Multi-port charger, flyback converter and its secondary side control circuit and control method
By setting a false turn-off protection stage at the start of secondary freewheeling and increasing the turn-off reference voltage of the synchronous rectifier, the problem of false turn-off of the synchronous rectifier transistor in the multi-port charger is solved, and the reliability of the equipment is improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JOULWATT TECH INC LTD
- Filing Date
- 2025-09-11
- Publication Date
- 2026-06-09
AI Technical Summary
In existing multi-port chargers with flyback time-sharing output schemes, secondary-side current jitter causes synchronous rectifier transistors to turn off erroneously, affecting equipment reliability.
A false turn-off protection phase is set at the start of the secondary side freewheeling, and the synchronous rectifier is turned off according to the first reference voltage during the false turn-off protection phase, thereby increasing the turn-off reference voltage and avoiding false turn-off.
This effectively avoids the synchronous rectifier tube from being accidentally turned off when switching between multiple output branches, thus improving the reliability of the flyback converter and multi-port charger.
Smart Images
Figure CN122178493A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of power electronics technology, and in particular to a multi-port charger, a flyback converter and its secondary-side control circuit and control method. Background Technology
[0002] With the increasing popularity of portable electronic devices, consumers have a growing demand for multi-port chargers. Multi-port chargers charge multiple devices. Flyback converters are widely used in chargers due to their simple circuit structure, input-output electrical isolation, wide voltage regulation range, and ease of multi-output.
[0003] Existing multi-port chargers generally adopt a flyback time-sharing output scheme for the sake of simple structure and lower cost. However, in the flyback time-sharing output scheme, when multiple output branches switch on, the secondary current jitters, which may cause the synchronous rectifier transistor to turn off erroneously. Summary of the Invention
[0004] In view of the above problems, the purpose of this disclosure is to provide a multi-port charger, flyback converter and its secondary-side control circuit and control method that can avoid the synchronous rectifier tube from being accidentally turned off during output switching.
[0005] According to a first aspect of this disclosure, a secondary-side control method for a flyback converter is provided. The flyback converter includes an input voltage circuit, a transformer, a main power transistor, a synchronous rectifier, and n output circuits. The n output circuits are connected in parallel to one end of the secondary winding of the transformer and output corresponding output voltages in a time-sharing manner, where n is an integer and n>1. The secondary-side control method includes: setting a false turn-off protection stage at the start of the secondary-side freewheeling; controlling the synchronous rectifier to turn off according to a first reference voltage during the false turn-off protection stage; and controlling the synchronous rectifier to turn off according to a second reference voltage outside the false turn-off protection stage, wherein the first reference voltage is greater than the second reference voltage.
[0006] Optionally, it also includes: predicting the end time of the secondary freewheeling current in the current switching cycle based on the time parameters in the previous switching cycle or based on the volt-second balance of the primary and secondary windings, and controlling the end of the false turn-off protection phase at or before the end time of the secondary freewheeling current.
[0007] Optionally, it also includes: triggering the end of the false turn-off protection phase based on the time parameters in the previous switching cycle or based on the volt-second balance of the primary and secondary windings.
[0008] Optionally, it also includes: triggering multiple judgment conditions to end the false shutdown protection stage based on the time parameters in the previous switching cycle and the volt-second balance setting of the primary and secondary windings; and triggering the end of the false shutdown protection stage based on the judgment condition that is met first.
[0009] Optionally, the time parameter of the previous switching cycle represents the switching cycle or freewheeling time, and the volt-second balance of the primary and secondary windings represents that the magnetizing energy of the primary winding is equal to the demagnetizing energy of the secondary winding.
[0010] Optionally, the time from the end of the freewheeling phase of the previous switching cycle to the end of the erroneous shutdown protection phase in the current switching cycle is less than or equal to that of the previous switching cycle.
[0011] Optionally, the previous switching cycle is obtained, and a timer is started at the end of the freewheeling phase of the previous switching cycle. The false shutdown protection phase is triggered to end when the timer reaches a first time, wherein the first time is less than or equal to the previous switching cycle.
[0012] Optionally, the duration of the false shutdown protection phase in the current switching cycle is less than or equal to the freewheeling time of the previous switching cycle.
[0013] Optionally, at the end of the false shutdown protection phase, the demagnetizing volt-second product of the secondary winding of the current switching cycle is less than or equal to the magnetizing volt-second product of the primary winding.
[0014] Optionally, the first volt-second product is acquired at the start of the freewheeling phase of the current switching cycle, and the false shutdown protection phase ends when the first volt-second product reaches the first volt-second product threshold. The first volt-second product is the product of the output voltage and time, and the first volt-second product threshold is less than or equal to the volt-second product of the output voltage in the secondary freewheeling phase of the previous switching cycle.
[0015] Optionally, the first volt-second product is acquired at the start of the freewheeling phase of the current switching cycle, and the false shutdown protection phase ends when the first volt-second product reaches the second volt-second product threshold. The first volt-second product is the product of the output voltage and time, and the second volt-second product threshold is less than or equal to the volt-second product of the voltage difference during the primary-side conduction phase of the current switching cycle. The voltage difference is the difference between the drain-source voltage of the synchronous rectifier and the output voltage.
[0016] According to a second aspect of this disclosure, a secondary-side control circuit for a flyback converter is provided. The flyback converter further includes an input voltage circuit, a transformer, a main power transistor, a primary-side control circuit, a synchronous rectifier, and n output circuits. The n output circuits are connected in parallel to one end of the secondary winding of the transformer and output corresponding output voltages in a time-sharing manner. n is an integer and n>1. The secondary-side control circuit is used to execute the secondary-side control method described above.
[0017] According to a third aspect of this disclosure, a flyback converter is provided, the flyback converter including an input voltage circuit, a transformer, a main power transistor, a primary-side control circuit, a synchronous rectifier, n output circuits, and a secondary-side control circuit, wherein the n output circuits are connected in parallel to one end of the secondary winding of the transformer and output corresponding output voltages in a time-division manner, where n is an integer and n>1, and the secondary-side control circuit is the secondary-side control circuit described above.
[0018] According to a fourth aspect of this disclosure, a multi-port charger is provided, including the flyback converter described above.
[0019] The beneficial effects of this disclosure include at least the following:
[0020] The multi-port charger, flyback converter, and their secondary-side control circuit and control method disclosed herein improve the reliability of the flyback converter and multi-port charger by setting a false turn-off protection stage at the start of secondary-side freewheeling and controlling the synchronous rectifier to turn off based on a second reference voltage outside the false turn-off protection stage, and controlling the synchronous rectifier to turn off based on a first reference voltage greater than the second reference voltage during the false turn-off protection stage. In other words, this disclosure sets a false turn-off protection stage at the start of secondary-side freewheeling and increases the turn-off reference of the synchronous rectifier during the false turn-off protection stage, rather than completely shielding the turn-off capability of the synchronous rectifier. This avoids the synchronous rectifier from being falsely turned off when the flyback converter switches between multiple output branches, and also addresses the situation where the synchronous rectifier is turned off suddenly when the main switch is turned on under abnormal conditions.
[0021] Furthermore, this disclosure reasonably sets the false turn-off protection stage in the freewheeling phase of the current switching cycle based on the time parameters in the previous switching cycle or based on the volt-second balance of the primary and secondary windings, so as to effectively avoid false turn-off of the synchronous rectifier tube.
[0022] It should be noted that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this disclosure. Attached Figure Description
[0023] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:
[0024] Figure 1 This diagram shows a circuit schematic of a flyback converter provided in an embodiment of the present disclosure;
[0025] Figure 2 This diagram illustrates a flowchart of a secondary-side control method for a flyback converter provided in an embodiment of this disclosure.
[0026] Figure 3The diagram shows a flowchart of step S210 in a flyback converter secondary-side control method provided in an embodiment of this disclosure;
[0027] Figure 4 This diagram illustrates the generation of a synchronous rectification control signal in a secondary-side control method for a flyback converter provided in an embodiment of this disclosure.
[0028] Figure 5 A timing diagram of a flyback converter provided in an embodiment of this disclosure is shown. Detailed Implementation
[0029] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.
[0030] This disclosure provides a multi-port charger, including a flyback converter that supports multiple outputs, wherein the flyback converter is a flyback converter with multiple time-division outputs.
[0031] Figure 1 A circuit diagram of a flyback converter provided in an embodiment of this disclosure is shown. Figure 2 The diagram shows a flowchart of a secondary-side control method for a flyback converter provided in an embodiment of this disclosure. Figure 3 The diagram shows a flowchart of step S210 in a flyback converter secondary-side control method provided in an embodiment of this disclosure. Figure 4 This diagram illustrates the generation of a synchronous rectification control signal in a secondary-side control method for a flyback converter provided in an embodiment of this disclosure. Figure 5 A timing diagram of a flyback converter provided in an embodiment of this disclosure is shown.
[0032] like Figure 1 As shown, the flyback converter 100 includes an input voltage circuit 120, a transformer T, a main power transistor Qp, a synchronous rectifier transistor Qs, n output circuits, and a control circuit 110.
[0033] The transformer T includes a primary winding Np and a secondary winding Ns. The voltage input circuit 120 and the main power transistor Qp are connected to the primary winding Np, while the synchronous rectifier transistor Qs and the n-way output circuit are connected to the secondary winding Ns.
[0034] For example, the voltage input circuit 120 includes a rectifier circuit 121, a capacitor EC1, a capacitor EC2, and an inductor L. DM Resistor Rrcd, capacitor Crcd, diode Drcd. Capacitor EC1, capacitor EC2, inductor L DMAn energy recovery circuit (exemplarily including resistor Rrcd, capacitor Crcd, and diode Drcd) connected between the first and second terminals of the primary winding Np is connected between the rectifier circuit 121 and the primary winding Np. Capacitor EC1, capacitor EC2, and inductor L... DM Used to realize the output signal V of rectifier circuit 121 DC It provides filtering and power factor calibration functions. In alternative embodiments, the filtering and power factor calibration functions can also be implemented using other common filtering circuits and power factor correction circuits.
[0035] n output circuits are connected in parallel to one end of the secondary winding Ns of transformer T, and output their corresponding output voltages in a time-sharing manner, where n is an integer and n>1.
[0036] For example, the n-channel output circuit includes a first output circuit 131 and a second output circuit 132. The first output circuit 131 includes switches Q1 and Q2, a capacitor Co1, a resistor Rl1, a resistor Rs1, and a switch Ql1 connected between the secondary winding N of the transformer T and the first output voltage Vbus1. Switches Q1, Q2, and Ql1 are controlled by control circuit 110 to output the first output voltage Vbus1. The second output circuit 132 includes switches Q3 and Q4, a capacitor Co2, a resistor Rl2, a resistor Rs2, and a switch Ql2 connected between the secondary winding N of the transformer T and the second output voltage Vbus2. Switches Q3, Q4, and Ql2 are controlled by control circuit 110 to output the second output voltage Vbus2.
[0037] Furthermore, a sampling resistor Rcs is also included. The main power transistor Qp and the sampling resistor Rcs are connected in series between the primary winding Np and the reference ground, and the synchronous rectifier Qs is connected between the secondary winding Ns and the reference ground. Exemplarily, the main power transistor Qp and the synchronous rectifier Qs are, for example, N-type field-effect transistors. In an alternative embodiment, the sampling resistor Rcs may not be provided in the flyback converter 100.
[0038] The control circuit 110 includes a primary-side control circuit 111 and a secondary-side control circuit 112.
[0039] For example, the primary-side control circuit 111 is connected to the main power transistor Qp and the sampling resistor Rcs. Based on the secondary-side feedback signal and the sampled primary-side current signal, it provides a primary-side control signal GON to the control terminal of the main power transistor Qp to control the main power transistor Qp to turn on or off.
[0040] For example, the secondary-side control circuit 112 is connected to the synchronous rectifier Qs and the connection terminal between the secondary-side winding Ns and the output circuit, and provides a synchronous rectification control signal SR to the control terminal of the synchronous rectifier Qs to control the synchronous rectifier Qs to turn on or off. It also generates switching control signals to control the switching transistors Q1, Q2, Q3, Q4, QL1, and QL2 to turn on or off, and controls at least n output circuits to switch and output different output voltages during the secondary-side freewheeling phase.
[0041] Further, see Figure 2 The secondary-side control circuit 112 can, for example, execute a secondary-side control method, which includes the following steps:
[0042] Step S210: Set the false shutdown protection stage at the start of secondary side freewheeling. The secondary side control circuit 112 in the flyback converter 100 sets the shutdown protection stage at the start of secondary side freewheeling.
[0043] Furthermore, such as Figure 3 As shown, step S210 includes the following steps:
[0044] Step S211: Enter the false shutdown protection stage at the start of secondary side freewheeling.
[0045] Based on the time parameters of the previous switching cycle or the volt-second balance of the primary and secondary windings, the end time of the secondary freewheeling in the current switching cycle is predicted, and the false turn-off protection phase ends at or before the end time of the secondary freewheeling.
[0046] Further, the end of the false shutdown protection phase is triggered based on the time parameters of the previous switching cycle or the volt-second balance of the primary and secondary windings. For example, step S212, S213, or S214 can be executed under different circumstances to determine the end time of the false shutdown protection phase in the current switching cycle. That is, multiple judgment conditions for triggering the end of the false shutdown protection phase are set based on the time parameters of the previous switching cycle and the volt-second balance of the primary and secondary windings, and the end of the false shutdown protection phase is triggered based on the first judgment condition met. For example, the end time of the false shutdown protection phase in the current switching cycle is determined by executing the first judgment condition met in steps S212, S213, and S214.
[0047] Next, step S215 is executed: the false shutdown protection phase ends. The false shutdown protection phase ends based on the end time of the false shutdown protection phase within the current switching cycle determined above.
[0048] Furthermore, the time parameter of the previous switching cycle characterizes the switching cycle or freewheeling time. Furthermore, the volt-second balance between the primary and secondary windings characterizes that the magnetizing energy of the primary winding equals the demagnetizing energy of the secondary winding.
[0049] In one embodiment, the duration of the false shutdown protection phase in the current switching cycle is less than or equal to the freewheeling time of the previous switching cycle. For example, step S212 is executed: at the start of the freewheeling in the current switching cycle, the product of the output voltage and time (the first volt-second product) is obtained, and the false shutdown protection phase ends when the first volt-second product reaches the first volt-second product threshold VT1. The first volt-second product threshold VT1 is less than or equal to the volt-second product VT(VO)_n-1 of the output voltage during the secondary freewheeling phase in the previous switching cycle. For example, VT1 = k × VT(VO)_n-1, k ≤ 1. Or VT1 = VT(VO)_n-1 - VT0, where VT0 is the bias volt-second product.
[0050] In one embodiment, at the end of the false shutdown protection phase, the demagnetizing volt-second product of the secondary winding in the current switching cycle is less than or equal to the magnetizing volt-second product of the primary winding. For example, step S213 is executed: at the start of the freewheeling phase of the current switching cycle, the product of the output voltage and time (first volt-second product) is obtained, and the end of the false shutdown protection phase is triggered when the first volt-second product reaches the second volt-second product threshold VT2. The second volt-second product threshold VT2 is less than or equal to the volt-second product VTGON of the voltage difference during the primary-side conduction phase of the current switching cycle, where the voltage difference is the difference between the drain-source voltage of the synchronous rectifier and the output voltage. For example, VT2 = k × VTGON, k ≤ 1. Or VT2 = VTGON - VT0, where VT0 is the bias volt-second product.
[0051] In one embodiment, the duration from the end of the freewheeling current in the previous switching cycle to the end of the false shutdown protection phase in the current switching cycle is less than or equal to that of the previous switching cycle. Step S214 is executed: timing begins at the end of the freewheeling current in the previous switching cycle, and the false shutdown protection phase ends when the timing reaches a first time T1, where the first time T1 is less than or equal to that of the previous switching cycle. For example, the first time T1 = k≤1. Or, in the first time T1= -T0, where T0 is the preset time. This refers to the previous switching cycle.
[0052] To further explain, step S214 is set as one of the conditions for triggering the turn-off protection stage because the flyback converter 100 may operate in continuous conduction mode (CCM) during startup or overcurrent, resulting in a gradual increase in the peak inductor current over several adjacent switching cycles. In this case, setting the end time of the false turn-off protection stage based on the volt-second product of the output voltage in the freewheeling phase of the previous switching cycle or the volt-second balance between the primary and secondary sides of the current cycle is unreasonable. This would cause the freewheeling end time to occur within the false turn-off protection stage, preventing the synchronous rectifier from turning off due to a large turn-off reference. Therefore, setting step S214 as one of the triggering conditions ensures that under the above operating conditions, this condition is prioritized to trigger the end of the false turn-off protection stage, preventing the synchronous rectifier from failing to turn off normally.
[0053] For example, the control mode of the flyback converter is determined based on the voltage difference (the voltage difference is the difference between the drain-source voltage Vds_SR of the synchronous rectifier Qs and the output voltage Vo) during the primary-side conduction phase of the current switching cycle, the volt-second product VTGON, and the switching frequency of the synchronous rectifier. Further, if the volt-second product VTGON is greater than or equal to a preset threshold, and the switching frequency of the synchronous rectifier Qs is less than or equal to a preset switching frequency fccm in continuous conduction mode, then continuous conduction mode is determined; otherwise, intermittent conduction mode is determined.
[0054] To further explain, in any mode, the flyback converter 100 executes the judgment condition that is met first in steps S212, S213, and S214 to trigger the end of the false shutdown protection phase.
[0055] Step S220: During the false shutdown protection phase, the synchronous rectifier is turned off according to the first reference voltage; outside the false shutdown protection phase, the synchronous rectifier is turned off according to the second reference voltage. The first reference voltage is greater than the second reference voltage.
[0056] The aforementioned secondary-side control method incorporates a false turn-off protection phase at the start of the secondary-side freewheeling. During this phase, the turn-off threshold of the synchronous rectifier is increased, rather than completely disabling its turn-off capability. This avoids false turn-off of the synchronous rectifier when multiple output branches switch on in the flyback converter, and also addresses the possibility of the synchronous rectifier being turned off suddenly by the main switch under abnormal conditions, thereby improving the reliability of the flyback converter and multi-port charger.
[0057] Furthermore, this disclosure reasonably sets the false turn-off protection stage in the freewheeling phase of the current switching cycle based on the time parameters in the previous switching cycle or based on the volt-second balance of the primary and secondary windings, so as to effectively avoid false turn-off of the synchronous rectifier tube.
[0058] like Figure 4As shown, a method for generating a synchronous rectification control signal SR includes the following steps.
[0059] During the false shutdown protection phase, when the drain-source voltage of the synchronous rectifier is greater than or equal to the first reference voltage, the synchronous rectifier is turned off based on the synchronous rectification control signal SR.
[0060] Outside of the false shutdown protection phase, the synchronous rectifier is turned off based on the synchronous rectification control signal SR when the drain-source voltage of the synchronous rectifier is greater than or equal to the second reference voltage. The first reference voltage is greater than the second reference voltage.
[0061] When the drain-source voltage of the synchronous rectifier is less than or equal to the conduction reference, the synchronous rectifier is turned on based on the synchronous rectification control signal SR.
[0062] See Figure 5 For example, t0-t8 is one switching cycle. At time t0, the primary-side control signal GON generated by the primary-side control circuit 111 controls the main power transistor Qp to turn on, the primary-side current Ip rises, and the drain-source voltage Vds_SR of the synchronous rectifier transistor Qs rises.
[0063] At time t1, the output control circuit in the secondary control circuit 112 controls the switch Q1 to turn on and the switches Q2-Q4 to turn off.
[0064] At time t2, the primary-side current Ip rises to its peak value, and the primary-side control signal GON generated by the primary-side control circuit 111 controls the main power transistor Qp to turn off. The synchronous rectification control signal SR generated by the synchronous rectification control circuit in the secondary-side control circuit 112 controls the synchronous rectifier transistor Qs to turn on, the secondary-side current I_SR decreases, and the leakage voltage Vdrain of the main power transistor Qp increases. The output control circuit in the secondary-side control circuit 112 controls the switching transistors Q1 and Q2 to turn on, and the switching transistors Q3-Q4 to turn off, correspondingly switching the first output circuit 131 to output the intermediate voltage Vo1 of the first output voltage. When the load requires the first output voltage Vbus1, it controls the switching transistor Ql1 to turn on and output the first output voltage Vbus1.
[0065] Between times t2 and t7, the secondary side is in the freewheeling conduction stage. At time t2, a false shutdown protection stage is set. For example, at time t3, the output control circuit in the secondary control circuit 112 controls switch Q1 to conduct and switches Q2-Q4 to turn off. At time t4, the output control circuit in the secondary control circuit 112 controls switches Q1 and Q3 to conduct and switches Q2 and Q4 to turn off. At time t5, the output control circuit in the secondary control circuit 112 controls switches Q3 and Q4 to conduct and switches Q1 and Q2 to turn off. Correspondingly, the second output circuit 132 outputs the intermediate voltage Vo2 of the second output voltage, and when the load requires the second output voltage Vbus2, it controls switch Q12 to conduct and output the second output voltage Vbus2. At time t6, the output control circuit in the secondary control circuit 112 still controls switches Q3 and Q4 to conduct and switches Q1 and Q2 to turn off. At time t7, the secondary current I_SR drops to zero, and the drain-source voltage Vds_SR of the synchronous rectifier Qs reaches the turn-off reference for the secondary freewheeling. The synchronous rectification control signal SR generated by the synchronous rectification control circuit in the secondary control circuit 112 controls the synchronous rectifier Qs to turn off. The output control circuit in the secondary control circuit 112 controls the switching transistor Q3 to turn on and the switching transistors Q1, Q2, and Q4 to turn off, thereby maintaining the intermediate voltage Vo2 of the second output voltage output by the second output circuit 132.
[0066] At time t8, the next switching cycle begins.
[0067] Further, taking the execution step S213 triggering the end of the false shutdown protection phase as an example, the false shutdown protection phase begins at time t2, and timing starts at time t2 to acquire the first volt-second product. The second volt-second product threshold VT2 is less than or equal to the volt-second product VTGON of the voltage difference during the primary-side conduction phase of the current switching cycle. The voltage difference is the difference between the drain-source voltage Vds_SR of the synchronous rectifier Qs and the output voltage Vo. That is, the volt-second product VTGON is the product of the voltage difference and the primary-side conduction time (time t2-t0) within the current switching cycle. For example, at time t7 or earlier, the moment when the first volt-second product reaches the second volt-second product threshold VT2 triggers the end of the false shutdown protection phase. In other words, the phase from time t2 to the end time is the false shutdown protection phase.
[0068] Further, taking the execution step S212 triggering the end of the false shutdown protection phase as an example, the false shutdown protection phase begins at time t2, and timing begins at time t2 to acquire the first volt-second product. The first volt-second product threshold VT1 is less than or equal to the volt-second product VT(VO)_n-1 of the output voltage during the secondary freewheeling phase in the previous switching cycle. That is, the volt-second product VT(VO)_n-1 is the product of the output voltage Vo and the secondary freewheeling time of the previous switching cycle (times t7-t2 in the previous switching cycle). For example, at time t7 of the current switching cycle or at a time before, the moment when the first volt-second product reaches the first volt-second product threshold VT1 triggers the end of the false shutdown protection phase. In other words, the period from time t2 to the end time is the false shutdown protection phase.
[0069] Furthermore, taking the execution step S214 triggering the end of the false shutdown protection phase as an example, the false shutdown protection phase begins at time t2, and timing starts at the end of the freewheeling cycle in the previous switching cycle (time t7 in the previous switching cycle). The false shutdown protection phase ends when the timing reaches a first time T1, where the first time T1 is less than or equal to the previous switching cycle. For example, at time t7 of the current switching cycle or at a time before, the timing reaches the first time, triggering the end of the false shutdown protection phase. That is, the period from time t2 to the end time is the false shutdown protection phase.
[0070] As described above, these embodiments of the present disclosure do not exhaustively cover all details, nor do they limit the disclosure to the specific embodiments described. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the present disclosure, thereby enabling those skilled in the art to make good use of the present disclosure and modifications based on it. This disclosure is limited only by the claims and their full scope and equivalents.
Claims
1. A secondary-side control method for a flyback converter, the flyback converter comprising an input voltage circuit, a transformer, a main power transistor, a synchronous rectifier transistor, and n output circuits, wherein the n output circuits are connected in parallel to one end of the secondary winding of the transformer and output corresponding output voltages in a time-sharing manner, where n is an integer and n>1, characterized in that, The secondary side control method includes: Set a false shutdown protection phase at the start of secondary side follow current; During the false shutdown protection phase, the synchronous rectifier is controlled to turn off based on a first reference voltage; outside the false shutdown protection phase, the synchronous rectifier is controlled to turn off based on a second reference voltage. Wherein, the first reference voltage is greater than the second reference voltage.
2. The secondary-side control method according to claim 1, characterized in that, Also includes: The end time of the secondary freewheeling in the current switching cycle is predicted based on the time parameters in the previous switching cycle or based on the volt-second balance of the primary and secondary windings, and the false shutdown protection phase is controlled to end at the end time of the secondary freewheeling or before the end time of the secondary freewheeling.
3. The secondary-side control method according to claim 2, characterized in that, Also includes: The false shutdown protection phase ends based on the time parameters within the previous switching cycle or based on the volt-second balance of the primary and secondary windings.
4. The secondary-side control method according to claim 2, characterized in that, Also includes: Based on the time parameters in the previous switching cycle and the volt-second balance setting of the primary and secondary windings, multiple judgment conditions are triggered to end the false shutdown protection stage. The false shutdown protection phase ends based on the first condition that is met.
5. The secondary-side control method according to claim 2, 3, or 4, characterized in that, The time parameter of the previous switching cycle characterizes the switching cycle or freewheeling time, and the volt-second balance of the primary and secondary windings characterizes that the magnetizing energy of the primary winding is equal to the demagnetizing energy of the secondary winding.
6. The secondary-side control method according to claim 2, characterized in that, The time from the end of the freewheeling phase of the previous switching cycle to the end of the erroneous shutdown protection phase in the current switching cycle is less than or equal to that of the previous switching cycle.
7. The secondary-side control method according to claim 2, characterized in that, The duration of the false shutdown protection phase in the current switching cycle is less than or equal to the freewheeling time of the previous switching cycle.
8. The secondary-side control method according to claim 2, characterized in that, At the end of the false shutdown protection phase, the demagnetization volt-second product of the secondary winding in the current switching cycle is less than or equal to the magnetization volt-second product of the primary winding.
9. The secondary-side control method according to claim 7, characterized in that, The first volt-second product is acquired at the start of the freewheeling phase of the current switching cycle, and the false shutdown protection phase ends when the first volt-second product reaches the first volt-second product threshold. The first volt-second product is the product of the output voltage and time, and the first volt-second product threshold is less than or equal to the volt-second product of the output voltage in the secondary freewheeling phase of the previous switching cycle.
10. The secondary-side control method according to claim 8, characterized in that, The first volt-second product is acquired at the start of the freewheeling phase of the current switching cycle, and the false shutdown protection phase ends when the first volt-second product reaches the second volt-second product threshold. The first volt-second product is the product of the output voltage and time. The second volt-second product threshold is less than or equal to the volt-second product of the voltage difference during the primary-side conduction phase of the current switching cycle. The voltage difference is the difference between the drain-source voltage of the synchronous rectifier and the output voltage.
11. The secondary-side control method according to claim 6, characterized in that, The previous switching cycle is obtained, and the timing starts at the end of the freewheeling of the previous switching cycle. When the timing reaches the first time, the false shutdown protection stage is triggered to end. The first time is less than or equal to the previous switching cycle.
12. A secondary-side control circuit for a flyback converter, the flyback converter further comprising an input voltage circuit, a transformer, a main power transistor, a primary-side control circuit, a synchronous rectifier transistor, and n output circuits, wherein the n output circuits are connected in parallel to one end of the secondary winding of the transformer and output corresponding output voltages in a time-sharing manner, where n is an integer and n>1, characterized in that, The secondary-side control circuit is used to execute the secondary-side control method as described in any one of claims 1-11.
13. A flyback converter, comprising an input voltage circuit, a transformer, a main power transistor, a primary-side control circuit, a synchronous rectifier, n output circuits, and a secondary-side control circuit, wherein the n output circuits are connected in parallel to one end of the secondary winding of the transformer and output corresponding output voltages in a time-sharing manner, where n is an integer and n>1, characterized in that, The secondary control circuit is the secondary control circuit described in claim 12.
14. A multi-port charger, characterized in that, Includes the flyback converter as described in claim 13.