Control circuit, chip and method for synchronous rectification

Abstract

The invention discloses a control circuit, chip and method for synchronous rectification, and the circuit comprises a drain-source voltage sampling circuit which is used for collecting the drain voltage of an MOS tube; the plurality of comparators are connected with the drain-source voltage sampling circuit and are used for comparing the drain voltage and generating a driving signal to the driving circuit, so that the driving circuit controls at least one of opening, closing and pre-closing of the MOS tube; and the pre-turn-off time adjusting circuit is connected with the pre-turn-off comparator, the driving circuit and the drain-source voltage sampling circuit, and is used for acquiring the pre-turn-off time of the current period and adjusting the pre-turn-off time of the next period based on the pre-turn-off time of the current period. According to the control circuit, the self-adaptive pre-turn-off time adjusting circuit is added, so that the pre-turn-off time can be adjusted in real time, and the conversion efficiency and reliability of the flyback converter are effectively ensured when different synchronous rectification MOS tubes are matched.

Description

Technical Field

[0001] This application relates to the technical fields of switching current and control circuits, and in particular to a control circuit, chip, and method for synchronous rectification. Background Technology

[0002] With the rapid development of switching power supply technology, power supply products are gradually moving towards higher efficiency, higher reliability, and higher integration. Flyback converters are widely favored in low-power power supplies due to their simple structure, small size, low cost, and ability to achieve input-output electrical isolation. However, as equipment circuits become increasingly complex and the required supply current gradually increases, the power loss of traditional power diodes as rectifiers in flyback converters has become significant. Therefore, the industry now widely uses synchronous rectifier MOSFETs with very low on-resistance to replace rectifier power diodes, i.e., synchronous rectification technology. This synchronous rectification technology can effectively improve the conversion efficiency of flyback converters.

[0003] Because flyback converters are more likely to enter CCM (Continuous Conduction Mode) operation mode when the load current is large, and CCM flyback converters are smaller in size than DCM (Discontinuous Conduction Mode) flyback converters, CCM operation mode has great potential for development in the trend of low-voltage, high-current power supplies. However, compared to DCM operation mode, the circuit control in CCM operation mode is more complex. This is because the current in the inductor does not drop to zero at the end of the switching cycle in CCM, making it difficult to control the turn-off of the MOSFET. If the turn-off is slow, the secondary-side synchronous rectification MOSFET will not be turned off when the primary-side switch is turned on, causing shoot-through between the primary and secondary sides. This can lead to reverse current on the secondary side, which may damage the power supply system in severe cases. To prevent shoot-through, a pre-turn-off circuit is usually added to the synchronous rectification control to lower the gate voltage in advance and reduce the turn-off time.

[0004] In related technologies, pre-turn-off is usually achieved by comparing the drain-source voltage of the synchronous rectifier MOSFET with a fixed threshold that has a relatively strong pre-turn-off capability. In practical applications, since the synchronous rectifier controller may be paired with synchronous rectifier MOSFETs with different on-resistances, the traditional pre-turn-off strategy may result in premature or late pre-turn-off. Summary of the Invention

[0005] Therefore, the purpose of this application is to propose a control circuit, chip, and method for synchronous rectification. A pre-turn-off time adjustment circuit is added to the control circuit for synchronous rectification to adjust the pre-turn-off time in real time, so as to avoid premature or late pre-turn-off and effectively ensure the conversion efficiency and reliability of the flyback converter when paired with different synchronous rectification MOSFETs.

[0006] This application provides a control circuit for synchronous rectification. The control circuit includes: a drain-source voltage sampling circuit for acquiring the drain voltage of a MOSFET; multiple comparators connected to the drain-source voltage sampling circuit for comparing and processing the drain voltage and generating a drive signal to a drive circuit, so that the drive circuit controls the MOSFET to perform at least one of turning on, turning off, or pre-turning off; and a pre-turning off time adjustment circuit, which is connected to the pre-turning off comparator, the drive circuit, and the drain-source voltage sampling circuit, for acquiring the pre-turning off time of the current cycle and adjusting the pre-turning off time of the next cycle based on the pre-turning off time of the current cycle.

[0007] For example, the pre-shutdown time adjustment circuit includes a pre-shutdown time sampling sub-circuit and a pre-shutdown time adjustment sub-circuit. The first terminal of the pre-shutdown time sampling sub-circuit is connected to the drain-source voltage sampling circuit, the second terminal of the pre-shutdown time sampling sub-circuit is connected to the output terminal of the pre-shutdown time adjustment sub-circuit, and the third terminal of the pre-shutdown time sampling sub-circuit is connected to the first terminal of the pre-shutdown time adjustment sub-circuit. The pre-shutdown time sampling sub-circuit is specifically used for: acquiring the time of the output signal of the pre-shutdown time adjustment sub-circuit in the current period and using it as the start time of the pre-shutdown time; acquiring the drain voltage in the current period and determining the time corresponding to the drain voltage being greater than a preset voltage threshold as the end time of the pre-shutdown time; determining the difference between the end time of the pre-shutdown time and the start time of the pre-shutdown time as the pre-shutdown time of the current period, and transmitting the pre-shutdown time of the current period to the pre-shutdown time adjustment sub-circuit.

[0008] For example, the second terminal of the pre-shutdown time adjustment sub-circuit is connected to the output terminal of the pre-shutdown comparator, and the third terminal of the pre-shutdown time adjustment sub-circuit is connected to the driving circuit. The pre-shutdown time adjustment sub-circuit is specifically used to: receive the pre-shutdown time of the current cycle; when the pre-shutdown time of the current cycle is greater than the reference time, decrease the pre-shutdown time of the next cycle; and when the pre-shutdown time of the current cycle is less than the reference time, increase the pre-shutdown time of the next cycle.

[0009] For example, the pre-shutdown time adjustment subcircuit includes a controllable delay subcircuit and a time comparison subcircuit. A first terminal of the time comparison subcircuit serves as the first terminal of the pre-shutdown time adjustment subcircuit. A second terminal of the time comparison subcircuit is connected to the first terminal of the controllable delay subcircuit, and the second terminal of the controllable delay subcircuit serves as the second terminal of the pre-shutdown time adjustment subcircuit. A third terminal of the controllable delay subcircuit serves as the third terminal of the pre-shutdown time adjustment subcircuit. Specifically, the time comparison subcircuit is used to: receive the pre-shutdown time of the current period. The pre-off time of the current cycle is compared with the reference time, and the comparison result is transmitted to the controllable delay sub-circuit. The controllable delay sub-circuit is specifically used to: increase the delay time of the controllable delay sub-circuit when the comparison result indicates that the pre-off time of the current cycle is greater than the reference time, so as to reduce the pre-off time of the next cycle; and decrease the delay time of the controllable delay sub-circuit when the comparison result indicates that the pre-off time of the current cycle is less than the reference time, so as to increase the pre-off time of the next cycle.

[0010] This application provides a control method for synchronous rectification, which is applied to the control circuit for synchronous rectification described above. The method includes: obtaining the pre-off time of the current cycle; and adjusting the pre-off time of the next cycle based on the pre-off time of the current cycle.

[0011] For example, the control circuit for synchronous rectification includes a pre-off time adjustment circuit, which includes a pre-off time sampling sub-circuit and a pre-off time adjustment sub-circuit. Obtaining the pre-off time for the current period includes: obtaining the time of the output signal of the pre-off time adjustment sub-circuit for the current period and using it as the start time of the pre-off time; obtaining the drain voltage for the current period and determining the time corresponding to the drain voltage being greater than a preset voltage threshold as the end time of the pre-off time; and determining the difference between the end time of the pre-off time and the start time of the pre-off time as the pre-off time for the current period.

[0012] For example, the pre-shutdown time adjustment subcircuit includes a controllable delay subcircuit. The adjustment of the pre-shutdown time for the next cycle based on the pre-shutdown time of the current cycle includes: when the pre-shutdown time of the current cycle is greater than a reference time, controlling the delay time of the controllable delay subcircuit to increase, thereby reducing the pre-shutdown time of the next cycle; when the pre-shutdown time of the current cycle is less than the reference time, controlling the delay time of the controllable delay subcircuit to decrease, thereby increasing the pre-shutdown time of the next cycle.

[0013] This application provides a synchronous rectification chip, which includes the control circuit for synchronous rectification as described above.

[0014] In the above embodiments, the control circuit includes: a drain-source voltage sampling circuit for acquiring the drain voltage of the MOSFET; multiple comparators connected to the drain-source voltage sampling circuit for comparing and processing the drain voltage and generating a drive signal to the drive circuit, so that the drive circuit controls the MOSFET to perform at least one of turning on, turning off, or pre-turning off; and a pre-turn-off time adjustment circuit, which is connected to the pre-turn-off comparator, the drive circuit, and the drain-source voltage sampling circuit, for acquiring the pre-turn-off time of the current cycle and adjusting the pre-turn-off time of the next cycle based on the pre-turn-off time of the current cycle. The control circuit of this invention adds an adaptive pre-turn-off time adjustment circuit, which can adjust the pre-turn-off time in real time, avoiding premature or late pre-turn-off, and effectively ensuring the conversion efficiency and reliability of the flyback converter when paired with different synchronous rectifier MOSFETs. Attached Figure Description

[0015] Figure 1 A schematic diagram of a control circuit provided for implementation of related technologies; Figure 2 A schematic diagram illustrating premature shutdown and late shutdown for implementation of related technologies; Figure 3 A schematic diagram of a control circuit for synchronous rectification provided in an embodiment of this application; Figure 4 A schematic diagram of the pre-shutdown time adjustment circuit provided for an embodiment of this application; Figure 5 A schematic diagram of the pre-shutdown time adjustment sub-circuit provided for an embodiment of this application; Figure 6 A schematic diagram of the adaptive adjustment waveform provided for an embodiment of this application; Figure 7 A flowchart of a control method for synchronous rectification provided in an embodiment of this application; Figure 8 A flowchart for obtaining the pre-shutdown time of the current cycle provided for an embodiment of this application; Figure 9 A flowchart for adjusting the pre-shutdown time of the next cycle, provided for an embodiment of this application. Detailed Implementation

[0016] The embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0017] The control circuit for synchronous rectification in this application is used in the flyback converter control system. The flyback converter control system is briefly introduced below.

[0018] Flyback converters are more likely to enter continuous conduction mode (CCM) when the load current is large. Furthermore, compared to discontinuous conduction mode (DCM), flyback converters are smaller in size. Therefore, with the trend towards low-voltage, high-current power supplies, CCM operation mode has significant development potential. However, compared to DCM operation mode, circuit control in CCM mode is more complex because the current in the inductor does not drop to zero at the end of the switching cycle in CCM, making it difficult to control the turn-off of the MOSFET. For example... Figure 1 The schematic diagram of the related technology control circuit shown shows that the flyback converter includes a transformer T, with the Np terminal of the transformer being the primary side and the Ns terminal of the transformer being the secondary side. Both the primary and secondary sides include switching transistors, which can be, for example, MOSFETs. This application uses a MOSFET as an example for illustration. The control circuit for synchronous rectification in this application is mainly applied to the control of the secondary side of the transformer.

[0019] In some examples, if the secondary-side MOSFET turns off slowly, the secondary-side synchronous rectifier MOSFET may not turn off when the primary-side switch turns on, causing a shoot-through between the primary and secondary sides. This can lead to reverse current flow on the secondary side, potentially damaging the power supply system. To prevent shoot-through, a pre-turn-off circuit is typically added to the synchronous rectification control to lower the gate voltage in advance and reduce the turn-off time. For example, a pre-turn-off comparator can be added.

[0020] In some examples, the pre-shutdown comparator samples the drain-source voltage V of the synchronous rectifier MOSFET via a synchronous rectifier control chip. DS Then, it is compared with a fixed threshold of the internal comparator to determine the pre-turn-off switch of the synchronous rectifier MOSFET. However, in practical applications, since the synchronous rectifier controller may be paired with synchronous rectifier MOSFETs with different on-resistances, the traditional pre-turn-off strategy may result in premature or late pre-turn-off.

[0021] like Figure 2 The diagram illustrates premature turn-off and late turn-off. V DSThis represents the sampled drain-source voltage of the synchronous rectifier MOSFET, Is represents the drain-source current of the synchronous rectifier MOSFET, and GATE represents the gate gate sequence of the synchronous rectifier MOSFET. The sampled drain-source voltage V of the synchronous rectifier MOSFET... DS The value is typically obtained by multiplying the drain-source current Is of the synchronous rectifier MOSFET by the known internal resistance of the synchronous rectifier MOSFET. However, the internal resistance of synchronous rectifier MOSFETs from different manufacturers varies. In this case, the same fixed threshold is used to adjust the drain-source voltage V. DS Using comparisons to determine pre-turn-off is not suitable for the above situations, as it may result in premature or late pre-turn-off. For example, if the internal resistance of a manufacturer's synchronous rectifier MOSFET is too high, the sampled drain-source voltage V of the synchronous rectifier MOSFET will be... DS The voltage is also too high, causing the synchronous rectifier MOSFET to turn off prematurely. The gate voltage is pulled down to an excessively low level, reducing rectification efficiency. If the internal resistance of a manufacturer's synchronous rectifier MOSFET is too low, the sampled drain-source voltage V of the synchronous rectifier MOSFET will be too high. DS The voltage is also too small, causing the synchronous rectifier MOSFET to turn off too late, resulting in insufficient gate voltage pre-pull-down, primary-secondary side shoot-through, and reduced system reliability.

[0022] Based on this, this application proposes a control circuit for synchronous rectification. A pre-turn-off time adjustment circuit is added to the control circuit to adjust the pre-turn-off time in real time, so as to avoid premature or late pre-turn-off. This effectively ensures the conversion efficiency and reliability of the flyback converter when paired with different synchronous rectification MOSFETs.

[0023] As an example, such as Figure 3 As shown, the control circuit 100 for synchronous rectification includes: The drain-source voltage sampling circuit 200 is used to acquire the drain voltage of the MOSFET; multiple comparators connected to the drain-source voltage sampling circuit 200 are used to measure the drain voltage V. DS The comparison is processed, and a drive signal is generated to the drive circuit so that the drive circuit controls the MOS transistor to perform at least one of turning on, turning off, or pre-turning off; the pre-turning time adjustment circuit 300 is connected to the pre-turning comparator, the drive circuit, and the drain-source voltage sampling circuit 200, and is used to obtain the pre-turning time of the current cycle and adjust the pre-turning time of the next cycle based on the pre-turning time of the current cycle.

[0024] For example, the control circuit 100 for synchronous rectification includes a drain-source voltage sampling circuit 200 for acquiring the drain voltage of the MOSFET, and denoting the drain voltage of the MOSFET as V. DSThe MOS transistor can be a MOSFET (Metal-Oxide-Semiconductor Transistor). This application uses a MOSFET as an example, but it is not limited to MOSFETs and can also be other types of MOS transistors. The drain voltage V of the MOS transistor... DS It can be obtained by multiplying the drain-source current Is of the MOSFET with the known internal resistance of the synchronous rectifier MOSFET.

[0025] For example, the drain-source voltage sampling circuit 200 samples the drain voltage V of the MOSFET. DS The voltage is transmitted to multiple comparators, including, for example, an enable comparator, a disable comparator, and a pre-disable comparator. These multiple comparators will transmit the drain voltage V... DS The voltage is compared with a built-in threshold; for example, enabling the comparator will compare the drain voltage V. DS The voltage V at the drain is compared with the threshold value of the comparator to turn it off. DS The pre-shutdown comparator compares the drain voltage V with the turn-off comparator threshold. DS The comparison is performed against the threshold of the pre-shutdown comparator. After comparison by multiple comparators, a drive signal is generated to the drive circuit, so that the drive circuit controls the MOSFET to perform at least one of the following: turn on, turn off, or pre-shutdown.

[0026] For example, this application provides a pre-turn-off time adjustment circuit 300 between the pre-turn-off comparator and the drive circuit. The pre-turn-off time adjustment circuit 300 is connected to the pre-turn-off comparator, the drive circuit, and the drain-source voltage sampling circuit 200. It is used to obtain the pre-turn-off time of the current cycle and adjust the pre-turn-off time of the next cycle in real time according to the pre-turn-off time of the current cycle, so that the pre-turn-off time tends to be stable.

[0027] It should be noted that the intersection of line segments in the circuit diagram is represented by the origin, and the pins are represented by boxes, which are connected to external chips.

[0028] This application optimizes the circuit control strategy of the synchronous rectification control chip and adds an adaptive pre-shutdown adjustment circuit, so as to effectively ensure the conversion efficiency and reliability of the flyback converter when paired with different synchronous rectification MOSFETs.

[0029] As an example, such as Figure 4 As shown, the pre-turn-off time adjustment circuit 300 includes a pre-turn-off time sampling sub-circuit 301 and a pre-turn-off time adjustment sub-circuit 302. The first terminal of the pre-turn-off time sampling sub-circuit 301 is connected to the drain-source voltage sampling circuit 200. The second terminal of the pre-turn-off time sampling sub-circuit 301 is connected to the output terminal of the pre-turn-off time adjustment sub-circuit 302. The third terminal of the pre-turn-off time sampling sub-circuit 301 is connected to the first terminal of the pre-turn-off time adjustment sub-circuit 302. Specifically, the pre-turn-off time sampling sub-circuit 301 is used for: The time of the output signal of the pre-off time adjustment sub-circuit 302 in the current cycle is obtained and used as the start time of the pre-off time. The drain voltage in the current cycle is obtained and the time when the drain voltage is greater than the preset voltage threshold is determined as the end time of the pre-off time. The difference between the end time of the pre-shutdown time and the start time of the pre-shutdown time is determined as the pre-shutdown time of the current cycle, and the pre-shutdown time of the current cycle is transmitted to the pre-shutdown time adjustment sub-circuit 302.

[0030] For example, the pre-turn-off time adjustment circuit 300 includes a pre-turn-off time sampling sub-circuit 301 and a pre-turn-off time adjustment sub-circuit 302. The pre-turn-off time sampling sub-circuit 301 is used to acquire the pre-turn-off time in real time, and the pre-turn-off time adjustment sub-circuit 302 is used to adjust the pre-turn-off time of the next cycle according to the pre-turn-off time of the current cycle. The first terminal of the pre-turn-off time sampling sub-circuit 301 is connected to the drain-source voltage sampling circuit 200 to acquire the drain voltage V of the synchronous rectifier MOSFET. DS The drain voltage, also known as the drain-source voltage, is equivalent to the drain-source voltage when the MOSFET source is grounded. The second terminal of the pre-turn-off time sampling sub-circuit 301 is connected to the output terminal of the pre-turn-off time adjustment sub-circuit 302, detecting the time of the output signal of the pre-turn-off time adjustment sub-circuit 302 in the current cycle, and using this as the start-up time of the pre-turn-off time. Theoretically, the end time of the pre-turn-off time should be the turn-on time of the primary-side MOSFET. When the primary-side MOSFET is turned on, the drain voltage V... DS It can change abruptly; this application is based on judging the drain voltage V. DS The time corresponding to whether the voltage exceeds the preset threshold is the end time of the pre-shutdown time.

[0031] For example, the pre-off time is obtained by subtracting the end time and the start time of the pre-off time. The pre-off time can be understood as the pre-off duration. The pre-off time sampling sub-circuit 301 transmits the calculated pre-off time of the current period to the pre-off time adjustment sub-circuit 302. The pre-off time adjustment sub-circuit 302 further compares and adjusts the pre-off time.

[0032] As an example, such as Figure 4 As shown, the second terminal of the pre-off time adjustment sub-circuit 302 is connected to the output terminal of the pre-off comparator, and the third terminal of the pre-off time adjustment sub-circuit 302 is connected to the drive circuit. The pre-off time adjustment sub-circuit 302 is specifically used to: receive the pre-off time of the current cycle; when the pre-off time of the current cycle is greater than the reference time, decrease the pre-off time of the next cycle; when the pre-off time of the current cycle is less than the reference time, increase the pre-off time of the next cycle.

[0033] For example, the pre-off time adjustment sub-circuit 302 receives the pre-off time of the current cycle calculated by the pre-off time sampling sub-circuit 301. The pre-off time adjustment sub-circuit 302 has a built-in reference time and compares the pre-off time of the current cycle with the reference time, which is a value obtained by this application based on a large number of experiments or experiences. When the pre-off time of the current cycle is greater than the reference time, it indicates that the pre-off time of the current cycle is too large, so the pre-off time of the next cycle is decreased. When the pre-off time of the current cycle is less than the reference time, it indicates that the pre-off time of the current cycle is too small, so the pre-off time of the next cycle is increased.

[0034] For example, the pre-turn-off time of the next cycle can be adjusted by a preset time step. This application continuously obtains the pre-turn-off time of the current cycle to adjust the pre-turn-off time of the next cycle. Ultimately, the pre-turn-off time will fluctuate around the reference time, making the switching time control of the synchronous rectification MOSFET more precise and avoiding premature or late pre-turn-off. This effectively ensures the conversion efficiency and reliability of the flyback converter when paired with different synchronous rectification MOSFETs.

[0035] As an example, such as Figure 5 As shown, the pre-shutdown time adjustment subcircuit 301 includes a controllable delay subcircuit 401 and a time comparison subcircuit 402. The first terminal of the time comparison subcircuit 402 serves as the first terminal of the pre-shutdown time adjustment subcircuit 301. The second terminal of the time comparison subcircuit 402 is connected to the first terminal of the controllable delay subcircuit 401. The second terminal of the controllable delay subcircuit 401 serves as the second terminal of the pre-shutdown time adjustment subcircuit 301. The third terminal of the controllable delay subcircuit 401 serves as the third terminal of the pre-shutdown time adjustment subcircuit 301. The time comparison sub-circuit 402 is specifically used to: receive the pre-off time of the current cycle, compare the pre-off time of the current cycle with the reference time, and transmit the comparison result to the controllable delay sub-circuit; The controllable delay sub-circuit 401 is specifically used to: increase the delay time of the controllable delay sub-circuit when the comparison result indicates that the pre-off time of the current cycle is greater than the reference time, so as to reduce the pre-off time of the next cycle; and decrease the delay time of the controllable delay sub-circuit when the comparison result indicates that the pre-off time of the current cycle is less than the reference time, so as to increase the pre-off time of the next cycle.

[0036] For example, the pre-shutdown time adjustment subcircuit 301 includes a controllable delay subcircuit 401 and a time comparison subcircuit 402. The first terminal of the time comparison subcircuit 402 serves as the first terminal of the pre-shutdown time adjustment subcircuit 301 and is connected to the pre-shutdown time sampling subcircuit 302 to receive the pre-shutdown time of the current period. The time comparison subcircuit 402 has a built-in reference time and is used to compare the pre-shutdown time of the current period with the reference time, transmitting the comparison result to the controllable delay subcircuit 401. The second terminal of the controllable delay subcircuit 401 serves as the second terminal of the pre-shutdown time adjustment subcircuit 301 and is connected to the output terminal of the pre-shutdown comparator to delay the output signal of the pre-shutdown comparator. Specifically, the delay time T can be adjusted accordingly. ADJ The output signal of the pre-turn-off comparator is delayed. The third terminal of the controllable delay sub-circuit 401 serves as the third terminal of the pre-turn-off time adjustment sub-circuit 301, connected to the drive circuit. The controllable delay sub-circuit 401 transmits the delayed output signal of the pre-turn-off comparator to the drive circuit, which then pre-turns off the gate of the synchronous rectifier MOSFET based on this signal. For example, the small current discharge path inside the drive circuit initiates the pre-turn-off of the synchronous rectifier gate voltage.

[0037] For example, the controllable delay sub-circuit 401 receives a comparison result from the time comparison sub-circuit 402, and when the comparison result indicates that the pre-off time of the current period is greater than the reference time, it controls the delay time T of the controllable delay sub-circuit 402. ADJ Increasing the pre-off time shifts the start time of the pre-off time later, thus reducing the pre-off time in the next cycle. When the comparison result indicates that the pre-off time of the current cycle is less than the reference time, the delay time T of the controllable delay sub-circuit 402 is controlled. ADJ By reducing the pre-shutdown time, the start time of the pre-shutdown period is moved forward, thereby increasing the pre-shutdown time in the next cycle.

[0038] This application adjusts the pre-turn-off time of the next cycle by controlling the delay time through a controllable delay sub-circuit using the output signal of the pre-turn-off comparator, thereby achieving adaptive adjustment of the pre-turn-off time.

[0039] like Figure 6 The diagram shows the adaptive adjustment waveform. When the pre-off time is greater than the reference time, the delay time T of the controllable delay sub-circuit 402 is controlled. ADJ Increase the delay time T of the next cycle. ADJ As the pre-off time increases, the pre-off time decreases. Through multiple cycles of control, the pre-off time eventually approaches the reference time, achieving adaptive adjustment of the pre-off time.

[0040] This application samples the pre-turn-off time using the results of the drain-source voltage sampling circuit and the pre-turn-off drive signal after passing through a controllable delay sub-circuit. Furthermore, it is designed so that after the pre-turn-off comparator reaches the pre-turn-off threshold, the comparator does not directly control the pre-turn-off drive to perform pre-turn-off, but instead waits for a delay time T. ADJ The delay sub-circuit generates a pre-turn-off control signal, which controls the small current discharge path inside the drive circuit to start the pre-turn-off of the synchronous rectified gate voltage, thus realizing the adjustment of the pre-turn-off time.

[0041] This application also proposes a control method for synchronous rectification.

[0042] As an example, such as Figure 7 As shown, the control methods used for synchronous rectification include: S701, obtain the pre-shutdown time for the current cycle.

[0043] S702, adjusts the pre-shutdown time of the next cycle based on the pre-shutdown time of the current cycle.

[0044] As an example, such as Figure 8 As shown, the control circuit for synchronous rectification includes a pre-turn-off time adjustment circuit, which further includes a pre-turn-off time sampling sub-circuit and a pre-turn-off time adjustment sub-circuit to obtain the pre-turn-off time of the current cycle, including: S801: Obtain the time of the output signal of the pre-off time adjustment sub-circuit of the current cycle and use it as the start time of the pre-off time. Obtain the drain voltage of the current cycle and determine the time when the drain voltage is greater than the preset voltage threshold as the end time of the pre-off time.

[0045] S802, determine the difference between the end time of the pre-shutdown time and the start time of the pre-shutdown time as the pre-shutdown time for the current cycle.

[0046] As an example, such as Figure 9 As shown, the pre-off time adjustment sub-circuit includes a controllable delay sub-circuit, which adjusts the pre-off time of the next cycle based on the pre-off time of the current cycle, including: When the pre-off time of the current cycle is greater than the reference time, the delay time of the controllable delay sub-circuit is increased to reduce the pre-off time of the next cycle. When the pre-off time of the current cycle is less than the reference time, the delay time of the controllable delay sub-circuit is reduced to increase the pre-off time of the next cycle.

[0047] For example, after the chip circuit starts working, the pre-off time of the current cycle is first detected. In the design, the gate start pre-off signal output by the controllable delay circuit of the current cycle can be detected as the start of the pre-off time detection. The end of the pre-off time, that is, the turn-on time of the primary MOSFET, can be detected by detecting the drain-source voltage V of the synchronous rectifier MOSFET. DS This is achieved by exceeding a certain voltage threshold value.

[0048] For example, after detecting the pre-shutdown time of the current cycle, it is compared with an internal reference time. If the pre-shutdown time of the current cycle is greater than the reference time, the next cycle will increase the delay time T. ADJ To reduce the pre-off time in the next cycle, as the circuit continuously adjusts, if the pre-off time in a certain cycle is less than the reference time, the next cycle will reduce the delay time T. ADJ This increases the pre-turn-off time for the next cycle, eventually maintaining a pre-turn-off time that fluctuates around the base time. The output of the pre-turn-off comparator is adjusted by a delay time T. ADJ Pre-shutdown is performed, enabling adaptive adjustment of the pre-shutdown time.

[0049] This application also proposes a synchronous rectification chip, which includes control circuitry for synchronous rectification.

[0050] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this application, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which programs can be printed, because programs can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0051] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0052] In the description of this application, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this application, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0054] Furthermore, the terms "first," "second," etc., used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance, or implicitly specifying the number of technical features indicated in this embodiment. Therefore, features defined with terms such as "first" and "second" in the embodiments of this application can explicitly or implicitly indicate that the embodiment includes at least one of those features. In the description of this application, the word "multiple" means at least two or more, such as two, three, four, etc., unless otherwise explicitly and specifically defined in the embodiments.

[0055] In this application, unless otherwise explicitly specified or limited in the embodiments, the terms "installation," "connection," "joining," and "fixing" appearing in the embodiments should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral part; it can also be a mechanical connection, an electrical connection, etc. Of course, it can also be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication between two components, or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific implementation.

[0056] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0057] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A control circuit for synchronous rectification, characterized in that, The control circuit includes: Drain-source voltage sampling circuit, used to acquire the drain voltage of MOSFET; Multiple comparators connected to the drain-source voltage sampling circuit are used to compare and process the drain voltage and generate a drive signal to the drive circuit so that the drive circuit controls the MOS transistor to perform at least one of turning on, turning off, or pre-turning off. A pre-turn-off time adjustment circuit is connected to a pre-turn-off comparator, the drive circuit, and the drain-source voltage sampling circuit. The circuit is used to obtain the pre-turn-off time of the current cycle and adjust the pre-turn-off time of the next cycle based on the pre-turn-off time of the current cycle.

2. The control circuit for synchronous rectification according to claim 1, characterized in that, The pre-turn-off time adjustment circuit includes a pre-turn-off time sampling sub-circuit and a pre-turn-off time adjustment sub-circuit. The first terminal of the pre-turn-off time sampling sub-circuit is connected to the drain-source voltage sampling circuit. The second terminal of the pre-turn-off time sampling sub-circuit is connected to the output terminal of the pre-turn-off time adjustment sub-circuit. The third terminal of the pre-turn-off time sampling sub-circuit is connected to the first terminal of the pre-turn-off time adjustment sub-circuit. Specifically, the pre-turn-off time sampling sub-circuit is used for: The time of the output signal of the pre-off time adjustment sub-circuit in the current cycle is obtained and used as the start time of the pre-off time. The drain voltage in the current cycle is obtained and the time when the drain voltage is greater than a preset voltage threshold is determined as the end time of the pre-off time. The difference between the end time of the pre-shutdown time and the start time of the pre-shutdown time is determined as the pre-shutdown time of the current cycle, and the pre-shutdown time of the current cycle is transmitted to the pre-shutdown time adjustment sub-circuit.

3. The control circuit for synchronous rectification according to claim 2, characterized in that, The second terminal of the pre-turn-off time adjustment sub-circuit is connected to the output terminal of the pre-turn-off comparator, and the third terminal of the pre-turn-off time adjustment sub-circuit is connected to the drive circuit. The pre-turn-off time adjustment sub-circuit is specifically used for: The system receives the pre-shutdown time for the current cycle. When the pre-shutdown time for the current cycle is greater than the reference time, the system decreases the pre-shutdown time for the next cycle. When the pre-shutdown time for the current cycle is less than the reference time, the system increases the pre-shutdown time for the next cycle.

4. The control circuit for synchronous rectification according to claim 3, characterized in that, The pre-shutdown time adjustment subcircuit includes a controllable delay subcircuit and a time comparison subcircuit. The first terminal of the time comparison subcircuit serves as the first terminal of the pre-shutdown time adjustment subcircuit. The second terminal of the time comparison subcircuit is connected to the first terminal of the controllable delay subcircuit, and the second terminal of the controllable delay subcircuit serves as the second terminal of the pre-shutdown time adjustment subcircuit. The third terminal of the controllable delay subcircuit serves as the third terminal of the pre-shutdown time adjustment subcircuit. The time comparison subcircuit is specifically used to: receive the pre-off time of the current period, compare the pre-off time of the current period with the reference time, and transmit the comparison result to the controllable delay subcircuit. The controllable delay sub-circuit is specifically used to: when the comparison result indicates that the pre-off time of the current cycle is greater than the reference time, control the delay time of the controllable delay sub-circuit to increase, so as to reduce the pre-off time of the next cycle; and when the comparison result indicates that the pre-off time of the current cycle is less than the reference time, control the delay time of the controllable delay sub-circuit to decrease, so as to increase the pre-off time of the next cycle.

5. A control method for synchronous rectification, characterized in that, The method is applied to a control circuit for synchronous rectification according to any one of claims 1-4, the method comprising: Get the estimated shutdown time for the current cycle; The pre-shutdown time for the next cycle is adjusted based on the pre-shutdown time of the current cycle.

6. The control method for synchronous rectification according to claim 5, characterized in that, The control circuit for synchronous rectification includes a pre-off time adjustment circuit, which further includes a pre-off time sampling sub-circuit and a pre-off time adjustment sub-circuit. Obtaining the pre-off time for the current cycle includes: The time of the output signal of the pre-off time adjustment sub-circuit in the current cycle is obtained and used as the start time of the pre-off time. The drain voltage in the current cycle is obtained and the time when the drain voltage is greater than a preset voltage threshold is determined as the end time of the pre-off time. The difference between the end time of the pre-shutdown time and the start time of the pre-shutdown time is determined as the pre-shutdown time of the current cycle.

7. The control method for synchronous rectification according to claim 5, characterized in that, The pre-shutdown time adjustment subcircuit includes a controllable delay subcircuit. The adjustment of the pre-shutdown time for the next cycle based on the pre-shutdown time of the current cycle includes: When the pre-off time of the current cycle is greater than the reference time, the delay time of the controllable delay sub-circuit is increased to reduce the pre-off time of the next cycle. When the pre-off time of the current cycle is less than the reference time, the delay time of the controllable delay sub-circuit is reduced to increase the pre-off time of the next cycle.

8. A synchronous rectification chip, characterized in that, The synchronous rectification chip includes a control circuit for synchronous rectification according to any one of claims 1-4.

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