Soft start circuit and method for a power supply

Abstract

The application provides a soft start circuit and method of a power supply. The circuit comprises a switching tube, an inductor, a first diode, a voltage sampling circuit and a controller. The first end of the switching tube is connected to the first output end of a power supply unit to receive a direct current input voltage. The first end of the inductor is connected to the second end of the switching tube, and the second end of the inductor is connected to the first end of a bus capacitor. The cathode of the first diode is connected to the first end of the inductor, and the anode of the first diode is connected to the second end of the bus capacitor. The voltage sampling circuit detects the direct current input voltage and the voltage across the bus capacitor, and outputs a signal representing the direct current input voltage and a capacitor voltage signal. The controller controls the switching tube to work in a high-frequency conduction and off state according to the input voltage signal and the capacitor voltage signal. The circuit can effectively inhibit the starting surge current and the re-surge current, and has the advantages of low cost, simple structure, less resource occupation, high reliability and strong stability.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a soft-start circuit and method for a power supply. Background Technology

[0002] With the explosive growth in computing power demand for Artificial Intelligence (AI), the power requirements of AI server clusters are increasing exponentially, with single-rack power increasing from the traditional 3-5kW to over 30kW, and even approaching the 100kW level. This trend presents new challenges to the power supply architecture of data centers. Traditional Alternating Current (AC) power supply architecture suffers from multi-stage conversion losses in the conversion process, limiting overall efficiency and making it difficult to meet the power density requirements of high-density computing scenarios.

[0003] To address these challenges, data center power distribution is shifting from AC power to high-voltage direct current (HVDC) power, such as 400V, ±400V, and 800V.

[0004] The introduction of high-voltage direct current (HVDC) power supply presents entirely new requirements and challenges for suppressing inrush current at the input of server power supplies. Power supplies typically incorporate large-capacity electrolytic capacitors as energy storage components to stabilize input voltage, absorb ripple current, and provide energy buffering during transient load changes. When a HVDC power supply is connected to the input, the initial voltage across the electrolytic capacitor is zero, essentially creating a near-short-circuit state, resulting in an extremely high-amplitude, short-duration inrush current. This inrush current can trigger or burn out circuit breakers, fuses, capacitors, and other equipment, seriously threatening the reliability and safety of the power supply.

[0005] Common surge current suppression methods mainly include the following two approaches: The first method limits the startup surge current by connecting a current-limiting resistor in parallel with a relay. At the moment the server power supply starts, the relay contacts open, and the input current charges the electrolytic capacitor through the current-limiting resistor, limiting the surge current. When the electrolytic capacitor is nearly fully charged, the relay contacts close, short-circuiting the current-limiting resistor to reduce power consumption during steady-state operation. However, once the relay contacts close, the current-limiting resistor is completely bypassed, and the circuit loses its ability to suppress subsequent surge currents. When the input voltage fluctuates, the load changes abruptly, or transient interference such as lightning strikes occurs, a large surge current may be generated again. At this time, the first method has no current-limiting measures, and the surge current will directly impact the internal components of the server power supply, posing a risk of damage. The second method uses a hot-swappable control chip to control the MOSFET to operate in constant current or linear mode to actively suppress the startup surge current. The first method uses a programmable gate drive to control the MOSFET's turn-on speed, ensuring the MOSFET operates in the saturation region during startup and thus limiting inrush current to a preset safe level. The second method places extremely high demands on the MOSFET's safe operating area, requiring the selection of high-voltage MOSFET devices with sufficient safety margin. This significantly increases the difficulty of device selection and material costs, and also imposes stringent requirements on thermal design and PCB layout. Furthermore, the high-voltage side hot-swap control necessitates a floating ground architecture design, further increasing circuit complexity and design difficulty.

[0006] In summary, existing surge current suppression methods have significant shortcomings when server power supplies face the new demands of high-voltage DC power supply: the first method cannot suppress re-inrush current, and the second method has excessively high requirements for the safe operating area of ​​MOSFETs, restricts device selection, and is costly. Therefore, the industry urgently needs to develop a new soft-start circuit and method for power supplies that can adapt to high-voltage DC input, actively limit the magnitude of surge current, and possess good reliability and cost-effectiveness. Summary of the Invention

[0007] In response to the issues mentioned above regarding the first method of existing surge current suppression methods being unable to suppress re-surge current, and the second method having excessively high requirements for the safe operating area of ​​MOSFETs, limited device selection, and high costs, this paper addresses these problems.

[0008] This application proposes a soft-start circuit for a power supply, wherein the soft-start circuit is located between the power supply unit and the bus capacitor, and the soft-start circuit includes:

[0009] A switching transistor, the first end of which is connected to the first output terminal of the power supply unit, is used to receive DC input voltage;

[0010] An inductor, wherein the first end of the inductor is connected to the second end of the switching transistor, and the second end of the inductor is connected to the first end of the bus capacitor;

[0011] The first diode has its cathode connected to the first terminal of the inductor and its anode connected to the second terminal of the bus capacitor and the second output terminal of the power supply unit, respectively.

[0012] A voltage sampling circuit is used to detect the DC input voltage and the voltage across the bus capacitor respectively, and output an input voltage signal representing the DC input voltage and a capacitor voltage signal representing the voltage across the bus capacitor respectively.

[0013] The controller is used to receive the input voltage signal and the capacitor voltage signal, and control the switching transistor to operate in a high-frequency on and off state according to the input voltage signal and the capacitor voltage signal; wherein, when the switching transistor is on, the power supply unit charges the bus capacitor through the switching transistor and the inductor, and when the switching transistor is off, the inductor charges the bus capacitor through the first diode to form a freewheeling circuit.

[0014] Optionally, the soft-start circuit further includes a current sampling circuit for detecting the current of the inductor and outputting a current signal characterizing the current of the inductor.

[0015] The controller is used to receive the current signal, the input voltage signal, and the capacitor voltage signal, and control the switching transistor to operate in a high-frequency on and off state according to the current signal, the input voltage signal, and the capacitor voltage signal.

[0016] Optionally, when the current signal reaches a preset overcurrent protection threshold, the controller controls the switching transistor to turn off.

[0017] Optionally, the controller includes:

[0018] The first arithmetic unit is used to perform differential operations on the input voltage signal received at the current moment and the capacitor voltage signal received at the current moment to obtain the voltage error signal;

[0019] A voltage regulator is used to output a current loop reference value based on the voltage error signal;

[0020] The second arithmetic unit is used to perform calculations on the current loop reference value, the given constant current value, and the current signal received at the current moment to obtain the current error signal;

[0021] A current regulator is used to output a digital signal based on the current error signal;

[0022] A PWM generator is used to convert the digital signal into a PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0023] Optionally, the controller further includes a third arithmetic unit for performing calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal;

[0024] A PWM generator is used to convert the digital compensation signal into a PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0025] Optionally, when the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, the controller controls the switch to remain in the on state.

[0026] Optionally, the soft-start circuit of the power supply further includes:

[0027] The second diode, the anode of which is connected to the first terminal of the switching transistor;

[0028] A current limiting device, wherein the first end of the current limiting device is connected to the cathode of the second diode;

[0029] An auxiliary power supply, wherein the first input terminal of the auxiliary power supply is connected to the second terminal of the current limiting device, the second input terminal of the auxiliary power supply is connected to the second terminal of the bus capacitor, and the auxiliary power supply provides auxiliary voltage to the controller;

[0030] The third diode has its anode connected to the first terminal of the bus capacitor and its cathode connected to the first input terminal of the auxiliary power supply.

[0031] Optionally, when the power supply unit is powered on, the auxiliary power supply draws power from the power supply unit through the second diode and the current limiting device;

[0032] When the DC input voltage reaches the power-on voltage of the auxiliary power supply, the auxiliary power supply operates and outputs an auxiliary voltage;

[0033] When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, or when the power supply unit loses power, the auxiliary power supply draws power from the bus capacitor through the third diode.

[0034] Optionally, when the input voltage signal is greater than a preset safe voltage threshold, or when the power supply unit loses power, the controller controls the switching transistor to turn off.

[0035] This application also proposes a startup method for a soft-start circuit of a power supply. The soft-start circuit includes a switching transistor, an inductor, a first diode, a voltage sampling circuit, and a controller. The first terminal of the switching transistor is connected to the first output terminal of the power supply unit to receive a DC input voltage. The first terminal of the inductor is connected to the second terminal of the switching transistor, and the second terminal of the inductor is connected to the first terminal of a bus capacitor. The cathode of the first diode is connected to the first terminal of the inductor, and the anode of the first diode is connected to the second terminal of the bus capacitor and the second output terminal of the power supply unit, respectively. The startup method includes:

[0036] S1: The voltage sampling circuit detects the DC input voltage and the voltage across the bus capacitor respectively, and outputs the input voltage signal representing the DC input voltage and the capacitor voltage signal representing the voltage across the bus capacitor respectively;

[0037] S2: The controller receives the input voltage signal and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state according to the input voltage signal and the capacitor voltage signal; wherein, when the switching transistor is on, the power supply unit charges the bus capacitor through the switching transistor and the inductor, and when the switching transistor is off, the inductor charges the bus capacitor through the first diode to form a freewheeling circuit.

[0038] Optionally, the soft-start circuit of the power supply further includes a current sampling circuit; before step S2, the current of the inductor is detected by the current sampling circuit, and a current signal characterizing the current of the inductor is output.

[0039] The controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal.

[0040] Optionally, when the current signal reaches a preset overcurrent protection threshold, the switching transistor is controlled to turn off.

[0041] Optionally, the controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal, including:

[0042] The system receives the input voltage signal and the capacitor voltage signal, and performs a differential operation on the input voltage signal and the capacitor voltage signal received at the current time to obtain a voltage error signal.

[0043] Output a current loop reference value based on the voltage error signal;

[0044] The system receives the current loop reference value, the given constant current value, and the current signal, and performs calculations on the current loop reference value, the given constant current value, and the current signal received at the current moment to obtain a current error signal.

[0045] A digital signal is output based on the current error signal;

[0046] The digital signal is converted into a PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0047] Optionally, the controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal, further comprising:

[0048] The system receives the mathematical signal and the input voltage feedforward signal, and performs calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal.

[0049] The digital compensation signal is converted into the PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0050] Optionally, when the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, the controller controls the switch to remain in the on state.

[0051] Optionally, the soft-start circuit of the power supply further includes a second diode, a third diode, a current limiting device, and an auxiliary power supply. The anode of the second diode is connected to the first terminal of the switching transistor; the first terminal of the current limiting device is connected to the cathode of the second diode; the first input terminal of the auxiliary power supply is connected to the second terminal of the current limiting device, and the second input terminal of the auxiliary power supply is connected to the second terminal of the bus capacitor. The auxiliary power supply provides an auxiliary voltage to the controller; the anode of the third diode is connected to the first terminal of the bus capacitor, and the cathode of the third diode is connected to the first input terminal of the auxiliary power supply.

[0052] When the power supply unit is powered on, the auxiliary power supply draws power from the power supply unit through the second diode and the current limiting device;

[0053] When the DC input voltage reaches the power-on voltage of the auxiliary power supply, the auxiliary power supply operates and outputs an auxiliary voltage;

[0054] When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, or when the power supply unit loses power, the auxiliary power supply draws power from the bus capacitor through the third diode.

[0055] Optionally, when the input voltage signal is greater than a preset safe voltage threshold, or when the power supply unit loses power, the controller controls the switching transistor to turn off.

[0056] The beneficial effects of this application include at least the following:

[0057] The soft-start circuit of this embodiment includes a switching transistor, an inductor, a first diode, a voltage sampling circuit, and a controller. The switching transistor and the inductor are connected in series between the power supply unit and the bus capacitor. The cathode of the first diode is connected to the inductor, and the anode of the first diode is connected to the bus capacitor. The voltage sampling circuit is used to detect the DC input voltage and the voltage across the bus capacitor, and outputs an input voltage signal representing the DC input voltage and a capacitor voltage signal representing the voltage across the bus capacitor, respectively. The controller receives the input voltage signal and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the input voltage signal and the capacitor voltage signal. When the switching transistor is on, the power supply unit charges the bus capacitor through the switching transistor and the inductor; when the switching transistor is off, the inductor charges the bus capacitor. This soft-start circuit can actively and controllably suppress the start-up inrush current and re-inrush current of the high-voltage DC input. This soft-start circuit has a simple structure, low cost, small resource and space requirements, and strong versatility and adaptability. In this soft-start circuit, the power devices do not always operate in the linear region, and the requirements for the power devices are not high. Therefore, it can repeatedly suppress surge current and re-surge current, and has high reliability and strong stability.

[0058] The features and technical advantages of this application have been broadly outlined above to facilitate a better understanding of the following detailed description. Additional features and advantages of this application, which form the subject matter of the claims, will be described below. Those skilled in the art will understand that the disclosed concepts and specific embodiments can be readily utilized as the basis for modifying or designing other structures or processes to achieve the same purpose as this application. Those skilled in the art will also recognize that such equivalent constructions do not depart from the spirit and scope of this application as set forth in the appended claims. Attached Figure Description

[0059] To gain a more comprehensive understanding of this application and its advantages, the following description is now taken in conjunction with the accompanying drawings, in which:

[0060] Figure 1 A schematic diagram of the soft-start circuit of a power supply according to an embodiment of this application is shown;

[0061] Figure 2 A schematic diagram of the soft-start circuit of a power supply according to another embodiment of this application is shown;

[0062] Figure 3 A schematic diagram of the controller according to an embodiment of this application is shown;

[0063] Figure 4 The control timing diagram of the soft-start circuit of the power supply according to an embodiment of this application is shown;

[0064] Figure 5 A flowchart illustrating the startup method of the soft-start circuit of the power supply according to an embodiment of this application is shown.

[0065] Unless otherwise indicated, corresponding numbers and symbols in different figures generally refer to corresponding parts. The accompanying drawings are provided to clearly illustrate relevant aspects of various embodiments and are not necessarily drawn to scale. Detailed Implementation

[0066] Various exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0067] The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment illustrated herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments. The terms "first," "second," "third," etc. (if present) in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence.

[0068] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "coupled," "connected," and "linked" should be interpreted broadly. For example, they can refer to electrical connection or mutual communication; they can be a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0069] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0070] The power supply includes a bus capacitor CB and an electrical device 3. The power supply is connected to a power supply unit 1, and the bus capacitor CB is connected in parallel to the two output terminals of the power supply unit 1. The bus capacitor CB can be a single capacitor or multiple capacitors connected in series. The electrical device 3 is connected in parallel to both ends of the bus capacitor CB. The electrical device can be a power converter such as a DC / DC converter or a DC / AC converter, or other equipment circuits; no specific limitations are specified here.

[0071] This embodiment provides a soft-start circuit for a power supply. Figure 1 This application shows a schematic diagram of the soft-start circuit of a power supply according to an embodiment of the present application. Figure 1 As shown, the soft-start circuit is located between the power supply unit 1 and the bus capacitor CB. The soft-start circuit includes a switching transistor S1, an inductor L1, a diode D1, a voltage sampling circuit 6, and a controller 7. In this embodiment, the switching transistor S1 can be a power switching transistor, such as a MOSFET, IGBT, or IGCT. The power supply unit 1 provides a DC input voltage, i.e., a high-voltage DC voltage, such as 400V, ±400V, or 800V.

[0072] The first terminal of the switching transistor S1 is connected to the first output terminal of the power supply unit 1 to receive the DC input voltage. The first terminal of the inductor L1 is connected to the second terminal of the switching transistor S1, and the second terminal of the inductor L1 is connected to the first terminal of the bus capacitor CB. The cathode of the diode D1 is connected to the first terminal of the inductor L1, and the anode of the diode D1 is connected to both the second terminal of the bus capacitor CB and the second output terminal of the power supply unit 1. The bus capacitor CB can represent the output filter capacitor of the soft-start circuit.

[0073] The voltage sampling circuit 6 is used to detect the DC input voltage and the voltage across the bus capacitor CB, respectively, and outputs an input voltage signal representing the DC input voltage and a capacitor voltage signal representing the voltage across the bus capacitor CB, respectively. In some embodiments, the voltage sampling circuit 6 can be an active voltage sampling circuit. The first and second input terminals of the active voltage sampling circuit are respectively connected to the first terminal of the switching transistor S1 and the second output terminal of the power supply unit 1. The third and fourth input terminals of the active voltage sampling circuit are respectively connected to the first and second terminals of the bus capacitor CB. The power supply terminal of the active voltage sampling circuit is used to receive an auxiliary voltage. When the active voltage sampling circuit receives the auxiliary voltage, it starts to detect the DC input voltage and the voltage across the bus capacitor CB, and outputs an input voltage signal representing the DC input voltage and a capacitor voltage signal representing the voltage across the bus capacitor CB, respectively. In other embodiments, the voltage sampling circuit 6 may be a passive voltage sampling circuit. The first and second input terminals of the passive voltage sampling circuit are respectively connected to the first terminal of the switching transistor S1 and the second output terminal of the power supply unit 1, and are used to detect the DC input voltage and output an input voltage signal characterizing the DC input voltage. The third and fourth input terminals of the passive voltage sampling circuit are respectively connected to the first and second terminals of the bus capacitor CB, and are used to detect the voltage across the bus capacitor and output a capacitor voltage signal characterizing the voltage across the bus capacitor CB.

[0074] The input terminal of the controller 7 is connected to the voltage sampling circuit 6, and the power supply terminal of the controller 7 is used to receive the auxiliary voltage. The controller 7 receives the input voltage signal and the capacitor voltage signal, and controls the switch S1 to operate in a high-frequency on and off state according to the input voltage signal and the capacitor voltage signal, so as to limit the input current (i.e., the current flowing from the power supply unit into the switch S1) within a safe current threshold. When the switch S1 is on, the power supply unit 1 charges the bus capacitor CB through the switch S1 and the inductor L1, that is, the current flows from the first terminal of the power supply unit 1 through the switch S1 and the inductor L1 to charge the bus capacitor CB. When the switch S1 is off, the inductor L1 forms a freewheeling circuit through the diode D1 to charge the bus capacitor CB. Specifically, when the controller 7 receives the auxiliary voltage and the DC input voltage reaches the preset power-on voltage value (i.e., the DC input voltage is greater than or equal to the preset power-on voltage value), it begins to receive the input voltage signal and the capacitor voltage signal, and controls the switch S1 to operate in a high-frequency on / off state based on the currently received input voltage signal and the currently received capacitor voltage signal. The controller 7 controls the switch S1 to operate in a high-frequency on / off state, that is, the switch S1 switches at high frequency to suppress inrush current.

[0075] As can be seen, the controllable step-down circuit composed of switch S1, inductor L1, and diode D1, combined with voltage sampling circuit 6 and controller 7, can suppress start-up inrush current and re-inrush current. Controller 7 controls switch S1 to operate in high-frequency conduction and cutoff states based on the input voltage signal and capacitor voltage signal. The switching frequency of switch S1 is a high-frequency switching frequency, and the switching frequency can be selected according to requirements. This effectively suppresses start-up inrush current and re-inrush current. Furthermore, in the event of input overvoltage, to ensure the safety of downstream electrical devices, the controller can control switch S1 to be in the cutoff state. This soft-start circuit has a simple structure, low cost, small resource and space requirements, and strong versatility and adaptability. It can withstand high input voltage and current stress, and no power device operates continuously in the linear region, so the requirements for power devices are not high. Therefore, it can repeatedly suppress start-up inrush current and re-inrush current, and has the advantages of high reliability and strong stability.

[0076] In this embodiment, an electromagnetic interference suppression circuit can also be placed between the power supply unit 1 and the switching transistor S1 for bidirectional filtering of electromagnetic interference. The electromagnetic interference suppression circuit can be composed of one or more X capacitors, Y capacitors, common-mode inductors and differential-mode inductors.

[0077] Continue to refer to Figure 1 The soft-start circuit further includes a current sampling circuit 5, used to detect the current of the inductor L1 and output a current signal characterizing the current of the inductor L1. The current sampling circuit 5 can be a Hall sensor or a sampling resistor, etc., and is not further limited thereto. The current sampling circuit 5 can be placed between the switching transistor S1 and the inductor L1, or between the inductor L1 and the bus capacitor CB, or between the anode of the diode D1 and the bus capacitor, but is not limited thereto. The output terminal of the current sampling circuit 5 is connected to the controller 7. The power supply terminal of the current sampling circuit 5 receives an auxiliary voltage. When the current sampling circuit 5 receives the auxiliary voltage, it begins to detect the current of the inductor L1, and outputs the current signal.

[0078] The controller 7 receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor S1 to operate in a high-frequency on / off state based on these signals. Specifically, when the controller 7 receives the auxiliary voltage and the DC input voltage reaches the preset power-on voltage value, it begins receiving the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor S1 to operate in a high-frequency on / off state based on the currently received current signal, the currently received input voltage signal, and the currently received capacitor voltage signal. It should be noted that the preset power-on voltage value is selected and set as needed. By adding a current sampling circuit, the soft-start circuit has good speed and anti-interference performance, and current limiting protection is provided for the inductor L1.

[0079] This embodiment preferably employs a dual-loop control strategy with an inner loop for inductor current and an outer loop for voltage. Both loops use PI regulators to reduce system steady-state error and improve voltage tracking capability. The controller controls the switch S1 to operate in a high-frequency on and off state, enabling the current of inductor L1 to rise and fall near the target value, thus achieving the purpose of constant current from inductor L1 to charge the bus capacitor CB.

[0080] When electrical device 3 malfunctions, or when an abnormal surge current spike occurs due to lightning strikes, the current signal reaches a preset overcurrent protection threshold. This causes the controller 7 to control the switch S1 to turn off, thereby cutting off power supply to the downstream electrical device 3 and isolating the input terminal to protect the downstream electrical device. It should be noted that the preset overcurrent protection threshold can be set or selected according to actual needs.

[0081] In this embodiment, the voltage sampling circuit 6 includes an input voltage sampling circuit and a capacitor voltage sampling circuit. The input voltage sampling circuit is used to detect the DC input voltage and output the input voltage signal. The input voltage sampling circuit is connected between the first terminal of the switching transistor S1 and the anode of the diode D1, and is used to detect the DC input voltage and provide an input voltage signal. The capacitor voltage sampling circuit is used to detect the voltage across the bus capacitor CB and output the capacitor voltage signal. The capacitor sampling circuit is connected across the bus capacitor CB, and is used to detect the voltage across the bus capacitor CB and provide a capacitor voltage signal.

[0082] Furthermore, when the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, the controller 7 controls the switch S1 to remain in the on state. The inductor L1 can be used as a differential-mode inductor, effectively suppressing electromagnetic interference and saving on the preceding electromagnetic interference suppression circuitry. It should be noted that the preset voltage is set or selected according to requirements.

[0083] like Figure 3 As shown, the controller 7 includes a first arithmetic unit 71, a voltage regulator 72, a second arithmetic unit 73, a current regulator 74, a third arithmetic unit 75, and a PWM generator 76. The first arithmetic unit 71 is connected to the input voltage sampling circuit 61 and the capacitor voltage sampling circuit 62, respectively receiving the input voltage signal Vi and the capacitor voltage signal Vcb, and performing differential operations on the input voltage signal Vi and the capacitor voltage signal Vcb received at the current time to obtain a voltage error signal.

[0084] The voltage regulator 72 is used to output a current loop reference value based on the voltage error signal. Specifically, the voltage regulator 72 receives the voltage error signal and performs PI regulation on the voltage error signal to output the current loop reference value.

[0085] The second arithmetic unit 73 receives a current loop reference value, a given constant current value, and a current signal, and performs calculations on the current loop reference value, the given constant current value, and the current signal received at the current moment to obtain a current error signal. Specifically, the second arithmetic unit 73 sums the current loop reference value and the given constant current value, and then performs a differential operation with the current signal received at the current moment to obtain the current error signal. It should be noted that the given constant current value can be a target value, which can be set or selected according to actual needs.

[0086] The current regulator 74 is used to output a digital signal based on the current error signal. Specifically, the current regulator 74 receives the current error signal and performs PI regulation on the current error signal to output a digital signal.

[0087] The third arithmetic unit 75 receives a digital signal and an input voltage feedforward signal, and performs calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal. Specifically, the third arithmetic unit 75 performs a summation operation on the digital signal and the input voltage feedforward signal to obtain the digital compensation signal.

[0088] The PWM generator 76 receives the digital compensation signal and converts the digital compensation signal into a PWM pulse width modulation signal Gs1 to control the switching transistor S1 to operate in a high-frequency on and off state.

[0089] In some embodiments, the current regulator 74 is directly connected to the PWM generator 76. The PWM generator 76 receives digital signals and converts the digital signals into the PWM pulse width modulation signal Gs1 to control the switching transistor S1 to operate in a high-frequency on and off state.

[0090] Continue to refer to Figure 1The soft-start circuit also includes diode D2, current limiting device 2, auxiliary power supply 4, and diode D3. The anode of diode D2 is connected to the first terminal of the switching transistor S1; the first terminal of the current limiting device 2 is connected to the cathode of diode D2. In this embodiment, the current limiting device 2 can be a device with impedance characteristics, such as a pure resistor, a positive temperature coefficient resistor, or a negative temperature coefficient resistor, or it can be a circuit with protection function or a fuse with fusing function. The current limiting device 2 can effectively suppress the inrush current of the auxiliary power supply 4 during startup, and connecting the current limiting device 2 in series can also improve efficiency.

[0091] The first input terminal of the auxiliary power supply 4 is connected to the second terminal of the current limiting device 2, the second input terminal of the auxiliary power supply 4 is connected to the second terminal of the bus capacitor CB, and the output terminal of the auxiliary power supply 4 is connected to the controller 7 to provide auxiliary voltage to the controller 7.

[0092] The anode of diode D3 is connected to the first terminal of bus capacitor CB, and the cathode of diode D3 is connected to the first input terminal of auxiliary power supply 4.

[0093] When power supply unit 1 is powered on for the first time, auxiliary power supply 4 draws power from the first terminal of the supply voltage 1 through diode D2 and current limiting device 2, or directly from the output terminal of the electromagnetic interference suppression circuit after power supply unit 1. The input current flows through diode D2 and current limiting device 2 into the auxiliary power supply, establishing auxiliary power supply to output auxiliary voltage. By drawing power from the first terminal of switching transistor S1 through the series connection of current limiting device 2 and diode D2, the inrush current of the auxiliary power supply at startup can be suppressed. This is because the auxiliary power supply usually has an input filter capacitor, and current limiting device 2 can suppress the spike current of the high-voltage DC input voltage charging the filter capacitor.

[0094] When the DC input voltage exceeds the auxiliary power supply's start-up voltage, the auxiliary power supply operates and outputs an auxiliary voltage to power the controller, voltage sampling circuit, and current sampling circuit, among other internal power supply circuits. This means the auxiliary power supply first establishes internal power supply, creating basic controllable conditions for the soft-start circuit. After internal power supply is established, if the DC input voltage reaches the preset power supply start-up voltage, the controller 7 controls the switch S1 to operate in a high-frequency on / off state based on the currently received input voltage signal, capacitor voltage signal, and current signal. This allows the inductor L1 to charge the bus capacitor CB with a constant current, gradually increasing the voltage across the bus capacitor CB. Note that the auxiliary power supply's start-up voltage is less than the preset power supply start-up voltage.

[0095] When the voltage across the bus capacitor approaches or equals the DC input voltage (i.e., the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to the preset voltage), the soft start is complete, meaning the power supply has started. The controller 7 keeps the switch S1 on, and diode D2 and current limiting device 2 are bypassed. The auxiliary power supply 4 draws power from the bus capacitor CB through diode D3. Because the total voltage drop across current limiting device 2 and diode D2 is greater than the voltage drop across diode D3, when switch S1 is on, diode D2 and current limiting device 2 are bypassed, thereby reducing power loss.

[0096] When an input overvoltage occurs, meaning the input voltage signal exceeds a preset safe voltage threshold, controller 7 controls switch S1 to turn off. The voltage across bus capacitor CB gradually decreases, and auxiliary power is drawn from the input terminal by diode D2 and current limiting device 2 to maintain internal power supply. Because the operating voltage range of the auxiliary power supply is wider than that of the electrical device, the auxiliary voltage can still provide power normally even under input overvoltage conditions. When power supply unit 1 loses power, controller 7 controls switch S1 to turn off, the voltage across bus capacitor CB gradually decreases, and auxiliary power is drawn from bus capacitor CB by diode D3 to maintain power supply for a certain period of time. When the voltage across the bus capacitor drops below the shutdown voltage of auxiliary power supply 4, auxiliary power supply 4 stops working and outputs no auxiliary voltage. Controller 7 stops working because it does not receive auxiliary voltage. If power supply unit 1 is powered on at this time, the working principle is the same as when power supply unit 1 is first powered on. Auxiliary power supply 4 first draws power from power supply unit 1 through diode D2 and current limiting device 2 until the auxiliary power supply is established to output auxiliary voltage. Controller 7 starts working after receiving the auxiliary voltage. If the DC input voltage is greater than the power supply startup voltage, controller 7 controls switch S1 to operate in a high-frequency on / off state based on the currently received input voltage signal, capacitor voltage signal, and current signal, so that the current from inductor L1 charges the bus capacitor CB with a constant current. The voltage across bus capacitor CB gradually rises until the bus capacitor voltage is close to or equal to the DC input voltage, completing the soft start. After the power supply restarts, controller 7 keeps switch S1 in the on state. If power supply unit 1 loses power, the bus capacitor voltage gradually decreases due to the continued load of the electrical equipment, but it remains higher than the auxiliary voltage's start-up voltage. If power supply unit 1 is powered on at this time, controller 7 controls switch S1 to operate in a high-frequency on / off state based on the currently received input voltage signal, capacitor voltage signal, and current signal. This allows the current from inductor L1 to charge the bus capacitor CB with a constant current, gradually increasing the voltage across the bus capacitor CB until it approaches or equals the DC input voltage. The soft start is then complete, and the power supply restarts, effectively suppressing the surge current. After the power supply restarts, controller 7 keeps switch S1 in the on state.

[0097] When the power supply unit experiences a momentary power outage and is then restored, the auxiliary power supply can maintain its output auxiliary voltage for a long time because diode D3 draws power from the bus capacitor. The power supply can then perform fault reporting, timing logic control, and timely protection measures.

[0098] Furthermore, when there is an input overvoltage, i.e., the input voltage signal exceeds a preset safe voltage threshold, or when the power supply unit 1 loses power, the controller 7 controls the switch S1 to turn off, thereby isolating the input terminal to protect the devices in the downstream electrical equipment. It should be noted that the preset safe voltage threshold can be set according to the withstand voltage of each stage of the circuit. For example, when the withstand voltage of the auxiliary power supply is greater than the withstand voltage of the bus capacitor CB and the withstand voltage of the electrical equipment, the preset safe voltage threshold can be set between the withstand voltage of the auxiliary power supply and the withstand voltage of the bus capacitor.

[0099] Furthermore, when an input overvoltage, undervoltage, overcurrent, or overtemperature event occurs, the controller 7 can shut down the switching transistor S1 to isolate the input terminal and protect the subsequent circuitry.

[0100] Figure 2 A schematic diagram of the soft-start circuit of a power supply according to another embodiment of this application is shown, as follows: Figure 2 As shown, the first terminal of the switching transistor S1 is connected to the power supply unit 1 through the rectifier circuit 8. The power supply unit 1 can provide AC input voltage, which is then rectified by the rectifier circuit 8 to output DC input voltage. Figure 2 and Figure 1 The soft-start circuit is the same as the one described above; you can refer to [the relevant documentation]. Figure 1 The relevant descriptions will not be repeated here. The auxiliary power supply 4 draws power from the output of the rectifier circuit through diode D2 and current limiting device 2.

[0101] In this embodiment, an electromagnetic interference suppression circuit can be placed between the power supply unit 1 and the rectifier circuit 8.

[0102] Combination Figure 1 and Figure 4 The period from time t0 to time t1 is the initial state in which power supply unit 1 is not powered on, and at this time the DC input voltage Vin is 0V.

[0103] Time t1 is the time when power supply unit 1 is powered on.

[0104] The period from time t1 to t2 is the power supply startup period. Auxiliary power supply 4 draws power from power supply unit 1 through diode D2 and current limiting device 2. The input current flows into auxiliary power supply 4 through diode D2 and current limiting device 2, establishing the auxiliary power supply and outputting auxiliary voltage. Controller 7 starts working after receiving the auxiliary voltage. If the DC input voltage reaches the power supply startup voltage, controller 7 controls switch S1 to operate in a high-frequency on / off state based on the currently received input voltage signal, capacitor voltage signal, and current signal. This ensures that the current IL of inductor L1 is constant, charging the bus capacitor CB, thereby limiting the magnitude of the input current Iin. During the period from time t1 to t2, the input current Iin gradually increases, and the voltage VCB across the bus capacitor CB gradually rises.

[0105] At time t2, the voltage VCB across the bus capacitor rises to near or equal to the DC input voltage Vin. That is, the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to the preset voltage. Soft start is then complete, the power supply starts up, and the inrush current is effectively suppressed.

[0106] The period from time t2 to time t3 represents the normal operating state under load after the power supply has completed startup. During the period from time t2 to time t3, the controller 7 controls the switch S1 to remain in the conducting state.

[0107] The period from t3 to t4 is the time when power supply unit 1 is de-energized, that is, when the DC input voltage Vin drops to 0V. Since the power supply output is still under load, the voltage VCB across the bus capacitor CB gradually decreases. During the period from t3 to t4, the controller 7 controls the switch S1 to remain in the off state.

[0108] t4 is the time when power supply unit 1 is powered on.

[0109] The period from t4 to t5 is the power supply restart time. During this period, auxiliary power supply 4 first draws power from power supply unit 1 through diode D2 and current limiting device 2 to establish auxiliary power supply and output auxiliary voltage. After receiving the auxiliary voltage, controller 7 starts working. If the DC input voltage reaches the power supply start-up voltage, controller 7 controls the switching transistor to operate in the high-frequency S1 conduction and cutoff state according to the input voltage signal, capacitor voltage signal, and current signal received at the current time. This achieves the purpose of constant current IL of inductor L1 charging bus capacitor CB, thereby limiting the magnitude of input current Iin. During the period from t4 to t5, the input current Iin gradually increases, and the voltage VCB across bus capacitor CB gradually rises.

[0110] At time t5, the voltage VCB across the bus capacitor rises to near or equal to the DC input voltage Vin. That is, the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to the preset voltage. The soft start is completed, the power supply restarts, and the surge current is effectively suppressed.

[0111] After time t5, the power supply completes its startup and enters normal load-bearing operation. After time t5, controller 7 controls switch S1 to remain on.

[0112] This embodiment provides a startup method for a power supply soft-start circuit. Figure 5 A flowchart illustrating a startup method of a power supply soft-start circuit according to an embodiment of this application is shown, as follows: Figure 5 As shown, this startup method is applied to Figure 1 and Figure 2 The soft-start circuit shown is located between power supply unit 1 and bus capacitor CB. This soft-start circuit includes a switching transistor S1, an inductor L1, a diode D1, a voltage sampling circuit 6, and a controller 7. In this embodiment, the switching transistor S1 can be a power switching transistor, such as a MOSFET, IGBT, or IGCT. Power supply unit 1 provides a DC input voltage, wherein the DC input voltage is high-voltage DC. The first terminal of the switching transistor S1 is connected to the first output terminal of the power supply unit 1 to receive the DC input voltage. The first terminal of the inductor L1 is connected to the second terminal of the switching transistor S1, and the second terminal of the inductor L1 is connected to the first terminal of the bus capacitor CB. The cathode of the diode D1 is connected to the first terminal of the inductor L1, and the anode of the diode D1 is connected to the second terminal of the bus capacitor CB and the second output terminal of the power supply unit 1, respectively. The starting method includes:

[0113] S1: The voltage sampling circuit 6 detects the DC input voltage and the voltage across the bus capacitor respectively, and outputs the input voltage signal representing the DC input voltage and the capacitor voltage signal representing the voltage across the bus capacitor respectively.

[0114] S2: The controller 7 receives the input voltage signal and the capacitor voltage signal, and controls the switch S1 to operate in a high-frequency on / off state according to the input voltage signal and the capacitor voltage signal; wherein, when the switch S1 is on, the power supply unit 1 charges the bus capacitor CB through the switch S1 and the inductor L1, and when the switch S1 is off, the inductor L1 charges the bus capacitor CB through the diode D1 forming a freewheeling circuit.

[0115] This startup method is simple in structure, low in cost, requires little resources and space, and is highly versatile and adaptable. It can withstand high input voltage and current stress, and since no power device operates continuously in the linear region, the requirements for power devices are not high. Therefore, it can repeatedly suppress inrush current and re-inrush current, exhibiting advantages of high reliability and strong stability.

[0116] Furthermore, the soft-start circuit of the power supply also includes a current sampling circuit 5; before step S2, the current of the inductor is detected by the current sampling circuit 5, and a current signal characterizing the current of the inductor is output. The controller 7 receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switch S1 to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal. This embodiment preferably adopts a dual-loop control strategy with an inner loop for inductor current and an outer loop for voltage. Both loops use PI regulators to reduce the steady-state error of the system and improve voltage tracking capability. The control signal controls the switch S1 to turn on and off, which enables the current of inductor L1 to rise and fall near the target value, achieving the purpose of constant current charging of bus capacitor CB by inductor L1.

[0117] Furthermore, when the current signal reaches the preset overcurrent protection threshold, the controller 7 controls the switch S1 to turn off, thereby cutting off the power supply to the downstream electrical device and isolating the input terminal to protect the downstream electrical device. It should be noted that the preset overcurrent protection threshold can be set or selected according to actual needs.

[0118] Furthermore, the controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal, including:

[0119] The system receives the input voltage signal and the capacitor voltage signal, and performs a differential operation on the input voltage signal and the capacitor voltage signal received at the current time to obtain a voltage error signal.

[0120] The first arithmetic unit 71 is connected to the input voltage sampling circuit 61 and the capacitor voltage sampling circuit 62. It receives the input voltage signal Vi and the capacitor voltage signal Vcb respectively, and performs differential operation on the input voltage signal Vi and the capacitor voltage signal Vcb received at the current time to obtain the voltage error signal.

[0121] The current loop reference value is output based on the voltage error signal.

[0122] Specifically, the voltage regulator 72 is used to output a current loop reference value based on the voltage error signal. Specifically, the voltage regulator 72 receives the voltage error signal and performs PI regulation on the voltage error signal to output the current loop reference value.

[0123] The system receives the current loop reference value, the given constant current value, and the current signal, and performs calculations on the current loop reference value, the given constant current value, and the current signal received at the current moment to obtain a current error signal.

[0124] The second arithmetic unit 73 receives a current loop reference value, a given constant current value, and a current signal. It then performs calculations on the current loop reference value, the given constant current value, and the currently received current signal to obtain a current error signal. Specifically, the second arithmetic unit 73 sums the current loop reference value and the given constant current value, and then performs a differential operation with the currently received current signal to obtain the current error signal. It should be noted that the constant current signal can be a target value, which can be set or selected according to actual needs.

[0125] A digital signal is output based on the current error signal.

[0126] The current regulator 74 is used to output a digital signal based on the current error signal. Specifically, the current regulator 74 receives the current error signal and performs PI regulation on the current error signal to output a digital signal.

[0127] The system receives the digital signal and the input voltage feedforward signal, and performs calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal.

[0128] The third arithmetic unit 75 receives a digital signal and an input voltage feedforward signal, and performs calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal. Specifically, the third arithmetic unit 75 performs a summation operation on the digital signal and the input voltage feedforward signal to obtain the digital compensation signal.

[0129] The digital compensation signal is converted into the PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0130] The PWM generator 76 receives the digital compensation signal and converts the digital compensation signal into the PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0131] In some embodiments, the third arithmetic unit 75 can be omitted, and the digital signal can be converted into the PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

[0132] The PWM generator 76 receives digital signals and converts them into PWM pulse width modulation signals to control the switching transistor to operate in a high-frequency on and off state.

[0133] Furthermore, when the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to the preset voltage, the controller 7 controls the switch S1 to remain in the conducting state, and the inductor L1 can be used as a differential mode inductor, effectively suppressing electromagnetic interference and saving the front-end electromagnetic interference suppression circuit.

[0134] Furthermore, the soft-start circuit of the power supply also includes diode D2, diode D3, current limiting device 2, and auxiliary power supply 4. The anode of diode D2 is connected to the first terminal of the switching transistor S1; the first terminal of the current limiting device 2 is connected to the cathode of diode D2; the first input terminal of the auxiliary power supply 4 is connected to the second terminal of the current limiting device 2, the second input terminal of the auxiliary power supply 4 is connected to the second terminal of the bus capacitor CB, and the output terminal of the auxiliary power supply 4 is connected to the controller 7; the anode of diode D3 is connected to the first terminal of the bus capacitor CB, and the cathode of diode D3 is connected to the first input terminal of the auxiliary power supply 4.

[0135] When the power supply unit is powered on, the auxiliary power supply 4 draws power from the power supply unit 1 through the diode D2 and the current limiting device 2. When the DC input voltage is greater than the start-up voltage of the auxiliary power supply, the auxiliary power supply operates and outputs an auxiliary voltage. The auxiliary power supply 4 can provide auxiliary voltage to circuits such as the controller, voltage sampling circuit, and current sampling circuit, creating basic controllable conditions for the soft-start circuit. The controller 7 starts working after receiving the auxiliary voltage. By drawing power from the first terminal of the switching transistor S1 through the series connection of the current limiting device 2 and the diode D2, the start-up inrush current of the auxiliary power supply can be suppressed. Because the auxiliary power supply usually has an input filter capacitor, the current limiting device 2 can suppress the spike current of the high-voltage DC input voltage charging the filter capacitor.

[0136] When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, the auxiliary power supply 4 draws power from the bus capacitor CB through the diode D3. Because the total voltage drop across the current limiting device 2 and the diode D2 is greater than the voltage drop across the diode D3, when the switching transistor S1 is turned on, the diode D2 and the current limiting device 2 are bypassed, thereby reducing power loss.

[0137] Furthermore, when the power supply unit loses power, the auxiliary power supply 4 draws power from the bus capacitor CB through the diode D3.

[0138] Furthermore, when the input voltage signal is greater than a preset safe voltage threshold, or when the power supply unit loses power, the controller 7 controls the switch S1 to turn off.

[0139] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations may be made herein without departing from the spirit and scope of the present application as defined by the appended claims.

[0140] Furthermore, the scope of this application is not limited to the specific embodiments of the processes, machines, manufactures, material compositions, methods, and steps described herein. Those skilled in the art will readily understand from the disclosure of this application that, according to this application, currently existing or to be developed processes, machines, manufactures, material compositions, methods, or steps that perform substantially the same function or achieve substantially the same results as the corresponding embodiments described herein can be utilized.

Claims

1. A soft-start circuit for a power supply, characterized in that, The soft-start circuit is located between the power supply unit and the bus capacitor, and the soft-start circuit includes: A switching transistor, the first end of which is connected to the first output terminal of the power supply unit, is used to receive DC input voltage; An inductor, wherein the first end of the inductor is connected to the second end of the switching transistor, and the second end of the inductor is connected to the first end of the bus capacitor; The first diode has its cathode connected to the first terminal of the inductor and its anode connected to the second terminal of the bus capacitor and the second output terminal of the power supply unit, respectively. A voltage sampling circuit is used to detect the DC input voltage and the voltage across the bus capacitor respectively, and output an input voltage signal representing the DC input voltage and a capacitor voltage signal representing the voltage across the bus capacitor respectively. The controller is used to receive the input voltage signal and the capacitor voltage signal, and control the switching transistor to operate in a high-frequency on and off state according to the input voltage signal and the capacitor voltage signal; wherein, when the switching transistor is on, the power supply unit charges the bus capacitor through the switching transistor and the inductor, and when the switching transistor is off, the inductor charges the bus capacitor through the first diode to form a freewheeling circuit.

2. The soft-start circuit of the power supply according to claim 1, characterized in that, The soft-start circuit also includes a current sampling circuit for detecting the current of the inductor and outputting a current signal characterizing the current of the inductor. The controller is used to receive the current signal, the input voltage signal, and the capacitor voltage signal, and control the switching transistor to operate in a high-frequency on and off state according to the current signal, the input voltage signal, and the capacitor voltage signal.

3. The soft-start circuit for the power supply according to claim 2, characterized in that, When the current signal reaches the preset overcurrent protection threshold, the controller controls the switching transistor to turn off.

4. The soft-start circuit for the power supply according to claim 2, characterized in that, The controller includes: The first arithmetic unit is used to perform differential operations on the input voltage signal received at the current moment and the capacitor voltage signal received at the current moment to obtain the voltage error signal; A voltage regulator is used to output a current loop reference value based on the voltage error signal; The second arithmetic unit is used to perform calculations on the current loop reference value, the given constant current value, and the current signal received at the current moment to obtain the current error signal; A current regulator is used to output a digital signal based on the current error signal; A PWM generator is used to convert the digital signal into a PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

5. The soft-start circuit for the power supply according to claim 4, characterized in that, The controller also includes a third arithmetic unit, which performs calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal; A PWM generator is used to convert the digital compensation signal into a PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

6. The soft-start circuit of the power supply according to claim 1, characterized in that, When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, the controller controls the switch to remain in the on state.

7. The soft-start circuit for the power supply according to claim 1, characterized in that, Also includes: The second diode, the anode of which is connected to the first terminal of the switching transistor; A current limiting device, wherein the first end of the current limiting device is connected to the cathode of the second diode; An auxiliary power supply, wherein the first input terminal of the auxiliary power supply is connected to the second terminal of the current limiting device, the second input terminal of the auxiliary power supply is connected to the second terminal of the bus capacitor, and the auxiliary power supply provides auxiliary voltage to the controller; The third diode has its anode connected to the first terminal of the bus capacitor and its cathode connected to the first input terminal of the auxiliary power supply.

8. The soft-start circuit for the power supply according to claim 7, characterized in that, When the power supply unit is powered on, the auxiliary power supply draws power from the power supply unit through the second diode and the current limiting device; When the DC input voltage reaches the power-on voltage of the auxiliary power supply, the auxiliary power supply operates and outputs an auxiliary voltage; When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, or when the power supply unit loses power, the auxiliary power supply draws power from the bus capacitor through the third diode.

9. The soft-start circuit for the power supply according to claim 1, characterized in that, When the input voltage signal is greater than a preset safe voltage threshold, or when the power supply unit loses power, the controller controls the switching transistor to turn off.

10. A method for starting a soft-start circuit of a power supply, characterized in that, The soft-start circuit of the power supply includes a switching transistor, an inductor, a first diode, a voltage sampling circuit, and a controller. The first terminal of the switching transistor is connected to the first output terminal of the power supply unit to receive DC input voltage. The first terminal of the inductor is connected to the second terminal of the switching transistor, and the second terminal of the inductor is connected to the first terminal of the bus capacitor. The cathode of the first diode is connected to the first terminal of the inductor, and the anode of the first diode is connected to both the second terminal of the bus capacitor and the second output terminal of the power supply unit. The starting method includes: S1: The voltage sampling circuit detects the DC input voltage and the voltage across the bus capacitor respectively, and outputs the input voltage signal representing the DC input voltage and the capacitor voltage signal representing the voltage across the bus capacitor respectively; S2: The controller receives the input voltage signal and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state according to the input voltage signal and the capacitor voltage signal; wherein, when the switching transistor is on, the power supply unit charges the bus capacitor through the switching transistor and the inductor, and when the switching transistor is off, the inductor charges the bus capacitor through the first diode to form a freewheeling circuit.

11. The starting method of the soft-start circuit of the power supply according to claim 10, characterized in that, The soft-start circuit of the power supply also includes a current sampling circuit; before step S2, the current of the inductor is detected by the current sampling circuit and a current signal characterizing the current of the inductor is output. The controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal.

12. The starting method of the soft-start circuit of the power supply according to claim 11, characterized in that, When the current signal reaches the preset overcurrent protection threshold, the switching transistor is controlled to turn off.

13. The starting method of the soft-start circuit of the power supply according to claim 11, characterized in that, The controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal, including: The system receives the input voltage signal and the capacitor voltage signal, and performs a differential operation on the input voltage signal and the capacitor voltage signal received at the current time to obtain a voltage error signal. Output a current loop reference value based on the voltage error signal; The system receives the current loop reference value, the given constant current value, and the current signal, and performs calculations on the current loop reference value, the given constant current value, and the current signal received at the current moment to obtain a current error signal. A digital signal is output based on the current error signal; The digital signal is converted into a PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

14. The starting method of the soft-start circuit of the power supply according to claim 13, characterized in that, The controller receives the current signal, the input voltage signal, and the capacitor voltage signal, and controls the switching transistor to operate in a high-frequency on / off state based on the current signal, the input voltage signal, and the capacitor voltage signal. The method also includes: The system receives the digital signal and the input voltage feedforward signal, and performs calculations on the digital signal and the input voltage feedforward signal to obtain a digital compensation signal. The digital compensation signal is converted into the PWM pulse width modulation signal to control the switching transistor to operate in a high-frequency on and off state.

15. The starting method of the soft-start circuit of the power supply according to claim 10, characterized in that, When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, the controller controls the switch to remain in the on state.

16. The starting method of the soft-start circuit of the power supply according to claim 10, characterized in that, The soft-start circuit of the power supply further includes a second diode, a third diode, a current limiting device, and an auxiliary power supply. The anode of the second diode is connected to the first terminal of the switching transistor; the first terminal of the current limiting device is connected to the cathode of the second diode; the first input terminal of the auxiliary power supply is connected to the second terminal of the current limiting device, and the second input terminal of the auxiliary power supply is connected to the second terminal of the bus capacitor. The auxiliary power supply provides auxiliary voltage to the controller; the anode of the third diode is connected to the first terminal of the bus capacitor, and the cathode of the third diode is connected to the first input terminal of the auxiliary power supply. When the power supply unit is powered on, the auxiliary power supply draws power from the power supply unit through the second diode and the current limiting device; When the DC input voltage reaches the power-on voltage of the auxiliary power supply, the auxiliary power supply operates and outputs an auxiliary voltage; When the voltage difference between the DC input voltage and the voltage across the bus capacitor is less than or equal to a preset voltage, or when the power supply unit loses power, the auxiliary power supply draws power from the bus capacitor through the third diode.

17. The starting method of the soft-start circuit of the power supply according to claim 10, characterized in that, When the input voltage signal is greater than a preset safe voltage threshold, or when the power supply unit loses power, the controller controls the switching transistor to turn off.

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