Flyback converter control device and method, flyback converter and power supply system

Abstract

The invention provides a flyback converter control device and method, a flyback converter and a power supply system. The control device is used for applying adjusting voltage or adjusting current to a connection point where the secondary winding is connected with the synchronous rectifier tube in a preset duration after the synchronous rectifier tube is turned off and before the power switch tube is turned on; and after the regulating voltage or the regulating current is applied, a request signal for conducting the power switch tube is sent to the primary side controller, and the primary side controller controls the power switch tube to be conducted according to the received request signal. Zero-voltage conduction of the power switch tube can be realized, efficiency can be improved, temperature rise can be reduced, simplicity of a peripheral circuit can be kept, the size and cost of the flyback converter are well controlled, and the flyback converter is easy to implement.

Description

Technical Field

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

[0002] See also Figure 1 , which schematically shows a typical structural diagram of a flyback converter in the prior art. Figure 1 It can be seen that in the prior art, the flyback converter includes a transformer T, a power switch tube Q1, a synchronous rectifier tube SR, a secondary controller 200, a primary controller 100, and a capacitor C0. Among them, the first end (for example, the drain) DRAIN of the power switch tube Q1 is connected to one end of the primary winding Np of the transformer T, the second end (for example, the source) of the power switch tube Q1 is connected to the negative DC bus PGND, the other end of the primary winding Np of the transformer T is connected to the positive DC bus, and the synchronous rectifier tube SR is connected in series with the secondary winding Ns of the transformer T and connected between the output end and the ground end of the flyback converter. During operation, the primary controller 100 outputs a control signal Q1_C to the control end of the power switch tube Q1 to control the on and off of the power switch tube Q1; the secondary controller 200 outputs a control signal SR_C to the control end of the synchronous rectifier tube SR to control the on and off of the synchronous rectifier tube SR. When the primary controller 100 controls the power switch tube Q1 to be turned on, current flows through the primary winding of the transformer T and the power switch tube Q1, and energy is stored in the magnetic field of the transformer T. When the primary controller 100 controls the power switch tube Q1 to be turned off and the secondary controller 200 controls the synchronous rectifier tube SR to be turned on, the transformer T releases energy, so that current flows through the secondary winding of the transformer T and the synchronous rectifier tube SR, and the energy is stored in the capacitor C0, thereby providing an output voltage VOUT for the load 300. Before the power switch tube Q1 of the flyback converter is turned on, the voltage of its drain DRAIN is often not zero. Therefore, when it is turned on, there will be a large switching loss, resulting in a decrease in efficiency and an increase in temperature rise. For details, please refer to Figure 2 , which schematically gives Figure 1 The key waveform diagram of the flyback converter is shown in Figure 1. Figure 2 It can be seen that at time t1, the primary controller 100 controls the power switch tube Q1 to turn off, and then the secondary controller 200 controls the synchronous rectifier tube SR to turn on, and the secondary winding of the transformer T starts to continue current through the synchronous rectifying tube SR; at time t2, the secondary controller 200 controls the synchronous rectifier tube SR to turn off, the secondary winding demagnetization ends, and the drain DRAIN of the power switch tube Q1 and the connection point V_Forw where the secondary winding is connected to the synchronous rectifier tube both enter the oscillation state; at time t3, the primary controller 100 controls the power switch tube Q1 to turn on, from Figure 1It can be seen that at time t3, the voltage of the drain DRAIN of the power switch tube Q1 begins to drop, and the non-zero voltage is turned on. Therefore, when the power switch tube Q1 is turned on, there will be a large switching loss, resulting in a decrease in efficiency and an increase in temperature rise.

[0003] In order to reduce switching losses, improve efficiency and reduce temperature rise, the related technology adopts active-clamp forward (ACF), which connects active clamp circuits at both ends of the primary winding of the flyback converter in parallel to clamp the voltage of the drain of the power switch tube when the power switch tube is disconnected. Although this solution can be improved, the effect is limited; and it requires complex peripheral circuits and timing control, which has the disadvantages of increased cost and increased size of the flyback converter.

[0004] It should be noted that the information disclosed in the background technology section of the invention is only intended to deepen the understanding of the general background technology of the invention, and should not be regarded as an admission or suggestion in any form that the information constitutes prior art already known to those skilled in the art. Summary of the invention

[0005] The purpose of the present invention is to provide a flyback converter control device, method, flyback converter and power supply system to solve the problem of switching loss and efficiency reduction caused by non-zero voltage conduction of power switch tube in the prior art. The present invention realizes zero voltage switching (ZVS) of the power switch tube, which can not only improve efficiency, reduce temperature rise, keep the peripheral circuit simple and do not increase the volume of the flyback converter; but also has low cost and is easy to implement.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: a control device for a flyback converter, the flyback converter comprising a transformer, a power switch connected to a primary winding of the transformer, a primary controller connected to a control end of the power switch, and a synchronous rectifier connected to a secondary winding of the transformer; an input end of the control device is configured to be connected to an output end of the flyback converter, a first output end of the control device is configured to be connected to a control end of the synchronous rectifier, and a second output end of the control device is configured to be connected to a connection point where the secondary winding and the synchronous rectifier are connected;

[0007] The control device is configured to apply a regulating voltage or a regulating current to the connection point within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on; and after applying the regulating voltage or the regulating current, send a request signal for turning on the power switch tube to the primary side controller through the third output terminal of the control device;

[0008] The primary side controller is configured to control the power switch tube to be turned on according to the received request signal.

[0009] Optionally, the control device includes a secondary side control module, a power supply module and a sending module;

[0010] The input end of the secondary side control module is configured to be connected to the input end of the control device, the first output end of the secondary side control module is connected to the first output end of the control device, the second output end of the secondary side control module is connected to the input end of the power module, the output end of the power module is connected to the second output end of the control device, the third output end of the secondary side control module is connected to the input end of the sending module, and the output end of the sending module is connected to the third output end of the control device;

[0011] The power module is configured to apply the regulated voltage or the regulated current to the connection point within a preset time after the synchronous rectifier tube is turned off and before the power switch tube is turned on;

[0012] The secondary side control module is configured to output a primary side conduction signal to the sending module after the power supply module completes applying the regulated voltage or the regulated current;

[0013] The sending module is configured to send a request signal for turning on the power switch tube to the primary side controller according to the primary side conduction signal.

[0014] Optionally, the secondary side control module is configured to detect the voltage of the connection point by using a voltage detection method, and obtain the starting time when the power supply module applies the regulated voltage or the regulated current according to the voltage of the connection point.

[0015] Optionally, the secondary side control module is configured to use the time when the peak voltage of the voltage at the connection point is located as the starting time when the power supply module applies the regulated voltage or the regulated current.

[0016] Optionally, the power supply module includes a charge pump, one of the input ends of the charge pump is connected to the secondary side control module, the other input end of the charge pump is connected to the output end of the flyback converter, and the output end of the charge pump is connected to the second output end of the control device;

[0017] The charge pump is configured to apply the regulating voltage or the regulating current to the connection point within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on, according to the output voltage of the flyback converter.

[0018] Optionally, the control device is integrated into a control circuit chip.

[0019] In order to achieve the above object, the present invention further provides a control method for a flyback converter, wherein the flyback converter comprises a transformer, a power switch tube connected to a primary winding of the transformer, a primary controller connected to a control end of the power switch tube, and a synchronous rectifier tube connected to a secondary winding of the transformer; the control method comprises:

[0020] Applying a regulating voltage or a regulating current to a connection point between the secondary winding and the synchronous rectifier tube within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on;

[0021] After applying the regulating voltage or the regulating current, sending a request signal for turning on the power switch tube to the primary side controller;

[0022] The primary side controller controls the power switch tube to be turned on according to the received request signal.

[0023] Optionally, a voltage detection method is used to detect the voltage of the connection point, and the starting time of applying the adjustment voltage or the adjustment current is obtained according to the voltage of the connection point.

[0024] In order to achieve the above-mentioned purpose, the present invention also provides a flyback converter, which includes a transformer, a power switch tube connected to the primary winding of the transformer, a primary controller connected to the control end of the power switch tube, and a synchronous rectifier tube connected to the secondary winding of the transformer; and the flyback converter adopts the above-mentioned flyback converter control method to achieve zero voltage conduction of the power switch tube, and / or includes a control device of the flyback converter described in any of the above items; wherein the input end of the control device is connected to the output end of the flyback converter, the first output end of the control device is connected to the control end of the synchronous rectifier tube, and the second output end of the control device is connected to the connection point where the secondary winding is connected to the synchronous rectifier tube.

[0025] Optionally, the source of the synchronous rectifier is grounded, the drain of the synchronous rectifier is connected to the opposite end of the secondary winding, and the output end of the power module of the control device is connected between the opposite end of the secondary winding and the drain of the synchronous rectifier;

[0026] Or the source of the synchronous rectifier is connected to the second end of the secondary winding at a connection point, the output end of the power module is configured to be connected to the connection point, and the drain of the synchronous rectifier is commonly connected to the output end of the flyback converter.

[0027] Optionally, the flyback converter further includes a first capacitor, one end of the first capacitor is connected to the output end of the flyback converter, and the other end of the first capacitor is grounded.

[0028] Optionally, the flyback converter also includes a rectifier circuit; the input end of the rectifier circuit is connected to an AC power supply, the first output end of the rectifier circuit is connected to the first end of the primary winding of the transformer, the second end of the primary winding of the transformer is connected to the first end of the power switch, and the second output end of the rectifier circuit is connected to the second end of the power switch.

[0029] Optionally, the flyback converter further includes an energy absorption circuit, and the energy absorption circuit is connected in parallel with two ends of the primary winding of the transformer.

[0030] In order to achieve the above object, the present invention further provides a power supply system, which includes the flyback converter described in any one of the above items.

[0031] Compared with the prior art, the control device and method of the flyback converter, the flyback converter and the power supply system provided by the present invention have the following beneficial effects:

[0032] The control device of the flyback converter provided by the present invention applies a regulating voltage or injects a regulating current to the connection point where the secondary winding is connected to the synchronous rectifier tube within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on, so that the current flowing through the secondary winding increases, and then the voltage of the drain of the power switch tube decreases, and after the application of the regulating voltage or the regulating current is completed, a request signal for turning on the power switch tube is sent to the primary controller through the third output terminal of the control device, and the primary controller controls the power switch tube to turn on according to the received request signal. Therefore, the control device of the flyback converter provided by the present invention can realize zero-voltage turn-on of the power switch tube, which can not only improve efficiency and reduce temperature rise, but also keep the peripheral circuit simple, well control the volume and cost of the control device of the flyback converter, and is easy to implement.

[0033] Since the control method, flyback converter and power supply system of the flyback converter provided by the present invention and the control device of the flyback converter provided by the present invention belong to the same inventive concept, the control method, flyback converter and power supply system of the flyback converter provided by the present invention at least have all the advantages of the control device of the flyback converter provided by the present invention. In order to avoid redundancy, they will not be described one by one here. For more details, please refer to the relevant description of the beneficial effects of the control device of the flyback converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a typical structural schematic diagram of a flyback converter in the prior art;

[0035] Figure 2 for Figure 1Schematic diagram of key waveforms of the flyback converter shown;

[0036] Figure 3 It is a structural schematic diagram of a flyback converter having a control device provided by the present invention;

[0037] Figure 4 A specific example diagram of a flyback converter having a control device provided in one embodiment of the present invention;

[0038] Figure 5 for Figure 4 Schematic diagram of key waveforms of the flyback converter shown in;

[0039] Figure 6 A specific example diagram of a flyback converter having a control device provided in another embodiment of the present invention;

[0040] Figure 7 A schematic flow chart of a control method for a flyback converter provided by an embodiment of the present invention;

[0041] Figure 8 FIG. 1 is another specific example diagram of a flyback converter having a control device provided in an embodiment of the present invention;

[0042] The reference numerals are described as follows:

[0043] Transformer-T, power switch tube-Q1, synchronous rectifier tube-SR, capacitor-C0, primary winding-Np, secondary winding-Ns, primary controller-100, secondary controller-200, bus voltage-VBUS, load-300, output voltage-VOUT, rectifier circuit-U, connection point-V_Forw;

[0044] Control device-400, control circuit chip-410, secondary side control module-411, power module-412, transmission module-413;

[0045] Isolator - 500;

[0046] A first capacitor-C1, a second capacitor-C2, a third capacitor-C3, a resistor-R, and a diode-D. DETAILED DESCRIPTION

[0047] In order to make the purpose, advantages and features of the present invention clearer, the control device, method, flyback converter and power supply system of the flyback converter proposed by the present invention are further described in detail below in conjunction with the accompanying drawings. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. It should be understood that the drawings in the specification do not necessarily show the specific structure of the present invention in proportion, and the illustrative features used to illustrate certain principles of the present invention in the drawings in the specification will also adopt a slightly simplified drawing method. The specific design features of the present invention disclosed herein include, for example, specific dimensions, directions, positions and shapes, which will be determined in part by the specific application and use environment. And, in the embodiments described below, sometimes the same figure mark is used in common between different drawings to represent the same part or the part with the same function, and its repeated description is omitted. In this specification, similar numbers and letters are used to represent similar items, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings. It should be understood that when an element is referred to as "connected to" or "coupled to" other elements, it can be directly connected to other elements, or there can be intermediate elements. In contrast, when an element is referred to as being “directly connected to” another element, there are no intervening elements present.

[0048] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0049] Where appropriate, these terms used in this manner are interchangeable. Similarly, if the method described herein includes a series of steps, the order in which these steps are presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described may be omitted and / or some other steps not described herein may be added to the method.

[0050] The core idea of ​​the present invention is to provide a control device, method, flyback converter and power supply system of a flyback converter to achieve zero voltage conduction of the power switch tube of the flyback converter, while improving efficiency and reducing temperature rise, keeping the peripheral circuit simple, and well controlling the cost and volume of the flyback converter.

[0051] In order to realize the above idea, one embodiment of the present invention provides a control device for a flyback converter. Figure 3 , Figure 3 FIG. 1 is a specific example diagram of a flyback converter having a control device provided in one embodiment of the present invention. Figure 3It can be seen that the flyback converter includes a transformer T, a power switch tube Q1 connected to the primary winding Np of the transformer T, a primary controller 100 connected to the control end of the power switch tube Q1, and a synchronous rectifier tube SR connected to the secondary winding Ns of the transformer T. One end of the primary winding Np of the transformer T is connected to the first end of the power switch tube Q1, the other end of the primary winding Np of the transformer T is connected to the positive DC bus, the second end of the power switch tube Q1 is connected to the negative DC bus, wherein the negative DC bus can be grounded, and one end of the secondary winding Ns of the transformer T is connected to the synchronous rectifier tube at a connection point V_Forw. In particular, the input end of the control device 400 is configured to be connected to the output end of the flyback converter, the first output end of the control device 400 is configured to be connected to the control end of the synchronous rectifier tube SR, and the second output end of the control device 400 is configured to be connected to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR. The control device 400 is configured to: after the synchronous rectifier SR is turned off and before the power switch Q1 is turned on, the preset time length (the preset time length can be obtained according to the parameters of the relevant functional components of the flyback converter, the voltage of the connection point V-Forw, or the output voltage of the flyback converter and other relevant parameters, such as Figure 5 The control device 400 applies a regulating voltage or a regulating current to the connection point V_Forw within the time length between the moment t3 and the moment t4 in the control device 400; and after applying the regulating voltage or the regulating current, sends a request signal for turning on the power switch tube Q1 to the primary controller 100 through the third output terminal of the control device 400; the primary controller 100 is configured to control the power switch tube Q1 to be turned on according to the received request signal. It should be noted that, in this embodiment, the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR can be any position on the wire connecting the secondary winding Ns and the synchronous rectifier tube SR. Preferably, the third output terminal of the control device 400 is configured to be connected to the input terminal of the isolator 500, and the output terminal of the isolator 500 is connected to the primary controller 100, for receiving the request signal and isolating the request signal and transmitting it to the primary controller 100.

[0052] The control device 400 of the flyback converter provided in this embodiment applies a regulating voltage or injects a regulating current to the connection point V_Forw within a preset time after the synchronous rectifier is turned off and before the power switch is turned on, so that the current flowing through the secondary winding Ns increases, thereby causing the voltage of the drain of the power switch Q1 to decrease, and after the application of the regulating voltage or the regulating current is completed, a request signal for turning on the power switch Q1 is sent to the primary controller 100 through the third output terminal of the control device 400; the primary controller 100 controls the power switch Q1 to turn on according to the received request signal. Therefore, the control device 400 of the flyback converter provided in this embodiment can realize the zero voltage turn-on of the power switch Q1, which can not only improve efficiency and reduce temperature rise, but also keep the peripheral circuit simple, well control the volume and cost of the flyback converter, and be easy to implement.

[0053] It should be noted that, based on the above-disclosed content, those skilled in the art should be able to understand that the basic principle of the flyback converter control device 400 provided by the present invention is as follows: before the power switch tube Q1 is turned on, the output voltage VOUT of the flyback converter can be detected. When it is determined that the output voltage VOUT of the flyback converter needs to be supplemented with energy, a voltage is applied or an input current is input at the connection point V_Forw, thereby causing the voltage at the first end (for example, the drain) of the power switch tube Q1 to drop, and after the application of the regulating voltage or the regulating current is completed (at this time, the voltage at the drain of the power switch tube Q1 has dropped to zero voltage or close to zero voltage), a request signal is sent, so that the primary side controller 100 controls the power switch tube Q1 to turn on, thereby reducing the switching loss of the power switch tube Q1 and reducing the temperature rise of the power switch tube Q1, thereby improving the efficiency of the flyback converter.

[0054] Preferably, in some of the exemplary embodiments, see Figure 4 , which schematically shows a specific example diagram of a flyback converter having a control device 400 provided in one embodiment of the present invention. Figure 4It can be seen that the control device 400 provided in these embodiments includes a secondary side control module 411 , a power module 412 and a sending module 413 . Specifically, the input end of the secondary control module 411 is configured to be connected to the input end of the control device 400, that is, the input end of the secondary control module 411 is configured to be connected to the output end of the flyback converter; the first output end of the secondary control module 411 is connected to the first output end of the control device 400, that is, the first output end of the secondary control module 411 is connected to the control end of the synchronous rectifier SR; the second output end of the secondary control module 411 is connected to the input end of the power supply module 412, and the output end of the power supply module 412 is connected to the second output end of the control device 400, that is, the output end of the power supply module 412 is connected to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier SR; the third output end of the secondary control module 411 is connected to the input end of the sending module 413, and the output end of the sending module 413 is connected to the third output end of the control device 400, that is, the output end of the sending module 413 is connected to the isolator 500. More specifically, the specific functions of the secondary side control module 411, the power module 412 and the sending module 413 are as follows:

[0055] The power supply module 412 is configured to apply the regulating voltage or the regulating current to the connection point V_Forw within a preset time period after the synchronous rectifier SR is turned off and before the power switch tube Q1 is turned on; that is, within the preset time period after the synchronous rectifier SR is turned off and before the power switch tube Q1 is turned on, the secondary side control module 411 controls the power supply module 412 to apply the regulating voltage or the regulating current to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier SR; the secondary side control module 411 is configured to output a primary side conduction signal to the sending module 413 after the power supply module 412 completes applying the regulating voltage or the regulating current; the sending module 413 is configured to send a request signal for turning on the power switch tube Q1 to the primary side controller 100 according to the primary side conduction signal. Specifically, the sending module 413 transmits the request signal to the primary controller 100 after isolation via the isolator 500; the secondary control module 411 is configured to control the synchronous rectifier SR to be turned on or off. In some embodiments, the secondary control module 411 is configured to control the power supply module 412 to apply the regulated voltage or the regulated current to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier SR within the preset time length.

[0056] Configured in this way, the control device 400 of the flyback converter provided in this embodiment includes a secondary control module 411, the power module 412 and the sending module 413, the power module 412 is used to provide a regulated voltage or a regulated current, and apply the regulated voltage or the regulated current to the output end of the secondary winding Ns within a preset time after the synchronous rectifier tube SR is turned off and before the power switch tube Q1 is turned on, and the secondary control module 411 outputs a primary side conduction signal to the sending module 413 after the power module 412 completes applying the regulated voltage or the regulated current, wherein the secondary control module 411 determines that the output end of the flyback converter needs to be supplemented with energy When the power supply module 412 is controlled to apply the regulating voltage or the regulating current to the output end of the secondary winding Ns within the preset time length, the sending module 413 sends the request signal according to the primary conduction signal, and the request signal is transmitted to the primary controller 100 via the isolator 500. This modular design method is more convenient for separately setting the secondary control module 411, the power supply module 412 and the sending module 413 related circuits and circuit elements according to the needs of actual applications, which can not only further enhance the applicability of the control device 400 of the flyback converter provided by the present invention, but also facilitate the maintenance of the control device 400 of the flyback converter provided by the present invention.

[0057] It should be noted that, as can be understood by those skilled in the art, the present invention does not limit the specific implementation of the secondary side control module 411, the power module 412 and the sending module 413. Specifically, the present invention does not limit the specific implementation of the secondary side control module 411, and the secondary side control module 411 includes but is not limited to being implemented by dedicated hardware, or can be implemented by a combination of dedicated hardware and computer instructions. Further, the present invention does not limit the specific type of the power module 412, and the power module 412 includes but is not limited to a voltage-to-voltage converter, a voltage-to-current converter, etc. In addition, the present invention does not limit the sending module 413 and the isolator 500, and the isolator 500 includes but is not limited to any one of an optocoupler device, an isolation capacitor, and a magnetic isolation device.

[0058] Preferably, in some exemplary embodiments, the control device 400 is integrated into a control circuit chip 410. Thus, not only the peripheral circuit of the flyback converter having the control device 400 is kept simple, and the cost and volume of the flyback converter are well controlled; but also the way of integrating the control device 400 into the control circuit chip 410 also makes it easier to deploy the control device 400 provided by the present invention on the flyback converter and to maintain the flyback converter having the control device 400.

[0059] Preferably, in one exemplary embodiment, the secondary side control module 411 is configured to detect the voltage of the connection point V_Forw by using a voltage detection method, and obtain the starting time when the power module 412 applies the regulating voltage or the regulating current according to the voltage of the connection point V_Forw.

[0060] Preferably, the control device 400 provided by the present invention further includes a sampling circuit (not shown in the figure) for collecting the output voltage VOUT of the flyback converter, and converting the collected output voltage VOUT into a sampling signal having a certain proportional relationship therewith and providing it to the secondary control module 411 to obtain the output voltage VOUT. In other embodiments, the sampling circuit is configured in the secondary control module 411. The secondary control module 411 receives the sampling signal and determines whether the output end of the flyback converter needs to be supplemented with energy. If necessary, the control power supply module 412 applies the regulated voltage or the regulated current to the output end of the secondary winding Ns within the preset time length, and outputs the primary conduction signal after completing the application of the regulated voltage or the regulated current.

[0061] Preferably, the control device 400 provided by the present invention also includes a voltage acquisition circuit for acquiring the voltage on the connection point V_Forw, and the secondary side control module 411 can obtain the starting time when the power module 412 applies the regulated voltage or the regulated current according to the voltage on the connection point V_Forw.

[0062] Preferably, the secondary control module 411 is configured such that after the synchronous rectifier SR is turned off, the first end of the power switch tube Q1 and the connection point V_Forw where the secondary winding is connected to the synchronous rectifier tube SR both enter an oscillation state, and the moment of the peak voltage at the connection point V_Forw can be used as the starting moment for the power module 412 to apply the regulated voltage or the regulated current. The power module 412 applies the regulated voltage or regulated current to the connection point V_Forw within a preset time period starting from the starting moment, so that the voltage of the first end DRAIN of the power switch tube Q1 is low, and then the secondary control module 411 generates a primary conduction signal and the sending module 413 sends a request signal according to the primary conduction signal, and the request signal is transmitted to the primary controller 100 via the isolator 500, so as to control the power switch tube Q1 to be turned on, so as to realize the zero-point voltage or near-zero-point voltage turn-on of the power switch tube Q1, and improve the efficiency of the flyback converter. Specifically, it should be noted that the present invention does not impose any limitation on the peak detection method for detecting the voltage at the connection point V_Forw, and the peak detection method can be any peak detection method and / or device known to those skilled in the art. In order to facilitate the understanding of the present invention and due to space limitations, the specific content of how to use the peak detection method to obtain the peak voltage of the output voltage will not be described here. For more detailed content, please refer to the relevant description of the relevant technology of the peak detection method.

[0063] It should be further explained that the preset duration can be a time period set between the moment when the synchronous rectifier SR is turned off and the moment when the control device 400 sends the request signal. This time period can be close to the moment when the control device 400 sends the request signal, or it can be close to the middle position between the moment when the synchronous rectifier SR is turned off and the moment when the control device 400 sends the request signal, or it can be close to the moment when the synchronous rectifier SR is turned off.

[0064] It should be further noted that, as those skilled in the art can understand, the flyback converter can operate in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The flyback converter control device 400 provided by the present invention is particularly suitable for the discontinuous conduction mode.

[0065] For example, Figure 5The moment t3 in the figure is the starting moment of applying the regulating voltage or current in a specific example of a flyback converter. The power module 412 can determine whether to control the power module 412 to apply the regulating voltage or the regulating current to the connection point V_Forw according to the output voltage VOUT of the flyback converter. With such a configuration, the circuit structure of the control device 400 of the flyback converter provided by the present invention is simpler and easier to implement. In other embodiments, the power module 412 can obtain energy through an external power supply and the output voltage of the flyback converter, so that the regulating voltage or the regulating current can be applied to the connection point V_Forw within the preset time period. It should be noted that the present invention does not limit the manner in which the power module 412 applies the regulating voltage or the regulating current.

[0066] In order to better understand and explain the present invention, the key timing of the flyback converter control device 400 provided by the present invention to realize the zero voltage conduction of the power switch Q1 is described as follows, taking the application of the regulated voltage or regulated current to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier SR as an example. The key timing of applying the regulated current to the output end of the secondary winding Ns is not described in detail. Please understand it adaptively. For details, please continue to refer to Figure 5 , which schematically gives Figure 4 Schematic diagram of the key waveforms of the flyback converter shown in . Figure 5 A complete switching cycle of the flyback converter is schematically shown. Figure 5 In the figure, Q1_C schematically shows the voltage waveform of the control terminal (i.e., gate) of the power switch tube Q1, SR-C schematically shows the voltage waveform of the control terminal (i.e., gate terminal) of the synchronous rectifier tube SR, DRAIN schematically shows the voltage waveform of the first terminal of the power switch tube Q1, V_Forw schematically shows the voltage waveform of the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR, Ipri schematically shows the current waveform of the primary winding Np, Isec schematically shows the current waveform of the secondary winding Ns, and Power_On schematically shows the timing diagram of the duration of the power module 412 injecting the regulated voltage or current into the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR. From Figure 5 It is not difficult to see that a complete switching cycle (t1-t5) of the flyback converter using the control device 400 provided by the present invention includes the following stages:

[0067] t0-t1 stage: the conduction stage of the power switch tube Q1 in the previous switching cycle: after the primary controller 100 receives the driving signal for turning on the power switch tube Q1, at time t0 (corresponding to the actual conduction time t4 of the power switch tube Q1 in this switching cycle), the voltage Q1_C at the control end of the power switch tube Q1 is converted from a low level to a high level and maintained at a high level until time t1. In the t0-t1 stage, the power switch tube Q1 is in the on state, the voltage DRAIN of the drain of the power switch tube Q1 is at a low level, the current Ipri on the primary winding of the transformer T rises linearly from zero, and the transformer T stores energy; the voltage SR_C at the control end of the synchronous rectifier tube SR maintains a low level, the synchronous rectifier tube SR is in the off state, the current Isec on the secondary winding Ns of the transformer T is zero, and the voltage of the connection point V_Forw of the secondary winding Ns of the transformer T connected to the synchronous rectifier tube SR is at a high level.

[0068] t1-t2 stage: At t1 (i.e., the moment when the current Ipri of the primary winding Np increases to the set value), the voltage Q1_C at the control end of the power switch tube Q1 is converted from a high level to a low level and maintained at a low level until the actual conduction time t4. In the t1-t2 stage, the power switch tube Q1 is in the off state, the current Ipri on the primary winding of the transformer T is zero, and the voltage DRAIN of the drain of the power switch tube Q1 starts to rise from t1. The voltage SR_C at the control end of the synchronous rectifier tube SR is converted to a high level, and the synchronous rectifier tube SR is in the on state. From t1, the voltage V_Forw at the connection point where the secondary winding Ns is connected to the synchronous rectifier tube SR drops, and the secondary side starts to freewheel. The energy of the transformer T is transferred from the primary side to the secondary side, and the current Isec on the secondary winding Ns decreases linearly until the demagnetization ends at t2 (i.e., the moment when the current Isec on the secondary winding Ns drops to zero). At t2, the voltage SR_C at the control end of the synchronous rectifier tube SR is converted to a low level.

[0069] Phase t2-t3: The voltage Q1_C at the control end of the power switch tube Q1 continues to maintain a low level, and the current Ipri on the primary winding is zero. The voltage SR_C at the control end of the synchronous rectifier tube SR continues to maintain a low level, and the current Isec on the secondary winding Ns is zero. The voltage DRAIN of the drain of the power switch tube Q1 and the voltage of the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR enter an oscillation state until time t3 (in this example, t3 is the starting time when the power module 412 applies the regulating voltage or the regulating current). It should be noted that those skilled in the art should be able to understand that the method disclosed above for determining the starting time when the power module 412 applies the regulating voltage or the regulating current is only an exemplary description of a preferred embodiment, and is not a limitation of the present invention. In other embodiments, the starting time when the power module 412 applies the regulating voltage or the regulating current can also be determined by detecting the voltage oscillation information of the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR.

[0070] Stage t3-t4: that is, the zero voltage conduction stage of the power switch tube Q1 is realized by the control device 400 of the flyback converter provided by the present invention. At time t3, the secondary control module 412 sends a control signal Power On to the power module 412, so that the power module 412 injects a regulating voltage to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR, and the current Isec on the secondary winding Ns rises linearly, wherein the pulse width of the control signal Power On corresponds to the duration of applying the regulating voltage or regulating current. Assuming that the regulated voltage applied is VBK, the voltage applied to the secondary winding Ns is: VBK-VOUT, wherein VOUT is the output voltage of the flyback converter. According to the turns ratio N of the primary winding Np and the secondary winding Ns, the voltage of the primary winding Np can be obtained to be N×(VBK-VOUT). Then, the voltage of the drain of the power switch tube Q1 drops to: VBUS-N×(VBK-VOUT), and oscillates freely with the leakage inductance and the parasitic capacitance of the drain of the power switch tube Q1, where VBUS is the voltage of the DC bus. In the t3-t4 stage, the voltage Q1_C at the control end of the power switch tube Q1 and the voltage SR_C at the control end of the synchronous rectifier tube SR continue to maintain a low level, the current Ipri on the primary winding Np rises linearly in the reverse direction, the current Isec on the secondary winding Ns rises linearly, and the voltage DRAIN of the drain of the power switch tube Q1 drops. By controlling the preset duration, the zero voltage or approximately zero voltage conduction of the power switch tube Q1 can be achieved. At time t4, the control device 400 sends a request signal to the primary controller 100 to turn on the power switch tube Q1, and the voltage Q1_C at the control end of the power switch tube Q1 is converted to a high level. For example, at time t3 to t4, the parasitic diode D of the power switch tube Q1 clamps the voltage DRAIN of its drain at -0.7V.

[0071] t4-t5 stage: This stage is the conduction stage of the power switch tube Q1 in this switching cycle, which has the same timing as the t0-t1 stage of the previous switching cycle mentioned above and will not be elaborated here.

[0072] Preferably, in some of the exemplary embodiments, see Figure 6 , which schematically shows a specific example diagram of a flyback converter having a control device 400 provided in another embodiment of the present invention. Figure 6It can be seen that the power module 412 includes a charge pump (not shown in the figure), one of the input ends of the charge pump is connected to the secondary control module 411, the other input end of the charge pump is connected to the output end of the flyback converter, and the output end of the charge pump is connected to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier SR; the charge pump is configured to double the output voltage of the flyback converter to apply a regulating voltage or a regulating current to the connection point V_Forw within a preset time after the synchronous rectifier is turned off and before the power switch is turned on. With such a configuration, compared with other forms of voltage conversion elements, the power module 412 of the control device 400 of the flyback converter provided by the present invention adopts a charge pump. Based on the high conversion efficiency of the charge pump (about 90%-95% according to relevant data), the power module 412 of the control device 400 of the flyback converter provided by the present invention is implemented by a charge pump, which can further improve the efficiency.

[0073] Another embodiment of the present invention provides a control method for a flyback converter. Figure 3 , Figure 4 , Figure 6 or Figure 8 as well as Figure 7 ,in, Figure 7 A schematic flow chart of a control method for a flyback converter provided in this embodiment is given; Figure 8 A structural block diagram of a flyback converter provided by an embodiment of the present invention; Figure 8 FIG. 4 is another specific example of a flyback converter having a control device 400 provided in one embodiment of the present invention. Figure 3 , Figure 4 , Figure 6 or Figure 8 It can be seen that the flyback converter includes a transformer T, a power switch tube Q1 connected to the primary winding Np of the transformer T, a primary controller 100 connected to the control end of the power switch tube Q1, and a synchronous rectifier tube SR connected to the secondary winding Ns of the transformer T. For more details, see Figure 7 ,from Figure 7 It can be seen that the control method provided in this embodiment includes:

[0074] S100: applying a regulating voltage or a regulating current to a connection point V_Forw where the secondary winding Ns and the synchronous rectifier SR are connected within a preset time period after the synchronous rectifier SR is turned off and before the power switch Q1 is turned on;

[0075] S200: after applying the regulating current or the regulating current, sending a request signal for turning on the power switch tube Q1 to the primary side controller 100;

[0076] S300: The primary-side controller 100 controls the power switch tube Q1 to be turned on according to the received request signal.

[0077] Preferably, the control method further comprises detecting the voltage of the connection point by a voltage detection method, and obtaining a starting time of applying the regulating voltage or the regulating current according to the voltage of the connection point.

[0078] Since the control method of the flyback converter provided in this embodiment has the same basic principle as the control device 400 of the flyback converter provided in the above embodiments, the control method of the flyback converter provided in this embodiment and the control device 400 provided in the above embodiments belong to the same inventive concept. Based on this, the control method of the flyback converter provided in this embodiment has at least all the advantages of the control device 400 of the flyback converter provided in the above embodiments. In order to avoid redundancy, it will not be described one by one here. For more details, please refer to the relevant description of the beneficial effects of the control device 400 provided in the above embodiments.

[0079] Another embodiment of the present invention provides a flyback converter. The flyback converter provided in this embodiment adopts the control method of the flyback converter provided in the above embodiment to achieve zero voltage conduction of the power switch tube Q1, and / or includes the control device 400 of the flyback converter described in any of the above embodiments. Figure 3 ,from Figure 3 It can be seen that the flyback converter provided in this embodiment includes a transformer T, a power switch tube Q1 connected to the primary winding Np of the transformer T, a primary controller 100 connected to the control end of the power switch tube Q1, and a synchronous rectifier tube SR connected to the secondary winding Ns of the transformer T. More specifically, the input end of the control device 400 is connected to the output end of the flyback converter, the first output end of the control device 400 is connected to the control end of the synchronous rectifier tube SR, and the second output end of the control device 400 is connected to the connection point V_Forw where the secondary winding Ns is connected to the synchronous rectifier tube SR.

[0080] Since the flyback converter provided in this embodiment has the same basic principle as the control method of the flyback converter provided in the above embodiment and / or has the control device 400 of the flyback converter provided in the above embodiments, the flyback converter provided in this embodiment and the control method of the flyback converter provided in the above embodiment and the control device 400 provided in each embodiment belong to the same inventive concept. Based on this, the flyback converter provided in this embodiment has at least all the advantages of the control device 400 of the flyback converter provided in the above embodiments. In order to avoid redundancy, it will not be described one by one here. For more details, please refer to the relevant description of the beneficial effects of the control device 400 provided in the above embodiments.

[0081] Specifically, the first end (e.g., the opposite end) of the primary winding Np is connected to the positive DC bus, the first end (e.g., the drain) of the power switch tube Q1 is connected to the second end (e.g., the same end) of the primary winding Np, and the second end (e.g., the source) of the power switch tube Q1 is connected to the negative DC bus, wherein the negative DC bus can be grounded. It should be noted that the flyback converter provided by the present invention does not limit the power switch tube Q1 and the synchronous rectifier tube SR. In some embodiments, the power switch tube Q1 can adopt an NMOS field effect transistor, and in other embodiments, the power switch tube Q1 can also adopt a PMOS field effect transistor. Similarly, the synchronous rectifier tube SR can also adopt an NMOS field effect transistor or a PMOS field effect transistor. Further, the flyback converter provided by the present invention does not limit the connection mode of the synchronous rectifier tube SR. The synchronous rectifier tube SR can be connected to the first end (e.g., the opposite end) of the secondary winding Ns, or it can be connected to the second end (e.g., the same end) of the secondary winding Ns.

[0082] For more details, please see Figure 4 , which schematically shows that the synchronous rectifier tube SR can be connected to the same end of the secondary winding Ns. Figure 4 It can be seen that in these embodiments, the source of the synchronous rectifier SR is grounded, the drain of the synchronous rectifier SR is connected to the opposite end of the secondary winding Ns, and the output end of the power module 412 of the control device 400 is connected to the connection point V_Forw where the opposite end of the secondary winding Ns and the drain of the synchronous rectifier SR are connected. Please continue to refer to Figure 8 ,and Figure 4 Unlike the flyback converter shown, Figure 8 The synchronous rectifier SR of the flyback converter shown is connected to the same end of the secondary winding Ns. More specifically, Figure 8It can be seen that the source of the synchronous rectifier SR is connected to the same-name end of the secondary winding Ns, the output end of the power module 412 is connected to the connection point V_Forw where the same-name end of the secondary winding Ns and the source of the synchronous rectifier SR are connected, and the drain of the synchronous rectifier SR is connected to the output end of the flyback converter. It can be seen that the flyback converter provided by the present invention does not limit the connection position between the control device 400 and the secondary winding Ns, and can be connected to the same-name end of the secondary winding Ns or the opposite-name end of the secondary winding Ns, but the control device 400 needs to be connected to the wire connecting the secondary winding Ns and the synchronous rectifier SR. It can be seen that the control device 400 provided by the present invention has good adaptability.

[0083] Preferably, in some of the exemplary embodiments, please continue to refer to Figure 3 , Figure 4 , Figure 6 or Figure 8 ,from Figure 3 , Figure 4 , Figure 6 or Figure 8 It can be seen that the flyback converter further includes a first capacitor C1, one end of the first capacitor C1 is connected to the output end of the flyback converter, and the other end of the first capacitor C1 is grounded. Such a configuration enables the load 300 to receive the electric energy (current and voltage) converted by the transformer T more smoothly. Specifically, in some embodiments (such as Figure 3 , Figure 4 and Figure 6 ), one end of the first capacitor C1 is connected to the same-name end of the secondary winding Ns, and the other end of the first capacitor C1 is connected in parallel with the source of the synchronous rectifier SR and then grounded; in some embodiments (such as Figure 8 As shown in FIG. 1 , one end of the first capacitor C1 is connected to the drain of the synchronous rectifier SR, and the other end of the first capacitor C1 is connected in parallel with the opposite end of the secondary winding Ns and then grounded.

[0084] The flyback converter provided by the present invention does not limit the load 300. The load 300 may include, but is not limited to, computing devices and related components, such as microprocessors, electrical components, circuits, laptop computers, desktop computers, tablet computers, mobile phones, batteries, speakers, lighting units, related components of automobiles / ships / aircraft / trains, motors, transformers T, or any other type of electrical equipment and / or circuits that receive voltage or current from the flyback converter.

[0085] Preferably, in some of the exemplary embodiments, please continue to refer to Figure 3 , Figure 4 , Figure 6 or Figure 8 ,from Figure 3 , Figure 4 , Figure 6 or Figure 8 It can be seen that the flyback converter provided in these embodiments further includes a rectifier circuit U; the input end of the rectifier circuit U is connected to the AC power supply, the first output end of the rectifier circuit U is connected to the first end of the primary winding Np of the transformer T, wherein the connection between the first output end of the rectifier circuit U and the first end of the primary winding Np of the transformer T is a positive DC bus. Thus, the electric energy provided by the AC power supply can be more conveniently provided to the transformer T, the second end of the primary winding Np of the transformer T is connected to the first end of the power switch Q1, the second output end of the rectifier circuit U is connected to the second end of the power switch Q1, wherein the connection between the second output end of the rectifier circuit U and the second end of the power switch Q1 is a negative DC bus. Preferably, the flyback converter may further include a second capacitor C2 connected in parallel with the first output end and the second output end of the rectifier circuit U. Thus, the unnecessary AC component after rectification can be filtered out to make the DC smooth. The AC power source may include, but is not limited to, a power grid, a generator, a transformer T, a solar panel, a wind turbine, a hydraulic or wind generator, or any other form of device capable of providing electrical energy to the flyback converter.

[0086] Preferably, please continue to see Figure 3 , Figure 4 , Figure 6 or Figure 8 ,from Figure 3 , Figure 4 , Figure 6 or Figure 8 It can be seen that the flyback converter provided in these embodiments further includes an energy absorption circuit, which is connected in parallel to both ends of the primary winding Np of the transformer T. Exemplarily, the energy absorption circuit includes a resistor R, a third capacitor C3, and a diode D. Specifically, after the resistor R and the third capacitor C3 are connected in parallel, one end thereof is connected to the cathode of the diode D, and after the resistor R and the third capacitor C3 are connected in parallel, the other end thereof is connected to the first end of the primary winding Np, and the anode of the diode D is connected to the second end of the primary winding Np.

[0087] Another embodiment of the present invention provides a power supply system, which includes the flyback converter described in any of the above embodiments. Since the power supply system provided by this embodiment has the flyback converter provided by any of the above embodiments, the flyback converter provided by this embodiment and the flyback converter provided by the above embodiments belong to the same inventive concept. Based on this, the power supply system provided by this embodiment should also have all the advantages of the flyback converter provided by the above embodiments, which will not be elaborated here. For more details, please refer to the relevant description of the beneficial effects of the flyback converter in the above related embodiments.

[0088] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0089] In summary, compared with the prior art, the control device and method of the flyback converter, the flyback converter and the power supply system provided by the present invention have the following advantages:

[0090] The control device of the flyback converter provided by the present invention applies a regulating voltage or injects a regulating current to the connection point where the secondary winding is connected to the synchronous rectifier tube within a preset time after the synchronous rectifier tube is turned off and before the power switch tube is turned on, so that the current flowing through the secondary winding increases, and then the voltage of the drain of the power switch tube decreases, and after the application of the regulating voltage or the regulating current is completed, a request signal for turning on the power switch tube is sent to the primary controller through the third output terminal of the control device, and the primary controller controls the power switch tube to turn on according to the received request signal. Therefore, the control device of the flyback converter provided by the present invention can realize the zero voltage turn-on of the power switch tube, which can not only improve efficiency and reduce temperature rise, but also keep the peripheral circuit simple, well control the volume and cost of the flyback converter, and be easy to implement.

[0091] Since the control method, flyback converter and power supply system of the flyback converter provided by the present invention and the control device of the flyback converter provided by the present invention belong to the same inventive concept, the control method, flyback converter and power supply system of the flyback converter provided by the present invention at least have all the advantages of the control device of the flyback converter provided by the present invention. In order to avoid redundancy, they will not be described one by one here. For more details, please refer to the relevant description of the beneficial effects of the control device of the flyback converter.

[0092] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0093] In summary, the above embodiments provide a detailed description of the different configurations of the flyback converter control device, method, flyback converter and power supply system proposed in the present invention. Of course, the above description is only a description of the preferred embodiments of the present invention, and is not any limitation to the scope of the present invention. The present invention includes but is not limited to the configurations listed in the above implementations. Those skilled in the art can draw inferences based on the contents of the above embodiments. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure are within the scope of protection of the claims.

Claims

1. A control device for a flyback converter, the flyback converter comprising a transformer, a power switch connected to a primary winding of the transformer, a primary controller connected to a control end of the power switch, and a synchronous rectifier connected to a secondary winding of the transformer; characterized in that: The input end of the control device is configured to be connected to the output end of the flyback converter, the first output end of the control device is configured to be connected to the control end of the synchronous rectifier, and the second output end of the control device is configured to be connected to the connection point where the secondary winding is connected to the synchronous rectifier; The control device is configured to apply a regulating voltage or a regulating current to the connection point within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on; and after applying the regulating voltage or the regulating current, send a request signal for turning on the power switch tube to the primary side controller through the third output terminal of the control device; The primary side controller is configured to control the power switch tube to be turned on according to the received request signal.

2. The control device according to claim 1, characterized in that: The control device includes a secondary side control module, a power supply module and a sending module; The input end of the secondary side control module is configured to be connected to the input end of the control device, the first output end of the secondary side control module is connected to the first output end of the control device, the second output end of the secondary side control module is connected to the input end of the power module, the output end of the power module is connected to the second output end of the control device, the third output end of the secondary side control module is connected to the input end of the sending module, and the output end of the sending module is connected to the third output end of the control device; The power supply module applies the regulated voltage or the regulated current to the connection point within a preset time after the synchronous rectifier tube is turned off and before the power switch tube is turned on; The secondary side control module is configured to output a primary side conduction signal to the sending module after the power supply module completes applying the regulated voltage or the regulated current; The sending module is configured to send a request signal for turning on the power switch tube to the primary side controller according to the primary side conduction signal.

3. The control device according to claim 2, characterized in that: The secondary side control module is configured to detect the voltage of the connection point by using a voltage detection method, and obtain the starting time when the power supply module applies the regulated voltage or the regulated current according to the voltage of the connection point.

4. The control device according to claim 3, characterized in that: The secondary side control module is configured to use the time at which the peak voltage of the voltage at the connection point is located as the starting time for the power module to apply the regulated voltage or the regulated current.

5. The control device according to claim 2, characterized in that: The power supply module comprises a charge pump, one of the input ends of the charge pump is connected to the secondary side control module, the other input end of the charge pump is connected to the output end of the flyback converter, and the output end of the charge pump is connected to the second output end of the control device; The charge pump is configured to apply the regulating voltage or the regulating current to the connection point within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on, according to the output voltage of the flyback converter.

6. The control device according to claim 5, characterized in that: The control device is integrated into a control circuit chip.

7. A control method for a flyback converter, the flyback converter comprising a transformer, a power switch connected to a primary winding of the transformer, a primary controller connected to a control end of the power switch, and a synchronous rectifier connected to a secondary winding of the transformer; characterized in that: The control method comprises: Applying a regulating voltage or a regulating current to a connection point between the secondary winding and the synchronous rectifier tube within a preset time period after the synchronous rectifier tube is turned off and before the power switch tube is turned on; After applying the regulating voltage or the regulating current, sending a request signal for turning on the power switch tube to the primary side controller; The primary side controller controls the power switch tube to be turned on according to the received request signal.

8. The control method according to claim 7, characterized in that: The method also includes detecting the voltage of the connection point by using a voltage detection method, and obtaining the starting time of applying the adjustment voltage or the adjustment current according to the voltage of the connection point.

9. A flyback converter, comprising a transformer, a power switch connected to a primary winding of the transformer, a primary controller connected to a control end of the power switch, and a synchronous rectifier connected to a secondary winding of the transformer; characterized in that: A control method for a flyback converter as described in claim 7 or 8 is used to achieve zero voltage conduction of the power switch tube, and / or includes a control device for a flyback converter as described in any one of claims 1 to 6; wherein the input end of the control device is connected to the output end of the flyback converter, the first output end of the control device is connected to the control end of the synchronous rectifier tube, and the second output end of the control device is connected to the connection point where the secondary winding is connected to the synchronous rectifier tube.

10. The flyback converter according to claim 9, characterized in that: The source of the synchronous rectifier is grounded, the drain of the synchronous rectifier and the first end of the secondary winding are connected to the connection point, and the output end of the power module of the control device is connected to the connection point; Or the source of the synchronous rectifier is connected to the second end of the secondary winding at a connection point, the output end of the power module is connected to the connection point, and the drain of the synchronous rectifier is connected to the output end of the flyback converter.

11. The flyback converter according to claim 9, characterized in that: The flyback converter further includes a first capacitor, one end of the first capacitor is connected to the output end of the flyback converter, and the other end of the first capacitor is grounded.

12. The flyback converter according to claim 9, characterized in that: It also includes a rectifier circuit; the input end of the rectifier circuit is connected to an AC power supply, the first output end of the rectifier circuit is connected to the first end of the primary winding of the transformer, the second end of the primary winding of the transformer is connected to the first end of the power switch, and the second output end of the rectifier circuit is connected to the second end of the power switch.

13. The flyback converter according to claim 9, characterized in that: It also includes an energy absorption circuit, which is connected in parallel with two ends of the primary winding of the transformer.

14. A power supply system, characterized in that: The invention comprises a flyback converter as claimed in any one of claims 9 to 13.

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