Overvoltage protection circuit, control circuit and switching power supply for switching power supply

Abstract

The application provides an overvoltage protection circuit, a control circuit and a switching power supply. Two overvoltage protection units are arranged to perform overvoltage protection detection based on sampling of input voltage and output voltage respectively, and overvoltage protection is triggered when one of the two overvoltage protection units meets the condition according to the connection of the main power tube in the switching power supply, i.e. the high / low side type of the switching power supply. The two overvoltage protection units do not need an auxiliary winding when performing overvoltage protection detection, so that the high-side switching power supply application and the low-side switching power supply application are compatible without an auxiliary winding, and the scheme is flexible and low in cost.

Description

Technical Field

[0001] This application relates to the field of overvoltage protection technology, specifically to an overvoltage protection circuit, control circuit, and switching power supply for a switching power supply. Background Technology

[0002] A power converter is a switching power supply that uses switching transistors to control the charging and discharging process of energy storage elements to provide power, and maintains stable output voltage and / or output current by controlling the on and off time ratio of the switching transistors. Most common power converters adopt Boost, Buck, and Buck-Boost topologies.

[0003] Taking a Buck topology switching power supply as an example, the same applies to other topologies. Switching power supplies commonly fall into two application categories: high-side Buck (where the main power transistor is connected to the input voltage) and low-side Buck (where the main power transistor is connected to ground). The overvoltage protection circuits differ between these two types. The commonly used method of sampling the input voltage for overvoltage protection is only suitable for low-side applications and incompatible with high-side applications. While sampling the output voltage allows for compatibility with both low-side and high-side applications, it requires an auxiliary winding in low-side applications, increasing costs.

[0004] Currently, there is no low-cost overvoltage protection circuit that is compatible with both of the above-mentioned switching power supplies. Therefore, the two types of switching power supplies currently require the separate fabrication of overvoltage protection circuits and corresponding chips, which is costly, time-consuming, and involves complicated circuit design, making it unsuitable for mass production. Summary of the Invention

[0005] In view of the above-mentioned technical problems, the purpose of this application is to provide an overvoltage protection circuit, a control circuit, and a switching power supply for a switching power supply. In this application, two overvoltage protection units are set up to perform overvoltage protection detection based on sampling of the input voltage and the output voltage, respectively, and overvoltage protection is triggered when either of them meets the conditions, thereby achieving compatibility with high-side switching power supply applications and low-side switching power supply applications without the need for an auxiliary winding.

[0006] According to a first aspect of this application, an overvoltage protection circuit for a switching power supply is provided, comprising:

[0007] The first overvoltage protection unit samples the output voltage of the switching power supply to obtain a first sampling signal, and generates a first overvoltage protection signal based on the first sampling signal and a first overvoltage protection threshold.

[0008] The second overvoltage protection unit obtains a second sampling signal characterizing the output voltage based on the input voltage sampling signal and duty cycle of the switching power supply, and generates a second overvoltage protection signal based on the second sampling signal and the second overvoltage protection threshold.

[0009] The selection unit selects the first overvoltage protection signal to provide overvoltage protection for the switching power supply when the main power transistor of the switching power supply is connected to the input voltage, or selects the second overvoltage protection signal to provide overvoltage protection for the switching power supply when the main power transistor is connected to the reference ground.

[0010] Optionally, the overvoltage protection circuit includes a first input terminal and a second input terminal;

[0011] When the first sampling signal is received at the first input terminal and the second input terminal is in a high impedance state, the first overvoltage protection unit outputs a valid first overvoltage protection signal, and the second overvoltage protection unit outputs an invalid second overvoltage protection signal.

[0012] When the first input terminal is connected to the reference ground and the second input terminal receives the second overvoltage protection threshold, the first overvoltage protection unit outputs an invalid first overvoltage protection signal, and the second overvoltage protection unit outputs an valid second overvoltage protection signal.

[0013] The selection unit includes:

[0014] The OR logic circuit performs OR logic processing on the first overvoltage protection signal and the second overvoltage protection signal, and the overvoltage protection circuit provides overvoltage protection to the switching power supply based on the output signal of the OR logic circuit.

[0015] Optionally, the selection unit selects one of the first overvoltage protection signal and the second overvoltage protection signal to perform overvoltage protection on the switching power supply according to the selection signal, wherein the selection signal represents the connection status of the main power transistor in the switching power supply relative to the input voltage and the reference ground.

[0016] Optionally, the selection unit includes:

[0017] The first switch, controlled by the selection signal, is used to provide the output voltage and / or the first overvoltage protection threshold to the first overvoltage protection unit when the selection signal characterizes the main power transistor connection input voltage;

[0018] The second switch, controlled by the selection signal, is used to provide the input voltage and / or the second overvoltage protection threshold to the second overvoltage protection unit when the selection signal indicates that the main power transistor is connected to the reference ground;

[0019] The OR logic circuit performs OR logic processing on the first overvoltage protection signal and the second overvoltage protection signal, and the overvoltage protection circuit provides overvoltage protection to the switching power supply based on the output signal of the OR logic circuit.

[0020] Optionally, the selection unit includes:

[0021] The third switch, controlled by the selection signal, is used to output the first overvoltage protection signal when the selection signal represents the input voltage connected to the main power transistor.

[0022] The fourth switch, controlled by the selection signal, is used to output the second overvoltage protection signal when the selection signal indicates that the main power transistor is connected to the reference ground.

[0023] Optionally, the selection unit is configured to:

[0024] The first overvoltage protection unit is continuously enabled, and the second overvoltage protection unit is enabled or disabled according to the selection signal.

[0025] Specifically, when the selection signal represents the connection input voltage of the main power transistor, the second overvoltage protection unit is controlled to be in an enabled state.

[0026] When the selection signal indicates that the main power transistor is connected to the reference ground, the second overvoltage protection unit is controlled to be in an enabled state.

[0027] Optionally, the overvoltage protection circuit includes: receiving a first sampling signal when the main power transistor is connected to the input voltage, and receiving a third input terminal of the second overvoltage protection threshold when the main power transistor is connected to the reference ground;

[0028] When powered on, the third input terminal has an initial voltage based on a preset current source;

[0029] The selection unit generates the selection signal by detecting the voltage range of the initial voltage at the third input terminal when it is first powered on.

[0030] Optionally, the first overvoltage protection unit includes:

[0031] The first voltage divider circuit is used to divide the output voltage at the output voltage terminal to obtain the first sampling signal;

[0032] The first comparison circuit compares the first sampled signal with the first overvoltage protection threshold, and outputs a valid first overvoltage protection signal when the first sampled signal is greater than the first overvoltage protection threshold.

[0033] Optionally, the second overvoltage protection unit includes:

[0034] The second voltage divider circuit divides the input voltage at the input voltage terminal to obtain the input voltage sampling signal;

[0035] A switching logic circuit converts the input voltage sampling signal according to the duty cycle of the switching power supply to obtain a second sampling signal that represents the product of the input voltage sampling signal and the duty cycle.

[0036] The second comparison circuit compares the second sampled signal with the second overvoltage protection threshold, and outputs a valid second overvoltage protection signal when the second sampled signal is greater than the second overvoltage protection threshold.

[0037] Optionally, the sampling ratio of the first sampling signal and the magnitude of the second overvoltage protection threshold are both continuously adjustable.

[0038] According to a second aspect of this application, an overvoltage protection chip is provided, wherein the overvoltage protection chip is provided with an overvoltage protection circuit as disclosed in any embodiment of this application.

[0039] According to a third aspect of this application, a control circuit for a switching power supply is provided, including an overvoltage protection circuit as disclosed in any embodiment of this application.

[0040] According to a fourth aspect of this application, a switching power supply is provided, comprising:

[0041] The overvoltage protection circuit disclosed in any embodiment of this application;

[0042] Alternatively, the control circuit as disclosed in any embodiment of this application.

[0043] Optionally, the switching power supply is a buck switching power supply or a buck-boost switching power supply.

[0044] The beneficial effects of this application include at least the following:

[0045] The overvoltage protection circuit, control circuit, and switching power supply provided in this application utilize two overvoltage protection units to perform overvoltage protection detection based on direct sampling of the output and input voltages, respectively. Overvoltage protection is triggered when one of the two overvoltage protection units meets a condition, depending on the connection of the main power transistor in the switching power supply (i.e., the high / low side type of the switching power supply). Since neither of these two overvoltage protection units requires auxiliary windings for voltage sampling during overvoltage protection detection, compared to traditional solutions, this application's solution achieves compatibility with both high-side switching power supply applications (i.e., switching power supplies where the main power transistor is connected to the input voltage) and low-side switching power supply applications (i.e., switching power supplies where the main power transistor is connected to ground) without the need for auxiliary windings. Furthermore, the solution is flexible and cost-effective.

[0046] In a further preferred embodiment, the overvoltage protection function is achieved by configuring the overvoltage protection circuit with two input terminals (or pins), which is simple in structure and low in cost.

[0047] In a further preferred embodiment, the overvoltage protection function is achieved by configuring the overvoltage protection circuit through an input terminal (or pin), which provides a high degree of flexibility.

[0048] It should be noted that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit this application. Attached Figure Description

[0049] Figure 1a A schematic diagram of a conventional switching power supply with its main power transistor connected to the input voltage and its overvoltage protection circuit is shown.

[0050] Figure 1b This diagram illustrates a typical switching power supply with the main power transistor connected to reference ground and its overvoltage protection circuit.

[0051] Figure 1c This diagram illustrates another schematic of a conventional switching power supply with the main power transistor connected to reference ground and its overvoltage protection circuit.

[0052] Figure 2a A schematic diagram of a switching power supply and its overvoltage protection circuit according to a first embodiment of this application is shown.

[0053] Figure 2b A schematic diagram of a switching power supply and its overvoltage protection circuit according to a second embodiment of this application is shown.

[0054] Figure 2c A schematic diagram of a switching power supply and its overvoltage protection circuit according to a third embodiment of this application is shown.

[0055] Figure 3 A schematic diagram of the structure of a first overvoltage protection unit provided according to an embodiment of this application is shown;

[0056] Figure 4 A schematic diagram of the structure of the second overvoltage protection unit provided according to an embodiment of this application is shown;

[0057] Figure 5 A schematic diagram of a control circuit according to a first embodiment of this application and its application example in a low-side switching power supply is shown.

[0058] Figure 6 A schematic diagram of a control circuit according to a first embodiment of this application and its application example in a high-side switching power supply is shown.

[0059] Figure 7 A schematic diagram of a control circuit according to a second embodiment of this application and its application example in a low-side switching power supply is shown.

[0060] Figure 8 A schematic diagram of a control circuit according to a second embodiment of this application and its application example in a high-side switching power supply is shown. Detailed Implementation

[0061] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application may be implemented in various forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0062] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0063] In the description of this application, words such as "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments. The term "and / or" in this document describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. "Multiple" refers to two or more. Furthermore, to facilitate a clear description of the technical solutions of the embodiments of this application, the terms "first," "second," etc., are used to distinguish identical or similar items with substantially the same function and effect. Those skilled in the art will understand that the terms "first," "second," etc., do not limit the quantity or execution order, and that "first," "second," etc., do not necessarily imply differences.

[0064] In addition, the same reference numerals in the figures indicate the same or similar structures, so repeated descriptions of them will be omitted. That is, the various parts in this specification are described in a combination of parallel and progressive manner. Each part focuses on the differences from other parts, and the same or similar parts between the various parts can be referred to each other.

[0065] Figure 1a A schematic diagram of a conventional switching power supply with its main power transistor connected to the input voltage and its overvoltage protection circuit is shown, as follows: Figure 1a As shown, the switching power supply 100 (e.g., using a Buck topology) includes a rectifier bridge 110, a power unit 120, and an overvoltage protection circuit 130. The power unit 120 includes a main power transistor M0, a freewheeling diode D0, an inductor L0, an input capacitor Ci, and an output capacitor Co. The rectifier bridge 110 rectifies the AC power supply and outputs the input voltage Vin. The main power transistor M0 and the inductor L0 are connected in series between the input and output terminals. The input capacitor Ci is connected between the input terminal and the reference ground of the switching power supply (located at point A). The output capacitor Co is connected between the output terminal and the reference ground. The anode of the freewheeling diode D0 is grounded, and the cathode is connected to the common node B of the main power transistor M0 and the inductor L0. The reference ground potential of its overvoltage protection circuit 130 is the potential of the common connection node B of the main power transistor M0 and the inductor L0. The overvoltage protection circuit 130 includes an output sampling unit 131 and an overvoltage control unit 132. The output sampling unit 131 directly samples the output voltage Vout. The sampled voltage is input to the overvoltage control unit 132. The overvoltage control unit 132 generates an overvoltage protection signal OVP based on the comparison result between the sampled voltage of the output voltage Vout and the internally set overvoltage protection threshold.

[0066] Figure 1b This diagram illustrates a typical switching power supply with the main power transistor connected to ground and its overvoltage protection circuit. Figure 1b The step-down switching power supply shown has a topology similar to... Figure 1a Similar, but different, Figure 1b In this circuit, the input and output terminals are directly connected, while the main power transistor M0 is connected to the reference ground of the switching power supply (located at point A). The reference ground potential of its overvoltage protection circuit 130 is the same as that of the switching power supply 100. The overvoltage protection circuit 130 includes an input sampling unit 133 and an overvoltage control unit 132. The input sampling unit 133 samples the input voltage Vin, and the sampled voltage is input to the overvoltage control unit 132. The overvoltage control unit 132 calculates the characteristic voltage of the output voltage based on the sampled voltage of the input voltage Vin and the duty cycle D, and then compares it with the internally set overvoltage protection threshold to generate an overvoltage protection signal OVP.

[0067] Figure 1cThis diagram illustrates another schematic of a conventional switching power supply with the main power transistor connected to reference ground and its overvoltage protection circuit. Figure 1c The flyback switching power supply 100 has a topology similar to... Figure 1b Similar, but different, Figure 1c In this circuit, a transformer TR is used instead of an inductor. The transformer TR includes a primary winding Np and an auxiliary winding Na. The primary winding Np is connected to the main power transistor M0. The flyback switching power supply 100 uses the auxiliary winding Na and resistors Ru and Rp connected to it to equivalently sample the output voltage Vout. Resistors Ru and Rp are used to measure the voltage Vout across the auxiliary winding Na. AUX Perform voltage division. Figure 1c The overvoltage protection circuit 130 in the circuit compares the sampled voltage Vs with the internally set overvoltage protection threshold to generate an overvoltage protection signal OVP.

[0068] However, Figure 1a The overvoltage protection method shown in the diagram, which achieves overvoltage protection by directly sampling the output voltage Vout, is only suitable for high-side switching power supply applications and is not compatible with low-side switching power supply applications. Figure 1b The overvoltage protection method shown in the diagram, which uses sampling input voltage Vin, is only suitable for low-side switching power supply applications and is not compatible with high-side switching power supply applications. Figure 1c The overvoltage protection method shown, which indirectly samples the output voltage Vout through the auxiliary winding Na, is only suitable for low-side switching power supply applications and is not compatible with high-side switching power supply applications.

[0069] To address the aforementioned issues, this application provides a new overvoltage protection scheme for switching power supplies, such as... Figure 2a , Figure 2b and Figure 2c As shown, schematic diagrams of different embodiments of the switching power supply and its overvoltage protection circuit provided in this application are presented. The overvoltage protection scheme for the switching power supply provided in this application can achieve compatibility with high-side switching power supply applications (i.e., switching power supply where the main power transistor is connected to the input voltage) and low-side switching power supply applications (i.e., switching power supply where the main power transistor is connected to the reference ground) without the need for an auxiliary winding. Moreover, the scheme is flexible and low in cost.

[0070] refer to Figure 2a , Figure 2b and Figure 2cThe switching power supply 200 disclosed in this application includes: a rectifier bridge 210, a power unit 220, and an overvoltage protection circuit 230. The rectifier bridge 210 rectifies the AC power supply and outputs it as the input voltage Vin; the power unit 220 converts the input voltage Vin into power and outputs it as the output voltage Vout; the overvoltage protection circuit 230 is used to detect one of the input voltage Vin and the output voltage Vout according to the application type of the switching power supply 200 (i.e., the connection status of the main power transistor in the switching power supply 200 relative to the input voltage and the reference ground), thereby providing overvoltage protection for the switching power supply 200.

[0071] It should be noted that in a high-side switching power supply, the main power transistor is connected to the input voltage; in this article, a high-side switching power supply is also referred to as a switching power supply where the main power transistor is connected to the input voltage. In a low-side switching power supply, the main power transistor is connected to ground; in this article, a low-side switching power supply is also referred to as a switching power supply where the main power transistor is connected to ground.

[0072] In this application, the switching power supply 200 is a buck switching power supply or a buck-boost switching power supply. The internal structure of the power unit 220 can be understood with reference to existing solutions. Taking the switching power supply 200 as a buck switching power supply as an example, in this case, the power unit 220 has the same... Figure 1a The power unit 120 in the middle has a basically the same structure.

[0073] The switching power supply 200 also includes a control circuit 240, see reference. Figure 5 , Figure 6 , Figure 7 and Figure 8 The control circuit 240 is shown in the form of a control chip. It is connected to the power unit 220 and is used to provide control signals to the main power transistor in the power unit 220. The power unit 220 includes a main power transistor M0, a freewheeling diode D0, an inductor L0, an input capacitor Ci, and an output capacitor Co.

[0074] Furthermore, this application also provides an overvoltage protection chip, which includes an overvoltage protection circuit 230 as disclosed in any embodiment of this application. Optionally, the overvoltage protection circuit 230 can be directly disposed within the control circuit 240, or it can be disposed within the control circuit 240 in the form of an overvoltage protection chip, or it can be disposed independently of the control circuit 240.

[0075] like Figure 2a , Figure 2b and Figure 2cAs shown, in this application, the overvoltage protection circuit 230 includes: a first overvoltage protection unit 231, a second overvoltage protection unit 232, and a selection unit. The first overvoltage protection unit 231 is used to directly sample the output voltage Vout of the switching power supply 200 at its output voltage terminal to obtain a first sampling signal (denoted as V). FB ), and according to the first sampled signal V FB and the first overvoltage protection threshold V FB-OVP A first overvoltage protection signal OVP1 is generated. The second overvoltage protection unit 232 samples the input voltage Vin of the switching power supply 200 at the input voltage terminal of the switching power supply 200, and obtains a second sampling signal (denoted as Vin_S2) representing the output voltage Vout based on the sampling signal of the input voltage Vin (i.e., the input voltage sampling signal, denoted as Vin_S1) and the duty cycle. It then uses the second sampling signal Vin_S2 and the second overvoltage protection threshold Vout... OVP-REF A second overvoltage protection signal OVP2 is generated. The selection unit is used to select the first overvoltage protection signal OVP1 (or the first overvoltage protection unit 231) to perform overvoltage protection on the switching power supply 200 when the main power transistor of the switching power supply 200 is connected to the input voltage Vin (i.e., the switching power supply 200 is a high-side switching power supply), or to select the second overvoltage protection signal OVP2 (or the second overvoltage protection unit 232) to perform overvoltage protection on the switching power supply 200 when the main power transistor of the switching power supply 200 is connected to the reference ground.

[0076] In specific implementation, refer to Figure 3 The first overvoltage protection unit 231 includes a first voltage divider circuit 241 and a first comparator circuit 243. The first voltage divider circuit 241 is used to divide the output voltage Vout at the output voltage terminal of the switching power supply 200 to obtain the first sampling signal V. FB The positive input terminal of the first comparator circuit 243 receives the first sampled signal V. FB The negative input terminal of the first comparator circuit 243 receives the first overvoltage protection threshold V. FB-OVP The first comparison circuit 243 is used to compare the first sampled signal V. FB and the first overvoltage protection threshold V FB-OVP And in the first sampled signal V FB Greater than the first overvoltage protection threshold V FB-OVP When this occurs, a valid first overvoltage protection signal OVP1 is output.

[0077] The first voltage divider circuit 241 includes, for example, resistors R1 and R2 connected in series between the output voltage terminal of the switching power supply 200 and a reference ground. The first voltage divider circuit 241 outputs a first sampling signal V near the common connection of resistors R1 and R2. FBFor example, the first voltage divider circuit 241 is usually located outside the overvoltage protection chip or control chip, but it can also be located inside the overvoltage protection chip or control chip.

[0078] In this application, the first overvoltage protection threshold V is used. FB-OVP This application's solution will be illustrated using an internally set threshold voltage as an example. However, it can be understood that the first overvoltage protection threshold V... FB-OVP It can also be an externally configured threshold voltage.

[0079] Optionally, in some embodiments, a fixed first overvoltage protection threshold V can be set. FB-OVP By adjusting the first sampling signal V FB The sampling coefficients (i.e., the voltage division ratio of resistors R1 and R2 in the first voltage divider circuit 241) are used to adjust the overvoltage protection point of the first overvoltage protection unit 231 for the output voltage Vout, i.e., the first sampling signal Vout. FB The sampling ratio is continuously adjustable; a fixed first sampling signal V can also be set. FB The sampling coefficients (i.e., the voltage division ratio of resistors R1 and R2 in the first voltage divider circuit 241) are adjusted by the first overvoltage protection threshold V. FB-OVP The size is adjusted to control the overvoltage protection point of the first overvoltage protection unit 231 on the output voltage Vout.

[0080] In a preferred embodiment, the first overvoltage protection unit 231 further includes a filter unit 242 connected between the first voltage divider circuit 241 and the positive input terminal of the first comparator circuit 243. The filter unit 242 includes a resistor R3 and a capacitor C1, and is used to compare the first sampled signal V with the first comparator circuit 243. FB and the first overvoltage protection threshold V FB-OVP Previously, for the first sampled signal V FB Perform filtering.

[0081] The first overvoltage protection unit 231 operates when the main power transistor of the switching power supply 200 is connected to the input voltage, and during operation, the first overvoltage protection unit 231 detects the first sampling signal V. FB Greater than the first overvoltage protection threshold V FB-OVP When this occurs, the overvoltage protection of the switching power supply 200 is triggered.

[0082] refer to Figure 4The second overvoltage protection unit 232 includes a second voltage divider circuit 251, a switching logic circuit 252, and a second comparator circuit 254. The second voltage divider circuit 251 divides the input voltage Vin at the input voltage terminal of the switching power supply 200 to obtain an input voltage sampling signal Vin_S1. The switching logic circuit 252 converts the input voltage sampling signal Vin_S1 output by the second voltage divider circuit 251 according to the duty cycle D of the switching power supply 200 to obtain a second sampling signal Vin_S2 representing the product of the input voltage sampling signal Vin_S1 and the duty cycle D, i.e., Vin_S2 = Vin_S1 * D. In a step-down switching power supply, the second sampling signal Vin_S2 can be used to represent the output voltage Vout. The positive input terminal of the second comparator circuit 254 receives the second sampling signal Vin_S2, and the negative input terminal of the second comparator circuit 254 is connected to the second overvoltage protection threshold Vout. OVP-REF The second comparison circuit 254 is used when the second sampled signal Vin_S2 is greater than the second overvoltage protection threshold V. OVP-REF When this occurs, a valid second overvoltage protection signal OVP2 is output.

[0083] The second voltage divider circuit 251 includes, for example, resistors R4 and R5 connected in series between the input voltage terminal of the switching power supply 200 and the reference ground. The second voltage divider circuit 251 outputs an input voltage sampling signal Vin_S1 near the common connection of resistors R4 and R5.

[0084] The switching logic circuit 252 includes, for example, switches S5 and S6. Switch S5 is connected between the output of the second voltage divider circuit 251 and the positive input of the second comparator circuit 254, and is controlled by the control signal Vgs of the main power transistor, and is turned on during the effective period of the control signal Vgs. Switch S6 is connected between the output of the switching logic circuit 252 and the reference ground, and is controlled by the inverted signal of the control signal Vgs of the main power transistor, and is turned on during the ineffective period of the control signal Vgs.

[0085] In this application, the second overvoltage protection threshold V is used. OVP-REF The solution in this application will be illustrated using an externally configured threshold voltage as an example. However, it can be understood that the second overvoltage protection threshold V... OVP-REF It can also be an internally set threshold voltage.

[0086] Optionally, in some embodiments, a fixed sampling coefficient for the second sampling signal Vin_S2 (i.e., the voltage division ratio of resistors R4 and R5 in the second voltage divider circuit 251) can be set, and the second overvoltage protection threshold V can be adjusted. OVP-REF The size of the value is used to adjust the overvoltage protection point of the second overvoltage protection unit 232, i.e., the second overvoltage protection threshold V. OVP-REF The value is continuously adjustable; a fixed second overvoltage protection threshold V can also be set.OVP-REF The overvoltage protection point of the second overvoltage protection unit 232 is adjusted by adjusting the sampling coefficient of the second sampling signal Vin_S2 (i.e., the voltage division ratio of resistors R4 and R5 in the second voltage divider circuit 251).

[0087] In a preferred embodiment, the second overvoltage protection unit 232 further includes a filter unit 253 connected between the positive input terminals of the switching logic circuit 252 and the second comparison circuit 254. The filter unit 253 includes a resistor R6 and a capacitor C2, and is used to compare the second sampling signal Vin_S2 and the second overvoltage protection threshold V in the second comparison circuit 254. OVP-REF Previously, the second sampled signal Vin_S was filtered.

[0088] The second overvoltage protection unit 232 operates when the main power transistor of the switching power supply 200 is connected to the reference ground. During operation, the second overvoltage protection unit 232 detects that the second sampling signal Vin_S2 is greater than the second overvoltage protection threshold V. OVP-REF When this occurs, the overvoltage protection of the switching power supply 200 is triggered.

[0089] Continue to refer to Figure 2a In some embodiments of this application, such as Figure 2a As shown, the selection unit includes an OR logic circuit 233. The first input terminal of the OR logic circuit 233 is connected to the output terminal of the first overvoltage protection unit 231, and the second input terminal of the OR logic circuit 233 is connected to the output terminal of the second overvoltage protection unit 232. The OR logic circuit 233 is used to perform OR logic processing on the first overvoltage protection signal OVP1 output by the first overvoltage protection unit 231 and the second overvoltage protection signal OVP2 output by the second overvoltage protection unit 232. The overvoltage protection circuit 230 performs overvoltage protection on the switching power supply 200 according to the output signal of the OR logic circuit 233.

[0090] Furthermore, in these embodiments, the overvoltage protection circuit 230 includes a first input terminal and a second input terminal. The overvoltage protection circuit 230 distinguishes the connection status of the main power transistor of the switching power supply 200 relative to the input voltage Vin and the reference ground based on the configuration of its first and second input terminals. Specifically, the overvoltage protection circuit 230 receives a first sampling signal V at its first input terminal. FB When its second input terminal is in a high-impedance state (e.g., floating), the first overvoltage protection unit 231 outputs a valid first overvoltage protection signal OVP1, and the second overvoltage protection unit 232 outputs an invalid second overvoltage protection signal OVP2; the overvoltage protection circuit 230 is connected to the reference ground at its first input terminal, and its second input terminal receives the second overvoltage protection threshold V. OVP-REFIn the event of this condition, the first overvoltage protection unit 231 outputs an invalid first overvoltage protection signal OVP1, and the second overvoltage protection unit 232 outputs a valid second overvoltage protection signal OVP2. Wherein, reference... Figure 5 and Figure 6 The first and second input terminals of the overvoltage protection circuit 230 correspond to the FB pin and OVP pin of the control circuit 240.

[0091] When the switching power supply 200 is a low-side switching power supply (i.e., the main power transistor M0 in the switching power supply 200 is connected to the reference ground), such as Figure 5 As shown, the first input terminal of the overvoltage protection circuit 230 is connected to the reference ground through the FB pin of the control circuit 240, and the second input terminal of the overvoltage protection circuit 230 is connected to the resistor R6 through the OVP pin of the control circuit 240. Figure 5 In the middle, the first sampling signal V received by the first overvoltage protection unit 231 FB The voltage is equal to the reference ground potential, causing the first overvoltage protection signal OVP1 output by the first overvoltage protection unit 231 to remain in an invalid (e.g., low level) state. Therefore, the first overvoltage protection unit 231 will not trigger overvoltage protection for the switching power supply 200. The second overvoltage protection threshold V received by the second overvoltage protection unit 232... OVP-REF The configuration is achieved by resistor R6. At this time, the output signal of the OR logic circuit 233 in the selection unit is the same as the state of the second overvoltage protection signal OVP2 output by the second overvoltage protection unit 232. This is equivalent to the selection unit automatically selecting the second overvoltage protection signal OVP2 output by the second overvoltage protection unit 232 to perform overvoltage protection on the switching power supply when the first input terminal of the overvoltage protection circuit 230 is connected to the reference ground.

[0092] When the switching power supply 200 is a high-side switching power supply (i.e., the main power transistor M0 in the switching power supply 200 is connected to the input voltage Vin), such as Figure 6 As shown, the first input terminal of the overvoltage protection circuit 230 samples the output voltage Vout through the FB pin of the control circuit 240 via resistors R8 and R9, and the second input terminal of the overvoltage protection circuit 230 is left floating through the OVP pin of the control circuit 240. Figure 6 In the first overvoltage protection unit 231, the first sampling signal V is obtained by sampling the output voltage Vout using resistors R8 and R9. FBWhen the second input terminal of the overvoltage protection circuit 230 is in a high-impedance state, the second overvoltage protection signal OVP2 output by the second overvoltage protection unit 232 remains in an invalid state (e.g., low level), and the second overvoltage protection unit 232 will not trigger overvoltage protection for the switching power supply 200. At this time, the output signal of the OR logic circuit 233 in the selection unit is in the same state as the first overvoltage protection signal OVP1 output by the first overvoltage protection unit 231. This is equivalent to the selection unit automatically selecting the first overvoltage protection signal OVP1 output by the first overvoltage protection unit 231 to perform overvoltage protection for the switching power supply when the second input terminal of the overvoltage protection circuit 230 is in a high-impedance state.

[0093] Understandable, Figure 5 and Figure 6 In the illustrated embodiment, the overvoltage protection circuit 230 is configured via two input terminals (or pins) so that after the switching power supply 200 is connected and configured, the overvoltage protection circuit 230 automatically invalidates one of the first overvoltage protection signals OVP1 and OVP2 based on the actual connection of its first and second input terminals. It can automatically select one of the first overvoltage protection unit 231 and the second overvoltage protection unit 232 to output an effective overvoltage protection signal without setting a selection signal, thus realizing the overvoltage protection function of the switching power supply 200. This overvoltage protection circuit 230 scheme can simultaneously provide overvoltage protection for both high-side and low-side switching power supplies, and its control logic and circuit structure are very simple, resulting in low implementation cost.

[0094] refer to Figure 2b and Figure 2c In some other embodiments of this application, the selection unit selects one of a first overvoltage protection signal OVP1 and a second overvoltage protection signal OVP2 to perform overvoltage protection on the switching power supply 200 based on the selection signal. This selection signal characterizes the connection status of the main power transistor in the switching power supply 200 relative to the input voltage Vin and the reference ground. For example, when the main power transistor in the switching power supply 200 is connected to the input voltage Vin, the selection signal has a first logic state; when the main power transistor in the switching power supply 200 is connected to the reference ground, the selection signal has a second logic state.

[0095] Optionally, in Figure 2b In the illustrated embodiment, the selection unit includes: switch S1, switch S2, and / or logic circuit 233. Switch S1 is controlled by a selection signal and is used to set the output voltage Vout and / or the first overvoltage protection threshold V when the selection signal represents the input voltage Vin of the main power transistor connection of the switching power supply 200. FB-OVPProvided to the first overvoltage protection unit 231. Switch S2 is controlled by a selection signal to set the input voltage Vin and / or the second overvoltage protection threshold V when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to the reference ground. OVP-REF The signal is provided to the second overvoltage protection unit 232. Alternatively, the first input terminal of logic circuit 233 is connected to the output terminal of the first overvoltage protection unit 231, or the second input terminal of logic circuit 233 is connected to the output terminal of the second overvoltage protection unit 232. Logic circuit 233 is used to perform OR logic processing on the first overvoltage protection signal OVP1 output by the first overvoltage protection unit 231 and the second overvoltage protection signal OVP2 output by the second overvoltage protection unit 232. The overvoltage protection circuit 230 provides overvoltage protection to the switching power supply 200 based on the output signal of the OR logic circuit 233.

[0096] Figure 2b In the diagram, switches S1 and S2, indicated by solid lines, represent an optional connection state for switches S1 and S2. In this state, switch S1 is controlled by a selection signal to control the first overvoltage protection threshold V. FB-OVP The on / off state of the transmission path to the first overvoltage protection unit 231 is controlled by the selection signal to control the second overvoltage protection threshold V. OVP-REF The transmission path to the second overvoltage protection unit 232 is switched on and off; switches S1 and S2, indicated by dashed lines, represent another optional connection state for switches S1 and S2. In this state, switch S1 is controlled by a selection signal to control the on / off state of the transmission path from the output voltage Vout to the first overvoltage protection unit 231, and switch S2 is controlled by a selection signal to control the on / off state of the transmission path from the input voltage Vin to the second overvoltage protection unit 232. Of course, switches S1 and S2 indicated by solid lines and switches S1 and S2 indicated by dashed lines can coexist. Furthermore, in conjunction with Figure 3 and Figure 4 Based on a similar principle, switch S1 can also be set between the output terminal of the first voltage divider circuit 241 and the positive input terminal of the first comparator circuit 243, and switch S2 can also be set between the output terminal of the second voltage divider circuit 251 and the positive input terminal of the second comparator circuit 254.

[0097] exist Figure 2c In the illustrated embodiment, the selection unit includes switch S3 and switch S4. Switch S3 is controlled by a selection signal and is used to output a first overvoltage protection signal OVP1 when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to the input voltage Vin. Switch S4 is controlled by the selection signal and is used to output a second overvoltage protection signal OVP2 when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to the reference ground. At this time, the overvoltage protection circuit 230 provides overvoltage protection to the switching power supply 200 according to the output signal of switch S3 or switch S4.

[0098] Based on the same principle, Figure 2c Switches S3 and S4 can also be replaced with a two-to-one selector switch. In this case, the first input terminal of the two-to-one selector switch receives the first overvoltage protection signal OVP1, and the second input terminal of the two-to-one selector switch receives the second overvoltage protection signal OVP2. The two-to-one selector switch is also controlled by the selection signal, and is used to output the first overvoltage protection signal OVP1 when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to the input voltage Vin, and to output the second overvoltage protection signal OVP2 when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to the reference ground. At this time, the overvoltage protection circuit 230 performs overvoltage protection on the switching power supply 200 according to the output signal of the two-to-one selector switch.

[0099] In some other embodiments, the selection unit is also configured to: continuously enable the first overvoltage protection unit 231, and control the enabling or disabling of the second overvoltage protection unit 232 according to a selection signal. Specifically, when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to the input voltage Vin, the selection unit controls the second overvoltage protection unit 232 to be in an disabled state; when the selection signal indicates that the main power transistor of the switching power supply 200 is connected to reference ground, the selection unit controls the second overvoltage protection unit 232 to be in an enabled state.

[0100] For example, the selection unit can control the enabling state of the first overvoltage protection unit 231 by controlling the enabling state of the first comparison circuit 243 in the first overvoltage protection unit 231, and control the enabling state of the second overvoltage protection unit 232 by controlling the enabling state of the second comparison circuit 254 in the second overvoltage protection unit 232.

[0101] Furthermore, in these embodiments, the overvoltage protection circuit 230 includes receiving a first sampling signal V when the main power transistor of the switching power supply 200 is connected to the input voltage Vin. FB When the main power transistor of the switching power supply 200 is connected to reference ground, it receives the second overvoltage protection threshold V. OVP-REF The third input terminal of the overvoltage protection circuit 230 has an initial voltage based on a preset current source when the power is first applied. The selection unit generates a selection signal by detecting the voltage range of the initial voltage at the third input terminal of the overvoltage protection circuit 230 when the power is first applied. It should be noted that the preset current source provides current output, for example, only for a very short time when the switching power supply 200 is initially powered on.

[0102] refer to Figure 7 and Figure 8 The third input terminal of the overvoltage protection circuit 230 corresponds to the FB pin of the control circuit 240. These embodiments are equivalent to implementing the protection circuit 240. Figure 5 and Figure 6The FB pin and OVP pin are multiplexed. Of course, the FB pin can also be changed to other pin names, such as the OVP pin.

[0103] In different application types of the switching power supply 200, the third input terminal of the overvoltage protection circuit 230 is connected to the reference ground via resistors of different resistance values. When powered on, the third input terminal of the overvoltage protection circuit 230 has different initial voltages in different switching power supply applications based on the same preset current source. This allows the overvoltage protection circuit 230 to distinguish the connection status of the main power transistor of the switching power supply 200 relative to the input voltage Vin and the reference ground according to the configuration of its third input terminal, and generate a corresponding selection signal.

[0104] For example, when the switching power supply 200 is a low-side switching power supply (i.e., the main power transistor M0 in the switching power supply 200 is connected to the reference ground), such as Figure 7 As shown, the third input terminal of the overvoltage protection circuit 230 is connected to resistor R6 through the FB pin of the control circuit 240, and is connected to the reference ground through resistor R6. When the switching power supply 200 is a high-side switching power supply (i.e., the main power transistor M0 in the switching power supply 200 is connected to the input voltage Vin), as... Figure 8 As shown, the third input terminal of the overvoltage protection circuit 230 samples the output voltage Vout through the FB pin of the control circuit 240 via resistors R8 and R9. That is, the third input terminal of the overvoltage protection circuit 230 is connected to the reference ground via resistor R9.

[0105] Examples are given below:

[0106] Assume the first overvoltage protection threshold V of the switching power supply 200 FB-OVP The voltage is set to 100V (meaning the overvoltage protection circuit 230 triggers overvoltage protection for the switching power supply 200 when the output voltage Vout of the switching power supply 200 exceeds 100V). The preset current source provides 20uA of current when the switching power supply 200 is initially powered on. Simultaneously, assuming that when the switching power supply 200 is initially powered on, the voltage threshold corresponding to the FB pin when the switching power supply 200 is a low-side switching power supply is in the range of 500mV to 2V, and the voltage threshold corresponding to the FB pin when the switching power supply 200 is a high-side switching power supply is in the range of 100mV to 500mV, then if the voltage of the FB pin is detected to be greater than 500mV when the switching power supply 200 is initially powered on, the application type of the switching power supply 200 can be determined to be a low-side switching power supply; if the voltage of the FB pin is detected to be less than 500mV when the switching power supply 200 is initially powered on, the application type of the switching power supply 200 can be determined to be a high-side switching power supply.

[0107] Based on this, Figure 7 The resistance of resistor R6 is 50kΩ. Figure 8Taking resistors R8 and R9 with resistances of 390kΩ and 10kΩ respectively as an example, when the switching power supply is 200V... Figure 7 When configured in the above manner, the voltage of the FB pin detected by the selection unit when the switching power supply 200 is initially powered on is equal to 20uA*50k=1V, which is greater than 500mV. Therefore, it can be determined that the application type of the switching power supply 200 is a low-side switching power supply, and a selection signal can be generated to indicate that the main power transistor in the switching power supply 200 is connected to the reference ground (at this time, the selection signal has, for example, a second logic state). This selection signal with the second logic state can control... Figure 2b When switch S1 is open, switch S2 is closed, and / or the selection signal with the second logic state can control... Figure 2c When switch S3 is open and switch S4 is closed, and / or the selection signal with the second logic state can control the second overvoltage protection unit 232 to be in the enabled state, so that the overvoltage protection circuit 230 can ultimately select the second overvoltage protection signal OVP2 output by the second overvoltage protection unit 232 to perform overvoltage protection on the switching power supply; when the switching power supply 200 is in Figure 8 When configured in the above manner, the voltage of the FB pin that the selection unit can detect when the switching power supply 200 is initially powered on is equal to 20uA*10k=200mV, which is less than 500mV. Therefore, it can be determined that the application type of the switching power supply 200 at this time is a high-side switching power supply, and a selection signal can be generated to indicate that the main power transistor in the switching power supply 200 is connected to the input voltage Vin (at this time, the selection signal has, for example, a first logic state). This selection signal with the first logic state can control Figure 2b When switch S1 is closed, switch S2 is open, and / or the selection signal with the first logic state can control... Figure 2c When switch S3 is closed and switch S4 is open, and / or the selection signal with the first logic state can control the second overvoltage protection unit 232 to be in an enabled state, the overvoltage protection circuit 230 can ultimately select the first overvoltage protection signal OVP1 output by the first overvoltage protection unit 232 to perform overvoltage protection on the switching power supply.

[0108] Understandable, Figure 7 and Figure 8In the illustrated embodiment, the overvoltage protection circuit 230 is configured via an input terminal (or pin). After the switching power supply 200 completes its connection configuration, the overvoltage protection circuit 230 determines the application type of the switching power supply 200 based on the actual connection status of its third input terminal and generates a corresponding selection signal. Based on the control of this selection signal, one of the first overvoltage protection signal OVP1 and the second overvoltage protection signal OVP2 is invalidated, and one of the first overvoltage protection unit 231 and the second overvoltage protection unit 232 is selected to output an effective overvoltage protection signal, thus realizing the overvoltage protection function of the switching power supply 200. This overvoltage protection circuit 230 scheme can simultaneously provide overvoltage protection for both high-side and low-side switching power supplies, and requires fewer pins, offering high control flexibility.

[0109] Furthermore, in some embodiments, such as Figures 5 to 8 As shown, the control circuit 240 further includes at least one of the following: a VIN pin for receiving the input voltage, a ZCD pin connected to the main power transistor M0 for zero-crossing detection, a GATE pin connected to the control terminal of the main power transistor M0 for outputting a control signal to the main power transistor M0, an ISP pin for receiving a sampling signal of the inductor current, a VCC pin for receiving the supply voltage, and a GND pin for providing a reference potential.

[0110] In summary, the overvoltage protection schemes disclosed in the various embodiments of this application are compatible with both high-side and low-side switching power supplies, and do not require auxiliary windings. The schemes are flexible and low-cost.

[0111] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating this application and are not intended to limit the implementation. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. An overvoltage protection circuit for a switching power supply, comprising: The first overvoltage protection unit samples the output voltage of the switching power supply to obtain a first sampling signal, and generates a first overvoltage protection signal based on the first sampling signal and a first overvoltage protection threshold. The second overvoltage protection unit obtains a second sampling signal characterizing the output voltage based on the input voltage sampling signal and duty cycle of the switching power supply, and generates a second overvoltage protection signal based on the second sampling signal and the second overvoltage protection threshold. The selection unit selects the first overvoltage protection signal to provide overvoltage protection for the switching power supply when the main power transistor of the switching power supply is connected to the input voltage, or selects the second overvoltage protection signal to provide overvoltage protection for the switching power supply when the main power transistor is connected to the reference ground.

2. The overvoltage protection circuit according to claim 1, wherein, The overvoltage protection circuit includes a first input terminal and a second input terminal; When the first sampling signal is received at the first input terminal and the second input terminal is in a high impedance state, the first overvoltage protection unit outputs a valid first overvoltage protection signal, and the second overvoltage protection unit outputs an invalid second overvoltage protection signal. When the first input terminal is connected to the reference ground and the second input terminal receives the second overvoltage protection threshold, the first overvoltage protection unit outputs an invalid first overvoltage protection signal, and the second overvoltage protection unit outputs an valid second overvoltage protection signal. The selection unit includes: The OR logic circuit performs OR logic processing on the first overvoltage protection signal and the second overvoltage protection signal, and the overvoltage protection circuit provides overvoltage protection to the switching power supply based on the output signal of the OR logic circuit.

3. The overvoltage protection circuit according to claim 1, wherein, The selection unit selects one of the first overvoltage protection signal and the second overvoltage protection signal to perform overvoltage protection on the switching power supply according to the selection signal. The selection signal represents the connection status of the main power transistor in the switching power supply relative to the input voltage and the reference ground.

4. The overvoltage protection circuit according to claim 3, wherein, The selection unit includes: The first switch, controlled by the selection signal, is used to provide the output voltage and / or the first overvoltage protection threshold to the first overvoltage protection unit when the selection signal characterizes the main power transistor connection input voltage; The second switch, controlled by the selection signal, is used to provide the input voltage and / or the second overvoltage protection threshold to the second overvoltage protection unit when the selection signal indicates that the main power transistor is connected to the reference ground; The OR logic circuit performs OR logic processing on the first overvoltage protection signal and the second overvoltage protection signal, and the overvoltage protection circuit provides overvoltage protection to the switching power supply based on the output signal of the OR logic circuit.

5. The overvoltage protection circuit according to claim 3, wherein, The selection unit includes: The third switch, controlled by the selection signal, is used to output the first overvoltage protection signal when the selection signal represents the input voltage connected to the main power transistor. The fourth switch, controlled by the selection signal, is used to output the second overvoltage protection signal when the selection signal indicates that the main power transistor is connected to the reference ground.

6. The overvoltage protection circuit according to claim 3, wherein, The selection unit is configured as follows: The first overvoltage protection unit is continuously enabled, and the second overvoltage protection unit is enabled or disabled according to the selection signal. Specifically, when the selection signal represents the connection input voltage of the main power transistor, the second overvoltage protection unit is controlled to be in an enabled state. When the selection signal indicates that the main power transistor is connected to the reference ground, the second overvoltage protection unit is controlled to be in an enabled state.

7. The overvoltage protection circuit according to any one of claims 3-6, wherein, The overvoltage protection circuit includes a third input terminal that receives a first sampling signal when the main power transistor is connected to the input voltage, and receives the second overvoltage protection threshold when the main power transistor is connected to the reference ground. When powered on, the third input terminal has an initial voltage based on a preset current source; The selection unit generates the selection signal by detecting the voltage range of the initial voltage at the third input terminal when it is first powered on.

8. The overvoltage protection circuit according to claim 1, wherein, The first overvoltage protection unit includes: The first voltage divider circuit is used to divide the output voltage at the output voltage terminal to obtain the first sampling signal; The first comparison circuit compares the first sampled signal with the first overvoltage protection threshold, and outputs a valid first overvoltage protection signal when the first sampled signal is greater than the first overvoltage protection threshold.

9. The overvoltage protection circuit according to claim 1, wherein, The second overvoltage protection unit includes: The second voltage divider circuit divides the input voltage at the input voltage terminal to obtain the input voltage sampling signal; A switching logic circuit converts the input voltage sampling signal according to the duty cycle of the switching power supply to obtain a second sampling signal that represents the product of the input voltage sampling signal and the duty cycle. The second comparison circuit compares the second sampled signal with the second overvoltage protection threshold, and outputs a valid second overvoltage protection signal when the second sampled signal is greater than the second overvoltage protection threshold.

10. The overvoltage protection circuit according to claim 1, wherein, The sampling ratio of the first sampling signal and the value of the second overvoltage protection threshold are both continuously adjustable.

11. An overvoltage protection chip, wherein the overvoltage protection chip is provided with an overvoltage protection circuit as described in any one of claims 1-10.

12. A control circuit for a switching power supply, comprising: The overvoltage protection circuit as described in any one of claims 1-10.

13. A switching power supply, comprising: Overvoltage protection circuit as described in any one of claims 1-10; Alternatively, the control circuit as described in claim 12.

14. The switching power supply according to claim 13, wherein, The switching power supply is a buck switching power supply or a buck-boost switching power supply.

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