Flyback converter control method and flyback converter

Abstract

The invention provides a flyback converter control method and a flyback converter, and the control method comprises the steps: obtaining a sampling signal representing the discharge current of a first capacitor during the conduction period of a second switching tube when the flyback converter operates; according to the sampling signal and the threshold signal, the second switching tube is controlled to be turned off, and the flyback converter is controlled to enter a discharging stage; wherein in the discharging stage, the first switching tube is switched off, and the second switching tube is intermittently switched on, so that the first capacitor is intermittently discharged. In the invention, as long as the resonance current exceeds the safety current, the system can immediately respond to the protection device and enter the discharge stage, so as to control the resonance current within the safety current. The control method provided by the invention can be suitable for any transient working condition, the magnitude of the resonance current can be effectively controlled under any transient working condition, and the safety of the device and the reliability of the system are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of switching power supplies, and in particular relates to a control method of a flyback converter and a flyback converter. Background Art

[0002] Asymmetric half-bridge flyback converter Figure 1 and Figure 2 There are two implementation methods. Under certain transient conditions, there is a large voltage difference between the voltage of the resonant capacitor C1 and the secondary side refracted voltage N*Vo. When the second switch tube Q2 is turned on, the resonant current i of the resonant capacitor C1 is LK If the voltage is too large, the current and voltage stress of the system components will exceed the specifications, which will cause damage and failure of the system components.

[0003] For example, when the power is turned off, the charge on the resonant capacitor C1 is not completely discharged. When the power is turned on again, there is a large voltage difference between the voltage of the resonant capacitor C1 and the secondary side refracted voltage N*Vo. Therefore, during the conduction period of the second switch tube Q2, a large resonant current i is generated when the leakage inductance Lk and the resonant capacitor C1 resonate. LK , such as Figure 3 As shown. The resonant current i LK The current and voltage stress specifications of the second switch tube Q2 and the rectifier tube D1 may be exceeded, causing them to fail. For another example, when the system is powered on and there is output, when the output capacitor C2 is short-circuited, there is a large voltage difference between the voltage of the resonant capacitor C1 and the secondary side refracted voltage N*Vo. Therefore, during the conduction period of the second switch tube Q2, the resonant capacitor C1 and the leakage inductance Lk will also resonate and produce the following Figure 3 The larger resonant current i LK , which can damage the system components. Figure 4 As shown, the active clamp flyback converter may also have a problem of excessive resonant current under the above transient conditions, which may damage system components. For example, when restarting after shutdown or when the output is short-circuited, the clamping capacitor Cclamp and the leakage inductance Lk may also generate a large resonant current when the second switch tube Q2 is turned on, thereby damaging system components.

[0004] Taking the asymmetric half-bridge flyback converter as an example, in order to solve the problem that the charge of the resonant capacitor C1 is not discharged when shutting down, resulting in excessive resonant current during restart and damaging system components, the prior art proposes to control the second switch tube Q2 to be intermittently turned on before restarting to transfer the energy of the resonant capacitor C1 to the output end and the input bus end. In addition, in order to solve the problem that the resonant current is too large and damages the system components when the output of the asymmetric half-bridge flyback converter is short-circuited, the prior art proposes to detect the resonant current, and when the resonant current is greater than the set threshold, the second switch tube Q2 is immediately turned off, thereby avoiding excessive resonant current and damaging the system components.

[0005] Obviously, the scheme of controlling the intermittent conduction of the second switch tube Q2 before restarting is only applicable to the condition of restarting after shutting down. Similarly, the scheme of controlling the second switch tube Q2 to turn off according to the magnitude of the resonant current is only applicable to the condition of output short circuit during operation, and is not applicable to the condition of restarting after shutting down. Because when the system is powered on and started, the second switch tube Q2 is controlled to turn off when the resonant current is too large, which will cause the resonant capacitor C1 to charge more than discharge in each switching cycle, making the voltage of the resonant capacitor C1 higher and higher, and eventually causing the system to fail to start.

[0006] In summary, the solutions proposed by the prior art for different transient conditions are not applicable to all transient conditions. Therefore, there is currently a lack of technical solutions applicable to all transient conditions that cause a large voltage difference between the voltage of the resonant capacitor (clamping capacitor) and the secondary side refracted voltage to solve the problem of system component damage. Summary of the invention

[0007] In order to solve the problem that the prior art lacks a technical solution applicable to all transient conditions that cause a large voltage difference between the voltage of the resonant capacitor (clamping capacitor) and the secondary side refracted voltage, and to solve the technical problem of damage to system components, the present invention proposes a control method of a flyback converter and a flyback converter, the control method comprising:

[0008] When the flyback converter is running, during the period when the second switch tube is turned on, obtaining a sampling signal representing the discharge current of the first capacitor;

[0009] According to the sampling signal and the threshold signal, the second switch tube is controlled to be turned off, and the flyback converter is controlled to enter a discharge phase;

[0010] Wherein, during the discharge phase, the first switch tube is turned off, and the second switch tube is intermittently turned on to make the first capacitor discharge intermittently, and the threshold signal represents a safe current.

[0011] Furthermore, the intermittent discharge of the first capacitor includes the steps of: acquiring the sampling signal when the first capacitor is discharging, and controlling the first capacitor to stop discharging according to the sampling signal and the threshold signal.

[0012] Furthermore, when the discharge current represented by the sampling signal exceeds the safety current, the first capacitor is controlled to stop discharging, and the first capacitor is controlled to discharge again after a set time.

[0013] Furthermore, when the maximum value of the discharge current represented by the sampling signal is within the safety current, the flyback converter exits the discharge phase and operates normally.

[0014] Furthermore, during the intermittent conduction period of the second switch tube, the conduction time of the second switch tube gradually increases.

[0015] Furthermore, when the discharge current represented by the sampling signal exceeds the safety current, the second switch tube is controlled to be turned off, and the flyback converter is controlled to enter a discharge phase.

[0016] A flyback converter comprises a transformer, a first switch tube and a second switch tube located on the primary side of the transformer and connected between an input terminal of the flyback converter and a reference ground, and a first capacitor and a first inductor forming a resonant circuit when the second switch tube is in a conducting state, and further comprises:

[0017] a sampling circuit for sampling a sampling signal representing a discharge current of the first capacitor during a period in which the second switch tube is turned on when the flyback converter is in operation;

[0018] A control circuit, according to the sampling signal and the threshold signal, controls the second switch tube to turn off and controls the flyback converter to enter a discharge phase;

[0019] Wherein, during the discharge phase, the first switch tube is turned off, and the second switch tube is intermittently turned on to make the first capacitor discharge intermittently, and the threshold signal represents a safe current.

[0020] Furthermore, in the discharging stage, when the first capacitor is discharging, the control circuit controls the second switch tube to be turned off according to the sampling signal and the threshold signal to stop the first capacitor from discharging.

[0021] Furthermore, when the discharge current represented by the sampling signal exceeds the safety current, the control circuit controls the second switch tube to be turned off, and controls the second switch tube to be turned on after a set time to discharge the first capacitor.

[0022] Furthermore, when the maximum value of the discharge current represented by the sampling signal is within the safety current, the control circuit controls the flyback converter to exit the discharge phase and operate normally.

[0023] Furthermore, the sampling circuit includes a first sampling resistor, the first sampling resistor is connected in series in the resonant circuit, and the voltage of the first sampling resistor when the second switch tube is turned on represents the discharge current of the first capacitor.

[0024] In one embodiment, a second sampling resistor is further included, the first sampling resistor and the second sampling resistor are connected in series between the second switch tube and the reference ground of the flyback converter, when the first switch tube is turned on, current flows through the second sampling resistor, the sampling interface of the control circuit is connected to the first sampling resistor, and the reference ground interface of the control circuit is connected to the reference ground of the flyback converter.

[0025] In one embodiment, one end of the first sampling resistor is connected to the reference ground of the flyback converter, and when the first switch tube is turned on, current flows through the first sampling resistor, the reference ground interface of the control circuit is connected to the reference ground of the flyback converter, and the sampling interface of the control circuit is connected to the other end of the first sampling resistor.

[0026] In one embodiment, a second sampling resistor is further included, the first sampling resistor and the second sampling resistor are connected in series between the second switch tube and the reference ground of the flyback converter, when the first switch tube is turned on, current flows through the second sampling resistor, the first sampling interface of the control circuit is connected to one end of the first sampling resistor, the second sampling interface of the control circuit is connected to the reference ground of the flyback converter, and the reference ground interface of the control circuit is connected to the other end of the first sampling resistor.

[0027] The control scheme proposed in the present invention detects the resonant current in real time when the second switch tube is turned on to generate resonance, and controls the second switch tube to turn off when the resonant current exceeds the safe current, thereby avoiding the resonant current from being too large to damage the device. At the same time, the flyback converter enters the discharge stage, during which the first switch tube is continuously turned off and the second switch tube is intermittently turned on, so that the charge of the first capacitor is discharged until the maximum value of the resonant current is within the safe current. Therefore, during the operation process, the resonant current can be timely controlled to be below the safe current, so that the first capacitor voltage is close to the secondary side refracted voltage, so as to ensure the normal operation of the flyback converter and avoid damage to the system components. Obviously, in the present invention, as long as the resonant current exceeds the safe current when the flyback converter is running, the system can immediately respond to the protection device and enter the discharge stage, controlling the resonant current to be below the safe current to protect the system components from damage. Therefore, the control method proposed in the present invention can be applied to any transient working condition, and the resonant current can be effectively controlled in any transient working condition to ensure the safety of the device and the reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 and Figure 2 It is the structural diagram of the asymmetric half-bridge flyback converter;

[0029] Figure 3 It is the waveform diagram of the asymmetric half-bridge flyback converter when it is running;

[0030] Figure 4 is a structural diagram of an active clamp flyback converter;

[0031] Figure 5 A flow chart of the control method proposed by the present invention;

[0032] Figure 6 A waveform diagram of a flyback converter using the control method proposed by the present invention;

[0033] Figure 7 is a structural diagram of a flyback converter in the first embodiment;

[0034] Figure 8 is a structural diagram of a flyback converter in a second embodiment;

[0035] Fig. 9 FIG. 4 is a structural diagram of a flyback converter in the third embodiment. DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0037] As described in the background technology, in certain transient conditions, the resonant capacitor voltage or the clamped capacitor voltage of the asymmetric half-bridge flyback converter (AHB) and the active clamped flyback converter (ACF) may be greater than the secondary side refracted voltage. Therefore, when the primary side resonates, the resonant current will be too large, damaging the system components and reducing the reliability of the system. However, the solutions proposed in the prior art have certain defects, and the existing solutions can only solve the problems under a certain transient condition, and cannot be applied to all transient conditions. In view of the defects of the prior art, the present invention proposes a control method for a flyback converter, wherein:

[0038] The flyback converter includes a transformer, a first switch tube Q1 and a second switch tube Q2 located on the primary side of the transformer and connected between an input terminal Vin and a reference ground Gnd, and a first capacitor C1 and a first inductor Lk that form a resonant circuit when the second switch tube Q2 is turned on. Obviously, the flyback converter includes Figure 1 , Figure 2 and Figure 4 The asymmetric half-bridge flyback converter and active clamp flyback converter are shown.

[0039] Furthermore, the control method comprises the steps of:

[0040] The flyback converter is powered on and operates, and a sampling signal representing the discharge current of the first capacitor C1 is obtained when the second switch tube Q2 is turned on;

[0041] According to the sampling signal and the threshold signal, the second switch tube Q2 is controlled to be turned off and the flyback converter is controlled to enter the discharge stage. The threshold signal represents the safety current. When the current flowing through the second switch tube Q2 exceeds the safety current, the second switch tube is damaged.

[0042] Specifically, in the discharge phase, the first switch tube Q1 is turned off and the second switch tube Q2 is intermittently turned on, so that the first capacitor is discharged intermittently.

[0043] It can be seen that the control scheme proposed in the present invention detects the resonant current in real time when the second switch tube is turned on to generate resonance, and controls the second switch tube to turn off when the resonant current exceeds the safe current, thereby avoiding the resonant current from being too large to damage the device. At the same time, the flyback converter enters the discharge stage, and the first switch tube is continuously turned off and the second switch tube is intermittently turned on during the discharge stage, so that the charge of the first capacitor is discharged until the maximum value of the resonant current is within the safe current. Therefore, during the operation process, the resonant current can be controlled in time to be below the safe current, so that the first capacitor voltage is close to the secondary side refracted voltage, so as to ensure the normal operation of the flyback converter and avoid damage to the system components. Obviously, in the present invention, as long as the resonant current exceeds the safe current when the flyback converter is running, the system can immediately respond to the protection device and enter the discharge stage, and control the resonant current to be below the safe current to protect the system components from damage. Therefore, the control method proposed in the present invention can be applied to any transient working condition, and the resonant current can be effectively controlled in any transient working condition to ensure the safety of the device and the reliability of the system.

[0044] It should be noted that, during the period when the first switch tube is turned off and the second switch tube is turned on, the resonant circuit resonates, a resonant current is generated in the resonant circuit, and the discharge current of the first capacitor is equivalent to the resonant current.

[0045] Furthermore, if Figure 5 As shown, in order to avoid the situation where the resonant current of the asymmetric half-bridge flyback converter and the active clamp flyback converter is too large to damage the components during operation, the present invention proposes the following control method:

[0046] During the operation of the flyback converter, when the second switch tube Q2 is turned on, the discharge current of the first capacitor is detected, so as to obtain a sampling signal representing the discharge current, and compare the sampling signal with the threshold signal;

[0047] If the resonant current exceeds the safety current (i.e. the sampling signal is greater than the threshold signal), the second switch tube Q2 is controlled to be turned off immediately and the flyback converter is controlled to enter the discharge stage; if the discharge current is within the safety current (i.e. the sampling signal is less than or equal to the threshold signal), the flyback converter is controlled to operate normally, the energy at the input end is transferred to the output end to power the load, and the above operation is repeated.

[0048] Specifically, in the discharge phase, the first switch tube Q1 remains off, and the second switch tube Q2 is intermittently turned on. In the process of the second switch tube Q2 being intermittently turned on, the discharge current is detected when the second switch tube Q2 is turned on to obtain a sampling signal, and the threshold signal of the sampling signal is compared. When the discharge current exceeds the safe current (that is, the sampling signal is greater than or equal to the threshold signal), the second switch tube Q2 is controlled to be turned off to stop the first capacitor C1 from discharging, and after a set time, the second switch tube Q2 is controlled to be turned on again to discharge the first capacitor C1 again. Repeat the above steps until the maximum value of the resonant current is within the safe current (that is, the maximum value of the sampling signal is less than the threshold signal), exit the discharge phase, the flyback converter operates normally and repeats the above steps.

[0049] Specifically, Figure 6 As shown, assuming that the flyback converter starts to power on at time t0 (or, time t0 is a certain time when the flyback converter is running), the PWM drive signal first drives the first switch tube Q1 to turn on and the second switch tube Q2 to turn off, and the primary winding stores energy, and then the PWM drive signal drives the first switch tube Q1 to turn off and the second switch tube Q2 to turn on, and the primary winding transfers energy to the secondary side. At the same time, when the first switch tube Q1 is turned off and the second switch tube Q2 is turned on, the discharge current iLK of the first capacitor C1 is collected in real time. At time t1, iLK is greater than the safety current iref, and the second switch tube Q2 is controlled to turn off immediately, and the flyback converter is controlled to enter the discharge stage. In the discharge stage, the first switch tube Q1 is controlled to be continuously turned off and the second switch tube Q2 is intermittently turned on. Specifically, at time t2, the first switch tube Q1 is controlled to be turned off and the second switch tube Q2 is turned on, and the discharge current iLK of the first capacitor C1 is collected in real time when the second switch tube Q2 is turned on. At t3, iLK is greater than the safety current iref, and the second switch tube Q2 is controlled to be turned off immediately. After a certain period of time, at t4, the first switch tube Q1 is controlled to be turned off and the second switch tube Q2 is turned on, and the discharge current iLK of the first capacitor C1 is collected in real time when the second switch tube Q2 is turned on. At t5, the maximum value of iLK is less than the safety current iref, then at t6, the second switch tube Q2 exits the discharge stage after the conduction ends, and the flyback converter starts to operate normally and repeats the above operation. In the discharge stage, as the voltage of the first capacitor C1 decreases, the duration of the conduction of the second switch tube Q2 gradually increases. Specifically, at t6, the first switch tube Q1 is driven to be turned on and the second switch tube Q2 is turned off, and the primary winding stores energy. At time t7, the first switch tube Q1 is turned off and the second switch tube Q2 is turned on. The primary winding transfers energy to the secondary side, and iLK is sampled when the second switch tube Q2 is turned on. At this time, iLK is less than iref. The operation is repeated until iLK is greater than iref, and the above operation is repeated again to enter the discharge stage.

[0050] It should be noted that in this field, the resonant current is usually obtained by collecting the voltage of the sampling resistor. Depending on the setting of the sampling resistor, the voltage of the sampling resistor may be positive voltage sampling or negative voltage sampling. Figure 5 In the shown flowchart and Figure 6 In the shown waveform diagram, the sampling signal takes positive voltage sampling as an example, and the corresponding threshold signal is also set to a positive voltage value. Therefore, the resonant current exceeding the safe current is equivalent to the sampling signal being greater than the threshold signal, and the resonant current being within the safe current is equivalent to the sampling signal being less than or equal to the threshold signal. However, when the sampling resistor is set for negative voltage sampling and the threshold signal is correspondingly set to a negative voltage value, the resonant current exceeding the safe current is equivalent to the sampling signal being less than the threshold signal, and the resonant current being within the safe current is equivalent to the sampling signal being greater than or equal to the threshold signal. Therefore, Figure 5 and Figure 6 This is just a schematic of positive voltage sampling of the sampling signal, and does not represent a limitation on the judgment condition for whether the resonant current exceeds the safe current.

[0051] In summary, once the flyback converter operates, during the conduction period of the second switching transistor Q2, the resonant current is detected in real time. As long as the resonant current exceeds the safe current, the first switching transistor Q1 is immediately controlled to continuously turn off and the second switching transistor Q2 is intermittently turned on, so that the amplitude of the resonant current decays to within the safe current, avoiding damage to system components and ensuring the normal operation of the flyback converter thereafter.

[0052] Correspondingly, the present invention also proposes a flyback converter, including: a transformer, a first switching transistor Q1 and a second switching transistor Q2 located on the primary side of the transformer and connected between the input terminal Vin and the reference ground GND, a first capacitor C1 and a first inductor Lk that form a resonant circuit in the conduction state of the second switching transistor Q2, and further including:

[0053] a sampling circuit that samples a sampling signal representing the discharge current of the first capacitor C1 during the conduction period of the second switching transistor Q2 when the flyback converter operates;

[0054] a control circuit that controls the second switching transistor Q2 to turn off and controls the flyback converter to enter a discharge stage according to the sampling signal and the threshold signal, where the threshold signal represents the safe current;

[0055] wherein, during the discharge stage, the first switching transistor Q1 remains off and the second switching transistor Q2 is intermittently turned on.

[0056] Specifically, taking an asymmetrical half-bridge flyback converter as an example, as Figure 7As shown, the sampling circuit includes a first sampling resistor Rcs1. When the first switch tube Q1 is turned on, the current flows through the first sampling resistor Rcs1, and the sampling resistor Rcs1 is connected in series in the resonant circuit. When the second switch tube Q2 is turned on, the current flows through the first sampling resistor Rcs1. One end of the first sampling resistor Rcs1 is connected to the reference ground of the flyback converter. The first sampling resistor Rcs1 is used to collect the primary current to output the sampling voltage Vcs1 when the first switch tube Q1 is turned on and the second switch tube Q2 is turned off. At the same time, the first sampling resistor Rcs1 is used to collect the resonant current (also the discharge current of the first capacitor C1) to output the sampling voltage Vcs2. The control circuit is provided with a sampling interface CS, which is connected to the other end of the first sampling resistor Rcs1, and the reference ground GND of the control circuit is connected to the reference ground of the flyback converter. In this embodiment, the sampling voltage Vcs2 is negative voltage sampling, and the corresponding threshold signal Vref can also be set to negative voltage. The control circuit receives the sampling voltage Vcs2, and when Vcs2 is less than Vref, controls the second switch tube Q2 to turn off immediately, and controls the flyback converter to enter the discharge stage. In the discharge stage, the control circuit controls the first switch tube Q1 to remain off, and the second switch tube Q2 to be intermittently turned on. In the process of the second switch tube Q2 being intermittently turned on, when the second switch tube Q2 is turned on, the control circuit controls the second switch tube Q2 to turn off to stop the first capacitor C1 from discharging when Vcs2 is less than Vref, and controls the second switch tube Q2 to be turned on again after a set time to discharge the first capacitor C1 again. Repeat the above steps of the second switch tube Q2 being intermittently turned on until the minimum value of Vcs2 is greater than Vref, exit the discharge stage, and the control circuit outputs a drive signal to control the flyback converter to operate normally, and repeats the above steps when the flyback converter operates normally. In this embodiment, Vcs2 and Vref are both set to negative voltages, but in practice, Vcs2 can also be processed by absolute value to make Vcs2 become positive voltage, then the corresponding Vref should be set to positive voltage. This embodiment does not limit the present solution.

[0057] In the second embodiment, if Figure 8As shown, the sampling circuit includes a first sampling resistor Rcs1 and a second sampling resistor Rcs2. The first sampling resistor Rcs1 and the second sampling resistor Rcs2 are connected in series between the second switching transistor Q2 and the reference ground of the flyback converter. The first sampling resistor Rcs1 is connected in series in the resonant circuit. When the first switching transistor Q1 is turned on, the current flows through the second sampling resistor Rcs2. The second sampling resistor Rcs2 is used to collect the primary current to output a sampling voltage Vcs2 when the first switching transistor Q1 is turned on and the second switching transistor Q2 is turned off. The first sampling resistor Rcs1 is used to collect the resonant current (which is also the discharge current of the first capacitor C1) to output a sampling voltage Vcs1. The control circuit (Controller) is provided with a sampling interface CS. The sampling interface CS is connected to the first sampling resistor Rcs1. The first sampling resistor Rcs1 and the second sampling resistor Rcs2 share this sampling interface. The reference ground GND of the control circuit is connected to the reference ground of the flyback converter. In this embodiment, the sampling voltage Vcs2 is a positive voltage sampling. The control circuit receives the sampling voltage Vcs2. When Vcs2 is greater than Vref, the control circuit immediately turns off the second switching transistor Q2 and controls the flyback converter to enter the discharge stage. During the discharge stage, the control circuit controls the first switching transistor Q1 to remain off and the second switching transistor Q2 to conduct intermittently. And during the intermittent conduction of the second switching transistor Q2, when the control circuit is in the state that Vcs2 is greater than Vref during the conduction of the second switching transistor Q2, the control circuit turns off the second switching transistor Q2 to stop the discharge of the first capacitor C1, and after a set time period, the control circuit controls the second switching transistor Q2 to conduct again to make the first capacitor C1 discharge again. Repeat the above steps of the intermittent conduction of the second switching transistor Q2 until the maximum value of Vcs2 is less than Vref, then exit the discharge stage. The control circuit outputs a drive signal to control the normal operation of the flyback converter, and repeats the above steps when the flyback converter is operating normally.

[0058] In the third embodiment, as Fig. 9 shown, the sampling circuit includes a first sampling resistor Rcs1 and a second sampling resistor Rcs2. The first sampling resistor Rcs1 and the second sampling resistor Rcs2 are connected in series between the second switching transistor Q2 and the reference ground of the flyback converter. The first sampling resistor Rcs1 is connected in series in the resonant circuit. When the first switching transistor Q1 is turned on, the current flows through the second sampling resistor Rcs2. The second sampling resistor Rcs2 is used to collect the primary current sampling voltage Vcs2 when the first switching transistor Q1 is turned on and the second switching transistor Q2 is turned off. The first sampling resistor Rcs1 is used to collect the resonant current (which is also the discharge current of the first capacitor C1) to output a sampling voltage Vcs1. The control circuit (Controller) is provided with two sampling interfaces. The first sampling interface CS1 is connected to the first sampling resistor Rcs1. The second sampling interface CS2 is connected to the reference ground of the flyback converter. The reference ground of the control circuit is connected to the first sampling resistor Rcs1. Similarly, the control circuit reference Figure 7The illustrated embodiments are not described in detail here.

[0059] In summary, when the flyback converter proposed in the present invention is in operation, the resonant current will be detected in real time during the conduction period of the second switch tube Q2. As long as the resonant current exceeds the safety current, the first switch tube Q1 will be immediately controlled to be continuously turned off and the second switch tube Q2 will be intermittently turned on, so that the amplitude of the resonant current is reduced to within the safety current, thereby avoiding damage to system components and ensuring the normal operation of the flyback converter thereafter.

[0060] It should be noted that the above sampling circuit takes an asymmetric half-bridge flyback circuit as an example, but those skilled in the art can also apply the above sampling circuit to an active clamp flyback circuit.

[0061] It should be noted that the specific implementation and corresponding illustrations given are merely a way of describing the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Various changes or modifications can be made to these implementation schemes without departing from the principle and essence of the present invention, but these changes and modifications fall within the scope of protection of the present invention.

[0062] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0063] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A control method for a flyback converter, the flyback converter comprising a transformer, a first switch tube and a second switch tube located at a primary side of the transformer and connected between an input terminal of the flyback converter and a reference ground, and a first capacitor and a first inductor forming a resonant circuit when the second switch tube is in a conducting state, characterized in that: The control method comprises: When the flyback converter is running, during the period when the second switch tube is turned on, obtaining a sampling signal representing the discharge current of the first capacitor; According to the sampling signal and the threshold signal, the second switch tube is controlled to be turned off, and the flyback converter is controlled to enter a discharge phase; Wherein, during the discharge phase, the first switch tube is turned off, and the second switch tube is intermittently turned on to make the first capacitor discharge intermittently, and the threshold signal represents a safe current.

2. The control method according to claim 1, characterized in that: The intermittent discharge of the first capacitor includes the steps of: acquiring the sampling signal when the first capacitor is discharging, and controlling the first capacitor to stop discharging according to the sampling signal and the threshold signal.

3. The control method according to claim 2, characterized in that: When the discharge current represented by the sampling signal exceeds the safety current, the first capacitor is controlled to stop discharging, and the first capacitor is controlled to discharge again after a set time.

4. The control method according to claim 2 or 3, characterized in that: When the maximum value of the discharge current represented by the sampling signal is within the safety current, the flyback converter exits the discharge phase and operates normally.

5. The control method according to claim 1, characterized in that: During the intermittent conduction period of the second switch tube, the conduction time of the second switch tube gradually increases.

6. The control method according to claim 1, characterized in that: When the discharge current represented by the sampling signal exceeds the safety current, the second switch tube is controlled to be turned off, and the flyback converter is controlled to enter a discharge phase.

7. A flyback converter, comprising a transformer, a first switch tube and a second switch tube located on the primary side of the transformer and connected between the input terminal of the flyback converter and a reference ground, and a first capacitor and a first inductor forming a resonant circuit when the second switch tube is in a conducting state, characterized in that: Also includes: a sampling circuit for sampling a sampling signal representing a discharge current of the first capacitor during a period in which the second switch tube is turned on when the flyback converter is in operation; A control circuit, according to the sampling signal and the threshold signal, controls the second switch tube to turn off and controls the flyback converter to enter a discharge phase; Wherein, during the discharge phase, the first switch tube is turned off, and the second switch tube is intermittently turned on to make the first capacitor discharge intermittently, and the threshold signal represents a safe current.

8. The flyback converter according to claim 7, characterized in that: In the discharging stage, when the first capacitor is discharging, the control circuit controls the second switch tube to be turned off according to the sampling signal and the threshold signal to stop the first capacitor from discharging.

9. The flyback converter according to claim 8, characterized in that: When the discharge current represented by the sampling signal exceeds the safety current, the control circuit controls the second switch tube to turn off, and controls the second switch tube to turn on after a set time to discharge the first capacitor.

10. The flyback converter according to claim 8 or 9, characterized in that: When the maximum value of the discharge current represented by the sampling signal is within the safety current, the control circuit controls the flyback converter to exit the discharge phase and operate normally.

11. The flyback converter according to claim 7, characterized in that: The sampling circuit includes a first sampling resistor, which is connected in series in the resonant circuit. When the second switch tube is turned on, the voltage of the first sampling resistor represents the discharge current of the first capacitor.

12. The flyback converter according to claim 11, characterized in that: It also includes a second sampling resistor, the first sampling resistor and the second sampling resistor are connected in series between the second switch tube and the reference ground of the flyback converter, when the first switch tube is turned on, current flows through the second sampling resistor, the sampling interface of the control circuit is connected to the first sampling resistor, and the reference ground interface of the control circuit is connected to the reference ground of the flyback converter.

13. The flyback converter according to claim 11, characterized in that: One end of the first sampling resistor is connected to the reference ground of the flyback converter, and when the first switch tube is turned on, current flows through the first sampling resistor, the reference ground interface of the control circuit is connected to the reference ground of the flyback converter, and the sampling interface of the control circuit is connected to the other end of the first sampling resistor.

14. The flyback converter according to claim 11, wherein: It also includes a second sampling resistor, the first sampling resistor and the second sampling resistor are connected in series between the second switch tube and the reference ground of the flyback converter, when the first switch tube is turned on, current flows through the second sampling resistor, the first sampling interface of the control circuit is connected to one end of the first sampling resistor, the second sampling interface of the control circuit is connected to the reference ground of the flyback converter, and the reference ground interface of the control circuit is connected to the other end of the first sampling resistor.

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