Switching power supply and overvoltage protection method thereof

Abstract

The invention discloses a switching power supply and an overvoltage protection method thereof, the switching power supply comprises a main power tube, a freewheeling tube, a center tap inductor and an overvoltage protection circuit, and the overvoltage protection circuit comprises an input sampling unit for sampling a voltage on a sampling point of the switching power supply to obtain an input sampling voltage representing an input voltage; and the overvoltage control unit is used for performing overvoltage protection on the switching power supply according to the duty ratio, the input sampling voltage and the reference voltage. The center tap inductor is connected with the main power tube and the follow current tube, the overvoltage protection threshold value is adjusted by adjusting the position of the center tap end in the center tap inductor, and the overvoltage protection threshold value is the output voltage when overvoltage protection is triggered. According to the overvoltage protection circuit, the center tap inductor is added in the switching power supply, and the position of the center tap end in the center tap inductor is randomly adjustable, so that an overvoltage protection threshold is continuously adjustable, the range of an overvoltage protection point is enlarged, the voltage protection range is widened, and the overvoltage protection capability is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a switching power supply and an overvoltage protection method thereof. Background Art

[0002] A switching power supply is a power supply that uses a main power tube to control the charging and discharging process of an energy storage element to achieve power supply, and maintains a stable output voltage and / or output current by controlling the on and off time ratio of the main power tube. Figure 1 FIG. 1 shows a schematic diagram of a conventional buck-boost switching power supply and its overvoltage protection circuit. Figure 1 As shown, the rectifier bridge 11 of the switching power supply 10 (for example, using Buck-boost topology) is a structure composed of four diodes, which rectifies the AC power provided by the AC power supply AC to form an input voltage Vin at the input end, and the input capacitor Ci is connected between the input end and the reference ground. The inductor L0, the main power tube M0 and the resistor Rcs are connected in series between the input end and the reference ground in sequence, the anode of the freewheeling diode D0 is connected to the common node of the main power tube M0 and the inductor L0, the cathode is connected to the output end, and the output capacitor Co is connected between the output end and the input end. The switching power supply 10 also includes a control circuit 20, the control circuit 20 includes an overvoltage protection circuit 22 and a drive unit 21, the drive unit 21 obtains a zero-crossing detection signal ZCD from the drain of the main power tube M0, and receives an overvoltage protection signal OVP provided by the overvoltage protection circuit 22, so as to provide a drive signal VG to the main power tube M0 to control the conduction and shutdown of the main power tube M0. The overvoltage protection circuit 22 is grounded through an external threshold setting resistor Rovp.

[0003] The overvoltage protection circuit 22 includes a resistor divider network (resistors Ru and Rd), a calculation unit 23, a current source IA0, an adjustment unit 24 and a comparator COM0. The resistor divider network samples the input voltage Vin from the node Q0 at the input end to obtain a sampled voltage Vins, and the calculation unit calculates the sampled voltage Vins and the duty cycle D to obtain an output characterization voltage Vos. The current source IA0 provides a current Ire to the resistor Rovp so that the voltage generated on the resistor Rovp generates a reference voltage Vref after passing through the adjustment unit 24, and the reference voltage Vref is compared with the output characterization voltage Vos through the comparator COM0 to generate an overvoltage protection signal OVP for overvoltage protection. When the output characterization voltage Vos exceeds the reference voltage Vref, it is considered that the output voltage has reached the overvoltage protection threshold, thereby triggering the overvoltage protection. The existing overvoltage protection circuit 22 determines the size of the overvoltage protection threshold by detecting the state of the threshold setting resistor Rovp. In order to prevent the noise generated by poor input contact or system switching from affecting the resistance detection, it is generally necessary to determine the overvoltage protection gear before the switching power supply works, that is, the resistance value of the resistor Rovp is allowed to change within a certain range, but the reference voltage Vref remains unchanged to resist noise interference, so the overvoltage protection threshold is also fixed. Therefore, in the current switching power supply, the overvoltage protection threshold is discrete and fixed, and cannot be continuously adjusted. The overvoltage protection gear is monotonically discrete and has poor protection capability. Summary of the invention

[0004] In order to solve the above technical problems, the present application provides a switching power supply and an overvoltage protection method thereof to solve the problems in the prior art.

[0005] According to one aspect of the present invention, a switching power supply is provided, comprising a main power tube and a freewheeling tube, wherein the switching power supply receives an input voltage and generates an output voltage by periodically turning on and off the main power tube, wherein the switching power supply also comprises a center tap inductor and an overvoltage protection circuit, wherein the overvoltage protection circuit comprises: an input sampling unit, which samples the voltage at a sampling point of the switching power supply to obtain an input sampling voltage representing the input voltage; an overvoltage control unit, which performs overvoltage protection on the switching power supply according to a duty cycle, the input sampling voltage and a reference voltage, wherein the center tap inductor is connected to the main power tube and the freewheeling tube, and the overvoltage protection threshold is adjusted by adjusting the position of the center tap end in the center tap inductor, and the overvoltage protection threshold is the output voltage when the overvoltage protection is triggered.

[0006] Optionally, the center tap end divides the center tap inductor into a first inductor and a second inductor, and when the overvoltage protection is triggered, the overvoltage protection threshold is the product of the reference voltage and a proportional coefficient, and the proportional coefficient includes a relationship formed by a mathematical operation of the number of turns of the first inductor and the number of turns of the second inductor.

[0007] Optionally, the center-tap inductor includes a first end, a second end and a center-tap end, the first inductor is between the first end and the center-tap end, and the second inductor is between the center-tap end and the second end, and different relationship equations are formed by adjusting the connection positions of the first end, the second end and the center-tap end in the switching power supply to adjust the overvoltage protection threshold.

[0008] Optionally, the duty cycle includes a turn-on duty cycle and a freewheeling duty cycle, the ratio of the turn-on duty cycle to the freewheeling duty cycle is equal to the ratio of the turn-on time of the main power tube to the freewheeling time of the freewheeling tube, and the input sampling voltage is adjusted or the ratio of the turn-on duty cycle to the freewheeling duty cycle is adjusted by adjusting the connection position of the first end, the second end and the center tap end in the switching power supply to adjust the proportional coefficient.

[0009] Optionally, by adjusting the connection positions of the first end, the second end and the center tap end, the number of inductors in the center tap inductor participating in the current loop during the on-time and the freewheeling time is made different, so as to adjust the ratio of the on-duty cycle to the freewheeling duty cycle, thereby adjusting the proportional coefficient.

[0010] Optionally, the position of the sampling point of the switching power supply is adjusted by adjusting the connection positions of the first end, the second end and the center tap end to adjust the input sampling voltage, thereby adjusting the proportionality coefficient.

[0011] Optionally, when the product of the ratio of the on-duty cycle to the freewheeling duty cycle and the input sampling voltage increases, the proportional coefficient decreases and the overvoltage protection threshold decreases; when the product of the ratio of the on-duty cycle to the freewheeling duty cycle and the input sampling voltage decreases, the proportional coefficient increases and the overvoltage protection threshold increases.

[0012] Optionally, the first end is connected to the input end, the second end is connected to the first end of the freewheeling tube, the second end of the freewheeling tube is connected to the output end, the center tap end is connected to the main power tube, the sampling point is the input end, the first inductor participates in the current loop during the conduction time, and the first inductor and the second inductor both participate in the current loop during the freewheeling time.

[0013] Optionally, the first end is connected to a common node between the first end of the freewheeling tube and the main power tube, the second end of the freewheeling tube is connected to the output end, the second end is connected to the input end, the center tap end is connected to the input sampling unit, the sampling point is the center tap end, the first inductor and the second inductor both participate in the current loop during the conduction time, and the first inductor and the second inductor both participate in the current loop during the freewheeling time.

[0014] Optionally, the proportional coefficient is K / a, where a is the sampling coefficient of the input sampling unit when sampling, K is 1+N2 / N1, N1 and N2 are the number of turns of the first inductor and the number of turns of the second inductor respectively, wherein a, K, N1 and N2 are all greater than zero.

[0015] Optionally, the first end is connected to the input end, the second end is connected to the drain of the main power tube, the center tap end is connected to the first end of the freewheeling tube, the second end of the freewheeling tube is connected to the output end, the sampling point is the input end, the first inductor and the second inductor both participate in the current loop during the conduction time, and the first inductor participates in the current loop during the freewheeling time.

[0016] Optionally, the first end is connected to the first end of the freewheeling tube and the drain of the main power tube, the second end of the freewheeling tube is connected to the output end, the second end is connected to the input sampling unit, the center tap end is connected to the input end, the sampling point is the second end, the first inductor participates in the current loop during the conduction time, and the first inductor participates in the current loop during the freewheeling time.

[0017] Optionally, the proportional coefficient is K / a, where a is the sampling coefficient when the input sampling unit samples, the sampling coefficient is the ratio of the input sampling signal to the input voltage, K is N1 / (N1+N2), N1 and N2 are the number of turns of the first inductor and the number of turns of the second inductor, respectively, wherein a, K, N1 and N2 are all greater than zero.

[0018] Optionally, the duty cycle includes a turn-on duty cycle and a freewheeling duty cycle, and the overvoltage control unit performs overvoltage protection on the switching power supply when the relationship between the turn-on duty cycle, the freewheeling duty cycle, the input sampling voltage and the reference voltage meets a trigger condition, and the trigger condition is: the product of the ratio of the turn-on duty cycle and the freewheeling duty cycle and the input sampling voltage is greater than or equal to the reference voltage.

[0019] Optionally, the input sampling unit samples the voltage at a sampling point of the switching power supply during the conduction time of the main power tube.

[0020] Optionally, the switching power supply further comprises a reference voltage acquisition unit, which acquires a voltage from a threshold setting resistor or a current source and performs calculation to obtain the reference voltage.

[0021] According to another aspect of the present invention, there is provided an overvoltage protection method for a switching power supply, wherein the switching power supply comprises a main power tube and a freewheeling tube, the switching power supply receives an input voltage, and generates an output voltage by periodically turning on and off the main power tube, wherein the switching power supply further comprises a center tap inductor, and the overvoltage protection method comprises: sampling the voltage at a sampling point of the switching power supply to obtain an input sampling voltage representing the input voltage; performing overvoltage protection on the switching power supply according to a duty cycle, the input sampling voltage and a reference voltage, wherein the center tap inductor is connected to the main power tube and the freewheeling tube, and an overvoltage protection threshold is adjusted by adjusting the position of the center tap end in the center tap inductor, and the overvoltage protection threshold is the output voltage when the overvoltage protection is triggered.

[0022] The beneficial effects of the present invention include at least:

[0023] The switching power supply and overvoltage protection method provided by the present invention obtain an input sampling voltage by sampling the voltage at the sampling point, perform overvoltage protection according to the relationship between the input sampling voltage, the duty cycle and the reference voltage, and use the output voltage when the overvoltage protection is triggered as the overvoltage protection threshold. The switching power supply uses a center tap inductor as an energy storage element, which is connected to the main power tube and the freewheeling tube of the switching power supply, so that it can affect the magnitude of the output voltage when the overvoltage protection is triggered. Therefore, by adjusting the position of the center tap end of the center tap inductor in the center tap inductor, the turns ratio of the center tap inductor can be adjusted, and then the value of the output voltage when the overvoltage protection is triggered can be adjusted, so that the output voltage at this time reaches the desired overvoltage protection threshold. Furthermore, by adjusting the position of the center tap end in the center tap inductor, the overvoltage protection threshold can also be continuously adjustable, and is no longer limited to a fixed protection gear. When the output voltage requires overvoltage protection of different gears, the center tap inductor can be used instead of the ordinary inductor, and then the position of the center tap end of the center tap inductor is adjusted to achieve multi-gear continuous adjustment, that is, the gear that triggers the overvoltage protection can be arbitrarily selected. The overvoltage protection has a wide voltage adjustment range and strong overvoltage protection capability. For a switching power supply with a fixed reference voltage set internally in advance, the overvoltage protection level of the output voltage can be changed through the center tap inductor, expanding the application scope and usage scenarios of the switching power supply.

[0024] Furthermore, the relationship between the input voltage, duty cycle and output voltage is obtained according to the topological structure of the switching power supply, and the trigger condition is set based on the input sampling voltage, the on-duty cycle, the freewheeling duty cycle and the reference voltage. When the relationship between them meets the trigger condition, overvoltage protection is performed, and the trigger condition is that the product of the ratio of the on-duty cycle and the freewheeling duty cycle and the input sampling voltage is greater than or equal to the reference voltage. In addition, overvoltage protection circuits with different circuit structures can be set to achieve corresponding overvoltage protection functions. The overvoltage protection threshold can be adjusted by adjusting the input sampling voltage or by adjusting the ratio of the on-duty cycle and the freewheeling duty cycle, that is, the overvoltage protection is triggered at different voltage levels. In addition, different switching power supplies can set different trigger conditions, so that the center tap inductor can be connected to different switching power supplies to achieve overvoltage protection, which has strong versatility.

[0025] Furthermore, when the overvoltage protection is triggered, the overvoltage protection threshold is in a certain proportional relationship with the preset reference voltage, that is, the overvoltage protection threshold is the product of the reference voltage and a proportional coefficient. The proportional coefficient can be adjusted by adjusting the position of the center tap end. In addition, the center tap end divides the center tap inductor into a first inductor and a second inductor, thereby forming a first end, a second end and a center tap end. The proportional coefficient can also be adjusted by adjusting the connection position of the three endpoints in the switching power supply. Specifically, adjusting the position of the three endpoints can change the input sampling voltage or change the ratio of the on-duty cycle and the freewheeling duty cycle, thereby adjusting the proportional coefficient, and also adjusting the overvoltage protection threshold. Different connection positions correspond to different proportional coefficients, so that the appropriate connection method can be selected according to the proportional coefficient, correspondingly increasing or decreasing the protection gear of the output voltage, and expanding the overvoltage protection range.

[0026] Furthermore, the overvoltage protection threshold is adjusted by adjusting the connection position of the three endpoints of the center-tapped inductor in the switching power supply to increase or decrease it relative to the reference voltage, and then combined with the position adjustment of the center-tap end, the overvoltage protection threshold is continuously adjustable, thereby achieving continuous increase or decrease in the output protection gear, which is suitable for more scenarios and has stronger adaptability of the switching power supply.

[0027] It should be noted that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a conventional buck-boost switching power supply and an overvoltage protection circuit thereof is shown;

[0029] Figure 2 A schematic diagram of a switching power supply and an overvoltage protection circuit thereof according to a first embodiment of the present invention is shown;

[0030] Figure 3A schematic diagram of a switching power supply and an overvoltage protection circuit thereof according to a second embodiment of the present invention is shown;

[0031] Figure 4 A schematic diagram of a switching power supply and an overvoltage protection circuit thereof according to a third embodiment of the present invention is shown;

[0032] Figure 5a and Figure 5b They are shown respectively Figure 4 Schematic diagrams of different embodiments of the absorption circuit;

[0033] Figure 6 A schematic diagram of a switching power supply and an overvoltage protection circuit thereof according to a fourth embodiment of the present invention is shown;

[0034] Figure 7 A detailed circuit diagram of an overvoltage control unit in an overvoltage protection circuit according to a first embodiment of the present invention is shown;

[0035] Figure 8 A detailed circuit diagram of an overvoltage control unit in an overvoltage protection circuit according to a second embodiment of the present invention is shown;

[0036] Fig. 9 A detailed circuit diagram of an input sampling unit in an overvoltage protection circuit according to a first embodiment of the present invention is shown;

[0037] Fig.10 A detailed circuit diagram of an input sampling unit in an overvoltage protection circuit according to a second embodiment of the present invention is shown;

[0038] Fig.11 A schematic flow chart of an overvoltage protection method for a switching power supply according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0040] Figure 2 A schematic diagram of a switching power supply and an overvoltage protection circuit thereof according to a first embodiment of the present invention is shown.

[0041] like Figure 2As shown, the switching power supply of this embodiment includes a power converter 100 and a control circuit 200, and the power converter 100 includes a main power tube M1, a freewheeling tube, a center tap inductor, an input capacitor Ci and an output capacitor Co. The power converter 100 takes a buck-boost topology as an example, receives an input voltage Vin at the input end, and the input capacitor Ci is connected between the input end and the reference ground. The center tap end of the center tap inductor divides the center tap inductor into a first inductor L1 and a second inductor L2 connected to each other, and the connection node of the first inductor L1 and the second inductor L2 is the center tap end A3, the other end of the first inductor L1 is the first end A1, and the other end of the second inductor L2 is the second end A2. The first inductor L1, the main power tube M1 and the resistor Rcs are sequentially connected in series between the input end and the reference ground, that is, the first end A1 is connected to the input end, and the center tap end A3 is connected to the drain of the main power tube M1. The second inductor L2 is connected to the freewheeling tube, which can be a freewheeling diode or a synchronous rectifier. Here, the freewheeling diode D1 is taken as an example, and the second end A2 is connected to the anode of the freewheeling diode D1, and the cathode of the freewheeling diode D1 is connected to the output end. The output capacitor Co is connected between the output end and the input end, and the voltage across the output capacitor Co is the output voltage Vout. A diode D2 is also connected between the center tap terminal A3 and the output end, which is used to discharge the leakage inductance current generated when the main power tube M1 is working.

[0042] The control circuit 200 is connected to the control end of the main power tube M1, and is used to output the switch drive signal VG to control the on and off of the main power tube M1. The control circuit 200 controls the main power tube M1 to turn on, the freewheeling diode D1 to turn off, the first inductor L1 and the main power tube M1 to form a current loop, the inductor L1 stores energy, and the inductor current rises. At this time, only the first inductor L1 participates in the current loop and the second inductor L2 does not participate in the current loop. The control circuit 200 controls the main power tube M1 to turn off, the freewheeling diode D1 to turn on, the first inductor L1, the second inductor L2 and the freewheeling diode D1 to form a current loop, and the first inductor L1 and the second inductor L2 both participate in the current loop to provide the electric energy stored in the first inductor L1 to the subsequent stage, so that the output terminal generates an output voltage Vout, and the inductor current decreases. The main power tube M1 is turned on and off once for a switching cycle, and the inductor current can first rise and then fall in a switching cycle. The power converter 100 operates in BCM (critical conduction) or DCM (discontinuous conduction) mode, and adjacent switching cycles are separated by a certain dead time. The time period from the main power tube M1 turning off to the inductor current reaching the zero crossing point is the freewheeling time Ta of the freewheeling tube, and the time period when the main power tube M1 is turned on according to the switch drive signal VG is the on-time Ton of the main power tube M1. In the following embodiments, the on-time Ton of the main power tube M1 and the freewheeling time Ta of the freewheeling tube also refer to this rule.

[0043] The control circuit 200 mainly includes an overvoltage protection circuit 220, a drive unit 210, a zero-crossing detection unit 270 and a reference voltage acquisition unit 260. The zero-crossing detection circuit 270 outputs a zero-crossing detection signal ZCD at the zero-crossing point of the inductor current, and the drive unit 210 acquires the zero-crossing detection signal ZCD, and receives the overvoltage control signal OVP provided by the overvoltage protection circuit 220 to provide a drive signal VG to the main power tube M1 to control the on and off of the main power tube M1. The zero-crossing detection signal ZCD represents the zero-crossing point of the inductor current. The switching power supply also includes a threshold setting resistor Rovp, which is connected to the outside of the control circuit 200, or can also be set inside the control circuit 200. The reference voltage acquisition unit 260 is connected to the threshold setting resistor Rovp to obtain the reference voltage Vref set by the system. The reference voltage Vref is the calculated value of the voltage on the threshold setting resistor Rovp. The reference voltage acquisition unit 260, for example, provides a current to the threshold setting resistor Rovp to obtain the voltage on the threshold setting resistor Rovp, and obtains the reference voltage Vref after calculation. Of course, the threshold setting resistor Rovp may not be set. In this case, the reference voltage acquisition unit 260 may include a current source to provide a reference voltage Vref with a fixed voltage value. Then the reference voltage Vref may be several optional discrete fixed voltage values. The overvoltage protection circuit 220 is used to output a valid overvoltage control signal OVP when the representative voltage of the output voltage exceeds the reference voltage Vref to trigger the overvoltage protection, so that the driving unit 210 controls the main power tube M1 to disconnect. Of course, the control circuit 200 of this embodiment may also include other circuits and modules, such as an overtemperature detection circuit, an undervoltage protection circuit, etc., which are not described in detail here.

[0044] Specifically, in this embodiment, the overvoltage protection circuit 220 includes an input sampling unit 230 and an overvoltage control unit 240. The input sampling unit 230 samples the voltage at the sampling point of the switching power supply to obtain an input sampling voltage Vins that can represent the input voltage Vin. In this embodiment, the sampling point is the input terminal or the first terminal A1, that is, Figure 2Node Q1 in. The overvoltage control unit 240 is used to perform overvoltage protection on the switching power supply according to the duty cycle, the input sampling voltage Vins and the reference voltage Vref. The duty cycle includes a conduction duty cycle D and a freewheeling duty cycle D'. The conduction duty cycle D is, for example, the ratio of the conduction time Ton of the main power tube to the entire switching period T, and the freewheeling duty cycle D' is the ratio of the freewheeling time Ta of the freewheeling tube to the entire switching period T. Alternatively, the conduction duty cycle D is, for example, the ratio of the conduction time Ton of the main power tube to the sum of the conduction time and the freewheeling time (Ton+Ta), and the freewheeling duty cycle D' is the ratio of the freewheeling time Ta of the freewheeling tube to the sum of the conduction time and the freewheeling time (Ton+Ta). The ratio D / D' of the conduction duty cycle and the freewheeling duty cycle is equal to the ratio Ton / Ta of the conduction time of the main power tube and the freewheeling time of the freewheeling tube. The overvoltage control unit 240 performs overvoltage protection on the switching power supply according to the ratio of the on-duty cycle to the freewheeling duty cycle, the product of the input sampling voltage Vins×D / D', and the reference voltage Vref. For the Buck-boost topology, the relationship between the input voltage Vin and the output voltage Vout is: Vout=Vin×D / D', so that the output voltage can be characterized according to the input sampling voltage Vins. In a specific embodiment, the overvoltage control unit 240 can perform overvoltage protection on the switching power supply when the relationship between the on-duty cycle D, the freewheeling duty cycle D', the input sampling voltage Vins, and the reference voltage Vref meets the trigger condition. The trigger condition is, for example: the ratio of the on-duty cycle to the freewheeling duty cycle D / D' and the product of the input sampling voltage Vins×D / D' is greater than or equal to the reference voltage Vref, that is, Vins×D / D'≥Vref. For example, the overvoltage control unit 240 can receive the switch drive signal VG and the zero-crossing detection signal ZCD to obtain the on-time Ton of the main power tube M1 and the freewheeling time Ta of the freewheeling tube, and obtain the on-duty cycle D and the freewheeling duty cycle D' according to the freewheeling time Ta and the on-time Ton. The overvoltage control unit 240 is also used to calculate the product of the ratio D / D' of the on-duty cycle D and the freewheeling duty cycle D' and the input sampling voltage Vins (Vins×D / D'), and then compare it with the reference voltage Vref to generate an overvoltage control signal OVP. When the overvoltage control signal OVP is valid, it indicates that the output voltage Vout has reached the overvoltage protection threshold Vovp. The overvoltage protection threshold Vovp is the output voltage Vout when the overvoltage protection is triggered, or the output voltage at this time is the overvoltage protection threshold Vovp.

[0045] In this embodiment, the center tap inductor is connected to both the main power tube M1 and the freewheeling tube. By adjusting the position of the center tap terminal A3 in the center tap inductor, the overvoltage protection threshold Vovp can be adjusted. Alternatively, the overvoltage protection threshold Vref can be adjusted by adjusting the magnitude of the reference voltage Vref. The reference voltage Vref can be adjusted, for example, by adjusting the resistance of the threshold setting resistor Rovp. Specifically, when the overvoltage protection is triggered, the overvoltage protection threshold Vovp is the product of the reference voltage Vref and the proportionality coefficient, that is, there is a proportional relationship between the overvoltage protection threshold Vovp and the reference voltage Vref, and there is also a proportional relationship between the ratio of the on-duty cycle to the freewheeling duty cycle and the product of the input sampling voltage (Vins×D / D') and the output voltage Vout, and the two proportional relationships can be the same. Specifically, the proportional relationship is related to the turns ratio of the center tap inductor, that is, the proportionality coefficient includes a relationship formed by mathematical operations of the number of turns N1 of the first inductor and the number of turns N2 of the second inductor, and the mathematical operations include addition, subtraction, multiplication, division, etc. Then, by adjusting the position of the center tap terminal A3 in the center tap inductor, the number of turns N1 of the first inductor and the number of turns N2 of the second inductor can be adjusted, and then Vins×D / D' can be adjusted, and finally the proportional coefficient can be adjusted to trigger the overvoltage protection and make the overvoltage control signal OVP effective. Therefore, adjusting the turns ratio is equivalent to indirectly adjusting the overvoltage protection threshold Vovp. When the proportional coefficient is adjusted according to the position of the center tap terminal A3, when the ratio of the on-duty cycle to the freewheeling duty cycle D / D' and the product of the input sampling voltage Vins (Vins×D / D') increase, that is, the proportional coefficient decreases, and the overvoltage protection threshold Vovp decreases; when the ratio of the on-duty cycle to the freewheeling duty cycle and the product of the input sampling voltage (Vins×D / D') decreases, the proportional coefficient increases, and the overvoltage protection threshold Vovp increases.

[0046] Then for a buck-boost switching power supply that includes a center-tapped inductor, for example Figure 2 The switching power supply can adjust the value of Vins×D / D' by adjusting the number of turns or the ratio of turns of the first inductor L1 and the second inductor L2, so that the overvoltage protection can be triggered under different output voltages. For an output voltage of a certain voltage value, the overvoltage protection is triggered by adjusting the proportional coefficient, which is equivalent to the overvoltage protection threshold Vovp being adjustable and continuously adjustable, and no longer limited to a fixed gear. Although the reference voltage Vref generated by the threshold setting resistor Rovp has not changed, the actual overvoltage protection gear has increased. Thereby expanding the overvoltage protection range of the switching power supply, the overvoltage protection gear can be flexibly adjusted, the application range is wider, and the overvoltage protection effect is better.

[0047] In addition, the first end A1, the second end A2 and the center tap end A3 of the center tap inductor can be connected to different positions in the circuit, or the center tap end A3 can also be moved to the first end A1 or the second end A2. By adjusting the connection positions of the first end A1, the second end A2 and the center tap end A3 in the switching power supply, different relationship expressions and different proportional coefficients can be formed. Therefore, by changing the connection mode of the center tap inductor, the overvoltage protection threshold Vovp can also be adjusted. That is, the size of Vins×D / D' can be adjusted by changing the connection positions of the three terminals of the center tap inductor. Specifically, the ratio between the input sampling voltage Vins and the input voltage Vin can be adjusted by adjusting the connection positions of the first terminal A1, the second terminal A2 and the center tap terminal A3 in the switching power supply to adjust the size of the input sampling voltage Vins, or the size of the ratio D / D' of the on-duty cycle to the freewheeling duty cycle can be adjusted by adjusting the connection positions of the first terminal A1, the second terminal A2 and the center tap terminal A3 in the switching power supply to adjust the proportional coefficient, or Vins and D / D' can be adjusted at the same time. In the circuit, by adjusting the connection positions of the first terminal A1, the second terminal A2 and the center tap terminal A3, the number of inductors in the center tap inductor participating in the current loop during the on-time and the freewheeling time is different, so as to adjust the size of the ratio D / D' of the on-duty cycle to the freewheeling duty cycle, thereby adjusting the proportional coefficient. Alternatively, the position of the sampling point of the switching power supply is adjusted by adjusting the connection position of the first terminal A1, the second terminal A2 and the center tap terminal A3 to adjust the input sampling voltage Vins, thereby adjusting the proportionality coefficient.

[0048] for Figure 2In this embodiment, the first terminal A1 is connected to the input terminal, the second terminal A2 is connected to the first terminal of the freewheeling tube, the second terminal of the freewheeling tube is connected to the output terminal, and the center tap terminal A3 is connected to the drain of the main power tube M1. When the freewheeling tube is a freewheeling diode D1, the first terminal is the anode and the second terminal is the cathode. The same-name terminal of the first inductor L1 is at the first terminal A1, and the same-name terminal of the second inductor L2 is at the center tap terminal A3. The sampling point of the switching power supply is the input terminal, then the input voltage Vin is sampled, and the input sampling voltage Vins=a×Vin, a is the sampling coefficient of the input sampling unit 230 during sampling. During the conduction time, the first inductor L1 participates in the current loop, and during the conduction period of the freewheeling tube D1, the first inductor L1 and the second inductor L2 both participate in the current loop. Then the number of inductors in the center tap inductor participating in the current loop during the conduction time and the freewheeling time is different, and the position of the sampling point does not change. That is, in this embodiment, the ratio D / D' of the on-duty cycle to the freewheeling duty cycle is adjusted by adjusting the connection positions of the first terminal A1, the second terminal A2 and the center tap terminal A3 in the switching power supply. Taking the first inductor L1 as an example, the voltage integral across the first inductor L1 during the on-time is equal to the voltage integral across the first inductor L1 during the freewheeling time. That is, according to the volt-second balance principle of the excitation inductance, it can be known that: Vin×D=Vo×N1 / (N1+N2)×D'. When Vins×D / D'>Vref, the overvoltage protection is triggered, the sampling point is the input terminal, and the input voltage Vin is sampled. The voltage at the sampling point is used as the input sampling voltage Vins, then Vins=a×Vin, that is, OVP is triggered when Vo×a×N1 / (N1+N2)>Vref. Then: Vovp=Vref×(1+N2 / N1) / a. At this time, the proportional coefficient is K / a, K is 1+N2 / N1, and a, K, N1 and N2 are all greater than zero. The size of K can be adjusted by adjusting the size of N1 and N2. By adjusting K, the overvoltage control signal OVP is effective, that is, the overvoltage protection can be triggered under different output voltages, thereby realizing the continuous adjustment of the overvoltage protection threshold Vovp.

[0049] Figure 3 A schematic diagram of a switching power supply and an overvoltage protection circuit thereof according to a second embodiment of the present invention is shown.

[0050] like Figure 3 As shown, the switching power supply of this embodiment is Figure 2 Similarly, the power converter 100 and the control circuit 200 are also included. Only the connection position of the center tap inductor in the power converter 100 is different, and the rest are the same as Figure 2 The control circuit 200 may also be connected with Figure 2 The embodiments are exactly the same, see Figure 2Description, no further details are given here. In this embodiment, the center tap inductor includes a first terminal A1, a second terminal A2 and a center tap terminal A3, a first inductor L1 is between the first terminal A1 and the center tap terminal A3, a second inductor L2 is between the center tap terminal A3 and the second terminal A2, the same-name end of the first inductor L1 is located at the center tap terminal A3, and the same-name end of the second inductor L2 is located at the second terminal A2. The first terminal A1 is connected to the first end of the freewheeling tube and the drain of the main power tube M1, the second end of the freewheeling tube is connected to the output end, the second terminal A2 is connected to the input end, and the center tap terminal A3 is connected to the input sampling unit 230. When the freewheeling tube is a freewheeling diode D1, the first end is the anode and the second end is the cathode. The sampling point of the switching power supply of this embodiment is the center tap terminal A3, the first inductor L1 and the second inductor L2 both participate in the current loop during the conduction time, and the first inductor L1 and the second inductor L2 both participate in the current loop during the freewheeling time.

[0051] Therefore, in this embodiment, the number of inductors in the center tap inductor participating in the current loop during the conduction time and the freewheeling time is the same, and the position of the sampling point changes. The sampling point (i.e., node Q2) is transferred from the input end to the center tap end A3. What is sampled is not the input voltage, but the voltage of the center tap end A3. The voltage Vs at the sampling point is Vin×N1 / (N1+N2). That is, in this embodiment, the ratio between the voltage Vs at the sampling point and the input voltage Vin is adjusted by adjusting the connection position of the first end A1, the second end A2, and the center tap end A3 in the switching power supply to adjust the ratio of the input sampling voltage Vins to the input voltage Vin, thereby adjusting the input sampling voltage Vins. Taking the first inductor L1 as an example, the voltage integral across the first inductor L1 during the conduction time is equal to the voltage integral across the first inductor L1 during the freewheeling time. That is, according to the volt-second balance principle of the excitation inductance, it can be known that: Vin×N1 / (N1+N2)×D=Vo×N1 / (N1+N2)×D', when Vins×D / D'>Vref, the overvoltage protection is triggered, and the voltage at the sampling point is used as the input sampling voltage Vins, then Vins=a×Vs=Vin×a×N1 / (N1+N2), a is the sampling coefficient when the input sampling unit 230 samples, that is, when Vin×a×N1 / (N1+N2)×D / D'>Vref, Vo×a×N1 / (N1+N2)>Vref, OVP is triggered. Then: Vovp=Vref×(1+N2 / N1) / a. At this time, the proportional coefficient K / a, K is 1+N2 / N1, and N1, N2, K and a are all greater than zero. By adjusting the sizes of N1 and N2, the size of K can be adjusted. By adjusting the proportional coefficient of K, the overvoltage control signal OVP is made effective, that is, the overvoltage protection can be triggered under different output voltages, thereby realizing continuous adjustment of the overvoltage protection threshold Vovp.

[0052] Figure 4A schematic diagram of an overvoltage protection circuit of a switching power supply according to a third embodiment of the present invention is shown. Figure 5a and Figure 5b They are shown respectively Figure 4 Schematic diagram of different embodiments of the absorption circuit.

[0053] like Figure 4 As shown, the switching power supply of this embodiment is Figure 2 Similarly, the power converter 100 and the control circuit 200 are also included. Only the connection position of the center tap inductor in the power converter 100 is different, and the rest are the same as Figure 2 The control circuit 200 may also be connected with Figure 2 The embodiments are exactly the same, see Figure 2 Description, no further details are given here. In this embodiment, the same-name end of the first inductor L1 is located at the input end, and the same-name end of the second inductor L2 is located at the center tap end A3. And the first end A1 of the center tap inductor is connected to the input end, the second end A2 is connected to the drain of the main power tube M1, the center tap end A3 is connected to the first end of the freewheeling tube, and the second end of the freewheeling tube is connected to the output end. When the freewheeling tube is a freewheeling diode D1, the first end is the anode and the second end is the cathode. The sampling point of the switching power supply is the input end. During the conduction time, the first inductor L1 and the second inductor L2 both participate in the current loop, and during the freewheeling time, only the first inductor L1 participates in the current loop.

[0054] Therefore, in this embodiment, the number of inductors in the center tap inductor participating in the current loop during the conduction time and the freewheeling time is different, the sampling point position does not change, the sampling point is still the input terminal, and the input voltage Vin is sampled. That is, in this embodiment, the ratio D / D' of the conduction duty cycle and the freewheeling duty cycle is adjusted by adjusting the connection position of the first terminal A1, the second terminal A2 and the center tap terminal A3 in the switching power supply. Taking the first inductor L1 as an example, the voltage integral across the first inductor L1 during the conduction time is equal to the voltage integral across the first inductor L1 during the freewheeling time. That is, according to the volt-second balance principle of the excitation inductance, it can be known that: Vin×N1 / (N1+N2)×D=Vo×D', when Vins×D / D'>Vref, the overvoltage protection is triggered, and the voltage at the sampling point is used as the input sampling voltage Vins, then Vins=a*Vin, a is the sampling coefficient when the input sampling unit 230 samples, that is, Vo×a×(1+N2 / N1)>Vref triggers OVP. Then: Vovp=Vref×(N1 / (N1+N2)) / a. At this time, the proportional coefficient is K / a, K is N1 / (N1+N2), and N1, N2, a and K are all greater than zero. Then, by adjusting the size of N1 and N2, the size of K can be adjusted. By adjusting K to adjust the proportional coefficient, the overvoltage control signal OVP is effective, that is, the overvoltage protection can be triggered under different output voltages, thereby realizing the continuous adjustment of the overvoltage protection threshold Vovp. Figure 4 In order to discharge the leakage inductance current generated during the operation of the main power tube M1, an absorption circuit 300 is also provided between the center tap terminal A2 and the cathode of the freewheeling diode D1. Figure 5a , the absorption circuit 300 may be an RCD circuit, that is, a resistor R, a capacitor C and a diode D are connected to each other, specifically, the center tap terminal A2 is connected to the anode of the diode D, and the cathode of the diode D is connected to the cathode of the freewheeling diode D1, i.e., the output terminal, through the parallel resistor R and capacitor C. Or, as Figure 5b As shown, the absorption circuit 300 can be a ZD circuit, that is, a voltage-stabilizing diode ZD and a diode D are connected. Specifically, the center tap terminal A2 is connected to the anode of the diode D, and the cathode of the diode D is connected to the cathode of the freewheeling diode D1, that is, the output terminal, through the voltage-stabilizing diode ZD. The cathode of the diode D is connected to the cathode of the voltage-stabilizing diode ZD, and the anode of the voltage-stabilizing diode ZD is connected to the input terminal.

[0055] Figure 6 A schematic diagram of an overvoltage protection circuit of a switching power supply according to a fourth embodiment of the present invention is shown.

[0056] like Figure 6 As shown, the switching power supply of this embodiment is Figure 2 Similarly, the power converter 100 and the control circuit 200 are also included. Only the connection position of the center tap inductor in the power converter 100 is different, and the rest are the same as Figure 2 The control circuit 200 may also be connected with Figure 2 The embodiments are exactly the same, see Figure 2 Description is omitted here. In this embodiment, the first end A1 of the center-tapped inductor is connected to the first end of the freewheeling tube and the drain of the main power tube M1, the second end of the freewheeling tube is connected to the output end, the second end A2 is connected to the input sampling unit 230, and the center-tap end A3 is connected to the input end. When the freewheeling tube is a freewheeling diode D1, the first end is the anode and the second end is the cathode. The same-name end of the first inductor L1 is connected to the center-tap end A3, and the same-name end of the second inductor L2 is connected to the input sampling unit 230. The sampling point of the switching power supply is the second end A2, that is, Figure 6 The voltage at the node Q3 in the sampling point is: Vno=Vin×N2 / N1+Vin=(1+N2 / N1)×Vin=Vin×(N1+N2) / N1. During the on-time, the first inductor L1 participates in the current loop, and during the freewheeling time, the first inductor L1 also participates in the current loop.

[0057] Therefore, in this embodiment, the number of inductors in the center tap inductor participating in the current loop during the on-time and the freewheeling time is the same, the sampling point position changes, and the sampled voltage is not the input voltage Vin. That is, in this embodiment, the ratio between the voltage Vno at the sampling point and the input voltage Vin is adjusted by adjusting the connection position of the first terminal A1, the second terminal A2 and the center tap terminal A3 in the switching power supply to adjust the ratio of the input sampling voltage Vins to the input voltage Vin, thereby adjusting the input sampling voltage Vins. Taking the first inductor L1 as an example, the voltage integral across the first inductor L1 during the on-time is equal to the voltage integral across the first inductor L1 during the freewheeling time. That is, according to the volt-second balance principle of the excitation inductance, it can be known that: Vin×D=Vo×D', when Vins×D / D'>Vref, the overvoltage protection is triggered, and the voltage at the sampling point is used as the input sampling voltage Vins, then Vins=a×Vno=a×Vin×(N1+N2) / N1, a is the sampling coefficient when the input sampling unit 230 samples, that is, when Vo×a×(N1+N2) / N1>Vref, OVP is triggered. Then: Vovp=Vref×(N1 / (N1+N2)) / a. At this time, the proportional coefficient is K / a, K is N1 / (N1+N2), and N1, N2, a and K are all greater than zero. Then, by adjusting the size of N1 and N2, the size of K can be adjusted, and by adjusting K to adjust the proportional coefficient, the overvoltage control signal OVP is effective, that is, the overvoltage protection can be triggered under different output voltages, thereby realizing the continuous adjustment of the overvoltage protection threshold Vovp.

[0058] Above Figure 2-Figure 6 These are just some examples of embodiments that can be implemented by the present invention. Of course, for the switching power supply, there can also be other ways of connecting the center-tapped inductor, so as to achieve technical effects similar to the above embodiments. For example, the positions of the same-named ends of the first inductor L1 and the second inductor L2 in the above embodiments can be changed to change the size of K, or the three ends of the center-tapped inductor can be connected to other positions to adjust K. Examples are not given here one by one. In addition to the buck-boost switching power supply, the overvoltage protection circuit and overvoltage protection method of the embodiments of the present invention can also be extended to switching power supplies of other topologies.

[0059] Figure 7 FIG. 2 shows a detailed circuit diagram of an overvoltage control unit in an overvoltage protection circuit according to a first embodiment of the present invention. Figure 7 As shown, for the above Figure 2-Figure 6 A specific implementation of the overvoltage protection circuit 220 is given. In this embodiment, the input sampling unit 230 samples the voltage from the sampling point (for example, obtains the voltage Vin or the voltage Vs or the voltage Vno) to obtain the input sampling voltage Vins.

[0060] Further, the overvoltage control unit 240 includes a voltage follower U3, the positive input end of the voltage follower U3 is connected to the common node of the third resistor R3 and the first capacitor C1, and the reverse input end of the voltage follower U3 is connected to the output end of the voltage follower U3 to transmit the input sampling voltage Vins to the next stage. The overvoltage control unit 240 also includes a second switch S2, a third switch S3, a first RC filter network, a fourth switch S4, a fifth switch S5, a second RC filter network and a first switch control unit. The comparison unit 250 includes a first comparator COM1. The first switch control unit includes a first RS trigger U1 and a NOT gate (or inverter) U2, the input end of the NOT gate U2 receives the switch drive signal VG, the output end outputs the inverted signal VGB of the switch drive signal, and is connected to the set end S of the first RS trigger U1, the reset end R of the first RS trigger U1 receives the zero crossing detection signal ZCD, and the output end Q outputs the first switch control signal KS1. The first RS trigger U1 is set according to the inverting signal VGB of the switch drive signal, and is reset according to the zero-crossing detection signal ZCD, so as to output a valid first switch control signal KS1 during the setting period, which is the time period of the freewheeling time of the freewheeling tube. The first end of the second switch S2 is connected to the output end of the voltage follower U3, and receives the input sampling voltage Vins. The first end of the third switch S3 is connected to the second end of the second switch S2, and the second end of the third switch S3 is connected to the ground end. The first RC filter network is connected between the first end of the third switch S3 and the ground end. The first RC filter network can be a single-stage filter network or a multi-stage filter network, at least including a second capacitor C2 and a fourth resistor R4, and the output end of the first RC filter network outputs a first voltage Vo1. The first end of the fourth switch S4 receives the reference voltage Vref, the first end of the fifth switch S5 is connected to the second end of the fourth switch S4, and the second end of the fifth switch S5 is connected to the ground end. The second RC filter network is connected between the first end and the ground end of the fifth switch S5. The second RC filter network is a single-stage or multi-stage filter network, at least including a third capacitor C3 and a fifth resistor R5. The output end of the second RC filter network outputs a second voltage Vo2. The second switch S2 and the fifth switch S5 are turned on and off by the switch drive signal GATE, and the third switch S3 and the fourth switch S4 are turned on and off by the first switch control signal KS1. Thus, the second switch S2 is turned on only during the on-time, and the third switch S3 is turned on only during the freewheeling time. The fourth switch S4 is turned on only during the freewheeling time, and the fifth switch S5 is turned on only during the on-time. The positive input end of the first comparator COM1 is connected to the output end of the first RC filter network, receiving the first voltage Vo1, the negative input end of the first comparator COM1 is connected to the output end of the second RC filter network, receiving the second voltage Vo2, and the output end of the first comparator COM1 outputs an overvoltage control signal OVP.

[0061] Since the switching power supply of this embodiment is a buck-boost topology, the corresponding relationship between its output voltage Vout and input voltage Vin is: D / D'=Vo / Vin, or Vo=Vin×D / D', and Vins×D / D' can be used to characterize the output voltage Vout. By comparing Vins×D / D' with Vref, it can be known whether the output voltage Vout exceeds the overvoltage protection threshold Vovp. Then when the switch drive signal VG is valid, the main power tube M1 is turned on, the first switch S1 is turned on, and the input voltage Vin is sampled. The sampled signal is maintained as the input sampling voltage Vins by the first capacitor C1 and the voltage follower U3. Moreover, during the period when the switch drive signal VG is at a high level, the second switch S2 and the fifth switch S5 are turned on, the fourth switch S4 and the third switch S3 are turned off, and the first RC filter network is charged according to the input sampling voltage Vins, and the second RC filter network is discharged to the ground. Due to the existence of the voltage follower U3, the input sampling voltage Vins remains unchanged during charging. After the switch drive signal VG becomes a low level, the second switch S2 and the fifth switch S5 are turned off, the KS1 signal controls the third switch S3 and the fourth switch S4 to turn on, the reference voltage Vref is used to charge the second RC filter network, and the first RC filter network is discharged to the ground. After entering the steady state, the first RC filter network outputs the first voltage Vo1, and the second RC filter network outputs the second voltage Vo2. After the input sampling voltage Vins passes through the filter network, a square wave signal with the same duty cycle can be obtained. Then the first voltage Vo1 is the product of the input sampling voltage Vins and the on-duty cycle D of the switching power supply, Vins×D. Similarly, the second voltage Vo2 is the product of the threshold voltage Vref and the freewheeling duty cycle D', Vref×D'. When Vo1>Vo2, the first comparator COM1 outputs a valid overvoltage control signal OVP. Therefore, when the first voltage Vo1 is greater than the second voltage Vo2, Vins×D>Vref×D', Vins×D / D'>Vref, that is, the output voltage Vout is considered to exceed the overvoltage protection threshold Vovp, and the first comparator COM1 outputs a valid overvoltage control signal OVP.

[0062] Figure 8 A detailed circuit diagram of an overvoltage control unit in an overvoltage protection circuit according to a second embodiment of the present invention is shown.

[0063] Figure 8 Provides the above Figure 2-Figure 6 Another specific implementation circuit of the overvoltage protection circuit 220 is as follows: Figure 8As shown, the overvoltage protection circuit 220 of this embodiment includes an input sampling unit 230 and an overvoltage control unit 240. In this embodiment, the overvoltage control unit 240 includes: a first switch control unit, a first voltage-controlled current source A1, a second voltage-controlled current source A2, a sixth switch S6, a seventh switch S7, an eighth switch S8, a ninth switch S9, a fourth capacitor C4, a fifth capacitor C5 and a second RS trigger U4. The comparison unit 250 includes a second comparator COM2 and an AND gate U5. The positive input terminal of the second comparator COM2 receives the third voltage Vo3, the reverse input terminal receives the zero voltage 0, and the output terminal outputs the overvoltage control signal OVP. The first end of the fourth capacitor C4 is connected to the positive input terminal of the second comparator COM2 to provide the third voltage Vo3, and the second end of the fourth capacitor C4 is connected to the ground terminal. The first voltage-controlled current source A1 is connected to the first end of the fourth capacitor C4 through the sixth switch S6 and the seventh switch S7, and the control end of the first voltage-controlled current source A1 is connected to the first end of the first capacitor C1 to receive the input sampling voltage Vins. The first end of the sixth switch S6 is connected to the output end of the first voltage-controlled current source A1. The first end of the seventh switch S7 is connected to the second end of the sixth switch S6, and the second end of the seventh switch S7 is connected to the first end of the fourth capacitor C4. The first end of the fifth capacitor C5 is connected to the second end of the sixth switch S6, and the second end of the fifth capacitor C5 is connected to the ground terminal. The first end of the eighth switch S8 is connected to the first end of the seventh switch S7, and the second end of the eighth switch S8 is connected to the ground terminal. The second voltage-controlled current source A2 is connected between the second end of the sixth switch S6 and the ground terminal, the control end of the second voltage-controlled current source A2 receives the reference voltage Vref, and the ninth switch S9 is connected between the output end of the second voltage-controlled current source A2 and the ground terminal. The set end S and the reset end R of the second RS trigger U4 receive the switch drive signal VG and the zero-crossing detection signal ZCD respectively, and the output end Q and the output inverting end Q - The second switch control signal KS2 and the inverted signal KS2B of the second switch control signal are output respectively. The sixth switch S6 is controlled by the switch drive signal VG, the seventh switch S7 is controlled by the second switch control signal KS2, the sixth switch S6 is turned on only during the on-time, the seventh switch S7 is turned on during both the on-time and the freewheeling time, and the seventh switch S7 is turned off after the second RS trigger U4 receives the zero-crossing detection signal ZCD. The ninth switch S9 is controlled by the first switch control signal KS1 and is turned on only during the freewheeling time. The eighth switch S8 is controlled by the inverted signal KS2B of the second switch control signal, and the eighth switch S8 is turned on when the second RS trigger U4 receives the zero-crossing detection signal ZCD to release the charge on the fifth capacitor C5. One input end of the AND gate U5 is connected to the output end of the second comparator COM2, the other input end receives the second switch control signal KS2, and the output end outputs the overvoltage control signal OVP.

[0064] For the overvoltage protection circuit 220, during the conduction time, the sixth switch S6 is turned on, the seventh switch S7 is turned on, and the eighth switch S8 and the ninth switch S9 are turned off. The first voltage-controlled current source A1 charges the fourth capacitor C4 and the fifth capacitor C5 with a current proportional to the input sampling voltage Vins. During the freewheeling time, the sixth switch S6 is turned off, the seventh switch S7 remains conducting, the eighth switch S8 remains off, and the ninth switch S9 is turned on. The second voltage-controlled current source A2 discharges the fourth capacitor C4 and the fifth capacitor C5 with a current proportional to the threshold voltage Vref. After the inductor current crosses zero, both the seventh switch S7 and the ninth switch S9 are turned off, and the eighth switch S8 is turned on to discharge the fifth capacitor C5, while the voltage of the fourth capacitor C4 is held and provides the third voltage Vo3 to the second comparator COM2 for overvoltage judgment. The conduction time of the main power transistor M1 is Ton, and the freewheeling time of the freewheeling diode is Toff. The third voltage Vo3 is the difference between the integral voltage of the input sampling voltage Vins during the conduction time Ton and the integral voltage of the reference voltage Vref during the freewheeling time Ta (i.e., Vins*Ton - Vref*Ta). When the third voltage Vo3 is greater than the zero voltage V0 (Vo3 > V0) (i.e., Vins*Ton - Vref*Ta > 0, Vins×D×T > Vref×D’×T, Vins×D / D’ > Vref), the second comparator COM2 outputs a valid level to control the AND gate U5 to output a valid overvoltage control signal OVP. At the same time, the voltage of the fifth capacitor C5 is released to zero. At the same time, the capacitance value of the fourth capacitor is set to be much smaller than that of the fifth capacitor C5, i.e., C4 << C5. Therefore, when the sixth switch S6 is turned on, the voltage on the fourth capacitor C4 is clamped by the fifth capacitor C5 to avoid the voltage on the fourth capacitor C4 affecting the initial value of the voltage of the fifth capacitor C5 when the sixth switch S6 is turned on next time. In addition, the proportionality coefficients of the first voltage-controlled current source A1 and the second voltage-controlled current source A2 are equal.

[0065] Fig. 9 Fig. shows a detailed circuit schematic diagram of the input sampling unit in the overvoltage protection circuit according to the first embodiment of the present invention.

[0066] For Figure 3 and Figure 6 switching power supplies, the sampling point is not at the input end, and the voltage change at the sampling point is related to the operating state of the center-tapped inductor. The voltage at the sampling point is different during the conduction period and the off period of the main power transistor. For this type of switching power supply, the input sampling unit 230 can sample the input voltage only during the conduction period of the main power transistor or only within the conduction time of the main power transistor to obtain an accurate input sampling voltage. For the switching power supplies corresponding to all embodiments of the present invention, the voltage at the sampling point can be sampled during the conduction time of the main power transistor to obtain the input sampling voltage.

[0067] Such as Fig. 9As shown, the input sampling unit 230 of the present embodiment includes a resistor voltage divider network, a first switch S1 and a first capacitor C1. The resistor voltage divider network includes a first resistor R1 and a second resistor R2 connected in series, which are used to obtain a voltage divider voltage (such as Vin or Vs or Vno) at a sampling point, and the middle node of the first resistor R1 and the second resistor R2 is the output end of the resistor voltage divider network. The first end of the first capacitor C1 is connected to the output end of the resistor voltage divider network, and the second end of the first capacitor C1 is connected to the ground terminal. The first capacitor C1 samples and holds the voltage divider to obtain an input sampling signal Vins. The first end of the first switch S1 is connected to the output end of the resistor voltage divider network, the second end of the first switch S1 is connected to the first end of the first capacitor C1, and the control end of the first switch S1 is controlled to be turned on and off by the switch drive signal VG. The sampling and holding unit 220 may also include a third resistor R3, which is connected between the second end of the first switch S1 and the first end of the first capacitor C1. Therefore, when the main power tube M1 is turned on, the voltage at the sampling point is sampled to obtain the input sampling voltage Vins, Vins = Vin×R2 / (R1+R2) or Vins = Vs×R2 / (R1+R2) or Vins = Vno×R2 / (R1+R2), then R2 / (R1+R2) is the sampling coefficient during sampling, that is, a mentioned in the above embodiment.

[0068] Fig.10 A detailed circuit diagram of an input sampling unit in an overvoltage protection circuit according to a second embodiment of the present invention is shown.

[0069] for Figure 2 and Figure 4 In the switching power supply and its overvoltage protection circuit, the input sampling unit 230 directly samples the input voltage Vin from the input terminal, that is, the sampling point is located at the input terminal, and the sampling of the input voltage is not affected by the center tap inductance, so the input voltage Vin can be sampled at any time. Fig.10 As shown, for this type of switching power supply, the input sampling unit 230 of its overvoltage protection circuit 220 can be a voltage divider network, such as a resistor voltage divider network, which includes, for example, a resistor R1 and a resistor R2 connected in series between the input terminal and the ground terminal, and provides an input sampling voltage Vins from a common node of the resistor R1 and the resistor R2, then Vins = Vin×R2 / (R1+R2) or Vins = Vs×R2 / (R1+R2) or Vins = Vno×R2 / (R1+R2), then R2 / (R1+R2) is the sampling coefficient during sampling, that is, a mentioned in the above embodiment.

[0070] Figure 7-Figure 10Only several possible circuit structures of the overvoltage protection circuit 220 of the present invention are shown. In other embodiments, other components may be used to form the overvoltage protection circuit 220 to achieve the above functions, which are not listed one by one here.

[0071] In the above-mentioned multiple embodiments, the Buck-boost topology is used as an example to introduce the switching power supply and its overvoltage protection circuit. However, in the switching power supply of other topological structures, a center tap inductor can also be set to connect the main power tube and the freewheeling tube, and the overvoltage protection threshold is adjusted by adjusting the position of the center tap end in the center tap inductor. Other topological structures include, for example, the Buck topology, and the specific circuit connection forms are not introduced one by one here.

[0072] Fig.11 A schematic flow chart of an overvoltage protection method for a switching power supply according to an embodiment of the present invention is shown.

[0073] The present invention provides an overvoltage protection method for a switching power supply, which is suitable for the above Figure 2-Figure 10 The switching power supply and its overvoltage protection circuit are shown to solve the problems of the prior art. The switching power supply includes a main power tube, a freewheeling tube and a center tap inductor. The main power tube is turned on and off to enable the switching power supply to provide power to the output end according to the input voltage of the input end to generate an output voltage at the output end. The overvoltage protection method of this embodiment specifically includes the following steps:

[0074] In step S101 , the voltage at a sampling point of the switching power supply is sampled to obtain an input sampling voltage representing the input voltage.

[0075] In step S102, overvoltage protection is performed on the switching power supply according to the duty cycle, the input sampling voltage and the reference voltage.

[0076] In the switching power supply of this embodiment, the center tap inductor is connected to the main power tube and the freewheeling tube, and the output voltage when the overvoltage protection is triggered is adjusted by adjusting the position of the center tap end in the center tap inductor, that is, the overvoltage protection threshold is adjusted. The center tap inductor includes a first end, a second end and a center tap end, a first inductor is between the first end and the center tap end, and a second inductor is between the center tap end and the second end. The first end, the second end and the center tap end can be connected to different positions in the switching power supply respectively. By adjusting the connection position of the first end, the second end and the center tap end, a different proportional relationship is formed between the output protection threshold and the reference voltage to adjust the overvoltage protection threshold. In this embodiment, when the product of the ratio of the on-duty cycle to the freewheeling duty cycle and the input sampling voltage increases, the overvoltage protection threshold decreases; when the product of the ratio of the on-duty cycle to the freewheeling duty cycle and the input sampling voltage decreases, the overvoltage protection threshold increases.

[0077] The overvoltage protection method of this embodiment is as follows: Figure 2-Figure 10 The switching power supply and the overvoltage protection circuit thereof described in the embodiment are implemented based on the embodiment. The specific circuit and working principle can be found in the above description and will not be repeated here.

[0078] In summary, the switching power supply and its overvoltage protection method provided by the present invention obtain an input sampling voltage by sampling the voltage at the sampling point, perform overvoltage protection according to the relationship between the input sampling voltage, the duty cycle and the reference voltage, and use the output voltage when the overvoltage protection is triggered as the overvoltage protection threshold. The switching power supply uses a center tap inductor as an energy storage element, so that it connects the main power tube and the freewheeling tube of the switching power supply, so that it can affect the magnitude of the output voltage when the overvoltage protection is triggered. Therefore, by adjusting the position of the center tap end of the center tap inductor in the center tap inductor, the turns ratio of the center tap inductor can be adjusted, and then the value of the output voltage when the overvoltage protection is triggered can be adjusted, so that the output voltage at this time reaches the desired overvoltage protection threshold. Furthermore, by adjusting the position of the center tap end in the center tap inductor, the overvoltage protection threshold can also be continuously adjustable, and is no longer limited to a fixed protection gear. When the output voltage requires overvoltage protection of different gears, a center tap inductor can be used instead of an ordinary inductor, and then the position of the center tap end of the center tap inductor is adjusted to achieve multi-gear continuous adjustment, that is, the gear that triggers the overvoltage protection can be arbitrarily selected. The overvoltage protection has a wide voltage adjustment range and strong overvoltage protection capability. For a switching power supply with a fixed reference voltage set internally in advance, the overvoltage protection level of the output voltage can be changed through the center tap inductor, expanding the application scope and usage scenarios of the switching power supply.

[0079] It should be noted that the numerical values ​​in this article are only used for exemplary description. In other embodiments of the present invention, other numerical values ​​can also be sampled to implement this solution. The specific settings should be reasonable according to the actual situation, and the present invention does not limit this.

[0080] Finally, it should be noted that: Obviously, the above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of the present invention.

[0081] It should also be understood that the terms and expressions used herein are for description only, and one or more embodiments of this specification should not be limited to these terms and expressions. The use of these terms and expressions does not mean to exclude any equivalent features of the illustrations and descriptions (or parts thereof), and it should be recognized that various modifications that may exist should also be included in the scope of the claims. Other modifications, changes and substitutions may also exist. Accordingly, the claims should be deemed to cover all such equivalents.

Claims

1. A switching power supply, comprising a main power tube and a freewheeling tube, wherein the switching power supply receives an input voltage and generates an output voltage by periodically turning on and off the main power tube, wherein: The switching power supply further includes a center-tapped inductor and an overvoltage protection circuit, and the overvoltage protection circuit includes: An input sampling unit samples the voltage at a sampling point of the switching power supply to obtain an input sampling voltage representing the input voltage; An overvoltage control unit performs overvoltage protection on the switching power supply according to the duty cycle, the input sampling voltage and the reference voltage. Among them, the center tap inductor is connected to the main power tube and the freewheeling tube, and the overvoltage protection threshold is adjusted by adjusting the position of the center tap end in the center tap inductor. The overvoltage protection threshold is the output voltage when the overvoltage protection is triggered.

2. The switching power supply according to claim 1, wherein: The center tap end divides the center tap inductor into a first inductor and a second inductor. When the overvoltage protection is triggered, the overvoltage protection threshold is the product of the reference voltage and a proportional coefficient. The proportional coefficient includes a relationship formed by a mathematical operation of the number of turns of the first inductor and the number of turns of the second inductor.

3. The switching power supply according to claim 2, wherein: The center-tapped inductor includes a first end, a second end, and a center-tapped end. The first inductor is between the first end and the center-tapped end, and the second inductor is between the center-tapped end and the second end. The connection positions of the first end, the second end and the center tap end in the switching power supply are adjusted to form different relationship equations, so as to adjust the overvoltage protection threshold.

4. The switching power supply according to claim 3, wherein: The duty cycle includes a conduction duty cycle and a freewheeling duty cycle, and the ratio of the conduction duty cycle to the freewheeling duty cycle is equal to the ratio of the conduction time of the main power tube to the freewheeling time of the freewheeling tube. The input sampling voltage is adjusted or the ratio of the on-duty cycle to the freewheeling duty cycle is adjusted by adjusting the connection positions of the first end, the second end and the center tap end in the switching power supply to adjust the proportional coefficient.

5. The switching power supply according to claim 4, wherein: By adjusting the connection positions of the first end, the second end and the center tap end, the number of inductors in the center tap inductor participating in the current loop during the on-time and the freewheeling time is made different, so as to adjust the ratio of the on-duty cycle to the freewheeling duty cycle, thereby adjusting the proportional coefficient.

6. The switching power supply according to claim 4, wherein: The position of the sampling point of the switching power supply is adjusted by adjusting the connection position of the first end, the second end and the center tap end, so as to adjust the input sampling voltage and thus adjust the proportional coefficient.

7. The switching power supply according to claim 4, wherein: When the product of the ratio of the on-duty cycle to the freewheeling duty cycle and the input sampling voltage increases, the proportional coefficient decreases and the overvoltage protection threshold decreases; when the product of the ratio of the on-duty cycle to the freewheeling duty cycle and the input sampling voltage decreases, the proportional coefficient increases and the overvoltage protection threshold increases.

8. The switching power supply according to claim 5, wherein: The first end is connected to the input end, the second end is connected to the first end of the freewheeling tube, the second end of the freewheeling tube is connected to the output end, the center tap end is connected to the main power tube, the sampling point is the input end, the first inductor participates in the current loop during the conduction time, and the first inductor and the second inductor both participate in the current loop during the freewheeling time.

9. The switching power supply according to claim 6, wherein: The first end is connected to the common node of the first end of the freewheeling tube and the main power tube, the second end of the freewheeling tube is connected to the output end, the second end is connected to the input end, the center tap end is connected to the input sampling unit, the sampling point is the center tap end, the first inductor and the second inductor both participate in the current loop during the conduction time, and the first inductor and the second inductor both participate in the current loop during the freewheeling time.

10. The switching power supply according to claim 8 or 9, wherein: The proportional coefficient is K / a, where a is the sampling coefficient of the input sampling unit during sampling, K is 1+N2 / N1, N1 and N2 are the number of turns of the first inductor and the number of turns of the second inductor respectively, wherein a, K, N1 and N2 are all greater than zero.

11. The switching power supply according to claim 5, wherein: The first end is connected to the input end, the second end is connected to the drain of the main power tube, the center tap end is connected to the first end of the freewheeling tube, the second end of the freewheeling tube is connected to the output end, the sampling point is the input end, the first inductor and the second inductor both participate in the current loop during the conduction time, and the first inductor participates in the current loop during the freewheeling time.

12. The switching power supply according to claim 6, wherein: The first end is connected to the first end of the freewheeling tube and the drain of the main power tube, the second end of the freewheeling tube is connected to the output end, the second end is connected to the input sampling unit, the center tap end is connected to the input end, the sampling point is the second end, the first inductor participates in the current loop during the conduction time, and the first inductor participates in the current loop during the freewheeling time.

13. The switching power supply according to claim 11 or 12, wherein: The proportional coefficient is K / a, where a is the sampling coefficient of the input sampling unit during sampling, the sampling coefficient is the ratio of the input sampling signal to the input voltage, K is N1 / (N1+N2), N1 and N2 are the number of turns of the first inductor and the number of turns of the second inductor respectively, wherein a, K, N1 and N2 are all greater than zero.

14. The switching power supply according to claim 1, wherein: The duty cycle includes a turn-on duty cycle and a freewheeling duty cycle. The overvoltage control unit performs overvoltage protection on the switching power supply when the relationship between the turn-on duty cycle, the freewheeling duty cycle, the input sampling voltage and the reference voltage meets a trigger condition. The trigger condition is: the product of the ratio of the turn-on duty cycle and the freewheeling duty cycle and the input sampling voltage is greater than or equal to the reference voltage.

15. The switching power supply according to claim 1, wherein: The input sampling unit samples the voltage at the sampling point of the switching power supply during the conduction time of the main power tube.

16. The switching power supply according to claim 1, wherein: The switching power supply further includes a reference voltage acquisition unit, which acquires voltage from a threshold setting resistor or a current source and performs calculation to obtain the reference voltage.

17. A method for overvoltage protection of a switching power supply, the switching power supply comprising a main power tube and a freewheeling tube, the switching power supply receiving an input voltage and generating an output voltage by periodically turning on and off the main power tube, wherein: The switching power supply further includes a center-tapped inductor, and the overvoltage protection method includes: Sampling the voltage at the sampling point of the switching power supply to obtain an input sampling voltage representing the input voltage; The switching power supply is protected against overvoltage according to the duty cycle, the input sampling voltage and the reference voltage. Among them, the center tap inductor is connected to the main power tube and the freewheeling tube, and the overvoltage protection threshold is adjusted by adjusting the position of the center tap end in the center tap inductor. The overvoltage protection threshold is the output voltage when the overvoltage protection is triggered.

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