Half-bridge flyback converter and control method, control circuit and chip thereof

Abstract

The embodiment of the invention provides a half-bridge flyback converter, a control method thereof, a control circuit and a chip. The control method comprises the steps that when the half-bridge flyback converter works in a free resonance state, in a first switching period, a second primary switching tube is controlled to be conducted for a first time length, and according to sampling voltage information of a secondary power loop, after it is detected that the second primary switching tube is conducted, a secondary switching tube is controlled to be conducted for a second time length, the half-bridge flyback converter can perform reverse excitation so as to generate negative excitation current, the zero voltage at the two ends of the first primary switch tube is reduced to zero, and when the first primary switch tube is controlled to be switched on, zero-voltage switching-on of the first primary switch tube can be realized. According to the method, the noise of the half-bridge flyback converter can be reduced, and zero-voltage switching-on of the first primary switching tube can be realized under the DCM of the wide-range output voltage of the half-bridge flyback converter, so that the efficiency of the half-bridge flyback converter under the DCM is improved.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to the field of integrated circuit technology, and in particular to a half-bridge flyback converter and a control method, a control circuit, and a chip thereof. Background Art

[0002] In the control scheme of the half-bridge flyback converter, the protocol controller transmits a feedback signal, i.e., output power information, to the primary controller through an isolation optocoupler. The primary controller controls the on and off of the first primary switch tube and the second primary switch tube in the half-bridge flyback converter according to the optocoupler feedback signal, wherein the first primary switch tube is connected in series with the primary winding, and the second primary switch tube is connected in parallel with the primary winding. Under light load, the half-bridge flyback converter enters DCM (Discontinue Conduction Mode) to reduce the switching loss of the half-bridge flyback converter. However, the excitation inductor storage current is insufficient, resulting in the first primary switch tube failing to achieve zero voltage switching (Zero Voltage Switching, ZVS).

[0003] In the prior art, the second primary switch tube can be turned on before the first primary switch tube is turned on, so that the excitation current passes through zero and becomes negative, so as to achieve zero voltage turn-on of the first primary switch tube. However, the resonant capacitor in the half-bridge flyback converter generally adopts a multi-layer ceramic capacitor (MLCC). Since the capacity of MLCC is limited and is affected by DC bias, the capacity of the resonant capacitor decreases significantly. When the second primary switch tube is turned on, the voltage fluctuation on the resonant capacitor is too large, resulting in the inability to achieve zero voltage turn-on of the first primary switch tube at a low output voltage. Summary of the invention

[0004] The present disclosure provides a half-bridge flyback converter and a control method, a control circuit and a chip thereof, which can realize zero-voltage turn-on of a first primary switch tube under DCM with a wide range of output voltages of the half-bridge flyback converter, thereby improving the efficiency of the half-bridge flyback converter under DCM, and can also reduce the audible noise of the half-bridge flyback converter.

[0005] In a first aspect, the present disclosure provides a control method for a half-bridge flyback converter, wherein the half-bridge flyback converter comprises: a primary power circuit and a secondary power circuit coupled to the primary power circuit, wherein the primary power circuit comprises a primary winding and a first primary switch tube and a second primary switch tube connected in series between a voltage input terminal and ground, and the secondary power circuit comprises a secondary winding and a secondary switch tube and an output capacitor respectively connected to two ends of the secondary winding.

[0006] The control method comprises:

[0007] When the half-bridge flyback converter operates in a free resonance state, in a first switching cycle, the second primary switch tube is controlled to be turned on for a first time period; after detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, the secondary switch tube is controlled to be turned on for a second time period so that the excitation current is a negative current; after the secondary switch tube is turned off, and at a moment separated by a dead time from the turning-off moment of the secondary switch tube, the first primary switch tube is controlled to be turned on.

[0008] In some embodiments of the present disclosure, before controlling the second primary switch tube to be turned on for a first time period in the first switching cycle, the method further includes:

[0009] In the first switching cycle, the second primary switch tube is controlled to be turned on for a third time period so that the excitation current is zero.

[0010] In some embodiments of the present disclosure, before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles, where N is an integer greater than or equal to 1.

[0011] Before controlling the second primary switch tube to be turned on for a third time period in the first switching cycle, the method further includes:

[0012] When the half-bridge flyback converter continuously operates for N second switching cycles in critical conduction mode (CrM), in the second switching cycle, the second primary switch tube is controlled to be turned on for a fourth time length so that the excitation current is a negative current, and the fourth time length is greater than the third time length; when the half-bridge flyback converter continuously operates for N second switching cycles in DCM, in the second switching cycle, the second primary switch tube is controlled to be turned on for the third time length.

[0013] In some embodiments of the present disclosure, before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles under CrM, where N is an integer greater than or equal to 1.

[0014] Before controlling the second primary switch tube to be turned on for a first time period in the first switching cycle, the method further includes:

[0015] In the first switching cycle, the second primary switch tube is controlled to be turned off.

[0016] In some embodiments of the present disclosure, before controlling the second primary switch tube to turn off in the first switching cycle, the method further includes:

[0017] In the second switching cycle, the first primary switch tube is controlled to be turned on for a fifth time period; in the first switching cycle, the first primary switch tube is controlled to be turned on for a sixth time period, and the sixth time period is shorter than the fifth time period.

[0018] In some embodiments of the present disclosure, after detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, controlling the secondary switch tube to be turned on for a second duration includes:

[0019] The turn-on time of the secondary switch tube is determined according to the drain voltage valley value of the secondary switch tube in the free resonance state; and at the turn-on time, the secondary switch tube is controlled to be turned on for the second time duration.

[0020] In a second aspect, the present disclosure provides a control circuit of a half-bridge flyback converter, wherein the half-bridge flyback converter comprises: a primary power circuit and a secondary power circuit coupled to the primary power circuit, wherein the primary power circuit comprises a primary winding and a first primary switch tube and a second primary switch tube connected in series between a voltage input terminal and ground, and the secondary power circuit comprises a secondary winding and a secondary switch tube and an output capacitor respectively connected to both ends of the secondary winding.

[0021] The control circuit includes a primary control module and a secondary control module. The primary control module is configured to control the second primary switch tube to be turned on for a first duration in a first switching cycle when the half-bridge flyback converter operates in a free resonance state.

[0022] The secondary control module is configured to, after detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, control the secondary switch tube to be turned on for a second time length so that the excitation current is a negative current. The primary control module is also configured to control the first primary switch tube to be turned on after the secondary switch tube is turned off and at a time interval of a dead time from the time when the secondary switch tube is turned off.

[0023] In some embodiments of the present disclosure, the primary control module is further configured to, in the first switching cycle, control the second primary switch tube to be turned on for a third time period so that the excitation current is zero.

[0024] In some embodiments of the present disclosure, before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles, where N is an integer greater than or equal to 1.

[0025] The primary control module is also configured to, when the half-bridge flyback converter continuously operates for N second switching cycles under CrM, control the second primary switch tube to be turned on for a fourth time period in the second switching cycle so that the excitation current is a negative current, and the fourth time period is greater than the third time period; when the half-bridge flyback converter continuously operates for N second switching cycles under DCM, control the second primary switch tube to be turned on for the third time period in the second switching cycle.

[0026] In some embodiments of the present disclosure, before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles under CrM, where N is an integer greater than or equal to 1.

[0027] The primary control module is further configured to control the second primary switch to be turned off during the first switching cycle.

[0028] In some embodiments of the present disclosure, the primary control module is further configured to, in the second switching cycle, control the first primary switch tube to be turned on for a fifth time period, and in the first switching cycle, control the first primary switch tube to be turned on for a sixth time period, and the sixth time period is less than the fifth time period.

[0029] In some embodiments of the present disclosure, the secondary control module is also configured to determine the turn-on time of the secondary switch tube according to the drain voltage valley value of the secondary switch tube in the free resonance state, and at the turn-on time, control the secondary switch tube to be turned on for the second duration.

[0030] In a third aspect, the present disclosure provides a half-bridge flyback converter, comprising a primary power circuit, a secondary power circuit coupled to the primary power circuit, and any control circuit provided in the second aspect, wherein the primary power circuit comprises a primary winding and a first primary switch tube and a second primary switch tube connected in series between a voltage input terminal and ground, and the secondary power circuit comprises a secondary winding and a secondary switch tube and an output capacitor respectively connected to both ends of the secondary winding.

[0031] In a fourth aspect, the present disclosure provides a chip, comprising a processor and a storage medium, wherein the processor implements the steps of any method provided in the first aspect when executing a computer program stored in the storage medium.

[0032] The technical solution disclosed in the present invention provides a control method for a half-bridge flyback converter. When the half-bridge flyback converter operates in a free resonance state, the second primary switch tube is controlled to be turned on for a first time period in a first switching cycle. After detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, the secondary switch tube is controlled to be turned on for a second time period. The half-bridge flyback converter can be reversely excited to generate a negative excitation current, and the zero voltage across the first primary switch tube is reduced to zero. After the secondary switch tube is turned off and at a dead time interval with the turn-off time of the secondary switch tube, the first primary switch tube is controlled to be turned on, so that the zero voltage turning on of the first primary switch tube can be achieved.

[0033] In addition, since the energy for the zero-voltage turn-on of the first primary switch tube comes from the output capacitor, and the output capacitor has a large capacity and is generally a solid-state capacitor, when the secondary switch tube is turned on, the voltage fluctuation of the output capacitor is small, thereby being able to reduce the audible noise of the half-bridge flyback converter, and also being able to achieve the zero-voltage turn-on of the first primary switch tube under the DCM of the wide range of output voltages of the half-bridge flyback converter, thereby improving the efficiency of the half-bridge flyback converter under DCM. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. It should be noted that the drawings described below only relate to some embodiments of the present disclosure, rather than limiting the present disclosure, wherein:

[0035] Figure 1 The present invention provides a structural schematic diagram of a half-bridge flyback converter provided in the prior art.

[0036] Figure 2 The present invention provides a schematic diagram of operating waveforms of a half-bridge flyback converter provided by the prior art.

[0037] Figure 3 A schematic diagram of the structure of a half-bridge flyback converter provided in an embodiment of the present disclosure.

[0038] Figure 4 A schematic diagram of the structure of another half-bridge flyback converter provided in an embodiment of the present disclosure.

[0039] Figure 5 A flow chart of a control method provided in an embodiment of the present disclosure.

[0040] Figure 6 A schematic diagram of operating waveforms of a half-bridge flyback converter provided in an embodiment of the present disclosure.

[0041] Figure 7 A schematic diagram of operating waveforms of another half-bridge flyback converter provided in an embodiment of the present disclosure.

[0042] Figure 8 A schematic diagram of operating waveforms of another half-bridge flyback converter provided in an embodiment of the present disclosure.

[0043] Fig. 9 A schematic diagram of operating waveforms of another half-bridge flyback converter provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work also fall within the scope of protection of the present disclosure.

[0045] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the disclosed subject matter belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the specification and the relevant art, and will not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein. As used herein, a statement that two or more parts are "connected" together shall mean that the parts are joined together directly or through one or more intermediate components.

[0046] Reference to "embodiments" in this disclosure means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase "embodiments" in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this disclosure may be combined with other embodiments.

[0047] In addition, the terms "first", "second", etc. in the specification and claims of the present disclosure or the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order, and may explicitly or implicitly include one or more of the features.

[0048] The term "and / or" in this disclosure is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0049] In the description of the present disclosure, unless otherwise specified, "plurality" and "at least two" mean more than two (including two), and similarly, "multiple groups" and "at least two groups" mean more than two groups (including two).

[0050] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0051] Figure 1 A schematic diagram of the structure of a half-bridge flyback converter is provided in the prior art. Figure 1 As shown, the half-bridge flyback converter 10 includes an input capacitor Cin, a first primary switch tube Q1, a second primary switch tube Q2, a resonant inductor Lr, a primary winding Np, a resonant capacitor Cr and a sampling resistor Rs.

[0052] Among them, the first electrode plate of the input capacitor Cin is connected to the voltage input end and the first end of the first primary switch tube Q1, the second end of the first primary switch tube Q1 is connected to the first end of the resonant inductor Lr and the first end of the second primary switch tube Q2, the second end of the resonant inductor Lr is connected to the first end of the sampling resistor Rs and the second end of the second primary switch tube Q2 through the primary winding Np and the resonant capacitor Cr, and the second end of the sampling resistor Rs and the second electrode plate of the input capacitor Cin are connected to the power ground PGND.

[0053] The half-bridge flyback converter 10 further includes an auxiliary winding Naux, a first auxiliary sampling resistor R1 and a second auxiliary sampling resistor R2, wherein a first end of the auxiliary winding Naux is connected to a first end of the first auxiliary sampling resistor R1, a second end of the auxiliary winding Naux is connected to a power ground PGND, and a second end of the first auxiliary sampling resistor R1 is connected to a power ground PGND through a second auxiliary sampling resistor R2.

[0054] The half-bridge flyback converter 10 also includes a secondary winding Ns, an output capacitor Cout and a secondary switch tube Q3, wherein a first end of the secondary winding Ns is connected to a voltage output end and a first plate of the output capacitor Cout, a second end of the secondary winding Ns is connected to a first end of the secondary switch tube Q3, and a second end of the secondary switch tube Q3 and a second plate of the output capacitor Cout are connected to a signal ground SGND.

[0055] The half-bridge flyback converter 10 also includes a controller 20, wherein the controller 20 includes a primary controller 21, a protocol controller 22, a secondary synchronous rectification controller 23 and an isolation optocoupler 24, a first input end of the primary controller 21 is connected to a connection point between a first auxiliary sampling resistor R1 and a second auxiliary sampling resistor R2, a second input end of the primary controller 21 is connected to an output end of the isolation optocoupler 24, and two output ends of the primary controller 21 are respectively connected to a control end of a first primary switch tube Q1 and a control end of a second primary switch tube Q2.

[0056] The first output end of the secondary synchronous rectification controller 23 is connected to the control end of the secondary switch tube Q3, the second output end of the secondary synchronous rectification controller 23 is connected to the input end of the protocol controller 22, and the output end of the protocol controller 22 is connected to the input end of the isolation optocoupler 24. The isolation optocoupler 24 includes a light emitting diode and a phototransistor, the positive electrode of the light emitting diode is connected to the output end of the protocol controller 22, the negative electrode of the light emitting diode is connected to the signal ground SGND, the first end of the phototransistor is connected to the second input end of the primary controller 21, and the second end of the phototransistor is connected to the power ground PGND.

[0057] The secondary synchronous rectification controller 23 can control the on and off of the secondary switch tube Q3, and generate a feedback signal reflecting the on and off of the secondary switch tube Q3. The secondary synchronous rectification controller 23 can transmit the feedback signal to the protocol controller 22. The protocol controller 22 transmits the feedback signal, that is, the output power information, to the primary controller 21 through the isolation optocoupler 24. The primary controller 21 can control the on and off of the first primary switch tube Q1 and the second primary switch tube Q2 according to the optocoupler feedback signal.

[0058] Under light load, the half-bridge flyback converter 10 enters DCM to reduce the switching loss of the half-bridge flyback converter 10. However, when the half-bridge flyback converter 10 is in DCM, the primary winding Np stores insufficient current when the first primary switch tube Q1 is turned on, thereby failing to achieve zero voltage turn-on of the first primary switch tube Q1.

[0059] In order to solve the above technical problem, the second primary switch tube Q2 can be turned on before the first primary switch tube Q1 is turned on, so that the excitation current passes through zero and becomes negative, thereby achieving zero voltage turn-on of the first primary switch tube Q1. Figure 2 As shown, Figure 2 The present invention provides a schematic diagram of operating waveforms of a half-bridge flyback converter provided by the prior art.

[0060] At time T0, the first primary control signal VQ1 and the secondary control signal VQ3 are both at low levels, then the first primary switch tube Q1 and the secondary switch tube Q3 are both turned off, and the primary controller 21 pulls up the second primary control signal VQ2 to turn on the second primary switch tube Q2, the half-bridge midpoint voltage VHB is pulled down to zero, and the excitation current Imag and the resonant current Ires are zero.

[0061] At time T1 , the primary controller 21 pulls down the second primary control signal VQ2 to turn off the second primary switch tube Q2 . At this time, the midpoint voltage VHB of the half bridge is maintained at zero, and the excitation current Imag and the resonant current Ires are negative currents.

[0062] At time T2, the primary controller 21 pulls up the first primary control signal VQ1 to turn on the first primary switch tube Q1, the half-bridge midpoint voltage VHB is pulled up to the input voltage, the excitation current Imag and the resonant current Ires are zero, and the zero voltage turn-on of the first primary switch tube Q1 can be achieved.

[0063] However, the resonant capacitor Cr generally adopts MLCC, and the capacity of MLCC is usually several hundred nF, and the DC-bias phenomenon is more obvious when the voltage of MLCC is higher, and the capacity of the resonant capacitor Cr decreases significantly. When the second primary switch tube Q2 is turned on, the voltage drop on the resonant capacitor Cr is too large, resulting in certain noise, and at low output voltage, for example, the output voltage is 3.3V, the zero voltage turn-on of the first primary switch tube Q1 cannot be achieved.

[0064] In view of this, the present disclosure provides a control method for a half-bridge flyback converter. When the half-bridge flyback converter operates in a free resonance state, the second primary switch tube is controlled to be turned on for a first time period. After detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, the secondary switch tube is controlled to be turned on for a second time period. The half-bridge flyback converter can be reversely excited to generate a negative excitation current, and the zero voltage across the first primary switch tube is reduced to zero. After the secondary switch tube is turned off and at a moment with a dead time interval between the secondary switch tube and the turn-off moment, the first primary switch tube is controlled to be turned on, so that zero voltage turning on of the first primary switch tube can be achieved.

[0065] In addition, since the energy for the zero-voltage turn-on of the first primary switch tube comes from the output capacitor, and the output capacitor has a large capacity and is generally a solid-state capacitor, when the secondary switch tube is turned on, the voltage fluctuation of the output capacitor is small, thereby being able to reduce the audible noise of the half-bridge flyback converter, and also being able to achieve the zero-voltage turn-on of the first primary switch tube under the DCM of the wide range of output voltages of the half-bridge flyback converter, thereby improving the efficiency of the half-bridge flyback converter under DCM.

[0066] The technical solution is described in detail below with reference to several specific embodiments.

[0067] Figure 3 A schematic diagram of the structure of a half-bridge flyback converter provided in an embodiment of the present disclosure is shown in FIG. Figure 3 As shown, the half-bridge flyback converter 100 includes a primary power circuit 110 and a secondary power circuit 120, and the primary power circuit 110 is coupled to the secondary power circuit 120. The primary power circuit 110 includes a first primary switch tube Q1, a second primary switch tube Q2 and a primary winding Np, and the first primary switch tube Q1 and the second primary switch tube Q2 are connected in series between the voltage input terminal and the power ground PGND.

[0068] For example, Figure 3As shown, the primary power circuit 110 also includes a resonant inductor Lr, a resonant capacitor Cr, an input capacitor Cin and a sampling resistor Rs. The first plate of the input capacitor Cin is a voltage input terminal, and the second plate of the input capacitor Cin is connected to the power ground PGND. The voltage input terminal is connected to the power ground PGND through the first primary switch tube Q1 and the second primary switch tube Q2 in sequence, and the connection point of the first primary switch tube Q1 and the second primary switch tube Q2 is connected to the power ground PGND through the resonant inductor Lr, the primary winding Np, the resonant capacitor Cr and the sampling resistor Rs in sequence.

[0069] In other embodiments, the voltage input terminal is connected to the power ground PGND through the first primary switch tube Q1, the second primary switch tube Q2 and the sampling resistor Rs in sequence, and the connection point of the first primary switch tube Q1 and the second primary switch tube Q2 is connected to the voltage input terminal through the resonant inductor Lr, the primary winding Np and the resonant capacitor Cr in sequence, such as Figure 4 As shown, Figure 4 A schematic diagram of the structure of another half-bridge flyback converter provided in an embodiment of the present disclosure.

[0070] Continue to see Figure 3 and Figure 4 As shown, the secondary power circuit 120 includes a secondary winding Ns, an output capacitor Cout and a secondary switch tube Q3. The first plate of the output capacitor Cout is a voltage output end, the second plate of the output capacitor Cout is connected to the signal ground SGND, and the two ends of the secondary winding Ns are respectively connected to the secondary switch tube Q3 and the output capacitor Cout.

[0071] Exemplarily, a first end of the secondary winding Ns is connected to a first plate of the output capacitor Cout, and a second end of the secondary winding Ns is connected to the signal ground SGND through the secondary switch tube Q3. Figure 3 In other embodiments, the first end of the secondary winding Ns is connected to the voltage output end through the secondary switch tube Q3, and the second end of the secondary winding Ns is connected to the second plate of the output capacitor Cout. Figure 4 shown.

[0072] Continue to see Figure 3 and Figure 4 As shown, the primary power circuit 110 also includes an auxiliary winding Naux, a first auxiliary sampling resistor R1 and a second auxiliary sampling resistor R2. The first end of the auxiliary winding Naux is connected to the power ground PGND through the first auxiliary sampling resistor R1 and the second auxiliary sampling resistor R2 in sequence, and the second end of the auxiliary winding Naux is connected to the power ground PGND.

[0073] The half-bridge flyback converter 100 also includes a control circuit 200, three output ends of the control circuit 200 are respectively connected to the control end of the first primary switch tube Q1, the control end of the second primary switch tube Q2 and the control end of the secondary switch tube Q3 to control the first primary switch tube Q1, the second primary switch tube Q2 and the secondary switch tube Q3.

[0074] The control circuit 200 is used to execute the steps of the control method provided by the present disclosure. The specific control method is described in detail below.

[0075] Figure 5 A flow chart of a control method provided by an embodiment of the present disclosure is shown in FIG. Figure 5 As shown, the specific steps of the control method include:

[0076] S101, when the half-bridge flyback converter operates in a free resonance state, in a first switching cycle, controlling the second primary switch tube to be turned on for a first time period.

[0077] For example, Figure 3 and Figure 4 As shown, the control circuit 200 includes a primary control module 210 and a secondary control module 220. The primary control module 210 includes a first primary drive unit 211, a second primary drive unit 212 and a primary control unit 213. For example, the primary control unit 213 is an asymmetric half-bridge (Asymmerical Half-Bridge, AHB) controller. The first output end of the primary control unit 213 is connected to the control end of the first primary switch tube Q1 through the first primary drive unit 211, and the second output end of the primary control unit 213 is connected to the control end of the second primary switch tube Q2 through the second primary drive unit 212.

[0078] The secondary control module 220 includes a secondary driving unit 221 and a secondary control unit 222 . For example, the secondary control unit 222 is a synchronous rectification (SR) controller. The output end of the secondary control unit 222 is connected to the control end of the secondary switch tube Q3 through the secondary driving unit 221 .

[0079] Figure 6 A schematic diagram of operating waveforms of a half-bridge flyback converter provided in an embodiment of the present disclosure is shown in FIG. Figure 6As shown, the half-bridge flyback converter 100 continuously operates for multiple switching cycles in DCM. At time T1 of the first switching cycle, the first primary control signal VQ1, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level. The primary control unit 213 controls the first primary drive unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and controls the second primary drive unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2. The secondary control unit 222 controls the secondary drive unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0080] Obviously, the first primary switch tube Q1 is not turned on, and the half-bridge flyback converter 100 is in a free resonance state. At this time, the primary control unit 213 pulls up the second primary control signal VQ2, and controls the second primary driving unit 330 to turn on the second primary switch tube Q2 according to the second primary control signal VQ2, and the drain voltage Vsrd of the secondary switch tube Q3 is pulled down to zero.

[0081] For example, the time T1 may be a time corresponding to the valley voltage at the midpoint of the half bridge in the free resonance state in the first switching cycle, or may be other time in the free resonance state in the first switching cycle.

[0082] After moment T1 of the first switching cycle and at moment T2 which is separated from moment T1 by a first time length Ton1, the first primary control signal VQ1 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the first primary drive unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and the secondary control unit 222 controls the secondary drive unit 221 to turn off the secondary switch tube Q3 according to the secondary control signal VQ3.

[0083] At this time, the primary control unit 213 pulls down the second primary control signal VQ2, and controls the second primary driving unit 212 to turn off the second primary switch tube Q2 according to the second primary control signal VQ2. At this point, a communication pulse signal indicating the turn-on of the secondary switch tube Q3 is generated, that is, the second primary control signal VQ2 between time T1 and time T2.

[0084] S102, after detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, controlling the secondary switch tube to be turned on for a second time period so that the excitation current is a negative current.

[0085] For example, see Figure 3 and Figure 4The secondary control module 220 also includes a secondary sampling unit 223, an input end of the secondary sampling unit 223 is connected to the drain of the secondary switch tube Q3, and an output end of the secondary sampling unit 223 is connected to the input end of the secondary control unit 222. The secondary sampling unit 223 can collect the drain voltage Vsrd of the secondary switch tube Q3 and transmit the drain voltage Vsrd of the secondary switch tube Q3 to the secondary control unit 222.

[0086] The secondary control unit 222 can determine the sampled voltage information of the secondary power loop 120 according to the drain voltage Vsrd of the secondary switch tube Q3. For example, the sampled voltage information can be a secondary synchronous rectification detection signal indicating whether the secondary power loop 120 is turned on, the change in the falling edge slope of the drain voltage Vsrd, the voltage valley value of the drain voltage Vsrd and the drop of the drain voltage Vsrd, etc.

[0087] When the sampled voltage information meets the preset conditions, the secondary switch tube Q3 is controlled to be turned on. For example, when the sampled voltage information is a secondary synchronous rectification detection signal, the preset condition is a secondary synchronous rectification turn-on signal indicating that the secondary power circuit 120 is turned on. When the sampled voltage information is a falling edge slope change of the drain voltage Vsrd, the preset condition is a slope change threshold.

[0088] like Figure 6 As shown, in the first switching cycle, when it is determined that the sampled voltage information meets the preset condition, at time T3 later than time T1, the first primary control signal VQ1 and the second primary control signal VQ2 maintain a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2.

[0089] At this time, the secondary control unit 222 pulls up the secondary control signal VQ3, and controls the secondary driving unit 212 to turn on the secondary switch tube Q3 according to the secondary control signal VQ3, and the output capacitor Cout provides energy to excite the secondary winding Ns, that is, the half-bridge flyback converter 100 is reversely excited.

[0090] After the moment T3 of the first switching cycle and at the moment T4 which is separated from the moment T3 by the second time length Ton2, the first primary control signal VQ1 and the second primary control signal VQ2 maintain a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2.

[0091] At this time, the secondary control unit 222 pulls down the secondary control signal VQ3, and controls the secondary driving unit 221 to turn off the secondary switch tube Q3 according to the secondary control signal VQ3. The parasitic capacitance of the primary winding Np and the first primary switch tube Q1 begins to resonate, and the energy stored in the secondary winding Ns is transmitted to the primary winding Np. Then, the excitation current Imag is a negative current, and the voltage across the first primary switch tube Q1 is reduced to zero.

[0092] It should be noted that Figure 6 It is only exemplified that the turn-on time T3 of the secondary switch tube Q3 is later than the turn-off time T2 of the second primary switch tube Q2. In practical applications, the turn-on time T3 of the secondary switch tube Q3 may be earlier than the turn-off time T2 of the second primary switch tube Q2.

[0093] S103, after the secondary switch tube is turned off, at a time that is separated from the turning-off time of the secondary switch tube by a dead time, controlling the first primary switch tube to be turned on.

[0094] For example, Figure 6 As shown, after the moment T4 of the first switching cycle and at the moment T0 separated from the moment T4 by a dead time Tdead, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the second primary drive unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2, and the secondary control unit 222 controls the secondary drive unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0095] At this time, the voltage across the first primary switch tube Q1 is zero, the primary control unit 213 pulls up the first primary control signal VQ1, and controls the first primary driving unit 211 to turn on the first primary switch tube Q1 according to the first primary control signal VQ1, thereby achieving zero voltage turn-on of the first primary switch tube Q1.

[0096] Continue to see Figure 6 At time T5 of the first switching cycle, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2, and the secondary control unit 222 controls the secondary driving unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0097] At this time, the excitation current Imag increases from zero to a preset value, and the primary control unit 213 pulls down the first primary control signal VQ1 , and controls the first primary driving unit 211 to turn off the first primary switch tube Q1 according to the first primary control signal VQ1 .

[0098] To sum up, when the half-bridge flyback converter 100 operates in the first switching cycle of DCM before the first primary switch tube Q1 is turned on, the half-bridge flyback converter 100 operates in a free resonance state. Then, in the first switching cycle, the secondary switch tube Q3 is controlled to be turned on for a period of time, and the half-bridge flyback converter 100 can be reversely excited to generate a negative excitation current Imag, and the voltage across the first primary switch tube Q1 is reduced to zero, thereby achieving zero voltage turn-on of the first primary switch tube Q1.

[0099] In addition, since the energy for the zero-voltage turn-on of the first primary switch tube Q1 comes from the output capacitor Cout, and the output capacitor Cout has a large capacity and is generally a solid capacitor, when the secondary switch tube Q3 is turned on, the voltage fluctuation of the output capacitor Cout is small, so the audible noise of the half-bridge flyback converter can be reduced, and the zero-voltage turn-on of the first primary switch tube Q1 can be achieved under the DCM of the wide range of output voltage of the half-bridge flyback converter 100, so as to improve the efficiency of the half-bridge flyback converter 100 under DCM.

[0100] Based on the above embodiment, before the first switching cycle, the half-bridge flyback converter 100 continuously operates for N second switching cycles, where N is an integer greater than or equal to 1. The half-bridge flyback converter 100 may continuously operate for N second switching cycles in DCM, such as Figure 6 As shown, the half-bridge flyback converter 100 may also continuously operate for N second switching cycles under CrM, such as Figure 7 As shown, Figure 7 A schematic diagram of operating waveforms of another half-bridge flyback converter provided in an embodiment of the present disclosure.

[0101] In some embodiments, before S101, the specific steps of the control method further include:

[0102] S201, in the first switching cycle, controlling the second primary switch tube to be turned on for a third time period to make the excitation current zero.

[0103] For example, Figure 6 and Figure 7 As shown, at time T6 of the first switching cycle, the first primary control signal VQ1 maintains a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1.

[0104] At this time, the primary control unit 213 pulls up the second primary control signal VQ2, and controls the second primary drive unit 212 to turn on the second primary switch tube Q2 according to the second primary control signal VQ2, and the secondary control unit 222 pulls up the secondary control signal VQ3, and controls the secondary drive unit 221 to turn on the secondary switch tube Q3 according to the secondary control signal VQ3. The resonant capacitor Cr and the resonant inductor Lr begin to resonate, the primary power circuit 110 transfers energy to the secondary power circuit 120, and the excitation current Imag decreases linearly.

[0105] After moment T6 of the first switching cycle and at moment T7 which is separated from moment T6 by a third time length Ton3, the excitation current Imag is zero, the primary control unit 213 pulls down the second primary control signal VQ2, and controls the second primary driving unit 212 to turn off the second primary switch tube Q2 according to the second primary control signal VQ2.

[0106] At this time, the first primary control signal VQ1 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the first primary drive unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and the secondary control unit 222 controls the secondary drive unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3, and the half-bridge flyback converter 100 enters a free resonance state.

[0107] In some embodiments, before the first switching cycle, the half-bridge flyback converter 100 continuously operates in DCM for N second switching cycles, and the specific steps of the control method before S201 further include:

[0108] S301, in a second switching cycle, controlling the second primary switch tube to be turned on for a third time period.

[0109] For example, Figure 6 As shown, at time T6 ′ of the second switching period, the first primary control signal VQ1 maintains a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch Q1 turned off according to the first primary control signal VQ1 .

[0110] At this time, the primary control unit 213 pulls up the second primary control signal VQ2, and controls the second primary drive unit 212 to turn on the second primary switch tube Q2 according to the second primary control signal VQ2, and the secondary control unit 222 pulls up the secondary control signal VQ3, and controls the secondary drive unit 221 to turn on the secondary switch tube Q3 according to the secondary control signal VQ3. The resonant capacitor Cr and the resonant inductor Lr begin to resonate, the primary power circuit 110 transfers energy to the secondary power circuit 120, and the excitation current Imag decreases linearly.

[0111] After the moment T6' of the second switching cycle and at the moment T7' which is separated from the moment T6' by the third time length Ton3, the excitation current Imag is zero, the primary control unit 213 pulls down the second primary control signal VQ2, and controls the second primary driving unit 212 to turn off the second primary switch tube Q2 according to the second primary control signal VQ2.

[0112] At this time, the first primary control signal VQ1 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the first primary drive unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and the secondary control unit 222 controls the secondary drive unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3, and the half-bridge flyback converter 100 enters a free resonance state.

[0113] In some embodiments, before the first switching cycle, the half-bridge flyback converter 100 continuously operates for N second switching cycles under CrM, and the specific steps of the control method before S201 further include:

[0114] S301 ′, in the second switching cycle, controlling the second primary switch tube to be turned on for a fourth time period, so that the excitation current is a negative current.

[0115] For example, Figure 7 As shown, at time T6 ′ of the second switching period, the first primary control signal VQ1 maintains a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch Q1 turned off according to the first primary control signal VQ1 .

[0116] At this time, the primary control unit 213 pulls up the second primary control signal VQ2, and controls the second primary drive unit 212 to turn on the second primary switch tube Q2 according to the second primary control signal VQ2, and the secondary control unit 222 pulls up the secondary control signal VQ3, and controls the secondary drive unit 221 to turn on the secondary switch tube Q3 according to the secondary control signal VQ3. The resonant capacitor Cr and the resonant inductor Lr begin to resonate, the primary power circuit 110 transfers energy to the secondary power circuit 120, and the excitation current Imag decreases linearly.

[0117] After moment T6' of the second switching cycle and at moment T6' which is separated by the third time Ton3, the excitation current Imag is zero. Then, after moment T6' of the second switching cycle and at moment T7' which is separated by the fourth time Ton4, since Ton4>Ton3, the excitation current Imag is a negative current.

[0118] At this time, the primary control unit 213 pulls down the second primary control signal VQ2, and controls the second primary driving unit 212 to turn off the second primary switch tube Q2 according to the second primary control signal VQ2. The first primary control signal VQ1 and the secondary control signal VQ3 are maintained at a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and the secondary control unit 222 controls the secondary driving unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0119] After the moment T7' of the second switching cycle and at a moment separated from the moment T7' by a preset dead time, the primary control unit 213 pulls up the first primary control signal VQ1 to enter the first switching cycle, and controls the first primary driving unit 211 to turn on the first primary switch tube Q1 according to the first primary control signal VQ1, thereby achieving zero voltage turn-on of the first primary switch tube Q1.

[0120] In some embodiments, before the first switching cycle, the half-bridge flyback converter 100 continuously operates for N switching cycles under CrM, and the specific steps of the control method before S101 further include:

[0121] S201', in the first switching cycle, controlling the second primary switch tube to be turned off.

[0122] For example, Figure 8 A schematic diagram of operating waveforms of another half-bridge flyback converter provided in an embodiment of the present disclosure is shown in FIG. Figure 8 As shown, at time T6 of the first switching cycle, the secondary control unit 222 pulls up the secondary control signal VQ3 until the resonant current Ires is zero and then pulls down the secondary control signal VQ3. The secondary control unit 222 can control the secondary driving unit 221 to turn on the secondary switch tube Q3 at time T6 according to the secondary control signal VQ3, and turn off the secondary switch tube Q3 until the resonant current Ires is zero.

[0123] In the first switching cycle, from moment T6 to the end of the first switching cycle, the first primary control signal VQ1 and the second primary control signal VQ2 maintain a low level, and the primary control unit 213 controls the first primary driving unit 211 to keep the first primary switch tube Q1 turned off according to the first primary control signal VQ1, and controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2.

[0124] In this way, when the resonant current Ires passes through zero, the resonant inductor Lr and the resonant capacitor Cr no longer resonate, and the voltage Vcr of the resonant capacitor Cr is greater than N p / N s *Vout, where Np is the number of turns of the primary winding Np, N s is the number of turns of the primary winding Ns, Vout is the output voltage of the half-bridge flyback converter 100, the excitation current Imag decreases linearly through the secondary switch tube Q3 until the excitation current Imag is zero, and the half-bridge flyback converter 100 enters a free resonance state. In addition, Vcr is greater than N p / N s *Vout, which can ensure that the communication pulse signal used to indicate the turn-on of the secondary switch tube Q3 can be reliably identified.

[0125] Based on the above embodiment, the specific steps of the control method before S201' further include:

[0126] S401, in the second switching cycle, controlling the first primary switch tube to be turned on for a fifth time period.

[0127] For example, Fig. 9 A schematic diagram of operating waveforms of another half-bridge flyback converter provided in an embodiment of the present disclosure is shown in FIG. Fig. 9 As shown, at time T8' of the second switching cycle, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2, and the secondary control unit 222 controls the secondary driving unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0128] At this time, the primary control unit 213 pulls up the first primary control signal VQ1 , and controls the first primary driving unit 211 to turn on the first primary switch Q1 according to the first primary control signal VQ1 , so that the excitation current Imag starts to increase.

[0129] After time T8' of the second switching cycle and at time T9' which is separated from time T8' by a fifth time period Ton5, the excitation current Imag rises to a preset value, the primary control unit 213 pulls down the first primary control signal VQ1, and controls the first primary driving unit 211 to turn off the first primary switch tube Q1 according to the first primary control signal VQ1.

[0130] At this time, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level. The primary control unit 213 controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2. The secondary control unit 222 controls the secondary driving unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0131] S402, in the first switching cycle, controlling the first primary switch tube to be turned on for a sixth time period.

[0132] For example, Fig. 9 As shown, at time T8 of the first switching cycle, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level, the primary control unit 213 controls the second primary drive unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2, and the secondary control unit 222 controls the secondary drive unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0133] At this time, the primary control unit 213 pulls up the first primary control signal VQ1 , and controls the first primary driving unit 211 to turn on the first primary switch Q1 according to the first primary control signal VQ1 , so that the excitation current Imag starts to increase.

[0134] After the moment T8 of the first switching cycle, at the moment T9 which is separated from the moment T8 by the sixth time length Ton6, the sixth time length Ton6 is less than the fifth time length Ton5, for example, the sixth time length Ton6 is 1 / 2, 1 / 3 or 2 / 3 of the fifth time length Ton5, then the excitation current Imag is less than the preset value. At this time, the primary control unit 213 pulls down the first primary control signal VQ1, and controls the first primary driving unit 211 to turn off the first primary switch tube Q1 according to the first primary control signal VQ1.

[0135] At the same time, the second primary control signal VQ2 and the secondary control signal VQ3 maintain a low level, and the primary control unit 213 controls the second primary driving unit 212 to keep the second primary switch tube Q2 turned off according to the second primary control signal VQ2, and the secondary control unit 222 controls the secondary driving unit 221 to keep the secondary switch tube Q3 turned off according to the secondary control signal VQ3.

[0136] Since the excitation current Imag is less than the preset value, when the resonant current Ires passes through zero, the voltage Vcr of the resonant capacitor Cr will not be much greater than N p / N s *Vout, thereby reducing the overcurrent risk when the second primary switch tube Q2 is turned on.

[0137] In some embodiments, a possible implementation method of executing S102 is specifically described as follows:

[0138] S1021, determining the turn-on time of the secondary switch tube according to the drain voltage valley value of the secondary switch tube in the free resonance state.

[0139] Exemplarily, the drain voltage Vsrd of the secondary switch tube Q3 oscillates and changes in the free resonance state, and the secondary control unit 222 can determine the sampled voltage information in the free resonance state according to the oscillation change of the drain voltage Vsrd in the free resonance state.

[0140] The sampled voltage information may include the drain voltage change rate of the secondary switch tube Q3 and the drain voltage change trend of the secondary switch tube Q3. The secondary control unit 222 may determine the drain voltage valley value according to the drain voltage change rate and the drain voltage change trend of the secondary switch tube Q3 in the free resonance state. For example, when the drain voltage change trend of the secondary switch tube Q3 in the free resonance state is decreasing and the drain voltage change rate is approximately zero, it may be determined that the drain voltage Vsrd reaches the drain voltage valley value.

[0141] Alternatively, the sampled voltage information may include the lowest valley voltage of each oscillation cycle, and the lowest valley voltage of the current oscillation cycle is compared with the lowest valley voltage of the previous oscillation cycle to determine whether the lowest valley voltage of the current oscillation cycle is the drain voltage valley value. When it is determined that the lowest valley voltage of the current oscillation cycle is not the drain voltage valley value, as time goes by, the current oscillation cycle is updated to the next oscillation cycle, and the previous oscillation cycle is updated to the current oscillation cycle, and the above determination steps are repeated until it is determined that the lowest valley voltage of the current oscillation cycle is the drain voltage valley value.

[0142] The secondary control unit 222 determines the time corresponding to the drain voltage valley value as the turn-on time of the secondary switch tube Q3.

[0143] S1022, at the turn-on moment, controlling the secondary switch tube to be turned on for a first time period.

[0144] Exemplarily, the secondary control unit 222 pulls up the secondary control signal VQ3 when the secondary switch tube Q3 is turned on, and controls the secondary driving unit 221 to turn on the secondary switch tube Q3 according to the secondary control signal VQ3.

[0145] The control circuit 200 provided by the present disclosure includes a primary control module 210 and a secondary control module 220, wherein a first output end of the primary control module 210 is connected to a control end of a first primary switch tube Q1, a second output end of the primary control module 210 is connected to a control end of a second primary switch tube Q2, and an output end of the secondary control module 220 is connected to a control end of a secondary switch tube Q3. Figure 3 and Figure 4 shown.

[0146] The primary control module 210 is configured to control the second primary switch tube Q2 to be turned on for a first duration Ton1 in a first switching cycle when the half-bridge flyback converter 100 operates in a free resonance state.

[0147] The secondary control module 220 is configured to, based on the sampled voltage information of the secondary power circuit 120 , control the secondary switch tube Q3 to be turned on for a second duration Ton2 after detecting that the second primary switch tube Q2 is turned on, so that the excitation current Image is a negative current.

[0148] The primary control module 210 is further configured to control the first primary switch tube Q1 to be turned on after the secondary switch tube Q3 is turned off and at a time interval of a dead time Tdead from the time when the secondary switch tube Q3 is turned off.

[0149] In some embodiments, the primary control module 210 is further configured to, in the first switching cycle, control the second primary switch tube Q2 to be turned on for a third duration Ton3 so that the excitation current Imag is zero.

[0150] In some embodiments, before the first switching cycle, the half-bridge flyback converter 100 continuously operates for N second switching cycles, where N is an integer greater than or equal to 1.

[0151] The primary control module 210 is also configured to, when the half-bridge flyback converter 100 continuously operates for N second switching cycles under CrM, in the second switching cycle, control the second primary switch tube Q2 to be turned on for a fourth time length Ton4 so that the excitation current Imag is a negative current, and the fourth time length Ton4 is greater than the third time length Ton3; when the half-bridge flyback converter 100 continuously operates for N second switching cycles under DCM, in the second switching cycle, control the second primary switch tube Q2 to be turned on for a third time length Ton3.

[0152] In some embodiments, before the first switching cycle, the half-bridge flyback converter 100 continuously operates at CrM for N second switching cycles, where N is an integer greater than or equal to 1.

[0153] The primary control module 210 is further configured to control the second primary switch tube Q2 to be turned off in the first switching cycle.

[0154] In some embodiments, the primary control module 210 is further configured to, in the second switching cycle, control the first primary switch tube Q1 to be turned on for a fifth time length Ton5, and in the first switching cycle, control the first primary switch tube Q1 to be turned on for a sixth time length Ton6, wherein the sixth time length Ton6 is less than the fifth time length Ton5.

[0155] In some embodiments, the secondary control module 220 is further configured to determine the turn-on time of the secondary switch tube Q3 according to the drain voltage valley value of the secondary switch tube Q3 in the free resonance state, and control the secondary switch tube Q3 to be turned on for a first duration Ton1 at the turn-on time of the secondary switch tube Q3.

[0156] In some embodiments, see Figure 3 and Figure 4 The primary control module 210 includes a first primary driving unit 211 , a second primary driving unit 212 , a primary control unit 213 , a first primary sampling unit 214 and a second primary sampling unit 215 .

[0157] The input end of the first primary sampling unit 214 is connected to the connection point of the first auxiliary sampling resistor R1 and the second auxiliary sampling resistor R2, the output end of the first primary sampling unit 214 is connected to the first input end of the primary control unit 213, the first output end of the primary control unit 213 is connected to the control end of the first primary switch tube Q1 through the first primary driving unit 211, and the second output end of the primary control unit 213 is connected to the control end of the second primary switch tube Q2 through the second primary driving unit 212.

[0158] For example, Figure 3 As shown, the output end of the second primary sampling unit 215 is connected to the second input end of the primary control unit 213, and the input end of the second primary sampling unit 215 is connected to the connection point of the sampling resistor Rs and the resonant capacitor Cr. Figure 4 As shown, the output end of the second primary sampling unit 215 is connected to the second input end of the primary control unit 213 , and the input end of the second primary sampling unit 215 is connected to the connection point of the sampling resistor Rs and the second primary switch tube Q2 .

[0159] In some embodiments, see Figure 3 and Figure 4 The secondary control module 220 includes a secondary driving unit 221, a secondary sampling unit 223 and a secondary control unit 222. The output end of the secondary control unit 222 is connected to the control end of the secondary switch tube Q3 through the secondary driving unit 221, the input end of the secondary sampling unit 223 is connected to the drain of the secondary switch tube Q3, and the output end of the secondary sampling unit 223 is connected to the input end of the secondary control unit 222.

[0160] The control circuit 200 provided in the embodiment of the present disclosure is used to execute the steps of any of the above-mentioned method embodiments, has functional modules corresponding to the method embodiments, and has the beneficial effects of the method embodiments, which will not be repeated here.

[0161] The present disclosure also provides a chip including a processor and a storage medium. When the processor executes a computer program stored in the storage medium, the processor implements the steps of any of the above method embodiments. The chip has functional modules corresponding to the method embodiments and has the beneficial effects of the method embodiments, which will not be repeated here.

[0162] Unless the context clearly indicates otherwise, the singular form of the words used herein and in the appended claims includes the plural form and vice versa. Thus, when referring to the singular, the plural form of the corresponding term is generally included. Similarly, the words "comprise" and "include" are to be interpreted as inclusive rather than exclusive. Likewise, the terms "include" and "or" should be interpreted as inclusive, unless such interpretation is expressly prohibited herein. Where the term "example" is used herein, the "example" is merely illustrative and should not be considered exclusive or comprehensive.

[0163] Several embodiments of the present disclosure are described in detail above, but it is obvious that those skilled in the art can make various modifications and variations to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. The protection scope of the present disclosure is defined by the attached claims.

Claims

1. A control method for a half-bridge flyback converter, characterized in that: The half-bridge flyback converter comprises: a primary power circuit and a secondary power circuit coupled to the primary power circuit, wherein the primary power circuit comprises a primary winding and a first primary switch tube and a second primary switch tube connected in series between a voltage input terminal and a ground, and the secondary power circuit comprises a secondary winding and a secondary switch tube and an output capacitor respectively connected to two ends of the secondary winding; The control method comprises: When the half-bridge flyback converter operates in a free resonance state, in a first switching cycle, controlling the second primary switch tube to be turned on for a first time period; After detecting, according to the sampled voltage information of the secondary power circuit, that the second primary switch tube is turned on, controlling the secondary switch tube to be turned on for a second time length so that the excitation current is a negative current; After the secondary switch tube is turned off, at a time that is separated from the turning-off time of the secondary switch tube by a dead time, the first primary switch tube is controlled to be turned on.

2. The control method according to claim 1, characterized in that: Before controlling the second primary switch tube to be turned on for a first time period in the first switching cycle, the method further includes: In the first switching cycle, the second primary switch tube is controlled to be turned on for a third time period so that the excitation current is zero.

3. The control method according to claim 2, characterized in that: Before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles, where N is an integer greater than or equal to 1; Before controlling the second primary switch tube to be turned on for a third time period in the first switching cycle, the method further includes: When the half-bridge flyback converter continuously operates for N second switching cycles in the critical conduction mode (CrM), in the second switching cycle, the second primary switch tube is controlled to be turned on for a fourth time period so that the excitation current is a negative current, and the fourth time period is greater than the third time period; When the half-bridge flyback converter continuously operates for N second switching cycles in a discontinuous conduction mode (DCM), in the second switching cycle, the second primary switch tube is controlled to be turned on for the third time length.

4. The control method according to claim 1, characterized in that: Before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles under CrM, where N is an integer greater than or equal to 1; Before controlling the second primary switch tube to be turned on for a first time period in the first switching cycle, the method further includes: In the first switching cycle, the second primary switch tube is controlled to be turned off.

5. The control method according to claim 4, characterized in that: Before controlling the second primary switch tube to turn off in the first switching cycle, the method further includes: In the second switching cycle, controlling the first primary switch tube to be turned on for a fifth time period; In the first switching cycle, the first primary switch tube is controlled to be turned on for a sixth time period, and the sixth time period is shorter than the fifth time period.

6. The control method according to any one of claims 1 to 5, characterized in that: After detecting, based on the sampled voltage information of the secondary power circuit, that the second primary switch tube is turned on, controlling the secondary switch tube to be turned on for a second duration includes: Determining a turn-on time of the secondary switch tube according to a drain voltage valley value of the secondary switch tube in the free resonance state; At the turn-on moment, the secondary switch tube is controlled to be turned on for the second time duration.

7. A control circuit for a half-bridge flyback converter, characterized in that: The half-bridge flyback converter comprises: a primary power circuit and a secondary power circuit coupled to the primary power circuit, wherein the primary power circuit comprises a primary winding and a first primary switch tube and a second primary switch tube connected in series between a voltage input terminal and a ground, and the secondary power circuit comprises a secondary winding and a secondary switch tube and an output capacitor respectively connected to two ends of the secondary winding; The control circuit includes a primary control module and a secondary control module; The primary control module is configured to, when the half-bridge flyback converter operates in a free resonance state, control the second primary switch tube to be turned on for a first time period in a first switching cycle; The secondary control module is configured to, after detecting that the second primary switch tube is turned on according to the sampled voltage information of the secondary power circuit, control the secondary switch tube to be turned on for a second time length so that the excitation current is a negative current; The primary control module is further configured to control the first primary switch tube to be turned on after the secondary switch tube is turned off and at a time that is separated from the turning-off time of the secondary switch tube by a dead time.

8. The control circuit according to claim 7, characterized in that: The primary control module is further configured to, in the first switching cycle, control the second primary switch tube to be turned on for a third time period so that the excitation current is zero.

9. The control circuit according to claim 8, characterized in that: Before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles, where N is an integer greater than or equal to 1; The primary control module is further configured to, when the half-bridge flyback converter continuously operates for N second switching cycles in the critical conduction mode (CrM), control the second primary switch tube to be turned on for a fourth time period in the second switching cycle so that the excitation current is a negative current, and the fourth time period is greater than the third time period; When the half-bridge flyback converter continuously operates for N second switching cycles in a discontinuous conduction mode (DCM), in the second switching cycle, the second primary switch tube is controlled to be turned on for the third time length.

10. The control circuit according to claim 7, characterized in that: Before the first switching cycle, the half-bridge flyback converter continuously operates for N second switching cycles under CrM, where N is an integer greater than or equal to 1; The primary control module is further configured to control the second primary switch tube to be turned off during the first switching cycle.

11. The control circuit according to claim 10, characterized in that: The primary control module is further configured to, in the second switching cycle, control the first primary switch tube to be turned on for a fifth duration, and in the first switching cycle, control the first primary switch tube to be turned on for a sixth duration, wherein the sixth duration is shorter than the fifth duration.

12. The control circuit according to any one of claims 7 to 11, characterized in that: The secondary control module is further configured to determine a turn-on time of the secondary switch tube according to a drain voltage valley value of the secondary switch tube in the free resonance state, and at the turn-on time, control the secondary switch tube to be turned on for the second duration.

13. A half-bridge flyback converter, characterized in that: include: A primary power circuit, a secondary power circuit coupled to the primary power circuit, and a control circuit as described in any one of claims 7 to 12, wherein the primary power circuit includes a primary winding and a first primary switch tube and a second primary switch tube connected in series between a voltage input terminal and ground, and the secondary power circuit includes a secondary winding and a secondary switch tube and an output capacitor respectively connected to both ends of the secondary winding.

14. A chip, characterized in that: The method comprises a processor and a storage medium, wherein the processor implements the steps of the method according to any one of claims 1 to 6 when executing a computer program stored in the storage medium.

Images