LLC synchronous rectification control method and device and LLC resonant converter

Abstract

The invention discloses an LLC synchronous rectification control method and device and an LLC resonant converter. The LLC synchronous rectification control method comprises the following steps: acquiring an LLC driving frequency fs and a resonance frequency fr; the fs is compared with the fr, if fs is smaller than or equal to fr, the rectification MOS tube and the LLC driving switch tube are controlled to be switched on and switched off synchronously, and if fs is larger than fr, the rectification MOS tube and the LLC driving switch tube are controlled to be switched on synchronously and switched off in a delayed mode relative to the LLC driving switch tube. Synchronous rectification control is carried out without adding an additional current detection circuit to carry out secondary side current detection, the hardware cost is saved, and meanwhile the control logic is simple, stable and reliable; besides, when fs is larger than fr, the rectification MOS tube and the LLC driving switch tube are controlled to be switched on synchronously and switched off in a delayed mode relative to the LLC driving switch tube, ZCS of the rectification MOS tube can be achieved under the current working condition, switching-off loss can be reduced, and device damage can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of switched-mode power supplies, and particularly to an LLC synchronous rectification control method, device, and LLC resonant converter. Background Art

[0002] In traditional LLC resonant converters, the rectification loss of the secondary diode is large when the output is at low voltage and high current. To improve the efficiency of the resonant converter, synchronous rectification technology is introduced into the LLC resonant converter, which greatly reduces the on-state loss of the secondary rectification side, making the application of the LLC synchronous rectification topology more and more widespread in the medium and high power fields. However, the current LLC synchronous rectification control method relies on complex control logic or additional current detection circuits to control the turning on and off of the synchronous rectifier tube, resulting in high cost and poor reliability. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an LLC synchronous rectification control method, device, and LLC resonant converter to solve the problem that the traditional LLC synchronous rectification control method relies on complex control logic or additional current detection circuits to control the turning on and off of the synchronous rectifier tube, resulting in high cost and poor reliability.

[0004] In a first aspect of the present invention, an LLC synchronous rectification control method is provided, including: obtaining the LLC driving frequency fs and the resonant frequency fr; comparing the LLC driving frequency fs with the resonant frequency fr, if fs ≤ fr, controlling the rectification MOS tube to turn on and off synchronously with the LLC driving switch tube, if fs > fr, controlling the rectification MOS tube to turn on synchronously with the LLC driving switch tube and controlling the rectification MOS tube to turn off with a delay relative to the LLC driving switch tube.

[0005] In a second aspect of the present invention, an LLC synchronous rectification control device is provided, including: a frequency acquisition module for obtaining the LLC driving frequency fs and the resonant frequency fr; a rectification MOS tube control module for comparing the LLC driving frequency fs with the resonant frequency fr, if fs ≤ fr, controlling the rectification MOS tube to turn on and off synchronously with the LLC driving switch tube, if fs > fr, controlling the rectification MOS tube to turn on synchronously with the LLC driving switch tube and controlling the rectification MOS tube to turn off with a delay relative to the LLC driving switch tube.

[0006] The third aspect of the present invention provides an LLC resonant converter, which includes a controller, a transformer, a primary-side LLC resonant circuit connected to the primary coil of the transformer, and a synchronous rectification circuit connected to the secondary coil of the transformer; the primary-side LLC resonant circuit includes a plurality of LLC drive switching tubes, and the synchronous rectification circuit includes a plurality of rectification MOS tubes; the controller is used to obtain the LLC drive frequency fs and the resonant frequency fr, and compare the LLC drive frequency fs with the resonant frequency fr. If fs ≤ fr, the rectification MOS tubes are controlled to be turned on and off synchronously with the LLC drive switching tubes. If fs > fr, the rectification MOS tubes are controlled to be turned on synchronously with the LLC drive switching tubes and the rectification MOS tubes are controlled to turn off with a delay relative to the LLC drive switching tubes.

[0007] The above LLC synchronous rectification control method, device and LLC resonant converter do not need to add an additional current detection circuit to detect the secondary current for synchronous rectification control, saving hardware costs, and at the same time, the control logic is simple, stable and reliable; in addition, when the LLC drive frequency is greater than the resonant frequency, the rectification MOS tubes are controlled to be turned on synchronously with the LLC drive switching tubes and the rectification MOS tubes are controlled to turn off with a delay relative to the LLC drive switching tubes, which can enable the rectification MOS tubes to achieve ZCS under the current working conditions, thereby reducing the turn-off loss and avoiding device damage. Description of the Drawings

[0008] Figure 1 is the circuit diagram of the LLC resonant converter of the present invention;

[0009] Figure 2 is the schematic diagram of the simulation waveform when the LLC resonant converter of the present invention works under the condition that the LLC drive frequency is greater than the resonant frequency;

[0010] Figure 3 is the schematic flow diagram of the LLC synchronous rectification control method of the present invention;

[0011] Figure 4 is the schematic structural diagram of the LLC synchronous rectification control device of the present invention. Detailed Embodiments

[0012] In order to make those of ordinary skill in the art more clearly understand the purpose, technical solution and advantages of the present invention, the present invention will be further described below with reference to the drawings and embodiments.

[0013] Such as Figure 1As shown, in an embodiment of the present invention, an LLC resonant converter includes a controller, a transformer T1, a primary LLC resonant circuit connected to the primary coil of the transformer T1, and a synchronous rectification circuit connected to the secondary coil of the transformer; the primary LLC resonant circuit includes a plurality of LLC drive switching tubes, and the synchronous rectification circuit includes a plurality of rectification MOS tubes; the controller, as the control core of the converter, is used to output control signals to control the turning on and off of the LLC drive switching tubes and the rectification MOS tubes.

[0014] In this embodiment, the primary LLC resonant circuit adopts an LLC full-bridge resonant circuit. The LLC full-bridge resonant circuit includes a resonant cavity and a full-bridge circuit connected in sequence. The resonant cavity includes a resonant inductor Lr and a resonant capacitor Cr connected in series. The full-bridge circuit includes a first LLC drive switching tube Q26, a second LLC drive switching tube Q24, a third LLC drive switching tube Q25, and a fourth LLC drive switching tube Q27 connected in a full-bridge manner. Of course, in other embodiments of the present invention, the primary LLC resonant circuit can also adopt an LLC half-bridge resonant circuit.

[0015] The synchronous rectification circuit includes a first rectification MOS tube Q6 and a second rectification MOS tube Q15. The drain of the first rectification MOS tube Q6 is connected to one end of the secondary coil of the transformer T1, the drain of the second rectification MOS tube Q15 is connected to the other end of the secondary coil of the transformer T1, the sources of the first rectification MOS tube Q6 and the second rectification MOS tube Q15 are connected to one end of the load Rload, and the other end of the load Rload is connected to the center tap of the secondary coil of the transformer T1.

[0016] Figure 2 The figure shows a schematic diagram of the simulation waveform when the LLC resonant converter operates under the condition that the LLC drive frequency is greater than the resonant frequency. From top to bottom in the figure are the first LLC drive signal, the second LLC drive signal, the first rectification drive signal, the second rectification drive signal, the current of the first rectification MOS tube, the current of the second rectification MOS tube, and the magnetizing current. As Figure 2 shown, when the secondary rectification MOS tube and the primary LLC drive switching tube are turned on and off simultaneously, if fs > fr, in the current working condition, at this time, there is a situation of reverse recovery of the rectification MOS tube current in the dead zone of the LLC drive signal. When the rectification MOS tube is turned off, there is still a large current flowing through the body diode, making it impossible for the secondary rectification MOS tube to achieve ZCS.

[0017] To solve the problem that the secondary rectifier MOSFET cannot achieve ZCS under the condition of fs>fr, the present invention configures the controller accordingly. The controller is configured to obtain the LLC driving frequency fs and the resonant frequency fr, and compare the LLC driving frequency fs with the resonant frequency fr. If fs≤fr, control the rectifier MOSFET to turn on and off synchronously with the LLC driving switch tube. If fs>fr, control the rectifier MOSFET to turn on synchronously with the LLC driving switch tube and control the rectifier MOSFET to turn off with a delay relative to the LLC driving switch tube.

[0018] In one embodiment, when fs≤fr, the specific steps for the controller to control the rectifier MOSFET to turn on and off synchronously with the LLC driving switch tube include: determining that the duty cycle of the rectifier driving signal is fs / 2fr, and determining the duty cycle and dead zone of the rectifier driving signal, so that the frequency, duty cycle and dead zone of the rectifier driving signal are the same as those of the LLC driving signal, and outputting the rectifier driving signal to control the rectifier MOSFET to turn on and off synchronously with the LLC driving switch tube.

[0019] When fs>fr, the specific steps for the controller to control the rectifier MOSFET to turn on synchronously with the LLC driving switch tube and control the rectifier MOSFET to turn off with a delay relative to the LLC driving switch tube include: determining the rectifier driving signal, so that the rectifier driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifier driving signal is smaller than the dead zone of the LLC driving signal, and outputting the rectifier driving signal to control the rectifier MOSFET to turn on synchronously with the LLC driving switch tube and control the rectifier MOSFET to turn off with a delay relative to the LLC driving switch tube.

[0020] Among them, the LLC driving signal includes a first LLC driving signal llca and a second LLC driving signal llcb that are opposite in phase. The first LLC driving signal llca is used to control the on and off of the first LLC driving switch tube and the fourth LLC driving switch tube. The second LLC driving signal llcb is used to control the on and off of the second LLC driving switch tube and the third LLC driving switch tube. The rectifier driving signal includes a first rectifier driving signal sra and a second rectifier driving signal srb that are opposite in phase. The first rectifier driving signal sra is used to control the on and off of the first rectifier MOSFET. The second rectifier driving signal srb is used to control the on and off of the second rectifier MOSFET. The first rectifier driving signal sra is in phase with the first LLC driving signal llca.

[0021] In one embodiment, when fs ≤ fr, the specific steps for the controller to control the synchronous turn-on and synchronous turn-off of the rectifying MOS transistor and the LLC driving switch transistor are as follows: Set the target duty cycle of the rectifying driving signal to fs / 2fr; sample the secondary current and perform output current ripple analysis and judgment. If the output current ripple exceeds the set value, reduce the duty cycle of the rectifying driving signal so that the duty cycle of the rectifying driving signal is lower than the target duty cycle; if the output current ripple does not exceed the set value, use the target duty cycle as the duty cycle of the rectifying driving signal; determine the duty cycle and dead zone of the rectifying driving signal, make the frequency, duty cycle and dead zone of the rectifying driving signal the same as those of the LLC driving signal, and output the rectifying driving signal to control the synchronous turn-on and synchronous turn-off of the rectifying MOS transistor and the LLC driving switch transistor.

[0022] When fs > fr, the specific steps for the controller to control the synchronous turn-on of the rectifying MOS transistor and the LLC driving switch transistor and to control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor are as follows: Determine the rectifying driving signal so that the rectifying driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifying driving signal is smaller than the dead zone of the LLC driving signal, and output the rectifying driving signal to control the synchronous turn-on of the rectifying MOS transistor and the LLC driving switch transistor and to control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

[0023] Among them, the LLC driving signal includes a first LLC driving signal llca and a second LLC driving signal llcb that are in opposite phases. The first LLC driving signal llca is used to control the turn-on and turn-off of the first LLC driving switch transistor and the fourth LLC driving switch transistor. The second LLC driving signal llcb is used to control the turn-on and turn-off of the second LLC driving switch transistor and the third LLC driving switch transistor; the rectifying driving signal includes a first rectifying driving signal sra and a second rectifying driving signal srb that are in opposite phases. The first rectifying driving signal sra is used to control the turn-on and turn-off of the first rectifying MOS transistor. The second rectifying driving signal srb is used to control the turn-on and turn-off of the second rectifying MOS transistor. The first rectifying driving signal sra is in the same phase as the first LLC driving signal llca.

[0024] The LLC resonant converter of this embodiment does not require an additional current detection circuit to detect the secondary current for synchronous rectification control, saving hardware costs, and at the same time, the control logic is simple, stable and reliable; in addition, when the LLC driving frequency is greater than the resonant frequency, controlling the synchronous turn-on of the rectifying MOS transistor and the LLC driving switch transistor and controlling the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor can enable the rectifying MOS transistor to achieve ZCS under the current working conditions, thereby reducing the turn-off loss and avoiding device damage.

[0025] The present invention also provides an LLC synchronous rectification control method. As Figure 3 shown, in an embodiment of the present invention, the LLC synchronous rectification control method includes steps S10 - S20:

[0026] S10. Obtain the LLC driving frequency fs and the resonant frequency fr.

[0027] Among them, the LLC driving frequency fs is the frequency of the LLC driving signal, and can be obtained by obtaining the switching frequency of the LLC driving switch tube in the steady state through the frequency scanning method.

[0028] The calculation method of the resonant frequency is: Lr is the value of the resonant inductor, and Cr is the value of the resonant capacitor.

[0029] S20. Compare the LLC driving frequency fs with the resonant frequency fr. If fs ≤ fr, control the rectifying MOS tube and the LLC driving switch tube to turn on synchronously and turn off synchronously. If fs > fr, control the rectifying MOS tube and the LLC driving switch tube to turn on synchronously and control the rectifying MOS tube to turn off with a delay relative to the LLC driving switch tube.

[0030] In this embodiment of the LLC synchronous rectification control method, there is no need to add an additional current detection circuit to detect the secondary side current for synchronous rectification control, saving hardware costs, and at the same time, the control logic is simple, stable and reliable; in addition, when the LLC driving frequency is greater than the resonant frequency, control the rectifying MOS tube and the LLC driving switch tube to turn on synchronously and control the rectifying MOS tube to turn off with a delay relative to the LLC driving switch tube, which can enable the rectifying MOS tube to achieve ZCS under the current working condition, thereby reducing the turn-off loss and avoiding device damage.

[0031] In an embodiment, the step S20 further includes S21 - S23:

[0032] S21. Compare the LLC driving frequency fs with the resonant frequency fr. If fs ≤ fr, execute step S22. If fs > fr, execute step S23.

[0033] S22. Determine that the duty cycle of the rectifying driving signal is fs / 2fr, and determine the duty cycle and dead zone of the rectifying driving signal, so that the frequency, duty cycle and dead zone of the rectifying driving signal are the same as those of the LLC driving signal, and output the rectifying driving signal to control the rectifying MOS tube and the LLC driving switch tube to turn on synchronously and turn off synchronously. It should be noted that since the frequency, duty cycle and dead zone of the rectifying driving signal are the same as those of the LLC driving signal, the duty cycle of the LLC driving signal also needs to be adjusted to fs / 2fr accordingly.

[0034] S23. Determine the rectifier drive signal to make the rectifier drive signal have the same frequency as the LLC drive signal, with the dead time of the rectifier drive signal being less than that of the LLC drive signal, and output the rectifier drive signal to control the synchronous turn-on of the rectifier MOS transistor and the LLC drive switch transistor and control the rectifier MOS transistor to turn off with a delay relative to the LLC drive switch transistor.

[0035] The interval setting between the dead time of the LLC drive signal and the dead time of the rectifier drive signal can be adjusted accordingly according to the situation. This invention does not make a limitation, as long as it is ensured that the reverse recovery current of the rectifier MOS transistor can be reduced to zero within this interval. In this embodiment, the dead time of the rectifier drive signal is set to be less than that of the LLC drive signal. After the LLC drive switch transistor turns off, the rectifier MOS transistor waits for the reverse recovery current to be reduced to zero before completely turning off the rectifier MOS transistor, thereby achieving ZCS, and further reducing the turn-off loss and avoiding device damage.

[0036] In one embodiment, the step S20 further includes steps S21 - S25:

[0037] S21. Compare the LLC drive frequency fs with the resonant frequency fr. If fs ≤ fr, then execute step S22; if fs > fr, then execute step S25.

[0038] S22. Set the target duty cycle of the rectifier drive signal to fs / 2fr.

[0039] S23. Sample the secondary side current and perform output current ripple analysis and judgment. If the output current ripple exceeds the set value, then reduce the duty cycle of the rectifier drive signal so that the duty cycle of the rectifier drive signal is lower than the target duty cycle; if the output current ripple does not exceed the set value, then use the target duty cycle as the duty cycle of the rectifier drive signal.

[0040] S24. Determine the duty cycle and dead time of the rectifier drive signal to make the frequency, duty cycle, and dead time of the rectifier drive signal the same as those of the LLC drive signal, and output the rectifier drive signal to control the synchronous turn-on and synchronous turn-off of the rectifier MOS transistor and the LLC drive switch transistor. It should be noted that since the frequency, duty cycle, and dead time of the rectifier drive signal are the same as those of the LLC drive signal, the duty cycle of the LLC drive signal also needs to be adjusted accordingly.

[0041] S25. Determine the rectifier drive signal to make the rectifier drive signal have the same frequency as the LLC drive signal, with the dead time of the rectifier drive signal being less than that of the LLC drive signal, and output the rectifier drive signal to control the synchronous turn-on of the rectifier MOS transistor and the LLC drive switch transistor and control the rectifier MOS transistor to turn off with a delay relative to the LLC drive switch transistor.

[0042] In this embodiment, the on and off control of the rectifying MOS transistor is performed through steps S21 - S25, which increases the control reliability on the basis of ensuring that the rectifying MOS transistor can achieve ZCS.

[0043] The present invention also provides an LLC synchronous rectification control device. As Figure 4 shown, in an embodiment of the present invention, the LLC synchronous rectification control device includes a frequency acquisition module 10 and a rectifying MOS transistor control module 20. The frequency acquisition module 10 is used to acquire the LLC driving frequency fs and the resonant frequency fr; the rectifying MOS transistor control module 20 is used to compare the LLC driving frequency fs with the resonant frequency fr. If fs ≤ fr, it controls the rectifying MOS transistor to be turned on and off synchronously with the LLC driving switch transistor. If fs > fr, it controls the rectifying MOS transistor to be turned on synchronously with the LLC driving switch transistor and controls the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

[0044] In this embodiment of the LLC synchronous rectification control device, there is no need to add an additional current detection circuit for secondary side current detection to perform synchronous rectification control, which saves hardware costs and has a simple, stable and reliable control logic. In addition, when the LLC driving frequency is greater than the resonant frequency, controlling the rectifying MOS transistor to be turned on synchronously with the LLC driving switch transistor and controlling the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor can enable the rectifying MOS transistor to achieve ZCS under the current working conditions, thereby reducing the turn-off loss and avoiding device damage.

[0045] In an embodiment, the rectifying MOS transistor control module 20 includes a frequency comparison unit, a first rectifying MOS transistor control unit, and a second rectifying MOS transistor control unit. Among them. The frequency comparison unit is used to compare the LLC driving frequency fs with the resonant frequency fr. If fs ≤ fr, it starts the first rectifying MOS transistor control unit. If fs > fr, it starts the second rectifying MOS transistor control unit. The first rectifying MOS transistor control unit is used to determine that the duty cycle of the rectifying driving signal is fs / 2fr, and to determine the duty cycle and dead zone of the rectifying driving signal, so that the frequency, duty cycle and dead zone of the rectifying driving signal are the same as those of the LLC driving signal, and outputs a rectifying driving signal to control the rectifying MOS transistor to be turned on and off synchronously with the LLC driving switch transistor. The second rectifying MOS transistor control unit is used to determine the rectifying driving signal, so that the rectifying driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifying driving signal is smaller than the dead zone of the LLC driving signal, and outputs a rectifying driving signal to control the rectifying MOS transistor to be turned on synchronously with the LLC driving switch transistor and control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

[0046] In one embodiment, the rectifier MOS transistor control module 20 includes a frequency comparison unit, a target duty cycle setting unit, a duty cycle determination unit, a first rectifier MOS transistor control unit, and a second rectifier MOS transistor control unit. Among them, the frequency comparison unit is used to compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, the target duty cycle setting unit, the duty cycle determination unit, and the first rectifier MOS transistor control unit are sequentially started. If fs > fr, the second rectifier MOS transistor control unit is started. The target duty cycle setting unit is used to set the target duty cycle of the rectifier driving signal to fs / 2fr. The duty cycle determination unit is used to sample the secondary side current and perform output current ripple analysis and judgment. If the output current ripple exceeds the set value, the duty cycle of the rectifier driving signal is reduced so that the duty cycle of the rectifier driving signal is lower than the target duty cycle. If the output current ripple does not exceed the set value, the target duty cycle is used as the duty cycle of the rectifier driving signal. The first rectifier MOS transistor control unit is used to determine the duty cycle and dead zone of the rectifier driving signal, so that the frequency, duty cycle, and dead zone of the rectifier driving signal are the same as those of the LLC driving signal, and output the rectifier driving signal to control the rectifier MOS transistor to turn on and off synchronously with the LLC driving switch transistor. The second rectifier MOS transistor control unit is used to determine the rectifier driving signal, so that the rectifier driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifier driving signal is smaller than the dead zone of the LLC driving signal, and output the rectifier driving signal to control the rectifier MOS transistor to turn on synchronously with the LLC driving switch transistor and control the rectifier MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

[0047] The above are only the preferred embodiments of the present invention, and do not impose any formal restrictions on the present invention. Those skilled in the art can make various equivalent changes and improvements based on the above embodiments. Any equivalent changes or modifications made within the scope of the claims shall fall within the protection scope of the present invention.

Claims

1. An LLC synchronous rectification control method, characterized in that, Including: S10. Obtain the LLC driving frequency fs and the resonance frequency fr; S20. Compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and turn off synchronously. If fs > fr, control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

2. The LLC synchronous rectification control method according to claim 1, wherein The step S20 further includes: S21. Compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, execute step S22. If fs > fr, execute step S23; S22. Determine that the duty cycle of the rectifying driving signal is fs / 2fr, and determine the duty cycle and dead zone of the rectifying driving signal, so that the frequency, duty cycle, and dead zone of the rectifying driving signal are the same as those of the LLC driving signal, and output the rectifying driving signal to control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and turn off synchronously; S23. Determine the rectifying driving signal, so that the rectifying driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifying driving signal is less than the dead zone of the LLC driving signal, and output the rectifying driving signal to control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

3. The LLC synchronous rectification control method according to claim 1, wherein The step S20 further includes: S21. Compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, execute step S22. If fs > fr, execute step S25; S22. Set the target duty cycle of the rectifying driving signal to fs / 2fr; S23. Sample the secondary side current and perform output current ripple analysis and judgment. If the output current ripple exceeds the set value, reduce the duty cycle of the rectifying driving signal so that the duty cycle of the rectifying driving signal is lower than the target duty cycle. If the output current ripple does not exceed the set value, use the target duty cycle as the duty cycle of the rectifying driving signal; S24. Determine the duty cycle and dead zone of the rectifying driving signal, so that the frequency, duty cycle, and dead zone of the rectifying driving signal are the same as those of the LLC driving signal, and output the rectifying driving signal to control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and turn off synchronously; S25. Determine the rectifying driving signal, so that the rectifying driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifying driving signal is less than the dead zone of the LLC driving signal, and output the rectifying driving signal to control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

4. An LLC synchronous rectification control device, characterized in that, Including: A frequency acquisition module, configured to obtain the LLC driving frequency fs and the resonance frequency fr; A rectifying MOS transistor control module, configured to compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and turn off synchronously. If fs > fr, control the rectifying MOS transistor and the LLC driving switch transistor to turn on synchronously and control the rectifying MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

5. The LLC synchronous rectification control device according to claim 4, wherein, The rectifier MOS transistor control module includes: A frequency comparison unit, configured to compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, the first rectifier MOS transistor control unit is started; if fs > fr, the second rectifier MOS transistor control unit is started; The first rectifier MOS transistor control unit, configured to determine that the duty cycle of the rectifier driving signal is fs / 2fr, and determine the duty cycle and dead zone of the rectifier driving signal, so that the frequency, duty cycle, and dead zone of the rectifier driving signal are the same as those of the LLC driving signal, and output the rectifier driving signal to control the rectifier MOS transistor to turn on and off synchronously with the LLC driving switch transistor; The second rectifier MOS transistor control unit, configured to determine the rectifier driving signal, so that the rectifier driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifier driving signal is smaller than that of the LLC driving signal, and output the rectifier driving signal to control the rectifier MOS transistor to turn on synchronously with the LLC driving switch transistor and control the rectifier MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

6. The LLC synchronous rectification control device according to claim 4, wherein The rectifier MOS transistor control module includes: A frequency comparison unit, configured to compare the LLC driving frequency fs with the resonance frequency fr. If fs ≤ fr, the target duty cycle setting unit, the duty cycle determination unit, and the first rectifier MOS transistor control unit are sequentially started; if fs > fr, the second rectifier MOS transistor control unit is started; The target duty cycle setting unit, configured to set the target duty cycle of the rectifier driving signal as fs / 2fr; The duty cycle determination unit, configured to sample the secondary side current and perform output current ripple analysis and judgment. If the output current ripple exceeds the set value, the duty cycle of the rectifier driving signal is reduced so that the duty cycle of the rectifier driving signal is lower than the target duty cycle; if the output current ripple does not exceed the set value, the target duty cycle is used as the duty cycle of the rectifier driving signal; The first rectifier MOS transistor control unit, configured to determine the duty cycle and dead zone of the rectifier driving signal, so that the frequency, duty cycle, and dead zone of the rectifier driving signal are the same as those of the LLC driving signal, and output the rectifier driving signal to control the rectifier MOS transistor to turn on and off synchronously with the LLC driving switch transistor; The second rectifier MOS transistor control unit, configured to determine the rectifier driving signal, so that the rectifier driving signal has the same frequency as the LLC driving signal, and the dead zone of the rectifier driving signal is smaller than that of the LLC driving signal, and output the rectifier driving signal to control the rectifier MOS transistor to turn on synchronously with the LLC driving switch transistor and control the rectifier MOS transistor to turn off with a delay relative to the LLC driving switch transistor.

7. An LLC resonant converter, characterized in that, It includes a controller, a transformer, a primary LLC resonant circuit connected to the primary coil of the transformer, and a synchronous rectification circuit connected to the secondary coil of the transformer; the primary LLC resonant circuit includes a plurality of LLC drive switching tubes, and the synchronous rectification circuit includes a plurality of rectification MOS tubes; the controller is used to obtain the LLC drive frequency fs and the resonant frequency fr, and compare the LLC drive frequency fs with the resonant frequency fr. If fs ≤ fr, it controls the rectification MOS tubes and the LLC drive switching tubes to turn on and off synchronously. If fs > fr, it controls the rectification MOS tubes and the LLC drive switching tubes to turn on synchronously and controls the rectification MOS tubes to turn off with a delay relative to the LLC drive switching tubes.

8. The LLC resonant converter according to claim 7, wherein The specific steps for the controller to control the rectification MOS tubes and the LLC drive switching tubes to turn on and off synchronously when fs ≤ fr include: setting the target duty cycle of the rectification drive signal to fs / 2fr; sampling the secondary current and performing output current ripple analysis and judgment. If the output current ripple exceeds the set value, the duty cycle of the rectification drive signal is reduced so that the duty cycle of the rectification drive signal is lower than the target duty cycle; if the output current ripple does not exceed the set value, the target duty cycle is used as the duty cycle of the rectification drive signal; determining the duty cycle and dead zone of the rectification drive signal so that the frequency, duty cycle, and dead zone of the rectification drive signal are the same as those of the LLC drive signal, and outputting the rectification drive signal to control the rectification MOS tubes and the LLC drive switching tubes to turn on and off synchronously; The specific steps for the controller to control the rectification MOS tubes and the LLC drive switching tubes to turn on synchronously and control the rectification MOS tubes to turn off with a delay relative to the LLC drive switching tubes when fs > fr include: determining the rectification drive signal so that the rectification drive signal has the same frequency as the LLC drive signal, and the dead zone of the rectification drive signal is smaller than the dead zone of the LLC drive signal, and outputting the rectification drive signal to control the rectification MOS tubes and the LLC drive switching tubes to turn on synchronously and control the rectification MOS tubes to turn off with a delay relative to the LLC drive switching tubes.

9. The LLC resonant converter according to claim 8, wherein The primary LLC resonant circuit adopts an LLC half-bridge resonant circuit.

10. The LLC resonant converter according to claim 9, wherein The primary LLC resonant circuit adopts an LLC full-bridge resonant circuit. The LLC full-bridge resonant circuit includes a resonant cavity and a full-bridge circuit connected in sequence. The resonant cavity includes a resonant inductor and a resonant capacitor connected in series. The full-bridge circuit includes a first LLC driving switch tube, a second LLC driving switch tube, a third LLC driving switch tube, and a fourth LLC driving switch tube connected in a full-bridge manner. The synchronous rectification circuit includes a first rectifying MOS tube and a second rectifying MOS tube. The drain of the first rectifying MOS tube is connected to one end of the secondary coil of the transformer. The drain of the second rectifying MOS tube is connected to the other end of the secondary coil of the transformer. The sources of the first rectifying MOS tube and the second rectifying MOS tube are connected to one end of the load. The other end of the load is connected to the center tap of the secondary coil of the transformer. The LLC driving signal includes a first LLC driving signal and a second LLC driving signal that are in anti-phase with each other. The first LLC driving signal is used to control the on and off of the first LLC driving switch tube and the fourth LLC driving switch tube. The second LLC driving signal is used to control the on and off of the second LLC driving switch tube and the third LLC driving switch tube. The rectifying driving signal includes a first rectifying driving signal and a second rectifying driving signal that are in anti-phase with each other. The first rectifying driving signal is used to control the on and off of the first rectifying MOS tube. The second rectifying driving signal is used to control the on and off of the second rectifying MOS tube. The first rectifying driving signal is in phase with the first LLC driving signal.

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