Protection circuit, flyback power supply circuit and circuit board

Abstract

The invention provides a protection circuit, a flyback power supply circuit and a circuit board, which are applied to the technical field of electronics, the protection circuit comprises a detection unit and a step-down unit, the detection unit is connected with a transformer primary side of the flyback power supply circuit and the step-down unit, and the step-down unit is connected with a first control end of a flyback switching tube. When the detection unit detects that abnormal peak voltage occurs on the primary side of the transformer, a trigger signal is sent to the step-down unit, and after the step-down unit receives the trigger signal, the voltage of the first control end is pulled down when the flyback switching tube is switched on, so that the switching-on current of the flyback switching tube is reduced. According to the protection circuit provided by the invention, the flyback power supply circuit can be effectively protected, and the reliability of the flyback power supply circuit is improved.

Description

Technical Field

[0001] The present application relates to the field of electronic technologies, and more particularly, to a protection circuit, a flyback power supply circuit, and a circuit board. Background Art

[0002] A flyback transformer, also known as a single-ended flyback or Buck-Boost converter, is widely used in various electronic devices due to its advantages such as simple structure and low cost. In a flyback power supply circuit mainly composed of a flyback transformer, the flyback power supply circuit is prone to damage when the load is large or the output is short-circuited, resulting in low reliability of the flyback power supply circuit. Summary of the Invention

[0003] The present application provides a protection circuit, a flyback power supply circuit, and a circuit board, and the protection circuit can improve the reliability of the flyback power supply circuit.

[0004] In a first aspect, a protection circuit is provided, which is applied to a flyback power supply circuit. An anti-flyback switch tube is provided on the primary side of the transformer of the flyback power supply circuit. The protection circuit includes a detection unit and a buck unit;

[0005] The detection unit is connected to the primary side of the transformer and the buck unit, and is configured to send a trigger signal to the buck unit when an abnormal spike voltage appears on the primary side of the transformer;

[0006] The buck unit is connected to the first control end of the anti-flyback switch tube, and is configured to pull down the voltage of the first control end when the anti-flyback switch tube is conducting after receiving the trigger signal, so as to reduce the conduction current of the anti-flyback switch tube.

[0007] In an embodiment of the present application, the protection circuit includes a detection unit and a buck unit. The detection unit is connected to the primary side of the transformer of the flyback power supply circuit and the buck unit, and the buck unit is connected to the first control end of the anti-flyback switch tube. When the detection unit detects an abnormal spike voltage on the primary side of the transformer, it sends a trigger signal to the buck unit. After receiving the trigger signal, the buck unit pulls down the voltage of the first control end when the anti-flyback switch tube is conducting, so as to reduce the conduction current of the anti-flyback switch tube. In this way, when the load of the flyback power supply circuit becomes larger or the output is short-circuited, the protection circuit can reduce the conduction current when the anti-flyback switch tube is conducting, thereby reducing the primary side current of the transformer of the flyback power supply circuit. It can not only effectively reduce the probability of inter-turn short circuit in the flyback power supply circuit, but also effectively reduce the probability of over-current damage of the anti-flyback switch tube, and thus can effectively protect the flyback power supply circuit and improve the reliability of the flyback power supply circuit.

[0008] Moreover, compared with the method of setting a sampling circuit and an IC chip in a flyback power supply circuit, the detection unit and the buck unit in the protection circuit provided in the embodiments of the present application can be implemented by a simple analog circuit. The circuit structure is simple and will not increase the complexity of the circuit structure of the flyback power supply circuit. Moreover, the cost is low and will not increase the cost of the flyback power supply circuit.

[0009] Optionally, the buck unit includes a control circuit and a buck switch tube; the control circuit is connected to the detection unit and the second control end of the buck switch tube, and is configured to control the buck switch tube to conduct when the flyback switch tube conducts after receiving the trigger signal; one connection end of the buck switch tube is grounded, and the other connection end is connected to the first control end, and is configured to pull down the voltage of the first control end after conduction.

[0010] In the embodiments of the present application, the buck unit includes a control circuit and a buck switch tube, which can not only achieve the purpose of pulling down the voltage of the first control end when the flyback switch tube conducts, but also enable the protection circuit to have a simple circuit structure and a low cost.

[0011] Optionally, the control circuit includes an energy storage capacitor; the detection unit is connected to the energy storage capacitor, and is configured to control the energy storage capacitor to charge when detecting the abnormal spike voltage on the primary side of the transformer; the energy storage capacitor is connected to the second control end, and is configured to control the buck switch tube to conduct when the flyback switch tube conducts through the voltage obtained by charging.

[0012] In the embodiments of the present application, when the control circuit is composed of an energy storage capacitor, it can not only achieve the purpose of pulling down the voltage of the first control end when the flyback switch tube conducts, but also enable the protection circuit to have a simple circuit structure and a low cost.

[0013] Optionally, the detection unit includes a voltage conversion circuit; the voltage conversion circuit is connected to the primary side of the transformer and the energy storage capacitor, and is configured to convert the abnormal spike voltage when the abnormal spike voltage appears on the primary side of the transformer, so as to charge the energy storage capacitor through the converted voltage.

[0014] In the embodiments of the present application, the detection unit is implemented by a voltage conversion circuit, which can not only charge the energy storage capacitor when an abnormal spike voltage appears on the primary side of the transformer, but also enable the protection circuit to have a simple circuit structure and a low cost.

[0015] Optionally, the voltage conversion circuit includes a first voltage stabilizing tube and a second voltage stabilizing tube connected in series between the primary side of the transformer and the ground point, and a connection node between the first voltage stabilizing tube and the second voltage stabilizing tube is connected to the energy storage capacitor.

[0016] In the embodiment of the present application, the voltage conversion circuit is composed of a first voltage stabilizing diode and a second voltage stabilizing diode connected in series, so that the voltage conversion circuit can charge the energy storage capacitor through two voltage stabilizing diodes, which can make the protection circuit have a simple circuit structure and low cost.

[0017] Optionally, the voltage conversion circuit includes two resistors connected in series between the primary side of the transformer and the ground point, and the connection node between the two resistors is connected to the energy storage capacitor.

[0018] In the embodiment of the present application, when the voltage conversion circuit is composed of two resistors connected in series, the voltage conversion circuit can charge the energy storage capacitor through two resistors, so that the voltage conversion circuit can not only stably charge the energy storage capacitor, accurately control the buck switch tube to conduct when the flyback switch tube conducts, but also has a simple circuit structure, thereby enabling the protection circuit to have a simple circuit structure and low cost.

[0019] Optionally, the above voltage conversion circuit further includes a third voltage stabilizing diode; the cathode of the third voltage stabilizing diode is connected to the connection node, and the anode of the third voltage stabilizing diode is connected to the energy storage capacitor.

[0020] In the embodiment of the present application, when the voltage conversion circuit is composed of a first voltage stabilizing diode, a second voltage stabilizing diode and a third voltage stabilizing diode, the voltage conversion circuit can not only stably charge the energy storage capacitor, accurately control the buck switch tube to conduct when the flyback switch tube conducts, but also has a simple circuit structure, thereby enabling the protection circuit to have a simple circuit structure and low cost.

[0021] Optionally, the voltage conversion circuit includes a fourth voltage stabilizing diode; the cathode of the fourth voltage stabilizing diode is connected to the primary side of the transformer, and the anode of the fourth voltage stabilizing diode is connected to the energy storage capacitor.

[0022] In the embodiment of the present application, when the detection unit is composed of a fourth voltage stabilizing diode, the detection unit can not only stably charge the energy storage capacitor, accurately control the buck switch tube to conduct when the flyback switch tube conducts, but also has a simple circuit structure, thereby enabling the protection circuit to have a simple circuit structure and low cost.

[0023] Optionally, the buck unit includes a discharge resistor; one end of the discharge resistor is connected to the second control end, and the other end is grounded.

[0024] In a second aspect, a flyback power supply circuit is provided, which includes an amplification module, a flyback switching transistor, a transformer primary side and a transformer secondary side that are mutually coupled, and the protection circuit as described in the first aspect; the output end of the amplification module is connected to the first control end of the flyback switching transistor; the first connection end of the flyback switching transistor is connected to the output end of the transformer primary side, and the second connection end is grounded; the input end of the protection circuit is connected to the transformer primary side, and the output end of the protection circuit is connected to the first control end.

[0025] Optionally, the flyback power supply circuit further includes an input circuit, the input end of the input circuit is connected to an input voltage, and the output end of the input circuit is connected to the input end of the transformer primary side.

[0026] Optionally, the flyback power supply circuit further includes an output capacitor, and the output capacitor is connected to the voltage output end of the transformer secondary side.

[0027] Optionally, the flyback power supply circuit further includes an output voltage stabilizing diode, and the output voltage stabilizing diode is connected to the voltage output end of the transformer secondary side.

[0028] In a third aspect, a circuit board is provided, which includes the flyback power supply circuit as described in the second aspect. Description of the Drawings

[0029] Figure 1 A schematic diagram of the principle of a flyback power supply circuit provided by an embodiment of the present application is shown;

[0030] Figure 2 It shows Figure 1 A schematic diagram of signal changes during the operation of the flyback power supply circuit shown;

[0031] Figure 3 A schematic diagram of the principle of a flyback power supply circuit provided by the present application is shown;

[0032] Figure 4 It shows Figure 3 A schematic diagram of signal changes during the operation of the flyback power supply circuit shown;

[0033] Figure 5 A schematic diagram of the principle of another flyback power supply circuit provided by the present application is shown;

[0034] Figure 6 A schematic diagram of the principle of another flyback power supply circuit provided by the present application is shown;

[0035] Figure 7 A schematic diagram of the principle of another flyback power supply circuit provided by the present application is shown;

[0036] Figure 8Shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application;

[0037] Figure 9 Shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application;

[0038] Figure 10 Shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application;

[0039] Figure 11 Shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. Detailed implementation manners

[0040] Next, the technical solutions in the present application will be clearly and elaborately described in conjunction with the accompanying drawings. Among them, in the description of the embodiments of the present application, unless otherwise specified, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of the present application, "a plurality" means two or more than two.

[0041] Hereinafter, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as implying or suggesting relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0042] See Figure 1 , Figure 1 shows a schematic diagram of the principle of a flyback power supply circuit provided by an embodiment of the present application. As Figure 1 shown, the flyback power supply circuit includes a coupled transformer primary side 11 (also called the primary winding) and a transformer secondary side 12 (also called the secondary winding). The transformer primary side 11 and the transformer secondary side 12 form a flyback transformer. The flyback power supply circuit also includes an input circuit 20, a flyback switch tube 13, an amplification module 14, etc. The input end of the input circuit 20 is used to connect to an input voltage, and the output end of the input circuit 20 is connected to the input end of the transformer primary side 11. The input circuit 20 can be composed of components such as diodes and capacitors, and is used to regulate and filter the input voltage. One connection end (hereinafter referred to as the first connection end) of the flyback switch tube 13 is connected to the output end of the transformer primary side 11, and the other connection end (hereinafter referred to as the second connection end) of the flyback switch tube 13 is grounded. The input end of the amplification module 14 is used to connect to a control signal, and the output end of the amplification module 14 is connected to the control end (hereinafter referred to as the first control end) of the flyback switch tube 13. The amplification module 14 can be composed of components such as triodes, capacitors, and resistors, and can amplify the control signal.

[0043] As Figure 1 shown, the input circuit 20 includes a buck module 201, a filtering module 202, and a freewheeling module 203. The buck module 201 can be formed by two diodes connected in parallel. The filtering module 202 can be composed of filter capacitors. The freewheeling module 203 can be composed of freewheeling diodes. The anodes of the two diodes in the buck module 201 are the input terminals of the buck module 201, which are connected to the voltage input terminal 16 of the input circuit 20. The cathodes of the two diodes are the output terminals of the buck module 201, which are connected to the input terminal of the filtering module 202. The output terminal of the filtering module 202 is connected to the input terminal of the freewheeling module 203, and the output terminal of the freewheeling module 203 is connected to the primary side 11 of the transformer. It should be understood that the specific implementation principles of the buck module 201, the filtering module 202, and the freewheeling module 203 may include but are not limited to Figure 1 shown

[0044] The input source is connected to the voltage input terminal 16. During the operation of the flyback power supply circuit, the input voltage provided by the input source is input into the buck module 201 through the voltage input terminal 16. After the input voltage is stepped down by the buck module 201 and filtered by the filtering module 202, it is then input into the primary side 11 of the transformer through the freewheeling module 203. The control signal of the flyback switch tube 13 is input into the amplification module 14 through the signal input terminal 17 of the amplification module 14. The amplification module 14 amplifies the control signal (the amplification factor is usually less than 1), and the amplified control signal is input into the control terminal of the flyback switch tube 13. The first voltage output terminal 18 and / or the second voltage output terminal 19 of the secondary side 12 of the transformer are connected to the load, and the output voltage is output to the load for power supply through the first voltage output terminal 18 and / or the second voltage output terminal 19. Among them, the buck module 201 can reduce the input voltage to prevent the input voltage from being too large and damaging the flyback transformer. The filtering module 202 can filter the input voltage to reduce the fluctuation of the input voltage. The freewheeling module 203 can, after the flyback switch tube 13 is turned off, feedback the electric energy stored in the flyback transformer to the input source to smooth the current in the primary side 11 of the transformer

[0045] As Figure 1 shown, the flyback power supply circuit may further include an output capacitor 15 and an output voltage regulator tube 21, as well as other components. There may be multiple output capacitors 15, and the multiple output capacitors 15 are connected between the voltage output terminals of the secondary side 12 of the transformer in a series and / or parallel manner for energy storage. The output voltage regulator tube 21 is connected between the voltage output terminals of the secondary side 12 of the transformer for regulating the voltage output by the secondary side 12 of the transformer

[0046] Among them, the flyback switch tube 13 is usually a N-type Metal-Oxide-Semiconductor Field-Effect Transistor (NMOS). The first control end is the gate of the NMOS tube, the first connection end is the drain of the NMOS tube, and the second connection end is the source of the NMOS tube. The control signal is usually a Pulse Width Modulation (PWM) signal, and the control signal can control the flyback switch tube 13 to conduct periodically during the operation of the flyback power supply circuit. When the flyback switch tube 13 conducts, the current in the primary side 11 of the transformer rises, and the flyback power supply circuit stores energy, and the load is powered by the output capacitor 15. When the flyback switch tube 13 is turned off, the current in the primary side 11 of the transformer drops, and the flyback power supply circuit releases energy to supply power to the load and charges the output capacitor 15 at the same time.

[0047] When the load is large or the output is short-circuited, the current in the primary side 11 of the transformer will increase, causing the temperature of the flyback power supply circuit to rise. When the temperature continues to rise, the primary side 11 of the transformer may suffer from inter-turn short circuit and be damaged. After the primary side 11 of the transformer has an inter-turn short circuit, when the flyback switch tube 13 conducts, the current in the primary side 11 of the transformer (i.e., the conduction current of the flyback switch tube 13) will increase significantly, and the flyback switch tube 13 may be damaged due to overcurrent.

[0048] See Figure 2 , Figure 2 shows Figure 1 a schematic diagram of signal changes during the operation of the flyback power supply circuit shown. During the operation of the flyback power supply circuit, the Micro Controller Unit (MCU) in the flyback power supply circuit inputs a control signal 21 to the signal input terminal 17. The flyback switch tube 13 conducts when the control signal 21 is at a high level and turns off when the control signal 21 is at a low level. Each cycle of the control signal 21 is a control cycle of the flyback switch tube 13. During each control cycle, when the flyback switch tube 13 conducts, the voltage 22 at the connection node 10 drops, the voltage stress on the flyback switch tube 13 drops accordingly, and the conduction current 23 of the flyback switch tube 13 (i.e., the current in the primary side 11 of the transformer) rises; when the flyback switch tube 13 is turned off, the voltage 22 at the connection node 10 rises, the voltage stress on the flyback switch tube 13 rises accordingly, and the conduction current 23 of the flyback switch tube 13 drops.

[0049] During the Nth control period, when the flyback switch tube 13 is conducting, if the load increases or the output is short-circuited, the current 23 in the primary side 11 of the transformer will rise at this time, and the temperature of the flyback power supply circuit 13 will rise. When the flyback switch tube 13 is turned off, the voltage 22 at the connection node 10 will rise abnormally, and a relatively large abnormal voltage value will appear. After several cycles, in the Mth cycle, the flyback power supply circuit may be damaged due to inter-turn short circuit caused by overheating. When the flyback switch tube 13 is conducting, the conduction current of the flyback switch tube 13 will increase significantly, and the voltage stress on the flyback switch tube 13 will increase significantly, which may cause the flyback switch tube 13 to be damaged due to overcurrent.

[0050] In some cases, when a relatively large current appears in the primary side 11 of the transformer, the voltage 22 at the connection node 10 may also rise abnormally. The primary side 11 of the transformer may not have an inter-turn short circuit, but the conduction current of the flyback switch tube 13 will increase, and the voltage stress on the flyback switch tube 13 may exceed the selection limit of the flyback switch tube 13, resulting in the flyback switch tube 13 being broken down and damaged.

[0051] Generally, in order to protect the flyback switch tube, an integrated circuit (IC) chip and a sampling circuit are arranged in the flyback power supply circuit. The sampling circuit collects the primary side current and the secondary side current of the transformer. The IC chip compares the primary side current and the secondary side current of the transformer. When the primary side current of the transformer increases, the duty cycle of the control signal is shortened to shorten the conduction duration of the flyback switch tube, reduce the primary side current of the transformer, and thus protect the flyback switch tube. The problem with this protection circuit is that a sampling circuit and an IC chip need to be arranged in the flyback power supply circuit. The structures of the sampling circuit and the IC chip are relatively complex and the cost is relatively high. This may not only increase the cost of the flyback power supply circuit, but also make the circuit structure of the flyback power supply circuit relatively complex.

[0052] To solve the above technical problems, an embodiment of the present application provides a protection circuit applied to a flyback power supply circuit. The protection circuit includes a detection unit and a buck unit. When the detection unit detects an abnormal spike voltage in the primary side of the transformer, it sends a trigger signal to the buck unit. After receiving the trigger signal, the buck unit pulls down the voltage of the first control end when the flyback switch tube is conducting, so as to reduce the conduction degree of the flyback switch tube, thereby reducing the primary side current of the transformer in the flyback power supply circuit. This can not only effectively reduce the probability of inter-turn short circuit in the flyback power supply circuit, but also effectively reduce the probability of overcurrent damage to the flyback switch tube, and thus can effectively protect the flyback power supply circuit and improve the reliability of the flyback power supply circuit.

[0053] See Figure 3 , Figure 3 shows a schematic diagram of the principle of a flyback power supply circuit provided by the present application. AsFigure 3 As shown, a protection circuit 30 is provided in the flyback power supply circuit. The protection circuit 30 includes a detection unit 31 and a step-down unit 32. The input end of the detection unit 31, which is the input end of the protection circuit, is connected to the primary side 11 of the transformer. The detection unit 31 can detect the voltage of the primary side 11 of the transformer, that is, detect the voltage at the connection node 10 between the primary side 11 of the transformer and the flyback switch tube 13. The detection unit 31 is also connected to the step-down unit 32. When the detection unit 31 detects an abnormal spike voltage at the connection node 10, it outputs a trigger signal to the step-down unit 32. The output end of the step-down unit 32, which is the output end of the protection circuit, is connected to the first control end of the flyback switch tube 13. It is used to pull down the voltage of the first control end when receiving the trigger signal while the flyback switch tube 13 is conducting, so as to reduce the conduction degree of the flyback switch tube 13. When the conduction degree of the flyback switch tube 13 decreases, the conduction current of the flyback switch tube 13 decreases. When the conduction current of the flyback switch tube 13 decreases, the primary side current of the transformer decreases, which can effectively inhibit the heating of the flyback power supply circuit, thereby reducing the probability of inter-turn short circuit in the flyback power supply circuit, and further reducing the probability of over-current damage to the flyback switch tube 13.

[0054] See Figure 4 , Figure 4 shows Figure 3 a schematic diagram of signal changes during the operation of the flyback power supply circuit shown in the figure. During the operation of the flyback power supply circuit, the MCU inputs a control signal 41 to the signal input terminal 17. The flyback switch tube 13 conducts when the control signal 41 is at a high level and turns off when the control signal 41 is at a low level. In each control cycle, when the flyback switch tube 13 conducts, the voltage 42 at the connection node 10 decreases, and the conduction current 43 of the flyback switch tube 13 increases; when the flyback switch tube 43 turns off, the voltage 42 at the connection node 10 increases, and the conduction current of the flyback switch tube 43 decreases. Among them, the conduction current 43 of the flyback switch tube 13 is the current in the primary side 11 of the transformer.

[0055] As Figure 4As shown, within the Nth control cycle, when the flyback switching transistor 13 is conducting and the load increases or the output is short-circuited, the conduction current 43 of the primary side 11 of the transformer increases at this time, and the temperature of the flyback power supply circuit 13 rises. When the flyback switching transistor 13 is turned off, an abnormal voltage value that exceeds the voltage during normal operation will appear at the connection node 10. At this time, the detection unit 31 can detect an abnormal spike voltage at the connection node 10 (the abnormal spike voltage is greater than the voltage during normal operation of the flyback power supply circuit and less than or equal to this abnormal voltage value), and the detection unit 31 outputs a trigger signal to the buck unit 32. After receiving the trigger signal, when entering the (N + 1)th control cycle, the flyback switching transistor 13 conducts, and the buck unit 32 pulls down the voltage of the first control terminal. Since the voltage of the first control terminal is pulled down, the conduction degree of the flyback switching transistor 13 decreases, causing the conduction current of the flyback switching transistor 13 to decrease. When the conduction current of the flyback switching transistor 13 decreases, the current of the primary side 11 of the transformer decreases, the heat generation of the flyback power supply circuit is suppressed, and the probability of inter-turn short circuit decreases. Further, when the probability of inter-turn short circuit decreases, the probability of overcurrent damage of the flyback switching transistor 13 decreases.

[0056] Among them, pulling down the voltage of the first control terminal means pulling down the voltage of the control signal input to the first control terminal, so that the voltage of the control signal actually input to the first control terminal decreases. When pulling down the voltage of the first control terminal, the voltage of the first control terminal can be pulled down below the conduction voltage of the flyback switching transistor to turn off the flyback switching transistor, or the voltage of the first control terminal can only be pulled down by a certain amplitude, and the flyback switching transistor remains in the conducting state, but the conduction degree decreases.

[0057] It can be understood that in the embodiment of the present application, when the protection circuit operates, the duty cycle of the control signal output by the MCU to the first control terminal does not change, and the voltage of the first control terminal is pulled down by the protection circuit, so that the amplitude of the control signal actually input to the first control terminal decreases, and the conduction degree of the flyback switching transistor 13 decreases.

[0058] In the embodiments of the present application, the protection circuit includes a detection unit and a buck unit. The detection unit is connected to the primary side of the transformer of the flyback power supply circuit and the buck unit, and the buck unit is connected to the first control end of the flyback switch tube. When the detection unit detects an abnormal spike voltage on the primary side of the transformer, it sends a trigger signal to the buck unit. After receiving the trigger signal, the buck unit pulls down the voltage of the first control end when the flyback switch tube is conducting, so as to reduce the conduction current of the flyback switch tube. In this way, when the load of the flyback power supply circuit becomes larger or the output is short-circuited, the protection circuit can reduce the conduction current when the flyback switch tube is conducting, effectively suppressing the heating of the flyback power supply circuit, thereby reducing the probability of inter-turn short circuit in the flyback power supply circuit, and further reducing the probability of over-current damage to the flyback switch tube, so as to ensure the stable operation of the flyback power supply circuit and improve the reliability of the flyback power supply circuit.

[0059] Moreover, compared with the method of setting a sampling circuit and an IC chip in the flyback power supply circuit, the detection unit and the buck unit in the protection circuit provided in the embodiments of the present application can be implemented by a simple analog circuit. The circuit structure is simple, which will not increase the complexity of the circuit structure of the flyback power supply circuit, and the cost is low, which will not increase the cost of the flyback power supply circuit.

[0060] Optionally, the buck unit includes a control circuit and a buck switch tube; the control circuit is connected to the detection unit and the second control end of the buck switch tube, and is used to control the buck switch tube to conduct when the flyback switch tube is conducting after receiving the trigger signal; one connection end of the buck switch tube is grounded, and the other connection end is connected to the first control end, and is used to pull down the voltage of the first control end after conduction.

[0061] In one implementation manner, the buck unit may be composed of a control circuit and a buck switch tube. The control circuit is connected to the detection unit and can receive the trigger signal output by the detection unit. The control circuit is also connected to the control end (hereinafter referred to as the second control end) of the buck switch tube. After receiving the trigger signal, the control circuit acts after a certain time delay, so as to control the buck switch tube to conduct when the flyback switch tube is conducting after entering the next control cycle of the flyback switch tube. As Figure 4 shown, in the Nth cycle, at the moment when the flyback switch tube is turned off, an abnormal spike voltage appears on the primary side of the transformer. At this time, the detection unit detects the abnormal spike voltage and sends a trigger signal to the control circuit. After receiving the trigger signal, the control circuit controls the buck switch tube to conduct after entering the (N + 1)th control cycle. Correspondingly, one connection end of the buck switch tube is grounded, and the other connection end is connected to the first control end. After the buck switch tube conducts, it can pull down the voltage of the first control end to reduce the conduction current when the flyback switch tube is conducting.

[0062] Optionally, the control circuit includes an energy storage capacitor; the detection unit is connected to the energy storage capacitor and is configured to control the energy storage capacitor to charge when an abnormal spike voltage appears on the primary side of the transformer; the energy storage capacitor is connected to the second control terminal and is configured to control the buck switch transistor to conduct when the flyback switch transistor conducts through the voltage obtained by charging.

[0063] In one embodiment, the control circuit may be constituted by an energy storage capacitor. When the detection unit detects an abnormal spike voltage, it can charge the energy storage capacitor. The energy storage capacitor is connected to the second control terminal, and the voltage obtained by charging the energy storage capacitor can control the buck switch transistor to conduct when the flyback switch transistor enters the next control cycle, so as to pull down the voltage of the first control terminal and reduce the conduction current of the flyback switch transistor.

[0064] See Figure 5 , Figure 5 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. As Figure 5 shown, the protection circuit includes a detection unit 31 and a buck unit 32. The buck unit 32 includes an energy storage capacitor 51 and a buck switch transistor 52, and the energy storage capacitor 51 is the control circuit. One end of the energy storage capacitor 51 is grounded, and the other end is connected to the detection unit 31. The detection unit 31 can charge the energy storage capacitor 51 when detecting an abnormal spike voltage. The buck switch transistor 52 may be an NMOS transistor. One connection end of the buck switch transistor 52 is the drain of the NMOS transistor, and the other connection end is the source of the NMOS transistor. The drain of the buck switch transistor 52 (i.e., the output terminal of the protection circuit) is connected to the first control terminal, the source of the buck switch transistor 52 is grounded, and the gate of the buck switch transistor 52 (i.e., the second control terminal) is connected to the energy storage capacitor 51.

[0065] Combined with Figure 4 shown, during the operation of the flyback power supply circuit, in the Nth control cycle of the flyback switch transistor 13, when the detection unit 31 detects an abnormal spike voltage at the connection node 10, it can charge the energy storage capacitor 51. At the end of the Nth control cycle, the abnormal spike voltage disappears, and the energy storage capacitor 51 stops charging. After entering the (N + 1)th control cycle of the flyback switch transistor 13, the flyback switch transistor 13 conducts, and the energy storage capacitor 51 starts to discharge. The voltage of the energy storage capacitor 51 can control the buck switch transistor 52 to conduct. After the buck switch transistor 52 conducts, it can pull down the voltage of the first control terminal to reduce the gate voltage of the flyback switch transistor 13, and further reduce the conduction degree of the flyback switch transistor 13 and the conduction current of the flyback switch transistor 13.

[0066] In the embodiment of the present application, when the control circuit is constituted by an energy storage capacitor, it can not only achieve the purpose of pulling down the voltage of the first control terminal when the flyback switch transistor conducts, but also make the protection circuit have a simple circuit structure and low cost.

[0067] Optionally, the detection unit includes a voltage conversion circuit; the voltage conversion circuit is connected to the primary side of the transformer and the energy storage capacitor, and is configured to convert an abnormal spike voltage when it appears on the primary side of the transformer, so as to charge the energy storage capacitor with the converted voltage.

[0068] In one embodiment, the detection unit can be implemented by a voltage conversion circuit. The voltage conversion circuit can convert an abnormal spike voltage when it appears on the primary side of the transformer, and charge the energy storage capacitor with the converted voltage. The converted voltage is the trigger signal. Exemplarily, the voltage conversion circuit can include an integrated circuit voltage regulator. The input terminal of the integrated circuit voltage regulator is connected to connection node 10, and the output terminal is connected to the energy storage capacitor 51. The integrated circuit voltage regulator operates when an abnormal spike voltage appears at connection node 10, converts the abnormal spike voltage to obtain a charging voltage (i.e., the trigger signal). The charging voltage is input to the energy storage capacitor 51 to charge the energy storage capacitor, so that the energy storage capacitor can control the step-down switch tube 52 to conduct after entering the next control cycle of the flyback switch tube 13, pull down the voltage at the first control terminal, so as to reduce the gate voltage of the flyback switch tube 13, and further reduce the conduction degree of the flyback switch tube 13 and the conduction current of the flyback switch tube 13.

[0069] It should be noted that the voltage conversion circuit can include, but is not limited to, an integrated circuit voltage regulator, a DCDC converter chip, and a circuit with voltage conversion function composed of various electronic components such as zener diodes, diodes, resistors, and capacitors.

[0070] In the embodiments of the present application, the detection unit is implemented by a voltage conversion circuit, which can not only charge the energy storage capacitor when an abnormal spike voltage appears on the primary side of the transformer, but also enable the protection circuit to have a simple circuit structure and low cost.

[0071] Optionally, the voltage conversion circuit includes a first zener diode and a second zener diode connected in series between the primary side of the transformer and the ground point, and the connection node between the first zener diode and the second zener diode is connected to the energy storage capacitor.

[0072] In one embodiment, the detection unit can be composed of a first zener diode and a second zener diode connected in series between the primary side of the transformer and the ground point. The series-connected first zener diode and second zener diode can stabilize the voltage when an abnormal spike voltage appears on the primary side of the transformer, so as to convert the abnormal spike voltage to obtain a charging voltage (i.e., the trigger signal), output the converted charging voltage through the connection node between the two zener diodes, and charge the energy storage capacitor with the charging voltage.

[0073] See Figure 6 , Figure 6 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. AsFigure 6 As shown in the figure, the detection unit 31 includes a first voltage stabilizing diode 61 and a second voltage stabilizing diode 62. The cathode of the first voltage stabilizing diode 61 (i.e., the input end of the protection circuit) is connected to the connection node 10. The cathode of the second voltage stabilizing diode 62 is connected to the anode of the first voltage stabilizing diode 61, and the anode of the second voltage stabilizing diode 62 is grounded, so that the first voltage stabilizing diode 61 and the second voltage stabilizing diode 62 are connected in series between the connection node 10 and the ground point of the flyback power supply circuit. The connection node 20 between the first voltage stabilizing diode 61 and the second voltage stabilizing diode 62 is connected to the energy storage capacitor 51. When an abnormal spike voltage appears on the connection node 10, the first voltage stabilizing diode 61 and the second voltage stabilizing diode 62 act to stabilize the voltage, so that the connection node 20 can output a regulated charging voltage, and the charging voltage charges the energy storage capacitor 51.

[0074] In practical applications, the specifications of the first voltage stabilizing diode 61, the second voltage stabilizing diode 62, the energy storage capacitor 51, and the buck switching transistor 52 can be set according to the abnormal spike voltage, so that when an abnormal spike voltage appears on the connection node 10, the connection node 20 can output a charging voltage to charge the energy storage capacitor 51, and the voltage obtained by charging can control the buck switching transistor 52 to conduct after the flyback switching transistor 13 enters the next control cycle.

[0075] In the embodiment of the present application, the voltage conversion circuit is composed of a series-connected first voltage stabilizing diode and a second voltage stabilizing diode, so that the voltage conversion circuit can charge the energy storage capacitor through two voltage stabilizing diodes, which can make the protection circuit have a simple circuit structure and low cost.

[0076] Optionally, the voltage conversion circuit further includes a third voltage stabilizing diode; the cathode of the third voltage stabilizing diode is connected to the connection node, and the anode of the third voltage stabilizing diode is connected to the energy storage capacitor.

[0077] See Figure 7 Figure 7 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. As Figure 7 shown, the voltage conversion circuit further includes a third voltage stabilizing diode 63. The cathode of the third voltage stabilizing diode 63 is connected to the connection node 20, and the anode of the third voltage stabilizing diode 63 is connected to the energy storage capacitor 51. When an abnormal spike voltage appears on the connection node 10, the connection node 20 outputs a charging voltage stabilized by the first voltage stabilizing diode 61 and the second voltage stabilizing diode 62. At this time, the third voltage stabilizing diode 63 can further stabilize the charging voltage and then charge the energy storage capacitor 51.

[0078] In practical applications, the specifications of the first voltage regulator diode 61, the second voltage regulator diode 62, the third voltage regulator diode 63, the energy storage capacitor 51, and the buck switch tube 52 can be set according to the abnormal peak voltage, so that when an abnormal peak voltage appears at the connection node 10, the connection node 20 can output a voltage to the energy storage capacitor 51 through the third voltage regulator diode 63 to charge the energy storage capacitor 51, and the voltage obtained by charging can control the buck switch tube 52 to conduct before the flyback switch tube 13 enters the next control cycle.

[0079] In the embodiment of the present application, when the voltage conversion circuit is composed of the first voltage regulator diode, the second voltage regulator diode, and the third voltage regulator diode, the voltage conversion circuit can not only stably charge the energy storage capacitor, accurately control the buck switch tube to conduct when the flyback switch tube conducts, but also has a simple circuit structure, so that the protection circuit can have a simple circuit structure and low cost.

[0080] Optionally, the voltage conversion circuit includes two resistors connected in series between the primary side of the transformer and the ground point, and the connection node between the two resistors is connected to the energy storage capacitor.

[0081] Exemplarily, the voltage conversion circuit includes two resistors connected in series between the primary side of the transformer and the ground point, namely the first resistor and the second resistor. The connection node between the first resistor and the second resistor is connected to the energy storage capacitor. When an abnormal peak voltage appears at the primary side of the transformer, the first resistor and the second resistor can divide the abnormal peak voltage to realize the conversion of the abnormal peak voltage to obtain a charging voltage, and output the divided charging voltage through the connection node between the first resistor and the second resistor, and charge the energy storage capacitor with the charging voltage.

[0082] See Figure 8 , Figure 8 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. As Figure 8 shown, the voltage conversion circuit includes a first resistor 81 and a second resistor 82. One end of the first resistor 81 (i.e., the input end of the protection circuit) is connected to the connection node 10, and the other end is connected to the second resistor 82. The other end of the second resistor 82 is connected to the ground point, so that the first resistor 81 and the second resistor 82 are connected in series between the primary side of the transformer and the ground point. The connection node 30 between the first resistor 81 and the second resistor 82 is connected to the energy storage capacitor 51. When an abnormal peak voltage appears at the connection node 10, the first resistor 81 and the second resistor 82 can divide the abnormal peak voltage, and the divided charging voltage can be input to the energy storage capacitor 51 through the connection node 30 to charge the energy storage capacitor 51.

[0083] In practical applications, the specifications of the first resistor 81, the second resistor 82, the energy storage capacitor 51, and the buck switch 52 can be set according to the abnormal peak voltage, so that when an abnormal peak voltage appears at the connection node 10, the connection node 30 can output a charging voltage (i.e., a trigger signal) to charge the energy storage capacitor 51, and the voltage obtained by charging can control the buck switch 52 to conduct before the flyback switch 13 enters the next control cycle.

[0084] In the embodiment of the present application, when the voltage conversion circuit is composed of two series resistors, the voltage conversion circuit can charge the energy storage capacitor through the two resistors, so that the voltage conversion circuit can not only stably charge the energy storage capacitor, accurately control the buck switch to conduct when the flyback switch conducts, but also has a simple circuit structure, so that the protection circuit can have a simple circuit structure and low cost.

[0085] In one embodiment, when the voltage conversion circuit includes two series resistors, the voltage conversion circuit may further include a third zener diode. At this time, the cathode of the third zener diode is connected to the connection node between the two resistors, and the anode of the third zener diode may be connected to the energy storage capacitor.

[0086] See Figure 9 , Figure 9 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. As Figure 9 shown, the detection unit 31 further includes a third zener diode 83. The cathode of the third zener diode 83 is connected to the connection node 30, and the anode of the third zener diode 83 is connected to the energy storage capacitor 51. When an abnormal peak voltage appears at the connection node 10, the charging voltage output by the connection node 30 is regulated by the third zener diode 83 and then charges the energy storage capacitor 51.

[0087] In practical applications, the specifications of the first resistor 81, the second resistor 82, the third zener diode 83, the energy storage capacitor 51, and the buck switch 52 can be set according to the abnormal peak voltage, so that when an abnormal peak voltage appears at the connection node 10, the connection node 30 can output a charging voltage (i.e., a trigger signal) to charge the energy storage capacitor 51 through the third zener diode 83, and the voltage obtained by charging can control the buck switch 52 to conduct before the flyback switch 13 enters the next control cycle.

[0088] In the embodiment of the present application, when the voltage conversion circuit is composed of two resistors and a third zener diode, the detection unit can not only stably charge the energy storage capacitor, accurately control the buck switch to conduct when the flyback switch conducts, but also has a simple circuit structure, so that the protection circuit can have a simple circuit structure and low cost.

[0089] Optionally, the voltage conversion circuit includes a fourth zener diode; the cathode of the fourth zener diode is connected to the primary side of the transformer, and the anode of the fourth zener diode is connected to the energy storage capacitor.

[0090] In one embodiment, the voltage conversion circuit can be constituted by a zener diode (i.e., the fourth zener diode). The fourth zener diode is connected to the primary side of the transformer and the energy storage capacitor, and can charge the energy storage capacitor with the voltage obtained by voltage regulation (i.e., the charging voltage) when an abnormal spike voltage appears on the primary side of the transformer.

[0091] See Figure 10 , Figure 10 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. As Figure 10 shown, the voltage conversion circuit includes a fourth zener diode 101. The cathode of the fourth zener diode 101 (i.e., the input end of the protection circuit) is connected to the connection node 10, and the anode of the fourth zener diode 101 is connected to the energy storage capacitor 51. When an abnormal spike voltage appears at the connection node 10, the fourth zener diode 101 stabilizes the abnormal spike, and charges the energy storage capacitor 51 with the charging voltage obtained by voltage regulation.

[0092] In practical applications, the specifications of the fourth zener diode 101, the energy storage capacitor 51, and the buck switch tube 52 can be set according to the abnormal spike voltage, so that when an abnormal spike voltage appears at the connection node 10, the anode voltage of the fourth zener diode 101 can charge the energy storage capacitor 51, and the voltage obtained by charging can control the buck switch tube 52 to conduct before the flyback switch tube 13 enters the next control cycle.

[0093] In the embodiment of the present application, when the detection unit is constituted by a fourth zener diode, it enables the detection unit to not only stably charge the energy storage capacitor, accurately control the buck switch tube to conduct when the flyback switch tube conducts, but also has a simple circuit structure, so that the protection circuit can have a simple circuit structure and a lower cost.

[0094] It should be noted that the above is only an exemplary example, and the voltage conversion circuit may include but is not limited to the above examples.

[0095] Optionally, the buck unit includes a discharge resistor. One end of the discharge resistor is connected to the second control end, and the other end is grounded. As Figure 3-10 shown, the buck unit 32 further includes a discharge resistor 53. One end of the discharge resistor 53 is connected to the ground connection point, and the other end is connected to the second control end. During the operation of the protection circuit, the discharge resistor 53 can discharge the energy storage capacitor 51 when the buck switch tube 52 is turned off, so as to improve the stability of the protection circuit.

[0096] Optionally, the detection unit includes a voltage comparator and a charging switch. The first input terminal of the voltage comparator is connected to the primary side of the transformer, the second input terminal is connected to the reference voltage terminal, and the output terminal is connected to the control terminal of the charging switch. One connection terminal of the charging switch is connected to the voltage terminal, and the other connection terminal is connected to the charging capacitor.

[0097] Among them, the reference voltage terminal is used to output a reference voltage, and the voltage terminal is used to output a charging voltage. The voltage comparator can determine that an abnormal spike voltage appears on the primary side of the transformer when the voltage on the primary side of the transformer is greater than the reference voltage, and send a closing signal to the charging switch. After receiving the closing signal, the charging switch closes to charge the energy storage capacitor through the charging voltage.

[0098] See Figure 11 , Figure 11 shows a schematic diagram of the principle of another flyback power supply circuit provided by the present application. As Figure 11 shown, the detection unit 31 includes a voltage comparator 111 and a charging switch 112. The first input terminal (i.e., the input terminal of the protection circuit) of the voltage comparator 111 is connected to the connection node 10, the second input terminal is connected to the reference voltage terminal 113, and the reference voltage terminal 113 can output a reference voltage. When the voltage of the connection node 10 is greater than the reference voltage, it indicates that an abnormal spike voltage appears at the connection node 10.

[0099] One connection terminal of the charging switch 112 is connected to the voltage terminal, and the other connection terminal is connected to the energy storage capacitor 51. The control terminal of the charging switch 112 is connected to the output terminal of the voltage comparator 111. The voltage comparator 111 compares the voltage of the connection node 10 with the reference voltage. When the voltage of the connection node 10 is greater than the reference voltage, a closing signal is output to the charging switch 112 to control the charging switch 112 to close. After the charging switch 112 closes, the energy storage capacitor 51 is charged through the charging voltage output by the voltage terminal 114. After the energy storage capacitor 51 is charged, the voltage obtained by charging can pull down the voltage of the first control terminal after the flyback switch tube 13 enters the next control cycle, so as to reduce the conduction current of the flyback switch tube 13.

[0100] It should be noted that Figure 3 - Figure 11 only exemplary examples of the detection unit and the buck unit are given. It should be understood that the specific implementation of the detection unit and the buck unit may include but is not limited to Figure 3 - Figure 11 shown.

[0101] The present application also provides a flyback power supply circuit, which includes the protection circuit in the above example. The specific structure of this flyback power supply circuit may include but is not limited to Figure 3 - Figure 11 shown.

[0102] The present application also provides a circuit board, which includes the flyback power supply circuit in the above examples. Among them, the circuit board can be an independent circuit board or a circuit board formed by splicing multiple circuit boards.

[0103] The above content is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A protection circuit, characterized in that: Applied to a flyback power supply circuit, the primary side of the transformer of the flyback power supply circuit is provided with a flyback switch tube, and the protection circuit includes a detection unit and a step-down unit; The detection unit is connected to the primary side of the transformer and the step-down unit, and is used to send a trigger signal to the step-down unit when an abnormal peak voltage is detected on the primary side of the transformer; The step-down unit is connected to the first control end of the flyback switch tube, and is used to pull down the voltage of the first control end when the flyback switch tube is turned on after receiving the trigger signal, so as to reduce the conduction current of the flyback switch tube.

2. The protection circuit according to claim 1, characterized in that: The step-down unit includes a control circuit and a step-down switch tube; The control circuit is connected to the detection unit and the second control end of the buck switch tube, and is used to control the buck switch tube to be turned on when the flyback switch tube is turned on after receiving the trigger signal; One connection end of the step-down switch tube is grounded, and the other connection end is connected to the first control end, and is used to pull down the voltage of the first control end after being turned on.

3. The protection circuit according to claim 2, characterized in that: The control circuit includes an energy storage capacitor; The detection unit is connected to the energy storage capacitor and is used to control the energy storage capacitor to charge when the abnormal peak voltage appears on the primary side of the transformer; The energy storage capacitor is connected to the second control end, and is used for controlling the buck switch tube to be turned on through a voltage obtained by charging when the flyback switch tube is turned on.

4. The protection circuit according to claim 3, characterized in that: The detection unit includes a voltage conversion circuit; The voltage conversion circuit is connected to the primary side of the transformer and the energy storage capacitor, and is used to convert the abnormal peak voltage when the abnormal peak voltage appears on the primary side of the transformer, so as to charge the energy storage capacitor with the voltage obtained by the conversion.

5. The protection circuit according to claim 4, characterized in that: The voltage conversion circuit includes a first voltage regulator tube and a second voltage regulator tube connected in series between the primary side of the transformer and a grounding point, and a connection node between the first voltage regulator tube and the second voltage regulator tube is connected to the energy storage capacitor.

6. The protection circuit according to claim 4, characterized in that: The voltage conversion circuit includes two resistors connected in series between the primary side of the transformer and a grounding point, and a connection node between the two resistors is connected to the energy storage capacitor.

7. The protection circuit according to claim 5 or 6, characterized in that: The voltage conversion circuit also includes a third voltage regulator tube; The cathode of the third voltage-stabilizing tube is connected to the connection node, and the anode of the third voltage-stabilizing tube is connected to the energy storage capacitor.

8. The protection circuit according to claim 4, characterized in that: The voltage conversion circuit includes a fourth voltage regulator tube; The cathode of the fourth voltage regulator tube is connected to the primary side of the transformer, and the anode of the fourth voltage regulator tube is connected to the energy storage capacitor.

9. The protection circuit according to claim 2, characterized in that: The voltage reduction unit includes a discharge resistor; One end of the discharge resistor is connected to the second control end, and the other end is grounded.

10. A flyback power supply circuit, characterized in that: It comprises an amplifying module, a flyback switch tube, a transformer primary side and a transformer secondary side coupled to each other, and a protection circuit as claimed in any one of claims 1 to 9; The output end of the amplifying module is connected to the first control end of the flyback switch tube; The first connection end of the flyback switch tube is connected to the output end of the primary side of the transformer, and the second connection end is grounded; The input end of the protection circuit is connected to the primary side of the transformer, and the output end of the protection circuit is connected to the first control end.

11. The flyback power supply circuit according to claim 10, characterized in that: The flyback power supply circuit further includes an input circuit, an input end of the input circuit is connected to an input voltage, and an output end of the input circuit is connected to an input end of the primary side of the transformer.

12. The flyback power supply circuit according to claim 10, characterized in that: The flyback power supply circuit also includes an output capacitor connected to the voltage output terminal of the secondary side of the transformer.

13. The flyback power supply circuit according to any one of claims 10 to 12, characterized in that: The flyback power supply circuit also includes an output voltage regulator tube, and the output voltage regulator tube is connected to the voltage output end of the secondary side of the transformer.

14. A circuit board, characterized in that: The invention comprises a flyback power supply circuit as claimed in any one of claims 10 to 13.

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