A synchronous rectification method and device

Abstract

The present invention discloses a synchronous rectification method and device, including: Step S1, obtaining the resonant current in the charge control circuit of an LLC resonant converter; Step S2, obtaining the magnetizing current in the charge control circuit of the LLC resonant converter; Step S3, obtaining a drive signal applied to a synchronous rectifier tube according to the resonant current and the magnetizing current. By adopting the technical solution of the present invention, the problem that it is difficult to determine the drive signal of the synchronous rectifier tube in a charge control type resonant converter is solved, and at the same time, the problems that the cost of using a synchronous rectification chip is high and it is difficult to achieve multi-degree-of-freedom phase-shift control are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of LLC resonant converters, and particularly relates to a synchronous rectification method and device. Background Art

[0002] When an LLC resonant converter is applied in a low-voltage and high-current scenario, the rectification loss on the secondary side will significantly affect the efficiency. At the same efficiency, the higher the power density, the more heat is generated per unit volume, which is not conducive to the heat dissipation of the radiator. Therefore, while increasing the power density, the efficiency of the converter also needs to be improved. Synchronous rectification is suitable for improving the efficiency of the converter in low-voltage and high-current scenarios. By using a MOSFET with a small on-resistance to replace the rectifier diode, the efficiency can be improved and the loss caused by the diode can be reduced. The driving methods of synchronous rectifier tubes are divided into voltage-mode driving and current-mode driving, and the voltage-mode driving can be further divided into self-driving and external driving.

[0003] External driving is divided into traditional driving and drain-source voltage detection driving; internal driving is divided into voltage-mode driving, current-mode driving, and hybrid driving.

[0004] Traditional external driving methods are as Figure 1 shown. The primary driving and secondary driving are independent of each other, and the primary and secondary driving signals are output from the controller. Due to the transformer electrical isolation between the primary and secondary sides, the primary or secondary driving signal needs to pass through a signal isolation circuit and then be input into the driving circuit to drive the power device to switch. When the resonant converter operates above the resonant frequency, the primary and secondary driving are consistent. However, when the operating frequency is lower than the resonant frequency, since the secondary current is in the discontinuous mode, at this time the primary and secondary driving cannot be consistent anymore, and the driving signal of the synchronous rectifier tube needs to be turned off earlier than the primary driving signal. At this time, the driving signal of the synchronous rectification can be obtained by looking up a table or by calculation.

[0005] Voltage-mode driving usually uses the secondary winding or auxiliary winding of the transformer to provide the driving voltage for the synchronous rectifier tube. The secondary voltage of the LLC is a square wave. When the amplitude meets the conditions, this voltage can be used to drive the synchronous rectifier tube, as Figure 2 shown. If the amplitude does not meet the requirements, the auxiliary winding can be used for adjustment.

[0006] Current-mode driving provides its driving signal based on the current situation flowing through the synchronous rectifier tube after a certain judgment and conversion. When there is current flowing through the synchronous rectifier tube, the SR is turned on; when the current flowing through the SR drops to 0, the SR is turned off. This driving method will not cause energy backflow, and compared with the traditional driving method, ZCS can be achieved. Therefore, this driving method is an ideal driving method, but this requires a current detection circuit, which increases the complexity of the circuit and the volume of the converter.

[0007] Professor Liu Heping of Chongqing University analyzed and deduced the unimodal relationship curve between the output voltage and the synchronous drive time of the LLC circuit. By changing the drive time on both sides of the peak, different change rates of the output voltage can be caused. Based on this, a sensorless synchronous rectification control strategy is proposed. This control strategy uses the optimal gradient loop comparison search method, which has high requirements for software computing resources and poor dynamic real-time adjustment performance.

[0008] In recent years, with the development of DSP, the application of digital control technology has become more and more extensive. By detecting the drain-source voltage of the synchronous rectifier tube, comparing it with the threshold voltage through a voltage comparator, and outputting the SR drive signal after being processed by DSP, continuously adjusting the drive to make the output pulse of the comparator zero to achieve precise control. Its schematic diagram is as Figure 3 shown.

[0009] The LLC resonant converter can control the input energy by detecting the change in charge within the switching period, and the control of the charge quantity is achieved through real-time control of the primary switch. Since the energy in the resonant cavity within each switching period is controlled in real time, this strategy has excellent dynamic response performance. Since this control method controls the operation of the primary switch in real time through the comparison of charge quantities, it is impossible to give the drive signal of the secondary synchronous rectifier tube through this controller. For this control strategy, currently, only a dedicated synchronous rectification chip can be used to drive the secondary synchronous rectifier tube, resulting in an increase in circuit cost. At the same time, it is not conducive to broadening the application scenario of the charge control technology, restricting the further improvement of its flexibility, and it is difficult to be applied to occasions such as phase shift between the primary and secondary sides of the converter. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a synchronous rectification method and device, which solve the problem that it is difficult to determine the drive signal of the synchronous rectifier tube in the charge control type resonant converter, and at the same time, the use of a synchronous rectification chip has a high cost and it is difficult to achieve multi-degree-of-freedom phase shift control.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] A synchronous rectification method, comprising:

[0013] Step S1, obtaining the resonant current in the charge control circuit of the LLC resonant converter;

[0014] Step S2, obtaining the magnetizing current in the charge control circuit of the LLC resonant converter;

[0015] Step S3, obtaining the drive signal applied to the synchronous rectifier tube according to the resonant current and the magnetizing current;

[0016] Among them, in the charge control circuit of the LLC resonant converter, the first constant current source I ramp and the second constant current source I ，ramp Connect the ramp compensation capacitor C ramp , and the second constant current source I ， ramp Connect a K1 switch controlled by the res signal, and the first constant current source I ramp is half of the second constant current source I ， ramp to keep the positive and negative half-cycles of the drive signal completely symmetric; the voltage v ramp on the ramp compensation capacitor C ramp , and the resonant capacitor voltage V sampled by the first operational amplifier cr Connect a K2 switch controlled by the res signal. When the K2 switch is closed, v ramp and V cr are added to obtain v sum ; when the K2 switch is open, v sum =v ramp , and this v sum is respectively input to the negative input terminal of the second comparator CMP2 and the positive input terminal of the third comparator CMP3; the positive input terminal of CMP2 is connected to ground, and the output terminal of CMP2 is connected to the set signal S terminal of the RS latch; the output voltage v o of the converter and the reference voltage v ref are input to the voltage loop control regulator, and the output Q ref [[ID= 35]]of the voltage loop control regulator is input to the negative input terminal of CMP3, and the output terminal of CMP3 is connected to the reset signal R terminal of the RS latch; the output terminal and the output Q terminal of the RS latch are connected to the dead zone module, the output terminal of the RS latch is connected to the reset signal res terminal, and the output signals Q1 and Q2 of the dead zone module are used to drive the primary side switching tube; the voltage across the sampled excitation inductor L m is connected to a differential proportional operation circuit, and its output is connected to an integral operation circuit, which integrates on the integral capacitor C m to obtain an integral voltage representing the excitation inductor current , and the integral voltage is input to the negative input terminal of the first comparator CMP1 and the positive input terminal of the fourth comparator CMP4; the resonant capacitor voltage V cr passes through C2 and the filter circuit composed of R8 and C3 to obtain a voltage value V cr_cal representing the resonant current, where C2 is connected to one end of R7, the other end of R7 is grounded, one end of C3 is connected to one end of R8, and the other end of R8 is grounded; the voltage value V cr_calThe positive input terminal of CMP1 and the negative input terminal of CMP4; the output signal of CMP1 is ANDed with Q1 to obtain the drive signal of synchronous rectifier SR1; the output of CMP4 is ANDed with Q2 to obtain the drive signal of synchronous rectifier SR2; according to the integral voltage characterizing the excitation inductor current the excitation current is obtained, and according to the voltage value V characterizing the resonant current cr_cal the resonant current is obtained;

[0017] When the resonant current is greater than the excitation current and the current direction is positive at this time, synchronous rectifier SR1 conducts; when the resonant current is less than the excitation current and the current direction is negative at this time, synchronous rectifier SR2 conducts; when the resonant current is equal to the excitation current, no drive signal is applied to the secondary synchronous rectifier.

[0018] Preferably, it further includes: performing ramp compensation on the LLC resonant converter charge control circuit by changing Qref, where the negative input terminal of CMP3 inputs where is the output of the voltage loop regulator, , T s (k-1) is the period value of the previous switching cycle under the control strategy.

[0019] The present invention also provides a synchronous rectification device, including:

[0020] A first acquisition module for acquiring the resonant current in the LLC resonant converter charge control circuit;

[0021] A second acquisition module for acquiring the excitation current in the LLC resonant converter charge control circuit;

[0022] A drive module for obtaining the drive signal applied to the synchronous rectifier according to the resonant current and the excitation current;

[0023] Among them, in the LLC resonant converter charge control circuit, the first constant current source I ramp and the second constant current source I ， ramp are connected to the ramp compensation capacitor C ramp , the second constant current source I ， ramp is connected to a K1 switch controlled by the res signal, and the first constant current source I ramp is half of the second constant current source I ， ramp to keep the positive and negative half-cycles of the drive signal completely symmetrical; the voltage v ramp on the ramp compensation capacitor C ramp , and the resonant capacitor voltage V cr obtained by sampling through the first operational amplifierConnect a K2 switch controlled by the res signal. When the K2 switch is closed, v ramp is added to V cr to obtain v sum ; when the K2 switch is open, v sum = v ramp , and this v sum is respectively input to the negative input terminal of the second comparator CMP2 and the positive input terminal of the third comparator CMP3; the positive input terminal of CMP2 is connected to ground, and the output terminal of CMP2 is connected to the set signal S terminal of the RS latch; the output voltage v o of the converter and the reference voltage v ref are input to the voltage loop control regulator, and the output Q ref of the voltage loop control regulator is input to the negative input terminal of CMP3. The output terminal of CMP3 is connected to the reset signal R terminal of the RS latch; the output terminal and the output Q terminal of the RS latch are connected to the dead zone module. The output terminal of the RS latch is connected to the reset signal res terminal. The output signals Q1 and Q2 of the dead zone module are used to drive the primary side switch tube; the voltage across the sampled excitation inductor L m is connected to the differential proportional operation circuit, and its output is connected to the integral operation circuit for integration on the integration capacitor C m to obtain the integration voltage representing the excitation inductor current. The integration voltage is input to the negative input terminal of the first comparator CMP1 and the positive input terminal of the fourth comparator CMP4; the resonant capacitor voltage V cr passes through C2 and the filter circuit composed of R8 and C3 to obtain the voltage value V cr_cal representing the resonant current, where C2 is connected to one end of R7, the other end of R7 is grounded, one end of C3 is connected to one end of R8, and the other end of R8 is grounded; the voltage value V cr_cal is input to the positive input terminal of CMP1 and the negative input terminal of CMP4; the output signal of CMP1 is ANDed with Q1 to obtain the drive signal of the synchronous rectifier SR1; the output of CMP4 is ANDed with Q2 to obtain the drive signal of the synchronous rectifier SR2; the excitation current is obtained based on the integration voltage representing the excitation inductor current, and the resonant current is obtained based on the voltage value V cr_cal representing the resonant current;

[0024] When the resonant current is greater than the excitation current and the current direction is positive at this time, the synchronous rectifier SR1 conducts; when the resonant current is less than the excitation current and the current direction is negative at this time, the synchronous rectifier SR2 conducts; when the resonant current is equal to the excitation current, no drive signal is applied to the secondary side synchronous rectifier.

[0025] Preferably, it further includes: a slope compensation module for performing slope compensation on the charge control circuit of the LLC resonant converter by changing Qref, where the negative input terminal of CMP3 inputs , where is the output of the voltage loop regulator, , T s (k-1) is the period value of the previous switching period under the control strategy.

[0026] The synchronous rectification circuit of the present invention is introduced into the charge control type resonant converter, which can solve the problem that it is difficult to obtain the current cycle frequency information by the charge control method and it is difficult to realize synchronous rectification. The present invention is simple and reliable, has a low learning cost, has strong versatility, and can effectively expand the application occasions of charge control. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0028] Figure 1 is a traditional external drive circuit diagram;

[0029] Figure 2 is a schematic diagram of providing an SR drive voltage for the secondary winding of the transformer;

[0030] Figure 3 is a schematic diagram of using DSP to control the synchronous rectification circuit;

[0031] Figure 4 is a schematic diagram of the relationship between the synchronous rectification drive of the LLC resonant converter and the primary side switch tube drive, where (a) is f s < f r , (b) is f s > f r ;

[0032] Figure 5 is a schematic flowchart of the synchronous rectification method of the embodiment of the present invention;

[0033] Figure 6 is a schematic circuit connection diagram of the synchronous rectification method of the embodiment of the present invention;

[0034] Figure 7 is a schematic diagram of the charge control synchronous rectification sampling calculation circuit;

[0035] Figure 8 It is a schematic diagram of digital ramp compensation. Specific implementation manners

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0038] Embodiment 1:

[0039] The conduction of the synchronous rectification tube on the secondary side of the LLC converter depends on the excitation current i m and the resonant current i r The relationship between the synchronous rectification drive of the LLC resonant converter and the primary side switch tube drive is as shown in Figure 4 When in the upper resonance (drive frequency f s > resonant frequency f r ), one of the synchronous rectification tubes SR 1, SR 2 is always conducting, and its conduction time is the same as the drive time on the primary side switch tube. However, when the converter operates in the lower resonance ( f s < f r ), the synchronous rectification tube only conducts when i m and i r are different in magnitude. When i m = i r , the converter no longer transfers energy to the output side, and at this time, no drive should be applied to the synchronous rectification tube. The conventional direct frequency control LLC converter adjusts the gain by directly changing the switching frequency. The controller can obtain the frequency information of the next switching cycle in advance. Therefore, when in the lower resonance, it only needs to make the drive frequency f s = resonant frequency f r, just make the two switching tubes turn on simultaneously. The drive of the charge-controlled LLC converter is generated by a hardware trigger method, and the controller cannot know the frequency information of the next switching cycle in advance. It is difficult for a resonant converter using the charge control method to obtain the frequency information of the current switching cycle in advance, so it is very difficult to control the drive duration of the secondary synchronous rectifier tube.

[0040] As Figure 5 shown, an embodiment of the present invention provides a synchronous rectification method, including:

[0041] Step S1, obtain the resonant current in the charge control circuit of the LLC resonant converter;

[0042] Step S2, obtain the magnetizing current in the charge control circuit of the LLC resonant converter;

[0043] Step S3, obtain the drive signal applied to the synchronous rectifier tube according to the resonant current and the magnetizing current.

[0044] As Figure 6 shown, in the charge control circuit of the LLC resonant converter, the first constant current source I ramp and the second constant current source I ， ramp are connected to the ramp compensation capacitor C ramp , the second constant current source I ， ramp is connected to a K1 switch controlled by the res signal, and the first constant current source I ramp is half of the second constant current source I ， ramp to keep the positive and negative half cycles of the drive signal completely symmetric; the voltage v ramp on the ramp compensation capacitor C ramp , the resonant capacitor voltage V cr sampled by the first operational amplifier is connected to a K2 switch controlled by the res signal. When the K2 switch is closed, v ramp is added to V cr to obtain v sum ; when the K2 switch is open, v sum = v ramp , and this v sum is respectively input to the negative input terminal of the second comparator CMP2 and the positive input terminal of the third comparator CMP3; the positive input terminal of CMP2 is connected to the ground, and the output terminal of CMP2 is connected to the set signal S terminal of the RS latch; the output voltage v o of the converter and the reference voltage v ref are input to the voltage loop control regulator, and the output Q ref of the voltage loop control regulator is input to the negative input terminal of CMP3, and the output terminal of CMP3 is connected to the reset signal R terminal of the RS latch; the output of the RS latch The output of the RS latch is connected to the dead zone module at the terminal and the output Q terminal. The output terminal is connected to the reset signal res terminal, and the output signals Q1 and Q2 of the dead zone module are used to drive the primary side switching tube; the voltage across the excitation inductor L obtained by sampling is connected to the differential proportional operation circuit, and its output is connected to the integral operation circuit, and is integrated on the integral capacitor C m to obtain an integral voltage characterizing the excitation inductor current. m The integral voltage is input to the negative input terminal of the first comparator CMP1 and the positive input terminal of the fourth comparator CMP4; the resonant capacitor voltage V cr passes through C2 and the filter circuit composed of R8 and C3 to obtain a voltage value V characterizing the resonant current cr_cal , where one end of C2 is connected to one end of R7, the other end of R7 is grounded, one end of C3 is connected to one end of R8, and the other end of R8 is grounded; the voltage value V cr_cal is input to the positive input terminal of CMP1 and the negative input terminal of CMP4; the output signal of CMP1 is ANDed with Q1 to obtain the drive signal of the synchronous rectifier SR1; the output of CMP4 is ANDed with Q2 to obtain the drive signal of the synchronous rectifier SR2; according to the integral voltage characterizing the excitation inductor current the excitation current is obtained, and according to the voltage value V characterizing the resonant current cr_cal the resonant current is obtained.

[0045] When the resonant current is greater than the excitation current and the current direction is positive at this time, the synchronous rectifier SR1 conducts; when the resonant current is less than the excitation current and the current direction is negative at this time, the synchronous rectifier SR2 conducts; when the resonant current is equal to the excitation current, no drive signal is applied to the secondary side synchronous rectifier.

[0046] As an implementation manner of the embodiment of the present invention, as Figure 7 shown, in step S1, for the resonant current i r , it is calculated through the capacitor C 2 and the resonant capacitor C r as follows:

[0047] (1)

[0048] where C2 << C r .

[0049] As Figure 7 shown, in step S2, the excitation current is obtained by integrating on the capacitor after collecting the voltages on both sides of the transformer in the LLC resonant converter charge control circuit.

[0050] The voltage-current relationship on the excitation inductor is as follows:

[0051] (2)

[0052] Let R 2 = R 4, R 1 = R 3, then the voltage relationship on the integration capacitor C m can be expressed as:

[0053] (3)

[0054] Furthermore, the variation of the excitation current :

[0055] (4)

[0056] Therefore, the variation of the excitation current has a one-to-one correspondence with the voltage C m on the integration capacitor . By collecting the voltages on both sides of the transformer, the excitation current can be calculated.

[0057] Furthermore, the second operational amplifier A2 is connected to both ends of the transformer excitation inductor V m1 and V m2 through resistors R1 and R3 respectively. Its output is connected to the negative input terminal of the third operational amplifier A3 through R5. The positive terminal of the third operational amplifier A3 is grounded. The output voltage of the third operational amplifier A3 has a relationship with the excitation inductor current expressed by Equation (4). The voltage of the resonant capacitor C r is output as V cr , which is input to the capacitor C2 and the adder respectively. After the voltage of V cr passes through the capacitor C2 and the resistor R7, the voltage corresponding to the resonant current is obtained, and then after low-pass filtering by R8 and C3, the obtained V cr_cal can be expressed by Equation (1). The output voltages and V cr_cal are respectively input to the comparator CMP1. When V cr_cal > , the output of CMP1 is high level, otherwise it is low level.

[0058] During the conduction period of the switching transistor S1, the res signal is at low level, K1 is disconnected, K2 is in closed-loop, and Iramp charges the C ramp with a constant current. Its voltage V camp rises linearly. This voltage is added to the capacitor voltage V cr to obtain the Vsum voltage. V sumThe voltages are respectively sent to the negative input terminal of CMP2 and the positive input terminal of CMP3. When V sum is greater than the positive input terminal Q of CMP3 ref , the RS flip-flop is reset, and the output of the Q terminal of the flip-flop is 0, is 1; during the conduction period of the switching transistor S2, the res signal is at a high level, K1 is turned on, K2 is turned off, and I ， ramp discharges C ramp at a constant current, and its voltage V camp decreases linearly. This voltage is equal to V sum voltage. When V sum is less than 0V at the positive input terminal of CMP2, the Q output terminal of the RS flip-flop is set to 1, is 0. The Q and output terminals of the RS flip-flop pass through a dead-time module to generate two complementary drives of Q1 and Q2 with dead time. The Q1 signal is ANDed with the output of CMP1 to generate the SR2 drive signal, and the Q2 signal is ANDed with the inverted signal of the output of CMP1 to generate the SR1 signal. SR1 and SR2 respectively drive the switching transistors S3 and S4.

[0059] As an implementation manner of the embodiment of the present invention, in order to avoid the subharmonic oscillation phenomenon similar to that in the peak current mode Buck converter in the charge control LLC converter, ramp compensation needs to be added. The ramp compensation is implemented by a digital method. As Figure 8 shown, the negative input terminal of CMP3 inputs , where is the output of the voltage loop regulator, , and T s (k-1) is the period value of the previous switching period under the control strategy.

[0060] Embodiment 2:

[0061] The embodiment of the present invention further provides a synchronous rectification device, including:

[0062] A first acquisition module for acquiring the resonant current in the charge control circuit of the LLC resonant converter;

[0063] A second acquisition module for acquiring the magnetizing current in the charge control circuit of the LLC resonant converter;

[0064] A driving module for obtaining a driving signal applied to the synchronous rectifier tube according to the resonant current and the magnetizing current;

[0065] Among them, in the charge control circuit of the LLC resonant converter, the first constant current source I ramp and the second constant current source I ， ramp are connected to the ramp compensation capacitor Cramp , the second constant current source I ， ramp Connect a K1 switch controlled by the res signal, the first constant current source I ramp The second constant current source I ， ramp Half of the slope compensation capacitor C is used to keep the positive and negative half cycles of the driving signal completely symmetrical; ramp The voltage v ramp , the resonant capacitor voltage V is obtained by sampling the first operational amplifier cr Connect a K2 switch controlled by the res signal. When the K2 switch is closed, v ramp With V cr Add up to get v sum ; When K2 switch is off, v sum =v ramp , the v sum The voltage is input to the negative input terminal of the second comparator CMP2 and the positive input terminal of the third comparator CMP3 respectively; the positive input terminal of CMP2 is connected to the ground, and the output terminal of CMP2 is connected to the set signal S terminal of the RS latch; the output voltage v o and reference voltage v ref Input to the voltage loop control regulator, and the output Q of the voltage loop control regulator ref Input to the negative input terminal of CMP3, the output terminal of CMP3 is connected to the reset signal R terminal of RS latch; the output of RS latch The output of the RS latch is connected to the dead zone module and the output Q of the RS latch is connected to the dead zone module. The terminal is connected to the reset signal res terminal, and the output signals Q1 and Q2 of the dead zone module are used to drive the primary switch tube; the sampled excitation inductance L m The voltage at both ends is connected to the differential proportional operation circuit, and its output is connected to the integral operation circuit. m Integrate the voltage to get the integral voltage representing the excitation inductor current. , the integrated voltage Input to the negative input terminal of the first comparator CMP1 and the positive input terminal of the fourth comparator CMP4; the resonant capacitor voltage V cr The voltage value V representing the resonant current is obtained through C2 and the filter circuit composed of R8 and C3. cr_cal , where C2 is connected to one end of R7, the other end of R7 is grounded, one end of C3 is connected to one end of R8, the other end of R8 is grounded; the voltage value V cr_cal Input to the positive input terminal of CMP1 and the negative input terminal of CMP4; the output signal of CMP1 and Q1 are ANDed to obtain the driving signal of synchronous rectifier SR1; the output of CMP4 and Q2 are ANDed to obtain the driving signal of synchronous rectifier SR2; according to the integral voltage representing the excitation inductor current Obtain the excitation current, based on the voltage value V characterizing the resonant current cr_cal Obtain the resonant current;

[0066] When the resonant current is greater than the excitation current and the current direction is positive at this time, the synchronous rectifier tube SR1 conducts; when the resonant current is less than the excitation current and the current direction is negative at this time, the synchronous rectifier tube SR2 conducts; when the resonant current is equal to the excitation current, no drive signal is applied to the secondary synchronous rectifier tube.

[0067] As an implementation manner of an embodiment of the present invention, it further includes: a ramp compensation module for performing ramp compensation on the charge control circuit of the LLC resonant converter by changing Qref, where the negative input terminal of CMP3 inputs , where is the output of the voltage loop regulator, , T s (k-1) is the period value of the previous switching period under this control strategy.

[0068] The above embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A synchronous rectification method, characterized in that: include: Step S1, obtaining the resonant current in the charge control circuit of the LLC resonant converter; Step S2: obtaining the excitation current in the charge control circuit of the LLC resonant converter; Step S3, obtaining a driving signal applied to the synchronous rectifier according to the resonant current and the excitation current; wherein, in the LLC resonant converter charge control circuit, the first constant current source I ramp and the second constant current source I ， ramp Connect the slope compensation capacitor C ramp , the second constant current source I ， ramp Connect a K1 switch controlled by the res signal, the first constant current source I ramp The second constant current source I ， ramp Half of the slope compensation capacitor C is used to keep the positive and negative half cycles of the driving signal completely symmetrical; ramp The voltage v ramp , the resonant capacitor voltage V is obtained by sampling the first operational amplifier cr Connect a K2 switch controlled by the res signal. When the K2 switch is closed, v ramp With V cr Add up to get v sum ; When K2 switch is off, v sum =v ramp , the v sum The voltage is input to the negative input terminal of the second comparator CMP2 and the positive input terminal of the third comparator CMP3 respectively; the positive input terminal of CMP2 is connected to the ground, and the output terminal of CMP2 is connected to the set signal S terminal of the RS latch; the output voltage v o and reference voltage v ref Input to the voltage loop control regulator, and the output Q of the voltage loop control regulator ref Input to the negative input terminal of CMP3, the output terminal of CMP3 is connected to the reset signal R terminal of RS latch; the output of RS latch The output of the RS latch is connected to the dead zone module and the output Q of the RS latch is connected to the dead zone module. The terminal is connected to the reset signal res terminal, and the output signals Q1 and Q2 of the dead zone module are used to drive the primary switch tube; the sampled excitation inductance L m The voltage at both ends is connected to the differential proportional operation circuit, and its output is connected to the integral operation circuit. m Integrate the voltage to get the integral voltage representing the excitation inductor current. , the integrated voltage Input to the negative input terminal of the first comparator CMP1 and the positive input terminal of the fourth comparator CMP4; the resonant capacitor voltage V cr The voltage value V representing the resonant current is obtained through C2 and the filter circuit composed of R8 and C3. cr_cal , where C2 is connected to one end of R7, the other end of R7 is grounded, one end of C3 is connected to one end of R8, the other end of R8 is grounded; the voltage value V cr_cal Input to the positive input terminal of CMP1 and the negative input terminal of CMP4; the output signal of CMP1 and Q1 are ANDed to obtain the driving signal of synchronous rectifier SR1; the output of CMP4 and Q2 are ANDed to obtain the driving signal of synchronous rectifier SR2; according to the integral voltage representing the excitation inductor current Get the excitation current, according to the voltage value V that represents the resonant current cr_cal Get the resonant current; When the resonant current is greater than the excitation current and the current direction is positive at this time, the synchronous rectifier tube SR1 is turned on; when the resonant current is less than the excitation current and the current direction is negative at this time, the synchronous rectifier tube SR2 is turned on; when the resonant current is equal to the excitation current, no driving signal is applied to the secondary synchronous rectifier tube.

2. The synchronous rectification method according to claim 1, wherein: Also includes: The LLC resonant converter charge control circuit is slope compensated by changing Qref, where the negative input terminal of CMP3 is input ,in, is the output of the voltage loop regulator, , T s (k-1) is the period value of the previous switching cycle under the control strategy.

3. A synchronous rectification device, characterized in that: include: A first acquisition module is used to obtain the resonant current in the charge control circuit of the LLC resonant converter; A second acquisition module is used to obtain the excitation current in the charge control circuit of the LLC resonant converter; A driving module, used to obtain a driving signal applied to the synchronous rectifier according to the resonant current and the excitation current; Among them, in the LLC resonant converter charge control circuit, the first constant current source I ramp and the second constant current source I ， ramp Connect the slope compensation capacitor C ramp , the second constant current source I ， ramp Connect a K1 switch controlled by the res signal, the first constant current source I ramp The second constant current source I ， ramp Half of the slope compensation capacitor C is used to keep the positive and negative half cycles of the driving signal completely symmetrical; ramp The voltage v ramp , the resonant capacitor voltage V is obtained by sampling the first operational amplifier cr Connect a K2 switch controlled by the res signal. When the K2 switch is closed, v ramp With V cr Add up to get v sum ; When K2 switch is off, v sum =v ramp , the v sum The voltage is input to the negative input terminal of the second comparator CMP2 and the positive input terminal of the third comparator CMP3 respectively; the positive input terminal of CMP2 is connected to the ground, and the output terminal of CMP2 is connected to the set signal S terminal of the RS latch; the output voltage v o and reference voltage v ref Input to the voltage loop control regulator, and the output Q of the voltage loop control regulator ref Input to the negative input terminal of CMP3, the output terminal of CMP3 is connected to the reset signal R terminal of RS latch; the output of RS latch The output of the RS latch is connected to the dead zone module and the output Q of the RS latch is connected to the dead zone module. The terminal is connected to the reset signal res terminal, and the output signals Q1 and Q2 of the dead zone module are used to drive the primary switch tube; the sampled excitation inductance L m The voltage at both ends is connected to the differential proportional operation circuit, and its output is connected to the integral operation circuit. m Integrate the voltage to get the integral voltage representing the excitation inductor current. , the integrated voltage Input to the negative input terminal of the first comparator CMP1 and the positive input terminal of the fourth comparator CMP4; the resonant capacitor voltage V cr The voltage value V representing the resonant current is obtained through C2 and the filter circuit composed of R8 and C3. cr_cal , where C2 is connected to one end of R7, the other end of R7 is grounded, one end of C3 is connected to one end of R8, the other end of R8 is grounded; the voltage value V cr_cal Input to the positive input terminal of CMP1 and the negative input terminal of CMP4; the output signal of CMP1 and Q1 are ANDed to obtain the driving signal of synchronous rectifier SR1; the output of CMP4 and Q2 are ANDed to obtain the driving signal of synchronous rectifier SR2; according to the integral voltage representing the excitation inductor current Get the excitation current, according to the voltage value V that represents the resonant current cr_cal Get the resonant current; When the resonant current is greater than the excitation current and the current direction is positive at this time, the synchronous rectifier tube SR1 is turned on; when the resonant current is less than the excitation current and the current direction is negative at this time, the synchronous rectifier tube SR2 is turned on; when the resonant current is equal to the excitation current, no driving signal is applied to the secondary synchronous rectifier tube.

4. The synchronous rectification device according to claim 3, wherein: Also includes: The slope compensation module is used to perform slope compensation on the LLC resonant converter charge control circuit by changing Qref, where the negative input terminal of CMP3 is input ,in, is the output of the voltage loop regulator, , T s (k-1) is the period value of the previous switching cycle under this control strategy.

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