Asymmetric half-bridge flyback converter and control circuit and control method thereof

Abstract

The invention provides a control circuit of an asymmetric half-bridge flyback converter, which comprises a lower tube control module, the lower tube control module is used for receiving a first signal and a second signal, the first signal comprises information at the moment when secondary side current returns to zero, and the second signal comprises information at the turn-off moment of a primary side lower tube. The lower tube control module indicates that the primary side lower tube can be turned off at the moment when the secondary side current returns to zero, and then indicates that the primary side lower tube is turned off at the turn-off moment of the primary side lower tube, so that the primary side is prevented from being mistakenly conducted, and the risk of explosion of the asymmetric half-bridge flyback converter is reduced. Correspondingly, the invention also provides an asymmetric half-bridge flyback converter and a control method thereof.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to an asymmetric half-bridge flyback converter and a control circuit and a control method thereof. Background Art

[0002] With the rapid development of the field of power electronics, the application of switching converters is becoming more and more extensive, especially people have put forward more requirements for high power density, high reliability and small size switching converters. Generally, traditional low-power switching converters are implemented using flyback topology, which has the advantages of simple structure and low cost. Among them, the asymmetric half-bridge flyback converter (Asymmetric half bridge Converter, referred to as AHB) has the additional advantage of isolation, and can achieve zero voltage conduction (ZVS) of two primary switch tubes under the condition that the number and complexity of components are close to those of ordinary flyback converters, recover leakage inductance energy, and easily realize self-driven synchronous rectification, effectively improving efficiency while reducing the size of the transformer.

[0003] Although the current asymmetric half-bridge flyback converter is simple and convenient, there is a risk of system explosion due to incorrect opening of the primary side. Although the probability of this risk can be reduced by optimizing the secondary side controller, the risk still exists. Summary of the invention

[0004] The object of the present invention is to provide an asymmetric half-bridge flyback converter and a control circuit and a control method thereof, so as to solve the problem that the existing asymmetric half-bridge flyback converter has the risk of system crash due to erroneous opening of the primary side.

[0005] In order to achieve the above-mentioned object, the present invention provides a control circuit of an asymmetric half-bridge flyback converter, wherein the asymmetric half-bridge flyback converter comprises a primary upper tube and a primary lower tube located on the primary side and connected in series, a synchronous rectifier located on the secondary side, and a transformer circuit coupled between a connection point between the primary upper tube and the primary lower tube and the synchronous rectifier, wherein the control circuit comprises a lower tube control module, wherein the lower tube control module is used to receive a first signal and a second signal, wherein the first signal comprises information of a time when the secondary side current returns to zero, and the second signal comprises information of a time when the primary lower tube is turned off; and

[0006] The lower tube control module indicates to turn off the primary lower tube at the turn-off time of the primary lower tube after the secondary side current returns to zero and indicates that the primary lower tube can be turned off.

[0007] Optionally, the first signal is a sampling signal of the voltage on the auxiliary winding, and the moment when the secondary side current returns to zero is the moment when the value of the first signal reaches a first predetermined value, wherein the auxiliary winding is coupled to the transformer circuit.

[0008] Optionally, the first predetermined value is a difference between a sampling value of the first signal within a predetermined time period and a predetermined offset, and the predetermined time period is between a moment when the primary lower tube is turned on and a moment when the secondary side current returns to zero.

[0009] Optionally, the first predetermined value is greater than 0V.

[0010] Optionally, the first signal is a sampling signal of the primary side current, and the moment when the secondary side current returns to zero is the moment corresponding to the inflection point of the first signal.

[0011] Optionally, the down tube control module obtains the slope of the first signal in real time, and the moment corresponding to the inflection point of the first signal is the moment when the slope of the first signal changes from a positive value to a negative value; or, the down tube control module obtains the value of the first signal in real time, and the moment corresponding to the inflection point of the first signal is the moment when the value of the first signal begins to gradually decrease.

[0012] Optionally, the second signal is a sampling signal of the primary side current, and the turn-off moment of the primary lower tube is the moment when the value of the second signal reaches a second predetermined value.

[0013] Optionally, it also includes an upper tube control module, which is used to receive a third signal, the third signal contains information about the opening time of the primary upper tube, and the upper tube control module opens the primary upper tube according to the instruction of the third signal.

[0014] Optionally, the upper tube control module is further used to receive a fourth signal, wherein the fourth signal includes information about the shutdown time of the primary upper tube, and the upper tube control module shuts down the primary upper tube according to an instruction of the fourth signal.

[0015] Optionally, the fourth signal is a sampling signal of the primary-side current, and the turn-off moment of the primary-side upper tube is the moment when the value of the fourth signal reaches a fourth predetermined value.

[0016] Optionally, after the upper tube control module instructs to turn on the primary upper tube, after a conduction time, the upper tube control module instructs to turn off the primary upper tube.

[0017] Optionally, the on-time is a fixed time or a time that varies with a switching frequency.

[0018] Optionally, the control circuit is located on the primary side of the asymmetric half-bridge flyback converter.

[0019] Optionally, the asymmetric half-bridge flyback converter includes a secondary side controller and a coupler located at a secondary side of the asymmetric half-bridge flyback converter; and,

[0020] The secondary-side controller is used to generate the third signal, and the coupler modulates the third signal and transmits it to the upper tube control module.

[0021] Optionally, the coupler includes a magnetic coupler, a capacitive isolator or a digital isolator.

[0022] The present invention also provides an asymmetric half-bridge flyback converter, including a control circuit of the asymmetric half-bridge flyback converter, wherein the control circuit is used to control the on and off of the primary upper tube and the primary lower tube of the asymmetric half-bridge flyback converter.

[0023] The present invention also provides a control method for an asymmetric half-bridge flyback converter, wherein the asymmetric half-bridge flyback converter comprises a primary upper tube and a primary lower tube located on the primary side and connected in series, a synchronous rectifier located on the secondary side, and a transformer circuit coupled between a connection point between the primary upper tube and the primary lower tube and the synchronous rectifier. The control method comprises:

[0024] receiving a first signal, wherein the first signal includes information about a time when the secondary-side current returns to zero, indicating that the primary-side lower tube can be turned off at the time when the secondary-side current returns to zero; and

[0025] A second signal is received, wherein the second signal includes information about a shutdown time of the primary lower tube and indicates to shut down the primary lower tube at the shutdown time of the primary lower tube.

[0026] Optionally, the first signal is obtained by sampling the voltage on the auxiliary winding, and the time when the secondary side current returns to zero is the time when the value of the first signal reaches a first predetermined value, wherein the auxiliary winding is coupled to the transformer circuit.

[0027] Optionally, the first signal is obtained by sampling a sampling signal of the primary side current, and the moment when the secondary side current returns to zero is the moment corresponding to the inflection point of the first signal.

[0028] The control circuit of the asymmetric half-bridge flyback converter provided by the present invention includes a lower tube control module, the lower tube control module is used to receive a first signal and a second signal, the first signal includes information about the time when the secondary side current returns to zero, and the second signal includes information about the time when the primary side lower tube is turned off. After the lower tube control module indicates that the primary side lower tube can be turned off at the time when the secondary side current returns to zero, it indicates to turn off the primary side lower tube at the time when the primary side lower tube is turned off, so as to avoid mis-conduction of the primary side and reduce the risk of explosion of the asymmetric half-bridge flyback converter. Correspondingly, the present invention also provides an asymmetric half-bridge flyback converter and a control method thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A circuit diagram of an asymmetric half-bridge flyback converter provided in Embodiment 1 of the present invention;

[0030] Figure 2 The working waveform diagram of the asymmetric half-bridge flyback converter provided in the first embodiment of the present invention;

[0031] Figure 3 A flow chart of a control method for an asymmetric half-bridge flyback converter provided in Embodiment 1 of the present invention;

[0032] Figure 4 A circuit diagram of an asymmetric half-bridge flyback converter provided in Embodiment 2 of the present invention;

[0033] Figure 5 The working waveform diagram of the asymmetric half-bridge flyback converter provided in the second embodiment of the present invention;

[0034] Figure 6 A circuit diagram of an asymmetric half-bridge flyback converter provided in Embodiment 3 of the present invention;

[0035] Wherein, the accompanying drawings are marked as follows:

[0036] 100-control circuit; 101-upper tube control module; 102-lower tube control module; 103-receiving module; 104-coupler; 105-secondary side controller;

[0037] T-transformer; Np-primary winding; MH-primary upper tube; ML-primary lower tube; Cr-resonant capacitor; Rcs-sampling resistor; VBUS-input voltage; PGND-primary reference ground; Lm, Lr-inductor; Ns-secondary winding; Na-auxiliary winding; R1, R2-voltage divider resistors; SR-synchronous rectifier; Co-output capacitor; VOUT-output voltage; SGND-secondary reference ground; Vaux-sampling signal of the voltage on the auxiliary winding; ILr-primary current; ILm-excitation current; Vcs-sampling signal of the primary current; PWML-lower tube control signal; PWMH-upper tube control signal; Request-third signal. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention will be described in more detail below in conjunction with the schematic diagram. The advantages and features of the present invention will become clearer based on the following description. It should be noted that the drawings are all in a very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0039] Figure 1 The circuit diagram of the asymmetric half-bridge flyback converter provided in this embodiment. Figure 1As shown, this embodiment provides an asymmetric half-bridge flyback converter and a control circuit thereof, wherein the asymmetric half-bridge flyback converter includes a primary upper tube MH and a primary lower tube ML located on the primary side and connected in series, a synchronous rectifier tube SR located on the secondary side, a transformer circuit coupled between a connection point between the primary upper tube MH and the primary lower tube ML and the synchronous rectifier tube SR, and a control circuit 100. The transformer circuit includes a transformer T.

[0040] Specifically, the primary side also has a primary winding Np of the transformer T, a resonant capacitor Cr and a sampling resistor Rcs. The drain of the primary upper tube MH is used to access the input voltage VBUS, and the gate of the primary upper tube MH is connected to the control circuit 100; the drain of the primary lower tube ML is connected to the source of the primary upper tube MH, the source of the primary lower tube ML is connected to the primary reference ground PGND, and the gate of the primary lower tube ML is connected to the control circuit 100. In the same switching cycle, the control circuit 100 controls the primary upper tube MH and the primary lower tube ML to be turned on in time to transfer the input voltage VBUS from the primary side of the transformer T to the secondary side. The excitation inductance and leakage inductance of the primary winding Np are equivalent to the inductance Lm and the inductance Lr, respectively, and form a resonant circuit with the resonant capacitor Cr, the sampling resistor Rcs and the primary lower tube ML (when turned on).

[0041] The secondary side also has a secondary winding Ns of the transformer T, an auxiliary winding Na, voltage-dividing resistors R1 and R2, an output capacitor Co, a secondary controller 105 and a coupler 104. The drain of the synchronous rectifier SR is connected to the same-name end of the secondary winding Ns, and the source of the synchronous rectifier SR is connected to the secondary reference ground SGND; the two ends of the output capacitor Co are respectively connected to the opposite-name end of the secondary winding Ns and the secondary reference ground SGND, and the opposite-name end of the secondary winding Ns provides an output voltage VOUT. The two ends of the auxiliary winding Na are connected in series with voltage-dividing resistors R1 and R2, and the sampling signal Vaux of the voltage on the auxiliary winding Na is output at the connection node of the voltage-dividing resistors R1 and R2.

[0042] Since the basic topology of the asymmetric half-bridge flyback converter is well known to those skilled in the art, it will not be described in detail here.

[0043] The control circuit 100 includes an upper tube control module 101, a lower tube control module 102 and a receiving module 103. The upper tube control module 101, the lower tube control module 102 and the receiving module 103 can be used as part of the primary side controller, and the coupler 104 is coupled between the primary side controller and the secondary side controller 105 (specifically, it is coupled between the receiving module 103 and the sending module (not shown) in the secondary side controller 105).

[0044] Specifically, the upper tube control module 101 is used to receive the third signal Request, which includes information about the opening time of the primary upper tube MH. The upper tube control module 101 instructs to open the primary upper tube MH at the opening time of the primary upper tube MH.

[0045] In this embodiment, the third signal Request comes from the secondary side. For example, the secondary controller 105 can receive the feedback signal of the output voltage VOUT and the voltage signal on the secondary winding Ns and generate the third signal Request; the coupler 104 receives the third signal Request, and modulates the third signal Request and sends it from the secondary side to the primary side; the receiving module 103 receives the third signal Request, and demodulates the third signal Request and sends it to the upper tube control module 101.

[0046] As an optional embodiment, the coupler 104 may be any common coupler. For example, the coupler 104 may be a magnetic coupler, a capacitive isolator, or a digital isolator.

[0047] It is understandable that after the primary upper tube MH is turned on, the upper tube control module 101 can be designed according to specific requirements and feedback characteristics to use appropriate signals to determine the turn-off time of the primary upper tube MH to indicate turning off the primary upper tube MH.

[0048] In this embodiment, the upper tube control module 101 is used to receive the fourth signal, and the fourth signal includes information about the shutdown time of the primary upper tube MH. The upper tube control module 101 instructs to shut down the primary upper tube MH at the shutdown time of the primary upper tube MH. In this embodiment, the fourth signal is the sampling signal Vcs of the primary side current ILr (the voltage signal at both ends of the sampling resistor Rcs), and the shutdown time of the primary upper tube MH is the time when the value of the fourth signal reaches the fourth predetermined value Vcslimit. This method is simple to control and includes an overcurrent protection function.

[0049] In some embodiments, after instructing to turn on the primary upper tube MH, the upper tube control module 101 turns off the primary upper tube MH by fixing the on-time of the primary upper tube MH, that is, after the primary upper tube MH is turned on, after the fixed on-time, the upper tube control module 101 instructs to turn off the primary upper tube MH. This control method is relatively simple, but it needs to be used in conjunction with the overcurrent protection function.

[0050] In some embodiments, after instructing to turn on the primary upper tube MH, the upper tube control module 101 can turn off the primary upper tube MH by adapting the on-time of the primary upper tube MH. For example, a switching frequency-on-time relationship curve is set. If the switching frequency changes, the on-time can be adjusted according to the relationship curve to limit the overall operating frequency to a smaller range and reduce ripple. This control method is more complicated and requires an additional overcurrent protection function.

[0051] In this embodiment, after the upper tube control module 101 receives the third signal and the fourth signal, it generates an upper tube control signal PWMH according to the information of the turn-on time of the primary upper tube MH contained in the third signal and the information of the turn-off time of the primary upper tube MH contained in the fourth signal, and acts on the gate of the primary upper tube MH to control the on and off of the primary upper tube MH.

[0052] Furthermore, after the primary upper tube MH is turned off, after a dead time, the body diode of the primary lower tube is turned on, and at this time the lower tube control module 102 instructs to turn on the primary lower tube ML, so that the primary lower tube ML is turned on at zero voltage.

[0053] The lower tube control module 102 is used to receive a first signal, which includes information about the time when the secondary side current returns to zero. The lower tube control module 102 indicates that the primary lower tube ML can be turned off when the secondary side current returns to zero, that is, the lower tube control module 102 allows the primary lower tube ML to be turned off.

[0054] In this embodiment, the first signal is a sampling signal Vaux of the voltage on the auxiliary winding Na, and the time when the secondary side current returns to zero is the time when the value of the sampling signal Vaux reaches a first predetermined value vth.

[0055] It should be noted that the first predetermined value vth can be the difference between the sampling value of the sampling signal Vaux in a predetermined time period and the predetermined offset Vsh. The predetermined time period is a certain time period after the primary lower tube ML is turned on to the moment when the secondary current returns to zero. In actual operation, a sampling time can be designed. After the primary lower tube ML is turned on, the sampling signal Vaux is sampled after a preset sampling time to obtain the sampling value of the sampling signal Vaux. Then, the sampling value of the sampling signal Vaux is subtracted from the predetermined offset Vsh to obtain the first predetermined value vth. In some embodiments, the first predetermined value vth is also an adaptive change value, that is, the sampling signal Vaux is resampled in each switching cycle, so as to recalculate the first predetermined value vth, so that the first predetermined value vth can follow the output voltage VOUT and adapt to a wide output voltage range.

[0056] As an optional embodiment, the predetermined offset Vsh may be set to, for example, 0.2V to 0.5V, but should not be limited thereto, as long as the first predetermined value vth is greater than 0V.

[0057] The lower tube control module 102 is further configured to receive a second signal, the second signal including information on the shutdown time of the primary lower tube ML, and the lower tube control module 102 instructs the primary lower tube ML to be shut down at the shutdown time of the primary lower tube ML. After the lower tube control module 102 receives the first signal and instructs the primary lower tube ML to be shut down, the primary lower tube ML is allowed to be shut down, and then the lower tube control module 102 instructs the primary lower tube ML to be shut down at the shutdown time of the primary lower tube ML.

[0058] In this embodiment, the second signal is the sampling signal Vcs of the primary current ILr, and the turn-off moment of the primary lower tube ML is the moment when the value of the sampling signal Vcs reaches the second predetermined value.

[0059] Further, after receiving the first signal and the second signal, the lower tube control module 102 generates a lower tube control signal PWML according to the information of the secondary side current returning to zero contained in the first signal and the information of the primary side lower tube ML turning off contained in the second signal, combined with the information of the turning off time of the primary side upper tube MH, and acts on the gate of the primary side lower tube ML to control the on and off of the primary side lower tube ML. In this embodiment, after the lower tube control module 102 indicates that the primary side lower tube ML can be turned off at the time when the secondary side current returns to zero, it indicates to turn off the primary side lower tube ML at the time when the primary side lower tube ML turns off, so as to avoid the primary side lower tube ML from being turned on by mistake, and reduce the risk of explosion of the asymmetric half-bridge flyback converter; and all the control of the primary side lower tube ML can be realized on the primary side, and the circuit is simple and reliable.

[0060] Figure 2 The working waveform diagram of the asymmetric half-bridge flyback converter provided in this embodiment. Figure 1 and Figure 2As shown, at time t0, a pulse appears in the third signal Request, indicating that the primary upper tube MH should be turned on. After some internal delays, the upper tube control signal PWMH flips to a high level, and the primary upper tube MH is turned on. At this time, the lower tube control signal PWML is a low level, and the primary lower tube ML is turned off; at time t1, the sampling signal Vcs voltage (reflecting the primary side current ILr in the figure) reaches the fourth predetermined value Vcslimit, the upper tube control signal PWMH flips to a low level, and the primary upper tube MH is turned off; the time period between t1 and t2 is the dead time, during which the primary upper tube MH and the primary lower tube ML are both turned off; at time t2, the lower tube control signal PWML flips to a high level, and the inductor current first extracts the charge on the parasitic capacitor of the primary lower tube ML to its VDS (the maximum voltage value that can be applied between the drain and the source) ) reaches a certain value (such as -0.7V), and then the body diode of the primary lower tube ML is used for freewheeling. The primary lower tube ML is turned on at zero voltage, the resonant circuit starts to resonate, and the primary side current ILr shows a sinusoidal waveform. At this time, due to the conduction of the body diode of the primary lower tube ML, its VDS voltage drop can be considered to be close to 0; at time t3, the sampling signal Vaux of the voltage on the auxiliary winding Na reaches the first predetermined value, indicating that the secondary side current returns to zero, and the lower tube control module 102 allows the primary lower tube ML to be turned off (at time t3, the lower tube control signal PWML is allowed to flip); at time t4, the value of the sampling signal Vcs reaches the second predetermined value, the lower tube control signal PWML flips to a low level, and the primary lower tube ML is turned off; at time t5, the third signal Request appears a pulse again, indicating that the primary upper tube MH should be turned on, and a switching cycle ends.

[0061] Figure 3 A flow chart of a control method for an asymmetric half-bridge flyback converter provided in this embodiment. Figure 1 and Figure 3 As shown, the control method of the asymmetric half-bridge flyback converter includes:

[0062] Step S100: receiving a first signal, the first signal including information of a time when the secondary current returns to zero, indicating that the primary lower tube can be turned off at the time when the secondary current returns to zero;

[0063] Step S200: receiving a second signal, wherein the second signal includes information about the shutdown time of the primary lower tube, and indicates to shut down the primary lower tube at the shutdown time of the primary lower tube.

[0064] The asymmetric half-bridge flyback converter has been described in detail above and will not be described in detail here.

[0065] For example, the upper tube control module 101 receives the third signal Request and the fourth signal, and instructs to turn on the primary upper tube MH at the turn-on time of the primary upper tube MH. After the primary upper tube MH is turned on, when the value of the fourth signal reaches the fourth predetermined value Vcslimit, the upper tube control module 101 instructs to turn off the primary upper tube MH.

[0066] After the primary upper tube MH is turned off, after a dead time, the lower tube control module 102 instructs to turn on the primary lower tube ML; after the primary lower tube ML is turned on, the lower tube control module 102 receives the first signal and the second signal, and after allowing the primary lower tube ML to turn off at the moment when the secondary side current returns to zero, it instructs to turn off the primary lower tube ML at the moment when the primary lower tube ML is turned off.

[0067] Correspondingly, the first signal may be a sampling signal Vaux of the voltage on the auxiliary winding Na, and the time when the secondary side current returns to zero may be the time when the value of the sampling signal Vaux reaches the first predetermined value vth.

[0068] Embodiment 2

[0069] Figure 4 The circuit diagram of the asymmetric half-bridge flyback converter provided in this embodiment. Figure 4 As shown, the difference from the first embodiment is that in this embodiment, the first signal is the sampling signal Vcs of the primary side current, and the time when the secondary side current returns to zero is the time corresponding to the inflection point of the sampling signal Vcs.

[0070] It should be noted that when the primary current ILr and the excitation current ILm are equal, since the secondary current is proportional to the difference between the primary current and the excitation current ILm, the current transmitted to the secondary side drops to 0 (the secondary current returns to zero). Therefore, at the moment when the secondary current returns to zero, the primary current ILr is no longer resonant but equal to the excitation current ILm, so the primary current ILr will have an inflection point, and the moment corresponding to the inflection point of the primary current ILr is the moment when the secondary current returns to zero.

[0071] Based on this, before the secondary side current returns to zero, the value of the sampling signal Vcs gradually increases, and the slope (i.e., the rate of change) of the sampling signal Vcs is always positive. When the slope of the sampling signal Vcs changes from a positive value to a negative value, it indicates that the inflection point of the sampling signal Vcs has arrived. Therefore, the lower tube control module 102 obtains the sampling value of the sampling signal Vcs in real time and calculates its slope. The inflection point of the sampling signal Vcs corresponds to the moment when the slope of the sampling signal Vcs changes from a positive value to a negative value.

[0072] In some embodiments, before the secondary current returns to zero, the value of the sampling signal Vcs gradually increases. When the value of the sampling signal Vcs begins to decrease, it indicates that the inflection point of the sampling signal Vcs has arrived. Therefore, the lower tube control module 102 can obtain the value of the sampling signal Vcs in real time, and use multiple comparators to continuously compare Vcs. The moment corresponding to the inflection point of the sampling signal Vcs is the moment when the value of the sampling signal Vcs begins to decrease. In this way, the calculation of the slope can be omitted, simplifying the control.

[0073] Figure 5 The working waveform diagram of the asymmetric half-bridge flyback converter provided in this embodiment. Figure 4 and Figure 5 As shown, at time t3, the secondary current returns to zero, the primary current ILr is equal to the excitation current ILm, the primary current ILr has an inflection point, and the lower tube control module 102 allows the primary lower tube ML to be turned off (after time t2, the lower tube control signal PWML is restricted from flipping, until time t3, the lower tube control signal PWML is allowed to flip); at time t4, the value of the sampling signal Vcs reaches the second predetermined value, the lower tube control signal PWML flips to a low level, and the primary lower tube ML is turned off; at time t5, the third signal Request has a pulse again, indicating that the primary upper tube MH should be turned on, and a switching cycle ends. The control of other switching actions is similar to that of the previous embodiment, and will not be repeated here.

[0074] Compared with the first embodiment, the present embodiment does not need to set up an auxiliary winding, and the control circuit 100 is simpler and suitable for being implemented using a digital circuit.

[0075] Embodiment 3

[0076] Figure 6 The circuit diagram of the asymmetric half-bridge flyback converter provided in this embodiment. Figure 6 As shown, compared with the first embodiment, the position of the resonant circuit in this embodiment is different, that is, the primary winding Np and the resonant capacitor Cr, the sampling resistor Rcs and the primary upper tube MH (when turned on) form a resonant circuit, and the control logic of the primary upper tube MH and the primary lower tube ML in the aforementioned embodiment can be adaptively replaced.

[0077] In summary, the control circuit of the asymmetric half-bridge flyback converter provided in the embodiment of the present invention includes a lower tube control module, which is used to receive a first signal and a second signal, wherein the first signal includes information about the time when the secondary side current returns to zero, and the second signal includes information about the time when the primary side lower tube is turned off. After the lower tube control module indicates that the primary side lower tube can be turned off at the time when the secondary side current returns to zero, it indicates to turn off the primary side lower tube at the time when the primary side lower tube is turned off, thereby avoiding mis-conduction of the primary side and reducing the risk of explosion of the asymmetric half-bridge flyback converter. Accordingly, the present invention also provides an asymmetric half-bridge flyback converter and a control method thereof.

[0078] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0079] It should also be noted that, although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

[0080] It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third", etc. in the specification are merely used to distinguish between the various components, elements, steps, etc. in the specification, and are not used to indicate the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0081] It should also be recognized that the terms described herein are only used to describe specific embodiments and are not intended to limit the scope of the invention. It should be noted that the singular forms "a" and "an" used herein and in the appended claims include plural references unless the context clearly indicates otherwise. For example, a reference to "a step" or "a device" means a reference to one or more steps or devices, and may include secondary steps and secondary devices. All conjunctions used should be understood in the broadest sense. And, the word "or" should be understood to have the definition of a logical "or", rather than a logical "exclusive or", unless the context clearly indicates otherwise. In addition, the implementation of the method and / or device in the embodiments of the present invention may include performing the selected task manually, automatically, or in combination.

Claims

1. A control circuit of an asymmetric half-bridge flyback converter, the asymmetric half-bridge flyback converter comprising a primary upper tube and a primary lower tube located on the primary side and connected in series, a synchronous rectifier located on the secondary side, and a transformer circuit coupled between a connection point between the primary upper tube and the primary lower tube and the synchronous rectifier, characterized in that: The control circuit includes a lower tube control module, the lower tube control module is used to receive a first signal and a second signal, the first signal includes information about the time when the secondary side current returns to zero, and the second signal includes information about the time when the primary side lower tube is turned off; and The lower tube control module indicates to turn off the primary lower tube at the turn-off time of the primary lower tube after the secondary side current returns to zero and indicates that the primary lower tube can be turned off.

2. The control circuit of the asymmetric half-bridge flyback converter according to claim 1, characterized in that: The first signal is a sampling signal of the voltage on the auxiliary winding, and the time when the secondary side current returns to zero is the time when the value of the first signal reaches a first predetermined value, wherein the auxiliary winding is coupled to the transformer circuit.

3. The control circuit of the asymmetric half-bridge flyback converter according to claim 2, characterized in that: The first predetermined value is the difference between a sampling value of the first signal within a predetermined time period and a predetermined offset, and the predetermined time period is between the moment when the primary lower tube is turned on and before the moment when the secondary current returns to zero.

4. The control circuit of the asymmetric half-bridge flyback converter according to claim 2 or 3, characterized in that: The first predetermined value is greater than 0V.

5. The control circuit of the asymmetric half-bridge flyback converter according to claim 1, characterized in that: The first signal is a sampling signal of the primary side current, and the time when the secondary side current returns to zero is the time corresponding to the inflection point of the first signal.

6. The control circuit of the asymmetric half-bridge flyback converter according to claim 5, characterized in that: The lower tube control module obtains the slope of the first signal in real time, and the moment corresponding to the inflection point of the first signal is the moment when the slope of the first signal changes from a positive value to a negative value; or, the lower tube control module obtains the value of the first signal in real time, and the moment corresponding to the inflection point of the first signal is the moment when the value of the first signal begins to gradually decrease.

7. The control circuit of the asymmetric half-bridge flyback converter according to claim 1, characterized in that: The second signal is a sampling signal of the primary-side current, and the turn-off moment of the primary lower tube is the moment when the value of the second signal reaches a second predetermined value.

8. The control circuit of the asymmetric half-bridge flyback converter according to claim 1, characterized in that: It also includes an upper tube control module, which is used to receive a third signal, the third signal contains information about the opening time of the primary upper tube, and the upper tube control module opens the primary upper tube according to the instruction of the third signal.

9. The control circuit of the asymmetric half-bridge flyback converter according to claim 8, characterized in that: The upper tube control module is further used to receive a fourth signal, wherein the fourth signal includes information about the shutdown time of the primary upper tube, and the upper tube control module shuts down the primary upper tube according to the instruction of the fourth signal.

10. The control circuit of the asymmetric half-bridge flyback converter according to claim 9, characterized in that: The fourth signal is a sampling signal of the primary-side current, and the primary-side upper tube is turned off at a time when the value of the fourth signal reaches a fourth predetermined value.

11. The control circuit of the asymmetric half-bridge flyback converter according to claim 8, characterized in that: After the upper tube control module instructs to turn on the primary upper tube, after a conduction time, the upper tube control module instructs to turn off the primary upper tube.

12. The control circuit of the asymmetric half-bridge flyback converter according to claim 11, characterized in that: The on-time is a fixed time or a time that varies with the switching frequency.

13. The control circuit of the asymmetric half-bridge flyback converter according to any one of claims 8 to 12, characterized in that: The control circuit is located on the primary side of the asymmetric half-bridge flyback converter.

14. The control circuit of the asymmetric half-bridge flyback converter according to any one of claims 8 to 12, characterized in that: The asymmetric half-bridge flyback converter comprises a secondary side controller and a coupler located at the secondary side of the asymmetric half-bridge flyback converter; and, The secondary-side controller is used to generate the third signal, and the coupler modulates the third signal and transmits it to the upper tube control module.

15. The control circuit of the asymmetric half-bridge flyback converter according to claim 14, characterized in that: The coupler includes a magnetic coupler, a capacitive isolator or a digital isolator.

16. An asymmetric half-bridge flyback converter, characterized in that: The invention comprises a control circuit of an asymmetric half-bridge flyback converter as claimed in any one of claims 1 to 15, wherein the control circuit is used to control the on and off of a primary upper tube and a primary lower tube of the asymmetric half-bridge flyback converter.

17. A control method for an asymmetric half-bridge flyback converter, the asymmetric half-bridge flyback converter comprising a primary upper tube and a primary lower tube located on a primary side and connected in series, a synchronous rectifier located on a secondary side, and a transformer circuit coupled between a connection point between the primary upper tube and the primary lower tube and the synchronous rectifier, characterized in that: The control method comprises: receiving a first signal, wherein the first signal includes information about a time when the secondary-side current returns to zero, indicating that the primary-side lower tube can be turned off at the time when the secondary-side current returns to zero; and A second signal is received, wherein the second signal includes information about a shutdown time of the primary lower tube and indicates to shut down the primary lower tube at the shutdown time of the primary lower tube.

18. The control method of the asymmetric half-bridge flyback converter according to claim 17, characterized in that: include: The first signal is obtained by sampling the voltage on the auxiliary winding, and the time when the secondary side current returns to zero is the time when the value of the first signal reaches a first predetermined value, wherein the auxiliary winding is coupled to the transformer circuit.

19. The control method of the asymmetric half-bridge flyback converter according to claim 17, characterized in that: include: The first signal is obtained by sampling a sampling signal of the primary side current, and the time when the secondary side current returns to zero is the time corresponding to the inflection point of the first signal.

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