Soft start circuit, switching power supply circuit and servo driver

Abstract

The utility model discloses a soft start circuit, a switching power supply circuit and a servo driver, and the soft start circuit comprises a power supply access end which is used for accessing a first voltage; the first end of the energy storage circuit is connected with the power supply access end, and the second end is grounded; the energy storage circuit is used for charging when a first voltage is accessed to the power supply access end, and the output end voltage rises and is used for charging to a first predetermined voltage value after a first predetermined duration. According to the soft start circuit, under the action of the first voltage, the voltage at the output end rises to the first preset voltage value through the first preset duration, and the temperature excursion of a device for storing energy in the energy storage circuit is small, so that the soft start circuit can operate in different temperature environments.

Description

Technical Field

[0001] The utility model relates to the technical field of servo drivers, in particular to a soft start circuit, a switch power supply circuit and a servo driver. Background Art

[0002] The soft-start technology increases the output voltage or current slowly from zero to the normal operating value, thereby avoiding voltage overshoot when the device starts.

[0003] In the AC servo drive industry, the primary side of the auxiliary switching power supply is usually soft-started with a transistor. However, the Vbe voltage drop of the transistor is greatly affected by temperature changes and the circuit control is complex. Utility Model Content

[0004] The utility model proposes a soft start circuit, which includes:

[0005] A power supply access terminal, used for accessing a first voltage;

[0006] An energy storage circuit, a first end of which is connected to the power access end and a second end of which is grounded; the energy storage circuit is used to charge when the power access end is connected to a first voltage, the output end voltage rises and is used to charge to a first predetermined voltage value after a first predetermined time.

[0007] Optionally, the soft start circuit further includes:

[0008] A discharge circuit, wherein a first end is connected to the output end of the energy storage circuit, and a second end is connected to the power access end; the discharge circuit is used to discharge the electric energy stored in the energy storage circuit when the power access end is disconnected from the first voltage;

[0009] A voltage follower circuit has an input end connected to the output end of the energy storage circuit; the voltage follower circuit is used to isolate and output the voltage at the output end of the energy storage circuit.

[0010] Optionally, the energy storage circuit includes:

[0011] a first resistor and a first capacitor;

[0012] The first end of the first resistor is connected to the power supply access end, and the second end is connected to the first end of the first capacitor and the input end of the voltage follower circuit; the second end of the first capacitor is grounded.

[0013] Optionally, the discharge circuit includes:

[0014] The first diode has an anode connected to the first end of the first capacitor and a cathode connected to the power supply access end.

[0015] Optionally, the voltage follower circuit includes:

[0016] The second diode has a cathode connected to the first end of the first capacitor and an anode connected to the load device.

[0017] The utility model also provides a switching power supply circuit, the switching circuit includes the soft start circuit; the switching power supply circuit also includes:

[0018] A voltage conversion control module, wherein the input end of the voltage conversion control module is connected to the output end of the soft start circuit; the voltage conversion control module is used to determine the duty cycle according to the output voltage of the soft start circuit, and output a square wave of the corresponding duty cycle;

[0019] A transformer, the transformer comprising a primary coil and a secondary coil; a first end of the primary coil is connected to a first DC voltage; and the secondary coil is connected to a load;

[0020] A switch circuit, wherein the input end is connected to the output end of the voltage conversion control module, the second end is connected to the second end of the primary coil of the transformer, and the third end is grounded; the switch circuit is used to turn on / off the path between the second end of the primary coil and the ground according to the high and low levels of the square wave after receiving the square wave output by the voltage conversion control module.

[0021] Optionally, the switch circuit includes:

[0022] A second resistor, a third resistor, a fourth resistor and a first MOS tube;

[0023] The first end of the second resistor is connected to the output end of the voltage conversion control module, and the second end is connected to the first end of the third resistor and the gate of the first MOS tube; the second end of the third resistor is connected to the first end of the fourth resistor and the source of the first MOS tube; the second end of the fourth resistor is grounded; the drain of the first MOS tube is connected to the second end of the primary coil.

[0024] Optionally, the transformer further includes:

[0025] a fifth resistor, a second capacitor and a third diode;

[0026] The first end of the fifth resistor, the first end of the second capacitor and the first end of the primary coil are connected; the second end of the fifth resistor and the second end of the second capacitor are connected to the cathode of the third diode; the anode of the third diode is connected to the second end of the primary coil and the drain of the first MOS tube.

[0027] The utility model also provides a servo driver, which comprises the switching power supply circuit.

[0028] The utility model discloses a soft start circuit, a switching power supply circuit and a servo driver, wherein the soft start circuit comprises: a power supply access terminal for accessing a first voltage; an energy storage circuit, wherein a first terminal is connected to the power supply access terminal and a second terminal is grounded; the energy storage circuit is used to charge when the power supply access terminal is connected to the first voltage, and the output terminal voltage rises and is used to charge to a first predetermined voltage value after a first predetermined time. In the utility model, the output terminal voltage rises to a first predetermined voltage value after a first predetermined time under the action of the first voltage through the energy storage circuit, and the temperature drift of the device storing energy in the energy storage circuit is small, which is conducive to the operation of the soft start circuit in different temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0030] Figure 1 This is a structural schematic diagram of an embodiment of a soft start circuit of the utility model;

[0031] Figure 2 This is a structural schematic diagram of another embodiment of the soft start circuit of the utility model;

[0032] Figure 3 This is a schematic diagram of the structure of an embodiment of a switching power supply circuit of the utility model;

[0033] Figure 4 It is a structural schematic diagram of another embodiment of the switching power supply circuit of the utility model;

[0034] Figure 5 It is a structural schematic diagram of another embodiment of the switching power supply circuit of the utility model.

[0035] Description of Figure Numbers:

[0036]

[0037]

[0038] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0039] 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 only 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.

[0040] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back...) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0041] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] In addition, in the present utility model, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.

[0043] The utility model provides a soft start circuit 110, and the soft start circuit 110 includes:

[0044] A power supply input terminal 1110, used for inputting a first voltage;

[0045] The energy storage circuit 1120 has a first end connected to the power supply input terminal 1110 and a second end grounded; the energy storage circuit 1120 is used to charge when the power supply input terminal 1110 is connected to a first voltage, the output terminal voltage rises and is used to charge to a first predetermined voltage value after a first predetermined time.

[0046] It should be noted that soft start is a process of slowly increasing the output voltage to reduce the voltage shock to the load device / component, so that the load device / component can start or run smoothly, thereby protecting the load device / component. In particular, the application of soft start technology to the motor can reduce the mechanical shock of the motor starting; the application of soft start technology to the power circuit can reduce the voltage that the power device bears at the moment of starting, solve the problem of excessive voltage stress and output voltage overshoot, and the power device can be a MOS tube.

[0047] The utility model aims to propose a soft start circuit 110 that is less affected by temperature, the soft start circuit 110 includes a power supply access terminal 1110 and the energy storage circuit 1120, wherein the energy storage circuit 1120 is used to, under the action of the first voltage connected to the power supply access terminal 1110, the voltage at the output terminal of the energy storage circuit 1120 rises to the first predetermined voltage value after a first predetermined time, so as to meet the demand of the load connected to the output terminal of the energy storage circuit 1120. Considering that the energy storage circuit 1120 serves the load connected to its output terminal in actual use; the first predetermined time and the first predetermined voltage value can be determined by the research and development personnel according to the required conduction time of the load and experiments; the voltage value at the output terminal of the energy storage circuit 1120 can rise slowly from zero to the first predetermined voltage value within the first predetermined time, thereby realizing the demand of providing a slowly rising output voltage value for the load. It is easy to understand that in order to reduce the impact of temperature on the soft start circuit 110, the energy storage circuit 1120 does not include a transistor, but includes a capacitor or an inductor; the temperature drift phenomenon of the transistor is more obvious than the temperature drift phenomenon of the capacitor and the inductor.

[0048] In one embodiment of the utility model, the energy storage circuit 1120 includes a current limiting resistor and a capacitor, and the first voltage can be a direct current with a constant amplitude; in this embodiment, the first end of the current limiting resistor is connected to the power supply access terminal 1110, and the second end is connected to the first end of the capacitor; the second end of the capacitor is grounded, and the first end of the capacitor is the output end of the energy storage circuit 1120; the output voltage of the capacitor when the power supply access terminal 1110 is not connected to the first voltage can be zero, when the power supply access terminal 1110 is connected to the first voltage, the capacitor is charged under the action of the first voltage, and the voltage value of the output end of the energy storage circuit 1120 slowly increases, and after a first predetermined time, it is charged to the first predetermined voltage value. The first voltage can be provided by an external device, such as a power generator.

[0049] The utility model discloses a soft start circuit 110, the soft start circuit 110 includes: a power supply access terminal 1110, for accessing a first voltage; an energy storage circuit 1120, the first end of which is connected to the power supply access terminal 1110, and the second end is grounded; the energy storage circuit 1120 is used to charge when the power supply access terminal 1110 is connected to the first voltage, the output terminal voltage rises and is used to charge to a first predetermined voltage value after a first predetermined time. In the utility model, the output terminal voltage of the energy storage circuit 1120 rises to the first predetermined voltage value after a first predetermined time under the action of the first voltage, and the temperature drift of the device storing energy in the energy storage circuit 1120 is small, which is conducive to the operation of the soft start circuit 110 in different temperature environments.

[0050] Reference Figure 1 In one embodiment of the present utility model, the soft start circuit 110 further includes:

[0051] A discharge circuit 1130, a first end of which is connected to the output end of the energy storage circuit 1120, and a second end of which is connected to the power supply access end 1110; the discharge circuit 1130 is used to discharge the electric energy stored in the energy storage circuit 1120 when the power supply access end 1110 is disconnected from the first voltage;

[0052] The voltage follower circuit 1140 has an input end connected to the output end of the energy storage circuit 1120 ; the voltage follower circuit 1140 is used to isolate and output the voltage at the output end of the energy storage circuit 1120 .

[0053] In this embodiment, considering that the soft start circuit 110 is applied to the start-up of the load device / component, the power supply access terminal 1110 is connected to the first voltage only when the load device / component needs to be started; and the power supply access terminal 1110 is continuously connected to the first voltage when the load device / component is running. When the load device / component stops running, the power supply access terminal 1110 is disconnected from the external device providing the first voltage; at this time, in order to start the load device / component normally next time, the energy storage circuit 1120 needs to discharge the stored electric energy when the power supply access terminal 1110 is disconnected from the first voltage, so that when the power supply access terminal 1110 is reconnected to the first voltage, the voltage value at the output end of the energy storage circuit 1120 can rise to the first predetermined voltage value within the first predetermined time length. Therefore, the soft start circuit 110 includes a discharge circuit 1130, and the discharge circuit 1130 is used to discharge the electric energy stored in the energy storage circuit 1120 when the power supply access terminal 1110 is disconnected from the first voltage. In particular, when the load device / device stops running, the power access terminal 1110 is disconnected from the external device providing the first voltage and is grounded, and the discharge circuit 1130 can discharge the electrical energy stored in the energy storage circuit 1120 through the electrical loop between the power access terminal 1110 and the ground.

[0054] It is easy to understand that the function of the soft start circuit 110 is only to provide a slowly rising voltage for the load device / device when starting; in order to avoid the mutual influence caused by the direct connection between the soft start circuit 110 and the load device / device, the soft start circuit 110 also includes a voltage follower circuit 1140, the input end of the voltage follower circuit 1140 is connected to the output end of the energy storage circuit 1120, and the output end is connected to the load device / device; the voltage follower circuit 1140 is used to isolate and output the voltage at the output end of the energy storage circuit 1120; the voltage follower circuit 1140 may include: a voltage follower or a transformer 130, etc.

[0055] Reference Figure 2 In one embodiment of the present utility model, the energy storage circuit 1120 includes:

[0056] A first resistor R1 and a first capacitor C1;

[0057] The first end of the first resistor R1 is connected to the power supply access terminal 1110 , and the second end is connected to the first end of the first capacitor C1 and the input end of the voltage follower circuit 1140 ; ​​the second end of the first capacitor C1 is grounded.

[0058] In this embodiment, the first resistor R1 is a current limiting resistor, the first capacitor C1 is charged when the power supply access terminal 1110 is connected to a first voltage, and the output terminal voltage rises to the first predetermined voltage value within the first predetermined time period.

[0059] In an embodiment of the present invention, the discharge circuit 1130 includes:

[0060] The first diode D1 has an anode connected to the first end of the first capacitor C1 and a cathode connected to the power supply access terminal 1110 .

[0061] In this embodiment, when the power access terminal 1110 is disconnected from the first voltage and grounded, the voltage difference between the anode and the cathode of the first diode D1 is greater than the conduction voltage, the first diode D1 is turned on, and the electric energy stored in the first capacitor C1 is discharged through the power access terminal 1110.

[0062] In an embodiment of the present invention, the voltage follower circuit 1140 includes:

[0063] The second diode D2 has a cathode connected to the first end of the first capacitor C1 and an anode connected to a load device.

[0064] In this embodiment, due to the characteristics of the diode, the voltage difference between the anode and cathode of the diode is a fixed value, which can be the conduction voltage value of the diode. Therefore, when the voltage of the first capacitor C1 connected to the cathode of the second diode D2 increases, the voltage of the anode of the second diode D2 also increases accordingly.

[0065] Reference Figure 3 The utility model further proposes a switching power supply circuit 10, wherein the switching power supply circuit 10 includes the soft start circuit 110; the switching power supply circuit 10 also includes:

[0066] A voltage conversion control module, the input end of which is connected to the output end of the soft start circuit 110; the voltage conversion control module is used to determine the duty cycle according to the output voltage of the soft start circuit 110, and output a square wave of the corresponding duty cycle;

[0067] A transformer 130, wherein the transformer 130 comprises a primary coil PS and a secondary coil SC; a first end of the primary coil PS is connected to a first DC voltage; and the secondary coil SC is connected to a load;

[0068] The switch circuit 140 has an input end connected to the output end of the voltage conversion control module, a second end connected to the second end of the primary coil PS of the transformer 130, and a third end connected to the ground; the switch circuit 140 is used to turn on / off the path between the second end of the primary coil PS and the ground according to the high and low levels of the square wave after receiving the square wave output by the voltage conversion control module.

[0069] In this embodiment, the voltage value at the output end of the soft start circuit 110 rises slowly. The input end of the voltage conversion control module is connected to the output end of the soft start circuit 110, and the duty cycle is determined according to the output voltage of the soft start circuit 110, and a square wave of the corresponding duty cycle is output to the switch circuit 140; it is easy to understand that when the soft start circuit 110 does not include the voltage follower circuit 1140, the output end of the soft start circuit 110 is the output end of the energy storage circuit 1120; when the soft start circuit 110 includes the voltage follower circuit 1140, the output end of the soft start circuit 110 is the output end of the voltage follower circuit 1140. The second end of the switch circuit 140 is connected to the second end of the primary coil PS of the transformer 130, and the third end is grounded; the switch circuit 140 is used to turn on / off the path between the primary coil PS and the ground according to the high and low levels of the square wave after receiving the square wave output by the voltage conversion control module. The square wave has a series of high and low levels, so that the switch circuit 140 continuously turns on and off the path between the primary coil PS and the ground; the first end of the primary coil PS of the transformer 130 is connected to the first DC voltage, and the second end is connected to the input end of the switch circuit 140. When the switch circuit 140 continuously turns on and off the path between the primary coil PS and the ground, the primary coil PS outputs a voltage to the secondary coil SC through a coupling connection with the secondary coil SC, wherein the output voltage is related to the turns ratio of the primary coil PS to the secondary coil SC, and the duty cycle of the square wave.

[0070] When the voltage at the output end of the soft start circuit 110 rises slowly, the duty cycle of the square wave output by the voltage conversion control module also increases slowly. The time that the switch circuit 140 conducts the path between the second end of the primary coil PS and the ground in one cycle of the square wave also becomes longer; causing the amplitude of the voltage received by the secondary coil SC of the transformer 130 to increase accordingly. The combination of the soft start circuit 110, the voltage conversion control circuit 120, the switch circuit 140 and the transformer 130 can enable the load connected to the secondary coil SC to receive a voltage that rises slowly from zero, thereby avoiding the influence of voltage overshoot on the load.

[0071] The voltage conversion control module may include a power management chip, such as SG3525, TL494 or FP7208. The switch circuit 140 includes a switch device, the control end of the switch device is electrically connected to the output end of the voltage conversion control module, and the first end and the second end of the switch device are arranged in the path between the second end of the primary coil PS and the ground; the switch device can turn on / off the path between the second end of the primary coil PS and the ground. The switch device can be a MOS tube, a triode or an FPGA tube, etc.

[0072] Reference Figure 4 In one embodiment of the present utility model, the switch circuit 140 includes:

[0073] A second resistor R2, a third resistor R3, a fourth resistor R4 and a first MOS tube;

[0074] The first end of the second resistor R2 is connected to the output end of the voltage conversion control module, and the second end is connected to the first end of the third resistor R3 and the gate of the first MOS tube; the second end of the third resistor R3 is connected to the first end of the fourth resistor R4 and the source of the first MOS tube; the second end of the fourth resistor R4 is grounded; the drain of the first MOS tube is connected to the second end of the primary coil PS.

[0075] In this embodiment, the fourth resistor R4 is a current limiting resistor, and the second resistor R2 and the third resistor R3 form a resistor voltage divider circuit, wherein the third resistor R3 is located between the gate and the source of the first MOS tube, ensuring that when the voltage conversion control module has a square wave output, there is a voltage difference between the gate and the source of the first MOS tube in the high level section of the square wave. Specifically, when the

[0076] When the first MOS tube is an NMOS tube, the first MOS tube is turned on in the high level section of the square wave.

[0077] In an embodiment of the present invention, the transformer 130 further includes:

[0078] A fifth resistor R5, a second capacitor C2 and a third diode D3;

[0079] The first end of the fifth resistor R5, the first end of the second capacitor C2 and the first end of the primary coil PS are connected; the second end of the fifth resistor R5 and the second end of the second capacitor C2 are connected to the cathode of the third diode D3; the anode of the third diode D3 is connected to the second end of the primary coil PS and the drain of the first MOS tube.

[0080] In this embodiment, the first end of the second capacitor C2 is connected to the first end of the primary coil PS, and is used to stabilize the amplitude of the first DC voltage connected to the primary coil PS. The fifth resistor R5 and the third diode D3 form a unidirectional conduction circuit, which is used to form a complete electrical circuit with the primary coil PS when the first MOS tube is turned off, and provide a channel for the current released from the primary coil PS. The third diode D3 is turned off when the first MOS tube is turned on.

[0081] Reference Figure 5In one embodiment of the utility model, the switching power supply circuit 10 further includes a rectifier circuit 150, the input end of the rectifier circuit 150 is connected to the secondary coil SC, and the output end is connected to the load. The rectifier circuit 150 may include a fourth diode and a third capacitor. The anode of the fourth diode is connected to the first end of the secondary coil SC, and the cathode is connected to the first end of the third capacitor and the load; the second end of the third capacitor is connected to the second end of the secondary coil SC. The fourth diode and the third capacitor rectify the AC voltage output by the secondary coil SC and output it to the load.

[0082] Considering the voltage stress of the first MOS tube when the load device is turned on, that is, the switching power supply starts to operate; the voltage stress formula is V ds =V indc +N(V o +V f )+V l , wherein the V indc is the first DC voltage; N is the ratio of the number of turns of the primary coil PS to the number of turns of the secondary coil SC; V o is the voltage at the output end of the rectifier circuit 150; f is the forward conduction voltage of the fourth diode; l is the peak voltage of the leakage inductance line generated by the transformer 130. When the output voltage value of the soft start circuit 110 rises slowly, the duty cycle of the square wave output by the voltage conversion control module increases accordingly, causing the voltage amplitude output from the primary coil PS to the secondary coil SC to rise slowly, so that the voltage at the output end of the rectifier circuit 150 rises slowly; it can be obtained from the formula of the voltage stress that when the voltage output of the rectifier circuit 150 just starts to rise slowly, the voltage amplitude at the output end of the rectifier circuit 150 is small, and at this time, the voltage stress of the first MOS tube is small; when a suitable N value is selected, the voltage stress of the first MOS tube will not exceed the standard.

[0083] The utility model also proposes a servo driver, which includes the switching power supply circuit 10. The specific structure of the switching power supply circuit 10 refers to the above embodiment. Since the servo driver adopts all the technical solutions of all the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0084] The above description is only an optional embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A soft start circuit, characterized in that: The soft start circuit comprises: A power supply access terminal, used for accessing a first voltage; An energy storage circuit, a first end of which is connected to the power access end and a second end of which is grounded; the energy storage circuit is used to charge when the power access end is connected to a first voltage, the output end voltage rises and is used to charge to a first predetermined voltage value after a first predetermined time.

2. The soft start circuit according to claim 1, characterized in that: The soft start circuit also includes: A discharge circuit, wherein a first end is connected to the output end of the energy storage circuit, and a second end is connected to the power access end; the discharge circuit is used to discharge the electric energy stored in the energy storage circuit when the power access end is disconnected from the first voltage; A voltage follower circuit has an input end connected to the output end of the energy storage circuit; the voltage follower circuit is used to isolate and output the voltage at the output end of the energy storage circuit.

3. The soft start circuit according to claim 2, characterized in that: The energy storage circuit comprises: a first resistor and a first capacitor; The first end of the first resistor is connected to the power supply access end, and the second end is connected to the first end of the first capacitor and the input end of the voltage follower circuit; the second end of the first capacitor is grounded.

4. The soft start circuit according to claim 3, characterized in that: The discharge circuit comprises: The first diode has an anode connected to the first end of the first capacitor and a cathode connected to the power supply access end.

5. The soft start circuit according to claim 3, characterized in that: The voltage follower circuit comprises: The second diode has a cathode connected to the first end of the first capacitor and an anode connected to the load device.

6. A switching power supply circuit, characterized in that: The switching power supply circuit comprises a soft start circuit as claimed in any one of claims 1 to 5; The switching power supply circuit also includes: A voltage conversion control module, wherein an input end of the voltage conversion control module is connected to an output end of the soft start circuit; The voltage conversion control module is used to determine the duty cycle according to the output voltage of the soft start circuit, and output a square wave of the corresponding duty cycle; A transformer, the transformer comprising a primary coil and a secondary coil; a first end of the primary coil is connected to a first DC voltage; and the secondary coil is connected to a load; A switch circuit, wherein the input end is connected to the output end of the voltage conversion control module, the second end is connected to the second end of the primary coil of the transformer, and the third end is grounded; the switch circuit is used to turn on / off the path between the second end of the primary coil and the ground according to the high and low levels of the square wave after receiving the square wave output by the voltage conversion control module.

7. The switching power supply circuit according to claim 6, characterized in that: The switch circuit comprises: A second resistor, a third resistor, a fourth resistor and a first MOS tube; The first end of the second resistor is connected to the output end of the voltage conversion control module, and the second end is connected to the first end of the third resistor and the gate of the first MOS tube; the second end of the third resistor is connected to the first end of the fourth resistor and the source of the first MOS tube; the second end of the fourth resistor is grounded; the drain of the first MOS tube is connected to the second end of the primary coil.

8. The switching power supply circuit according to claim 7, characterized in that: The transformer also includes: a fifth resistor, a second capacitor and a third diode; The first end of the fifth resistor, the first end of the second capacitor and the first end of the primary coil are connected; the second end of the fifth resistor and the second end of the second capacitor are connected to the cathode of the third diode; the anode of the third diode is connected to the second end of the primary coil and the drain of the first MOS tube.

9. A servo driver, characterized in that: The servo driver comprises a switching power supply circuit as claimed in any one of claims 6 to 8.

Images