Multi-mode soft switching control system

Abstract

This application relates to the field of integrated circuits and discloses a multi-mode soft-switching control system. The system includes a secondary-side control chip and a primary-side control chip, which work together to achieve efficient energy conversion. The secondary-side control chip collects the transformer secondary-side current, the drain voltage of the secondary-side switch, and the output voltage through a sampling circuit. Based on this, the control circuit determines the position and duration of the secondary-side switch's two conductions, and the drive circuit executes specific control. The primary-side control chip collects the drain voltage, source voltage, and operating frequency of the primary-side switch through a sampling circuit. Based on this, the control circuit determines the position where zero-voltage conduction is possible and the appropriate conduction duration, and the drive circuit executes corresponding control. The system can effectively eliminate conduction losses; simultaneously, it automatically switches the operating mode according to the load current and adaptively adjusts the conduction duration of the primary-side switch and the conduction position of the secondary-side switch, significantly improving overall efficiency and applicability.

Description

Technical Field

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

[0002] With the rapid development of electronic power technology, the relationship between people and electronic products is becoming increasingly close, and the requirements for power management modules in various electronic devices are rising. Switching power supplies, with their advantages of high efficiency, small size, and light weight, are gradually becoming the mainstream choice for power management in electronic devices. Flyback converters are an important topology of switching power supplies, widely used in AC / DC and DC / DC conversion switching power supply circuits.

[0003] In existing technologies, flyback converters typically employ optocouplers or transformer auxiliary windings to acquire secondary-side voltage and current information on the primary side. However, optocouplers have relatively low transmission rates, are significantly affected by external temperature factors, have high static power consumption, and are large in size, increasing system cost and volume. While transformer auxiliary windings offer the same information transmission rate and operating frequency, the sampled voltage and current information contains significant errors. Furthermore, using transformer auxiliary windings increases transformer size, further increasing cost and volume.

[0004] Flyback converters typically operate in pulse-width modulation (PWM) mode. At higher load currents, flyback converters operating in this mode are highly efficient. However, at lower load currents, their efficiency is very low. Therefore, a multi-mode control system is needed to adapt to different load current conditions.

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

[0006] In summary, existing flyback converter control systems face technical problems such as low information sampling accuracy, high system cost, large size, uneven efficiency under different load conditions, and large conduction losses of primary-side switches. A new type of 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 mentioned in the background art.

[0008] This application discloses a multi-mode soft-switching control system applied in a flyback converter. The flyback converter includes a secondary-side switch, a primary-side switch, 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 switching transistor, 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 switching transistor.

[0010] The primary-side control chip includes a sampling circuit, a control circuit, and a driving circuit. The first input terminal of the sampling circuit is electrically connected to the drain terminal of the primary-side switching transistor, the second input terminal is electrically connected to the source terminal of the primary-side switching transistor, the third input terminal is electrically connected to the first output terminal of the control circuit, the output terminal is electrically connected to the input terminal of the control circuit, the second and third output terminals of the control circuit are electrically connected to the input terminal of the driving circuit, and the output terminal of the driving circuit is electrically connected to the gate terminal of the primary-side switching transistor.

[0011] In a preferred embodiment, the sampling circuit is configured to acquire the transformer secondary side current, the drain voltage of the secondary side switch, and the output voltage of the flyback converter to obtain the transformer secondary side sampling current, the secondary side switch drain 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 transistor for the first conduction based on the sampled current on the secondary side of the transformer, and to determine the conduction position and conduction duration of the secondary-side switch transistor for the second conduction based on the sampled voltage at the drain terminal and the sampled voltage at the output terminal of the secondary-side switch transistor.

[0013] The drive circuit is configured to turn the secondary-side switching transistor on or off according to the control signal output by the control circuit.

[0014] The sampling circuit is configured to acquire the drain voltage, source voltage, and operating frequency of the primary-side switch transistor to obtain the primary-side switch transistor drain sampling voltage, source sampling voltage, and operating frequency sampling signals.

[0015] The control circuit is configured to determine the conduction position where the primary-side switch can conduct at zero voltage based on the sampled voltage at the drain terminal and the sampled voltage at the source terminal of the primary-side switch, and to determine the conduction duration based on the operating frequency sampled signal.

[0016] The drive circuit is configured to turn the primary-side switching transistor on or off according to the control signal output by the control circuit.

[0017] The second conduction of the secondary-side switch pulls the drain voltage of the primary-side switch down to zero, thus achieving soft switching of the primary-side switch. The control circuit automatically switches between different conduction duration modes according to the load current. When the load current is less than a preset threshold, a fixed conduction duration is used. When the load current is greater than the preset threshold, a conduction duration that increases linearly with 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 terminal of the current sampling module is electrically connected to the secondary side of the transformer, and the output terminal is electrically connected to the first input terminal of the control circuit. It is configured to sample the current on the secondary side of the transformer to obtain the sampled current on the secondary side of the transformer.

[0020] The first input terminal of the voltage sampling module is electrically connected to the drain terminal of the secondary-side switching transistor, the second input terminal is electrically connected to the output terminal of the flyback converter, and the output terminal is electrically connected to the second and third input terminals of the control circuit. It is configured to sample the drain voltage of the secondary-side switching transistor and the output voltage of the flyback converter, respectively, to obtain the drain sampling voltage of the secondary-side switching transistor 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 conduction duration setting module;

[0022] The input terminal of the zero-crossing detection module is electrically connected to the first output terminal of the sampling circuit, and the output terminal is electrically connected to the input terminal of the driving circuit. It is configured to detect the zero-crossing point of the sampling current on the secondary side of the transformer, so as to obtain the conduction position and conduction duration of the first conduction of the secondary side switch.

[0023] The input terminal of the constant voltage control module is electrically connected to the second and third output terminals of the sampling circuit, and the output terminal is electrically connected to the input terminal of the fixed conduction duration setting module. It is configured to obtain the conduction position information of the second conduction of the secondary side switch based on the sampling voltage at the drain terminal of the secondary side switch and the output sampling voltage.

[0024] The input terminal of the fixed conduction duration setting module is electrically connected to the output terminal of the constant voltage control module, and the output terminal is electrically connected to the input terminal of the drive circuit. It is configured to determine the fixed conduction duration based on the conduction position information of the second conduction of the secondary-side switch.

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

[0026] The voltage sampling module has its first input terminal electrically connected to the drain terminal of the primary-side switching transistor, its second input terminal electrically connected to the source terminal of the primary-side switching transistor, its first output terminal electrically connected to the first input terminal of the control circuit, and its second output terminal electrically connected to the second input terminal of the control circuit. It is configured to sample the drain terminal voltage and the source terminal voltage of the primary-side switching transistor respectively to obtain the drain terminal sampling voltage and the source terminal sampling voltage of the primary-side switching transistor.

[0027] The input terminal of the frequency sampling module is electrically connected to the first output terminal of the control circuit, and the output terminal is electrically connected to the third input terminal of the control circuit. It is configured to sample the operating frequency of the primary-side switching transistor 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 duration calculation module, a fixed conduction duration setting module, and a selection module;

[0029] The first input terminal of the zero-crossing detection module is electrically connected to the first output terminal of the sampling circuit, the second input terminal is electrically connected to the second output terminal of the sampling circuit, and the output terminal is electrically connected to the first input terminal of the driving circuit, the input terminal of the frequency calculation module, the input terminal of the fixed conduction duration setting module, and the first input terminal of the conduction duration calculation module. It is configured to detect the zero-crossing point of the sampling voltage at the source terminal of the primary-side switching transistor based on the sampling voltage at the drain terminal of the primary-side switching transistor, and obtain the conduction position information of the primary-side switching transistor that can achieve soft switching.

[0030] The input terminal of the frequency calculation module is electrically connected to the output terminal of the zero-crossing detection module, and the output terminal is electrically connected to the third input terminal of the sampling circuit. It is configured to obtain the operating frequency of the primary-side switching transistor based on the conduction position information of the primary-side switching transistor, which can achieve soft switching.

[0031] The input terminal of the comparison module is electrically connected to the third output terminal of the sampling circuit, and the output terminal is electrically connected to the first and second input terminals of the selection module. It 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. It is configured to obtain the conduction duration of the primary-side switch based on the sampling signal of the operating frequency.

[0033] The input terminal of the fixed conduction duration setting module is electrically connected to the output terminal of the zero-crossing detection module, and the output terminal is electrically connected to the fourth input terminal of the selection module. It is configured to set a fixed conduction duration based on the conduction position information of the primary-side switching transistor that can achieve 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 duration calculation module, the fourth input terminal is electrically connected to the output terminal of the fixed conduction duration setting module, and the output terminal is electrically connected to the second input terminal of the drive circuit. It is configured to select the conduction duration based on comparison information. When the potential of the first comparison information is greater than or equal to the potential of the second comparison information, the fixed conduction duration is selected. When the potential of the first comparison information is less than the potential of the second comparison information, the conduction duration is selected.

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

[0036] By precisely controlling the secondary-side switching transistor to conduct twice within a switching cycle through the secondary-side control chip, especially the second conduction, the drain voltage of the primary-side switching transistor can be pulled down to zero, realizing zero-voltage conduction of the primary-side switching transistor, i.e. soft switching. This effectively eliminates the conduction loss when the primary-side switching transistor is hard switched, and significantly improves the energy conversion efficiency of the system.

[0037] By using a primary-side control chip to adaptively adjust the conduction time and operating frequency of the primary-side switch based on the sampled drain voltage, source voltage, and operating frequency signals, multi-mode optimized control under light and heavy load conditions is achieved. For example... Figure 5 and Figure 6 As shown, when the load current is less than the threshold, a fixed on-time is maintained, 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 initial value with the load to adapt to load changes. This strategy enables the system to maintain efficient operation under a wide range of load conditions.

[0038] The fine division and collaborative operation 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 the secondary-side and primary-side switching transistors is achieved. The zero-crossing detection module, constant voltage control module, and fixed conduction duration setting module of the secondary-side control chip respectively control the position and duration of the secondary-side switching transistor's two conduction cycles. The zero-crossing detection module, frequency calculation module, comparison module, conduction duration calculation module, fixed conduction duration setting module, and selection module of the primary-side control chip flexibly control the soft-switching conduction position and conduction duration of the primary-side switching transistor through frequency adaptation and comparison selection. This modular structural design and clear control strategy improve control accuracy and reliability, and enhance system stability and anti-interference capabilities.

[0039] This application avoids the drawbacks of traditional flyback converter control schemes that use optocouplers or transformer auxiliary windings. Traditional methods suffer from low transmission rates, significant temperature susceptibility, high static power consumption, and large size. This application, however, simplifies the complexity of primary-side control and reliably achieves soft switching on the primary side by using a secondary-side control chip to assist in the control of the primary-side switching transistor. This innovative control architecture offers advantages such as simple structure, low cost, high efficiency, and wide applicability, effectively replacing existing flyback converter control schemes and possessing broad application prospects.

[0040] The specification of this application contains numerous technical features distributed across various technical solutions. Listing all possible combinations of these technical features (i.e., technical solutions) would make the specification excessively lengthy. To avoid this problem, the various technical features disclosed in the above-described invention, the various technical features disclosed in the following embodiments and examples, and the various technical features disclosed in the accompanying drawings can be freely combined to form various new technical solutions (all of which are considered to have been described in this specification), unless such a combination of technical features is technically infeasible. For example, one example discloses feature A+B+C, and another example discloses feature A+B+D+E. Features C and D are equivalent technical means that serve the same function, and technically only one needs to be used; they cannot be used simultaneously. Feature E can technically be combined with feature C. Therefore, the solution A+B+C+D should not be considered as described because it is technically infeasible, while the solution A+B+C+E should be considered as described. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of a multi-mode soft-switching control system according to an embodiment of this application;

[0042] Figure 2 This is a schematic diagram of the current and voltage waveforms of each node of a flyback converter, which is applied to a multi-mode soft-switching control system according to an embodiment of this application, as the load changes.

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

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

[0045] Figure 5 This is a schematic diagram showing the on-time of the primary-side switch tube of a multi-mode soft-switching control system according to an embodiment of this application as a function of load.

[0046] Figure 6 This is a schematic diagram of the system operating frequency of a multi-mode soft-switching control system according to an embodiment of this application as a function of load.

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

[0048] Figure 8 This is a schematic diagram of the structure of another primary-side control chip of a multi-mode soft-switching control system according to an embodiment of this application. Detailed Implementation

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

[0050] Explanation of some concepts:

[0051] In this application, a flyback converter refers to a topology of a switching power supply, including a secondary-side switch, a primary-side switch, and a transformer, which achieves voltage conversion through the storage and release of energy by the transformer.

[0052] In this application, a secondary-side control chip refers to a chip used to control the on and off of a secondary-side switching transistor, including a sampling circuit, a control circuit, and a drive circuit, which is responsible for collecting relevant secondary-side signals and controlling the switching action.

[0053] In this application, the primary-side control chip refers to a chip used to control the on and off of the primary-side switching transistor, including a sampling circuit, a control circuit, and a driving circuit, which is responsible for collecting relevant primary-side signals and determining the position and duration of the soft-switching of the switching transistor.

[0054] In this application, soft switching refers to a switching method in which the voltage across the switching transistor is reduced to zero or near zero before the transistor is turned on, which can significantly reduce the conduction loss of the switching transistor.

[0055] Zero Voltage Switching (ZVS), in this application, refers to a soft-switching mode in which the drain voltage of the primary-side switch is pulled down in advance by the action of the secondary-side switch at the instant the primary-side switch is turned on, and then the source voltage is detected. When the drain voltage and the source voltage are the same, the switch is turned on, so that there is no voltage difference across the switch when it is turned on, thereby avoiding conduction losses.

[0056] In this application, conduction duration refers to the duration during which the switching transistor remains in the conducting state in each switching cycle. It is automatically determined and adjusted by the control circuit based on the load current to achieve efficient energy conversion.

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

[0058] In this application, the fixed on-time mode refers to the conduction mode adopted by the primary-side switch when the load current is lower than a 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 when the load current exceeds a preset threshold. The on-time increases linearly with the load current, and the operating frequency is fixed at the maximum value to meet the energy demand under heavy load conditions.

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

[0061] In summary, this application addresses the technical bottlenecks of high primary-side switching losses, large sampling errors of optocouplers or auxiliary windings in traditional flyback converters, which increase system complexity and cost. By establishing a composite modulation mechanism based on bidirectional conduction of the secondary-side switch and synchronous adaptive control of the primary-side switch, a breakthrough in a non-obvious technical challenge is achieved. Specifically, this application designs a distributed control architecture in which a secondary-side control chip and a primary-side control chip work together. The secondary-side control chip accurately detects the zero-crossing point of the transformer's secondary-side current and changes in the output voltage. Within a single switching cycle, it controls the secondary-side switch to perform two asymmetric conduction operations. In particular, the precise regulation of the transformer's energy distribution during the second conduction pulls the drain voltage of the primary-side switch to zero at a specific moment, thereby realizing the complex timing control of zero-voltage soft switching. At the same time, based on the drain-source voltage and operating frequency information of the switch, the primary-side control chip achieves seamless dual-mode switching between "fixed conduction time - variable frequency" and "fixed frequency - variable conduction time" under light and heavy load conditions through multi-module cascade processing and adaptive threshold determination. This solves 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, a systemic breakthrough has been achieved in multiple technical goals, including improved efficiency, reduced size, lower cost, and expanded applicability.

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

[0063] In this application's specification, to make the description clearer and more concise, some technical features are represented using English letter codes. It should be clarified that the technical features represented solely by letter codes in this application have the same meaning as those represented by their corresponding Chinese names plus letter codes. For example, "Isec" and "transformer secondary side current Isec" refer to the same technical feature, and "Vswp" and "primary side switch drain voltage Vswp" refer to the same technical feature. Other similar technical features represented by English letter codes are also equivalent to their corresponding Chinese names plus letter codes. When reading and understanding this application, please treat the technical features represented solely by letter codes as equivalent to their corresponding Chinese names plus letter codes. The technical features involving English letter codes include, but are not limited to:

[0064] Transformer secondary side current Isec;

[0065] The transformer secondary side sampling current Isec_sen;

[0066] Secondary-side switch drain voltage Vsec;

[0067] Secondary-side switch drain terminal sampling voltage Vsec_sen;

[0068] Flyback converter output voltage Vout;

[0069] Output sampling voltage Vout_sen;

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

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

[0072] Primary-side switch drain voltage Vswp;

[0073] The primary-side switch's drain terminal sampling voltage Vswp_sen;

[0074] Primary-side switch source terminal voltage Vcs;

[0075] The primary-side switch source terminal sampling voltage Vcs_sen;

[0076] The primary-side switching transistor's operating frequency is fre;

[0077] Operating frequency sampling signal Vfre;

[0078] Primary-side switch transistor soft-switching on-state information Vset;

[0079] Comparison information Sel1;

[0080] Compare information Sel2;

[0081] Fixed conduction duration Tb;

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

[0083] Transformer primary side current Ipri;

[0084] Secondary-side switch control voltage VS1;

[0085] Primary-side switching transistor control voltage VS2;

[0086] Load current Iload;

[0087] Input voltage Vin;

[0088] The system's minimum operating frequency, fmin;

[0089] The system's maximum operating frequency, fmax;

[0090] Load threshold current Iload1.

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

[0092] S1: Secondary-side switching transistor;

[0093] S2: Primary-side switching transistor;

[0094] 11: Secondary-side control chip;

[0095] 12: Primary-side control chip;

[0096] 1110: Sampling circuit;

[0097] 1120: Control circuit;

[0098] 113: Drive 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 conduction duration setting module;

[0104] 1210: Sampling circuit;

[0105] 1220: Control circuit;

[0106] 123: Drive 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 conduction duration setting module;

[0114] 1226: Select module.

[0115] The first embodiment of this application relates to a multi-mode soft-switching control system applied in a flyback converter, such as... Figure 1 , Figure 3 and Figure 7 As shown, the flyback converter includes: a secondary-side switch S1, a primary-side switch 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 terminal of the sampling circuit 1110 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 switching transistor S1, 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 1120, the output terminal of the control circuit 1120 is electrically connected to the input terminal of the drive circuit 113, and the output terminal of the drive circuit 113 is electrically connected to the gate terminal of the secondary-side switching transistor S1.

[0117] The sampling circuit 1110 is configured to collect 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 sampling current Isec_sen, the secondary side switch drain 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 S1 for the first conduction based on the secondary-side sampling current Isec_sen of the transformer, and to determine the conduction position and conduction duration Ta of the secondary-side switch S1 for the second conduction based on the drain sampling voltage Vsec_sen and the output sampling voltage Vout_sen of the secondary-side switch.

[0119] The drive 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 driving circuit 123. The first input terminal of the sampling circuit 1210 is electrically connected to the drain terminal of the primary-side switching transistor S2, the second input terminal is electrically connected to the source terminal of the primary-side switching transistor S2, the third input terminal is electrically connected to the first output terminal of the control circuit 1220, the output terminal is electrically connected to the input terminal of the control circuit 1220, the second and third output terminals of the control circuit 1220 are electrically connected to the input terminal of the driving circuit 123, and the output terminal of the driving circuit 123 is electrically connected to the gate terminal of the primary-side switching transistor S2.

[0121] The sampling circuit 1210 is configured to acquire the drain voltage Vswp, source voltage Vcs, and operating frequency fre of the primary-side switch S2, and obtain the primary-side switch 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 of the primary-side switch S2 that can be turned on with zero voltage based on the primary-side switch drain sampling voltage Vswp_sen and the primary-side switch source sampling voltage Vcs_sen, and to determine the conduction duration by the operating frequency sampling signal Vfre.

[0123] The drive 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] The second conduction of the secondary-side switch S1 pulls the drain voltage Vswp of the primary-side switch S2 down to zero, thus achieving soft switching of the primary-side switch S2. The control circuit 1220 automatically switches between different conduction duration modes according to the load current. When the load current is less than a preset threshold, a fixed conduction duration Tb is used. When the load current is greater than the preset threshold, a conduction duration Tc that increases linearly with 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 terminal of the current sampling module 1111 is electrically connected to the secondary side of the transformer, and the output terminal is electrically connected to the first input terminal of the control circuit 1120. It is configured to sample the current Isec on the secondary side of the transformer to obtain the sampled current Isec_sen on the secondary side of the transformer.

[0127] The first input terminal of the voltage sampling module 1112 is electrically connected to the drain terminal of the secondary-side switching transistor S1, the second input terminal is electrically connected to the output terminal of the flyback converter, and the output terminal is electrically connected to the second and third input terminals of the control circuit 1120. It is configured to sample the drain terminal voltage Vsec of the secondary-side switching transistor S1 and the output voltage Vout of the flyback converter, respectively, to obtain the drain terminal sampling voltage Vsec_sen of the secondary-side switching transistor 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 conduction duration setting module 1123.

[0129] The input terminal of the zero-crossing detection module 1121 is electrically connected to the first output terminal of the sampling circuit 1110, and the output terminal is electrically connected to the input terminal of the driving circuit 113. It 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 secondary side switch S1 when it is first turned on.

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

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

[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 its first input terminal electrically connected to the drain terminal of the primary-side switching transistor S2, its second input terminal electrically connected to the source terminal of the primary-side switching transistor S2, its first output terminal electrically connected to the first input terminal of the control circuit 1220, and its second output terminal electrically connected to the second input terminal of the control circuit 1220. It is configured to sample the drain terminal voltage Vswp and the source terminal voltage Vcs of the primary-side switching transistor S2, respectively, to obtain the primary-side switching transistor drain terminal sampling voltage Vswp_sen and the source terminal sampling voltage Vcs_sen.

[0134] The input terminal of the frequency sampling module 1212 is electrically connected to the first output terminal of the control circuit 1220, and the output terminal is electrically connected to the third input terminal of the control circuit 1220. It is configured to sample the operating frequency fre of the primary-side switch 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, a conduction duration calculation module 1224, a fixed conduction duration setting module 1225, and a selection module 1226.

[0136] 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 is electrically connected to the second output terminal of the sampling circuit 1210, and the output terminal is electrically connected to the first input terminal of the driving circuit 123, the input terminal of the frequency calculation module 1222, the input terminal of the fixed conduction duration setting module 1225, and the first input terminal of the conduction duration calculation module 1224. It is configured to detect the zero-crossing point of the sampling voltage Vcs_sen at the source terminal of the primary-side switch based on the sampling voltage Vswp_sen at the drain terminal of the primary-side switch, and obtain the conduction position information Vset of the primary-side switch S2 that enables soft switching.

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

[0138] The input terminal of the comparison module 1223 is electrically connected to the third output terminal of the sampling circuit 1210, and the output terminal is electrically connected to the first input terminal and the second input terminal of the selection module 1226. It is configured to compare the working 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. It is configured to obtain the conduction duration Tc of the primary-side switch S2 based on the sampling signal Vfre of the operating frequency.

[0140] The input terminal of the fixed conduction duration setting module 1225 is electrically connected to the output terminal of the zero-crossing detection module 1221, and the output terminal is electrically connected to the fourth input terminal of the selection module 1226. It is configured to set a fixed conduction duration Tb according to the conduction 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 duration calculation module 1224, the fourth input terminal is electrically connected to the output terminal of the fixed conduction duration setting module 1225, and the output terminal is electrically connected to the second input terminal of the drive circuit 123. It is configured to select the conduction duration based on the comparison information Sel1 and Sel2. When the potential of Sel1 is greater than or equal to the potential of Sel2, the fixed conduction duration Tb is selected, and when the potential of Sel1 is less than the potential of Sel2, the conduction duration Tc is selected.

[0142] To make the technical solution of the present invention clearer and more understandable, it is now combined with Figures 1 to 8 Preferred embodiments of the present invention will be described in detail, but it should be understood that the described embodiments are merely exemplary 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 primary side of the transformer is electrically connected to the input voltage Vin, and the second terminal of the 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 S2 contains a parasitic capacitance Cswp. The first terminal of the secondary side of the transformer and the first plate of the output capacitor Cout are both electrically connected to the load current Iload. The second terminal of the secondary side of the transformer 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.

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

[0145] In terms of operating principle, when the primary-side control chip 12 controls the primary-side switch S2 to turn on, the input voltage Vin charges the primary side of the transformer. At this time, the secondary-side control chip 11 controls the secondary-side switch S1 to turn off, and the load current Iload is provided by the output capacitor Cout. When the primary-side control chip 12 controls the primary-side switch S2 to turn off, since the current in the primary side of the transformer cannot change abruptly, a reverse voltage difference will be formed on the primary side of the transformer. According to the transformer principle, a reverse voltage is also generated on the secondary side of the transformer at this time, and the secondary-side control chip 11 controls the secondary-side switch S1 to turn on accordingly.

[0146] A key aspect of this embodiment is that within one 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 can be pulled low. Then, by detecting the source voltage Vcs, zero-voltage conduction of the primary-side switch S2 can be achieved, i.e., soft switching, thereby significantly reducing the conduction losses caused by hard switching. Simultaneously, the control system of this embodiment can automatically switch the conduction duration of the primary-side switch S2 according to the load current. A fixed short conduction duration is used under light loads, while the conduction duration increases with the load current under heavy loads, further improving the converter's efficiency and applicability.

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

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

[0149] After a period of time Ta, i.e. at time t2, the control voltage VS1 of the secondary-side switch S1 goes low, and S1 is turned off. The primary-side current Ipri of the transformer reverses, and the charge in the parasitic capacitance Cswp of the primary-side switch S2 is drawn away, causing its drain voltage Vswp to be pulled low. When Vswp is pulled low to zero, the control voltage VS2 of the primary-side switch S2 goes high, and S2 turns on under zero-voltage conditions, realizing soft switching and effectively reducing the conduction loss of hard switching.

[0150] It should be noted that as the load current Iload increases, the secondary-side switch S1 will turn on earlier for the second time. For example... Figure 2 As shown, at time t11, the second conduction position of S1 is earlier than at time t6, resulting in an increase in the system operating frequency. When the load current Iload further increases, the primary-side control chip 12 will adjust the conduction duration of the primary-side switch S2 from a fixed value Tb to Tc, which varies with the load. As shown in the figure, during the time period t13-t14, the conduction duration of S2 is Tc, and it increases linearly with the increase of Iload, while the system operating frequency remains at its maximum value fmax.

[0151] This adaptive load-change control strategy enables the system to maintain high efficiency under different load conditions and ensures reliable soft switching, significantly improving the overall performance of the flyback converter.

[0152] Figure 3 This is a schematic diagram of the structure of a secondary-side control chip according to 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 connected to the secondary side of the transformer, the drain terminal of the secondary-side switch S1, and the output terminal of the flyback converter, respectively, to acquire the transformer secondary-side current Isec, the drain terminal voltage Vsec of the secondary-side switch S1, and the output voltage Vout. The output terminal of sampling circuit 1110 is electrically connected to the gate terminal of the secondary-side switch S1 through control circuit 1120 and drive circuit 113. The signals acquired by sampling circuit 1110 are the transformer secondary-side sampling current Isec_sen, the secondary-side switch drain terminal sampling voltage Vsec_sen, and the output sampling voltage Vout_sen.

[0154] The control circuit 1120 determines the conduction position and conduction duration OUT_sec of the secondary-side switch S1 for the first conduction based on the acquired secondary-side sampling current Isec_sen. Simultaneously, the control circuit 1120 also determines the conduction position and fixed conduction duration Ta of the secondary-side switch S1 for the second conduction based on the secondary-side drain sampling voltage Vsec_sen and the output sampling voltage Vout_sen.

[0155] The drive 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 secondary-side switch S1's second conduction, enables the primary-side switch S2 to achieve zero-voltage conduction, i.e., soft switching, effectively reducing switching losses and improving energy conversion efficiency.

[0157] Figure 4 This is a schematic diagram of another secondary-side control chip in this embodiment. As shown in the figure, in Figure 3 Based on this, 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 conduction duration setting module 1123.

[0158] The input terminal of the current sampling module 1111 is connected to the secondary side of the transformer, and the output terminal is connected to the first input terminal 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 sampled current Isec_sen on the secondary side of the transformer.

[0159] The first input terminal of the voltage sampling module 1112 is connected to the drain terminal of the secondary-side switch S1, the second input terminal is connected to the output terminal of the flyback converter, and the output terminal is connected to the second and third input terminals 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 the secondary-side switch drain sampling voltage Vsec_sen and the output sampling voltage Vout_sen.

[0160] The input terminal of the zero-crossing detection module 1121 is connected to the first output terminal of the sampling circuit 1110, that is, to receive the sampled current Isec_sen from the secondary side of the transformer, and the output terminal is connected to the input terminal of the drive circuit 113. The zero-crossing detection module 1121 obtains the conduction position and conduction duration OUT_sec of the secondary side switch S1 when it first turns on by detecting the zero-crossing point of Isec_sen.

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

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

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

[0164] Figure 5 This is a schematic diagram showing the on-time of the primary-side switch S2 as a function of load in this embodiment. As shown in the figure, 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 visually illustrates the adaptive control strategy of the system 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 a fixed value Tb. This corresponds to a light-load condition, where the system adapts to load changes by adjusting the operating frequency rather than the on-time. When the load current Iload is greater than the threshold Iload1, the on-time of the primary-side switch S2 switches to Tc, and increases linearly with the increase of the load current. This corresponds to a heavy-load condition, where the system increases the on-time to meet the greater load demand.

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

[0167] When the load current Iload is less than or equal to the threshold Iload1, the system operating frequency increases linearly with the load current from the minimum value fmin. This is consistent with... Figure 5 The fixed on-time Tb of the corresponding region is matched. 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, the on-time Tc is increased to adapt to the larger load, such as... Figure 5 As shown.

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

[0169] Figure 7 This is a schematic diagram of the structure of a primary-side control chip according to this embodiment. As shown in the figure, the primary-side control chip 12 includes a sampling circuit 1210, a control circuit 1220, and a driving circuit 123.

[0170] The first input terminal of the sampling circuit 1210 is connected to the drain terminal of the primary-side switching transistor S2, the second input terminal is connected to the source terminal of the primary-side switching transistor S2, and the third input terminal is connected to the first output terminal of the control circuit 1220. The output terminal is connected to the input terminal of the control circuit 1220. The sampling circuit 1210 is used to acquire the drain voltage Vswp, the source voltage Vcs, and the system operating frequency fre of the primary-side switching transistor S2, and obtain the primary-side switching transistor drain sampling voltage Vswp_sen, the source sampling voltage Vcs_sen, and the frequency information Vfre of the first output terminal 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 drive circuit 123. The control circuit 1220 determines the conduction position Vset of the primary-side switch S2 to achieve soft switching based on the sampled primary-side switch drain voltage Vswp_sen and source voltage Vcs_sen, and determines the conduction duration based on the frequency information Vfre.

[0172] The input terminal of the drive 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 drive circuit 123 drives the primary-side switch S2 to turn 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 turn-on timing of the primary-side switching transistors based on real-time sampled voltage and frequency information, ensuring that the transistors conduct under zero-voltage conditions and reducing switching losses. Simultaneously, it can dynamically optimize the turn-on duration according to load conditions, improving system efficiency and applicability.

[0174] Figure 8 This is a schematic diagram of another primary-side control chip in this embodiment. As shown in the figure, in... Figure 7 Based on this, 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 duration calculation module 1224, a fixed conduction duration 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 switching transistor S2, respectively, and 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 switching transistor S2, respectively, to obtain the drain sampling voltage Vswp_sen and the 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 S2 to obtain the 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 is connected to 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. Based on the drain sampling voltage Vswp_sen, the zero-crossing detection module 1221 detects the zero-crossing point of the source sampling voltage Vcs_sen to obtain the conduction position information Vset of the primary-side switch S2, which enables soft switching.

[0178] The input of the frequency calculation module 1222 is connected to the output of the zero-crossing detection module 1221, and the output is connected to the third input 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 a preset reference frequency to obtain comparison information Sel1 and Sel2.

[0180] The second input terminal of the conduction duration 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 conduction duration calculation module 1224 calculates the conduction duration Tc that varies with the load based on the operating frequency sampling signal Vfre.

[0181] The input terminal of the fixed conduction duration 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 conduction duration setting module 1225 sets a fixed conduction duration 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 conduction duration calculation module 1224, and the fixed conduction duration 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 a fixed conduction duration Tb and a conduction duration Tc that varies with the load 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 the load conditions. Under light load, it fixes the conduction duration and adjusts the frequency, while under heavy load, it fixes the maximum frequency and adjusts the conduction duration, ensuring efficient operation under various working conditions and significantly improving the system's adaptability and efficiency.

[0184] Working principle:

[0185] The multi-mode soft-switching control system of this embodiment can precisely control the switching timing of the secondary-side switch S1 and the primary-side switch S2 in the flyback converter, achieving high-efficiency energy conversion. The following section combines... Figures 1 to 8 The working principle of the system will be explained in detail.

[0186] 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, generating a primary-side current Ipri. At this time, 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, since the primary-side current Ipri cannot change abruptly, a reverse voltage difference is generated on the primary side of the transformer. According to the transformer principle, the secondary-side voltage Vsec also reverses. The secondary-side control chip 11 then turns on the secondary-side switch S1, allowing energy to be transferred from the transformer to the output terminal.

[0187] It should be noted that, such as Figure 2 As shown, within one switching cycle, the secondary-side control chip 11 can control the secondary-side switch S1 to conduct for the second time. Specifically, at time t1, the secondary-side control chip 11 pulls up 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 electrical energy is charged into the transformer through S1, raising the drain voltage Vswp of the primary-side switch S2. After time Ta, at time t2, the secondary-side control chip 11 pulls down VS1, turning S1 off. The transformer primary-side current Ipri reverses, causing the parasitic capacitance Cswp to discharge, and the drain voltage Vswp of S2 is pulled down. When the drain voltage Vswp and the source voltage Vcs are equal, the primary-side control chip 12 pulls up the control voltage VS2 of S2, turning S2 on under zero-voltage conditions, realizing soft switching and eliminating the conduction losses of hard switching.

[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 Iload1, the system operates in light load mode, the on-time of the primary-side switch S2 remains a fixed short duration 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 Figure 3 and Figure 4The sampling circuit 1110 of the secondary-side control chip 11 collects the transformer secondary-side current Isec, the drain voltage Vsec of the secondary-side switch S1, and the output voltage Vout, respectively. In the control circuit 1120, the zero-crossing detection module 1121 detects the zero-crossing point of the secondary-side sampling 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 sampling voltage Vsec_sen and the output sampling voltage Vout_sen; and the fixed conduction duration setting module 1123 sets the fixed conduction duration Ta for the second conduction.

[0190] See Figure 7 and Figure 8 The sampling circuit 1210 of the primary-side control chip 12 collects 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 sampling voltage Vcs_sen to determine the soft-switching conduction position Vset of S2; the comparison module 1223 compares the operating frequency sampling signal Vfre with the reference frequency and outputs comparison information Sel1 and Sel2; the selection module 1226 selects between the light-load conduction duration Tb and the heavy-load conduction duration Tc accordingly; and the drive circuit 123 finally drives S2 to turn on or off.

[0191] Through the aforementioned collaborative mechanism, this embodiment can achieve high-efficiency energy conversion under a wide range of load conditions. In particular, the second turn-on of the secondary-side switch S1 enables the primary-side switch S2 to achieve zero-voltage soft switching, significantly reducing switching losses and substantially improving system efficiency. Simultaneously, the load-adaptive dual-mode switching further broadens the applicability and enhances the practicality of the flyback converter.

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

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

[0194] This multi-mode soft-switching control system is applied in a flyback converter, which includes a secondary-side control chip, a primary-side control chip, a secondary-side switch, a primary-side switch, 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 switching transistor, the third input terminal of the secondary-side control chip is electrically connected to the output terminal of the flyback converter, and the output terminal of the secondary-side control chip is electrically connected to the gate terminal of the secondary-side switching transistor. The first input terminal of the primary-side control chip is electrically connected to the drain terminal of the primary-side switching transistor, the second input terminal of the primary-side control chip is electrically connected to the source terminal of the primary-side switching transistor, and the output terminal of the primary-side control chip is electrically connected to the gate terminal of the primary-side switching transistor.

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

[0197] The first input terminal of the sampling circuit is electrically connected to the secondary side of the transformer, the second input terminal of the sampling circuit is electrically connected to the drain terminal of the secondary-side switching transistor, the third input terminal of the sampling circuit is electrically connected to the output terminal of the flyback converter, the output terminal of the sampling circuit is electrically connected to the input terminal of the 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 switching transistor.

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

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

[0200] The driving circuit is configured to drive the secondary-side switch to turn on and off based on the determined on-position of the secondary-side switch.

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

[0202] The input terminal of the current sampling module is electrically connected to the primary side of the transformer, the output terminal of the current sampling module is electrically connected to the first input terminal of the control circuit, the first input terminal of the voltage sampling module is electrically connected to the drain terminal of the secondary side switching transistor, the second input terminal of the voltage sampling module is electrically connected to the output terminal of the flyback converter, and the output terminal of the voltage sampling module is electrically connected to the second and third input terminals 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 sampled current on the secondary side of the transformer.

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

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

[0206] The input terminal of the zero-crossing detection module is electrically connected to the first output terminal of the sampling circuit, the output terminal of the zero-crossing detection module is electrically connected to the input terminal of the driving circuit, the input terminal of the constant voltage control module is electrically connected to the second and third output terminals of the sampling circuit, the output terminal of the constant voltage control module is electrically connected to the input terminal of the fixed conduction duration setting module, and the output terminal of the fixed conduction duration setting module is electrically connected to the input terminal of the driving circuit.

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

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

[0209] The fixed conduction duration setting module is configured to determine the fixed conduction duration based on the conduction position information of the second conduction of the secondary-side switch.

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

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

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

[0213] The control circuit is configured to determine the conduction position of the primary-side switch that enables soft switching based on the sampled drain voltage and the sampled source voltage of the primary-side switch, and to determine the conduction duration by the operating frequency of the primary-side switch.

[0214] The driving circuit is configured to drive the primary-side switch to turn on and off based on the determined on-position and on-time of the primary-side switch.

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

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

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

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

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

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

[0221] The zero-crossing detection module is configured to detect the zero-crossing point of the source-side sampling voltage of the primary-side switching transistor based on the drain-side sampling voltage of the primary-side switching transistor, thereby obtaining the conduction position information of the primary-side switching transistor to achieve soft switching.

[0222] The frequency calculation module is configured to obtain the operating frequency of the primary-side switching transistor based on the conduction position information of the primary-side switching transistor, which enables 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 conduction duration calculation module is configured to obtain the conduction duration of the primary-side switch corresponding to the sampled operating frequency based on the sampled operating frequency.

[0225] The fixed conduction duration setting module is configured to determine the fixed conduction duration based on the conduction position information of the primary-side switching transistor, which enables soft switching.

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

[0227] More specifically, in this example, the primary-side input voltage of the flyback converter can be a power factor-calibrated DC voltage or an AC voltage rectified by a rectifier bridge. Generally, the primary-side input voltage has a wide range, approximately 60V to 400V.

[0228] The following explanation of this example is further illustrated with the accompanying diagram.

[0229] Figure 1 This is a schematic diagram of the flyback converter and its control system in this example, as shown below. 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 primary side of the transformer is electrically connected to the input voltage Vin. The second terminal of the 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 capacitance Cswp exists in the primary-side switch S2. The first terminal of the secondary side of the transformer 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 secondary side of the transformer 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 control system of the flyback converter 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, and 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 controls the primary-side switch S2 to turn on, the input voltage Vin charges the primary side of the transformer. At this time, the secondary-side control chip 11 controls the secondary-side switch S1 to turn off, and energy is provided by the output capacitor Cout. When the primary-side control chip 12 controls the primary-side switch S2 to turn off, since the current in the primary side of the transformer cannot change abruptly, a reverse voltage difference will form on the primary side of the transformer. At this time, the voltage difference on the secondary side of the transformer will also reverse, and the secondary-side control chip 11 controls the secondary-side switch S1 to turn on.

[0231] Within one cycle, the secondary-side control chip 11 can also control the secondary-side switching transistor S1 to conduct for the second time. Figure 2 This is a schematic diagram showing the current and voltage waveforms at each node of a flyback converter as the load changes. (Example:) Figure 2As shown, at time t1, the control voltage VS1 of the secondary-side switch S1 goes high, turning on S1. The drain voltage Vsec of S1 is pulled down to 0, the secondary current of the transformer reverses, and energy is injected into the transformer, converting electrical energy into magnetic energy. The drain voltage Vswp of the primary-side switch S2 is raised. After a period of time Ta, i.e., at time t1, the control voltage VS1 of the secondary-side switch S1 goes low, turning off S1. The primary current of the transformer reverses, and the charge in the parasitic capacitance Cswp of the primary-side switch S2 is removed, pulling down the drain voltage Vswp of S2. When the drain voltage Vswp of the primary-side switch S2 is pulled down to zero, the control voltage VS1 of the primary-side switch S2 goes high, turning on S2. This achieves soft switching, thus reducing the conduction losses caused by hard switching. Here, Ta is the conduction time of the second turn-on of the secondary-side switch S1.

[0232] Obviously, the fact that the secondary-side switch S1 is turned on at the appropriate position is the decisive factor for the primary-side switch S2 to achieve soft switching. Therefore, the secondary-side control chip 11 is needed to determine the turn-on position.

[0233] The following are some specific examples to illustrate the secondary-side control chip 11 in detail.

[0234] Figure 3 This is a schematic diagram of the secondary-side control chip, as shown below. Figure 3 As shown, the secondary-side control chip 11 includes a sampling circuit 1110, a control circuit 1120, and a drive circuit 1113. The first input terminal of the sampling circuit 1110 is electrically connected to the secondary side of the transformer; the second input terminal of the sampling circuit 1110 is electrically connected to the drain terminal of the secondary-side switching transistor S1; the third input terminal of the sampling circuit 1110 is electrically connected to the output terminal of the flyback converter; the output terminal of the sampling circuit 1110 is electrically connected to the input terminal of the control circuit 1120; the output terminal of the control circuit 1120 is electrically connected to the input terminal of the drive circuit 113; and the output terminal of the drive circuit 113 is electrically connected to the gate terminal of the secondary-side switching transistor S1.

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

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

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

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

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

[0240] In this way, the secondary-side switch S1 can be turned on at the appropriate position for the appropriate duration.

[0241] When the load current Iload increases, the conduction position of the secondary-side switch S1 will change for the second time. For example... Figure 2 As shown, at time t11, the second conduction position of the secondary-side switch S1 is earlier than that at time t6, resulting in a higher system operating frequency. Simultaneously, as the load current Iload further increases, the primary-side control chip 2 will select the conduction duration of the primary-side switch S2 to be Tc. At this time, the system operating frequency will remain unchanged. Figure 2 As shown, during the time period t13 to t14, the on-time of the primary-side switch S2 is Tc. The on-time Tc of the primary-side switch S2 increases with the increase of the load current Iload. During this time, the operating frequency of the system remains unchanged. Figure 5 This is a schematic diagram showing the curve of the on-time of the primary-side switch as a function of load. Figure 6 This is a schematic diagram showing the curve of system operating frequency versus load. For example... Figure 5As shown, when the load current Iload is less than or equal to Iload1, the conduction time of the primary-side switch S2 is Tb; when the load current Iload is greater than Iload1, the conduction time of the primary-side switch 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 system's operating frequency increases linearly from the minimum frequency value fmin until the load current Iload is greater than the value Iload1, at which point the system's operating frequency will stabilize at the maximum frequency value fmax.

[0242] Obviously, the primary-side switch S2 needs an appropriate on-time, and the system needs a suitable operating frequency for the system to work stably. The primary-side control chip 2 is needed to determine the on-time of the primary-side switch S2.

[0243] The following are some specific examples to illustrate the primary-side control chip 2 in detail.

[0244] Figure 7 This is a schematic diagram of the primary-side control chip, as shown below. Figure 7 As shown, 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 switching transistor S2; the second input terminal of the sampling circuit 1210 is electrically connected to the source terminal of the primary-side switching transistor S2; the third input terminal of the sampling circuit 1210 is electrically connected to the first output terminal of the control circuit 1220; the output terminal of the sampling circuit 1210 is electrically connected to the input terminal of the control circuit 1220; the second and third output terminals of the control circuit 1220 are electrically connected to the input terminals 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 switching transistor S2.

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

[0246] Figure 8 This is a schematic diagram of another type of 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. The first input terminal of the voltage sampling module 1211 is electrically connected to the drain terminal of the primary-side switching transistor S2, the second input terminal of the voltage sampling module 1211 is electrically connected to the source terminal of the primary-side switching transistor S2, the first output terminal of the voltage sampling module 1211 is electrically connected to the first input terminal of the control circuit 1220, the second output terminal of the voltage sampling module 1211 is electrically connected to the second input terminal of the control circuit 1220, the input terminal of the frequency sampling module 1212 is electrically connected to the first output terminal of the control circuit 1220, and the output terminal of the frequency sampling module 1212 is electrically connected to the third input terminal of the control circuit 1220.

[0247] The voltage sampling module 1211 can sample the drain voltage Vswp and the source voltage Vcs of the primary-side switch S2 respectively to obtain the drain sampling voltage Vswp_sen and the source sampling voltage Vcs_sen of the primary-side switch S2; the frequency sampling module 1212 can sample the operating frequency fre of the primary-side switch S2 to obtain the operating frequency Vfre of the primary-side switch 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, and the second input terminal of the zero-crossing detection module 1221 is electrically connected to the second output terminal of the sampling circuit 1210. The output terminal of the zero-crossing detection module 1221 is electrically connected to the first input terminal of the drive 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 of the frequency calculation module 1222 is electrically connected to the third input of the sampling circuit 1210. The input of the comparison module 1223 is electrically connected to the third output of the sampling circuit 1210. The output of the comparison module 1223 is electrically connected to the first and second inputs of the selection module 1226. The second input of the conduction duration calculation module 1224 is electrically connected to the third output of the sampling circuit 1210. The output of the conduction duration calculation module 1224 is electrically connected to the third input of the selection module 1226. The output of the fixed conduction duration setting module 1225 is electrically connected to the fourth input of the selection module 1226. The output of the selection module 1226 is electrically connected to the second input of the drive 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, and obtain the conduction position information Vset of the primary-side switch S2 that enables soft switching. The frequency calculation module 1222 can receive the conduction position information Vset of the primary-side switch S2 that enables 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 pre-set reference frequency, and obtain comparison information Sel1 and Sel2 based on the comparison result. The conduction duration calculation module 1224 can receive the operating frequency Vfre of the primary-side switch S2 and obtain the conduction duration Tc of the primary-side switch S2 corresponding to the operating frequency Vfre. The fixed on-time setting module 1225 can receive the on-position information Vset of the primary-side switch S2, which enables soft switching, and determine the fixed on-time Tb. The selection module 1226 can receive comparison information Sel1 and Sel2, and select either the on-time Tb or the on-time Tc based on the potential magnitudes of Sel1 and Sel2. When the potential of Sel1 is greater than or equal to the potential of Sel2, the on-time Tb is selected; when the potential of Sel1 is less than the potential of Sel2, the 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, realizing zero-voltage conduction of the primary-side switch S2, i.e. soft switching. This effectively eliminates the conduction loss when the primary-side switch S2 is hard switched, and significantly improves the energy conversion efficiency of the system.

[0252] The primary-side control chip 12 adaptively adjusts the conduction time and operating frequency of the primary-side switch S2 based on the sampled drain voltage Vswp, source voltage Vcs, and operating frequency signal Vfre, thus achieving multi-mode optimized control under light and heavy load conditions. Figure 5 and Figure 6 As shown, when the load current Iload is less than the threshold Iload1, a fixed on-time Tb is maintained, 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 value 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 efficient operation under a wide range of load conditions.

[0253] The fine division and collaborative operation of the internal modules of the secondary-side control chip 11 and the primary-side control chip 12, 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 conduction duration setting module 1123 of the secondary-side control chip 11 respectively control the position and duration of the secondary-side switch S1 during its two conduction cycles. The zero-crossing detection module 1221, frequency calculation module 1222, comparison module 1223, conduction duration calculation module 1224, fixed conduction duration setting module 1225, and selection module 1226 of the primary-side control chip 12 flexibly control the soft-switching conduction position and conduction duration 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 capability of the system.

[0254] The above embodiments avoid the drawbacks of using optocouplers or transformer auxiliary windings in traditional flyback converter control schemes. Traditional methods suffer from low transmission rates, significant temperature susceptibility, high static power consumption, and large size. The above embodiments, however, simplify the complexity of primary-side control and reliably achieve soft switching on the primary side by using the secondary-side control chip 11 to assist in the control of the primary-side switch S2. This innovative control architecture offers advantages such as simple structure, low cost, high efficiency, and wide applicability, effectively replacing existing flyback converter control schemes and possessing broad application prospects.

[0255] It should be noted that in this patent application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this patent application, if it refers to performing an action according to an element, it means performing the action at least according to that element, including two cases: performing the action only according to that element, and performing the action according to that element and other elements. Expressions such as "multiple," "repeatedly," and "various" include two, two times, 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 incorporated in their entirety into the disclosure of this application so that they can serve as a basis for modifications if necessary. Furthermore, it should be understood that after reading the foregoing disclosure of this application, those skilled in the art can make various alterations 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, The method is applied in flyback converters, which include: secondary-side switching transistors, primary-side switching transistors, and transformers; 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 secondary-side sampling circuit, a secondary-side control circuit, and a secondary-side drive circuit; the first input terminal of the secondary-side sampling circuit is electrically connected to the secondary side of the transformer, the second input terminal of the secondary-side sampling circuit is electrically connected to the drain terminal of the secondary-side switching transistor, the third input terminal of the secondary-side sampling circuit is electrically connected to the output terminal of the flyback converter, the output terminal of the secondary-side sampling circuit is electrically connected to the input terminal of the secondary-side control circuit, the output terminal of the secondary-side control circuit is electrically connected to the input terminal of the secondary-side drive circuit, and the output terminal of the secondary-side drive circuit is electrically connected to the gate terminal of the secondary-side switching transistor. The secondary-side sampling circuit is configured to collect the transformer secondary-side current, the drain voltage of the secondary-side switch, and the output voltage of the flyback converter to obtain the transformer secondary-side sampling current, the secondary-side switch drain voltage, and the output sampling voltage. The secondary-side control circuit is configured to determine the conduction position and conduction duration of the secondary-side switch transistor for the first conduction based on the sampled current of the secondary-side of the transformer, and to determine the conduction position of the secondary-side switch transistor for the second conduction based on the sampled voltage at the drain terminal of the secondary-side switch transistor and the sampled voltage at the output terminal, and to fix the conduction duration of the secondary-side switch transistor. The secondary-side drive circuit is configured to turn the secondary-side switching transistor on or off according to the control signal output by the secondary-side control circuit. The primary-side control chip includes: a primary-side sampling circuit, a primary-side control circuit, and a primary-side driving circuit; the first input terminal of the primary-side sampling circuit is electrically connected to the drain terminal of the primary-side switching transistor, the second input terminal of the primary-side sampling circuit is electrically connected to the source terminal of the primary-side switching transistor, the third input terminal of the primary-side sampling circuit is electrically connected to the first output terminal of the primary-side control circuit, the output terminal of the primary-side sampling circuit is electrically connected to the input terminal of the primary-side control circuit, the second and third output terminals of the primary-side control circuit are electrically connected to the input terminal of the primary-side driving circuit, and the output terminal of the primary-side driving circuit is electrically connected to the gate terminal of the primary-side switching transistor. The primary-side sampling circuit is configured to acquire the drain voltage, source voltage, and operating frequency of the primary-side switching transistor, and obtain the primary-side switching transistor drain sampling voltage, source sampling voltage, and operating frequency sampling signals. The primary-side control circuit is configured to determine the conduction position where the primary-side switch can conduct at zero voltage based on the drain sampling voltage and the source sampling voltage of the primary-side switch, and to determine the conduction duration by the operating frequency sampling signal. The primary-side drive circuit is configured to turn the primary-side switching transistor on or off according to the control signal output by the primary-side control circuit. The second conduction of the secondary-side switch causes the drain voltage of the primary-side switch to be pulled down to zero, thereby achieving soft switching of the primary-side switch. The primary-side control circuit automatically switches between different conduction duration modes according to the load current. When the load current is less than a preset threshold, a fixed conduction duration is used on the primary side. When the load current is greater than the preset threshold, a conduction duration that increases linearly with the load is used.

2. The multi-mode soft switching control system of claim 1, wherein, The secondary-side sampling circuit includes: a current sampling module and a secondary-side voltage sampling module; The input terminal of the current sampling module is electrically connected to the secondary side of the transformer, and the output terminal of the current sampling module is electrically connected to the first input terminal of the secondary side control circuit. It is configured to sample the current on the secondary side of the transformer to obtain the sampled current on the secondary side of the transformer. The first input terminal of the secondary-side voltage sampling module is electrically connected to the drain terminal of the secondary-side switching transistor, the second input terminal of the secondary-side voltage sampling module is electrically connected to the output terminal of the flyback converter, and the output terminal of the secondary-side voltage sampling module is electrically connected to the second and third input terminals of the secondary-side control circuit. It is configured to sample the drain voltage of the secondary-side switching transistor and the output voltage of the flyback converter, respectively, to obtain the drain sampling voltage of the secondary-side switching transistor and the output sampling voltage.

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

4. The multi-mode soft switching control system of claim 1, wherein, The primary-side sampling circuit includes: a primary-side voltage sampling module and a frequency sampling module; The first input terminal of the primary-side voltage sampling module is electrically connected to the drain terminal of the primary-side switching transistor, the second input terminal of the primary-side voltage sampling module is electrically connected to the source terminal of the primary-side switching transistor, the first output terminal of the primary-side voltage sampling module is electrically connected to the first input terminal of the primary-side control circuit, and the second output terminal of the primary-side voltage sampling module is electrically connected to the second input terminal of the primary-side control circuit. It is configured to sample the drain terminal voltage and the source terminal voltage of the primary-side switching transistor respectively to obtain the drain terminal sampling voltage and the source terminal sampling voltage of the primary-side switching transistor. The input terminal of the frequency sampling module is electrically connected to the first output terminal of the primary-side control circuit, and the output terminal of the frequency sampling module is electrically connected to the third input terminal of the primary-side control circuit. It is configured to sample the operating frequency of the primary-side switching transistor to obtain the operating frequency sampling signal.

5. The multi-mode soft switching control system of claim 1, wherein, The primary-side control circuit includes: a primary-side zero-crossing detection module, a frequency calculation module, a comparison module, a conduction duration calculation module, a primary-side fixed conduction duration setting module, and a selection module; The first input terminal of the primary-side zero-crossing detection module is electrically connected to the first output terminal of the primary-side sampling circuit, the second input terminal of the primary-side zero-crossing detection module is electrically connected to the second output terminal of the primary-side sampling circuit, and the output terminal of the primary-side zero-crossing detection module is electrically connected to the first input terminal of the primary-side driving circuit, the input terminal of the frequency calculation module, the input terminal of the primary-side fixed on-time setting module, and the first input terminal of the on-time calculation module. It is configured to detect the zero-crossing point of the source-side sampling voltage based on the drain sampling voltage of the primary-side switching transistor, and obtain the on-time position information of the primary-side switching transistor that can achieve soft switching. The input terminal of the frequency calculation module is electrically connected to the output terminal of the primary-side zero-crossing detection module, and the output terminal of the frequency calculation module is electrically connected to the third input terminal of the primary-side sampling circuit. It is configured to obtain the operating frequency of the primary-side switching transistor based on the conduction position information of the primary-side switching transistor that enables soft switching. The input terminal of the comparison module is electrically connected to the third output terminal of the primary side sampling circuit, and the output terminal of the comparison module is electrically connected to the first and second input terminals of the selection module. It 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 primary side sampling circuit, and the output terminal of the conduction duration calculation module is electrically connected to the third input terminal of the selection module. It is configured to obtain the conduction duration of the primary side switch tube that increases linearly with the increase of load based on the sampling signal of the working frequency. The input terminal of the primary side fixed conduction duration setting module is electrically connected to the output terminal of the primary side zero-crossing detection module, and the output terminal of the primary side fixed conduction duration setting module is electrically connected to the fourth input terminal of the selection module. It is configured to set the primary side fixed conduction duration according to the conduction position information of the primary side switching transistor that can achieve 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 of the selection module is electrically connected to the output terminal of the conduction duration calculation module, the fourth input terminal of the selection module is electrically connected to the output terminal of the primary side fixed conduction duration setting module, and the output terminal of the selection module is electrically connected to the second input terminal of the primary side drive circuit. The selection module is configured to select the conduction duration based on the comparison information. When the potential of the first comparison information is greater than or equal to the potential of the second comparison information, the primary side fixed conduction duration is selected; when the potential of the first comparison information is less than the potential of the second comparison information, the conduction duration that increases linearly with the load is selected.

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