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

Abstract

The utility model provides a surge suppression circuit applied to a switching power supply and the switching power supply, and relates to the field of power electronics. 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 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 working states of the controllable switch and the main power switch according to the working state of the switching power supply and the voltage difference value. The circuit can effectively reduce surge current of different conditions in the switching power supply, and is high in response speed, high in reliability and simple to control.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, and in particular to a surge suppression circuit and a switching power supply for use in switching power supplies. Background Technology

[0002] With the rapid development of power electronics technology, switching power supplies are widely used in power supply systems. During sudden voltage spikes in the power grid or the instantaneous restoration of power after a power outage, large inrush currents are generated within the switching power supply. These inrush currents can not only cause circuit breakers in the power supply system to malfunction, but also affect the power quality of the grid and the safe operation of other electrical equipment. Therefore, reducing the inrush current of switching power supplies is urgently needed.

[0003] Currently, there are two main approaches to surge current suppression in switching power supplies. The first approach uses a parallel connection of a switching transistor and a resistor to limit cold-start surge current. This works by charging the internal capacitor of the power supply through the resistor during a cold start. Once the input voltage matches the capacitor voltage, the switching transistor closes, thus reducing the surge current. However, this approach cannot suppress thermal shock surge currents caused by sudden voltage spikes in the mains power supply or power outages followed by voltage recovery. The second approach uses the switching transistor to operate in its linear region to limit thermal shock surge current. This works by controlling the switching transistor to operate in its linear region when the input current exceeds the design value after a voltage spike or power outage, thereby reducing the thermal shock surge current. However, this approach is prone to overpower damage to the switching transistor under severe mains voltage fluctuations. The drawbacks of these two surge current suppression methods are obvious: they are only effective at reducing specific surge currents and cannot reduce surge currents under various operating conditions.

[0004] In order to meet the surge current suppression requirements under various operating 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. Utility Model Content

[0005] The surge current suppression scheme mentioned above is only effective in reducing specific surge currents and cannot reduce surge currents generated under various operating conditions.

[0006] This application proposes a surge current suppression circuit for switching power supplies, comprising:

[0007] The first current limiting circuit includes a first terminal and a second terminal. The first terminal is used to receive the input voltage, and the second terminal is coupled to the capacitor inside the switching power supply.

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

[0009] The main power switch is connected in parallel with the first current-limiting current;

[0010] A voltage sampling circuit is used to detect the voltage difference between the input voltage and the voltage of the capacitor; and

[0011] A control circuit is used to control the operating states of the controllable switch and the main power switch according to the operating state of the switching power supply and the voltage difference.

[0012] Optionally, when the switching power supply is in cold start mode, the control circuit controls the main power switch to open, so that the input voltage charges the capacitor through the first current limiting circuit, and controls the main power switch to close when the voltage difference is less than the first voltage preset value.

[0013] Optionally, when the operating state of the switching power supply is a sudden input voltage change state, the control circuit determines the voltage difference level corresponding to the voltage difference value, and controls the main power switch to open and the controllable switch of the second current limiting circuit to close when the voltage difference level is higher than the first preset level, and controls the controllable switch of the second current limiting circuit to open and the main power switch to operate in the on state after the voltage difference value drops to the second preset voltage value, or controls the main power switch to operate in the on state when the voltage difference level is the first preset level.

[0014] Optionally, the second current limiting circuit includes n parallel-connected second current limiting branches. Each second current limiting branch includes a first resistor and a controllable switch connected in series. 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, where n≥1 and 1≤i≤n.

[0015] Optionally, the differential pressure levels include m preset levels, wherein the k-th preset level is higher than the (k-1)-th preset level, m≥2, 2≤k≤m;

[0016] 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.

[0017] 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 sequence, so that the resistance of the second current-limiting circuit gradually decreases.

[0018] Optionally, 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 current limiting branch to close.

[0019] As the voltage difference decreases, the control circuit controls the controllable switch of the second current-limiting branch to open and the controllable switch of the first current-limiting branch to close. After the voltage difference drops to the second voltage preset value, the controllable switch of the first current-limiting branch is opened and the main power switch is turned on.

[0020] 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 preset voltage value, controls the controllable switch of the first second current limiting branch to open and the main power switch to operate in the on state.

[0021] Optionally, the number n of the n second current-limiting branches is set according to the current preset level of the surge current and the voltage difference level.

[0022] Optionally, the control circuit further includes a constant current control unit;

[0023] The open state includes the linear region and the closed state;

[0024] 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 the closed state.

[0025] Optionally, the main power switch includes a plurality of power switching transistors connected in parallel.

[0026] Optionally, the first current limiting circuit includes multiple first current limiting branches connected in parallel, and each first current limiting branch includes a second resistor.

[0027] Optionally, each of the first current-limiting branches further includes a semiconductor device connected in series with the second resistor.

[0028] Optionally, the first terminal of the first current limiting circuit is used to receive a first input voltage or a second input voltage.

[0029] This application also proposes a switching power supply, comprising:

[0030] Surge suppression circuits applied to switching power supplies as described in any embodiment of this application;

[0031] The first power conversion circuit, after being connected in series with the surge suppression circuit, forms a series branch. One end of the series branch is connected to the power supply, and the other end is connected to a capacitor.

[0032] The second power conversion circuit includes an input terminal and an output terminal. The input terminal is connected to the capacitor, and the output terminal is used to output electrical energy.

[0033] The beneficial effects of this application include at least the following:

[0034] The surge suppression circuit in 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 first current-limiting circuit and the main power switch reduce the inrush current caused by cold starts of the switching power supply. The voltage difference obtained by the voltage sampling circuit and the control circuit's optimization of the controllable switching sequence of the second current-limiting circuit effectively reduce the thermal shock inrush current caused by sudden input voltage changes. This surge suppression circuit can effectively reduce the inrush current under different conditions of the switching power supply and has high reliability. This surge suppression circuit uses only simple hardware circuitry and control strategies to limit the inrush current within a reasonable range, and is low-cost and simple to control.

[0035] 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

[0036] To gain a more comprehensive understanding of this application and its advantages, the following description is now presented in conjunction with the accompanying drawings.

[0037] In the picture:

[0038] Figure 1 A schematic diagram of the surge suppression circuit according to an embodiment of this application is shown;

[0039] Figure 2 A schematic diagram of another surge suppression circuit according to an embodiment of this application is shown;

[0040] Figure 3 The control timing diagram of the surge suppression circuit according to an embodiment of this application is shown;

[0041] Figure 4 Another control timing diagram of the surge suppression circuit according to an embodiment of this application is shown.

[0042] 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

[0043] 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.

[0044] 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 utility model are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence.

[0045] In the description of this utility model, 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, direct connection or indirect connection through an intermediate medium, or 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 utility model according to the specific circumstances.

[0046] Furthermore, to better illustrate this utility model, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this utility model can be implemented even without certain specific details. In some instances, methods, means, components, and circuits well-known to those skilled in the art have not been described in detail, in order to highlight the main points of this utility model.

[0047] Figure 1 A schematic diagram of the surge suppression circuit according to an embodiment of this application is shown. 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. The first current limiting circuit 12 includes a first terminal and a second terminal. The first terminal is used to receive the input voltage, and the second terminal is coupled to the capacitor CB inside the switching power supply. In this embodiment, the first terminal of the first current limiting circuit 12 is coupled to the 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 that provides mains power.

[0048] 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 characterizing the input voltage, the second sampling unit detects the voltage of the capacitor CB to obtain a capacitor voltage signal characterizing 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 two to obtain a voltage difference signal, wherein the voltage difference signal characterizes 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 example described above.

[0049] The control circuit 18 is used to control the operating state of the controllable switch and the main power switch 14 according to the operating state of the switching power supply and the voltage difference.

[0050] The embodiments of this application can reduce the inrush current caused by cold start of the switching power supply through the first current limiting circuit and the main power switch 14. Furthermore, the voltage difference obtained through the voltage sampling circuit and the control circuit controlling the operating state of the controllable switch and the main power switch 14 effectively reduce the thermal shock inrush current caused by sudden input voltage changes. This surge suppression circuit can effectively reduce the inrush current under different conditions of the switching power supply and has high reliability. This surge suppression circuit uses only simple hardware circuitry and control strategies to limit the inrush current within a reasonable range, and is low in cost and simple to control.

[0051] Furthermore, when the switching power supply is in cold start mode, the control circuit 18 controls the main power switch 14 to open, allowing the input voltage to charge the capacitor CB through the first current limiting circuit 12. When the voltage difference is less than a first preset voltage value, the control circuit 18 controls the main power switch 14 to close. This embodiment reduces the cold start inrush current through the first current limiting circuit 12 and the main power switch 14.

[0052] Furthermore, when the operating state of the switching power supply is a sudden change in input voltage, the control circuit 18 determines the voltage difference level corresponding to the voltage difference value, and controls the main power switch 14 to open and the controllable switch of the second current limiting circuit 13 to close when the voltage difference level is higher than the first preset level. After the voltage difference value drops to the second preset voltage value, it controls the controllable switch of the second current limiting circuit 13 to open and the main power switch 14 to operate in the on state, or controls the main power switch 14 to operate in the on state when the voltage difference level is the first preset level.

[0053] The surge suppression circuit in this embodiment can effectively reduce thermal shock surge current by optimizing the turn-on sequence of the controllable switch of the second current limiting circuit 13 and the main power switch 14. It has the advantages of fast response speed, high reliability and simple control.

[0054] In this embodiment, when the switching power supply undergoes a cold start, the control circuit 18 controls the main power switch 14 to open, allowing the input voltage to charge the capacitor CB through the first current limiting circuit 12. The first current limiting circuit 12 includes a second resistor, which effectively reduces the inrush 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 decreases until the voltage difference is less than a first preset voltage value. At this point, the control circuit 18 controls the main power switch 14 to close, thereby bypassing the first current limiting circuit 12. It should be noted that the first preset voltage value can be a small value, such as close to 0V; a voltage difference less than the first preset voltage value means that the voltage of the capacitor CB is approximately equal to the input voltage. In this embodiment, after the switching power supply starts, the input voltage charges the capacitor CB through the first current limiting circuit 12, causing the voltage of the capacitor CB to rise until the voltage difference is less than the first preset voltage value. At this point, the control circuit 18 controls the main power switch 14 to close, thereby effectively suppressing the inrush current.

[0055] Furthermore, a sudden input voltage change can refer to a sudden increase in input voltage. It can also refer to the period from power failure to power restoration of the power supply module 11, where the input voltage drops when the power supply module 11 fails and returns to its normal operating voltage when the power supply module 11 resumes power. It should be noted that during the power failure to power restoration process of the power supply module 11, the energy stored in capacitor CB is drawn away by other circuits in the switching power supply. The longer the power failure time, the greater the voltage drop of capacitor CB, and the larger the voltage difference between the input voltage and the capacitor voltage when the power supply module 11 resumes power.

[0056] Furthermore, the main power switch 14 has two states: a linear region and a closed state. When the main power switch 14 is in the linear region, it exhibits impedance characteristics, which limit thermal surge current when the input voltage changes abruptly and the voltage difference level is at a first preset level or the voltage difference drops to a second 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, it is fully conductive, and its resistance is at its minimum, close to 0Ω.

[0057] Furthermore, the second current-limiting circuit 12 includes n parallel-connected second current-limiting branches. Each second current-limiting branch includes a first resistor and a controllable switch connected in series. The resistance of the first resistor in the i-th second current-limiting branch is greater than the resistance of the first resistor in the (i-1)-th second current-limiting branch, where 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, up to the n-th second current-limiting branch, which includes a first resistor Rn and a controllable switch Qn connected in series. The impedance of the first resistor in each second current-limiting branch is different, i.e., the resistance of Rn > the resistance of Rn-1, ... > the resistance of R2 > the resistance of R1.

[0058] Furthermore, the first resistor can 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 can be a switching device such as a MOSFET, GaN, or SiC.

[0059] Furthermore, the differential voltage levels include m preset levels, where the k-th 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, meaning the minimum value of the preset voltage range for the k-th preset level is greater than or equal to the maximum value of the preset voltage range for the (k-1)-th preset level. Specifically, the number of preset differential voltage levels can be set based on the power rating of the switching power supply, the current preset level of the surge current, and the capacitance of capacitor CB. When the differential voltage level corresponding to the voltage difference is the k-th preset level, the control circuit controls the controllable switch of the second current-limiting branch corresponding to the k-th preset level to close; as the voltage difference decreases, the control circuit controls the previously closed controllable switches to open and the corresponding controllable switches of the second current-limiting branches to close in a preset sequence, causing the resistance of the second current-limiting circuit 13 to gradually decrease. It should be noted that by controlling the closing of the controllable switches of different second current limiting branches, different resistance values ​​of the second current limiting circuit 13 can be obtained. The preset order can refer to the order in which the resistance values ​​of the second current limiting circuit 13 gradually decrease from large to small.When the voltage difference level corresponding to the voltage difference is determined to be 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 close. 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 becomes the resistance value of the second current-limiting circuit 13. The thermal shock surge current is reduced through 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 a set value or the closing time of the controllable switch Q(k-1) of the (k-1)th second current-limiting branch reaches a preset time, the control circuit 18 controls the controllable switch Q(k-1) of the (k-1)th second current-limiting branch to open and controls the controllable switch Q(k-2) of the (k-2)th second current-limiting branch to close. 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 serves as the second current-limiting circuit 13. The resistance value is used to limit the thermal surge current through the first resistor R(k-2) of the second current limiting branch. The controllable switches are controlled in the order of decreasing resistance value of the second current limiting circuit 13 until the controllable switch Q2 of the second current limiting branch is opened and the controllable switch Q1 of the first second current limiting branch is closed. The input voltage charges the capacitor CB through the first resistor R1 of the first second current limiting branch, making the resistance value of the first resistor R1 of the first second current limiting branch the resistance value of the second current limiting circuit 13. A resistor R1 limits the thermal surge current. When the current flowing through the first second current-limiting branch drops to a set value, or when 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 preset voltage value, the control circuit 18 controls the controllable switch Q1 of the first second current-limiting branch to open and the main power switch 14 to operate in the on state. When the main power switch 14 operates in the linear region, the input voltage charges the capacitor CB through the main power switch 14, and the thermal surge current is limited by the resistance of the main power switch 14. At this time, the voltage difference across the main power switch 14 is small, meeting the SOA (Safe Operating Area) specification requirements, so that the main power switch 14 has a safe operating voltage and current range. It should be noted that the setting value can be set as needed. The setting value can be the current value within the current preset level, where the current preset level is the preset current range; the second voltage preset value is set according to the safety operating area specification of the main power switch 14, and the preset time can be set in advance according to the design parameters or according to the measured value.

[0060] In the above embodiments, the control circuit 18 controls the closing of a controllable switch of a corresponding second current-limiting branch 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 resistance of the second current-limiting circuit, thereby limiting the thermal surge current. In other embodiments, the control circuit 18 controls the closing of controllable switches of one or more second current-limiting branches according to the voltage difference level corresponding to the voltage difference and the gradually decreasing resistance value of the second current-limiting circuit from large to small.

[0061] In this embodiment, the controllable switch of the corresponding second current limiting branch is closed by controlling the voltage difference level corresponding to the voltage difference value, and the resistance value of the second current limiting circuit 13 is gradually reduced. This not only limits the thermal shock surge current within the current preset level, but also reduces power consumption and protects the main power switch 14 to work safely and reliably.

[0062] 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 current preset value, the constant current control unit controls the main power switch 14 to operate in the linear region; when the surge current received by the main power switch 14 is less than the current preset value, the constant current control unit controls the main power switch 14 to operate in the closed state.

[0063] Furthermore, when the voltage difference corresponds to the third preset voltage level, the control circuit controls the controllable switch Q2 of the second current-limiting branch to close, and the input voltage charges the capacitor CB through the first resistor R2, and reduces the surge current through the first resistor R2; as the voltage difference decreases, and the current flowing through the second current-limiting branch drops to a set value or the closing time of the controllable switch Q2 of the second current-limiting branch reaches a first preset time, the control circuit 18 controls the controllable switch Q2 of the second current-limiting branch to open and the controllable switch Q2 of the first current-limiting branch to close. When Q1 is closed, the input voltage charges capacitor CB through the first resistor R1, and also reduces the inrush current. After the current flowing through the first second current-limiting branch drops to a set value, or after the closing time of the controllable switch Q1 in the first second current-limiting branch reaches a second preset time, and the voltage difference drops to the second preset voltage value, the control circuit 18 controls the controllable switch Q1 of the first second current-limiting branch to open and the main power switch 14 to operate in the on state. The input voltage charges capacitor CB through the main power switch 14, and also reduces the inrush current. If the inrush current exceeds the design value of the constant current control unit at this time, the main power switch 18 operates in the linear region to limit the inrush current. When the controllable switches Q1 and Q2 of the first and second second current-limiting branches are both open, if the voltage difference is still large, in order to prevent the main power switch 14 from exceeding the safe operating range specification, the control circuit 18 can simultaneously control the controllable switches Q1 and Q2 of the first and second second current-limiting branches to close, so that the resistance value of the first resistor R1 and R2 in parallel is used as the resistance value 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 then controls the main power switch 14 to work 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, which meets its SOA specification requirements.

[0064] Figure 3 A control timing diagram of a surge suppression circuit according to an embodiment of this application is shown. Figure 3 As shown, Vin represents the input voltage waveform, VCB represents the voltage waveform across capacitor CB, Q2 represents the control signal waveform of the controllable switch Q2 in the second current-limiting branch, Q1 represents the control signal waveform of the controllable switch Q1 in the first 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. Combined with... 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 current limiting branch changes from low level to high level, causing the controllable switch Q2 to close. At this time, the control signal CS1 of the main power switch 14 changes from high level to low level, causing the main power switch 14 to open. At this time, the input current Iin drops to 0A, and the voltage VCB of capacitor CB decreases as the input voltage drops. At time t2, the input voltage Vin returns to its normal operating voltage. The input voltage Vin charges capacitor CB through the first resistor R2, which also limits the thermal surge current. As the voltage of 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 (which could be the input current value at time t3, or the closing time of controllable switch Q2 reaching a first preset time, which could be the time interval between time t3 and time t1), the control signal CQ2 of controllable switch Q2 changes from high to low, causing controllable switch Q2 to open. At this time, the control signal CQ1 of controllable switch Q1 changes from low to high, causing controllable switch Q1 to close. The input voltage Vin then charges capacitor CB through the first resistor R1, which also limits the thermal surge current. When the current flowing through the first resistor R2... When the current I1 drops to a predetermined value, which can be the input current value at time t4, or the closing time of controllable switch Q1 reaches a second preset time, which can be the time period between time t4 and time t3, the control signal CQ1 of controllable switch Q1 changes from high to low, causing controllable switch Q1 to open. At time t4, the voltage difference drops to the second preset voltage value, and the control signal CS1 of main power switch 14 changes from low to first level, causing main power switch 14 to operate in the linear region. The input voltage charges capacitor CB through main power switch 14 and limits thermal surge current. As the voltage CB of capacitor rises to near the input voltage Vin, i.e., at time t5, the control signal CS1 of main power switch 14 changes from low to second level, causing main power switch 14 to operate in the closed state, and the input current Iin to operate in a stable state. By gradually reducing the resistance value of the second current limiting circuit, the surge current can be effectively limited to a reasonable range, which has the advantages of fast response speed, low power consumption, high reliability and simple control.

[0065] Figure 4 Another control timing diagram of the surge suppression circuit according to an embodiment of this application is shown. Figure 4 The control timing shown is Figure 3The difference in the control timing shown lies in the timing of the transition of the control signal CQ2 of the controllable switch Q2 from low to high. The other similarities will not be elaborated upon here. Figure 4 As shown, at time t2, the control signal of the controllable switch Q2 changes from low level to high level, meaning that the controllable switch Q2 is closed only when the input voltage recovers.

[0066] Furthermore, the main power switch 14 can be disconnected when the input voltage drops, or before the input voltage returns to normal operating conditions.

[0067] Furthermore, when the voltage difference level corresponding to the voltage difference value 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 reduces the surge current 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 preset voltage value, the control circuit 18 controls the controllable switch of the first second current limiting branch to open and the main power switch 14 to work in the on state. 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, which meets its SOA specification requirements.

[0068] Furthermore, when the voltage difference level corresponding to the voltage difference value is the first preset level, the control circuit 18 controls all controllable switches of the second current-limiting branches to be disconnected and the main power switch 14 to be turned on. The input voltage charges the capacitor CB through the main power switch 14, and the surge current is reduced when the main power switch 14 is operating 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.

[0069] Furthermore, the number n of the second current-limiting branches can be set according to the current preset level of the surge current and the voltage difference level, which can limit the cold start and thermal shock surge current within the specifications and ensure the reliable operation of the device.

[0070] Continue to refer to Figure 1 The main power switch 14 may include multiple power switch transistors S1, S2, ..., Sn connected in parallel.

[0071] Furthermore, the first current-limiting circuit 12 includes multiple first current-limiting branches connected in parallel, and each first current-limiting branch includes a second resistor. Specifically, the second resistors Rs1, Rs2, and Rsn are connected in parallel. It should be noted that the second resistor can be a positive temperature coefficient resistor, a negative temperature coefficient resistor, or a pure resistor.

[0072] It should be noted that the number of power switching transistors and the number of second resistors are related to the power rating and the capacitance of capacitor CB.

[0073] Figure 2 A schematic diagram of another surge suppression circuit according to an embodiment of this application is shown. Figure 2 As shown, the surge suppression circuit in this embodiment is... Figure 1 The difference in the surge suppression circuits shown lies in the first current limiting circuit; the other identical parts will not be described again here. (Refer to...) Figure 2 It is known that each first current-limiting branch also includes a semiconductor device, such as a thyristor or bidirectional thyristor, connected in series with the second resistor. 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, with the second resistor Rsn being connected in series with the semiconductor device SCRn to form the nth first current-limiting branch.

[0074] like Figure 2 As shown, the input terminal 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 terminal of the first current limiting circuit 12 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, the semiconductor device in the first current limiting branch needs to be disconnected to protect the switching power supply.

[0075] An embodiment of this application discloses a switching power supply, which includes:

[0076] Surge suppression circuit applied to switching power supplies in any of the foregoing embodiments;

[0077] The first power conversion circuit, after being connected in series with the surge suppression circuit, forms a series branch. One end of the series branch is connected to the power supply, and the other end is connected to a capacitor.

[0078] The second power conversion circuit includes an input terminal and an output terminal. The input terminal is connected to the capacitor, and the output terminal is used to output electrical energy.

[0079] 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. The first terminal of the first current limiting circuit 12 (the input terminal of the switching power supply) is connected to the power supply module 11 to receive the input voltage. The second terminal of the first current limiting circuit 12 is connected to the input terminal of the first power conversion circuit 15. The output terminal of the first power conversion circuit 15 is connected to one end of the capacitor CB and the input terminal of the second power conversion circuit 16. The other end of the capacitor CB is grounded. The output terminal of the second power conversion circuit 16 is used to output electrical energy to provide power 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.

[0080] 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 open during the cold start of the switching power supply, so that the input voltage charges the capacitor through the first current limiting circuit, and to control the main power switch 14 to operate in the closed state when the voltage difference is less than a first preset voltage value; after a sudden change in the input voltage, the controllable voltage level corresponding to the voltage difference is determined, and when the voltage difference level is higher than the first preset level, the controllable switch of the second current limiting circuit 13 is opened and the controllable switch of the second current limiting circuit 13 is closed, and when the voltage difference drops to the second preset voltage value, the controllable switch of the second current limiting circuit 13 is opened and the main power switch 14 is operated in the on state, or the main power switch 14 is operated in the on state when the voltage difference level is the first preset level.

[0081] The surge suppression circuit in this embodiment can effectively reduce surge current under different conditions of the switching power supply by optimizing the turn-on sequence of the controllable switch for the second current limiting current and the main power switch. It has the advantages of fast response speed, high reliability and simple control.

[0082] In other embodiments, the input terminal of the first power conversion circuit 15 is connected to the power supply module 11, the output terminal of the first power conversion circuit 15 is connected to the first terminal of the first current limiting circuit 12, and the second terminal of the first current limiting circuit 12 is connected to one end of a capacitor and the input terminal of the second power conversion circuit 16.

[0083] like Figure 2As shown, the first terminal (switching power supply input terminal) 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 terminal of the first current limiting circuit 12 is connected to the input terminal of the first power conversion circuit 15. The output terminal of the first power conversion circuit 15 is connected to one end of the capacitor CB and the input terminal of the second power conversion circuit 16. The other end of the capacitor CB is grounded. The output terminal of the second power conversion circuit 16 is used to output electrical energy to provide power to the load. In this embodiment, the first current limiting circuit includes multiple first current limiting branches, each of which includes a related second resistor and a semiconductor device connected in series. It should be noted that the second resistor can be a positive temperature coefficient resistor, a negative temperature coefficient resistor, or a pure resistor, etc., which have impedance characteristics. The number of second resistors is related to the power rating and the capacitance of the capacitor CB. In addition, the semiconductor device can be a thyristor, a bidirectional thyristor, or other semiconductor devices.

[0084] In this embodiment, when it is necessary to switch from the first power supply module 21 to the second power supply module 22, the semiconductor devices in the first current limiting branch need to be disconnected to protect the switching power supply.

[0085] This application describes a surge suppression circuit for switching power supplies. During cold starts, the main power switch is first disconnected, and the capacitor is charged by the input voltage through a first current-limiting circuit. When the voltage difference between the input voltage and the capacitor is less than a first preset voltage value, the main power switch is kept closed, effectively reducing cold-start surge current. When the input voltage changes abruptly, the voltage difference level corresponding to the voltage difference between the input voltage and the capacitor is determined. When the voltage difference level is greater than a first preset level, the main power switch is first disconnected, and the corresponding controllable switch in the second current-limiting circuit is gradually reduced. When the voltage difference is less than the second preset voltage value, the controllable switch in the second current-limiting circuit is disconnected, and the main power switch is kept on. This effectively reduces thermal shock surge current and has advantages such as fast response speed, low power consumption, high reliability, and simple control.

[0086] 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.

[0087] Furthermore, the scope of this application is not limited to the specific embodiments of the processes, machines, manufactures, compositions of matter, 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, compositions of matter, methods, or steps that perform substantially the same function or achieve substantially the same results as the corresponding embodiments described herein can be utilized. Therefore, it is intended that the appended claims encompass such processes, machines, manufactures, compositions of matter, methods, or steps within their scope.

Claims

1. A surge suppression circuit for use in switching power supplies, characterized in that, The application relates to a switching power supply, which comprises the following parts: a first current-limiting circuit, which comprises a first end for receiving an input voltage and a second end for connecting a capacitor inside the switching power supply; a second current-limiting circuit connected in parallel with the first current-limiting circuit, which comprises 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 for detecting a voltage difference between the input voltage and the voltage of the capacitor; and a control circuit for controlling the working states of the controllable switch and the main power switch according to the working state of the switching power supply and the voltage difference. When the working state of the switching power supply is cold start, the control circuit controls the main power switch to be off, so that the input voltage charges the capacitor through the first current-limiting circuit, and controls the main power switch to be in a closed state when the voltage difference is less than a first voltage preset value.

2. The surge suppression circuit for use in a switching power supply according to claim 1, wherein When the working state of the switching power supply is input voltage mutation, the control circuit judges the voltage difference grade corresponding to the voltage difference, controls the main power switch to be off and the controllable switch of the second current-limiting circuit to be on when the voltage difference grade is higher than a first preset grade, and controls the controllable switch of the second current-limiting circuit to be off and the main power switch to be in an open state when the voltage difference drops to a second voltage preset value, or controls the main power switch to be in an open state when the voltage difference grade is the first preset grade.

3. The surge suppression circuit for use in a switching power supply according to claim 1, wherein The second current-limiting circuit comprises n second current-limiting branches connected in parallel, each of the second current-limiting branches comprises a first resistor and a controllable switch connected in series, the resistance of the first resistor of the ith second current-limiting branch is greater than the resistance of the first resistor of the (i-1)th second current-limiting branch, n>=1, 1<=i<=n.

4. The surge suppression circuit for use in a switching power supply according to claim 3, wherein The voltage difference grade comprises m preset grades, the kth preset grade is higher than the (k-1)th preset grade, m>=2, 2<=k<=m.

5. The surge suppression circuit for use in a switching power supply according to claim 4, wherein When the voltage difference grade corresponding to the voltage difference is the kth preset grade, the control circuit controls the controllable switch of the second current-limiting branch corresponding to the kth preset grade to be on. With the decrease of the voltage difference, the control circuit controls the controllable switches of the previously closed second current-limiting branches to be off and the controllable switches of the corresponding second current-limiting branches to be on in a preset order, so that the resistance of the second current-limiting circuit gradually decreases. When the voltage difference grade corresponding to the voltage difference is the third preset grade, the control circuit controls the controllable switch of the second second current-limiting branch to be on.

6. The surge suppression circuit for use in a switching power supply according to claim 5, wherein With the decrease of the voltage difference, the control circuit controls the controllable switch of the second second current-limiting branch to be off and the controllable switch of the first second current-limiting branch to be on, and controls the controllable switch of the first second current-limiting branch to be off and the main power switch to be in an open state when the voltage difference drops to the second voltage preset value. ​ 7. The surge suppression circuit for use in a switching power supply according to claim 5, wherein When the voltage difference corresponds to the second preset level, the control circuit controls the first controllable switch of the first current limiting branch to be closed, and controls the first controllable switch of the first current limiting branch to be opened and the main power switch to be in the on state when the voltage difference drops to the second preset value.

8. The surge suppression circuit for use in a switching power supply according to claim 4, wherein The number n of the n second current limiting branches is set according to the current preset level of the inrush current and the voltage difference level.

9. The surge suppression circuit for use in a switching power supply according to claim 3, wherein The control circuit further comprises a constant current control unit. The on state comprises a linear region and a closed state. When the inrush current received by the main power switch exceeds the current preset value, the constant current control unit controls the main power switch to work in the linear region; when the inrush current received by the main power switch is less than the current preset value, the constant current control unit controls the main power switch to work in the closed state.

10. The surge suppression circuit for use in a switching power supply according to claim 1, wherein The main power switch comprises a plurality of parallelly connected power switch tubes.

11. The surge suppression circuit for use in a switching power supply according to claim 1, wherein The first current limiting circuit comprises a plurality of parallelly connected first current limiting branches, and each first current limiting branch comprises a second resistor.

12. The surge suppression circuit for use in a switching power supply according to claim 11, wherein Each first current limiting branch further comprises a semiconductor device connected in series with the second resistor.

13. The surge suppression circuit for use in a switching power supply according to claim 12, wherein The first end of the first current limiting circuit is used for receiving a first input voltage or a second input voltage.

14. A switching power supply, characterized by Comprise: The inrush suppression circuit applied to the switching power supply according to any one of claims 1 to 13; A first power conversion circuit is connected in series with the inrush 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; A second power conversion circuit comprises an input end and an output end, the input end is connected to the capacitor, and the output end is used for outputting electric energy.

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