Surge suppression circuit applied to switching power supply and switching power supply

Abstract

The invention provides a surge suppression circuit applied to a switching power supply and the switching power supply, the surge suppression circuit comprises a first current limiting circuit, a second current limiting circuit and a main power switch which are connected in parallel, one end of the first current limiting circuit receives an input voltage, and the other end of the first current limiting circuit is coupled with a capacitor in the switching power supply; the voltage sampling circuit detects a voltage difference value between the input voltage and the voltage of the capacitor; the control circuit is used for controlling the main power switch to be switched off during cold start and controlling the main power switch to work in a closed state when the voltage difference value is smaller than a first voltage preset value; and after the input voltage is suddenly changed, the voltage difference level corresponding to the voltage difference value is judged, the controllable switch of the second current limiting circuit is controlled to be switched on when the voltage difference level is higher than a first preset level, and the controllable switch of the second current limiting circuit is controlled to be switched off and the main power switch works in an on state after the voltage difference value is reduced to a second voltage preset value. The circuit can effectively reduce the surge current in the switching power supply under different conditions, and is high in response speed.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a surge suppression circuit applied to a switching power supply and the switching power supply. Background Art

[0002] With the rapid development of power electronics technology, switching power supply equipment is widely used in power supply systems. When the voltage of the power grid suddenly increases or the power grid recovers after power failure, a large surge current will be generated inside the switching power supply. This surge current will not only cause the circuit breaker in the power supply system to malfunction, but also affect the power supply quality of the power grid and the safe operation of other electrical equipment. Therefore, it is urgent to reduce the surge current of the switching power supply.

[0003] There are currently two main solutions for switching power supply surge current suppression in the industry. The first solution is to limit the cold start surge current by connecting a switch tube in parallel with a resistor. The working principle of this solution is that when the switching power supply is cold started, the input voltage charges the capacitor inside the switching power supply through a resistor. When the input voltage is consistent with the capacitor voltage inside the switching power supply, the switch tube is closed to reduce the surge current of the switching power supply cold start machine. This solution cannot suppress the thermal shock surge current caused by the sudden increase in the voltage of the power grid or the power grid power failure to the voltage recovery. The second solution uses the switch tube to work in the linear region to limit the thermal shock surge current. The principle of this solution is that when the voltage of the power grid suddenly increases or the power grid power fails to the voltage recovery, when the input current value exceeds the design value, the constant current circuit controls the switch tube to work in the linear region to reduce the thermal shock surge current of the power supply. When the voltage of the power grid changes badly, the switch tube is easily damaged by overpower. The disadvantages of the above two surge current suppression schemes are obvious. They are only effective in reducing specific surge currents and cannot reduce surge currents generated under various working conditions.

[0004] In order to meet the surge current suppression needs under various working conditions, the industry urgently needs to develop a surge current suppression circuit for switching power supplies to limit the surge current within a reasonable range. Summary of the invention

[0005] The surge current suppression solution mentioned above is only effective in reducing specific surge currents, but cannot reduce the surge currents generated under various working conditions.

[0006] The present application proposes an inrush current suppression circuit applied to a switching power supply, comprising:

[0007] A first current limiting circuit comprises a first terminal and a second terminal, wherein the first terminal is used to receive an input voltage, and the second terminal is coupled to a capacitor inside the switching power supply;

[0008] a second current limiting circuit connected in parallel with the first current limiting circuit, the second current limiting circuit comprising a controllable switch and a first resistor connected in series;

[0009] a main power switch connected in parallel with the first current limiting circuit;

[0010] a voltage sampling circuit, used for detecting a voltage difference between the input voltage and the voltage of the capacitor; and

[0011] a control circuit, for controlling the main power switch to be disconnected when the switching power supply is cold started, so that the input voltage charges the capacitor through the first current limiting circuit, and controlling the main power switch to operate in a closed state when the voltage difference is less than a first voltage preset value; after a sudden change in the input voltage, judging the voltage difference level corresponding to the voltage difference, and controlling the main power switch to be disconnected and the controllable switch of the second current limiting circuit to be closed when the voltage difference level is higher than a first preset level, and controlling the controllable switch of the second current limiting circuit to be disconnected and the main power switch to operate in an open state after the voltage difference drops to a second voltage preset value, or controlling the main power switch to operate in an open state when the voltage difference level is the first preset level.

[0012] Optionally, the second current limiting circuit includes n second current limiting branches connected in parallel, each of the second current limiting branches includes a first resistor and a controllable switch connected in series, wherein the resistance value of the first resistor of the i-th second current limiting branch is greater than the resistance value of the first resistor of the (i-1)th second current limiting branch, wherein n≥1, 1≤i≤n.

[0013] Optionally, the pressure difference level includes m preset levels, wherein the kth preset level is higher than the (k-1)th preset level, m≥2, 2≤k≤m;

[0014] When the voltage difference level corresponding to the voltage difference value is the kth preset level, the control circuit controls the controllable switch of the second current limiting branch corresponding to the kth preset level to close;

[0015] As the voltage difference decreases, the control circuit controls the previously closed controllable switch to open and the corresponding controllable switch of the second current limiting branch to close in a preset order, so that the resistance of the second current limiting circuit gradually decreases.

[0016] Optionally, when the voltage difference level corresponding to the voltage difference value is a third preset level, the control circuit controls the controllable switch of the second second current limiting branch to close;

[0017] As the voltage difference decreases, the control circuit controls the controllable switch of the second second current limiting branch to open and the controllable switch of the first second current limiting branch to close. After the voltage difference drops to the second voltage preset value, the control circuit controls the controllable switch of the first second current limiting branch to open and the main power switch to operate in the on state.

[0018] Optionally, when the voltage difference level corresponding to the voltage difference is the second preset level, the control circuit controls the controllable switch of the first second current limiting branch to close, and after the voltage difference drops to the second voltage preset value, controls the controllable switch of the first second current limiting branch to disconnect and the main power switch to operate in the on state.

[0019] Optionally, the number n of the n second current limiting branches is set according to a preset current level of the surge current and the voltage difference level.

[0020] Optionally, the control circuit further includes a constant current control unit;

[0021] The open state includes a linear region and a closed state;

[0022] When the surge current received by the main power switch exceeds the preset current value, the constant current control unit controls the main power switch to operate in the linear region; when the surge current received by the main power switch is less than the preset current value, the constant current control unit controls the main power switch to operate in a closed state.

[0023] Optionally, the main power switch includes a plurality of power switch tubes connected in parallel.

[0024] Optionally, the first current limiting circuit includes a plurality of first current limiting branches connected in parallel, and each of the first current limiting branches includes a second resistor.

[0025] Optionally, each of the first current limiting branches further includes a semiconductor device connected in series with the second resistor.

[0026] Optionally, the first end of the first current limiting circuit is used to receive a first input voltage or a second input voltage.

[0027] The present application also proposes a switching power supply, comprising:

[0028] A surge suppression circuit applied to a switching power supply as described in any embodiment of the present application;

[0029] A first power conversion circuit is connected in series with the surge suppression circuit to form a series branch, one end of the series branch is connected to a power supply, and the other end is connected to a capacitor;

[0030] The second power conversion circuit includes an input end and an output end, wherein the input end is connected to the capacitor, and the output end is used to output electric energy.

[0031] The beneficial effects of this application include at least:

[0032] The surge suppression circuit of this embodiment includes a first current limiting circuit, a second current limiting circuit and a main power switch connected in parallel, a voltage sampling circuit and a control circuit. The surge current caused by the cold start of the switching power supply can be reduced by the first current limiting circuit and the main power switch. The voltage difference obtained by the voltage sampling circuit and the control circuit optimize the closing sequence of the controllable switches of the second current limiting circuit, effectively reducing the surge current caused by the sudden change of the input voltage. The surge suppression circuit can effectively reduce the surge current of the switching power supply in different situations, and has high reliability. The surge suppression circuit only uses simple hardware circuits and control strategies, which can limit the surge current within a reasonable range, with low cost and simple control.

[0033] The above is a fairly broad overview of the features and technical advantages of the present application, so that the following detailed description of the present application can be better understood. The additional features and advantages of the present application will be described below, and they form the subject matter of the claims of the present application. It will be appreciated by those skilled in the art that the disclosed concepts and specific embodiments can be easily utilized as the basis for modifying or designing other structures or processes for realizing the same purpose of the present application. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present application as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more fully understand the present application and its advantages, reference is now made to the following description in conjunction with the accompanying drawings:

[0035] In the figure:

[0036] Figure 1 A schematic diagram of the structure of a surge suppression circuit according to an embodiment of the present application is shown;

[0037] Figure 2 A schematic diagram showing the structure of another surge suppression circuit according to an embodiment of the present application is shown;

[0038] Figure 3 A control timing diagram of a surge suppression circuit according to an embodiment of the present application is shown;

[0039] Figure 4 Another control timing diagram of the surge suppression circuit according to an embodiment of the present application is shown.

[0040] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0041] Various exemplary embodiments, features and aspects of the present invention will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0042] The word "exemplary" is used herein to mean "serving as an example, embodiment or illustration". Any embodiment described herein as "exemplary" is not necessarily to be construed as being superior or better than other embodiments. The terms "first", "second", "third", etc. (if any) in the specification and claims of the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "coupled", "connected", and "connected" should be understood in a broad sense. For example, it can be an electrical connection or mutual communication, it can be a direct connection, it can also be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0045] Figure 1 FIG. 2 is a schematic diagram showing the structure of a surge suppression circuit according to an embodiment of the present application. Figure 1 As shown, the surge suppression circuit applied to the switching power supply includes: a first current limiting circuit 12, a second current limiting circuit 13, a main power switch 14, a voltage sampling circuit 17 and a control circuit 18. The first current limiting circuit 12, the second current limiting circuit 13 and the main power switch 14 are connected in parallel with each other. The first current limiting circuit 12 includes a first end and a second end, the first end is used to receive an input voltage, and the second end is coupled to the capacitor CB inside the switching power supply. In this embodiment, the first end of the first current limiting circuit 12 is coupled to a power supply module 11, and the input voltage is provided by the power supply module 11, wherein the power supply module 11 can be a device for providing AC power.

[0046] The voltage sampling circuit 17 is used to detect the voltage difference between the input voltage and the voltage of the capacitor CB. In this embodiment, the voltage sampling circuit may include a first sampling unit, a second sampling unit and a subtractor; the first sampling unit detects the input voltage to obtain an input voltage signal representing the input voltage, the second sampling unit detects the voltage of the capacitor CB to obtain a capacitor voltage signal representing the voltage of the capacitor CB, and the subtractor receives the input voltage signal and the capacitor voltage signal and calculates the difference between the input voltage signal and the capacitor voltage signal to obtain a voltage difference signal between the two, wherein the voltage difference signal represents the voltage difference between the input voltage and the voltage of the capacitor CB. The voltage sampling circuit may also directly detect the voltage across the first current limiting circuit 12 to obtain the voltage difference between the input voltage and the voltage of the capacitor CB. It should be noted that, in this embodiment, the voltage sampling circuit for detecting the voltage difference between the input voltage and the voltage of the capacitor is not limited to the above-mentioned example.

[0047] The control circuit 18 is used to control the main power switch 14 to be disconnected when the switching power supply is cold started, so that the input voltage charges the capacitor CB through the first current limiting circuit 12, and controls the main power switch 14 to work in a closed state when the voltage difference is less than a first voltage preset value; after a sudden change in the input voltage, judge the voltage difference level corresponding to the voltage difference, and control the main power switch 14 to be disconnected and the controllable switch of the second current limiting circuit 13 to be closed when the voltage difference level is higher than the first preset level, and control the controllable switch of the second current limiting circuit 13 to be disconnected and the main power switch 14 to work in an open state after the voltage difference drops to the second voltage preset value, or control the main power switch 14 to work in an open state when the voltage difference level is the first preset level.

[0048] The surge suppression circuit of this embodiment can effectively reduce the surge current in different situations of the switching power supply by optimizing the sequence of turning on the controllable switch of the second current limiting circuit 13 and the main power switch 14, and has the advantages of fast response speed, high reliability and simple control.

[0049] In this embodiment, when the switching power supply is cold started, the control circuit 18 controls the main power switch 14 to be disconnected, so that the input voltage charges the capacitor CB through the first current limiting circuit 12, wherein the first current limiting circuit 12 includes a second resistor, and the second resistor can effectively reduce the surge current of the switching power supply. As the voltage on the capacitor CB rises, the voltage difference between the input voltage and the voltage of the capacitor CB is reduced until the voltage difference is less than the first voltage preset value, and the control circuit 18 controls the main power switch 14 to work in a closed state, thereby bypassing the first current limiting circuit 12. It should be noted that the first voltage preset value can be a smaller value, such as close to 0V; the voltage difference is less than the first voltage preset value, which means that the voltage of the capacitor CB is approximately equal to the input voltage. After the switching power supply is cold started, the control circuit 18 of the surge suppression circuit of this embodiment controls the main power switch 14 to be disconnected, so that the input voltage charges the capacitor CB through the first current limiting circuit 12, and the voltage of the capacitor CB rises accordingly, until the voltage difference is less than the first voltage preset value, and the control circuit 18 controls the main power switch 14 to work in a closed state, thereby effectively suppressing the surge current.

[0050] Furthermore, a sudden change in input voltage may refer to a sudden increase in input voltage. A sudden change in input voltage may also refer to a power failure to power restoration of the power supply voltage module 11, wherein the input voltage drops when the power supply module 11 fails, and the input voltage returns to a normal operating voltage when the power supply module 11 resumes power. It should be noted that in the process of power failure to power restoration of the power supply voltage module 11, the energy stored in the capacitor CB is drawn away by other circuits in the switching power supply. The longer the power failure time, the more the voltage of the capacitor CB drops. When the power supply voltage module 11 resumes power, the greater the voltage difference between the input voltage and the voltage of the capacitor.

[0051] Furthermore, the on state of the main power switch 14 includes a linear region and a closed state. When the on state of the main power switch 14 is in the linear region, the main power switch 14 exhibits an impedance characteristic, which is used to limit the thermal shock surge current when the input voltage suddenly changes and the voltage difference corresponding to the voltage difference is the first preset level or the voltage difference drops to the second voltage preset value. As the voltage difference decreases, the resistance of the main power switch 14 also decreases. When the main power switch 14 is in the closed state, the main power switch 14 is fully turned on, and its resistance value is the smallest, close to 0Ω.

[0052] Further, the second current limiting circuit 13 includes n second current limiting branches connected in parallel, each of which includes a first resistor and a controllable switch connected in series, wherein the resistance of the first resistor of the i-th second current limiting branch is greater than the resistance of the first resistor of the (i-1)-th second current limiting branch, wherein n≥1, 1≤i≤n. Specifically, the first second current limiting branch includes a first resistor R1 and a controllable switch Q1 connected in series, the second second current limiting branch includes a first resistor R2 and a controllable switch Q2 connected in series, and so on, the n-th second current limiting branch includes a first resistor Rn and a controllable switch Qn connected in series. The impedance of the first resistor of each second current limiting branch is different, that is, the resistance of Rn> the resistance of Rn-1...> the resistance of R2> the resistance of R1.

[0053] Furthermore, the first resistor may be a device with impedance characteristics such as a pure resistor, a positive temperature coefficient resistor or a negative temperature coefficient resistor. The controllable switch may be a device capable of switching operation such as MOSFET, GaN or SiC.

[0054] Further, the voltage difference level includes m preset levels, wherein the kth preset level is higher than the (k-1)th preset level, m≥2, 2≤k≤m. It should be noted that each preset level corresponds to a preset voltage range, that is, the minimum value of the preset voltage range of the kth preset level is greater than or equal to the maximum value of the preset voltage range of the (k-1)th preset level. Specifically, the number of preset levels of the voltage difference level can be set according to the power level of the switching power supply, the current preset level of the surge current, and the capacity of the capacitor CB. When the voltage difference level corresponding to the voltage difference is the kth preset level, the control circuit controls the controllable switch of the second current limiting branch corresponding to the kth preset level to close; as the voltage difference decreases, the control circuit controls the previously closed controllable switch to open and the corresponding controllable switch of the second current limiting branch to close in a preset order, so that the resistance of the second current limiting circuit 13 gradually decreases. It should be noted that by controlling the controllable switches of different second current limiting branches to close, different resistance values ​​of the second current limiting circuit 13 can be obtained, and the preset sequence can refer to the sequence in which the resistance value of the second current limiting circuit 13 gradually decreases from large to small.When it is determined that the voltage difference level corresponding to the voltage difference is the kth preset level, the control circuit 18 controls the controllable switch Q(k-1) of the (k-1)th second current limiting branch to be closed, and the input voltage charges the capacitor CB through the first resistor R(k-1), so that the resistance value of the first resistor R(k-1) of the (k-1)th second current limiting branch is used as the resistance value of the second current limiting circuit 13, and the thermal shock surge current is reduced by the first resistor R(k-1). As the voltage of the capacitor CB rises, that is, the voltage difference decreases, the current flowing through the (k-1)th second current limiting branch After the voltage drops to the set value or the closing time of the controllable switch Q(k-1) of the (k-1)th second current limiting branch reaches the preset time, the control circuit 18 controls the controllable switch Q(k-1) of the (k-1)th second current limiting branch to be disconnected and controls the controllable switch Q(k-2) of the (k-2)th second current limiting branch to be closed, and the input voltage charges the capacitor CB through the first resistor R(k-2) of the (k-2)th second current limiting branch, so that the resistance value of the first resistor R(k-2) of the (k-2)th second current limiting branch is used as the resistance of the second current limiting circuit 13. The thermal shock surge current is limited by the first resistor R(k-2) of the (k-2)th second current limiting branch, and the corresponding controllable switches are controlled in the order of gradually decreasing resistance of the second current limiting circuit 13, until the controllable switch Q2 of the second second current limiting branch is disconnected and the controllable switch Q1 of the first second current limiting branch is closed, and the input voltage charges the capacitor CB through the first resistor R1 of the first second current limiting branch, so that the resistance value of the first resistor R1 of the first second current limiting branch is used as the resistance value of the second current limiting circuit 13, and the controllable switch Q2 of the second second current limiting branch is controlled to be ... and the controllable switch Q2 of the second second current limiting branch is controlled to be disconnected and the controllable switch Q1 of the first second current limiting branch is closed, and the controllable switch Q2 of the second second current limiting branch is controlled to be disconnected and the controllable switch Q1 of the first second current limiting branch is closed, and the controllable switch Q2 of the second second current limiting branch is controlled to be disconnected and the controllable switch Q1 of A resistor R1 limits the thermal shock surge current. When the current flowing through the first second current limiting branch drops to a set value or the closing time of the controllable switch Q1 of the first second current limiting branch reaches a preset time and the voltage difference drops to a second voltage preset value, the control circuit 18 controls the controllable switch Q1 of the first second current limiting branch to be disconnected and the main power switch 14 to operate in an open state. When the main power switch 14 operates in a linear region, the input voltage charges the capacitor CB through the main power switch 14, and the thermal shock surge current is limited by the resistance of the main power switch 14. At this time, the voltage difference between the two ends of the main power switch 14 is small, meeting the SOA (Safe Operating Area) specification requirements, so that the main power switch 14 has a voltage and current range that can operate safely. It should be noted that the set value can be set as needed, and the set value can be a current value within a preset current level, where the preset current level is a preset current range; the second voltage preset value is set according to the safe working area specifications of the main power switch 14, and the preset time can be set in advance according to the design parameters, or set according to the measured value.

[0055] In the above embodiment, the control circuit 18 controls the corresponding controllable switch of the second current limiting branch to close according to the voltage difference level corresponding to the voltage difference, so that the first resistor in the second current limiting branch where the closed controllable switch is located serves as the resistor of the second current limiting circuit to limit the thermal shock surge current. In other embodiments, the control circuit 18 controls the corresponding controllable switch of one or more second current limiting branches to close according to the voltage difference level corresponding to the voltage difference and the resistance of the second current limiting circuit gradually decreases from large to small.

[0056] This embodiment controls the closing of the controllable switch of the corresponding second current limiting branch by the voltage difference level corresponding to the voltage difference, and gradually reduces the resistance of the second current limiting circuit 13, which not only limits the thermal shock surge current to the preset current level, but also reduces power consumption and protects the main power switch 14 to operate safely and reliably.

[0057] Furthermore, the control circuit 18 also includes a constant current control unit; when the surge current received by the main power switch 14 exceeds the preset current value, the constant current control unit controls the main power switch 14 to operate in a linear region; when the surge current received by the main power switch 14 is less than the preset current value, the constant current control unit controls the main power switch 14 to operate in a closed state.

[0058] Further, when the voltage difference level corresponding to the voltage difference is the third preset level, the control circuit controls the controllable switch Q2 of the second second current limiting branch to close, the input voltage charges the capacitor CB through the first resistor R2, and the surge current is reduced through the first resistor R2; as the voltage difference decreases, and the current flowing through the second second current limiting branch drops to the set value or the closing time of the controllable switch Q2 of the second second current limiting branch reaches the first preset time, the control circuit 18 controls the controllable switch Q2 of the second second current limiting branch to open and the controllable switch Q2 of the first second current limiting branch to close. The switch Q1 is closed, the input voltage charges the capacitor CB through the first resistor R1, and the inrush current is reduced through the first resistor R1. After the current flowing through the first second current limiting branch drops to the set value or the closing time of the controllable switch Q1 of the first second current limiting branch reaches the second preset time and the voltage difference drops to the second voltage preset value, the control circuit 18 controls the controllable switch Q1 of the first second current limiting branch to be disconnected and the main power switch 14 to work in the on state, the input voltage charges the capacitor CB through the main power switch 14, and the inrush current is reduced through the main power switch 14. If the inrush current exceeds the design value of the constant current control unit at this time, the main power switch 14 works in the linear region to limit the inrush current. When the controllable switches Q1 and Q2 of the first second current limiting branch and the second second current limiting branch are disconnected, if the voltage difference is still large, in order to prevent the main power switch 14 from exceeding the safe working area specifications, the control circuit 18 can simultaneously control the controllable switches Q1 and Q2 of the first second current limiting branch and the second second current limiting branch to close, so that the resistance of the first resistors R1 and R2 in parallel is used as the resistance of the second current limiting circuit 13 to further reduce the surge current. When the voltage difference drops to the second voltage preset value, the control circuit 18 controls the main power switch 14 to operate in the on state, and reduces the surge current through the main power switch 14. At this time, the voltage difference across the main power switch 14 is small, meeting its SOA specification requirements.

[0059] Figure 3 FIG. 2 shows a control timing diagram of a surge suppression circuit according to an embodiment of the present application. Figure 3 As shown, Vin represents the input voltage waveform, VCB represents the voltage waveform of the capacitor CB, Q2 represents the control signal waveform of the controllable switch Q2 of the second second current limiting branch, Q1 represents the control signal waveform of the controllable switch Q1 of the first second current limiting branch, S1 represents the control signal waveform of the main power switch, and Iin represents the input current waveform of the switching power supply. Figure 1 and Figure 3It can be seen that at time t1, the input voltage Vin drops, that is, the power supply module 11 loses power. At this time, the control signal CQ2 of the controllable switch Q2 of the second second current limiting branch jumps from a low level to a high level, so that the controllable switch Q2 is closed. At this time, the control signal CS1 of the main power switch 14 jumps from a high level to a low level, so that the main power switch 14 is disconnected. At this time, the input current Iin drops to 0A, and the voltage VCB of the capacitor CB decreases as the input voltage drops. At time t2, the input voltage Vin returns to the normal working voltage, the input voltage Vin charges the capacitor CB through the first resistor R2, and limits the thermal shock surge current through the first resistor R2. As the voltage of the capacitor CB rises, the voltage difference between the input voltage Vin and the capacitor voltage VCB decreases. When the current flowing through the first resistor R2 drops to a predetermined value, wherein the predetermined value may be the input current value corresponding to time t3, or the closing time of the controllable switch Q2 reaches a first preset time, wherein the first preset time may be a time period between time t3 and time t1, the control signal CQ2 of the controllable switch Q2 changes from a high level to a low level, so that the controllable switch Q2 is disconnected. At this time, the control signal CQ1 of the controllable switch Q1 changes from a low level to a high level, so that the controllable switch Q1 is closed. The input voltage Vin charges the capacitor CB through the first resistor R1, and limits the thermal shock surge current through the first resistor R1 ... 1 drops to a predetermined value, wherein the predetermined value may be the input current value corresponding to the time t4, or the closing time of the controllable switch Q1 reaches a second preset time, wherein the second preset time may be the time period between the time t4 and the time t3, the control signal CQ1 of the controllable switch Q1 changes from a high level to a low level, so that the controllable switch Q1 is disconnected, at the time t4 the voltage difference drops to the second voltage preset value, the control signal CS1 of the main power switch 14 changes from a low level to a first level, so that the main power switch 14 works in a linear region, the input voltage charges the capacitor CB through the main power switch 14, and the thermal shock surge current is limited by the main power switch 14, as the voltage CB of the capacitor rises to be close to the input voltage Vin, that is, at the time t5, the control signal CS1 of the main power switch 14 changes from a low level to a second level, so that the main power switch 14 works in a closed state, so that the input current Iin works in a stable state. By gradually reducing the resistance value of the second current limiting circuit, the surge current can be effectively limited within a reasonable range, with the advantages of fast response speed, low power consumption, high reliability and simple control.

[0060] Figure 4 Another control timing diagram of the surge suppression circuit according to an embodiment of the present application is shown. Figure 4 The control timing shown is similar to Figure 3The difference in the control timing shown is that the moment when the control signal CQ2 of the controllable switch Q2 jumps from a low level to a high level is different, and the other identical parts are not repeated here. Figure 4 As shown, at time t2, the control signal of the controllable switch Q2 jumps from a low level to a high level, that is, the controllable switch Q2 is controlled to close only when the input voltage recovers.

[0061] Furthermore, the main power switch 14 can be disconnected when the input voltage drops, or before the input voltage recovers to normal operation.

[0062] Further, when the voltage difference level corresponding to the voltage difference is the second preset level, the control circuit 18 controls the controllable switch of the first second current limiting branch to close, the input voltage charges the capacitor CB through the first resistor R1, and the surge current is reduced through the first resistor R1. After the current flowing through the first second current limiting branch drops to the set value or the closing time of the controllable switch of the first second current limiting branch reaches the preset time and the voltage difference drops to the second voltage preset value, the control circuit 18 controls the controllable switch of the first second current limiting branch to disconnect and the main power switch 14 to operate in the on state, and the surge current is reduced through the main power switch 14. At this time, the voltage difference across the main power switch 14 is small, meeting its SOA specification requirements.

[0063] Further, when the voltage difference level corresponding to the voltage difference is the first preset level, the control circuit 18 controls all the controllable switches of the second current limiting branches to be disconnected and the main power switch 14 to operate in the on state, the input voltage charges the capacitor CB through the main power switch 14, and reduces the surge current when the main power switch 14 operates in the linear region. At this time, the voltage difference across the main power switch 14 is small, meeting its SOA specification requirements. It should be noted that the first preset level is the first preset level.

[0064] Furthermore, the number n of the second current limiting branches can be set according to the preset current level of the surge current and the voltage difference level, so that the cold start and thermal shock surge currents can be limited within the specifications, thereby ensuring the reliability of the device.

[0065] Continue to refer to Figure 1 The main power switch 14 may include a plurality of power switch tubes S1, S2, ..., Sn connected in parallel.

[0066] Further, the first current limiting circuit 12 includes a plurality of first current limiting branches connected in parallel, and each first current limiting branch includes a second resistor. Specifically, the second resistor Rs1 is connected in parallel with the second resistor Rs2 and the second resistor Rsn. It should be noted that the second resistor can be a positive temperature coefficient resistor, a negative temperature coefficient resistor or a pure resistor.

[0067] It should be noted that the number of power switch tubes and the number of second resistors are related to the power level and the capacity of the capacitor CB.

[0068] Figure 2 FIG. 2 shows a schematic diagram of the structure of another surge suppression circuit according to an embodiment of the present application. Figure 2 As shown, the surge suppression circuit of this embodiment is Figure 1 The difference between the surge suppression circuit shown in FIG. 1 and FIG. 2 is the first current limiting circuit, and the other identical parts are not described in detail here. Figure 2 It can be seen that each first current limiting branch also includes a semiconductor device connected in series with the second resistor, such as a thyristor, a bidirectional thyristor, or other semiconductor device. Specifically, the second resistor Rs1 is connected in series with the semiconductor device SCR1 to form the first first current limiting branch, the second resistor Rs2 is connected in series with the semiconductor device SCR2 to form the second first current limiting branch, and so on, the second resistor Rsn is connected in series with the semiconductor device SCRn to form the nth first current limiting branch.

[0069] like Figure 2 As shown, the input end of the switching power supply is connected to the first power supply module 21 and the second power supply module 22, so that the first end of the first current limiting circuit is used to receive the first input voltage or the second input voltage, wherein the first power supply module 21 is used to provide the first input voltage, and the second power supply module 22 is used to provide the second input voltage. When it is necessary to switch from the first power supply module 21 to the second power supply module 22 for power supply, it is necessary to disconnect the semiconductor device in the first current limiting branch to protect the switching power supply.

[0070] According to an embodiment of the present application, a switching power supply is disclosed, and the switching power supply includes:

[0071] The surge suppression circuit applied to a switching power supply in any of the aforementioned embodiments;

[0072] A first power conversion circuit is connected in series with the surge suppression circuit to form a series branch, one end of the series branch is connected to a power supply, and the other end is connected to a capacitor;

[0073] The second power conversion circuit includes an input end and an output end, wherein the input end is connected to the capacitor, and the output end is used to output electric energy.

[0074] like Figure 1As shown, the switching power supply includes: a surge suppression circuit, a first power conversion circuit 15, a capacitor CB and a second power conversion circuit 16. The surge suppression circuit includes: a first current limiting circuit 12, a second current limiting circuit 13, a main power switch 14, a voltage sampling circuit 17 and a control circuit 18. The first current limiting circuit 12, the second current limiting circuit 13 and the main power switch 14 are connected in parallel with each other. The first end of the first current limiting circuit 12 (the input end of the switching power supply) is connected to the power supply module 11 for receiving the input voltage, the second end of the first current limiting circuit 12 is connected to the input end of the first power conversion circuit 15, the output end of the first power conversion circuit 15 is connected to one end of the capacitor CB and the input end of the second power conversion circuit 16, the other end of the capacitor CB is grounded, and the output end of the second power conversion circuit 16 is used to output electric energy to provide electric energy to the load. It should be noted that the first power conversion circuit 15 can be an AC / DC converter or a DC / DC converter, and the second power conversion circuit 16 can be a DC / DC converter or a DC / AC converter.

[0075] The voltage sampling circuit 17 is used to detect the voltage difference between the input voltage and the voltage of the capacitor CB. The control circuit 18 is used to control the main power switch 14 to be disconnected when the switching power supply is cold started, so that the input voltage charges the capacitor through the first current limiting circuit 12, and control the main power switch 14 to work in a closed state when the voltage difference is less than the first voltage preset value; after the input voltage suddenly changes, the voltage difference level corresponding to the voltage difference is judged, and when the voltage difference level is higher than the first preset level, the main power switch 14 is controlled to be disconnected and the controllable switch of the second current limiting circuit 13 is closed, and after the voltage difference drops to the second voltage preset value, the controllable switch of the second current limiting circuit 13 is controlled to be disconnected and the main power switch 14 is controlled to work in an open state, or when the voltage difference level is the first preset level, the main power switch 14 is controlled to work in an open state.

[0076] The surge suppression circuit of this embodiment can effectively reduce the surge current in response to the surge current of the switching power supply in different situations by optimizing the sequence of turning on the controllable switch of the second current limiting current and the main power switch 14. It has the advantages of fast response speed, high reliability and simple control.

[0077] In other embodiments, the input end of the first power conversion circuit 15 is connected to the power supply module 11, the output end of the first power conversion circuit 15 is connected to the first end of the first current limiting circuit 12, and the second end of the first current limiting circuit 12 is connected to one end of the capacitor and the input end of the second power conversion circuit 16.

[0078] like Figure 2As shown, the first end (switching power supply input end) of the first current limiting circuit 12 is connected to the first power supply module 21 and the second power supply module 22, the second end of the first current limiting circuit 12 is connected to the input end of the first power conversion circuit 15, the output end of the first power conversion circuit 15 is connected to one end of the capacitor CB and the input end of the second power conversion circuit 16, the other end of the capacitor CB is grounded, and the output end of the second power conversion circuit 16 is used to output electric energy to provide electric energy to the load. In this embodiment, the first current limiting circuit includes a plurality of first current limiting branches, and each first current limiting branch includes a related second resistor and a semiconductor device connected in series. It should be noted that the second resistor can be a device with impedance characteristics such as a positive temperature coefficient resistor, a negative temperature coefficient resistor or a pure resistor, and the number of the second resistors is related to the power level and the capacity of the capacitor CB. In addition, the semiconductor device can be a semiconductor device such as a thyristor and a bidirectional thyristor.

[0079] In this embodiment, when it is necessary to switch power supply from the first power supply module 21 to the second power supply module 22 , the semiconductor device in the first current limiting branch needs to be disconnected to protect the switching power supply.

[0080] The surge suppression circuit and the switching power supply applied to the switching power supply of the present application first control the main power switch to be disconnected during cold start, realize the charging of the capacitor by the input voltage through the first current limiting circuit, and control the main power switch to work in a closed state when the voltage difference between the input voltage and the voltage difference of the capacitor is less than the first voltage preset value, which can well reduce the cold start surge current; when the input voltage suddenly changes, the voltage difference level corresponding to the voltage difference between the input voltage and the voltage difference of the capacitor is judged, and when the voltage difference level is greater than the first preset level, the main power switch and the corresponding controllable switch in the second current limiting circuit are first controlled to be disconnected, and the resistance of the second current limiting circuit is gradually reduced. When the voltage difference is less than the second voltage preset value, the controllable switch in the second current limiting circuit is controlled to be disconnected and the main power switch is controlled to work in an open state, which can well reduce the thermal shock surge current, and has the advantages of fast response speed, low power consumption, high reliability and simple control.

[0081] Although the embodiments of the present application and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

[0082] In addition, the scope of the present application is not limited to the specific embodiments of the processes, machines, manufactures, material compositions, modes, methods, and steps described in this specification. Those skilled in the art will readily understand from the disclosure of the present application that, according to the present application, currently existing or later to be developed processes, machines, manufactures, material compositions, modes, methods, or steps that perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein may be utilized. Therefore, it is intended that the appended claims include such processes, machines, manufactures, material compositions, modes, methods, or steps within their scope.

Claims

1. A surge suppression circuit applied to a switching power supply, characterized in that: include: A first current limiting circuit comprises a first terminal and a second terminal, wherein the first terminal is used to receive an input voltage, and the second terminal is coupled to a capacitor inside the switching power supply; a second current limiting circuit connected in parallel with the first current limiting circuit, the second current limiting circuit comprising a controllable switch and a first resistor connected in series; a main power switch connected in parallel with the first current limiting circuit; A voltage sampling circuit, used for detecting a voltage difference between the input voltage and the voltage of the capacitor; as well as a control circuit, for controlling the main power switch to be disconnected when the switching power supply is cold started, so that the input voltage charges the capacitor through the first current limiting circuit, and controlling the main power switch to operate in a closed state when the voltage difference is less than a first voltage preset value; after a sudden change in the input voltage, judging the voltage difference level corresponding to the voltage difference, and controlling the main power switch to be disconnected and the controllable switch of the second current limiting circuit to be closed when the voltage difference level is higher than a first preset level, and controlling the controllable switch of the second current limiting circuit to be disconnected and the main power switch to operate in an open state after the voltage difference drops to a second voltage preset value, or controlling the main power switch to operate in an open state when the voltage difference level is the first preset level.

2. The surge suppression circuit for a switching power supply according to claim 1, characterized in that: The second current limiting circuit includes n second current limiting branches connected in parallel, each of the second current limiting branches includes a first resistor and a controllable switch connected in series, wherein the resistance value of the first resistor of the i-th second current limiting branch is greater than the resistance value of the first resistor of the (i-1)th second current limiting branch, wherein n≥1,1≤i≤n.

3. The surge suppression circuit for a switching power supply according to claim 2, characterized in that: The pressure difference level includes m preset levels, wherein the kth preset level is higher than the (k-1)th preset level, m≥2, 2≤k≤m; When the voltage difference level corresponding to the voltage difference value is the kth preset level, the control circuit controls the controllable switch of the second current limiting branch corresponding to the kth preset level to close; As the voltage difference decreases, the control circuit controls the previously closed controllable switch to open and the corresponding controllable switch of the second current limiting branch to close in a preset order, so that the resistance of the second current limiting circuit gradually decreases.

4. The surge suppression circuit for a switching power supply according to claim 3, characterized in that: When the voltage difference level corresponding to the voltage difference value is the third preset level, the control circuit controls the controllable switch of the second second current limiting branch to close; As the voltage difference decreases, the control circuit controls the controllable switch of the second second current limiting branch to open and the controllable switch of the first second current limiting branch to close. After the voltage difference drops to the second voltage preset value, the control circuit controls the controllable switch of the first second current limiting branch to open and the main power switch to operate in the on state.

5. The surge suppression circuit for a switching power supply according to claim 3, characterized in that: When the voltage difference level corresponding to the voltage difference is the second preset level, the control circuit controls the controllable switch of the first second current limiting branch to close, and after the voltage difference drops to the second voltage preset value, controls the controllable switch of the first second current limiting branch to disconnect and the main power switch to operate in the on state.

6. The surge suppression circuit for a switching power supply according to claim 2, characterized in that: The number n of the n second current limiting branches is set according to the preset current level of the surge current and the voltage difference level.

7. The surge suppression circuit for a switching power supply according to claim 1, characterized in that: The control circuit also includes a constant current control unit; The open state includes a linear region and a closed state; When the surge current received by the main power switch exceeds the preset current value, the constant current control unit controls the main power switch to operate in the linear region; when the surge current received by the main power switch is less than the preset current value, the constant current control unit controls the main power switch to operate in a closed state.

8. The surge suppression circuit for a switching power supply according to claim 1, characterized in that: The main power switch includes a plurality of power switch tubes connected in parallel.

9. The surge suppression circuit for a switching power supply according to claim 1, characterized in that: The first current limiting circuit includes a plurality of first current limiting branches connected in parallel, and each of the first current limiting branches includes a second resistor.

10. The surge suppression circuit for a switching power supply according to claim 9, characterized in that: Each of the first current limiting branches further includes a semiconductor device connected in series with the second resistor.

11. The surge suppression circuit for a switching power supply according to claim 10, characterized in that: The first end of the first current limiting circuit is used to receive a first input voltage or a second input voltage.

12. A switching power supply, characterized in that: include: A surge suppression circuit applied to a switching power supply as claimed in any one of claims 1 to 11; A first power conversion circuit is connected in series with the surge suppression circuit to form a series branch, one end of the series branch is connected to a power supply, and the other end is connected to a capacitor; The second power conversion circuit includes an input end and an output end, wherein the input end is connected to the capacitor, and the output end is used to output electric energy.

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