Multi-mode soft switching control system

Abstract

The invention relates to the field of integrated circuits, and discloses a multi-mode soft switching control system. The system comprises a secondary side control chip and a primary side control chip which work cooperatively to realize efficient energy conversion. The secondary side control chip collects the secondary side current of the transformer, the drain end voltage of the secondary side switching tube and the output voltage through the sampling circuit, the control circuit determines the positions and the duration of two times of conduction of the secondary side switching tube accordingly, and the driving circuit executes specific control; the primary side control chip collects the drain end voltage, the source end voltage and the working frequency of the primary side switching tube through the sampling circuit, the control circuit determines the position capable of achieving zero-voltage conduction and the proper conduction duration accordingly, and the driving circuit executes corresponding control. The system can effectively eliminate conduction loss; and meanwhile, the working modes are automatically switched according to the magnitude of the load current, and the conduction duration of the primary side switch tube and the conduction position of the secondary side switch tube are adaptively adjusted, so that the overall efficiency and applicability are remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of integrated circuits, and in particular to a switching power supply control technology. Background Art

[0002] With the rapid development of electronic power technology, people's relationship with electronic products has become increasingly close, and the requirements for power management modules in various electronic devices are increasing. Switching power supplies, with their high efficiency, compact size, and light weight, have gradually become the mainstream choice for power management in electronic devices. The flyback converter is a key switching power supply topology and is widely used in switching power supply circuits for AC / DC and DC / DC conversion.

[0003] In existing technology, flyback converters typically use optocouplers or transformer auxiliary windings to acquire secondary-side voltage and current information on the primary side. However, optocouplers have a relatively low transmission rate, are significantly affected by external temperature factors, consume high static power, and have a large footprint, increasing system cost and size. While using transformer auxiliary windings maintains the same information transmission rate and operating frequency, the sampled voltage and current information exhibits significant errors. Furthermore, using transformer auxiliary windings increases transformer size, leading to increased cost and size.

[0004] Flyback converters typically operate in pulse-width modulation (PWM) mode. This mode offers high efficiency at high load currents. However, at low load currents, the efficiency is significantly lower. Therefore, a multi-mode control system is required to accommodate varying load currents.

[0005] Because the flyback converter operates over a wide input voltage range, the primary-side switch requires a higher voltage withstand capability and must withstand greater voltage stress. This not only places higher demands on the selection of the primary-side switch, but also results in significant conduction losses when the primary-side switch is turned on. Therefore, soft switching of the primary-side switch is necessary to reduce switching losses and improve system efficiency.

[0006] In summary, the existing flyback converter control system faces technical problems such as low information sampling accuracy, high system cost, large size, uneven efficiency under different load conditions, and large conduction loss of the primary-side switch tube. A new control system is urgently needed to solve these problems. Summary of the Invention

[0007] The purpose of this application is to provide a multi-mode soft switching control system to solve the problems raised in the above background technology.

[0008] The present application discloses a multi-mode soft switching control system, which is applied to a flyback converter. The flyback converter includes: a secondary-side switch tube, a primary-side switch tube and a transformer; the multi-mode soft switching control system includes: a secondary-side control chip and a primary-side control chip;

[0009] The secondary-side control chip includes: a sampling circuit, a control circuit, and a drive circuit; the first input terminal of the sampling circuit is electrically connected to the secondary side of the transformer, the second input terminal is electrically connected to the drain terminal of the secondary-side switch tube, the third input terminal is electrically connected to the output terminal of the flyback converter, the output terminal is electrically connected to the input terminal of the control circuit, the output terminal of the control circuit is electrically connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is electrically connected to the gate terminal of the secondary-side switch tube;

[0010] The primary-side control chip includes: a sampling circuit, a control circuit, and a drive circuit; the first input end of the sampling circuit is electrically connected to the drain end of the primary-side switch tube, the second input end is electrically connected to the source end of the primary-side switch tube, the third input end is electrically connected to the first output end of the control circuit, the output end is electrically connected to the input end of the control circuit, the second output end and the third output end of the control circuit are electrically connected to the input end of the drive circuit, and the output end of the drive circuit is electrically connected to the gate end of the primary-side switch tube.

[0011] In a preferred embodiment, the sampling circuit is configured to collect the transformer secondary side current, the drain terminal voltage of the secondary side switch tube and the output voltage of the flyback converter to obtain the transformer secondary side sampling current, the secondary side switch tube drain terminal sampling voltage and the output sampling voltage;

[0012] The control circuit is configured to determine the conduction position and conduction duration of the secondary-side switch tube for the first time according to the secondary-side sampled current of the transformer, and determine the conduction position and fixed conduction duration of the secondary-side switch tube for the second time according to the drain-end sampled voltage and the output sampled voltage of the secondary-side switch tube;

[0013] The driving circuit is configured to turn on or off the secondary-side switch tube according to the control signal output by the control circuit;

[0014] The sampling circuit is configured to collect the drain terminal voltage, source terminal voltage and operating frequency of the primary side switch tube, and obtain the drain terminal sampling voltage, source terminal sampling voltage and operating frequency sampling signal of the primary side switch tube;

[0015] The control circuit is configured to determine a conduction position at which the primary-side switch tube can be turned on at zero voltage based on a drain-end sampling voltage and a source-end sampling voltage of the primary-side switch tube, and determine a conduction duration based on the operating frequency sampling signal;

[0016] The driving circuit is configured to turn on or off the primary-side switch tube according to the control signal output by the control circuit;

[0017] Among them, the second conduction of the secondary side switch tube causes the drain terminal voltage of the primary side switch tube to be pulled down to zero, thereby realizing soft switching of the primary side switch tube; and the control circuit automatically switches to different conduction time modes according to the load current size. When the load current is less than the preset threshold, a fixed conduction time is used. When the load current is greater than the preset threshold, a conduction time that increases linearly with the increase of the load is used.

[0018] In a preferred embodiment, the sampling circuit includes: a current sampling module and a voltage sampling module;

[0019] The input end of the current sampling module is electrically connected to the secondary side of the transformer, and the output end is electrically connected to the first input end of the control circuit, and is configured to sample the current on the secondary side of the transformer to obtain the transformer secondary side sampling current;

[0020] The first input end of the voltage sampling module is electrically connected to the drain end of the secondary side switch tube, the second input end is electrically connected to the output end of the flyback converter, and the output end is electrically connected to the second input end and the third input end of the control circuit. The voltage sampling module is configured to sample the drain end voltage of the secondary side switch tube and the output voltage of the flyback converter respectively to obtain the drain end sampling voltage of the secondary side switch tube and the output sampling voltage.

[0021] In a preferred embodiment, the control circuit includes: a zero-crossing detection module, a constant voltage control module and a fixed on-time setting module;

[0022] The input end of the zero-crossing detection module is electrically connected to the first output end of the sampling circuit, and the output end is electrically connected to the input end of the driving circuit, and is configured to detect the zero-crossing point of the sampling current on the secondary side of the transformer, and obtain the conduction position and conduction duration of the secondary side switch tube when it is first turned on;

[0023] The input end of the constant voltage control module is electrically connected to the second output end and the third output end of the sampling circuit, and the output end is electrically connected to the input end of the fixed conduction time setting module, and is configured to obtain the conduction position information of the secondary side switch tube when it is turned on for the second time based on the drain terminal sampling voltage of the secondary side switch tube and the output sampling voltage;

[0024] The input end of the fixed conduction time setting module is electrically connected to the output end of the constant voltage control module, and the output end is electrically connected to the input end of the drive circuit. It is configured to determine the fixed conduction time based on the conduction position information of the secondary side switch tube when it is turned on for the second time.

[0025] In a preferred embodiment, the sampling circuit includes: a voltage sampling module and a frequency sampling module;

[0026] The voltage sampling module has a first input terminal electrically connected to the drain terminal of the primary-side switch tube, a second input terminal electrically connected to the source terminal of the primary-side switch tube, a first output terminal electrically connected to the first input terminal of the control circuit, and a second output terminal electrically connected to the second input terminal of the control circuit, and is configured to sample the drain terminal voltage and the source terminal voltage of the primary-side switch tube respectively to obtain the drain terminal sampling voltage and the source terminal sampling voltage of the primary-side switch tube;

[0027] The input end of the frequency sampling module is electrically connected to the first output end of the control circuit, and the output end is electrically connected to the third input end of the control circuit. The module is configured to sample the operating frequency of the primary-side switch tube to obtain the operating frequency sampling signal.

[0028] In a preferred embodiment, the control circuit includes: a zero-crossing detection module, a frequency calculation module, a comparison module, a conduction time calculation module, a fixed conduction time setting module and a selection module;

[0029] The zero-crossing detection module has a first input terminal electrically connected to the first output terminal of the sampling circuit, a second input terminal electrically connected to the second output terminal of the sampling circuit, and an output terminal electrically connected to the first input terminal of the drive circuit, the input terminal of the frequency calculation module, the input terminal of the fixed on-time setting module, and the first input terminal of the on-time calculation module. The module is configured to detect a zero-crossing point of a sampled voltage at the source terminal of the primary-side switching tube based on a sampled voltage at the drain terminal of the primary-side switching tube, and obtain on-position information of the primary-side switching tube capable of achieving soft switching;

[0030] The frequency calculation module has an input terminal electrically connected to an output terminal of the zero-crossing detection module, and an output terminal electrically connected to a third input terminal of the sampling circuit, and is configured to obtain an operating frequency of the primary-side switching tube based on information about a conduction position of the primary-side switching tube capable of achieving soft switching;

[0031] The comparison module has an input terminal electrically connected to the third output terminal of the sampling circuit, and an output terminal electrically connected to the first input terminal and the second input terminal of the selection module, and is configured to compare the operating frequency sampling signal with a preset reference frequency, and obtain comparison information based on the comparison result;

[0032] The second input terminal of the conduction duration calculation module is electrically connected to the third output terminal of the sampling circuit, and the output terminal is electrically connected to the third input terminal of the selection module, and is configured to obtain the conduction duration of the primary-side switch tube based on the operating frequency sampling signal;

[0033] The input end of the fixed on-time setting module is electrically connected to the output end of the zero-crossing detection module, and the output end is electrically connected to the fourth input end of the selection module, and is configured to set a fixed on-time according to the on-position information of the primary-side switch tube capable of achieving soft switching;

[0034] The first and second input terminals of the selection module are electrically connected to the output terminal of the comparison module, the third input terminal is electrically connected to the output terminal of the conduction time calculation module, the fourth input terminal is electrically connected to the output terminal of the fixed conduction time setting module, and the output terminal is electrically connected to the second input terminal of the drive circuit. The selection module is configured to select the conduction time based on the comparison information, select the fixed conduction time when the potential of the first comparison information is greater than or equal to the potential of the second comparison information, and select the conduction time when the potential of the first comparison information is less than the potential of the second comparison information.

[0035] In summary, the multi-mode soft switching control system provided by this application has the following beneficial effects:

[0036] The secondary-side control chip precisely controls the secondary-side switch to conduct twice within one switching cycle. In particular, the second conduction can pull the drain voltage of the primary-side switch down to zero, achieving zero-voltage conduction of the primary-side switch, i.e., soft switching. This effectively eliminates the conduction loss of the primary-side switch during hard switching, significantly improving the energy conversion efficiency of the system.

[0037] The primary side control chip adaptively adjusts the on-time and operating frequency of the primary side switch tube according to the sampled drain voltage, source voltage and operating frequency signal of the primary side switch tube, thus realizing multi-mode optimized control under light load and heavy load conditions. Figure 5 and Figure 6 As shown in the figure, when the load current is less than the threshold, the on-time is fixed, and the operating frequency is linearly adjusted from the minimum frequency to the maximum frequency to adapt to load changes. When the load current is greater than the threshold, the operating frequency is fixed at the maximum value, and the on-time is linearly increased from the starting value to adapt to load changes. This strategy enables the system to maintain high efficiency under a wide range of load conditions.

[0038] The fine division and coordinated work of the internal modules of the secondary side control chip and the primary side control chip, such as Figure 3 、 Figure 4 、 Figure 7 and Figure 8As shown, precise control of both the secondary and primary switches is achieved. The secondary-side control chip's zero-crossing detection module, constant voltage control module, and fixed on-time setting module respectively control the position and duration of the secondary switch's two conduction cycles. The primary-side control chip's zero-crossing detection module, frequency calculation module, comparison module, on-time calculation module, fixed on-time setting module, and selection module flexibly control the primary-side switch's soft-switching position and on-time through frequency adaptation and comparison selection. This modular design and clear control strategy improve control accuracy and reliability, enhancing system stability and anti-interference capabilities.

[0039] This application avoids the shortcomings of traditional flyback converter control schemes that use optocouplers or transformer auxiliary windings. Traditional methods suffer from low transmission rates, significant temperature sensitivity, high static power consumption, and large size. However, this application uses secondary-side control chips to assist in controlling the primary-side switching transistors, simplifying the complexity of primary-side control while reliably achieving soft switching on the primary side. This innovative control architecture offers advantages such as simple structure, low cost, high efficiency, and a wide range of applications. It can effectively replace existing flyback converter control schemes and has broad application prospects.

[0040] The specification of this application records a large number of technical features, which are distributed in various technical solutions. If all possible combinations of technical features of this application (i.e., technical solutions) are to be listed, the specification will be too lengthy. In order to avoid this problem, the various technical features disclosed in the above-mentioned invention content of this application, the various technical features disclosed in the various embodiments and examples below, and the various technical features disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions are all deemed to have been recorded in this specification), unless such a combination of technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed. Features C and D are equivalent technical means that play the same role. Technically, only one of them can be used, and it is impossible to use them at the same time. Feature E can be technically combined with feature C. Then, the solution of A+B+C+D should not be considered as having been recorded because it is technically infeasible, while the solution of A+B+C+E should be considered as having been recorded. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a structural diagram of a multi-mode soft switching control system according to an embodiment of the present application;

[0042] Figure 2 1 is a schematic diagram of current and voltage waveforms of various nodes of a flyback converter to which a multi-mode soft switching control system according to an embodiment of the present application is applied as the load changes;

[0043] Figure 3 1 is a schematic structural diagram of a secondary-side control chip of a multi-mode soft switching control system according to an embodiment of the present application;

[0044] Figure 4 is a structural schematic diagram of another secondary-side control chip of a multi-mode soft switching control system according to an embodiment of the present application;

[0045] Figure 5 is a schematic diagram of a curve showing how the conduction time of the primary-side switch tube of the multi-mode soft switching control system varies with the load according to an embodiment of the present application;

[0046] Figure 6 is a schematic diagram of a curve showing changes in system operating frequency versus load of a multi-mode soft switching control system according to an embodiment of the present application;

[0047] Figure 7 1 is a schematic structural diagram of a primary-side control chip of a multi-mode soft switching control system according to an embodiment of the present application;

[0048] Figure 8 3 is a structural diagram of another primary-side control chip of a multi-mode soft switching control system according to an embodiment of the present application. DETAILED DESCRIPTION

[0049] In the following description, many technical details are provided to help readers better understand this application. However, those skilled in the art will understand that even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in this application can be implemented.

[0050] Description of some concepts:

[0051] In this application, a flyback converter refers to a topology of a switching power supply, including a secondary-side switch tube, a primary-side switch tube and a transformer, and realizes voltage conversion by storing and releasing energy in the transformer.

[0052] The secondary side control chip, in this application, refers to a chip used to control the conduction and shutdown of the secondary side switch tube, including a sampling circuit, a control circuit and a drive circuit, which is responsible for collecting secondary side related signals and controlling the switching action.

[0053] The primary side control chip, in this application, refers to a chip used to control the conduction and shutdown of the primary side switch tube, including a sampling circuit, a control circuit and a drive circuit. It is responsible for collecting primary side related signals and determining the position and conduction duration of the soft switch of the switch tube.

[0054] In this application, soft switching refers to a switching mode in which the voltage across the switch tube is reduced to zero or close to zero in advance before the switch tube is turned on, which can significantly reduce the conduction loss of the switch tube.

[0055] Zero Voltage Switching (ZVS), in this application, refers to a soft switching mode. At the moment the primary-side switch tube is turned on, its drain voltage is pulled down in advance by the secondary-side switch tube, and then its source voltage is detected. It is turned on when the drain voltage and source voltage are the same. There is no voltage difference between the two ends of the tube when it is turned on, thereby avoiding conduction loss.

[0056] In this application, the on-time refers to the duration that the switch tube is in the on state during each switching cycle, which is automatically determined and adjusted by the control circuit according to the load current to achieve efficient energy conversion.

[0057] In this application, the sampling circuit refers to a voltage sampling module, a current sampling module and a frequency sampling module, which are used to collect the current, voltage and system operating frequency signals on both sides of the transformer in real time for use in control circuit decision-making.

[0058] In this application, the fixed on-time mode refers to the conduction mode adopted by the primary-side switch tube when the load current is lower than the preset threshold. The on-time is fixed and the operating frequency is adjusted to adapt to load changes.

[0059] In this application, the variable on-time mode refers to the conduction mode adopted by the primary side switch tube when the load current exceeds the preset threshold. The on-time increases linearly with the load current, and the operating frequency is fixed to the maximum value to meet the energy requirements under heavy load conditions.

[0060] The following is a summary of some of the innovative features of this application:

[0061] In general, this application addresses the technical bottlenecks of high primary-side switching losses, large sampling errors of the optocoupler or auxiliary winding, and increased system complexity and cost in traditional flyback converters. By establishing a composite modulation mechanism based on bidirectional conduction of the secondary-side switch tube and synchronous adaptive control of the primary-side switch tube, this application achieves a breakthrough in non-obvious technical difficulties. Specifically, the present application designs a distributed control architecture in which a secondary-side control chip and a primary-side control chip cooperate with each other, wherein the secondary-side control chip accurately detects the zero-crossing point of the secondary-side current of the transformer and the change in the output voltage, and controls the secondary-side switch tube to perform two asymmetric conduction operations within a single switching cycle. In particular, the second conduction precisely regulates the energy distribution of the transformer, so that the drain voltage of the primary-side switch tube is pulled down to zero level at a specific moment, thereby realizing the complex timing control of zero-voltage soft switching; at the same time, the primary-side control chip realizes dual-mode seamless switching of "fixed conduction time-variable frequency" and "fixed frequency-variable conduction time" between light load and heavy load conditions through multi-module cascade processing and adaptive threshold judgment based on the drain-source voltage and operating frequency information of the switch tube, solving the deep-seated problem of uneven efficiency in different load ranges under the traditional single control mode. This innovative control strategy is integrated with the hardware topology to form a coupled system of nonlinear control and energy transmission. Its complexity and technical threshold far exceed the control strategies of conventional power conversion systems. Ultimately, through this deeply integrated system architecture, it achieves systematic breakthroughs in multiple technical goals such as efficiency improvement, size reduction, cost reduction and applicability expansion.

[0062] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0063] In the specification of this application, in order to make the article more clear and concise, some technical features are represented by English letter codes. It should be clarified that the technical features represented by letter codes in this application are exactly the same as the technical features represented by the corresponding Chinese names plus letter codes. For example, "Isec" and "transformer secondary side current Isec" refer to the same technical feature, "Vswp" and "primary side switch tube drain voltage Vswp" refer to the same technical feature, and other similar technical features represented by English letter codes are also equivalent to the technical features represented by their corresponding Chinese names plus letter codes. When reading and understanding this application, please treat the technical features represented by letter codes only as the same as the technical features represented by their corresponding Chinese names plus letter codes. The technical features with English letter codes involved include but are not limited to:

[0064] Transformer secondary side current Isec;

[0065] Transformer secondary side sampling current Isec_sen;

[0066] Secondary side switch drain voltage Vsec;

[0067] The sampling voltage Vsec_sen at the drain end of the secondary side switch tube;

[0068] Flyback converter output voltage Vout;

[0069] Output sampling voltage Vout_sen;

[0070] The first conduction position and conduction duration OUT_sec of the secondary-side switch;

[0071] The fixed duration Ta of the second conduction of the secondary-side switch tube;

[0072] Primary side switch drain voltage Vswp;

[0073] Primary side switch drain sampling voltage Vswp_sen;

[0074] Primary side switch source voltage Vcs;

[0075] Primary side switch source end sampling voltage Vcs_sen;

[0076] Primary side switch operating frequency fre;

[0077] Working frequency sampling signal Vfre;

[0078] Primary side switch tube soft switch conduction position information Vset;

[0079] Comparison information Sel1;

[0080] Comparison information Sel2;

[0081] Fixed on-time Tb;

[0082] The on-time Tc increases linearly with the load;

[0083] Transformer primary side current Ipri;

[0084] Secondary side switch control voltage VS1;

[0085] Primary side switch control voltage VS2;

[0086] Load current Iload;

[0087] Input voltage Vin;

[0088] System minimum operating frequency fmin;

[0089] The maximum operating frequency of the system is fmax;

[0090] Load threshold current Iload1.

[0091] Furthermore, the same reference numerals are used throughout the drawings to denote the same elements or structures, wherein:

[0092] S1: secondary side switch tube;

[0093] S2: primary side switch tube;

[0094] 11: Secondary side control chip;

[0095] 12: Primary side control chip;

[0096] 1110: sampling circuit;

[0097] 1120: control circuit;

[0098] 113: driving circuit;

[0099] 1111: current sampling module;

[0100] 1112: voltage sampling module;

[0101] 1121: zero-crossing detection module;

[0102] 1122: constant pressure control module;

[0103] 1123: Fixed on-time setting module;

[0104] 1210: sampling circuit;

[0105] 1220: control circuit;

[0106] 123: driving circuit;

[0107] 1211: voltage sampling module;

[0108] 1212: frequency sampling module;

[0109] 1221: zero-crossing detection module;

[0110] 1222: frequency calculation module;

[0111] 1223: comparison module;

[0112] 1224: On-time calculation module;

[0113] 1225: Fixed on-time setting module;

[0114] 1226: Select module.

[0115] The first embodiment of the present application relates to a multi-mode soft switching control system, which is applied to a flyback converter, such as Figure 1 , Figure 3 and Figure 7 As shown, the flyback converter includes: a secondary-side switch tube S1, a primary-side switch tube S2 and a transformer; the multi-mode soft switching control system includes: a secondary-side control chip 11 and a primary-side control chip 12.

[0116] The secondary-side control chip 11 includes: a sampling circuit 1110, a control circuit 1120 and a drive circuit 113; the first input end of the sampling circuit 1110 is electrically connected to the secondary side of the transformer, the second input end is electrically connected to the drain end of the secondary-side switch tube S1, the third input end is electrically connected to the output end of the flyback converter, the output end is electrically connected to the input end of the control circuit 1120, the output end of the control circuit 1120 is electrically connected to the input end of the drive circuit 113, and the output end of the drive circuit 113 is electrically connected to the gate end of the secondary-side switch tube S1.

[0117] The sampling circuit 1110 is configured to collect the transformer secondary side current Isec, the drain terminal voltage Vsec of the secondary side switch tube S1 and the output voltage Vout of the flyback converter, and obtain the transformer secondary side sampling current Isec_sen, the secondary side switch tube drain terminal sampling voltage Vsec_sen and the output sampling voltage Vout_sen.

[0118] The control circuit 1120 is configured to determine the conduction position and conduction duration OUT_sec of the secondary side switch tube S1 for the first time according to the secondary side sampling current Isec_sen of the transformer, and to determine the conduction position and fixed conduction duration Ta of the secondary side switch tube S1 for the second time according to the secondary side switch tube drain sampling voltage Vsec_sen and the output sampling voltage Vout_sen.

[0119] The driving circuit 113 is configured to turn on or off the secondary-side switch S1 according to the control signal output by the control circuit 1120 .

[0120] The primary-side control chip 12 includes: a sampling circuit 1210, a control circuit 1220, and a drive circuit 123; the first input terminal of the sampling circuit 1210 is electrically connected to the drain terminal of the primary-side switch tube S2, the second input terminal is electrically connected to the source terminal of the primary-side switch tube S2, the third input terminal is electrically connected to the first output terminal of the control circuit 1220, and the output terminal is electrically connected to the input terminal of the control circuit 1220; the second output terminal and the third output terminal of the control circuit 1220 are electrically connected to the input terminal of the drive circuit 123, and the output terminal of the drive circuit 123 is electrically connected to the gate terminal of the primary-side switch tube S2;

[0121] The sampling circuit 1210 is configured to collect the drain voltage Vswp, source voltage Vcs and operating frequency fre of the primary side switch tube S2 to obtain the primary side switch tube drain sampling voltage Vswp_sen, source sampling voltage Vcs_sen and operating frequency sampling signal Vfre.

[0122] The control circuit 1220 is configured to determine the conduction position Vset at which the primary-side switch S2 can be turned on at zero voltage based on the drain-end sampling voltage Vswp_sen and the source-end sampling voltage Vcs_sen of the primary-side switch, and determine the conduction duration based on the operating frequency sampling signal Vfre.

[0123] The driving circuit 123 is configured to turn on or off the primary-side switch S2 according to the control signal output by the control circuit 1220 .

[0124] Among them, the second conduction of the secondary side switch tube S1 causes the drain terminal voltage Vswp of the primary side switch tube S2 to be pulled down to zero, thereby realizing soft switching of the primary side switch tube S2; and the control circuit 1220 automatically switches to different conduction time modes according to the load current size. When the load current is less than the preset threshold, a fixed conduction time Tb is used. When the load current is greater than the preset threshold, a conduction time Tc that increases linearly with the increase of the load is used.

[0125] Optionally, the sampling circuit 1110 includes: a current sampling module 1111 and a voltage sampling module 1112 .

[0126] The input end of the current sampling module 1111 is electrically connected to the secondary side of the transformer, and the output end is electrically connected to the first input end of the control circuit 1120. It is configured to sample the current Isec on the secondary side of the transformer to obtain the transformer secondary side sampling current Isec_sen.

[0127] The first input end of the voltage sampling module 1112 is electrically connected to the drain end of the secondary-side switch tube S1, the second input end is electrically connected to the output end of the flyback converter, and the output end is electrically connected to the second input end and the third input end of the control circuit 1120. The voltage sampling module 1112 is configured to sample the drain end voltage Vsec of the secondary-side switch tube S1 and the output voltage Vout of the flyback converter respectively to obtain the secondary-side switch tube drain end sampling voltage Vsec_sen and the output sampling voltage Vout_sen.

[0128] Optionally, the control circuit 1120 includes: a zero-crossing detection module 1121 , a constant voltage control module 1122 and a fixed on-time setting module 1123 .

[0129] The input end of the zero-crossing detection module 1121 is electrically connected to the first output end of the sampling circuit 1110, and the output end is electrically connected to the input end of the driving circuit 113. The module is configured to detect the zero-crossing point of the sampling current Isec_sen on the secondary side of the transformer, and obtain the conduction position and conduction duration OUT_sec of the first conduction of the secondary-side switch tube S1.

[0130] The input end of the constant voltage control module 1122 is electrically connected to the second output end and the third output end of the sampling circuit 1110, and the output end is electrically connected to the input end of the fixed conduction time setting module 1123. The constant voltage control module 1122 is configured to obtain the conduction position information of the second conduction of the secondary side switch tube S1 based on the secondary side switch tube drain terminal sampling voltage Vsec_sen and the output sampling voltage Vout_sen.

[0131] The input end of the fixed on-time setting module 1123 is electrically connected to the output end of the constant voltage control module 1122, and the output end is electrically connected to the input end of the drive circuit 113. It is configured to determine the fixed on-time Ta based on the on-position information of the second conduction of the secondary-side switch tube S1.

[0132] Optionally, the sampling circuit 1210 includes: a voltage sampling module 1211 and a frequency sampling module 1212 .

[0133] The voltage sampling module 1211 has a first input terminal electrically connected to the drain terminal of the primary-side switch tube S2, a second input terminal electrically connected to the source terminal of the primary-side switch tube S2, a first output terminal electrically connected to the first input terminal of the control circuit 1220, and a second output terminal electrically connected to the second input terminal of the control circuit 1220. The module is configured to sample the drain terminal voltage Vswp and the source terminal voltage Vcs of the primary-side switch tube S2 respectively to obtain the drain terminal sampling voltage Vswp_sen and the source terminal sampling voltage Vcs_sen of the primary-side switch tube.

[0134] The input end of the frequency sampling module 1212 is electrically connected to the first output end of the control circuit 1220, and the output end is electrically connected to the third input end of the control circuit 1220. It is configured to sample the operating frequency fre of the primary-side switch tube S2 to obtain the operating frequency sampling signal Vfre.

[0135] Optionally, the control circuit 1220 includes: a zero-crossing detection module 1221 , a frequency calculation module 1222 , a comparison module 1223 , an on-time calculation module 1224 , a fixed on-time setting module 1225 and a selection module 1226 .

[0136] The first input end of the zero-crossing detection module 1221 is electrically connected to the first output end of the sampling circuit 1210, the second input end is electrically connected to the second output end of the sampling circuit 1210, and the output end is electrically connected to the first input end of the driving circuit 123, the input end of the frequency calculation module 1222, the input end of the fixed on-time setting module 1225, and the first input end of the on-time calculation module 1224. The zero-crossing detection module 1221 is configured to detect the zero-crossing point of the sampled voltage Vcs_sen at the source end of the primary-side switch tube based on the sampled voltage Vswp_sen at the drain end of the primary-side switch tube, and obtain the on-position information Vset of the primary-side switch tube S2 that can achieve soft switching.

[0137] The input end of the frequency calculation module 1222 is electrically connected to the output end of the zero-crossing detection module 1221, and the output end is electrically connected to the third input end of the sampling circuit 1210. The frequency calculation module 1222 is configured to obtain the operating frequency fre of the primary-side switch tube S2 based on the conduction position information Vset at which the primary-side switch tube S2 can achieve soft switching.

[0138] The input end of the comparison module 1223 is electrically connected to the third output end of the sampling circuit 1210, and the output end is electrically connected to the first input end and the second input end of the selection module 1226. The comparison module 1223 is configured to compare the operating frequency sampling signal Vfre with a preset reference frequency and obtain comparison information Sel1 and Sel2 based on the comparison result.

[0139] The second input terminal of the conduction duration calculation module 1224 is electrically connected to the third output terminal of the sampling circuit 1210, and the output terminal is electrically connected to the third input terminal of the selection module 1226. The module is configured to obtain the conduction duration Tc of the primary-side switch tube S2 based on the operating frequency sampling signal Vfre.

[0140] The input end of the fixed on-time setting module 1225 is electrically connected to the output end of the zero-crossing detection module 1221, and the output end is electrically connected to the fourth input end of the selection module 1226. It is configured to set a fixed on-time Tb according to the on-position information Vset of the primary-side switch tube S2 that can achieve soft switching.

[0141] The first and second input terminals of the selection module 1226 are electrically connected to the output terminal of the comparison module 1223, the third input terminal is electrically connected to the output terminal of the conduction time calculation module 1224, the fourth input terminal is electrically connected to the output terminal of the fixed conduction time setting module 1225, and the output terminal is electrically connected to the second input terminal of the driving circuit 123. The selection module 1226 is configured to select the conduction time based on the comparison information Sel 1 and Sel2, select the fixed conduction time Tb when the potential of Sel 1 is greater than or equal to the potential of Sel2, and select the conduction time Tc when the potential of Sel 1 is less than the potential of Sel2.

[0142] In order to make the technical solution of the present invention clearer, Figures 1 to 8 The preferred embodiments of the present invention are described in detail, but it should be understood that the described embodiments are only illustrative and not restrictive.

[0143] like Figure 1 As shown, the flyback converter includes a transformer with a turns ratio of N:1, a primary-side switch S2, a secondary-side switch S1, an output capacitor Cout, and a load current Iload. The first terminal of the transformer's primary side is electrically connected to the input voltage Vin, the second terminal of the transformer's primary side is electrically connected to the drain of the primary-side switch S2, the source of the primary-side switch S2 is grounded, and a parasitic capacitor Cswp exists in S2. The first terminal of the transformer's secondary side and the first plate of the output capacitor Cout are both electrically connected to the load current Iload, the second terminal of the transformer's secondary side is electrically connected to the drain of the secondary-side switch S1, the source of the secondary-side switch S1, the second plate of the output capacitor Cout, and the second terminal of the load current Iload are all grounded. The voltage across the output capacitor Cout is the output voltage Vout.

[0144] The flyback converter control system includes a secondary-side control chip 11 and a primary-side control chip 12. The output of the secondary-side control chip 11 is electrically connected to the gate of the secondary-side switch S1 to control its on / off state. The output of the primary-side control chip 12 is electrically connected to the gate of the primary-side switch S2 to control its on / off state.

[0145] In terms of operating principle, when the primary-side control chip 12 turns on the primary-side switch S2, the input voltage Vin charges the primary side of the transformer. At this time, the secondary-side control chip 11 turns off the secondary-side switch S1, and the load current Iload is provided by the output capacitor Cout. When the primary-side control chip 12 turns off the primary-side switch S2, a reverse voltage difference forms on the primary side of the transformer, as the current in the primary side of the transformer cannot change suddenly. According to transformer principles, a reverse voltage also occurs on the secondary side of the transformer. The secondary-side control chip 11 then turns on the secondary-side switch S1.

[0146] A key feature of this embodiment is that within a switching cycle, the secondary-side control chip 11 can control the secondary-side switch S1 to conduct a second time. By precisely controlling the position and duration of this second conduction, the drain voltage Vswp of the primary-side switch S2 is lowered. By detecting the source voltage Vcs, zero-voltage conduction of the primary-side switch S2 is achieved, i.e., soft switching, thereby significantly reducing the conduction losses caused by hard switching. Furthermore, the control system of this embodiment can automatically adjust the conduction duration of the primary-side switch S2 based on the load current. Under light load conditions, a fixed short conduction duration is used, while under heavy load conditions, the conduction duration increases with the load current, further improving the efficiency and applicability of the converter.

[0147] Figure 2 This is a schematic diagram of the current and voltage waveforms of each node of the flyback converter provided by this application as the load changes. As shown in the figure, as the load current Iload changes, the key signals of the system change accordingly.

[0148] At time t1, the control voltage VS1 of the secondary-side switch S1 goes high, turning on S1 and pulling the drain voltage Vsec of the secondary-side switch down to 0. At this point, the transformer's secondary-side current Isec reverses direction, and energy begins to flow into the transformer, converting electrical energy into magnetic energy. Simultaneously, the drain voltage Vswp of the primary-side switch S2 increases.

[0149] After a period of time Ta, at time t2, the control voltage VS1 of the secondary-side switch S1 drops to a low level, turning off S1. The transformer's primary-side current Ipri reverses direction, draining the charge from the parasitic capacitor Cswp in the primary-side switch S2, causing its drain voltage Vswp to drop. When Vswp drops to zero, the control voltage VS2 of the primary-side switch S2 drops to a high level, turning S2 on under zero-voltage conditions. This achieves soft switching and effectively reduces hard-switching conduction losses.

[0150] It should be noted that as the load current Iload increases, the second conduction position of the secondary side switch S1 will be advanced. Figure 2 As shown, at time t11, S1's second conduction position is further forward than at time t6, resulting in an increase in the system operating frequency. As the load current Iload increases further, the primary-side control chip 12 adjusts the on-time of primary-side switch S2 from a fixed value Tb to a load-dependent Tc. As shown in the figure, during the time period t13-t14, S2's on-time is Tc, increasing linearly with Iload, while the system operating frequency remains at its maximum value fmax.

[0151] This control strategy, which is adaptive to load changes, enables the system to always maintain efficient operation under different load conditions and ensures reliable soft switching, significantly improving the overall performance of the flyback converter.

[0152] Figure 3 FIG. 1 is a schematic diagram of the structure of a secondary-side control chip of this embodiment. As shown in the figure, the secondary-side control chip 11 includes a sampling circuit 1110 , a control circuit 1120 and a driving circuit 113 .

[0153] The three input terminals of sampling circuit 1110 are respectively connected to the secondary side of the transformer, the drain terminal of secondary-side switch S1, and the output terminal of the flyback converter, for collecting the transformer secondary-side current Isec, the secondary-side switch drain voltage Vsec, and the output voltage Vout. The output terminal of sampling circuit 1110 is electrically connected to the gate terminal of secondary-side switch S1 through control circuit 1120 and drive circuit 113. The signals collected by sampling circuit 1110 are the transformer secondary-side sampled current Isec_sen, the secondary-side switch drain voltage Vsec_sen, and the output sampled voltage Vout_sen.

[0154] The control circuit 1120 determines the initial conduction position and conduction duration (OUT_sec) of the secondary-side switch S1 based on the collected transformer secondary-side sampled current Isec_sen. Simultaneously, the control circuit 1120 also determines the initial conduction position and conduction duration (Ta) of the secondary-side switch S1 based on the secondary-side switch drain sampled voltage Vsec_sen and the output sampled voltage Vout_sen.

[0155] The driving circuit 113 turns on or off the secondary-side switch S1 according to the control signal output by the control circuit 1120 , thereby achieving precise control of energy transmission.

[0156] This structural design of the secondary-side control chip, especially the control of the second conduction of the secondary-side switch tube S1, can enable the primary-side switch tube S2 to achieve zero-voltage conduction, that is, soft switching, effectively reducing switching losses and improving energy conversion efficiency.

[0157] Figure 4 This is a structural diagram of another secondary side control chip of this embodiment. Figure 3 On the basis of, the sampling circuit 1110 further includes a current sampling module 1111 and a voltage sampling module 1112 , and the control circuit 1120 further includes a zero-crossing detection module 1121 , a constant voltage control module 1122 and a fixed on-time setting module 1123 .

[0158] The input end of the current sampling module 1111 is connected to the secondary side of the transformer, and the output end is connected to the first input end of the control circuit 1120. The current sampling module 1111 is used to sample the current Isec on the secondary side of the transformer to obtain the transformer secondary side sampled current Isec_sen.

[0159] The voltage sampling module 1112 has a first input connected to the drain of the secondary-side switch S1, a second input connected to the output of the flyback converter, and an output connected to the second and third inputs of the control circuit 1120. The voltage sampling module 1112 samples the drain voltage Vsec of the secondary-side switch S1 and the output voltage Vout of the flyback converter, respectively, to obtain a secondary-side switch drain sampled voltage Vsec_sen and an output sampled voltage Vout_sen.

[0160] The input of the zero-crossing detection module 1121 is connected to the first output of the sampling circuit 1110, that is, it receives the transformer secondary-side sampled current Isec_sen, and the output is connected to the input of the drive circuit 113. The zero-crossing detection module 1121 detects the zero-crossing point of Isec_sen to obtain the first conduction position and conduction duration OUT_sec of the secondary-side switch S1.

[0161] The input of constant voltage control module 1122 is connected to the second and third output terminals of sampling circuit 1110, that is, it receives the drain-side sampled voltage Vsec_sen and the output sampled voltage Vout_sen of the secondary-side switch. The output of constant voltage control module 1122 is connected to the input of fixed on-time setting module 1123. Based on Vsec_sen and Vout_sen, constant voltage control module 1122 obtains the conduction position information of the second conduction of secondary-side switch S1.

[0162] The input of the fixed on-time setting module 1123 is connected to the output of the constant voltage control module 1122, and the output is connected to the input of the driving circuit 113. The fixed on-time setting module 1123 determines the fixed on-time Ta based on the on-position information of the second on-state of the secondary-side switch S1.

[0163] The driving circuit 113 turns on or off the secondary side switch tube S1 according to the control signal output by the zero-crossing detection module 1121 and the control signal output by the fixed on-time setting module 1123, thereby achieving precise control of the secondary side switch tube and realizing soft switching of the primary side switch tube.

[0164] Figure 5 The following is a diagram showing how the on-time of the primary-side switch S2 changes with load in this embodiment. As shown, the horizontal axis represents the load current Iload, and the vertical axis represents the on-time T of the primary-side switch S2. This curve intuitively demonstrates the system's adaptive control strategy under different load conditions.

[0165] When the load current Iload is less than or equal to the threshold Iload1, the on-time of the primary-side switch S2 remains fixed at Tb. This corresponds to light-load conditions, where the system adapts to load changes by adjusting the operating frequency rather than the on-time. When the load current Iload exceeds the threshold Iload1, the on-time of the primary-side switch S2 switches to Tc and increases linearly with increasing load current. This corresponds to heavy-load conditions, where the system increases the on-time to accommodate increased load demands.

[0166] Figure 6 This is a curve diagram showing the system operating frequency of this embodiment changing with load. As shown in the figure, the horizontal axis is the load current Iload and the vertical axis is the system operating frequency f. Figure 5 They echo each other and reflect the system's working mode switching mechanism.

[0167] When the load current Iload is less than or equal to the threshold value Iload1, the system operating frequency increases linearly with the load current from the minimum value fmin. Figure 5 When the load current Iload is greater than the threshold Iload1, the system operating frequency is fixed at the maximum value fmax and no longer changes with the load. Instead, it adapts to the larger load by increasing the on-time Tc, such as Figure 5 shown.

[0168] This dual-mode control strategy with adaptive load current enables the system to maintain high-efficiency operation by adjusting the frequency under light load and by adjusting the conduction duration under heavy load, effectively broadening the scope of application of the flyback converter and having significant practical value.

[0169] Figure 7 FIG. 1 is a structural diagram of a primary-side control chip according to an embodiment of the present invention. As shown in the figure, the primary-side control chip 12 includes a sampling circuit 1210 , a control circuit 1220 and a drive circuit 123 .

[0170] The sampling circuit 1210 has a first input connected to the drain of the primary-side switch S2, a second input connected to the source of the primary-side switch S2, a third input connected to the first output of the control circuit 1220, and an output connected to the input of the control circuit 1220. The sampling circuit 1210 is configured to collect the drain voltage Vswp and source voltage Vcs of the primary-side switch S2, and the system operating frequency fre, to obtain a sampled drain voltage Vswp_sen, a sampled source voltage Vcs_sen, and frequency information Vfre from the first output of the control circuit.

[0171] The input terminal of the control circuit 1220 is connected to the output terminal of the sampling circuit 1210, and the second and third output terminals are connected to the input terminal of the driving circuit 123. The control circuit 1220 determines the on-position Vset of the primary-side switch S2 that enables soft switching based on the sampled drain-end voltage Vswp_sen and source-end voltage Vcs_sen of the primary-side switch, and determines the on-time based on the frequency information Vfre.

[0172] The input terminal of the driver circuit 123 is connected to the second and third output terminals of the control circuit 1220, and the output terminal is connected to the gate terminal of the primary-side switch S2. The driver circuit 123 drives the primary-side switch S2 on and off according to the conduction position Vset and conduction duration signal output by the control circuit 1220.

[0173] This structural design enables the primary-side control chip to adaptively adjust the conduction timing of the primary-side switch based on real-time sampled voltage and frequency information, ensuring that the switch conducts under zero voltage conditions and reducing switching losses. It also dynamically optimizes the conduction duration based on load conditions, improving system efficiency and applicability.

[0174] Figure 8 This is a structural diagram of another primary side control chip of this embodiment. Figure 7 On the basis of, the sampling circuit 1210 further includes a voltage sampling module 1211 and a frequency sampling module 1212, and the control circuit 1220 further includes a zero-crossing detection module 1221, a frequency calculation module 1222, a comparison module 1223, a conduction time calculation module 1224, a fixed conduction time setting module 1225 and a selection module 1226.

[0175] The first and second input terminals of the voltage sampling module 1211 are connected to the drain and source terminals of the primary-side switch S2, respectively. The first and second output terminals are connected to the first and second input terminals of the control circuit 1220, respectively. The voltage sampling module 1211 samples the drain voltage Vswp and the source voltage Vcs of the primary-side switch S2, respectively, to obtain a drain sampling voltage Vswp_sen and a source sampling voltage Vcs_sen.

[0176] The input terminal of the frequency sampling module 1212 is connected to the first output terminal of the control circuit 1220, and the output terminal is connected to the third input terminal of the control circuit 1220. The frequency sampling module 1212 samples the operating frequency fre of the primary side switch tube S2 to obtain an operating frequency sampling signal Vfre.

[0177] The first and second input terminals of the zero-crossing detection module 1221 are connected to the first and second output terminals of the sampling circuit 1210, respectively. The output terminal of the zero-crossing detection module 1221 is connected to the input terminal of the frequency calculation module 1222, the first input terminal of the on-time calculation module 1224, and the input terminal of the fixed on-time setting module 1225. Based on the drain-side sampled voltage Vswp_sen, the zero-crossing detection module 1221 detects the zero-crossing point of the source-side sampled voltage Vcs_sen and obtains the on-position information Vset at which the primary-side switch S2 can achieve soft switching.

[0178] The input terminal of the frequency calculation module 1222 is connected to the output terminal of the zero-crossing detection module 1221, and the output terminal is connected to the third input terminal of the sampling circuit 1210. The frequency calculation module 1222 calculates the operating frequency fre of the primary-side switch S2 based on the conduction position information Vset.

[0179] The input terminal of the comparison module 1223 is connected to the third output terminal of the sampling circuit 1210, and the output terminal is connected to the first and second input terminals of the selection module 1226. The comparison module 1223 compares the operating frequency sampling signal Vfre with the preset reference frequency to obtain comparison information Sel1 and Sel2.

[0180] The second input terminal of the on-time calculation module 1224 is connected to the third output terminal of the sampling circuit 1210, and the output terminal is connected to the third input terminal of the selection module 1226. The on-time calculation module 1224 calculates the on-time Tc that varies with the load based on the operating frequency sampling signal Vfre.

[0181] The input terminal of the fixed on-time setting module 1225 is connected to the output terminal of the zero-crossing detection module 1221, and the output terminal is connected to the fourth input terminal of the selection module 1226. The fixed on-time setting module 1225 sets the fixed on-time Tb according to the conduction position information Vset.

[0182] The four input terminals of the selection module 1226 are respectively connected to the output terminals of the comparison module 1223, the on-time calculation module 1224, and the fixed on-time setting module 1225, and the output terminal is connected to the second input terminal of the drive circuit 123. The selection module 1226 selects between the fixed on-time Tb and the load-variable on-time Tc based on the comparison information Sel1 and Sel2.

[0183] This modular structural design and sophisticated signal processing mechanism enable the primary-side control chip to automatically switch operating modes according to load conditions, fixing the on-time and adjusting the frequency under light load, and fixing the maximum frequency and adjusting the on-time under heavy load, ensuring efficient operation under various working conditions and greatly improving the system's adaptability and efficiency.

[0184] Working principle:

[0185] The multi-mode soft switching control system of this embodiment can accurately control the switching timing of the secondary side switch S1 and the primary side switch S2 in the flyback converter to achieve efficient energy conversion. Figures 1 to 8 , explaining in detail how the system works.

[0186] When the primary-side control chip 12 turns on the primary-side switch S2, the input voltage Vin charges the transformer primary, generating a primary-side current Ipri. At this point, the secondary-side control chip 11 turns off the secondary-side switch S1, and the output capacitor Cout provides energy to the load current Iload. When the primary-side switch S2 is turned off, because the transformer primary-side current Ipri cannot change suddenly, a reverse voltage difference is generated on the transformer primary side. According to transformer principles, the secondary-side voltage Vsec also reverses. The secondary-side control chip 11 then turns on the secondary-side switch S1, transferring energy from the transformer to the output.

[0187] It should be pointed out that if Figure 2 As shown, within a switching cycle, the secondary-side control chip 11 can control the secondary-side switch S1 to conduct a second time. Specifically, at time t1, the secondary-side control chip 11 raises the control voltage VS1 of S1, turning S1 on. Its drain voltage Vsec is pulled down to 0, the transformer secondary-side current Isec reverses, and energy is charged into the transformer through S1, raising the drain voltage Vswp of the primary-side switch S2. After a time Ta, at time t2, the secondary-side control chip 11 lowers VS1, turning S1 off. The transformer primary-side current Ipri reverses, discharging the parasitic capacitor Cswp and lowering the drain voltage Vswp of S2. When the drain voltage Vswp and the source voltage Vcs are equal, the primary-side control chip 12 raises the control voltage VS2 of S2, turning S2 on under zero voltage conditions, achieving soft switching and eliminating hard switching conduction losses.

[0188] according to Figure 5 and Figure 6 This embodiment also implements dual-mode operation with adaptive load: when the load current Iload is less than or equal to the threshold value Iload1, the system operates in light-load mode, the on-time of the primary-side switch S2 is maintained at a fixed short time Tb, and the operating frequency f increases linearly from the minimum value fmin to the maximum value fmax as Iload increases; when Iload is greater than Iload1, the system switches to heavy-load mode, the operating frequency f is fixed at fmax, and the on-time Tc of S2 increases linearly from Tb as Iload increases.

[0189] See also Figure 3 and Figure 4The sampling circuit 1110 of the secondary-side control chip 11 respectively samples the transformer secondary-side current Isec, the drain voltage Vsec of the secondary-side switch S1, and the output voltage Vout. In the control circuit 1120, the zero-crossing detection module 1121 detects the zero-crossing point of the secondary-side sampled current Isec_sen and determines the position and duration of the first conduction of S1. The constant voltage control module 1122 determines the position of the second conduction of S1 based on the drain voltage Vsec_sen and the output voltage Vout_sen. The fixed conduction duration setting module 1123 sets the fixed conduction duration Ta of the second conduction.

[0190] See also Figure 7 and Figure 8 The sampling circuit 1210 of the primary-side control chip 12 samples the drain voltage Vswp, source voltage Vcs, and operating frequency fre of the primary-side switch S2. In the control circuit 1220, the zero-crossing detection module 1221 detects the zero-crossing point of the source-side sampled voltage Vcs_sen and determines the soft-switching on position Vset for S2. The comparison module 1223 compares the operating frequency sampling signal Vfre with the reference frequency and outputs comparison information Sel1 and Sel2. Based on this information, the selection module 1226 selects between the light-load on-time duration Tb and the heavy-load on-time duration Tc. Finally, the drive circuit 123 drives S2 on or off.

[0191] Through this synergistic mechanism, this embodiment achieves high-efficiency energy conversion over a wide range of load conditions. In particular, the second conduction of secondary-side switch S1 enables primary-side switch S2 to achieve zero-voltage soft switching, significantly reducing switching losses and significantly improving system efficiency. Furthermore, load-adaptive dual-mode switching further broadens the scope of application and enhances the practicality of the flyback converter.

[0192] In order to better understand the technical solution of the present application, a specific example is provided below for illustration. The details listed in the example are mainly for ease of understanding and are not intended to limit the scope of protection of the present application.

[0193] In general, the multi-mode soft switching control system proposed in this example can control the secondary-side switch tube to conduct for the second time to achieve soft switching of the primary-side switch tube, eliminating the conduction loss of the primary-side switch tube; in addition, it can also switch modes according to the load current size, thereby improving overall efficiency, and can adaptively adjust the conduction time of the primary-side switch tube and the conduction position of the secondary-side switch tube, thereby improving applicability.

[0194] The multi-mode soft switching control system is applied to a flyback converter, which includes: a secondary-side control chip, a primary-side control chip, a secondary-side switch tube, a primary-side switch tube and a transformer; the multi-mode soft switching control system includes a secondary-side control chip and a primary-side control chip.

[0195] The first input terminal of the secondary side control chip is electrically connected to the secondary side of the transformer, the second input terminal of the secondary side control chip is electrically connected to the drain terminal of the secondary side switch tube, the third input terminal of the secondary side control chip is electrically connected to the output terminal of the flyback converter, the output terminal of the secondary side control chip is electrically connected to the gate terminal of the secondary side switch tube, the first input terminal of the primary side control chip is electrically connected to the drain terminal of the primary side switch tube, the second input terminal of the primary side control chip is electrically connected to the source terminal of the primary side switch tube, and the output terminal of the primary side control chip is electrically connected to the gate terminal of the primary side switch tube.

[0196] In this example, optionally, the secondary-side control chip includes: a sampling circuit, a control circuit, and a driving circuit.

[0197] The first input end of the sampling circuit is electrically connected to the secondary side of the transformer, the second input end of the sampling circuit is electrically connected to the drain end of the secondary side switch tube, the third 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 control circuit, the output end of the control circuit is electrically connected to the input end of the drive circuit, and the output end of the drive circuit is electrically connected to the gate end of the secondary side switch tube.

[0198] The sampling circuit is configured to obtain the transformer secondary side sampling current, the secondary side switching tube drain terminal sampling voltage and the flyback converter output terminal sampling voltage based on sampling the transformer secondary side current, the secondary side switching tube drain terminal sampling voltage and the flyback converter output terminal sampling voltage.

[0199] The control circuit is configured to determine the conduction position and conduction duration of the secondary side switch tube for the first time based on the sampled current of the secondary side of the transformer, and determine the conduction position and fixed conduction duration of the secondary side switch tube for the second time based on the sampled drain terminal sampled voltage of the secondary side switch tube and the sampled output terminal sampled voltage of the flyback converter.

[0200] The driving circuit is configured to drive the secondary-side switching tube to be turned on and off based on the determined conduction position of the secondary-side switching tube.

[0201] In this example, optionally, the secondary-side control chip and the sampling circuit include: a current sampling module and a voltage sampling module.

[0202] The input end of the current sampling module is electrically connected to the primary side of the transformer, the output end of the current sampling module is electrically connected to the first input end of the control circuit, the first input end of the voltage sampling module is electrically connected to the drain end of the secondary side switch tube, the second input end of the voltage sampling module is electrically connected to the output end of the flyback converter, and the output end of the voltage sampling module is electrically connected to the second input end and the third input end of the control circuit.

[0203] The current sampling module is configured to sample the current on the secondary side of the transformer to obtain the transformer secondary side sampled current.

[0204] The voltage sampling module is configured to sample the drain terminal voltage of the secondary side switch tube and the output terminal voltage of the flyback converter respectively to obtain the drain terminal sampling voltage of the secondary side switch tube and the output terminal sampling voltage of the flyback converter.

[0205] In this example, optionally, in the secondary-side control chip, the control circuit includes: a zero-crossing detection module, a constant voltage control module, and a fixed on-time setting module.

[0206] The input end of the zero-crossing detection module is electrically connected to the first output end of the sampling circuit, the output end of the zero-crossing detection module is electrically connected to the input end of the drive circuit, the input end of the constant voltage control module is electrically connected to the second output end and the third output end of the sampling circuit, the output end of the constant voltage control module is electrically connected to the input end of the fixed on-time setting module, and the output end of the fixed on-time setting module is electrically connected to the input end of the drive circuit.

[0207] The zero-crossing detection module is configured to detect the zero-crossing point of the sampling current on the secondary side of the transformer, and obtain the conduction position and conduction duration of the secondary side switch tube when it is first turned on.

[0208] The constant voltage control module is configured to obtain the conduction position information of the secondary side switch tube when it is turned on for the second time based on the drain terminal sampling voltage of the secondary side switch tube and the output terminal sampling voltage of the flyback converter.

[0209] The fixed on-time setting module is configured to determine the fixed on-time based on the on-position information of the secondary-side switch tube when it is turned on for the second time.

[0210] In this example, optionally, the primary-side control chip includes: a sampling circuit, a control circuit, and a driving circuit.

[0211] The first input terminal of the sampling circuit is electrically connected to the drain terminal of the primary-side switching tube, the second input terminal of the sampling circuit is electrically connected to the source terminal of the primary-side switching tube, the third input terminal of the sampling circuit is electrically connected to the first output terminal of the control circuit, the output terminal of the sampling circuit is electrically connected to the input terminal of the control circuit, the second output terminal and the third output terminal of the control circuit are electrically connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is electrically connected to the gate terminal of the primary-side switching tube.

[0212] The sampling circuit is configured to obtain the drain-end sampling voltage of the primary-side switching tube, the source-end sampling voltage of the primary-side switching tube, and the operating frequency of the primary-side switching tube based on sampling the drain-end voltage of the primary-side switching tube, the source-end voltage of the primary-side switching tube, and the operating frequency of the primary-side switching tube.

[0213] The control circuit is configured to determine the conduction position of the primary-side switch tube at which soft switching can be achieved based on the sampled drain-end sampling voltage of the primary-side switch tube and the sampled source-end sampling voltage of the primary-side switch tube, and the conduction duration is determined by the operating frequency of the primary-side switch tube.

[0214] The driving circuit is configured to drive the primary-side switching tube to be turned on and off based on the determined conduction position and conduction duration of the primary-side switching tube.

[0215] In this example, optionally, in the primary-side control chip, the sampling circuit includes: a voltage sampling module and a frequency sampling module.

[0216] The first input end of the voltage sampling module is electrically connected to the drain end of the primary-side switching tube, the second input end of the voltage sampling module is electrically connected to the source end of the primary-side switching tube, the first output end of the voltage sampling module is electrically connected to the first input end of the control circuit, the second output end of the voltage sampling module is electrically connected to the second input end of the control circuit, the input end of the frequency sampling module is electrically connected to the first output end of the control circuit, and the output end of the frequency sampling module is electrically connected to the third input end of the control circuit.

[0217] The voltage sampling module is configured to sample the drain voltage of the primary-side switch tube and the source voltage of the primary-side switch tube respectively to obtain the drain-end sampling voltage of the primary-side switch tube and the source-end sampling voltage of the primary-side switch tube.

[0218] The frequency sampling module is configured to sample the operating frequency of the primary-side switching tube to obtain the operating frequency of the primary-side switching tube.

[0219] In this example, optionally, in the primary-side control chip, the control circuit includes: a zero-crossing detection module, a frequency calculation module, a comparison module, a conduction time calculation module, a fixed conduction time setting module and a selection module.

[0220] A first input end of the zero-crossing detection module is electrically connected to a first output end of the sampling circuit, a second input end of the zero-crossing detection module is electrically connected to a second output end of the sampling circuit, an output end of the zero-crossing detection module is electrically connected to a first input end of the driving circuit, an input end of the frequency calculation module, a first input end of the conduction duration calculation module, and an input end of the fixed conduction duration setting module, an output end of the frequency calculation module is electrically connected to a third input end of the sampling circuit, an input end of the comparison module is electrically connected to a third output end of the sampling circuit, an output end of the comparison module is electrically connected to a first input end and a second input end of the selection module, a second input end of the conduction duration calculation module is electrically connected to a third output end of the sampling circuit, an output end of the conduction duration calculation module is electrically connected to a third input end of the selection module, an output end of the fixed conduction duration setting module is electrically connected to a fourth input end of the selection module, and an output end of the selection module is electrically connected to a second input end of the driving circuit.

[0221] The zero-crossing detection module is configured to detect the zero-crossing point of the source-end sampling voltage of the primary-side switching tube based on the drain-end sampling voltage of the primary-side switching tube, and obtain the conduction position information of the primary-side switching tube that can achieve soft switching.

[0222] The frequency calculation module is configured to obtain the operating frequency of the primary-side switching tube based on the conduction position information of the primary-side switching tube that can achieve soft switching.

[0223] The comparison module is configured to compare the sampled operating frequency with a preset reference frequency, and obtain comparison information based on the comparison result.

[0224] The on-time calculation module is configured to obtain the on-time of the primary-side switch tube corresponding to the sampled operating frequency based on the sampled operating frequency.

[0225] The fixed on-time setting module is configured to determine the fixed on-time based on the on-position information of the primary-side switch tube capable of achieving soft switching.

[0226] The selection module is configured to select the appropriate conduction duration based on the comparison information.

[0227] More specifically, in this example, the primary-side input voltage of the flyback converter can be a power-factor-corrected DC voltage or an AC voltage rectified by a bridge rectifier. Typically, the primary-side input voltage ranges widely, from approximately 60V to 400V.

[0228] This example is further explained below with reference to the accompanying drawings.

[0229] Figure 1 This is a schematic diagram of the flyback converter and its control system in this example. Figure 1 As shown, the flyback converter includes a transformer with a turns ratio of N:1, a primary-side switch S2, a current load Iload, and a secondary-side switch S1. The first terminal of the transformer's primary side is electrically connected to the input voltage Vin, the second terminal of the transformer's primary side is electrically connected to the drain terminal of the primary-side switch S2, the source terminal of the primary-side switch S2 is grounded, and a parasitic capacitor Cswp exists in the primary-side switch S2. The first terminal of the transformer's secondary side and the first plate of the output capacitor Cout are electrically connected to the first terminal of the load current Iload, the second terminal of the transformer's secondary side is electrically connected to the drain terminal of the secondary-side switch S1, the source terminal of the secondary-side switch S1, the second plate of the output capacitor Cout, and the second terminal of the load current Iload are all grounded. The voltage across the output capacitor Cout is the output voltage Vout.

[0230] The flyback converter's control system includes a secondary-side control chip 11 and a primary-side control chip 12. The output of the secondary-side control chip 11 is electrically connected to the gate of the secondary-side switch S1, while the output of the primary-side control chip 12 is electrically connected to the gate of the primary-side switch S2. When the primary-side control chip turns on the primary-side switch S2, the input voltage Vin charges the transformer's primary side. At this point, the secondary-side control chip 11 turns off the secondary-side switch S1, and energy is supplied by the output capacitor Cout. When the primary-side control chip 12 turns off the primary-side switch S2, a reverse voltage difference forms on the transformer's primary side because the current in the transformer's primary side cannot change suddenly. At this point, the voltage difference on the transformer's secondary side also reverses, and the secondary-side control chip 11 turns on the secondary-side switch S1.

[0231] In one cycle, the secondary side control chip 11 can also control the secondary side switch tube S1 to be turned on for the second time. Figure 2 Figure 1 is a schematic diagram of the current and voltage waveforms of each node of the flyback converter as the load changes. Figure 2As shown, at time t1, the control voltage VS1 of secondary-side switch S1 goes high, turning on secondary-side switch S1. The drain voltage Vsec of secondary-side switch S1 is pulled down to zero, the transformer secondary-side current reverses, energy is charged into the transformer, converting electrical energy into magnetic energy, and the drain voltage Vswp of primary-side switch S2 is raised. After a period of time Ta, at time t1, the control voltage VS1 of secondary-side switch S1 goes low, turning off secondary-side switch S1. The transformer primary-side current reverses, and the charge in the parasitic capacitor Cswp of primary-side switch S2 is drained, lowering the drain voltage Vswp of primary-side switch S2. When the drain voltage Vswp of primary-side switch S2 is pulled down to zero, the control voltage VS1 of primary-side switch S2 goes high, turning on primary-side switch S2. This achieves soft switching, thereby reducing conduction losses caused by hard switching. Ta is the duration of the second turn-on of secondary-side switch S1.

[0232] Obviously, the conduction of the secondary-side switch tube S1 at the appropriate position is a decisive factor for the primary-side switch tube S2 to achieve soft switching. Therefore, the secondary-side control chip 11 is required to determine the conduction position.

[0233] Several specific examples are given below to explain the secondary-side control chip 11 in detail.

[0234] Figure 3 It is a structural diagram of the secondary side control chip, as shown in Figure 3 As shown, the secondary-side control chip 11 includes: a sampling circuit 1110, a control circuit 1120, and a drive circuit 1113. A first input terminal of the sampling circuit 1110 is electrically connected to the secondary side of the transformer, a second input terminal of the sampling circuit 1110 is electrically connected to the drain terminal of the secondary-side switch S1, a third input terminal of the sampling circuit 1110 is electrically connected to the output terminal of the flyback converter, an output terminal of the sampling circuit 1110 is electrically connected to an input terminal of the control circuit 1120, an output terminal of the control circuit 1120 is electrically connected to an input terminal of the drive circuit 113, and an output terminal of the drive circuit 113 is electrically connected to the gate terminal of the secondary-side switch S1.

[0235] The sampling circuit 1110 is configured to sample the transformer secondary-side current Isec, the drain voltage Vsec of the secondary-side switch S1, and the output voltage Vout of the flyback converter to obtain the transformer secondary-side sampled current Isec_sen, the drain voltage Vsec_sen of the secondary-side switch S1, and the output voltage Vout_sen of the flyback converter. The control circuit 1120 is configured to determine the first conduction position and on-time OUT_sec of the secondary-side switch based on the sampled transformer secondary-side sampled current Isec_sen. The second conduction position of the secondary-side switch is determined based on the sampled drain voltage Vsec_sen of the secondary-side switch S1 and the output voltage Vout_sen of the flyback converter, and the second conduction position and fixed on-time Ta of the secondary-side switch. The driving circuit 113 is configured to drive the secondary-side switch S1 on and off based on the determined conduction position of the secondary-side switch S1.

[0236] Figure 4 This is a structural diagram of another secondary side control chip. Figure 4 exist Figure 3 Based on the above, the sampling circuit 1110 includes: a current sampling module 1111 and a voltage sampling module 1112. The input end of the current sampling module 1111 is electrically connected to the primary side of the transformer, the output end of the current sampling module 1111 is electrically connected to the first input end of the control circuit 1120, the first input end of the voltage sampling module 1112 is electrically connected to the drain end of the secondary-side switch S1, the second input end of the voltage sampling module 1112 is electrically connected to the output end of the flyback converter, and the output end of the voltage sampling module 1112 is electrically connected to the second input end and the third input end of the control circuit 1120.

[0237] The current sampling module 1111 can sample the current Isec on the secondary side of the receiving transformer to obtain the transformer secondary side sampling current Isec_sen. The voltage sampling module 1112 can respectively sample the drain voltage Vsec of the secondary side switch tube S1 and the output voltage Vout of the flyback converter to obtain the drain sampling voltage Vsec_sen of the secondary side switch tube and the output sampling voltage Vout_sen of the flyback converter.

[0238] For example, see Figure 4The control circuit 1120 includes: a zero-crossing detection module 1121, a constant voltage control module 1122 and a fixed conduction time setting module 1123, wherein the input end of the zero-crossing detection module 1121 is electrically connected to the first output end of the sampling circuit 1110, the output end of the zero-crossing detection module 1121 is electrically connected to the input end of the driving circuit 113, the input end of the constant voltage control module 1122 is electrically connected to the second output end and the third output end of the sampling circuit 1110, the output end of the constant voltage control module 1122 is electrically connected to the input end of the fixed conduction time setting module 1123, and the output end of the fixed conduction time setting module 1123 is electrically connected to the input end of the driving circuit 113.

[0239] like Figure 4 As shown, the zero-crossing detection module 1121 can detect the zero-crossing point of the transformer secondary-side sampled current Isec_sen to obtain the conduction position and conduction duration OUT_sec of the secondary-side switch S1 for the first conduction. The constant voltage control module 1122 can receive the drain-end sampled voltage Vsec_sen of the secondary-side switch S1 and the output-end sampled voltage Vout_sen of the flyback converter to obtain the conduction position information of the secondary-side switch S1 for the second conduction. The fixed conduction duration setting module 1123 can receive the conduction position information of the secondary-side switch S1 for the second conduction to determine the fixed conduction duration Ta.

[0240] In this way, the secondary side switch tube S1 can be turned on at a suitable position and for a suitable duration.

[0241] When the load current Iload increases, the conduction position of the secondary side switch S1 at the second conduction will change. Figure 2 As shown in FIG. 1 , at time t11, the second conduction position of the secondary side switch tube S1 is further forward than the second conduction position of the secondary side switch tube S1 at time t6, and the system operating frequency becomes higher. At the same time, as the load current Iload further increases, the primary side control chip 2 will select the conduction time of the primary side switch tube S2 to be Tc. At this time, the operating frequency of the system will remain unchanged. Figure 2 As shown in the figure, during the time period t13 to t14, the conduction time of the primary side switch tube S2 is Tc. The conduction time Tc of the primary side switch tube S2 will increase with the increase of the load current Iload. At this time, the operating frequency of the system remains unchanged. Figure 5 This is a curve diagram showing how the conduction time of the primary-side switch changes with load. Figure 6 This is a curve diagram showing how the system operating frequency changes with load. Figure 5As shown, when the load current Iload is less than or equal to the value Iload1, the conduction time of the primary side switch tube S2 is Tb, and when the load current Iload is greater than the value Iload1, the conduction time of the primary side switch tube S2 is Tc, and the conduction time Tc increases linearly with the increase of the load current Iload. Figure 6 As shown, when the load current Iload is less than or equal to the value Iload1, the operating frequency of the system increases linearly from the minimum frequency value fmin until the load current Iload is greater than the value Iload1, at which time the operating frequency of the system stabilizes at the maximum frequency value fmax.

[0242] Obviously, the primary-side switch tube S2 requires an appropriate conduction time, and the system requires a suitable operating frequency so that the system can operate stably. The primary-side control chip 2 is required to determine the conduction time of the primary-side switch tube S2.

[0243] Several specific examples are given below to explain the primary-side control chip 2 in detail.

[0244] Figure 7 This is a structural diagram of the primary side control chip, as shown in Figure 7 As shown, the primary-side control chip 12 includes a sampling circuit 1210, a control circuit 1220, and a drive circuit 123. A first input terminal of the sampling circuit 1210 is electrically connected to the drain terminal of the primary-side switch S2, a second input terminal of the sampling circuit 1210 is electrically connected to the source terminal of the primary-side switch S2, a third input terminal of the sampling circuit 1210 is electrically connected to a first output terminal of the control circuit 1220, an output terminal of the sampling circuit 1210 is electrically connected to an input terminal of the control circuit 1220, a second output terminal and a third output terminal of the control circuit 1220 are electrically connected to an input terminal of the drive circuit 123, and an output terminal of the drive circuit 123 is electrically connected to a gate terminal of the primary-side switch S2.

[0245] The sampling circuit 1210 is configured to obtain a drain-side sampled voltage Vswp_sen of the primary-side switch S2, a source-side sampled voltage Vcs_sen of the primary-side switch S2, and the system operating frequency fre based on the sampled drain-side sampled voltage Vswp_sen of the primary-side switch S2, the source-side sampled voltage Vcs_sen of the primary-side switch S2, and the system operating frequency fre at the first output terminal of the control circuit 123. The control circuit 1220 is configured to determine, based on the sampled drain-side sampled voltage Vswp_sen and the sampled source-side sampled voltage Vcs_sen of the primary-side switch S2, a conduction position Vset of the primary-side switch S2 that enables soft switching, and to determine the conduction duration according to the system operating frequency Vfre. The driving circuit 123 is configured to drive the primary-side switch S2 on and off based on the determined conduction position Vset and conduction duration of the primary-side switch S2.

[0246] Figure 8 This is a structural diagram of another primary side control chip. Figure 8 for Figure 7 Based on the illustrated embodiment, the sampling circuit 1210 includes: a voltage sampling module 1211 and a frequency sampling module 1212. A first input terminal of the voltage sampling module 1211 is electrically connected to the drain terminal of the primary-side switch S2, a second input terminal of the voltage sampling module 1211 is electrically connected to the source terminal of the primary-side switch S2, a first output terminal of the voltage sampling module 1211 is electrically connected to a first input terminal of a control circuit 1220, a second output terminal of the voltage sampling module 1211 is electrically connected to a second input terminal of the control circuit 1220, an input terminal of the frequency sampling module 1212 is electrically connected to a first output terminal of the control circuit 1220, and an output terminal of the frequency sampling module 1212 is electrically connected to a third input terminal of the control circuit 1220.

[0247] The voltage sampling module 1211 can sample the drain voltage Vswp of the primary-side switch tube S2 and the source voltage Vcs of the primary-side switch tube S2 respectively to obtain the drain-end sampling voltage Vswp_sen of the primary-side switch tube S2 and the source-end sampling voltage Vcs_sen of the primary-side switch tube S2; the frequency sampling module 1212 can sample the operating frequency fre of the primary-side switch tube S2 to obtain the operating frequency Vfre of the primary-side switch tube S2.

[0248] Optional, see Figure 8The control circuit 1220 includes: a zero-crossing detection module 1221, a frequency calculation module 1222, a comparison module 1223, a conduction duration calculation module 1224, a fixed conduction duration setting module 1225, and a selection module 1226. The first input terminal of the zero-crossing detection module 1221 is electrically connected to the first output terminal of the sampling circuit 1210, the second input terminal of the zero-crossing detection module 1221 is electrically connected to the second output terminal of the sampling circuit 1210, and the output terminal of the zero-crossing detection module 1221 is electrically connected to the first input terminal of the driving circuit 123, the input terminal of the frequency calculation module 1222, the first input terminal of the conduction duration calculation module 1224, and the input terminal of the fixed conduction duration setting module 1225. The output end of the frequency calculation module 1222 is electrically connected to the third input end of the sampling circuit 1210, the input end of the comparison module 1223 is electrically connected to the third output end of the sampling circuit 1210, the output end of the comparison module 1223 is electrically connected to the first input end and the second input end of the selection module 1226, the second input end of the conduction duration calculation module 1224 is electrically connected to the third output end of the sampling circuit 1210, the output end of the conduction duration calculation module 1224 is electrically connected to the third input end of the selection module 1226, the output end of the fixed conduction duration setting module 1225 is electrically connected to the fourth input end of the selection module 1226, and the output end of the selection module 1226 is electrically connected to the second input end of the driving circuit 123.

[0249] like Figure 8 As shown, the zero-crossing detection module 1221 can detect the zero-crossing point of the source-side sampling voltage Vcs_sen of the primary-side switch S2 based on the drain-side sampling voltage Vswp_sen of the primary-side switch S2, and obtain the on-position information Vset at which the primary-side switch S2 can achieve soft switching. The frequency calculation module 1222 can receive the on-position information Vset at which the primary-side switch S2 can achieve soft switching, and obtain the operating frequency fre of the primary-side switch S2. The comparison module 1223 can receive the operating frequency Vfre of the primary-side switch S2 and compare it with an internally preset reference frequency, and obtain comparison information Sel1 and Sel2 based on the comparison result. The on-time calculation module 1224 can receive the operating frequency Vfre of the primary-side switch S2 and obtain the on-time Tc of the primary-side switch S2 corresponding to the operating frequency Vfre of the primary-side switch S2. Fixed on-time setting module 1225 can receive information Vset about the on-position of primary-side switch S2 that enables soft switching and determine a fixed on-time Tb. Selection module 1226 can receive comparison information Sel1 and Sel2 and select either on-time Tb or on-time Tc based on the potentials of Sel1 and Sel2. When the potential of Sel1 is greater than or equal to that of Sel2, on-time Tb is selected; when the potential of Sel1 is less than that of Sel2, on-time Tc is selected.

[0250] The above embodiments have the following technical effects:

[0251] The secondary-side control chip 11 precisely controls the secondary-side switch S1 to conduct twice within one switching cycle. In particular, the second conduction can pull the drain voltage Vswp of the primary-side switch S2 down to zero, thereby achieving zero-voltage conduction of the primary-side switch S2, i.e., soft switching. This effectively eliminates the conduction loss of the primary-side switch S2 during hard switching, and significantly improves the energy conversion efficiency of the system.

[0252] The primary side control chip 12 adaptively adjusts the on-time and operating frequency of the primary side switch S2 according to the sampled drain voltage Vswp, source voltage Vcs and operating frequency signal Vfre of the primary side switch S2, thus achieving multi-mode optimization control under light load and heavy load conditions. Figure 5 and Figure 6 As shown in the figure, when the load current Iload is less than the threshold Iload1, the on-time Tb is maintained at a fixed value, and the operating frequency is linearly adjusted from the minimum frequency fmin to the maximum frequency fmax to adapt to load changes. When the load current Iload is greater than the threshold Iload1, the operating frequency is fixed at the maximum frequency fmax, and the on-time is linearly increased with the load starting from Tc to adapt to load changes. This strategy enables the system to maintain high efficiency under a wide range of load conditions.

[0253] The secondary side control chip 11 and the primary side control chip 12 have fine division and coordinated work of internal modules, such as Figure 3 、 Figure 4 、 Figure 7 and Figure 8 As shown, precise control of the secondary-side switch S1 and the primary-side switch S2 is achieved. The zero-crossing detection module 1121, constant voltage control module 1122, and fixed on-time setting module 1123 of the secondary-side control chip 11 respectively control the position and duration of the two conduction times of the secondary-side switch S1. The zero-crossing detection module 1221, frequency calculation module 1222, comparison module 1223, on-time calculation module 1224, fixed on-time setting module 1225, and selection module 1226 of the primary-side control chip 12 flexibly control the soft-switching on-position and on-time of the primary-side switch S2 through frequency adaptation and comparison selection. This modular structural design and clear control strategy improve the accuracy and reliability of control and enhance the stability and anti-interference ability of the system.

[0254] The above embodiment avoids the shortcomings of conventional flyback converter control schemes that use optocouplers or transformer auxiliary windings. Conventional approaches suffer from low transmission rates, significant temperature susceptibility, high static power consumption, and large size. However, the above embodiment, through auxiliary control of primary-side switch S2 by the secondary-side control chip 11, simplifies primary-side control complexity while reliably achieving soft switching on the primary side. This innovative control architecture offers advantages such as simple structure, low cost, high efficiency, and wide applicability. It is an effective alternative to existing flyback converter control schemes and has broad application prospects.

[0255] It should be noted that in this patent application, relational terms such as first and second, etc., are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. Without further limitation, an element specified by the phrase "comprising a" does not preclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element. In this patent application, reference to performing an action in accordance with an element means performing the action in accordance with at least that element, including two situations: performing the action in accordance with that element alone, and performing the action in accordance with that element and other elements. Expressions such as "plurality," "multiple times," and "many" include "two," "twice," "two kinds," and "more than two," "more than two times," and "more than two kinds."

[0256] All documents mentioned in this application are considered to be included in their entirety in the disclosure of this application so that they can be used as a basis for modification when necessary. In addition, it should be understood that after reading the above disclosure of this application, those skilled in the art may make various changes or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. A multi-mode soft switching control system, characterized in that: Applied to a flyback converter, the flyback converter includes: a secondary-side switch tube, a primary-side switch tube and a transformer; the multi-mode soft switching control system includes: a secondary-side control chip and a primary-side control chip; The secondary-side control chip includes: a sampling circuit, a control circuit, and a drive circuit; the first input terminal of the sampling circuit is electrically connected to the secondary side of the transformer, the second input terminal is electrically connected to the drain terminal of the secondary-side switch tube, the third input terminal is electrically connected to the output terminal of the flyback converter, the output terminal is electrically connected to the input terminal of the control circuit, the output terminal of the control circuit is electrically connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is electrically connected to the gate terminal of the secondary-side switch tube; The primary-side control chip includes: a sampling circuit, a control circuit, and a drive circuit; the first input end of the sampling circuit is electrically connected to the drain end of the primary-side switch tube, the second input end is electrically connected to the source end of the primary-side switch tube, the third input end is electrically connected to the first output end of the control circuit, the output end is electrically connected to the input end of the control circuit, the second output end and the third output end of the control circuit are electrically connected to the input end of the drive circuit, and the output end of the drive circuit is electrically connected to the gate end of the primary-side switch tube.

2. The multi-mode soft switching control system according to claim 1, characterized in that: The sampling circuit is configured to collect the transformer secondary side current, the drain terminal voltage of the secondary side switch tube and the output voltage of the flyback converter to obtain the transformer secondary side sampling current, the secondary side switch tube drain terminal sampling voltage and the output sampling voltage; The control circuit is configured to determine the conduction position and conduction duration of the secondary-side switch tube for the first time according to the secondary-side sampled current of the transformer, and determine the conduction position and fixed conduction duration of the secondary-side switch tube for the second time according to the drain-end sampled voltage and the output sampled voltage of the secondary-side switch tube; The driving circuit is configured to turn on or off the secondary-side switch tube according to the control signal output by the control circuit; The sampling circuit is configured to collect the drain terminal voltage, source terminal voltage and operating frequency of the primary side switch tube, and obtain the drain terminal sampling voltage, source terminal sampling voltage and operating frequency sampling signal of the primary side switch tube; The control circuit is configured to determine a conduction position at which the primary-side switch tube can be turned on at zero voltage based on a drain-end sampling voltage and a source-end sampling voltage of the primary-side switch tube, and determine a conduction duration based on the operating frequency sampling signal; The driving circuit is configured to turn on or off the primary-side switch tube according to the control signal output by the control circuit; Among them, the second conduction of the secondary side switch tube causes the drain terminal voltage of the primary side switch tube to be pulled down to zero, thereby realizing soft switching of the primary side switch tube; and the control circuit automatically switches to different conduction time modes according to the load current size. When the load current is less than the preset threshold, a fixed conduction time is used. When the load current is greater than the preset threshold, a conduction time that increases linearly with the increase of the load is used.

3. The multi-mode soft switching control system according to claim 1, characterized in that: The sampling circuit includes: a current sampling module and a voltage sampling module; The input end of the current sampling module is electrically connected to the secondary side of the transformer, and the output end is electrically connected to the first input end of the control circuit, and is configured to sample the current on the secondary side of the transformer to obtain the transformer secondary side sampling current; The first input end of the voltage sampling module is electrically connected to the drain end of the secondary side switch tube, the second input end is electrically connected to the output end of the flyback converter, and the output end is electrically connected to the second input end and the third input end of the control circuit. The voltage sampling module is configured to sample the drain end voltage of the secondary side switch tube and the output voltage of the flyback converter respectively to obtain the drain end sampling voltage of the secondary side switch tube and the output sampling voltage.

4. The multi-mode soft switching control system according to claim 1, characterized in that: The control circuit includes: a zero-crossing detection module, a constant voltage control module and a fixed on-time setting module; The input end of the zero-crossing detection module is electrically connected to the first output end of the sampling circuit, and the output end is electrically connected to the input end of the driving circuit, and is configured to detect the zero-crossing point of the sampling current on the secondary side of the transformer, and obtain the conduction position and conduction duration of the secondary side switch tube when it is first turned on; The input end of the constant voltage control module is electrically connected to the second output end and the third output end of the sampling circuit, and the output end is electrically connected to the input end of the fixed conduction time setting module, and is configured to obtain the conduction position information of the secondary side switch tube when it is turned on for the second time based on the drain terminal sampling voltage of the secondary side switch tube and the output sampling voltage; The input end of the fixed conduction time setting module is electrically connected to the output end of the constant voltage control module, and the output end is electrically connected to the input end of the drive circuit. It is configured to determine the fixed conduction time based on the conduction position information of the secondary side switch tube when it is turned on for the second time.

5. The multi-mode soft switching control system according to claim 1, characterized in that: The sampling circuit includes: a voltage sampling module and a frequency sampling module; The voltage sampling module has a first input terminal electrically connected to the drain terminal of the primary-side switch tube, a second input terminal electrically connected to the source terminal of the primary-side switch tube, a first output terminal electrically connected to the first input terminal of the control circuit, and a second output terminal electrically connected to the second input terminal of the control circuit, and is configured to sample the drain terminal voltage and the source terminal voltage of the primary-side switch tube respectively to obtain the drain terminal sampling voltage and the source terminal sampling voltage of the primary-side switch tube; The input end of the frequency sampling module is electrically connected to the first output end of the control circuit, and the output end is electrically connected to the third input end of the control circuit. The module is configured to sample the operating frequency of the primary-side switch tube to obtain the operating frequency sampling signal.

6. The multi-mode soft switching control system according to claim 1, characterized in that: The control circuit includes: a zero-crossing detection module, a frequency calculation module, a comparison module, a conduction time calculation module, a fixed conduction time setting module and a selection module; The zero-crossing detection module has a first input terminal electrically connected to the first output terminal of the sampling circuit, a second input terminal electrically connected to the second output terminal of the sampling circuit, and an output terminal electrically connected to the first input terminal of the drive circuit, the input terminal of the frequency calculation module, the input terminal of the fixed on-time setting module, and the first input terminal of the on-time calculation module. The module is configured to detect a zero-crossing point of a sampled voltage at the source terminal of the primary-side switching tube based on a sampled voltage at the drain terminal of the primary-side switching tube, and obtain on-position information of the primary-side switching tube capable of achieving soft switching; The frequency calculation module has an input terminal electrically connected to an output terminal of the zero-crossing detection module, and an output terminal electrically connected to a third input terminal of the sampling circuit, and is configured to obtain an operating frequency of the primary-side switching tube based on information about a conduction position of the primary-side switching tube capable of achieving soft switching; The comparison module has an input terminal electrically connected to the third output terminal of the sampling circuit, and an output terminal electrically connected to the first input terminal and the second input terminal of the selection module, and is configured to compare the operating frequency sampling signal with a preset reference frequency, and obtain comparison information based on the comparison result; The second input terminal of the conduction duration calculation module is electrically connected to the third output terminal of the sampling circuit, and the output terminal is electrically connected to the third input terminal of the selection module, and is configured to obtain the conduction duration of the primary-side switch tube based on the operating frequency sampling signal; The input end of the fixed on-time setting module is electrically connected to the output end of the zero-crossing detection module, and the output end is electrically connected to the fourth input end of the selection module, and is configured to set a fixed on-time according to the on-position information of the primary-side switch tube capable of achieving soft switching; The first and second input terminals of the selection module are electrically connected to the output terminal of the comparison module, the third input terminal is electrically connected to the output terminal of the conduction time calculation module, the fourth input terminal is electrically connected to the output terminal of the fixed conduction time setting module, and the output terminal is electrically connected to the second input terminal of the drive circuit. The selection module is configured to select the conduction time based on the comparison information, select the fixed conduction time when the potential of the first comparison information is greater than or equal to the potential of the second comparison information, and select the conduction time when the potential of the first comparison information is less than the potential of the second comparison information.

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