A secondary side controller, control method and control system of a flyback converter

Abstract

Embodiments of the present application provide a secondary side controller, a control method and a control system of a flyback converter. The secondary side controller comprises a sampling circuit, a processing circuit and a control circuit; two input ends of the sampling circuit are electrically connected to a drain end of a secondary side power tube and an output end of the flyback converter respectively, and an output end of the sampling circuit is electrically connected to a control end of the secondary side power tube through the processing circuit and the control circuit in sequence; the sampling circuit is configured to determine an output sampling voltage and an input sampling voltage based on a drain end voltage and an output voltage; the processing circuit is configured to determine a conduction duration based on the output sampling voltage, the input sampling voltage and a preset value; and the control circuit is configured to control on-off of the secondary side power tube based on the conduction duration, so that a valley value of a drain end voltage of a primary side power tube is zero. The secondary side controller can realize zero voltage conduction of the primary side power tube by controlling the secondary side power tube, thereby reducing loss of the converter; in addition, the conduction duration can be adaptively adjusted, thereby improving applicability.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of flyback converter, in particular to a secondary side controller, a control method and a control system of flyback converter. BACKGROUND

[0002] In the design field of AC-DC converter, the primary side power tube needs to bear a high voltage, usually a voltage of hundreds of volts, for example, the drain voltage of the primary side power tube bears a voltage of: the product of the output voltage of the converter and the turns ratio, and the sum of the input voltage of the converter when it is off. This not only puts higher requirements on the voltage withstand selection of the primary side power tube, but also forms a large cross loss when the primary side power tube is converted from off to on state, thereby causing the problem of temperature rise. Therefore, the zero voltage turn-on of the primary side power tube is an important proposition in the design of AC-DC converter.

[0003] The prior art cannot realize the zero voltage turn-on of the primary side power tube by controlling the secondary side, resulting in large loss of the converter. SUMMARY

[0004] In view of the above problems, the embodiment of the present application provides a secondary side controller, a control method and a control system of flyback converter, which can realize the zero voltage turn-on of the primary side power tube by controlling the secondary side power tube, thereby reducing the loss of the converter; in addition, it can also adaptively adjust the turn-on time, thereby improving the applicability of the secondary side controller.

[0005] In a first aspect, the embodiment of the present application provides a secondary side controller applied to a flyback converter, the flyback converter comprising a primary side power tube and a secondary side power tube, comprising: a sampling circuit, a processing circuit and a control circuit;

[0006] The first input end of the sampling circuit is electrically connected to the drain end of the secondary side power tube, the second input end of the sampling circuit is electrically connected to the output end of the flyback converter, the output end of the sampling circuit is electrically connected to the input end of the processing circuit, the output end of the processing circuit is electrically connected to the input end of the control circuit, and the output end of the control circuit is electrically connected to the control end of the secondary side power tube;

[0007] The sampling circuit is configured to determine an output sampling voltage and an input sampling voltage based on the drain voltage of the secondary side power tube and the output voltage of the flyback converter;

[0008] The processing circuit is configured to determine the turn-on time of the secondary side power tube based on the output sampling voltage, the input sampling voltage and a preset value;

[0009] The control circuit is configured to control on-off of the secondary-side power tube based on the on duration, so that a valley value of the drain end voltage of the primary-side power tube is zero.

[0010] In some embodiments, the sampling circuit comprises a voltage sampling module and a voltage calculation module.

[0011] The first input end of the voltage sampling module is electrically connected to the drain end of the secondary-side power tube, the second input end of the voltage sampling module is electrically connected to the output end of the flyback converter, the first output end of the voltage sampling module is electrically connected to the first input end of the processing circuit and the first input end of the voltage calculation module, the second output end of the voltage sampling module is electrically connected to the second input end of the voltage calculation module, and the output end of the voltage calculation module is electrically connected to the second input end of the processing circuit.

[0012] The voltage sampling module is configured to sample the drain end voltage of the secondary-side power tube and the output voltage of the flyback converter respectively to obtain a drain end sampling voltage and an output sampling voltage.

[0013] The voltage calculation module is configured to determine the input sampling voltage based on the drain end sampling voltage and the output sampling voltage.

[0014] In some embodiments, the processing circuit comprises a ratio calculation module, a comparison module and a duration calculation module.

[0015] The input end of the ratio calculation module is electrically connected to the output end of the sampling circuit, the output end of the ratio calculation module is electrically connected to the input end of the comparison module, the output end of the comparison module is electrically connected to the input end of the duration calculation module, and the output end of the duration calculation module is electrically connected to the input end of the control circuit.

[0016] The ratio calculation module is configured to determine a target ratio based on a ratio of the input sampling voltage and the output sampling voltage.

[0017] The comparison module is configured to compare the target ratio and a preset value, and generate a comparison signal based on a comparison result.

[0018] The duration calculation module is configured to determine the on duration based on the comparison signal.

[0019] In some embodiments, the duration calculation module comprises a logic processing unit and a time calculation unit.

[0020] An input end of the logic processing unit is electrically connected to an output end of the comparison module, a first output end of the logic processing unit is electrically connected to an input end of the time calculation unit, a second output end of the logic processing unit is electrically connected to a first input end of the control circuit, and an output end of the time calculation unit is electrically connected to a second input end of the control circuit.

[0021] The logic processing unit is configured to generate a selection signal based on the comparison signal, wherein the selection signal is one of a plurality of preset selection signals.

[0022] The time calculation unit is configured to select one of a plurality of preset linear calculation sub-units corresponding to the selection signal as a linear calculation sub-unit, input the target ratio to the linear calculation sub-unit, and determine the conduction duration based on the linear calculation sub-unit.

[0023] In a second aspect, an embodiment of the present application provides a control method of a flyback converter, which is applicable to any of the auxiliary-side controllers provided in the first aspect. The control method comprises:

[0024] Determining an output sampling voltage and an input sampling voltage based on the drain voltage of the auxiliary-side power tube and the output voltage of the flyback converter.

[0025] Determining the conduction duration of the auxiliary-side power tube based on the output sampling voltage, the input sampling voltage, and a preset value.

[0026] Controlling the on-off of the auxiliary-side power tube based on the conduction duration, so that the valley value of the drain voltage of the primary-side power tube is zero.

[0027] In some embodiments, the determination of the output sampling voltage and the input sampling voltage based on the drain voltage of the auxiliary-side power tube and the output voltage of the flyback converter comprises:

[0028] Sampling the drain voltage of the auxiliary-side power tube and the output voltage of the flyback converter respectively to obtain a drain sampling voltage and the output sampling voltage.

[0029] Determining the input sampling voltage based on the drain sampling voltage and the output sampling voltage.

[0030] In some embodiments, the determination of the conduction duration of the auxiliary-side power tube based on the output sampling voltage, the input sampling voltage, and a preset value comprises:

[0031] Determining a target ratio based on the ratio of the input sampling voltage to the output sampling voltage.

[0032] Comparing the target ratio with the preset value and generating a comparison signal based on the comparison result.

[0033] determine the on duration based on the comparison signal.

[0034] In some embodiments, the determining the on duration based on the comparison signal comprises:

[0035] generating a selection signal based on the comparison signal, wherein the selection signal is one of a plurality of preset selection signals;

[0036] selecting one of a plurality of preset linear calculation sub-units corresponding to the selection signal as a linear calculation sub-unit, and inputting the target ratio to the linear calculation sub-unit;

[0037] determining the on duration based on the linear calculation sub-unit.

[0038] In some embodiments, the determining the target ratio based on the ratio of the input sampling voltage and the output sampling voltage comprises:

[0039] determining the target ratio based on the ratio of the input sampling voltage and the output sampling voltage, and the turns ratio of the flyback converter.

[0040] In a third aspect, the embodiments of the present application provide a control system of a flyback converter, comprising a primary side controller and any one of the secondary side controllers provided in the first aspect; an output end of the primary side controller is electrically connected to a control end of a primary side power tube, and an output end of the secondary side controller is electrically connected to a control end of a secondary side power tube.

[0041] In the technical scheme of the embodiments of the present application, the secondary side controller comprises a sampling circuit, a processing circuit and a control circuit, a first input end of the sampling circuit is electrically connected to a drain end of the secondary side power tube, a second input end of the sampling circuit is electrically connected to an output end of the flyback converter, an output end of the sampling circuit is electrically connected to an input end of the processing circuit, an output end of the processing circuit is electrically connected to an input end of the control circuit, and an output end of the control circuit is electrically connected to a control end of the secondary side power tube; the output sampling voltage and the input sampling voltage can be determined based on the drain end voltage of the secondary side power tube and the output voltage of the flyback converter through the sampling circuit; the on duration of the secondary side power tube can be determined based on the output sampling voltage, the input sampling voltage and the preset value through the processing circuit; the on-off of the secondary side power tube can be controlled based on the on duration through the control circuit, so that the valley value of the drain end voltage of the primary side power tube is zero, and thus the zero voltage on of the primary side power tube can be realized at the valley value of the drain end voltage of the primary side power tube, so as to reduce the loss of the converter; in addition, the on duration is determined based on the drain end voltage of the secondary side power tube and the output voltage of the flyback converter, so that the on duration can be adaptively adjusted based on the actual working condition, thereby improving the applicability of the secondary side controller.

[0042] The above description is only a summary of the technical solutions of the embodiments of the present application, in order to enable the technical means of the embodiments of the present application to be more clearly understood, and can be implemented according to the content of the specification, and in order to enable the above and other purposes, characteristics and advantages of the embodiments of the present application to be more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0044] Figure 1 A structure schematic diagram of a flyback converter and a control system thereof provided by the present application is shown in the figure.

[0045] Figure 2 A voltage and current waveform schematic diagram of each node of a flyback converter provided by the embodiments of the present application is shown in the figure.

[0046] Figure 3 A structure schematic diagram of a secondary side controller provided by the present application is shown in the figure.

[0047] Figure 4 A structure schematic diagram of another secondary side controller provided by the present application is shown in the figure.

[0048] Figure 5 A curve schematic diagram of the conduction time changing with the target ratio provided by the embodiments of the present application is shown in the figure.

[0049] Figure 6 A structure schematic diagram of still another secondary side controller provided by the embodiments of the present application is shown in the figure.

[0050] Figure 7 A flow schematic diagram of a control method of a flyback converter provided by the embodiments of the present application is shown in the figure.

[0051] Figure 8 A flow schematic diagram of another control method of a flyback converter provided by the embodiments of the present application is shown in the figure. DETAILED DESCRIPTION

[0052] In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application; the use herein of terms such as "comprise" and "comprising", and "have" and "having", and any variations thereof, is intended to cover a non-exclusive inclusion.

[0054] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the application. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that any of the embodiments described herein can be combined with any of the other embodiments unless explicitly stated otherwise.

[0055] In addition, the terms "first", "second", and the like, herein and in the claims, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. Such a term can be expressly or implicitly understood and / or defined to include one or also more of the indicated number of items unless specifically stated otherwise.

[0056] In the description of the application, unless otherwise clearly specified and limited, the terms "connected", "connecting" should be understood broadly, for example, the "connected" or "connecting" of circuit structure can be not only the physical connection, but also the electrical connection or signal connection, for example, it can be directly connected, that is, the physical connection, or indirectly connected through at least one element, as long as the circuit is connected, it can also be the internal connection of two elements; signal connection can be not only through the circuit for signal connection, but also through the media medium for signal connection, for example, radio wave.

[0057] In order to make the person skilled in the art better understand the scheme of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings.

[0058] The primary side input of the flyback switching power supply can be a pulsating voltage after the alternating current is rectified by the diode rectifier bridge, or can be a direct current voltage after power factor correction, wherein the ripple of the pulsating voltage is large, and the ripple of the direct current voltage is small. Generally, the range of the primary side input voltage is wide, the minimum value can be about 60V, and the maximum value can be about 400V, and the wide voltage range brings great challenges to the control design of the flyback switching power supply.

[0059] Figure 1 A structure schematic diagram of a flyback converter and a control system thereof provided by the present application is shown in the figure Figure 1As shown, the flyback converter includes an input capacitor CIN, a primary coil L1, a primary power tube M1, an output capacitor COUT, a secondary coil L2 and a secondary power tube M2. The first plate of the input capacitor CIN and the first end of the primary coil L1 are electrically connected to an input voltage VIN, the second end of the primary coil L1 is electrically connected to the drain of the primary power tube M1, the source of the primary power tube M1 and the second plate of the input capacitor CIN are both grounded, and there is a parasitic capacitor Cp in the primary power tube M1. The primary coil L1 is coupled to the secondary coil L2, the first end of the secondary coil L2 is electrically connected to the first plate of the output capacitor COUT, the second end of the secondary coil L2 is electrically connected to the drain of the secondary power tube M2, the source of the secondary power tube M2 and the second plate of the output capacitor COUT are both grounded, and the voltage across the output capacitor COUT is the output voltage VOUT.

[0060] The control system of the flyback converter includes a secondary controller 100 and a primary controller 200, wherein the output end of the primary controller 200 is electrically connected to the control end of the primary power tube M1, and the output end of the secondary controller 100 is electrically connected to the control end of the secondary power tube M2. When the primary controller 200 controls the primary power tube M1 to be in a conducting state, the voltage difference across the primary coil L1 is VIN, and the voltage at the same end of the secondary coil L2 is VOUT+VIN / N, wherein N is the turns ratio of the flyback converter; at this time, the secondary controller 100 controls the secondary power tube M2 to be in a cut-off state, and the output capacitor COUT supplies power. When the primary controller 200 controls the primary power tube M1 to be in a cut-off state, the voltage difference across the primary coil L1 reverses due to the inability of the current to suddenly change, and the voltage difference across the secondary coil L2 also reverses, and the secondary controller 100 controls the secondary power tube M2 to be in a conducting state.

[0061] In this way, in one working cycle, the secondary controller 100 can control the on-off state of the secondary power tube M2 based on the change of the drain voltage of the secondary power tube M2, so as to realize the synchronous rectification control of the flyback converter.

[0062] In addition, the secondary controller 100 can also control the secondary power tube M2 to be turned on twice in one working cycle, Figure 2 The voltage and current waveform diagram of each node of the flyback converter is provided for the embodiments of the present application. As shown in FIG. 2, the voltage and current waveform diagram of each node of the flyback converter includes an input voltage VIN, an output voltage VOUT, a primary coil voltage Vp, a secondary coil voltage Vs, a primary power tube voltage Vd, a secondary power tube voltage Vs, a primary power tube current Ip, a secondary power tube current Is, an input capacitor current Ic, an output capacitor current Io, a primary power tube current Ip, a secondary power tube current Is, an input capacitor current Ic, and an output capacitor current Io. Figure 2As shown, at t1, the control voltage VG2 of the secondary-side power tube M2 is pulled from a low-level signal to a high-level signal, the secondary-side power tube M2 is turned on, the drain voltage VD2 of the secondary-side power tube M2 is pulled low, the secondary-side inductor L2 is reversely excited, the current IM2 of the secondary-side inductor L2 reversely charges the flyback converter, so that the ringing of the primary side is assigned, that is, the drain voltage VD1 of the primary-side power tube M1 sharply rises. After experiencing a Tc duration, that is, at t2, the control voltage VG2 of the secondary-side power tube M2 is pulled from a high-level signal to a low-level signal, the secondary-side power tube M2 is turned off, and the drain voltage VD2 of the secondary-side power tube M2 can be understood as the on duration of the secondary-side power tube M2.

[0063] At this time, the drain voltage VD1 of the primary-side power tube M1 starts to resonate with damping due to the existence of the primary-side inductor L1 and the parasitic capacitor Cp, and the drain voltage VD1 of the primary-side power tube M1 can resonate to zero voltage. In this way, the primary-side controller 200 pulls the control voltage VG1 of the primary-side power tube M1 from a low-level signal to a high-level signal when the drain voltage VD1 of the primary-side power tube M1 resonates to the valley value, controls the primary-side power tube M1 to turn on, and can realize zero voltage turn-on of the primary-side power tube M1, thereby reducing the loss of the converter.

[0064] Obviously, the on duration Tc is a decisive factor of the valley value of the drain voltage VD1 of the primary-side power tube M1, that is, based on the on duration Tc, the valley value of the drain voltage VD1 of the primary-side power tube M1 can be determined, so the secondary-side controller 100 is needed to determine the on duration Tc.

[0065] The following gives several specific embodiments to illustrate the secondary-side controller 100 in detail.

[0066] Figure 3 A structure schematic diagram of a secondary-side controller provided by the embodiment of the application is shown in Figure 3 As shown, the secondary-side controller 100 includes a sampling circuit 110, a processing circuit 120, and a control circuit 130. The first input end of the sampling circuit 110 is electrically connected to the drain of the secondary-side power tube M2, the second input end of the sampling circuit 110 is electrically connected to the output end of the flyback converter, the output end of the sampling circuit 110 is electrically connected to the input end of the processing circuit 120, the output end of the processing circuit 120 is electrically connected to the input end of the control circuit 130, and the output end of the control circuit 130 is electrically connected to the control end of the secondary-side power tube M2.

[0067] Sampling circuit 110 is used to determine the output sampling voltage VOUT_SNS and the input sampling voltage VIN_SNS based on the drain voltage VD2 of the secondary power transistor M2 and the output voltage VOUT of the flyback converter. Processing circuit 120 is used to determine the conduction duration Tc of the secondary power transistor M2 based on the output sampling voltage VOUT_SNS, the input sampling voltage VIN_SNS and the preset value a_th. Control circuit 130 is used to control the on-off state of the secondary power transistor M2 based on the conduction duration Tc, so that the valley value of the drain voltage VD1 of the primary power transistor M1 is zero.

[0068] For example, based on the charging and discharging resonance principle of the primary inductance L1 and parasitic capacitance Cp, the formula for calculating the conduction time Tc can be obtained as follows:

[0069]

[0070] Where L1 is the inductance value of the primary inductance L1, and C p This is the capacitance value of the parasitic capacitance Cp of the primary-side power transistor M1.

[0071] For a given flyback converter, L1, C p With N as a fixed value, it can be seen from formula (1) that the conduction time Tc is related to both the input voltage VIN and the output voltage VOUT. Therefore, the conduction time Tc can be determined based on the input voltage VIN and the output voltage VOUT.

[0072] Figure 4 This is a schematic diagram of another secondary-side controller provided in an embodiment of this application. Figure 4 for Figure 3 Based on the illustrated embodiment, the sampling circuit 110 includes a voltage sampling module 111 and a voltage calculation module 112. Specifically, the first input terminal of the voltage sampling module 111 is electrically connected to the drain terminal of the secondary power transistor M2; the second input terminal of the voltage sampling module 111 is electrically connected to the output terminal of the flyback converter; the first output terminal of the voltage sampling module 111 is electrically connected to the first input terminal of the processing circuit 120 and the first input terminal of the voltage calculation module 112; the second output terminal of the voltage sampling module 111 is electrically connected to the second input terminal of the voltage calculation module 112; and the output terminal of the voltage calculation module 112 is electrically connected to the second input terminal of the processing circuit 120.

[0073] Exemplarily, the voltage sampling module 111 can receive the output voltage VOUT and scale it in a certain proportion to obtain an output sampling voltage VOUT SNS for facilitating subsequent circuit processing; the voltage sampling module 111 can also receive the drain voltage VD2 of the secondary-side power tube M2 and scale it in a certain proportion to obtain a drain sampling voltage VD2 SNS for facilitating subsequent circuit processing. The voltage sampling module 111 transmits the output sampling voltage VOUT SNS to the voltage calculation module 112 and the processing circuit 120, and transmits the drain sampling voltage VD2 SNS to the voltage calculation module 112.

[0074] When the secondary-side power tube M2 is off, the relationship of VD2 = VOUT + VIN / N holds, and accordingly, the voltage calculation module 112 can calculate the input sampling voltage VIN SNS based on the received drain sampling voltage VD2 SNS and the output sampling voltage VOUT SNS.

[0075] In this way, the voltage sampling module 111 in the sampling circuit 110 can sample the drain voltage VD2 of the secondary-side power tube M2 and the output voltage VOUT of the flyback converter respectively to obtain the drain sampling voltage VD2 SNS and the output sampling voltage VOUT SNS; the voltage calculation module 112 can determine the input sampling voltage VIN SNS based on the drain sampling voltage VD2 SNS and the output sampling voltage VOUT SNS.

[0076] Exemplarily, continuing to refer to Figure 4 The processing circuit 120 includes a ratio calculation module 121, a comparison module 122 and a time length calculation module 123, wherein the input end of the ratio calculation module 121 is electrically connected to the output end of the sampling circuit 110, the output end of the ratio calculation module 121 is electrically connected to the input end of the comparison module 122, the output end of the comparison module 122 is electrically connected to the input end of the time length calculation module 123, and the output end of the time length calculation module 123 is electrically connected to the input end of the control circuit 130.

[0077] As Figure 4As shown, the first input terminal of the ratio calculation module 121 is electrically connected to the first output terminal of the voltage sampling module 111, and the second input terminal of the ratio calculation module 121 is electrically connected to the output terminal of the voltage calculation module 112. The ratio calculation module 121 can receive the output sampling voltage VOUT_SNS output by the voltage sampling module 111 and the input sampling voltage VIN_SNS output by the voltage calculation module 112. The ratio calculation module 121 can determine the ratio of the input sampling voltage VIN_SNS to the output sampling voltage VOUT_SNS, i.e., VIN_SNS / VOUT_SNS, and determine the product of VIN_SNS / VOUT_SNS and 1 / N as the target ratio a, i.e., a = VIN_SNS / (N*VOUT_SNS).

[0078] The default value a_th can be based on L1, C p N, VIN, and VOUT are determined in advance; for example, L1 = 1mH, C p =200pF, N=6, VIN ranges from 90 to 300V, and VOUT ranges from 5 to 20V. Based on the ranges of VIN and VOUT, the range of a is 0.75 ≤ a ≤ 10. However, due to the limitation of the square root operation, the value of a is 1 ≤ a ≤ 10. Substituting the target ratio a into formula (1) yields the following formula:

[0079]

[0080] Based on formula (2), with a as the abscissa and Tc as the ordinate, we can obtain the following: Figure 5 The curve shown, Figure 5 This is a schematic diagram of the conduction duration changing with a target ratio, provided in an embodiment of this application. Clearly, Tc has a significant inflection point at a = 1.25. Therefore, 1.25 divides the Tc curve into two segments: when a < 1.25, the function relationship of the curve corresponding to Tc is: Tc = k1*a + b1; when a < 1.25, the function relationship of the curve corresponding to Tc is: Tc = k2*a + b2. 1.25 can be used as the preset value a_th.

[0081] It should be noted that the preset value a_th can be selected in a way that considers L1 and C. p Determine L1, C, N, VIN, and VOUT; or, for L1, C p Comparison and judgment after operations on N, VIN, and VOUT; or L1, C p Determining the interrelationships of N, VIN, and VOUT after performing operations; or, for Figure 5 The determination can be made by performing differential and integral transformations on the curve shown; or by determining the conditions required for actual working conditions. In this embodiment of the application, the selection method of the preset value a_th is not specifically limited.

[0082] The preset value a th is internally preset in the comparison module 122, and the comparison module 122 can compare the preset value a th with the received target ratio a to generate a comparison result. The comparison result of the preset value a th and the target ratio a includes a≤a th and a>a th. The comparison result of a≤a th can be further divided into a≤1 and 1<a≤a th, and the actual physical meaning of a≤1 is that the ringing formed by the primary side inductance L1 and the parasitic capacitance Cp is sufficient to reduce the valley value of the drain voltage VD1 of the primary side power tube M1 to zero.

[0083] The comparison module 122 can also generate a corresponding comparison signal based on the comparison result. For example, the comparison signal can include a first sub-signal C0, a second sub-signal C1, and a third sub-signal C2. If the comparison result is a≤1, the corresponding comparison signal is C0=1, C1=0, and C2=0; if the comparison result is 1<a≤a th, the corresponding comparison signal is C0=0, C1=1, and C2=0; and if the comparison result is a>a th, the corresponding comparison signal is C0=0, C1=0, and C2=1.

[0084] The time length calculation module 123 internally presets a plurality of preset comparison signals SEL_pre, and each preset comparison signal SEL_pre corresponds to a preset calculation model. The time length calculation module 123 determines the preset calculation model corresponding to the comparison signal output by the comparison module 122 from the plurality of preset calculation models, and inputs the target value a into the preset calculation model to calculate the conduction time Tc.

[0085] In this way, the ratio calculation module 121 in the processing circuit 120 can determine the target ratio a based on the ratio of the input sampling voltage VIN SNS and the output sampling voltage VOUT SNS; the comparison module 122 can compare the target ratio a with the preset value a th and generate a comparison signal based on the comparison result; and the time length calculation module 123 can determine the conduction time Tc based on the comparison signal.

[0086] The control circuit 130 can control the secondary side power tube M2 to conduct twice when the secondary side power tube is in the off state after conducting once, and control the secondary side power tube M2 to be in the off state when the conduction time of the secondary side power tube M2 is the conduction time Tc. The primary side controller 200 can determine the valley value of the drain voltage VD1 of the primary side power tube M1 based on the conduction time Tc, and control the primary side power tube M1 to conduct when the drain voltage VD1 of the primary side power tube M1 resonates to the valley value, thereby realizing zero voltage conduction of the primary side power tube M1.

[0087] In summary, the secondary side controller 100 can determine the conduction time Tc of the secondary side power tube M2 based on the drain voltage VD2 of the secondary side power tube M2 and the output voltage VOUT of the flyback converter, that is, the conduction time Tc can be adaptively changed based on the change of the application working condition, so that the secondary side controller 100 can achieve zero voltage conduction of the primary side power tube under different application conditions and working conditions.

[0088] In the embodiment of the application, the secondary side controller comprises a sampling circuit, a processing circuit and a control circuit, the first input end of the sampling circuit is electrically connected to the drain end of the secondary side power tube, the second input end of the sampling circuit is electrically connected to the output end of the flyback converter, the output end of the sampling circuit is electrically connected to the input end of the processing circuit, the output end of the processing circuit is electrically connected to the input end of the control circuit, and the output end of the control circuit is electrically connected to the control end of the secondary side power tube; the output sampling voltage and the input sampling voltage can be determined based on the drain voltage of the secondary side power tube and the output voltage of the flyback converter through the sampling circuit; the conduction time of the secondary side power tube can be determined based on the output sampling voltage, the input sampling voltage and the preset value through the processing circuit; and the on-off of the secondary side power tube can be controlled based on the conduction time through the control circuit, so that the valley value of the drain voltage of the primary side power tube is zero. In this way, the primary side power tube is turned on at the valley value of the drain voltage of the primary side power tube, and zero voltage conduction of the primary side power tube can be achieved, thereby reducing the loss of the converter. In addition, the conduction time is determined based on the drain voltage of the secondary side power tube and the output voltage of the flyback converter, so that the conduction time can be adaptively adjusted based on the actual working condition, thereby improving the applicability of the secondary side controller.

[0089] In some embodiments, Figure 6 A structure schematic diagram of another secondary side controller provided by the embodiment of the application is shown in Figure 6 A structure schematic diagram of another secondary side controller provided by the embodiment of the application is shown in Figure 4 Based on the embodiment shown in the foregoing, the time calculation module 123 comprises a logic processing unit 1231 and a time calculation unit 1232. The input end of the logic processing unit 1231 is electrically connected to the output end of the comparison module 122, the first output end of the logic processing unit 1231 is electrically connected to the input end of the time calculation unit 1232, the second output end of the logic processing unit 1231 is electrically connected to the first input end of the control circuit 130, and the output end of the time calculation unit 1232 is electrically connected to the second input end of the control circuit 130.

[0090] The logic processing unit 1231 is configured to generate a selection signal SEL based on the comparison signal, wherein the selection signal SEL is one of a plurality of preset selection signals SEL_pre; and the time calculation unit 1232 is configured to select one corresponding to SEL from a plurality of preset linear calculation sub-units as a linear calculation sub-unit, input the target ratio a into the linear calculation sub-unit, and determine the conduction time Tc based on the linear calculation sub-unit.

[0091] For example, the logic processing unit 1231 can generate different selection signals SEL based on different comparison signals. For instance, based on the above embodiment, when the comparison signals are C0=1, C1=0, and C2=0, the generated selection signal SEL is a preset selection signal SEL_pre0; if the comparison signals are C0=0, C1=1, and C2=0, the generated selection signal SEL is a preset selection signal SEL_pre1; and if the comparison signals are C0=0, C1=0, and C2=1, the generated selection signal SEL is a preset selection signal SEL_pre2.

[0092] The time calculation unit 1232 has multiple preset linear calculation subunits internally, each corresponding to a preset selection signal SEL_pre. For example, as... Figure 6 As shown, the time calculation unit 1232 has three preset linear calculation sub-units, namely preset linear calculation sub-unit 0, preset linear calculation sub-unit 1 and preset linear calculation sub-unit 2. Among them, preset linear calculation sub-unit 0 corresponds to the preset selection signal SEL_pre0, preset linear calculation sub-unit 1 corresponds to the preset selection signal SEL_pre1, and preset linear calculation sub-unit 2 corresponds to the preset selection signal SEL_pre2.

[0093] If the selection signal SEL received by the time calculation unit 1232 is one of a plurality of preset selection signals SEL_pre, then the corresponding linear calculation subunit can be selected from a plurality of preset linear calculation subunits as the linear calculation subunit. For example, based on the above embodiment, if the selection signal SEL is a preset selection signal SEL_pre0, then the linear calculation subunit is preset linear calculation subunit 0; if the selection signal SEL is a preset selection signal SEL_pre1, then the linear calculation subunit is preset linear calculation subunit 1; if the selection signal SEL is a preset selection signal SEL_pre2, then the linear calculation subunit is preset linear calculation subunit 2. Afterwards, the time calculation unit 1232 inputs the target ratio a to the linear calculation subunit, and the linear calculation subunit can calculate the conduction duration Tc based on the target ratio a.

[0094] In the embodiment of the present application, the time length calculation module comprises a logic processing unit and a time calculation unit, the input end of the logic processing unit is electrically connected to the output end of the comparison module, the first output end of the logic processing unit is electrically connected to the input end of the time calculation unit, the second output end of the logic processing unit is electrically connected to the first input end of the control circuit, and the output end of the time calculation unit is electrically connected to the second input end of the control circuit; the logic processing unit can generate a selection signal based on the comparison signal, wherein the selection signal is one of a plurality of preset selection signals; the time calculation unit can select one corresponding to the selection signal from a plurality of preset linear calculation sub-units as a linear calculation sub-unit, and input the target ratio to the linear calculation sub-unit to determine the conduction time length based on the linear calculation sub-unit. In this way, without performing square root processing on the target ratio, the calculation complexity of the secondary side controller can be reduced, that is, the circuit complexity can be reduced and the circuit reliability can be improved, and the cost can also be saved.

[0095] The embodiment of the present application also provides a control method of a flyback converter, which is suitable for the secondary side controller provided in any of the above-mentioned embodiments. Figure 7 As shown in the flowchart of the control method of the flyback converter provided in the embodiment of the present application, Figure 7 the control method specifically comprises the following steps.

[0096] S101, determining an output sampling voltage and an input sampling voltage based on the drain voltage of the secondary side power tube and the output voltage of the flyback converter.

[0097] As a specific description of one possible implementation manner of performing S101, the following is provided.

[0098] S1011, respectively sampling the drain voltage of the secondary side power tube and the output voltage of the flyback converter to obtain a drain sampling voltage and the output sampling voltage.

[0099] For example, the sampling circuit can receive the drain voltage VD2 of the secondary side power tube and the output voltage VOUT of the flyback converter, sample the drain voltage VD2 of the secondary side power tube to obtain the drain sampling voltage VD2_SNS, and sample the output voltage VOUT to obtain the output sampling voltage VOUT_SNS.

[0100] S1012, determining the input sampling voltage based on the drain sampling voltage and the output sampling voltage.

[0101] When the secondary side power tube is off, the relationship of VD2=VOUT+VIN / N is established, the sampling circuit can substitute the drain sampling voltage VD2_SNS and the output sampling voltage VOUT_SNS into this relationship, and the input sampling voltage VIN_SNS can be determined.

[0102] S102, determining the on duration of the secondary-side power tube based on the output sampling voltage, the input sampling voltage and a preset value.

[0103] As a possible implementation of S102, the following is a specific description:

[0104] S1021, determining a target ratio based on the ratio of the input sampling voltage and the output sampling voltage.

[0105] For example, the processing circuit can receive the output sampling voltage VOUT_SNS output by the voltage sampling module 111 and the input sampling voltage VIN_SNS output by the voltage calculation module 112, and determine the ratio VIN_SNS / VOUT_SNS of the input sampling voltage VIN_SNS and the output sampling voltage VOUT_SNS.

[0106] The processing circuit can determine the target ratio a based on the ratio VIN_SNS / VOUT_SN of the input sampling voltage VIN_SNS and the output sampling voltage VOUT_SNS, and the turns ratio N of the flyback converter. For example, the product of the ratio VIN_SNS / VOUT_SN of the input sampling voltage VIN_SNS and the output sampling voltage VOUT_SNS and 1 / N is the target ratio a, i.e. a=VIN_SNS / (N*VOUT_SNS).

[0107] S1022, comparing the target ratio and the preset value, and generating a comparison signal based on the comparison result.

[0108] For example, the processing circuit has a preset value a_th set in advance, and the processing circuit can compare the size of the preset value a_th and the received target ratio a, and generate a comparison result. For example, the comparison result of the preset value a_th and the target ratio a includes a≤1, 1<a≤a_th and a>a_th.

[0109] The processing circuit can also generate a corresponding comparison signal based on the comparison result. For example, the comparison signal can include a first sub-signal C0, a second sub-signal C1 and a third sub-signal C2. If the comparison result is a≤1, the corresponding comparison signal is: C0=1, C1=0, C2=0; if the comparison result is 1<a≤a_th, the corresponding comparison signal is: C0=0, C1=1, C2=0; if the comparison result is a>a_th, the corresponding comparison signal is: C0=0, C1=0, C2=1.

[0110] S1023, determining the on duration based on the comparison signal.

[0111] The processing circuit has multiple preset comparison signals SEL_pre preset inside, each preset comparison signal SEL_pre corresponds to a preset calculation model, the processing circuit can determine the preset calculation model corresponding to the comparison signal from the multiple preset calculation models, and bring the target value a into the preset calculation model to calculate the on duration Tc.

[0112] In S103, the on-off of the secondary-side power tube is controlled based on the on duration, so that the valley value of the drain end voltage of the primary-side power tube is zero.

[0113] For example, when the secondary-side power tube is in the off state after the first on, the control circuit can control the secondary-side power tube to be in the second on, and when the on duration of the second on is the on duration Tc, the secondary-side power tube is controlled to be in the off state. The primary-side controller can determine the valley value of the drain end voltage VD1 of the primary-side power tube based on the on duration Tc, and control the primary-side power tube to be on when the drain end voltage VD1 of the primary-side power tube resonates to the valley value, so as to realize the zero voltage on of the primary-side power tube M1, thereby reducing the loss of the converter.

[0114] In summary, based on the drain end voltage VD2 of the secondary-side power tube and the output voltage VOUT of the flyback converter, the on duration Tc of the secondary-side power tube can be determined, that is, the on duration Tc can be adaptively changed based on the change of the application working condition, so that the secondary-side controller 100 can realize the zero voltage on of the primary-side power tube under different application conditions and working conditions.

[0115] In the embodiments of the present application, the output sampling voltage and the input sampling voltage are determined based on the drain end voltage of the secondary-side power tube and the output voltage of the flyback converter; the on duration of the secondary-side power tube is determined based on the output sampling voltage, the input sampling voltage and the preset value; the on-off of the secondary-side power tube is controlled based on the on duration, so that the valley value of the drain end voltage of the primary-side power tube is zero, and the primary-side power tube can be turned on at the valley value of the drain end voltage of the primary-side power tube, so as to realize the zero voltage on of the primary-side power tube, thereby reducing the loss of the converter; in addition, the on duration is determined based on the drain end voltage of the secondary-side power tube and the output voltage of the flyback converter, so that the on duration can be adaptively adjusted based on the actual working condition, thereby improving the applicability.

[0116] In some embodiments, Figure 8 A flowchart of another control method of a flyback converter provided by the embodiments of the present application is shown in FIG. 12, Figure 8 A specific description of one possible implementation for performing S1023 is shown in FIG. 13.

[0117] In S201, a selection signal is generated based on the comparison signal.

[0118] The selection signal is one of multiple preset selection signals.

[0119] For example, the processing circuit is internally preset with a plurality of preset selection signals, and one of the plurality of preset selection signals is determined as the generated selection signal SEL based on different comparison signals. For example, the processing circuit is internally preset with three preset selection signals, namely, preset selection signals SEL_pre0, SEL_pre1 and SEL_pre2. When the comparison signals are C0=1, C1=0 and C2=0, the selection signal SEL is the preset selection signal SEL_pre0. When the comparison signals are C0=0, C1=1 and C2=0, the selection signal SEL is the preset selection signal SEL_pre1. When the comparison signals are C0=0, C1=0 and C2=1, the selection signal SEL is the preset selection signal SEL_pre2.

[0120] S202, selecting one of the plurality of preset linear calculation subunits corresponding to the selection signal as a linear calculation subunit, and inputting the target ratio to the linear calculation subunit.

[0121] For example, the processing circuit is internally preset with a plurality of preset linear calculation subunits, and each preset linear calculation subunit corresponds to a preset selection signal SEL_pre. For example, the time calculation unit 1232 is internally preset with three preset linear calculation subunits, namely, preset linear calculation subunit 0, preset linear calculation subunit 1 and preset linear calculation subunit 2. The preset linear calculation subunit 0 corresponds to the preset selection signal SEL_pre0, the preset linear calculation subunit 1 corresponds to the preset selection signal SEL_pre1, and the preset linear calculation subunit 2 corresponds to the preset selection signal SEL_pre2.

[0122] The processing circuit can select one of the plurality of preset linear calculation subunits corresponding to the selection signal SEL as a linear calculation subunit. For example, based on the above embodiment, if the selection signal SEL is the preset selection signal SEL_pre0, the linear calculation subunit is the preset linear calculation subunit 0. If the selection signal SEL is the preset selection signal SEL_pre1, the linear calculation subunit is the preset linear calculation subunit 1. If the selection signal SEL is the preset selection signal SEL_pre2, the linear calculation subunit is the preset linear calculation subunit 2.

[0123] S203, determining the conduction duration based on the linear calculation subunit.

[0124] The processing circuit inputs the target ratio a to the linear calculation subunit, and the linear calculation subunit can calculate the conduction duration Tc according to the target ratio a.

[0125] In the embodiments of the present application, the selection signal is generated based on the comparison signal, wherein the selection signal is one of a plurality of preset selection signals; one of a plurality of preset linear calculation subunits corresponding to the selection signal is selected as the linear calculation subunit, and the target ratio is input into the linear calculation subunit, and the conduction duration is determined based on the linear calculation subunit. In this way, the square root processing of the target ratio is not required, the calculation complexity can be reduced, that is, the circuit complexity can be reduced and the circuit reliability can be improved, and the cost can be saved.

[0126] The above disclosure is only specific embodiments of the present application, but the embodiments of the present application are not limited thereto, and any changes that can be thought of by those skilled in the art shall fall within the protection scope of the present application.

[0127] The description of the present application does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" before the element does not exclude the presence of multiple such elements. The present application can be implemented by means of hardware including several distinct elements and by means of a suitably programmed computer. In a claim enumerating several means, those means can be embodied by one and the same item of hardware. The use of the terms first, second and third, etc. does not denote any order. These terms are to be interpreted as names. The steps of the above-described embodiments, unless otherwise specified, are not to be understood as being ordered chronologically. The above-described embodiments are merely intended to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features; and these modifications or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

[0128] The above-described embodiments are merely intended to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features; and these modifications or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary-side controller, characterized in that, This is applied in a flyback converter, which includes a primary-side power transistor and a secondary-side power transistor; the secondary-side controller includes a sampling circuit, a processing circuit, and a control circuit. The first input terminal of the sampling circuit is electrically connected to the drain terminal of the secondary power transistor, the second input terminal of the sampling circuit is electrically connected to the output terminal of the flyback converter, the output terminal of the sampling circuit is electrically connected to the input terminal of the processing circuit, the output terminal of the processing circuit is electrically connected to the input terminal of the control circuit, and the output terminal of the control circuit is electrically connected to the control terminal of the secondary power transistor. The sampling circuit is used to determine the output sampling voltage and the input sampling voltage based on the drain voltage of the secondary power transistor and the output voltage of the flyback converter. The processing circuit is used to determine the conduction duration of the secondary power transistor based on the output sampling voltage, the input sampling voltage, and a preset value. The control circuit is used to control the switching on and off of the secondary power transistor based on the on-time, so that the valley value of the drain voltage of the primary power transistor is zero. The processing circuit includes: a ratio calculation module, a comparison module, and a duration calculation module; The input terminal of the ratio calculation module is electrically connected to the output terminal of the sampling circuit, the output terminal of the ratio calculation module is electrically connected to the input terminal of the comparison module, the output terminal of the comparison module is electrically connected to the input terminal of the duration calculation module, and the output terminal of the duration calculation module is electrically connected to the input terminal of the control circuit. The ratio calculation module is used to determine the target ratio based on the ratio of the input sampling voltage and the output sampling voltage; The comparison module is used to compare the target ratio with the preset value, and generate a comparison signal based on the comparison result; The duration calculation module is used to determine the conduction duration based on the comparison signal.

2. The secondary-side controller according to claim 1, characterized in that, The sampling circuit includes: a voltage sampling module and a voltage calculation module; The first input terminal of the voltage sampling module is electrically connected to the drain terminal of the secondary power transistor, the second input terminal of the voltage sampling module is electrically connected to the output terminal of the flyback converter, the first output terminal of the voltage sampling module is electrically connected to the first input terminal of the processing circuit and the first input terminal of the voltage calculation module, the second output terminal of the voltage sampling module is electrically connected to the second input terminal of the voltage calculation module, and the output terminal of the voltage calculation module is electrically connected to the second input terminal of the processing circuit. The voltage sampling module is used to sample the drain voltage of the secondary power transistor and the output voltage of the flyback converter respectively to obtain the drain sampling voltage and the output sampling voltage. The voltage calculation module is used to determine the input sampling voltage based on the drain sampling voltage and the output sampling voltage.

3. The secondary-side controller according to claim 1, characterized in that, The duration calculation module includes a logic processing unit and a time calculation unit; The input terminal of the logic processing unit is electrically connected to the output terminal of the comparison module, the first output terminal of the logic processing unit is electrically connected to the input terminal of the time calculation unit, the second output terminal of the logic processing unit is electrically connected to the first input terminal of the control circuit, and the output terminal of the time calculation unit is electrically connected to the second input terminal of the control circuit. The logic processing unit is configured to generate a selection signal based on the comparison signal, wherein the selection signal is one of a plurality of preset selection signals; The time calculation unit is used to select one of the multiple preset linear calculation sub-units corresponding to the selection signal as a linear calculation sub-unit, input the target ratio into the linear calculation sub-unit, and determine the conduction duration based on the linear calculation sub-unit.

4. A control method for a flyback converter, characterized in that, The method, applicable to the secondary-side controller according to any one of claims 1-3, comprises: The output sampling voltage and input sampling voltage are determined based on the drain voltage of the secondary power transistor and the output voltage of the flyback converter. The conduction duration of the secondary power transistor is determined based on the output sampling voltage, the input sampling voltage, and the preset value. The on / off state of the secondary power transistor is controlled based on the on-time, so that the valley value of the drain voltage of the primary power transistor is zero. The step of determining the conduction duration of the secondary power transistor based on the output sampling voltage, the input sampling voltage, and a preset value includes: The target ratio is determined based on the ratio of the input sampling voltage to the output sampling voltage; The target ratio is compared with the preset value, and a comparison signal is generated based on the comparison result; The conduction duration is determined based on the comparison signal.

5. The method according to claim 4, characterized in that, The determination of the output sampling voltage and input sampling voltage based on the drain voltage of the secondary power transistor and the output voltage of the flyback converter includes: The drain voltage of the secondary power transistor and the output voltage of the flyback converter are sampled respectively to obtain the drain sampling voltage and the output sampling voltage. The input sampling voltage is determined based on the drain sampling voltage and the output sampling voltage.

6. The method according to claim 4, characterized in that, Determining the conduction duration based on the comparison signal includes: A selection signal is generated based on the comparison signal, wherein the selection signal is one of a plurality of preset selection signals; Select one of the multiple preset linear calculation sub-units corresponding to the selection signal as the linear calculation sub-unit, and input the target ratio into the linear calculation sub-unit; The conduction duration is determined based on the linear calculation subunit.

7. The method according to claim 4, characterized in that, Determining the target ratio based on the ratio of the input sampled voltage to the output sampled voltage includes: The target ratio is determined based on the ratio of the input sampling voltage to the output sampling voltage, and the turns ratio of the flyback converter.

8. A control system for a flyback converter, characterized in that, Includes the primary-side controller and the secondary-side controller as described in any one of claims 1-3; The output terminal of the primary-side controller is electrically connected to the control terminal of the primary-side power transistor, and the output terminal of the secondary-side controller is electrically connected to the control terminal of the secondary-side power transistor.

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