CN116780881A

CN116780881A - Start-up circuit for switching power supply

Info

Publication number: CN116780881A
Application number: CN202210222691.4A
Authority: CN
Inventors: 王洋; 窦艳
Original assignee: Schneider Electric China Co Ltd
Current assignee: Schneider Electric China Co Ltd
Priority date: 2022-03-09
Filing date: 2022-03-09
Publication date: 2023-09-19

Abstract

The present disclosure relates to a start-up circuit for a switching power supply, comprising: the detection module is used for detecting the working pulse of the switching power supply, wherein the existence of the working pulse indicates that the switching power supply is in a working state; and a start module for transmitting a start signal to the switching power supply after a delay of a predetermined time interval to start the switching power supply in the absence of the operation pulse, and not transmitting the start signal in the presence of the operation pulse.

Description

Start-up circuit for switching power supply

Technical Field

The present disclosure relates to a start-up circuit for a switching power supply.

Background

Switching power supplies, also known as power supplies (Power supply unit, abbreviated PSU), convert ac or dc power supplied by a power grid into rated dc power for the respective consumer by means of rectification, chopping and/or inversion, so that the consumer can be operated normally.

The switching power supply generally has an overload protection function and a short-circuit protection function, i.e., in the event of an overload current or a short-circuit current caused by a malfunction of a consumer connected to the switching power supply, the switching power supply automatically enters a protection state and stops supplying power. If it is desired to have the switching power supply re-supplied, it is necessary to restore it by manual operation after the fault has been cleared.

In order to enable the switching power supply to automatically restore the power supply, an auxiliary circuit for automatic restoration needs to be designed for the switching power supply.

Disclosure of Invention

The present disclosure discloses a start-up circuit for a switching power supply. The starting circuit according to the present disclosure can automatically restart the switching power supply and restore the power supply after a delay period after the switching power supply is stopped, so that a fault may have been removed when the switching power supply is restarted.

Embodiments of the present disclosure provide a start-up circuit for a switching power supply, comprising: the detection module is used for detecting the working pulse of the switching power supply, wherein the existence of the working pulse indicates that the switching power supply is in a working state; and a start module for transmitting a start signal to the switching power supply after a delay of a predetermined time interval to start the switching power supply in the absence of the operation pulse, and not transmitting the start signal in the presence of the operation pulse.

According to an embodiment of the disclosure, the start signal is one or more pulse signals, and the predetermined time interval is spaced between the pulse signals.

According to an embodiment of the disclosure, the detection module comprises: and the rectifying and filtering unit is used for carrying out low-pass filtering on the working pulse and rectifying the working pulse into a direct current signal.

According to an embodiment of the disclosure, the detection module comprises: a control pulse generating unit for generating a control pulse having a predetermined pulse amplitude from the operation pulse; and the rectification filtering unit is used for carrying out low-pass filtering on the control pulse and rectifying the control pulse into a direct current signal.

According to an embodiment of the present disclosure, the rectifying and filtering unit includes: the first resistor, the first capacitor and the first zener diode; a first end of the first resistor receives the working pulse; the first end of the first capacitor is connected with the second end of the first resistor, and the second end of the first capacitor is grounded; and the cathode of the first zener diode is connected with the first end of the first capacitor, and the anode of the first zener diode is grounded.

According to an embodiment of the present disclosure, the control pulse generating unit includes a first diode, a first electronic switch; the rectifying and filtering unit comprises a first resistor, a first capacitor and a first zener diode; the anode of the first diode receives the working pulse, and the cathode of the first diode is connected with the control end of the first electronic switch; the first end of the first electronic switch is connected with a power supply voltage, the second end of the first electronic switch is connected with the first end of the first resistor, and the conduction of the first electronic switch is controlled based on the voltage difference between the control end and the second end of the first electronic switch; the first end of the first capacitor is connected with the second end of the first resistor, and the second end of the first capacitor is grounded; and the cathode of the first zener diode is connected with the first end of the first capacitor, and the anode of the first zener diode is grounded.

According to an embodiment of the disclosure, the start-up module comprises a capacitive charge-discharge circuit for delaying the predetermined time interval.

According to an embodiment of the disclosure, the starting module includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a second capacitor, a first voltage comparator, and a second voltage comparator; the first end of the second resistor is connected with the power supply voltage, the second end of the second resistor is connected with the first end of the third resistor, and the second end of the third resistor is grounded; the positive input end of the first voltage comparator is connected with the first end of the third resistor, the negative input end of the first voltage comparator is connected with the first end of the first capacitor, and the first voltage comparator is powered by the power supply voltage; the first end of the fourth resistor is connected with the power supply voltage, the second end of the fourth resistor is connected with the first end of the second capacitor, and the second end of the second capacitor is grounded; the first end of the fifth resistor is connected with the power supply voltage, the second end of the fifth resistor is connected with the first end of the sixth resistor, and the second end of the sixth resistor is grounded; the positive input end of the second voltage comparator is connected with the first end of the second capacitor, the negative input end of the second voltage comparator is connected with the first end of the sixth resistor, the output end of the second voltage comparator is used for outputting the starting signal, and the second voltage comparator is powered by the power supply voltage; the first end of the seventh resistor is connected with the output end of the second voltage comparator, and the second end of the seventh resistor is connected with the positive input end of the first voltage comparator; and a first end of the eighth resistor is connected with the output end of the second voltage comparator, and a second end of the eighth resistor is connected with the first end of the first capacitor.

According to an embodiment of the present disclosure, the starting module further includes a ninth resistor, a third capacitor, and a second zener diode; the first end of the ninth resistor is connected with the power supply voltage, and the second end of the ninth resistor is connected with the first end of the second resistor; the first end of the third capacitor is connected with the second end of the ninth resistor, and the second end of the third capacitor is grounded; and the cathode of the second zener diode is connected with the first end of the third capacitor, and the anode of the third zener diode is grounded.

According to an embodiment of the present disclosure, the start-up circuit includes: and the reversing circuit is used for reversing the high and low levels of the starting signal output by the second voltage comparator and outputting the reversed high and low levels to the switching power supply.

According to an embodiment of the present disclosure, the operation pulse includes: a Pulse Width Modulation (PWM) signal of a control unit in the switching power supply or a voltage signal generated based on the PWM signal; or a voltage signal on a current sensor connected to a primary winding of a transformer in the switching power supply; or a voltage signal generated at an auxiliary winding of a transformer in the switching power supply.

The starting circuit can automatically judge whether the switching power supply is in normal operation or not by detecting the working pulse of the switching power supply. Under the condition that the switching power supply enters a protection state to stop supplying power due to the fault of the electric equipment, the starting circuit can enable the switching power supply to automatically restart and restore the power supply after a period of time. In addition, before the fault of the electric equipment is removed, the starting circuit can enable the switching power supply to be in a standby running state with lower power consumption, so that energy consumption and heating are reduced, and finally, the protection of the switching power supply is realized, and the service life of the switching power supply is prolonged.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings that are required to be used in the description of the embodiments will be briefly described below. It should be apparent that the drawings in the following description are only some exemplary embodiments of the present disclosure, and that other drawings may be obtained from these drawings by those of ordinary skill in the art without undue effort.

Fig. 1 illustrates an application scenario of a start-up circuit and a block diagram thereof according to an embodiment of the present disclosure;

FIG. 2 shows a circuit diagram of a startup circuit according to an embodiment of the present disclosure;

fig. 3 illustrates a start-up signal and a voltage at a first end of a second capacitor over time according to an embodiment of the present disclosure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present disclosure more apparent, exemplary embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. It should be apparent that the described embodiments are only some of the embodiments of the present disclosure and not all of the embodiments of the present disclosure, and that the present disclosure is not limited by the example embodiments described herein.

In the present specification and drawings, substantially the same or similar method steps and elements are denoted by the same or similar reference numerals, and repeated descriptions of the method steps and elements will be omitted. Meanwhile, in the description of the present disclosure, the terms "first," "second," and the like are used merely to distinguish the descriptions, and are not to be construed as indicating or implying relative importance or order. In embodiments of the present disclosure, "connected" does not necessarily mean "directly connected" or "directly contacted" and only requires electrical communication, unless explicitly stated otherwise.

The switching power supply is used for providing rated direct-current voltage or alternating-current voltage for the electric equipment so as to enable the electric equipment to normally operate. For example, the switching power supply first rectifies the ac or dc power fed by the power grid into dc power by means of a rectifier circuit arranged therein, and then regulates the dc power into a consumer-rated dc power by means of a chopper circuit arranged therein, or inverts the dc power into a consumer-rated ac power by means of an inverter circuit arranged therein. The controller of the switching power supply, whether chopping or inverting, may control the switches in the chopper circuit or inverter circuit in a pulse width modulated (Pulse width modulation, PWM) manner.

Under the condition that the switching power supply works normally, a pulse width modulation signal is always present in the switching power supply, otherwise, under the condition that the switching power supply enters a protection state and stops running due to the fault of electric equipment, a controller of the switching power supply can not generate the pulse width modulation signal. Therefore, the pulse width modulation signal can be used as an operating pulse of the switching power supply to reflect the operating state of the switching power supply.

Thus, according to an embodiment of the present disclosure, the operating pulse comprises: a Pulse Width Modulated (PWM) signal of a control unit in the switching power supply or a voltage signal generated based on the PWM signal.

In addition, depending on the specific circuit configuration in the switching power supply, the operating pulse may also be a voltage signal on a current sensor connected to the primary winding of a transformer in the switching power supply; or a voltage signal generated at an auxiliary winding of a transformer in the switching power supply. These signals, which are generated by further processing the voltage signal, may also reflect the operating state of the switching power supply.

In the case that the switching power supply enters the protection state to stop operation due to a failure of the electric equipment, the starting circuit according to the embodiment of the disclosure may determine that the switching power supply enters the protection state based on the operation pulse, and may transmit a starting signal to the switching power supply after delaying for a period of time.

Fig. 1 shows a block diagram of a switching power supply 120 and a start-up circuit 110 according to an embodiment of the present disclosure. The start-up circuit 110 for the switching power supply 120 according to an embodiment of the present disclosure includes a detection module 111 and a start-up module 112. The detection module 111 is configured to detect an operation pulse of the switching power supply 120, where the presence of the operation pulse indicates that the switching power supply is in an operating state. The start-up module 112 is configured to delay a predetermined time interval before sending a start-up signal to the switching power supply 120 to start up the switching power supply 120 in the absence of an operation pulse, and to not send the start-up signal in the presence of the operation pulse.

By the start-up circuit 110 according to the embodiment of the present disclosure, a start-up signal may be automatically sent to the switching power supply 120 after a predetermined time interval is delayed after the switching power supply 120 is stopped, if a fault of the switching power supply 120 is removed, the switching power supply may be restarted and normal operation may be restored, and if the fault still exists, the start-up circuit 110 may continuously attempt to restart the switching power supply 120 at the predetermined time interval.

According to an embodiment of the present disclosure, the predetermined time interval may be implemented by a capacitive charge-discharge circuit in the start-up module. The capacitor charge takes time and a capacitor charge-discharge circuit may be used to set a predetermined time interval. For example, since the start signal is issued when the capacitor is charged to a certain voltage, the time for charging the capacitor to the certain voltage is a predetermined time interval.

According to an embodiment of the present disclosure, the detection module may comprise a rectifying and filtering unit for low-pass filtering the working pulse and rectifying the working pulse into a direct current signal. Which is described in more detail below with reference to fig. 3.

According to an embodiment of the present disclosure, the detection module may include a control pulse generation unit for generating a control pulse having a predetermined pulse amplitude according to the operation pulse, and a rectifying and filtering unit. The control pulse may reflect the operating state of the switching power supply 120. Based on the normalized predetermined amplitude, the control pulse has a more regular waveform than the working pulse. The rectification filter unit is used for carrying out low-pass filtering on the control pulse and rectifying the control pulse into a direct current signal. Which is described in more detail below with reference to fig. 3.

Fig. 3 shows a circuit diagram of the startup circuit 110 according to an embodiment of the present disclosure. The operation pulse of the switching power supply 120 is input from the input terminal of the start-up circuit 110, and the start-up signal for the switching power supply 120 is output from the output terminal of the start-up circuit 110.

According to an embodiment of the present disclosure, the detection module 111 includes a first resistor R1, a first capacitor C1, and a first zener diode ZD1. The first end of the first resistor R1 receives the operating pulse. The first end of the first capacitor C1 is connected with the second end of the first resistor R1, and the second end of the first capacitor C1 is grounded; and the cathode of the first zener diode ZD1 is connected to the first end of the first capacitor C1, and the anode of the first zener diode ZD1 is grounded. The first resistor R1, the first capacitor C1 and the first zener diode ZD1 form a rectifying and filtering unit 1112, the first resistor R1 and the first capacitor C1 form a low-pass filter to perform low-pass filtering on an input working pulse, and as the first capacitor C1 is charged, a stable direct current voltage is formed at the first end of the first capacitor C1, and the first zener diode ZD1 can stabilize the direct current voltage to a specific voltage stabilizing threshold, that is, the voltage stabilizing threshold is not exceeded, for example, the voltage stabilizing threshold is not exceeded by 5V.

According to another embodiment of the present disclosure, the detection module 111 includes a control pulse generation unit 1111 and a rectifying and filtering unit 1112. The control pulse generation unit 1111 includes a first diode D1 and a first electronic switch S1. The rectifying and filtering unit 1112 includes a first resistor R1, a first capacitor C1, and a first zener diode ZD1. The anode of the first diode D1 receives the working pulse, and the cathode of the first diode D1 is connected to the control terminal of the first electronic switch S1. The first end of the first electronic switch S1 is connected to the power supply voltage VCC, the second end of the first electronic switch S1 is connected to the first end of the first resistor R1, and the conduction of the first electronic switch S1 is controlled based on the voltage difference between the control end and the second end of the first electronic switch S1. The first end of the first capacitor C1 is connected with the second end of the first resistor R1, and the second end of the first capacitor C1 is grounded; and the cathode of the first zener diode ZD1 is connected to the first end of the first capacitor C1, and the anode of the first zener diode ZD1 is grounded.

The first electronic switch S1 may be, for example, an electronic device such as a bipolar junction transistor or a mosfet. In the case where the first electronic switch S1 is a bipolar junction transistor, the control terminal thereof is a base, the first terminal connected to the power supply voltage VCC is a collector, and the second terminal is an emitter. In the case where the first electronic switch S1 is a mosfet, the control terminal thereof is a gate, the first terminal connected to the power supply voltage VCC is a source, and the second terminal is a drain.

The control pulse generation unit 1111 includes the first diode D1 and the first electronic switch S1. Through the first diode D1, the input operation pulse is removed from the negative voltage. The high level of the operation pulse turns on the first electronic switch S1, so that the power supply voltage VCC is applied to the first end of the first resistor R1, and the low level of the positive pulse signal turns off the first electronic switch S1, and the first end of the first resistor R1 is low. The amplitude of the operation pulse itself is greatly different depending on the load, and the operation pulse can be converted into a control pulse with stable amplitude by the control pulse generation unit 111, and the control pulse can reflect the operation state of the switching power supply 120.

The rectifying and filtering unit 1112 includes a first resistor R1, a first capacitor C1, and a first zener diode ZD1. The first resistor R1 and the first capacitor C1 form a low-pass filter, which can perform low-pass filtering on the input control pulse, and as the first capacitor C1 is charged, a stable direct current voltage is formed at the first end of the first capacitor C1, and the first zener diode ZD1 can regulate the direct current voltage to a specific voltage regulation threshold, that is, the voltage regulation threshold is not exceeded, for example, the voltage regulation threshold is not exceeded, such as not exceeding 5V.

In the case where the operation pulse of the switching power supply 120 is present, the dc voltage is always present on the first capacitor C1, and thus the presence of the dc voltage may indicate that the switching power supply 120 is in a normal operation state. Conversely, if the operating pulse disappears, the first capacitor C1 discharges through the back-end circuit, and the voltage at the first end of the first capacitor C1 also gradually decreases, and if it is smaller than the predetermined threshold value, the switching power supply 120 is considered to stop supplying power.

According to an embodiment of the present disclosure, the starting module 112 includes a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a second capacitor C2, a first voltage comparator VC1, and a second voltage comparator VC2.

The first end of the second resistor R2 is connected to the supply voltage VCC, the second end of the second resistor R2 is connected to the first end of the third resistor R3, the second end of the third resistor R3 is grounded, wherein the voltage dropped across the third resistor R3 is then used as the first threshold voltage at the positive input of the first voltage comparator VC 1.

The positive input end of the first voltage comparator VC1 is connected to the first end of the third resistor R3, the negative input end of the first voltage comparator VC1 is connected to the first end of the first capacitor, the first voltage comparator VC1 is powered by the power supply voltage VCC, wherein when the direct current voltage at the first connection end of the first capacitor C1 is higher than the first threshold voltage, the output end of the first voltage comparator VC1 outputs a low level, for example, a zero voltage, and when the direct current voltage is lower than the first threshold voltage, the output end of the first voltage comparator VC1 outputs a high level.

The first end of the fourth resistor R4 is connected with the power supply voltage VCC, the second end of the fourth resistor R4 is connected with the first end of the second capacitor C2, the second end of the second capacitor C2 is grounded, wherein when the output end of the first voltage comparator VC1 outputs zero voltage, the voltage of the first end of the second capacitor C2 is zero, the second capacitor C2 is not charged, when the output end of the first voltage comparator VC1 outputs high level, the second capacitor C2 is charged, and therefore the voltage V at the first end of the second capacitor C2 _C2 The charge time constant of the second capacitor C2 increases, wherein the charge time constant of the second capacitor C2 depends on the size of the fourth resistor R4 and the second capacitor C2. In the example shown in fig. 3, the voltage V at the first end of the second capacitor C2 is shown by a dotted line _C2 Gradually increasing from zero to about 5V over about 1.6s.

The first end of the fifth resistor R5 is connected to the supply voltage VCC, the second end of the fifth resistor R5 is connected to the first end of the sixth resistor R6, and the second end of the sixth resistor R6 is grounded, wherein the voltage dropped across the sixth resistor R6 is then used as the second threshold voltage at the negative input of the second voltage comparator VC2.

The positive input end of the second voltage comparator VC2 is connected with the first end of the second capacitor C2, the negative input end of the second voltage comparator VC2 is connected with the first end of the sixth resistor R6, the output end of the second voltage comparator VC2 is used for outputting a starting signal, the second voltage comparator VC2 is powered by a power supply voltage VCC, wherein when the voltage of the first end of the second capacitor C2 is higher than the second threshold voltage, the output end of the second voltage comparator VC2 outputs a high level, and when the voltage on the second capacitor C2 is lower than the second threshold voltage, the output end of the second voltage comparator VC2 outputs a low level.

The first end of the seventh resistor R7 is connected to the output end of the second voltage comparator VC2, and the second end of the seventh resistor R7 is connected to the positive input end of the first voltage comparator VC 1. When the output terminal of the second voltage comparator VC2 outputs a high level, the first threshold voltage at the positive input terminal of the first voltage comparator VC1 is slightly raised by arranging the seventh resistor R7, so that when the voltage at the first terminal of the first capacitor C1 is just lower than the original first threshold value, the output signal of the second voltage comparator VC2 is prevented from being unstable, i.e., frequent jumps between the high level and the low level, due to the fact that the voltage at the first terminal of the first capacitor C1 is too close to the original first threshold value.

The first end of the eighth resistor R8 is connected to the output end of the second voltage comparator VC2, and the second end of the eighth resistor R8 is connected to the first end of the first capacitor. When the output terminal of the second voltage comparator VC2 outputs a high level, the first capacitor C1 is charged and thus the voltage at the first terminal of the first capacitor C1 rises, and in the case where the voltage at the first terminal of the first capacitor C1 is higher than the above-mentioned rising first threshold value, the first voltage comparator VC1 outputs a low level, for example, a zero voltage, which causes the second capacitor C2 to rapidly discharge and the voltage at the second terminal of the second capacitor C2 to rapidly become zero, and thus the second voltage comparator VC2 outputs a low level.

In the case where the second voltage comparator VC2 outputs a low level, the first capacitor C1 is discharged and thus the voltage of the first terminal of the first capacitor C1 decreases, and when it is less than the first threshold value of the positive input terminal of the first voltage comparator VC1, the first voltage comparator VC1 outputs a high level, thereby starting the next cycle of the start signal.

In each cycle, the second capacitor C2 is charged first and the voltage V at its first end _C2 Gradually rising, eventually causing the second voltage comparator VC2 to output a high level. The second capacitor C2 is then discharged rapidly, so that the high level drops back to the low level after a short duration. The switching power supply 120 detects this transition from a high level to a low level for restart. If there is still a fault, the switching power supply 120 may be protected again after a short start-up and power supply is stopped, and the process is repeated after a predetermined time interval has elapsed until the switching power supply 120 can be operated normally.

According to an embodiment of the present disclosure, the starting module 112 further includes a ninth resistor R9, a third capacitor C3, and a second zener diode ZD2; a first end of the ninth resistor R9 is connected to the power supply voltage VCC, and a second end of the ninth resistor R9 is connected to a first end of the second resistor R2; the first end of the third capacitor C3 is connected with the second end of the ninth resistor R9, and the second end of the third capacitor C3 is grounded; and the cathode of the second zener diode ZD2 is connected to the first end of the third capacitor C3, and the anode of the third zener diode ZD2 is grounded.

Since the power supply voltage VCC may fluctuate with a change in load, such fluctuation may be eliminated by arranging the ninth resistor R9, the third capacitor C3, and the second zener diode ZD2, so that a stable voltage may be provided at the second end of the ninth resistor R2, thereby ensuring normal operation of the entire circuit.

According to an embodiment of the present disclosure, the start signal may be one or more pulse signals, which are spaced apart by the predetermined time interval. FIG. 3 shows a start-up signal and a voltage V at a first end of a second capacitor C2 in accordance with an embodiment of the present disclosure _C2 Going over time. As shown, in the case where the switching power supply 120 stops operating, the start-up circuit110, which is indicated by a solid line in the figure, is composed of a plurality of pulse signals, each pulse lasting only a few milliseconds, for example 4ms, the predetermined time interval between the pulse signals being a few seconds, for example 1.6s as shown in the figure. The switching power supply 120 detects this transition from a high level to a low level for restart.

According to an embodiment of the present disclosure, the start-up circuit 110 may further include an inverting circuit for inverting a high-low level of a start-up signal of the output of the second voltage comparator VC2 to be output to the switching power supply.

As mentioned in the previous embodiments of the present disclosure, the switching power supply 120 detects such a transition from a high level to a low level for restart. But for other types of switching power supplies it may be necessary to detect a transition from a low level to a high level for restart, in which case the inverting circuit needs to be additionally connected at the output of the circuit 110 that is started.

The block diagrams of circuits, units, devices, apparatus, devices, systems referred to in this disclosure are only illustrative examples and are not intended to require or imply that the connections, arrangements, configurations must be made in the manner shown in the block diagrams. As will be appreciated by one of skill in the art, the circuits, units, devices, apparatuses, devices, systems may be connected, arranged, configured in any manner as long as the desired purpose is achieved. Circuits, elements, devices, means referred to in this disclosure may be implemented in any suitable manner, e.g., as an application specific integrated circuit, field Programmable Gate Array (FPGA), etc. or may be implemented with a general purpose processor in combination with a program.

It will be appreciated by persons skilled in the art that the above-described embodiments are merely examples and that various modifications, combinations, partial combinations and substitutions may be made to the embodiments of the present disclosure according to design requirements and other factors, provided that they fall within the scope of the appended claims or their equivalents, i.e., within the scope of the claims to be protected by the present disclosure.

Claims

1. A start-up circuit for a switching power supply, comprising:

the detection module is used for detecting the working pulse of the switching power supply, wherein the existence of the working pulse indicates that the switching power supply is in a working state; and

and the starting module is used for delaying a preset time interval to send a starting signal to the switching power supply to start the switching power supply in the case that the working pulse is not present, and not sending the starting signal in the case that the working pulse is present.

2. The starting circuit of claim 1, wherein,

the start signal is one or more pulse signals, and the preset time interval is formed between the pulse signals.

3. The starting circuit of claim 1, wherein,

the detection module comprises:

and the rectifying and filtering unit is used for carrying out low-pass filtering on the working pulse and rectifying the working pulse into a direct current signal.

4. The starting circuit of claim 1, wherein,

the detection module comprises:

a control pulse generating unit for generating a control pulse having a predetermined pulse amplitude from the operation pulse;

and the rectification filtering unit is used for carrying out low-pass filtering on the control pulse and rectifying the control pulse into a direct current signal.

5. A start-up circuit as claimed in claim 3, wherein the rectifying and filtering unit comprises:

the first resistor, the first capacitor and the first zener diode;

a first end of the first resistor receives the operating pulse,

the first end of the first capacitor is connected with the second end of the first resistor, and the second end of the first capacitor is grounded; and is also provided with

And the cathode of the first zener diode is connected with the first end of the first capacitor, and the anode of the first zener diode is grounded.

6. The startup circuit of claim 4, wherein,

the control pulse generation unit comprises a first diode and a first electronic switch;

the rectifying and filtering unit comprises a first resistor, a first capacitor and a first zener diode;

the anode of the first diode receives the working pulse, and the cathode of the first diode is connected with the control end of the first electronic switch;

the first end of the first electronic switch is connected with a power supply voltage, the second end of the first electronic switch is connected with the first end of the first resistor, and the conduction of the first electronic switch is controlled based on the voltage difference between the control end and the second end of the first electronic switch;

7. The starting circuit of claim 1, wherein,

the start-up module includes a capacitive charge-discharge circuit for delaying the predetermined time interval.

8. The startup circuit of claim 7, wherein,

the starting module comprises a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a second capacitor, a first voltage comparator and a second voltage comparator;

the first end of the second resistor is connected with the power supply voltage, the second end of the second resistor is connected with the first end of the third resistor, and the second end of the third resistor is grounded;

the positive input end of the first voltage comparator is connected with the first end of the third resistor, the negative input end of the first voltage comparator is connected with the first end of the first capacitor, and the first voltage comparator is powered by the power supply voltage;

the first end of the fourth resistor is connected with the power supply voltage, the second end of the fourth resistor is connected with the first end of the second capacitor, and the second end of the second capacitor is grounded;

the first end of the fifth resistor is connected with the power supply voltage, the second end of the fifth resistor is connected with the first end of the sixth resistor, and the second end of the sixth resistor is grounded;

the positive input end of the second voltage comparator is connected with the first end of the second capacitor, the negative input end of the second voltage comparator is connected with the first end of the sixth resistor, the output end of the second voltage comparator is used for outputting the starting signal, and the second voltage comparator is powered by the power supply voltage;

the first end of the seventh resistor is connected with the output end of the second voltage comparator, and the second end of the seventh resistor is connected with the positive input end of the first voltage comparator; and is also provided with

The first end of the eighth resistor is connected with the output end of the second voltage comparator, and the second end of the eighth resistor is connected with the first end of the first capacitor.

9. The startup circuit of claim 8, wherein

The starting module further comprises a ninth resistor, a third capacitor and a second zener diode;

the first end of the ninth resistor is connected with the power supply voltage, and the second end of the ninth resistor is connected with the first end of the second resistor;

the first end of the third capacitor is connected with the second end of the ninth resistor, and the second end of the third capacitor is grounded; and is also provided with

And the cathode of the second zener diode is connected with the first end of the third capacitor, and the anode of the third zener diode is grounded.

10. The startup circuit of claim 8, further comprising:

and the reversing circuit is used for reversing the high and low levels of the starting signal output by the second voltage comparator and outputting the reversed high and low levels to the switching power supply.

11. The start-up circuit of claim 1, wherein the operating pulse comprises:

a Pulse Width Modulation (PWM) signal of a control unit in the switching power supply or a voltage signal generated based on the PWM signal; or (b)

A voltage signal on a current sensor connected to a primary winding of a transformer in the switching power supply; or (b)

A voltage signal generated at an auxiliary winding of a transformer in the switching power supply.