.

[0046] by Figure 4 Taking the circuit structure shown in the figure as an example, the specific working principle of the switching power supply provided in this embodiment is as follows:

[0047] When the switch tube S1 is turned on, the primary inductor of the main transformer M1 begins to store energy, the inductor voltage is positive at the top and negative at the bottom, and the inductor current gradually increases. Since the primary coil of the main transformer generates an induced voltage that is positive at the top and negative at the bottom, and the secondary coil generates an induced voltage that is negative at the top and positive at the bottom, the output diode is in a cut-off state at this time, and the delay module 11 is provided with energy by the output capacitor.

[0048] When the switch tube S1 is turned off, the primary coil of the main transformer M1 starts to transfer energy to the secondary coil. The induced voltage of the primary coil of the main transformer M1 is negative at the top and positive at the bottom, and the induced voltage of the secondary coil is positive at the top and negative at the bottom. At this time, the output diode is turned on, and the energy in the main transformer M1 supplies power to the delay module 11 through the output diode, and at the same time charges the output capacitor to replenish the lost energy.

[0049] When the main transformer M1 starts to output voltage, the PWM control module 13 starts to output the PWM control signal. When the PWM control signal is a first level voltage, the first switch unit 111 is turned off, the third terminal of the first switch unit 111 is pulled up to a high potential, the second switch unit 112 is turned off, and the delay module 11 outputs a second level voltage.

[0050] When the PWM control signal is a second level voltage, the first switch unit 111 is turned on, the third terminal of the first switch unit 111 is pulled down to a low potential, the second switch unit 112 is turned on, and the delay module 11 outputs a first level voltage.

[0051] Since the first switch unit 111 and the second switch unit 112 need a certain conduction time to be turned on, the first switch unit 111 and the second switch unit 112 can delay the output voltage of the main transformer M1 to the drive transformer M2. That is, only when the output voltage of the main transformer M1 is established, the drive transformer M2 will receive the drive signal and start to act, reducing the instantaneous starting current of the main transformer M1, so that the switch tube S1 is turned on and off normally, so that the main transformer M1 can output voltage normally.

[0052] Optionally, based on the above embodiment, continue to refer to Figure 4 The delay module 11 further includes a sampling unit 113. The first end of the sampling unit 113 is respectively connected to the second end of the first switch unit 111 and the current detection input end of the PWM control module 13, and the second end of the sampling unit 113 is connected to the second end of the secondary coil of the main transformer M1. The sampling unit 113 is used to convert the current flowing through the first switch unit 111 into a voltage and input it into the PWM control module 13.

[0053] The PWM control module 13 is further configured to stop outputting the PWM control signal when the voltage across the sampling unit 113 is greater than a set value.

[0054] Specifically, when the PWM control module 13 includes a switch power control chip U1 , and the switch power control chip U1 is UC2845, the third pin ISENSe of the UC2845 chip serves as the current detection input terminal of the PWM control module 13 .

[0055] The sampling unit 113 includes a sampling resistor Rs1, a first end of the sampling resistor Rs1 serves as a first end of the first switch unit 111, and a second end of the sampling resistor Rs1 serves as a second end of the second switch unit 112. When the output voltage of the main transformer M1 is abnormal, the current flowing through the first switch unit 111 increases, and when the voltage on the sampling resistor is greater than a set value, such as 1V, the UC2845 chip reduces the pulse width of the output PWM control signal, so that the main transformer M1 is in an intermittent working state, and the UC2845 chip stops outputting the PWM control signal, thereby effectively protecting the first switch unit 111.

[0056] Figure 5 FIG. 1 is a schematic diagram of another switching power supply provided by an embodiment of the utility model. Based on the above embodiment, optionally, Figure 5 As shown, the first switch unit 111 includes a first transistor Q1, a first diode D1 and a first current limiting resistor R1.

[0057] The first end of the first current limiting resistor R1 serves as a control end of the first switch unit 111 , and the second end of the first current limiting resistor R1 is connected to the gate of the first transistor Q1 .

[0058] The first electrode of the first transistor Q1 is connected to the anode of the first diode D1, the cathode of the first diode D1 serves as the first end of the first switch unit 111, the second electrode of the first transistor Q1 serves as the second end of the first switch unit 111, and the anode of the first diode D1 serves as the third end of the first switch unit 111.

[0059] Based on the above embodiment, optionally, continue to refer to Figure 5 The first switch unit 111 further includes a pull-down resistor Rd1. A first end of the pull-down resistor Rd1 is connected to the gate of the first transistor Q1, and a second end of the pull-down resistor Rd1 is connected to the first electrode of the first transistor Q1.

[0060] Specifically, the pull-down resistor Rd1 is used to clamp the gate potential of the first transistor Q1 to a low level, thereby preventing the first transistor Q1 from being mis-turned on and improving circuit stability.

[0061] Based on the above embodiment, optionally, continue to refer to Figure 5 The second switch unit 112 includes a second transistor Q2, a second diode D2 and a second current limiting resistor R2. The first end of the second current limiting resistor R2 is connected to the second end of the primary coil of the driving transformer M2 and serves as the control end of the second switch unit. The second end of the first current limiting resistor R2 is connected to the gate of the second transistor.

[0062] The first electrode of the second transistor Q2 serves as the first end of the second switch unit 112, the second electrode of the second transistor Q2 is respectively connected to the cathode of the second diode D2 and the first end of the primary coil of the driving transformer M2, and the anode of the second diode D2 serves as the second end of the second switch unit 112. The first transistor Q1 and the second transistor Q2 have different channel types.

[0063] Optionally, the second switch unit further includes a pull-up resistor Ru1. A first end of the pull-up resistor Ru1 is connected to a first electrode of the second transistor Q2, and a second end of the pull-up resistor Ru1 is connected to a gate of the second transistor Q2.

[0064] Specifically, the first transistor Q1 and the second transistor Q2 may be field effect transistors or insulated gate bipolar transistors. When the first transistor Q1 is a P-channel transistor, the second transistor Q2 is an N-channel transistor; when the first transistor Q1 is an N-channel transistor, the second transistor Q2 is a P-channel transistor. Figure 5 The case where the first transistor Q1 is an N-channel transistor and the second transistor Q2 is a P-channel transistor is schematically shown.

[0065] The first diode D1 and the second diode D2 are freewheeling diodes.

[0066] The pull-up resistor Ru1 is used to clamp the gate potential of the second transistor Q2 to a high level to avoid mis-turning on of the second transistor Q2 and improve circuit stability.

[0067] by Figure 5 Taking the circuit structure shown in the figure as an example, the specific working principle of the switching power supply provided in this embodiment is as follows:

[0068] When the main transformer M1 starts to output voltage, the PWM control module 13 starts to output the PWM control signal. When the PWM control signal is a first level voltage, the first transistor Q1 is turned off, the first level of the first transistor Q1 is pulled up to a high potential, the second transistor Q2 is turned off, and the delay module 11 outputs a second level voltage.

[0069] When the PWM control signal is a second level voltage, the first transistor Q1 is turned on, the first electrode of the first transistor Q1 is pulled down to a low potential, and the second transistor Q2 is turned on. At this time, the delay module 11 outputs a first level voltage.

[0070] Figure 6 FIG. 1 is a schematic diagram of another switching power supply provided by an embodiment of the utility model. Based on the above embodiment, optionally, Figure 6 As shown, the switching power supply further includes a filtering module 14 .

[0071] The filter module 14 is connected to the secondary coil of the main transformer M1 and is used to filter out voltage noise input from the main transformer M1 to the delay module 13 .

[0072] Optionally, the filtering module 14 includes a first capacitor C1 and a second capacitor C2. The first end of the first capacitor C1 is connected to the first end of the secondary coil of the main transformer M1, and the second end of the first capacitor C1 is connected to the second end of the secondary coil of the main transformer M1. The second capacitor C2 is connected in parallel with the first capacitor C1.

[0073] The above specific implementations do not constitute a limitation on the protection scope of the present utility model. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A switching power supply, characterized in that: include: A main transformer, a delay module and at least one drive transformer; The primary coil of the main transformer is connected in series with the control switch for accessing the power supply; The delay module is connected to the secondary coil of the main transformer and the primary coil of the drive transformer respectively, and the delay module is used to delay the output voltage of the main transformer to the drive transformer.

2. The switching power supply according to claim 1, characterized in that: It also includes a PWM control module, which is connected to the delay module and is used to generate a PWM control signal to control the operation of the delay module.

3. The switching power supply according to claim 2, characterized in that: The delay module includes a first switch unit and a second switch unit, and the PWM control signal includes an alternating first level voltage and a second level voltage; The control end of the first switch unit is connected to the output end of the PWM control module, the first end of the first switch unit is connected to the first end of the secondary coil of the main transformer, the second end of the first switch unit is connected to the second end of the secondary coil of the main transformer, and the first switch unit is used to be turned off according to the first level voltage and turned on according to the second level voltage; The control end of the second switch unit is connected to the third end of the first switch unit, the first end of the second switch unit is connected to the first end of the first switch unit, the second end of the second switch unit is connected to the second end of the secondary coil of the main transformer, and the second switch unit is turned off when the first switch unit is turned off, and is turned on when the first switch unit is turned on.

4. The switching power supply according to claim 3, characterized in that: The delay module also includes a sampling unit; The first end of the sampling unit is connected to the second end of the first switch unit and the current detection input end of the PWM control module respectively, the second end of the sampling unit is connected to the second end of the secondary coil of the main transformer, and the sampling unit is used to convert the current flowing through the first switch unit into a voltage and input it into the PWM control module; The PWM control module is further configured to stop outputting the PWM control signal when the voltage across the sampling unit is greater than a set value.

5. The switching power supply according to claim 3, characterized in that: The first switch unit includes a first transistor, a first diode and a first current limiting resistor; The first end of the first current limiting resistor serves as the control end of the first switch unit, and the second end of the first current limiting resistor is connected to the gate of the first transistor; The first electrode of the first transistor is connected to the anode of the first diode, the cathode of the first diode serves as the first end of the first switch unit, the second electrode of the first transistor serves as the second end of the first switch unit, and the anode of the first diode serves as the third end of the first switch unit.

6. The switching power supply according to claim 5, characterized in that: The first switch unit further includes a pull-down resistor; A first end of the pull-down resistor is connected to the gate of the first transistor, and a second end of the pull-down resistor is connected to the first electrode of the first transistor.

7. The switching power supply according to claim 5, characterized in that: The second switch unit includes a second transistor, a second diode and a second current limiting resistor; The first end of the second current limiting resistor is connected to the second end of the primary coil of the driving transformer and serves as the control end of the second switch unit, and the second end of the first current limiting resistor is connected to the gate of the second transistor; The first electrode of the second transistor serves as the first end of the second switch unit, the second electrode of the second transistor is respectively connected to the cathode of the second diode and the first end of the primary coil of the driving transformer, and the anode of the second diode serves as the second end of the second switch unit; The first transistor and the second transistor have different channel types.

8. The switching power supply according to claim 7, characterized in that: The second switch unit further includes a pull-up resistor; A first end of the pull-up resistor is connected to a first electrode of the second transistor, and a second end of the pull-up resistor is connected to a gate of the second transistor.

9. The switching power supply according to claim 1, characterized in that: Also includes a filtering module; The filtering module is connected to the secondary coil of the main transformer and is used to filter out voltage clutter input from the main transformer to the delay module.

10. The switching power supply according to claim 9, characterized in that: The filtering module includes a first capacitor and a second capacitor; The first end of the first capacitor is connected to the first end of the secondary coil of the main transformer, and the second end of the first capacitor is connected to the second end of the secondary coil of the main transformer; The second capacitor is connected in parallel with the first capacitor.

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