CN111313365B

CN111313365B - Overvoltage protection circuit, overvoltage protection method and display device

Info

Publication number: CN111313365B
Application number: CN202010238704.8A
Authority: CN
Inventors: 陈信; 刁凯; 侯清娜; 陈美珍; 查文; 胡晔; 余仁惠; 郑上涛; 谢洪洲
Original assignee: BOE Technology Group Co Ltd; Fuzhou BOE Optoelectronics Technology Co Ltd
Current assignee: BOE Technology Group Co Ltd; Fuzhou BOE Optoelectronics Technology Co Ltd
Priority date: 2020-03-30
Filing date: 2020-03-30
Publication date: 2022-07-12
Anticipated expiration: 2040-03-30
Also published as: CN111313365A

Abstract

The invention provides an overvoltage protection circuit, an overvoltage protection method and a display device, relates to the technical field of display, and aims to solve the problem of how to better perform overvoltage protection. An overvoltage protection circuit comprising: a control voltage supply sub-circuit configured to supply a control voltage to the first node; an output sub-circuit connected to the first node and the output terminal, the output sub-circuit configured to output a first output voltage corresponding to a first control voltage of the first node to the output terminal; the detection sub-circuit is configured to detect the magnitude relation between the voltage of the output end and a preset voltage and output a detection result signal to the second node; and the regulating sub-circuit is configured to regulate the control voltage supply sub-circuit to be open or closed according to the detection result signal, so as to adjust the voltage supplied by the control voltage supply sub-circuit to the first node.

Description

Overvoltage protection circuit, overvoltage protection method and display device

Technical Field

The invention relates to the technical field of display, in particular to an overvoltage protection circuit, an overvoltage protection method and a display device.

Background

An overvoltage protection circuit (may be referred to as an "overvoltage protection circuit") is generally disposed in the display device, and is used to adjust an output voltage provided from an output terminal of the system board to a power supply circuit of the display device, so that when the voltage at the output terminal exceeds a preset voltage, a system power supply is quickly cut off, and the voltage at the output terminal is zeroed, thereby avoiding damage to components and devices due to an overvoltage phenomenon, and hidden dangers such as fire.

However, when the overvoltage phenomenon disappears, the voltage at the output end is still zero, and the output end can be recovered to be normal after restarting, so that the user experience is poor.

Disclosure of Invention

The embodiment of the invention provides an overvoltage protection circuit, an overvoltage protection method and a display device, which are used for solving the problem of better performing overvoltage protection.

In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:

in a first aspect, an overvoltage protection circuit is provided, comprising: a control voltage supply sub-circuit configured to supply a first control voltage to the first node; an output sub-circuit connected to the first node and an output terminal Vo, the output sub-circuit configured to output a first output voltage corresponding to a first control voltage of the first node to the output terminal; the detection sub-circuit is connected with the output end and is configured to detect the magnitude relation between the voltage of the output end Vo and a preset voltage and output a detection result signal to a second node; a regulation sub-circuit connected to the first voltage terminal GND, the second node and the control voltage supply sub-circuit, the regulation sub-circuit being configured to form an open circuit between the control voltage supply sub-circuit and the first voltage terminal GND if the detection result signal indicates that the voltage of the detection output Vo is less than a preset voltage, and to form a loop between the control voltage supply sub-circuit and the first voltage terminal GND if the detection result signal indicates that the voltage of the detection output Vo is greater than the preset voltage, so as to adjust the voltage supplied from the control voltage supply sub-circuit to the first node to a second control voltage; wherein the output sub-circuit is further configured to output a second output voltage corresponding to a second control voltage of the first node to the output terminal, the first output voltage is less than the preset voltage, and a difference between the second output voltage and 0V is less than a threshold.

Optionally, the detection sub-circuit includes a first comparator U1, an anode of the first comparator U1 is connected to the output terminal Vo, a cathode of the first comparator U1 is connected to a reference voltage terminal Vref, a first power supply terminal of the first comparator U1 is connected to the first voltage terminal GND, a second power supply terminal of the first comparator U1 is connected to a second voltage terminal V_CDAnd the output end of the first comparator U1 is connected with the second node.

Optionally, the detection sub-circuit further comprises a first resistor R2 and a second resistor R3; the output Vo is connected to the first voltage terminal GND through the first resistor R2 and the second resistor R3 connected in series, and the anode of the first comparator U1 is connected between the first resistor R2 and the second resistor R3.

Optionally, the detection sub-circuit further comprises a third resistor R5 and a fourth resistor R13; the reference voltage terminal Vref is connected to the first voltage terminal GND through the third resistor R5 and the fourth resistor R13 which are connected in series, and the negative electrode of the first comparator U1 is connected between the third resistor R5 and the fourth resistor R13.

Optionally, the detection sub-circuit further comprises a first diode D3 and a fifth resistor R6; the first diode D3 and the fifth resistor R6 are connected in series between the positive terminal of the first comparator U1 and the output terminal of the first comparator U1 to allow current to pass from the output terminal of the first comparator U1 to the positive terminal of the first comparator U1.

Optionally, the detection sub-circuit further comprises a sixth resistor R7 and a seventh resistor R8; an output end of the first comparator U1 is connected to the first voltage end GND through the sixth resistor R7 and the seventh resistor R8 which are connected in series, and the second node is connected between the sixth resistor R7 and the seventh resistor R8.

Optionally, the detection sub-circuit further includes an eighth resistor R4 and a first capacitor C2, the anode of the first comparator U1 is connected to the first voltage terminal GND through the eighth resistor R4 and the first capacitor C2 connected in series, and the anode of the first comparator U1 is connected to the first voltage terminal GND through the second resistor R3 and the eighth resistor R4 connected in series.

Optionally, the regulator sub-circuit comprises a first switching tube Q1 and an opto-coupler U2, the opto-coupler U2 comprises a first input end, a second input end, a first output end and a second output end; a first pole of the first switch Q1 is connected to the first input terminal, a gate terminal of the first switch Q1 is connected to the second node, and a second pole of the first switch Q1 is connected to the first voltage terminal GND; the second input end is connected with a third voltage end Vcc, the first output end is connected with the first node, and the second output end is connected with the first voltage end GND.

Optionally, the adjusting sub-circuit further includes a ninth resistor R12, and the first pole of the first switch Q1 is connected to the first input end through the ninth resistor R12.

Optionally, the third voltage terminal Vcc is the second voltage terminal V_CD。

Optionally, the control voltage providing sub-circuit comprises a current source and a tenth resistor R14, the current source being connected to the first node in series with the tenth resistor R14.

Optionally, the control voltage providing sub-circuit further comprises a second diode D5, the second diode D5 being connected between the tenth resistor R14 and the first node to allow a current to pass from the tenth resistor R14 to the first node.

Optionally, the control voltage supply sub-circuit further comprises an eleventh resistor R9 and a twelfth resistor R10; the current source is connected to the first voltage terminal GND through the tenth resistor R14, the eleventh resistor R9 and the twelfth resistor R10 which are connected in series, and the first node is connected between the eleventh resistor R9 and the twelfth resistor R10.

Optionally, the control voltage supply sub-circuit further includes a voltage regulator tube, an anode of the voltage regulator tube is connected to the first voltage terminal GND, and a cathode of the voltage regulator tube is connected to the first node.

Optionally, the output sub-circuit includes a second comparator U3, a latch, a second switching tube Q2, a thirteenth resistor R11, a transformer T1, a third diode D7, and a second capacitor C3; wherein the transformer T1 comprises a third input terminal, a fourth input terminal, a third output terminal and a fourth output terminal; the negative electrode of the second comparator U3 is connected to the first node, the positive electrode of the second comparator U3 and the thirteenth resistor R11 are connected to the first voltage end GND in series, and the output end of the second comparator U3 is connected to the R end of the latch; the S end of the latch is connected with a clock pulse end, and the Q end of the latch is connected with the gating end of the second switch tube Q2; a first pole of the second switch Q2 is connected to the third input terminal, and a second pole of the second switch Q2 is connected to the first voltage terminal GND through the thirteenth resistor R11; the fourth input terminal of the transformer T1 is connected to a fourth voltage terminal VBUS, the third output terminal is connected to the first voltage terminal GND, the fourth output terminal is connected to the first voltage terminal GND through the third diode D7 and the second capacitor C3 in series, and the output terminal Vo is connected between the third diode D7 and the second capacitor C3 to allow a current to pass from the fourth output terminal to the output terminal Vo.

In a second aspect, a method of overvoltage protection is provided, comprising: detecting the magnitude relation between the voltage of the output end Vo and the preset voltage, and outputting a detection result signal; under the condition that the voltage of the detection output Vo is smaller than the preset voltage represented by the detection result signal, outputting a first output voltage to the output Vo; under the condition that the voltage of the detection output Vo is larger than the preset voltage represented by the detection result signal, outputting a second output voltage to the output Vo; the first output voltage is smaller than the preset voltage, and the difference between the second output voltage and 0V is smaller than a threshold value.

In a third aspect, a display device is provided, which includes the overvoltage protection circuit of the first aspect.

The embodiment of the invention provides an overvoltage protection circuit, an overvoltage protection method and a display device. The detection sub-circuit detects the magnitude relation between the voltage of the output end Vo and the preset voltage, and transmits a detection result signal to the regulation sub-circuit through a second node N. Under the condition that the voltage of the detection output Vo is greater than the preset voltage, namely, when an overvoltage phenomenon occurs, the adjusting sub-circuit forms a loop between the control voltage providing sub-circuit and the first voltage end, and the voltage provided by the control voltage providing sub-circuit to the first node M is adjusted to be the second control voltage. The output sub-circuit outputs a second output voltage corresponding to the second control voltage of the first node M to the output terminal Vo. The second output voltage is close to 0V or equal to 0V, so that the voltage of the output end Vo is pulled down to be close to 0V or equal to 0V, and the purpose of over-voltage locking the circuit is achieved. And after the overvoltage phenomenon is removed, the detection sub-circuit transmits a detection result signal representing that the voltage of the detection output end Vo is smaller than the preset voltage to the regulation sub-circuit. The regulator sub-circuit forms an open circuit between the control voltage supply sub-circuit and the first voltage terminal GND. The control voltage supply sub-circuit supplies a first control voltage to the first node M, and the output sub-circuit outputs a first output voltage corresponding to the first control voltage of the first node M to the output terminal Vo. The first output voltage is a normal output voltage when no overvoltage phenomenon occurs, so that the overvoltage protection circuit can automatically recover the normal output voltage after the overvoltage phenomenon is relieved.

Therefore, the overvoltage protection circuit provided by the embodiment of the application can pull the voltage of the output end Vo down to be close to 0V or equal to 0V when the overvoltage phenomenon occurs, and the purpose of locking the circuit by overvoltage is achieved, so that circuit components are protected, and safety problems such as fire disasters are prevented. When the overvoltage phenomenon is relieved, the overvoltage protection circuit can automatically recover normal output voltage, other operations such as restarting are not needed, convenience and simplicity are achieved, and user experience can be remarkably improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic circuit diagram of a TFT-LCD according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of an overvoltage protection circuit for a TFT-LCD provided in the related art;

fig. 3 is a schematic structural diagram of an overvoltage protection circuit according to an embodiment of the present application;

FIG. 4 is a schematic diagram of a specific structure of sub-circuits in the overvoltage protection circuit of FIG. 3;

fig. 5 is a timing diagram illustrating an operation of an overvoltage protection circuit according to an embodiment of the present application when an overvoltage phenomenon occurs;

fig. 6 is a timing diagram illustrating an operation of the overvoltage protection circuit according to the embodiment of the present application when the overvoltage phenomenon is removed;

FIG. 7 is a schematic diagram of another embodiment of the sub-circuits of the overvoltage protection circuit of FIG. 3;

fig. 8 is a flowchart of an overvoltage protection method according to an embodiment of the present application.

Reference numerals:

1-system; 2-a system interface; 3-a power supply circuit; 30-an overvoltage protection circuit; 31-a control voltage supply sub-circuit; 32-an output sub-circuit; 33-a detection sub-circuit; 34-regulating sub-circuit.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

In the related art, an overvoltage protection circuit is provided in a display device to regulate an output voltage supplied from an output terminal of a system board to a power supply circuit of the display device. For example, the display device may include a mobile phone, a tablet computer, a Personal Digital Assistant (PDA), an in-vehicle computer, and the like. The embodiment of the present application does not specifically limit the specific form of the display device. The following description will be made by taking a display device as a thin film transistor liquid crystal display (TFT-LCD) as an example.

Fig. 1 shows a circuit configuration of a TFT-LCD, and referring to fig. 1, an output voltage Vout from a system (a main board of a complete machine, which is a main board in a display device in general) 1 is transmitted to an input terminal of a power supply circuit 3 via a system interface 2 (i.e., an output terminal of the system 1), so that the output voltage Vout can be used as an input voltage of the power supply circuit 3. However, the voltage at the output terminal of the system 1 is not always the output voltage Vout, and the voltage at the output terminal of the system 1 may be affected by the power supply circuit 3 or other application circuits connected thereafter, for example, when the circuit components in the power supply circuit 3 are short-circuited or the user of the display device operates improperly, the voltage at the output terminal of the system 1 may be increased. When the voltage at the output terminal of the system 1 increases to exceed the preset voltage, an overvoltage phenomenon occurs, which may cause damage to components of the circuit and even cause a fire. Therefore, the voltage at the output of the system 1 needs to be adjusted in time to relieve the overvoltage phenomenon.

Fig. 2 shows an overvoltage protection circuit 30 for a TFT-LCD provided in the related art. As shown in fig. 2, the overvoltage protection circuit 30 includes a voltage regulator D2, a resistor R1, a capacitor C1, and a thyristor D1. Wherein, the anode terminal (can be represented by A) of the thyristor D1 is connected with the supply voltage V_CCThe cathode terminal (which can be represented by K) of the thyristor D1 is grounded, and the reference terminal (which can also be referred to as the control terminal and is represented by G) of the thyristor D1 is connected between the voltage regulator tube D2 and the resistor R1. After being connected in series, a voltage regulator tube D2 and a resistor R1 are grounded at one end, and the other end is connected withAnd the negative electrode of the voltage regulator tube D2 is connected with the output voltage end Vo. One end of the capacitor C1 is connected between the voltage regulator D2 and the resistor R1, and the other end is grounded.

The principle of the overvoltage protection circuit 30 shown in fig. 2 is as follows:

due to short circuit of circuit components in the power circuit 3 or improper operation of a user of the display device, and the like, when the voltage of the output end of the system 1 exceeds a preset voltage, the voltage regulator tube D2 is conducted due to zener breakdown. When D2 is turned on, R1 has current flowing through it, so that there is voltage across R1, and a voltage difference is generated between the reference terminal G of thyristor D1 and the cathode terminal K, forming a trigger voltage, triggering thyristor D1 to turn on. The thyristor D1 is turned on to make the supply voltage V_CCThe voltage is pulled to ground, thereby supplying a voltage V_CCAnd no output is performed, the voltage of the output voltage end Vo is 0, and the effect of protecting the safety of the circuit and the equipment is achieved.

However, the overvoltage protection circuit 30 has disadvantages: when the abnormal condition of the overvoltage of the output voltage end Vo is relieved, the voltage regulator tube D2 is cut off, no current passes through the R1, the voltage on the R1 is 0, and the voltage of the reference end G of the controllable silicon D1 is 0. However, after the thyristor D1 is turned on, even if the voltage at the reference terminal G is 0, the thyristor D1 can still be kept in the on state, and V is required_CCThe voltage is off or the current is less than the value required to turn on to prevent it from turning on. Thus, V_CCThe voltage cannot be automatically recovered, the voltage of the output voltage end Vo is still 0, and the voltage can be recovered only by restarting. Moreover, the price of the thyristor is relatively expensive, and the manufacturing cost of the overvoltage protection circuit 30 is relatively high.

Based on this, the embodiment of the present application provides an overvoltage protection circuit 30, as shown in fig. 3, including:

a control voltage providing sub-circuit 31 configured to provide a first control voltage to the first node M.

And an output sub circuit 32 connected to the first node M and the output terminal Vo, the output sub circuit 32 configured to output a first output voltage corresponding to the first control voltage of the first node M to the output terminal Vo.

The first output voltage corresponding to the first control voltage is used to represent the output voltage when no overvoltage phenomenon occurs, and therefore, the first output voltage may also be referred to as a normal output voltage.

And a detection sub-circuit 33 connected to the output terminal Vo, wherein the detection sub-circuit 33 is configured to detect a magnitude relationship between a voltage of the output terminal Vo and a preset voltage, and output a detection result signal to the second node N.

The preset voltage is a preset critical voltage for representing an overvoltage phenomenon. And when the voltage of the output end Vo is greater than the preset voltage, the overvoltage phenomenon is considered to occur. For example, the preset voltage may be 1.2 times, 1.5 times, 2 times, 3 times, or the like of the normal output voltage. Of course, the preset voltage may be set according to a specific circuit application scenario, and a specific value of the preset voltage is not limited in this embodiment of the application.

And a regulation sub-circuit 34 connected to the first voltage terminal, the second node N, and the control voltage supply sub-circuit 31. The regulating sub-circuit 34 is configured to form a break between the control voltage providing sub-circuit 31 and the first voltage terminal in case the detection result signal indicates that the voltage of the detection output Vo is less than the preset voltage; under the condition that the detection result signal represents that the voltage of the detection output Vo is greater than the preset voltage, a loop is formed between the control voltage supply sub-circuit 31 and the first voltage end, so as to adjust the voltage provided by the control voltage supply sub-circuit 31 to the first node M to be the second control voltage.

As shown in fig. 3, the first voltage terminal may be a ground terminal GND. For convenience of description, the first voltage terminal is taken as the ground terminal GND and will be referred to as the first voltage terminal GND.

In addition, the output sub-circuit 32 is further configured to output a second output voltage corresponding to a second control voltage of the first node M to the output terminal Vo, the first output voltage being less than a preset voltage, and a difference of the second output voltage from 0V being less than a threshold.

And the second output voltage corresponding to the second control voltage is used for representing the output voltage when the overvoltage phenomenon occurs. Also, the threshold may be close to or equal to 0V. That is, the second output voltage may be close to 0V or equal to 0V.

In the overvoltage protection circuit provided in the embodiment of the application, the detection sub-circuit 33 detects a magnitude relation between the voltage of the output Vo and a preset voltage, and transmits a detection result signal to the adjustment sub-circuit 34 through the second node N.

Under the condition that the voltage of the detection output Vo is smaller than the preset voltage, namely, no overvoltage phenomenon occurs, the adjusting sub-circuit 34 forms an open circuit between the control voltage providing sub-circuit 31 and the first voltage end GND; that is, the control voltage supply sub-circuit 31 cannot form a loop with the first voltage terminal GND through the regulator sub-circuit 34, the circuit connection between the control voltage supply sub-circuit 31 and the regulator sub-circuit 34 is disconnected, and the regulator sub-circuit 34 does not adjust the voltage supplied to the first node M by the control voltage supply sub-circuit 31. At this time, the control voltage supply sub-circuit 31 supplies the first control voltage to the first node M, and the output sub-circuit 32 outputs a first output voltage corresponding to the first control voltage of the first node M to the output terminal Vo.

Under the condition that the voltage of the detection output Vo is greater than the preset voltage, that is, the overvoltage phenomenon occurs, the adjusting sub-circuit 34 forms a loop between the control voltage providing sub-circuit 31 and the first voltage end, so as to adjust the voltage provided by the control voltage providing sub-circuit 31 to the first node M to the second control voltage. At this time, the output sub-circuit 32 outputs a second output voltage corresponding to the second control voltage of the first node M to the output terminal Vo. The second output voltage is close to 0V or equal to 0V, so that the voltage of the output end Vo is reduced to be close to 0V or equal to 0V, the purpose of over-voltage locking of the circuit is achieved, and the problems that circuit components are damaged and fire disasters are caused possibly due to over-voltage phenomena are solved.

When the overvoltage phenomenon is removed, the detection sub-circuit 33 transmits a detection result signal indicating that the voltage at the detection output Vo is less than the preset voltage to the adjustment sub-circuit 34. The adjusting sub-circuit 34 forms a break between the control voltage providing sub-circuit 31 and the first voltage terminal GND, and the adjusting sub-circuit 34 does not adjust the voltage provided by the control voltage providing sub-circuit 31 to the first node M. The control voltage supply sub-circuit 31 supplies a first control voltage to the first node M, and the output sub-circuit 32 outputs a first output voltage corresponding to the first control voltage of the first node M to the output terminal Vo. The first output voltage is the normal output voltage when the overvoltage phenomenon does not occur, so that the overvoltage protection circuit can automatically recover the normal output voltage after the overvoltage phenomenon is relieved.

Therefore, the overvoltage protection circuit 30 provided in the embodiment of the present application can pull down the voltage of the output Vo to be close to 0V or equal to 0V when the overvoltage phenomenon occurs, so as to achieve the purpose of locking the circuit by overvoltage, thereby protecting circuit components and preventing safety problems such as fire hazard. When the overvoltage phenomenon is relieved, the overvoltage protection circuit can automatically recover normal output voltage, other operations such as restarting are not needed, convenience and simplicity are achieved, and user experience can be remarkably improved.

The various sub-circuits included in the overvoltage protection circuit 30 are described in detail below.

In some embodiments, as shown in fig. 4, the detection sub-circuit 33 includes a first comparator U1, a positive terminal of the first comparator U1 is connected to the output terminal Vo, a negative terminal of the first comparator U1 is connected to the reference voltage terminal Vref, a first power supply terminal of the first comparator U1 is connected to the first voltage terminal GND, and a second power supply terminal of the first comparator U1 is connected to the second voltage terminal V_CDThe output terminal of the first comparator U1 is connected to the second node N.

When the voltage of the positive electrode of the first comparator U1 is less than the voltage of the negative electrode of the first comparator U1, the output end of the first comparator U1 may output a low level. When the voltage of the anode of the first comparator U1 is greater than the voltage of the cathode of the first comparator U1, the output terminal of the first comparator U1 may output a high level.

Since the positive terminal of the first comparator U1 is connected to the output terminal Vo and the negative terminal of the first comparator U1 is connected to the reference voltage terminal Vref, it is possible to set the value of the reference voltage terminal Vref such that: when the voltage of the output Vo is greater than the preset voltage (i.e., the overvoltage phenomenon occurs), the output of the first comparator U1 outputs a high level; when the voltage of the output Vo is less than the preset voltage (i.e., no overvoltage phenomenon occurs), the output of the first comparator U1 outputs a low level. Accordingly, the detection sub-circuit 33 may use the first comparator U1 to detect the magnitude relationship between the voltage of the output Vo and the preset voltage, and output a high-level detection result signal to the second node N when the voltage of the output Vo is greater than the preset voltage, and output a low-level detection result signal to the second node N when the voltage of the output Vo is less than the preset voltage.

That is, by using the first comparator U1, it is possible to realize a function of the detection sub-circuit 33 for detecting a magnitude relation of the voltage of the output terminal Vo and the preset voltage and outputting a corresponding detection result signal to the second node N.

In some embodiments, as shown in fig. 4, the regulator sub-circuit 34 may include a first switching tube Q1 and an opto-coupler U2. The optocoupler U2 includes a first input a1, a second input a2, a first output B1, and a second output B2. A first pole of the first switch Q1 is connected to the first input terminal a1, a gate terminal of the first switch Q1 is connected to the second node N, and a second pole of the first switch Q1 is connected to the first voltage terminal GND; the second input terminal a2 is connected to the third voltage terminal Vcc, the first output terminal B1 is connected to the first node, and the second output terminal B2 is connected to the first voltage terminal GND.

The first switching tube Q1 may be a triode, a thin film transistor, or a field effect transistor. For convenience of description, the first switching tube Q1 is exemplarily shown as a triode in fig. 4 and subsequent figures, which are described in the same specification and will not be described again.

Referring to fig. 4, the photocoupler U2 may be a light emitting device U2-1 and a photosensor device U2-2 assembled in a sealed package. Wherein pins of the light emitting device U2-1 serve as two input terminals (i.e., a first input terminal a1 and a second input terminal a2), and pins of the light sensing device U2-2 serve as two output terminals (i.e., a first output terminal B1 and a second output terminal B2). When a signal is applied to both inputs, light emitting device U2-1 emits light. Thus, the photo sensor U2-2 generates photo current after being illuminated due to the photo effect and outputs the photo current from two output terminals.

It should be noted that fig. 4 shows, by way of example only, the photocoupler U2 when the light emitting device U2-1 is the light emitting diode U2-1 and the light sensing device U2-2 is the phototriode U2-2. However, it is understood that the light emitting device U2-1 is not limited to the light emitting diode U2-1 shown in fig. 4, the light sensing device U2-2 is not limited to the photo transistor U2-2 shown in fig. 4, and any other photo coupler U2 capable of implementing the above circuit functions is also included in the scope of the present application.

The specific operation of the regulator sub-circuit 34 shown in fig. 4 will now be described.

Under the condition that the detection result signal indicates that the voltage of the detection output Vo is less than the preset voltage (no overvoltage occurs), the detection sub-circuit 33 outputs a low-level detection result signal to the second node N, and since the second node N is connected to the gate terminal of the first switching tube Q1, the first switching tube Q1 is not turned on, no current flows through the path from the third voltage terminal Vcc → the light emitting diode U2-1 → the first switching tube Q1 → the first voltage terminal GND, and the light emitting diode U2-1 of the photocoupler U2 does not emit light, so that the phototriode U2-2 of the photocoupler U2 is not turned on, thereby forming an open circuit between the control voltage supply sub-circuit 31 and the first voltage terminal GND.

In case that the detection result signal indicates that the voltage of the detection output Vo is greater than the preset voltage (overvoltage phenomenon occurs), the detection sub-circuit 33 outputs a high-level detection result signal to the second node N, the first switch tube Q1 is turned on, a current flows through a path from the third voltage terminal Vcc → the light emitting diode U2-1 → the first switch tube Q1 → the first voltage terminal GND, the light emitting diode U2-1 of the photocoupler U2 emits light to cause the phototriode U2-2 of the photocoupler U2 to be turned on, thereby forming a loop between the control voltage supply sub-circuit 31 and the first voltage terminal GND, since the first node M is connected to the first pole of the phototransistor U2-2, the second pole of the phototransistor U2-2 is connected to the first voltage terminal GND, therefore, the voltage at the first node M is pulled down to approximately 0V after the phototransistor U2-2 is turned on.

Thus, by using the first switching tube Q1 and the photo coupler U2, the regulator sub-circuit 34 can form an open circuit between the control voltage supply sub-circuit and the first voltage terminal GND without an overvoltage phenomenon; in case of an overvoltage phenomenon, a loop is formed between the control voltage supply sub-circuit and the first voltage terminal GND to adjust the voltage supplied from the control voltage supply sub-circuit 31 to the first node M to the second control voltage. At this time, the second control voltage approaches 0V.

In some embodiments, as shown in fig. 4, the control voltage supply sub-circuit 31 includes a current source I and a tenth resistor R14, the current source I and the tenth resistor R14 being connected in series to the first node M.

In the case that no overvoltage occurs, the adjusting sub-circuit 34 forms an open circuit between the control voltage providing sub-circuit 31 and the first voltage terminal, and the control voltage providing sub-circuit 31 can provide the first control voltage to the first node M through the current source I and the tenth resistor R14.

In the case where the overvoltage phenomenon occurs, as described above, the regulation sub-circuit 34 forms a loop between the control voltage supply sub-circuit 31 and the first voltage terminal, and the voltage supplied from the control voltage supply sub-circuit 31 to the first node M is adjusted to the second control voltage, which is close to 0V.

After the over-voltage phenomenon is removed, the adjusting sub-circuit 34 forms an open circuit between the control voltage providing sub-circuit 31 and the first voltage terminal, and the control voltage providing sub-circuit 31 still provides the first control voltage to the first node M through the current source I and the tenth resistor R14, at this time, the first output voltage corresponding to the first control voltage is the normal output voltage. That is, after the overvoltage phenomenon is removed, the output voltage automatically returns to normal.

That is, in the case where the overvoltage phenomenon does not occur, the control voltage supply sub-circuit 31 supplies the first control voltage corresponding to the normal output voltage to the first node M through the current source I and the tenth resistor R14. In the case where the overvoltage phenomenon occurs, the control voltage supply sub-circuit 31 supplies the second control voltage close to 0V to the first node M, so that the output sub-circuit 32 outputs the second output voltage close to 0V corresponding to the second control voltage. After the overvoltage phenomenon is removed, the control voltage supply sub-circuit 31 continues to supply the first control voltage corresponding to the normal output voltage to the first node M through the current source I and the tenth resistor R14, and the output voltage automatically recovers to the normal output voltage.

In some embodiments, as shown in fig. 4, the output sub-circuit 32 includes a second comparator U3, a latch U4, a second switch tube Q2, a thirteenth resistor R11, a transformer T1, a third diode D7, and a second capacitor C3. The transformer T1 may include a third input terminal A3, a fourth input terminal a4, a third output terminal B3, and a fourth output terminal B4.

The second switching tube Q2 may be a triode, a thin film transistor, or a field effect transistor. For convenience of description, the second switching tube Q2 is exemplarily shown as a triode in fig. 4 and subsequent figures, which are described in the same specification and will not be described again.

Illustratively, referring to FIG. 4, the transformer T1 may include a primary coil T1-1 and a secondary coil T1-2. The two ends of the primary coil T1-1 are respectively a third input end A3 and a fourth input end a4, and the two ends of the secondary coil T1-2 are respectively a third output end B3 and a fourth output end B4.

The negative pole of the second comparator U3 is connected to the first node M, the positive pole of the second comparator U3 and the thirteenth resistor R11 are connected in series to the first voltage terminal GND, and the output terminal of the second comparator U3 is connected to the R terminal of the latch U4.

The S end of the latch U4 is connected to the CLOCK pulse end CLOCK, and the Q end of the latch U4 is connected to the gating end of the second switch tube Q2.

The first pole of the second switch tube Q2 is connected to the fourth voltage terminal V through the primary coil T1-1_BUSThe second pole of the second switch Q2 is connected to the first voltage terminal GND through a thirteenth resistor R11.

One end (i.e., the third output terminal B3) of the secondary winding T1-2 of the transformer T1 is connected to the first voltage terminal GND, the other end (i.e., the fourth output terminal B4) is connected to the first voltage terminal GND through the third diode D7 and the second capacitor C3 connected in series, and the output terminal Vo is connected between the third diode D7 and the second capacitor C3 to allow a current from the secondary winding T1-2 to the output terminal Vo to pass.

The third diode D7 and the second capacitor C3 connected in series may be used to convert the ac power output from the secondary winding T1-2 into dc power to form a rectifier circuit.

Next, the operation of the output sub-circuit 32 of the overvoltage protection circuit 30 when an overvoltage occurs will be described with reference to fig. 5.

As described above, when the overvoltage phenomenon occurs, the voltage of the first node M is pulled down to the second control voltage close to 0V, and since the negative pole of the second comparator U3 is connected to the first node M, the voltage Ve of the negative pole of the second comparator U3 is pulled down to close to 0V, and the waveform of Ve is shown in fig. 5. The positive pole of the second comparator U3 and the thirteenth resistor R11 are connected in series to the first voltage terminal GND, so the voltage Vs of the positive pole of the second comparator U3 is the voltage across the thirteenth resistor R11, and the voltage Vs of the positive pole of the second comparator U3 is characterized by the fourth voltage terminal V due to the resistance of the thirteenth resistor R11_BUS→ the primary winding T1-1 of the transformer T1 → the second switching tube Q2 → the thirteenth resistor R11. The waveform of the positive voltage Vs of the second comparator U3 is shown in fig. 5.

When the Ve is larger than the Vs, the second comparator U3 outputs a low level by combining the waveforms of the voltage Ve of the negative electrode of the second comparator U3 and the voltage Vs of the positive electrode of the second comparator U3; when Ve is less than Vs, the second comparator U3 outputs a high level.

The output terminal of the second comparator U3 is connected to the R terminal of the latch U4, and the CLOCK terminal CLOCK connected to the S terminal of the latch U4 has the waveform shown in FIG. 5. Also, the truth table for latch U4 is shown in Table 1 below:

S	R	Q
			0	0	is not changed
0	1	0
			1	0	1
1	1	Indefinite article

TABLE 1

As can be seen from table 1 and fig. 5, when Ve is greater than Vs, the second comparator U3 outputs a low level, and when CLOCK is at a high level, the voltage V of Q of the latch U4 is high_QIs high. When Ve is smaller than Vs, the second comparator U3 outputs a high level, and if CLOCK is low, the voltage V of Q of the latch U4 is high_QIs low. Then, when Ve is greater than Vs, the second comparator U3 outputs a low level, and if CLOCK is low, the voltage V of Q of the latch U4 is low_QRemains unchanged and remains low. Thus, the voltage V at the Q terminal of latch U4 is present when an overvoltage condition occurs_QAs shown in fig. 5, is a single pulse waveform.

Since the Q terminal of the latch U4 is connected to the gating terminal of the second switch Q2, the single pulse signal turns on the second switch Q2 or the turn-on current is small, approximately 0, so that the current of the primary winding T1-1 of the transformer T1 is close to 0, the current of the secondary winding T1-2 is close to 0, and a second output voltage close to 0 is output to the output Vo, thereby over-voltage locking the circuit, protecting the components in the circuit and preventing fire and the like from occurring accidentally.

When the overvoltage phenomenon is removed, the overvoltage protection circuit 30 will respond quickly and recover the normal output voltage. Next, an operation of the output sub-circuit 32 of the overvoltage protection circuit 30 when the overvoltage phenomenon is released will be described with reference to fig. 6.

As described above, after the overvoltage phenomenon is removed, the regulator sub-circuit 34 forms an open circuit between the control voltage supply sub-circuit 31 and the first voltage terminal GND, and the regulator sub-circuit 34 does not adjust the voltage supplied from the control voltage supply sub-circuit 31 to the first node M. The control voltage supply sub-circuit 31 supplies the normal first control voltage to the first node M, so that the voltage Ve of the negative pole of the second comparator U3 rises, and the waveform of Ve can be seen in fig. 6.

As Ve increases, the time that Ve is greater than Vs is extended. As can be seen from the above description, when Ve is greater than Vs, the second comparator U3 outputs a low level, and when CLOCK is at a high level, the voltage V of Q of the latch U4_QIs high. Thus, the rise in Ve causes the voltage V at the Q terminal of latch U4_QThe high level is prolonged, so that the second switch tube Q2 can generate a larger conducting current. Further, the current on the primary winding T1-1 of the transformer T1 returns to normal, so that the current on the secondary winding T1-2 returns to normal, and thus, the normal first output voltage is output to the output terminal Vo. That is, after the overvoltage phenomenon is removed, the overvoltage protection circuit 30 can respond quickly to recover the normal first output voltage without restarting the circuit, thereby significantly improving the user experience.

In addition, on the basis of the overvoltage protection circuit 30 shown in fig. 4, in order to better implement the functions of overvoltage locking and automatic recovery, each sub-circuit in the overvoltage protection circuit 30 may further include more components, which will be described in detail below.

In some embodiments, referring to fig. 7, the detection subcircuit 33 further includes a first resistor R2 and a second resistor R3. The output Vo is connected to the first voltage terminal GND through a first resistor R2 and a second resistor R3 connected in series, and the anode of the first comparator U1 is connected between the first resistor R2 and the second resistor R3.

The voltage at the output Vo can be divided by the first resistor R2 and the second resistor R3 connected in series, so that the divided voltage is provided to the anode of the first comparator U1 connected between the first resistor R2 and the second resistor R3. The voltage V3 of the positive electrode of the first comparator U1 can be represented by the following formula (1):

therefore, when the voltage of the output Vo is larger than the voltage of the anode of the first comparator U1, the R2 and the R3 are set to supply an appropriate voltage to the anode of the first comparator U1.

In other embodiments, referring to fig. 7, the detection sub-circuit 33 further includes a third resistor R5 and a fourth resistor R13. The reference voltage terminal Vref is connected to the first voltage terminal GND through a third resistor R5 and a fourth resistor R13 connected in series, and the negative pole of the first comparator U1 is connected between the third resistor R5 and the fourth resistor R13.

Similar to the functions of the first resistor R2 and the second resistor R3, the third resistor R5 and the fourth resistor R13 are used to divide the voltage of the reference voltage terminal Vref, so as to provide a suitable voltage to the cathode of the first comparator U1 connected between the third resistor R5 and the fourth resistor R13. The voltage V2 of the negative pole of the first comparator U1 can be represented by the following formula (2):

therefore, when the voltage of the reference voltage terminal Vref is large as the voltage of the negative electrode of the first comparator U1, by setting the R5 and the R13, a suitable voltage can be supplied to the negative electrode of the first comparator U1.

In other embodiments, referring to fig. 7, the detection sub-circuit 33 further includes a first diode D3 and a fifth resistor R6; a first diode D3 and a fifth resistor R6 are connected in series between the positive terminal of the first comparator U1 and the output terminal of the first comparator U1 to allow current to pass from the output terminal of the first comparator U1 to the positive terminal of the first comparator U1.

The first diode D3 and the fifth resistor R6 are used to form a feedback holding circuit between the positive electrode of the first comparator U1 and the output end of the first comparator U1, and can hold the high level of the output end of the first comparator U1 for a period of time when the overvoltage phenomenon at the output end Vo lasts for a short time, so that the high level signal can turn on the subsequently connected first switch Q1, thereby triggering the overvoltage locking process.

That is, even if the overvoltage phenomenon occurs for a short time, the detection sub-circuit 33 can detect the overvoltage state through the first diode D3 and the fifth resistor R6 and trigger the overvoltage locking process.

In other embodiments, referring to FIG. 7, the detection sub-circuit 33 further includes a sixth resistor R7 and a seventh resistor R8; an output terminal of the first comparator U1 is connected to the first voltage terminal GND through a sixth resistor R7 and a seventh resistor R8 connected in series, and a second node is connected between the sixth resistor R7 and the seventh resistor R8.

Similarly, the sixth resistor R7 and the seventh resistor R8 are used to divide the voltage at the output terminal of the first comparator U1, so as to provide a suitable voltage to the second node N, i.e., a suitable turn-on voltage to the gate terminal of the first switching tube Q1 connected to the second node N.

In other embodiments, referring to fig. 7, the detection sub-circuit 33 further includes an eighth resistor R4 and a first capacitor C2, the anode of the first comparator U1 is connected to the first voltage terminal GND through the eighth resistor R4 and the first capacitor C2 connected in series, and the anode of the first comparator U1 is connected to the first voltage terminal GND through the second resistor R3 and the eighth resistor R4 connected in series.

The eighth resistor R4 can increase the impedance value on the path from the output Vo to the positive electrode of the first comparator U1, so as to limit the current flowing into the positive electrode of the first comparator U1 to be small, thereby avoiding the influence of the large current on the first comparator U1.

Referring to fig. 7, the first capacitor C2 is substantially connected in parallel with the second resistor R3, so that the first capacitor C2 can filter the alternating current flowing through the second resistor R3, stabilize the voltage of R3, and provide a stable voltage for the positive electrode of the first comparator U1.

In addition, in some embodiments, the adjusting sub-circuit 34 may further include a ninth resistor R12, and the first pole of the first switch Q1 is connected to the cathode of the light emitting diode U2-1 through the ninth resistor R12.

The ninth resistor R12 may be used to limit the current on the path from the third voltage terminal Vcc → the led U2-1 → the first switch tube Q1 → the first voltage terminal GND, so as to avoid the component damage caused by the excessive current flowing through the led U2-1 and the first switch tube Q1.

Referring to FIG. 7, in other embodiments, the third voltage terminal Vcc is the second voltage terminal V_CD. That is, the third voltage terminal Vcc and the second voltage terminal V_CDThe same voltage end simplifies the circuit structure.

Referring to fig. 7, in other embodiments, the control voltage supply sub-circuit 31 further includes a second diode D5, and the second diode D5 is connected between the tenth resistor R14 and the first node to allow the current from the tenth resistor R14 to pass through to the first node.

The second diode D5 allows current from the tenth resistor R14 to pass through to the first node M, and limits current from the first node M to the tenth resistor R14, thereby limiting current backflow back to the current source I and reducing the influence on the current source I.

In other embodiments, the control voltage supply sub-circuit 31 further includes an eleventh resistor R9 and a twelfth resistor R10; the current source is connected to the first voltage terminal GND through a tenth resistor R14, an eleventh resistor R9, and a twelfth resistor R10 connected in series, and the first node is connected between the eleventh resistor R9 and the twelfth resistor R10.

The eleventh resistor R9 and the twelfth resistor R10 are used to divide the voltage across the tenth resistor R14, so as to provide the proper voltage for the first node M, i.e., the negative pole of the second comparator U3 connected to the first node M.

The control voltage supply sub-circuit 31 further includes a voltage regulator D4, an anode of the voltage regulator D4 is connected to the first voltage terminal (GND), and a cathode of the voltage regulator D4 is connected to the first node.

When the voltage of the first node M is larger and exceeds the breakdown voltage of the zener diode D4, the zener diode D4 may be turned on to prevent the voltage of the cathode of the second comparator U3 from being too large, and protect the second comparator U3.

An embodiment of the present application further provides an overvoltage protection method, as shown in fig. 8, the overvoltage protection method may include the following steps:

and S10, detecting the magnitude relation between the voltage of the output end Vo and the preset voltage, and outputting a detection result signal.

S20, outputting a first output voltage to the output end Vo under the condition that the voltage of the detection output end Vo is smaller than the preset voltage represented by the detection result signal; the first output voltage is less than a preset voltage.

S30, outputting a second output voltage to the output end Vo under the condition that the detection result signal represents that the voltage of the detection output end Vo is greater than the preset voltage; and the difference value of the second output voltage and 0V is smaller than the threshold value.

The beneficial effects of the overvoltage protection method provided by the embodiment of the application are the same as those of the overvoltage protection circuit, and are not repeated here.

In addition, the embodiment of the application also provides a display device, and the display device comprises the overvoltage protection circuit. For example, the display device may include a cell phone, a tablet computer, a personal digital assistant, a vehicle-mounted computer, and the like. The embodiment of the present application does not specifically limit the specific form of the display device.

Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An overvoltage protection circuit, comprising:

a control voltage providing sub-circuit configured to provide a first control voltage to a first node (M);

an output sub-circuit connected to the first node and an output terminal (Vo), the output sub-circuit configured to output a first output voltage corresponding to a first control voltage of the first node to the output terminal;

a detection sub-circuit connected to the output terminal, the detection sub-circuit being configured to detect a magnitude relation between a voltage of the output terminal (Vo) and a preset voltage, and to output a detection result signal to a second node (N);

a regulation sub-circuit connected to a first voltage terminal (GND), the second node and the control voltage supply sub-circuit, the regulation sub-circuit being configured to form an open circuit between the control voltage supply sub-circuit and the first voltage terminal (GND) in case that the detection result signal indicates that the voltage of the detection output (Vo) is less than a preset voltage, and to form a loop between the control voltage supply sub-circuit and the first voltage terminal (GND) in case that the detection result signal indicates that the voltage of the detection output (Vo) is greater than the preset voltage, so as to adjust the voltage supplied by the control voltage supply sub-circuit to the first node to a second control voltage;

wherein the output sub-circuit is further configured to output a second output voltage corresponding to a second control voltage of the first node to the output terminal, the first output voltage being less than the preset voltage, a difference between the second output voltage and 0V being less than a threshold;

the control voltage providing sub-circuit comprises a current source and a tenth resistor (R14), the current source and the tenth resistor (R14) being connected in series to the first node;

the control voltage supply sub-circuit further comprises a second diode (D5), the second diode (D5) being connected between the tenth resistance (R14) and the first node to allow a current to pass from the tenth resistance (R14) to the first node; and/or

The control voltage supply sub-circuit further comprises an eleventh resistor (R9) and a twelfth resistor (R10); the current source is connected to the first voltage terminal (GND) through the tenth resistor (R14), the eleventh resistor (R9) and the twelfth resistor (R10) in series, the first node is connected between the eleventh resistor (R9) and the twelfth resistor (R10); and/or

The control voltage supply sub-circuit further comprises a voltage-regulator tube, wherein the anode of the voltage-regulator tube is connected with the first voltage end (GND), and the cathode of the voltage-regulator tube is connected with the first node.

2. The overvoltage protection circuit of claim 1,

the detection sub-circuit comprises a first comparator (U1), the positive pole of the first comparator (U1) is connected with the output end (Vo), the negative pole of the first comparator (U1) is connected with a reference voltage end (Vref), the first power supply end of the first comparator (U1) is connected with the first voltage end (GND), and the second power supply end of the first comparator (U1) is connected with the second voltage end (V)_CD) And the output end of the first comparator (U1) is connected with the second node.

3. The overvoltage protection circuit of claim 2,

the detection sub-circuit further comprises a first resistor (R2) and a second resistor (R3); the output (Vo) is connected to the first voltage terminal (GND) through the first resistor (R2) and the second resistor (R3) in series, and the positive pole of the first comparator (U1) is connected between the first resistor (R2) and the second resistor (R3); and/or

The detection sub-circuit further comprises a third resistor (R5) and a fourth resistor (R13); the reference voltage terminal (Vref) is connected to the first voltage terminal (GND) through the third resistor (R5) and the fourth resistor (R13) in series, and the negative pole of the first comparator (U1) is connected between the third resistor (R5) and the fourth resistor (R13); and/or

The detection sub-circuit further comprises a first diode (D3) and a fifth resistor (R6); the first diode (D3) and the fifth resistor (R6) are connected in series between the positive pole of the first comparator (U1) and the output of the first comparator (U1) to allow the passage of current from the output of the first comparator (U1) to the positive pole of the first comparator (U1); and/or

The detection sub-circuit further comprises a sixth resistor (R7) and a seventh resistor (R8); an output terminal of the first comparator (U1) is connected to the first voltage terminal (GND) through the sixth resistor (R7) and the seventh resistor (R8) which are connected in series, and the second node is connected between the sixth resistor (R7) and the seventh resistor (R8);

the detection sub-circuit further comprises an eighth resistor (R4) and a first capacitor (C2), the anode of the first comparator (U1) is connected to the first voltage terminal (GND) through the eighth resistor (R4) and the first capacitor (C2) in series, and the anode of the first comparator (U1) is connected to the first voltage terminal (GND) through the second resistor (R3) and the eighth resistor (R4) in series.

4. The overvoltage protection circuit according to any one of claims 1-3 wherein the regulator sub-circuit comprises a first switching transistor (Q1) and an opto-coupler (U2), the opto-coupler (U2) comprising a first input, a second input, a first output and a second output;

a first pole of the first switch tube (Q1) is connected to the first input end, a gating end of the first switch tube (Q1) is connected to the second node, and a second pole of the first switch tube (Q1) is connected to the first voltage end (GND);

the second input end is connected with a third voltage end (Vcc), the first output end is connected with the first node, and the second output end is connected with the first voltage end (GND).

5. The overvoltage protection circuit of claim 4, wherein the regulation sub-circuit further comprises a ninth resistor (R12), and the first pole of the first switch (Q1) is connected to the first input terminal through the ninth resistor (R12).

6. The overvoltage protection circuit according to claim 4, wherein the third voltage terminal (Vcc) is a second voltage terminal (V) connected to a second supply terminal of the first comparator (U1)_CD）。

7. The overvoltage protection circuit of any one of claims 1-3,

the output sub-circuit comprises a second comparator (U3), a latch (U4), a second switching tube (Q2), a thirteenth resistor (R11), a transformer (T1), a third diode (D7) and a second capacitor (C3); wherein the transformer (T1) comprises a third input, a fourth input, a third output and a fourth output;

a negative electrode of the second comparator (U3) is connected to the first node, a positive electrode of the second comparator (U3) and the thirteenth resistor (R11) are connected in series to the first voltage terminal (GND), and an output terminal of the second comparator (U3) is connected to the R terminal of the latch;

the S end of the latch is connected with a clock pulse end, and the Q end of the latch is connected with the gating end of the second switching tube (Q2);

a first pole of the second switch tube (Q2) is connected to the third input terminal, and a second pole of the second switch tube (Q2) is connected to the first voltage terminal (GND) through the thirteenth resistor (R11);

the fourth input terminal of the transformer (T1) is connected to a fourth voltage terminal (VBUS), the third output terminal is connected to the first voltage terminal (GND), the fourth output terminal is connected to the first voltage terminal (GND) through the third diode (D7) and the second capacitor (C3) in series, and the output terminal (Vo) is connected between the third diode (D7) and the second capacitor (C3) to allow a current to pass from the fourth output terminal to the output terminal (Vo).

8. A method of overvoltage protection for an overvoltage protection circuit according to any one of claims 1 to 7, comprising:

detecting the magnitude relation between the voltage of the output end (Vo) and a preset voltage, and outputting a detection result signal;

under the condition that the voltage of the detection output end (Vo) represented by the detection result signal is less than a preset voltage, outputting a first output voltage to the output end (Vo);

under the condition that the voltage of the detection output end (Vo) represented by the detection result signal is greater than a preset voltage, outputting a second output voltage to the output end (Vo);

the first output voltage is smaller than the preset voltage, and the difference between the second output voltage and 0V is smaller than a threshold value.

9. A display device comprising the overvoltage protection circuit according to any one of claims 1 to 7.