Synchronous rectification control circuit, direct current converter and synchronous rectification control method

Abstract

The invention discloses a synchronous rectification control circuit, a direct current converter and a synchronous rectification control method.The circuit comprises a current detection resistor, a comparator, a switch, a driving circuit and a digital controller, and the digital controller outputs a synchronous rectification tube turn-off enable signal to the switch to turn on the switch; the current detection resistor collects rectified current output by the synchronous rectifier tube at the turn-off moment, the comparator carries out negative value judgment on the rectified current to obtain a judgment result, and the digital controller determines first turn-off delay time and first turn-on delay time of the synchronous rectifier tube relative to the primary side switch tube based on the judgment result and preset increment time. And generating a synchronous rectification control signal to control the synchronous rectification tube, and enabling the error between the first turn-off delay time and the second turn-off delay time to be within a preset range through self-adaptive adjustment of a plurality of control periods. Therefore, synchronous rectification control is realized, the method does not depend on parameters and working models of the direct-current converter, and the method is high in adaptability and good in generalization performance.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and more specifically, to a synchronous rectification control circuit, a direct current converter and a synchronous rectification control method. Background Art

[0002] With the development of new energy power generation, battery energy storage systems, electric vehicles and other industrial fields, resonant DC converters have been widely used. Resonant DC converters use high-frequency resonance to achieve high-efficiency, high-power density power conversion, and have become one of the research hotspots in academia and industry. With the increase of power level, the output current capacity of DC converters is also continuously improved. In order to reduce the conduction loss of the secondary synchronous rectifier device, active devices such as MOSFET are often used as synchronous rectifier tubes to further improve the operating efficiency of the converter. Therefore, the synchronous rectification control technology of the synchronous rectifier tube is the key to achieve efficient operation of the converter.

[0003] In summary, how to provide a synchronous rectification control circuit to realize the control of the synchronous rectifier tube has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0004] In view of this, the present invention discloses a synchronous rectification control circuit, a DC converter and a synchronous rectification control method to achieve control of a synchronous rectifier tube.

[0005] A synchronous rectification control circuit, comprising:

[0006] A current detection resistor, wherein the current detection resistor is connected to the output end of the synchronous rectifier tube of the main power circuit of the DC converter;

[0007] A comparator, wherein an input terminal of the comparator is connected to the current detection resistor;

[0008] a switch connected to an output terminal of the comparator;

[0009] A driving circuit, wherein the driving circuit is connected to a control end of the synchronous rectifier;

[0010] a digital controller, the digital controller being connected to the switch and the drive circuit respectively, and being used for outputting a synchronous rectifier tube shutdown enable signal to the switch to turn on the switch in a current control cycle, so that the current detection resistor collects the rectified current output by the synchronous rectifier tube at the shutdown moment, and obtains the determination result of the negative value determination of the rectified current output by the comparator, and determines the first shutdown delay time and the first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube based on the determination result and the preset incremental time, and generates a synchronous rectification control signal based on the first shutdown delay time and the first turn-on delay time, and performs synchronous rectification control on the synchronous rectifier tube through the drive circuit, and enters the next control cycle to perform synchronous rectification control on the synchronous rectifier tube again until the error between the first shutdown delay time and the second shutdown delay time is within a preset range;

[0011] Among them, the second shutdown delay time is: the shutdown delay time of the rectifier current zero crossing relative to the primary switch tube, and the value of the preset incremental time is limited by the accuracy of the synchronous rectification control signal output by the digital controller.

[0012] Optionally, the switch is a MOS tube.

[0013] A DC converter, comprising: a DC converter main power circuit and the above-mentioned synchronous rectification control circuit;

[0014] The DC converter main power circuit comprises: a primary switch tube, a synchronous rectifier tube and a resonant circuit, wherein the resonant circuit is respectively connected to the output end of the primary switch tube and the input end of the synchronous rectifier tube;

[0015] The current detection resistor in the synchronous sorting control circuit is connected to the output end of the synchronous rectifier tube, and the driving circuit in the synchronous sorting control circuit is connected to the control end of the synchronous rectifier tube.

[0016] Optionally, the resonant circuit comprises: a first transformer and a first resonant branch, wherein the first resonant branch comprises a first inductor and a first capacitor connected in series;

[0017] The primary side of the first transformer is connected to the primary side switch tube through the first resonant branch, and the secondary side of the first transformer is connected to the synchronous rectifier tube.

[0018] Optionally, the resonant circuit includes: a second transformer, a second resonant branch and a third resonant branch;

[0019] The second resonant branch comprises a second inductor and a second capacitor connected in series;

[0020] The third resonant branch comprises a third inductor and a third capacitor connected in series;

[0021] The primary side of the second transformer is connected to the primary side switch tube through the second resonant branch, and the secondary side of the second transformer is connected to the synchronous rectifier tube through the third resonant branch.

[0022] A synchronous rectification control method is applied to a digital controller in the above-mentioned synchronous rectification control circuit, the method comprising:

[0023] In the current control cycle, a synchronous rectifier tube shutdown enable signal is output to the switch to turn on the switch, so that the current detection resistor collects the rectified current output by the synchronous rectifier tube at the shutdown moment;

[0024] Obtaining a determination result of a negative value determination of the rectified current output by the comparator;

[0025] Based on the determination result and the preset incremental time, determine a first turn-off delay time and a first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube, wherein the value of the preset incremental time is limited by the accuracy of the synchronous rectification control signal output by the digital controller;

[0026] generating the synchronous rectification control signal based on the first turn-off delay time and the first turn-on delay time;

[0027] Based on the synchronous rectification control signal, the synchronous rectification tube is synchronously controlled by the driving circuit;

[0028] Entering the next control cycle, the synchronous rectifier tube is again subjected to synchronous rectification control until the error between the first turn-off delay time and the second turn-off delay time is within a preset range, wherein the second turn-off delay time is: the turn-off delay time of the rectifier current zero-crossing relative to the primary switch tube.

[0029] Optionally, determining a first turn-off delay time and a first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube based on the determination result and the preset incremental time includes:

[0030] Determining whether the determination result indicates that the rectified current is a negative value;

[0031] If yes, determining the difference between the initial value of the shutdown delay time and the preset incremental time as the first shutdown delay time;

[0032] If not, the sum of the initial value of the turn-off delay time and the preset incremental time is determined as the first turn-off delay time.

[0033] Optionally, also include:

[0034] Determine whether the first shutdown delay time is less than 0;

[0035] If yes, determining that the value of the first activation delay time is 0;

[0036] If not, it is determined that the value of the first turn-on delay time is the same as the value of the first turn-off delay time.

[0037] Optionally, the initial value of the shutdown delay time is -T s / 2, where T s Represents the control period of the digital controller on the synchronous rectifier.

[0038] It can be seen from the above technical scheme that the present invention discloses a synchronous rectification control circuit, a DC converter and a synchronous rectification control method. The synchronous rectification control circuit includes a current detection resistor, a comparator, a switch, a drive circuit and a digital controller. The digital controller outputs a synchronous rectifier tube shutdown enable signal to the switch to turn on the switch. The current detection resistor collects the rectified current output by the synchronous rectifier tube at the shutdown moment and outputs it to the comparator. The comparator performs a negative value judgment on the rectified current to obtain a determination result. The digital controller determines the first shutdown delay time and the first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube based on the determination result and the preset incremental time, generates a synchronous rectification control signal based on the first shutdown delay time and the first turn-on delay time, and performs synchronous rectification control on the synchronous rectifier tube through the drive circuit. The synchronous rectification control method in a single control cycle is terminated until the next control cycle is entered. The same adaptive synchronous rectification control process is performed on the original basis. After adaptive adjustment of multiple control cycles, the error between the first shutdown delay time and the second shutdown delay time is within a preset range. Since the second turn-off delay time is the turn-off delay time of the rectifier current zero-crossing relative to the primary switch tube, the present invention realizes synchronous rectification control. In addition, the implementation of the synchronous rectification control of the present invention does not depend on the parameters and working model of the DC converter, so it has the advantages of strong adaptability and good generalizability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without paying creative work.

[0040] Figure 1 A schematic diagram of a synchronous rectification control circuit disclosed in an embodiment of the present invention;

[0041] Figure 2A schematic diagram of a DC converter disclosed in an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of a CLLC resonant converter disclosed in an embodiment of the present invention;

[0043] Figure 4 A main power circuit diagram of an LLC type resonant DC converter disclosed in an embodiment of the present invention;

[0044] Figure 5 An LLC type resonant converter disclosed in an embodiment of the present invention is sw >f r Schematic diagram of ideal synchronous rectification control signal when ;

[0045] Figure 6 An LLC type resonant converter disclosed in an embodiment of the present invention is sw >f r And T lag1 >T lag1 'Working waveform diagram;

[0046] Figure 7 An LLC type resonant converter disclosed in an embodiment of the present invention is sw >f r And T lag1 <T lag1 'Working waveform diagram;

[0047] Figure 8 An LLC type resonant converter disclosed in an embodiment of the present invention is sw <f r Ideal synchronous rectification control signal diagram when ;

[0048] Fig. 9 An LLC type resonant converter disclosed in an embodiment of the present invention is sw <f r And T lag1 >T lag1 '(ie |T lag1 |<|T lag1 '|) working waveform diagram;

[0049] Fig.10 The present invention discloses a flow chart of a synchronous rectification control method. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] The embodiment of the present invention discloses a synchronous rectification control circuit, a DC converter and a synchronous rectification control method. The synchronous rectification control circuit includes a current detection resistor, a comparator, a switch, a drive circuit and a digital controller. The digital controller outputs a synchronous rectification tube shutdown enable signal to the switch to turn on the switch. The current detection resistor collects the rectified current output by the synchronous rectification tube at the shutdown time and outputs it to the comparator. The comparator performs a negative value judgment on the rectified current to obtain a determination result. The digital controller determines a first shutdown delay time and a first turn-on delay time of the synchronous rectification tube relative to the primary switch tube based on the determination result and a preset incremental time, generates a synchronous rectification control signal based on the first shutdown delay time and the first turn-on delay time, and performs synchronous rectification control on the synchronous rectification tube through the drive circuit. The synchronous rectification control method in a single control cycle is terminated until the next control cycle is entered. The same adaptive synchronous rectification control process is performed on the original basis. After adaptive adjustment of multiple control cycles, the error between the first shutdown delay time and the second shutdown delay time is within a preset range. Since the second turn-off delay time is the turn-off delay time of the rectifier current zero-crossing relative to the primary switch tube, the present invention realizes synchronous rectification control. In addition, the implementation of the synchronous rectification control of the present invention does not depend on the parameters and working model of the DC converter, so it has the advantages of strong adaptability and good generalizability.

[0052] See also Figure 1 , a schematic diagram of a synchronous rectification control circuit disclosed in an embodiment of the present invention, the synchronous rectification control circuit comprises: a current detection resistor R sense , comparator 11, switch S, drive circuit 12 and digital controller 13.

[0053] Among them, the current detection resistor R sense The synchronous rectifier connected to the main power circuit of the DC converter (see Figure 1 S 5 ~S 8 ) output terminal, used to collect the rectified current i output by the synchronous rectifier at the turn-off time rec .

[0054] The input terminal of the comparator 11 is connected to the current detection resistor R sense connect.

[0055] Specifically, the current detection resistor R senseThe end close to the synchronous rectifier is connected to the negative input terminal of the comparator 11, and the current detection resistor R sense The end away from the synchronous rectifier is connected to the positive input end of the comparator 11 .

[0056] The switch S is connected to the output terminal of the comparator 11 .

[0057] Preferably, the switch S can be a MOS tube.

[0058] The output end of the drive circuit 12 is connected to the synchronous rectifier (see Figure 1 S 5 ~S 8 ) and is used to output a synchronous rectification control signal to the synchronous rectifier tube.

[0059] The digital controller 13 is connected to the switch S and the driving circuit 12 respectively, and is used to output a synchronous rectifier off enable signal to the switch S in the current control cycle to turn on the switch S, so that the current detection resistor R sense The rectifier current output by the synchronous rectifier tube at the shutdown time is collected, and the judgment result of the rectifier current output by the comparator 11 is obtained. Based on the judgment result and the preset increment time, the synchronous rectifier tube relative to the primary switch tube is determined (see Figure 1 S 1 ~S 4 ), a synchronous rectification control signal is generated based on the first turn-off delay time and the first turn-on delay time, and the synchronous rectifier is controlled synchronously through the driving circuit 12, and the synchronous rectifier is controlled synchronously again when entering the next control cycle until the error between the first turn-off delay time and the second turn-off delay time is within a preset range.

[0060] The preset range represents the degree of proximity between the first shutdown delay time and the second shutdown delay time, and the specific value is determined according to actual needs, and the present invention is not limited here.

[0061] The second turn-off delay time is: the zero crossing of the rectifier current relative to the primary switch tube (see Figure 1 S 1 ~S 4 ) of the turn-off delay time.

[0062] The value of the preset increment time △T is limited by the accuracy of the synchronous rectification control signal output by the digital controller 13. The accuracy of △T of common digital controllers can reach the level of picoseconds to nanoseconds, which is relatively accurate to the control period T. s For , this value is very small and can be ignored. Therefore, this method can achieve relatively ideal synchronous rectification control through adaptive adjustment within multiple cycles.

[0063] It should be noted that before the digital controller 13 executes the synchronous rectification control method shown above, it is necessary to set the preset increment time △T of each step of the synchronous rectification control signal and the first turn-off delay time T of the synchronous rectifier tube relative to the primary switch tube. lag1 The initial value of the shutdown delay time, that is, the initial value of the shutdown delay time, can be set to -T to avoid affecting the working waveform of the DC converter. s / 2,T s It represents the control period of the synchronous rectifier by the digital controller 13. At this time, the synchronous rectifier does not perform switching action, and the rectification is performed by relying on the body diode of the synchronous rectifier.

[0064] It should be noted that the digital controller 13 executes the synchronous rectification control algorithm once in each control cycle. The digital controller 13 starts to adaptively execute the synchronous rectification control algorithm in each control cycle. Specifically, the digital controller 13 outputs a synchronous rectification tube turn-off enable signal to the switch S to turn on the switch S. At this time, the current detection resistor R sense Collect the rectified current i output by the synchronous rectifier at the turn-off time rec , and outputs it to the comparator 11, which processes the rectified current i rec The negative value judgment is performed and the judgment result is output to the digital controller 13. The digital controller 13 determines the synchronous rectifier tube relative to the primary switch tube (see Figure 1 S 1 ~S 4 ) of the first turn-off delay time T lag1 and the first opening delay time T lag2 , and based on the first turn-off delay time T lag1 and the first opening delay time T lag2 A synchronous rectification control signal is generated and output to the driving circuit 12. The driving circuit 12 uses the synchronous rectification control signal to perform synchronous rectification control on the synchronous rectifier tube, thereby ending the synchronous rectification control method within a single control cycle until entering the next control cycle. The same adaptive synchronous rectification control method is performed on the original basis. After multiple control cycles, the error between the first shutdown delay time and the second shutdown delay time is within a preset range, thereby achieving a more ideal synchronous rectification control.

[0065] In summary, the present invention discloses a synchronous rectification control circuit, including a current detection resistor R sense , comparator 11, switch S, drive circuit 12 and digital controller 13, the digital controller 13 outputs a synchronous rectifier off enable signal to switch S to turn on switch S, and the current detection resistor R senseThe rectifier current output by the synchronous rectifier tube at the turn-off moment is collected and output to the comparator 11. The comparator 11 performs a negative value judgment on the rectifier current to obtain a judgment result. The digital controller 13 determines the first turn-off delay time and the first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube based on the judgment result and the preset increment time, generates a synchronous rectification control signal based on the first turn-off delay time and the first turn-on delay time, and performs synchronous rectification control on the synchronous rectifier tube through the drive circuit 12, so as to end the synchronous rectification control method within a single control cycle until entering the next control cycle, and execute the same adaptive synchronous rectification control process on the original basis. After adaptive adjustment of multiple control cycles, the error between the first turn-off delay time and the second turn-off delay time is within a preset range. Since the second turn-off delay time is the turn-off delay time of the rectifier current zero-crossing relative to the primary switch tube, the present invention realizes synchronous rectification control. In addition, the implementation of the synchronous rectification control of the present invention does not depend on the parameters and working model of the DC converter, so it has the advantages of strong adaptability and good generalizability.

[0066] Corresponding to the above embodiment, the present invention also discloses a DC converter.

[0067] See also Figure 2 , a schematic diagram of a DC converter disclosed in an embodiment of the present invention, the DC converter includes: a DC converter main power circuit and the synchronous rectification control circuit described in the above embodiment.

[0068] The main power circuit of the DC converter includes: a primary switch tube 21, a synchronous rectifier tube 22 and a resonant circuit 23. The resonant circuit is connected to the output end of the primary switch tube 21 and the input end of the synchronous rectifier tube 22 respectively.

[0069] Current detection resistor R in synchronous control circuit sense The drive circuit 12 in the synchronous rectification control circuit is connected to the control end of the synchronous rectifier 22 .

[0070] In this embodiment, the primary switch tube 21 can be a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor). The primary switch tube 21 converts the input DC power U in Converted to primary AC u ab .

[0071] The primary switch tube 21 includes four switch tubes, see Figure 2 S 1 -S4 .

[0072] The resonant circuit 23 outputs the primary AC power u of the primary switch tube 21. ab Resonance processing is performed to obtain the secondary side AC voltage u cd , and output to the synchronous rectifier 22.

[0073] The synchronous rectifier tube 22 includes four switch tubes, see Figure 2 S 5 -S 8 .

[0074] The synchronous rectifier 22 can also be a MOSFET followed by an IGBT, and the secondary AC voltage u cd After processing, the output DC voltage U out , and the output rectified current i rec ,

[0075] The control signal of the primary switch tube 21 is usually provided by a closed-loop controller and can be regarded as a signal determined or detectable inside the controller. The synchronous rectification control needs to determine the control signal of the synchronous rectifier tube 22 based on the control signal of the primary switch tube 21, converter parameters, converter operating mode, etc.

[0076] exist Figure 2 In, C in Represents the input capacitance, C out Represents the output capacitance.

[0077] The working principle of the DC converter is as follows:

[0078] The primary switch tube 21 converts the input DC current U in Converted to primary AC u ab The resonant circuit 23 outputs the primary AC power u of the primary switch tube 21. ab Resonance processing is performed to obtain the secondary side AC voltage u cd , and output to the synchronous rectifier 22, the synchronous rectifier 22 to the secondary AC voltage u cd After processing, the output DC voltage U out , and the output rectified current i rec .

[0079] The working principle of synchronous rectification control circuit can be found in Figure 1 The corresponding parts of the illustrated embodiment will not be described in detail here.

[0080] In summary, the DC converter disclosed in the present invention includes: a DC converter main power circuit and a synchronous rectification control circuit, and the synchronous rectification control circuit can perform adaptive adjustment of the synchronous rectification control of the DC converter main power circuit, thereby realizing relatively ideal synchronous rectification control. At the same time, the realization of synchronous rectification control does not depend on the parameters and working model of the DC converter, so it has the advantages of strong adaptability and good scalability.

[0081] It should be particularly noted that the DC converter in the present invention is mainly a resonant DC converter, and the corresponding resonant circuits 23 in different resonant DC converters are different.

[0082] For examples, see Figure 2 The LLC type resonant current converter shown.

[0083] The resonant circuit 23 includes: a first transformer (with a transformation ratio of n:1) and a first resonant branch, wherein the first resonant branch includes a first inductor L connected in series. r and the first capacitor C r ;

[0084] The primary side of the first transformer is connected to the primary switch tube 21 through the first resonant branch, and the secondary side of the first transformer is connected to the synchronous rectifier tube 22 .

[0085] See Figure 2 ,i Lr is the resonant current, L m is the transformer excitation inductance, i Lm is the excitation current, the inductance L r and capacitor C r The resonant frequency f r As shown below:

[0086]

[0087] It should be noted that the adaptive synchronous rectification control method proposed in the present invention can be applied not only to LLC resonant current converters, but also to other forms of resonant DC converters, for example, Figure 3 The CLLC type resonant converter shown.

[0088] The resonant circuit in the CLLC type resonant converter includes: a second transformer, a second resonant branch and a third resonant branch;

[0089] The second resonant branch includes a second inductor L connected in series. r1 and the second capacitor C r1 ;

[0090] The third resonant branch includes a third inductor L connected in series. r2 and the third capacitor C r2;

[0091] The primary side of the second transformer is connected to the primary side switch tube through the second resonant branch, and the secondary side of the second transformer is connected to the synchronous rectifier tube through the third resonant branch.

[0092] In order to further understand that the existing DC converter needs to perform synchronous rectification control, and that the synchronous rectification control is achieved by using the synchronous rectification control circuit disclosed in the present invention, the present invention also provides the entire derivation process, as follows:

[0093] See also Figure 4 , an LLC type resonant DC converter main power circuit diagram disclosed in an embodiment of the present invention, wherein the primary switch tube (see Figure 4 S 1 ~S 4 )) The input DC voltage U in Converted to primary AC u ab The inductance L in the resonant circuit r and capacitor C r To form a resonant network, i Lr is the resonant current, L m is the transformer excitation inductance, i Lm is the excitation current, the transformer ratio is n:1, u cd is the secondary AC voltage, the synchronous rectifier 22 (see Figure 4 S 5 ~S 8 ) to the secondary side AC voltage u cd After processing, the output DC voltage U out , and the output rectified current i rec .

[0094] LLC type resonant DC converter is generally controlled by frequency conversion method. There are two states in actual operation, namely switching frequency f sw Greater or less than the resonant frequency f r status.

[0095] Assume that T lag1 It represents the turn-off delay time of the synchronous rectifier tube relative to the primary switch tube, which is recorded as the first turn-off delay time;

[0096] T lag1 ' represents the delay time of the rectifier current zero-crossing relative to the turn-off of the primary switch tube, recorded as the second turn-off delay time;

[0097] T lag2 It represents the turn-on delay time of the synchronous rectifier tube relative to the primary switch tube, which is recorded as the first turn-on delay time;

[0098] T lag2' represents the delay time of the rectifier current zero crossing relative to the turn-on delay time of the primary switch tube, recorded as the second turn-on delay time.

[0099] When f sw >f r When the converter is ideally synchronously rectified, the control signal is as follows: Figure 5 As shown, the primary switch tube S 1 -S 4 The control signal frequency is f s , with a period of T s , the primary H bridge emits a high-frequency square wave u with the same period ab The converter operation waveform is positively and negatively symmetrical in the first half cycle and the second half cycle. s / 2 as an example, when S 1 and S 4 When activated, rec Gradually decreases, after T lag2 '(>0) time later, i rec Reduced to 0, the current i Lr with i Lm equal, at this time the synchronous rectifier tube S 5 and S 8 Open, if you remember from S 1 and S 4 Open to S 5 and S 8 The opening time is T lag2 , then we know that at this time T lag2 '=T lag2 . S 5 and S 8 After opening, rec Gradually increase until S 1 and S 4 Shutdown, i rec Gradually decrease again, after T lag1 '(>0) time later, i rec Reduced to 0, the current i Lr with i Lm equal, at this time the synchronous rectifier tube S 5 and S 8 Shut down, if the record from S 1 and S 4 Shutdown to S 5 and S 8 The off time is T lag1 , then we know that at this time T lag1 '=T lag1 At the same time, due to the current i Lr with i Lm The frequency is the same as the switching frequency, so T lag1 '=T lag2'. Therefore, in actual control, T lag1 =T lag2 , when controlling the synchronous rectifier S 1 and S 4 Shutdown to S 5 and S 8 Turn-off time T lag1 Exactly equal to T lag1 '(that is, control T lag2 '=T lag2 ), the ideal synchronous rectification control can be achieved.

[0100] When T lag1 >T lag1 '(At the same time T lag2 >T lag2 '), the actual working waveform of the converter is as follows Figure 6 As shown, at this time, the control signal of the synchronous rectifier tube has a deviation, S 1 and S 4 After shutdown, due to T lag1 Too big, rec Reduce to 0 and continue to decrease, S 5 and S 8 Before shutdown rec It has dropped to a negative value, causing power reflux and affecting the operating state of the converter.

[0101] When T lag1 <T lag1 '(At the same time T lag2 <T lag2 '), the actual working waveform of the converter is as follows Figure 7 As shown, the control signal of the synchronous rectifier also deviates at this time, S 1 and S 4 After opening, due to T lag1 Too small, rec When S has not yet dropped to 0 5 and S 8 After activation, the same rec When negative values ​​appear, power reflux occurs, affecting the operating state of the converter.

[0102] When f sw <f r When the converter is ideally synchronously rectified, the control signal is as follows: Figure 7 As shown in the figure, the converter operation waveform is positively and negatively symmetrical in the first half cycle and the second half cycle. s / 2 as an example, S 1 and S 4 Before opening, rec is 0, i Lr with i Lm Equal, S1 , S 4 With S 5 , S 8 At the same time, so the previous Figure 5 T defined in lag2 ' is 0. Then i rec Gradually increases and then gradually decreases to 0, at which time S 1 , S 4 It has not been shut down yet, so the previous Figure 5 T defined in lag1 ' is less than 0, the synchronous rectifier S 5 , S 8 It should also be turned off at this moment to ensure the above Figure 5 T defined in lag1 =T lag1 '. Therefore, in actual control, T lag2 =0, when controlling the synchronous rectifier tube S 1 and S 4 Shutdown to S 5 and S 8 Turn-off time T lag1 Exactly equal to T lag1 ', the ideal synchronous rectification control can be achieved.

[0103] When T lag1 <T lag1 '(ie |T lag1 |>|T lag1 '|), the current i rec Flows through the body diode of the rectifier. Since the body diode voltage drop of the rectifier is generally larger than the input and output voltages U in , U out The actual operating waveform of the converter will not change significantly, but the higher loss caused by the body diode voltage drop of the rectifier will lead to lower converter efficiency. lag1 >T lag1 '(ie |T lag1 |<|T lag1 '|), the converter's operating waveform is as follows Fig. 9 As shown, due to the long conduction time of the rectifier tube, i rec After reaching 0A, it continues to decrease, and negative current appears until the synchronous rectifier is turned off. Since the control signal of the synchronous rectifier also deviates, power reflux occurs, affecting the operation state of the converter.

[0104] comprehensive Figures 5 to 9 From the analysis, it can be seen that in order to ensure the correctness of the synchronous rectification control signal, T lag1 =T lag1 ', and T lag2 =max{T lag1', 0}, where max{T lag1 ',0} is T lag1 ' and 0. And when T lag1 >T lag1 ', the synchronous rectifier tube S 5 and S 8 Before shutting down rec Negative current occurs. Based on this, the present invention proposes Figure 1 The synchronous rectification control circuit shown in FIG. 1 realizes relatively ideal synchronous rectification control.

[0105] Corresponding to the above embodiment, the present invention also discloses a synchronous rectification control method.

[0106] See also Fig.10 , a flow chart of a synchronous rectification control method disclosed in an embodiment of the present invention, the method is applied to the digital controller in the synchronous rectification control circuit described in the above embodiment, the method comprising:

[0107] Step S101: In the current control cycle, a synchronous rectifier tube shutdown enable signal is output to the switch to turn on the switch, so that the current detection resistor collects the rectified current output by the synchronous rectifier tube at the shutdown moment.

[0108] The digital controller outputs a synchronous rectifier tube turn-off enable signal to the switch to turn on the switch. At this time, the current detection resistor collects the rectified current output by the synchronous rectifier tube at the turn-off moment and outputs it to the comparator.

[0109] Step S102, obtaining a result of a negative value determination of the rectified current output by the comparator.

[0110] The determination result includes: the rectified current is a negative value, or the rectified current is a non-negative value.

[0111] Step S103: Based on the determination result and the preset incremental time, determine a first turn-off delay time and a first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube.

[0112] The value of the preset increment time △T is limited by the accuracy of the synchronous rectification control signal output by the digital controller. In common digital controllers, the accuracy of △T can reach the level of picoseconds to nanoseconds, which is relatively close to the control period T. s Therefore, the present invention can realize relatively ideal synchronous rectification control through adaptive adjustment in multiple cycles.

[0113] Specifically, determining whether the determination result indicates that the rectified current is a negative value;

[0114] If yes, determining the difference between the initial value of the shutdown delay time and the preset incremental time as the first shutdown delay time;

[0115] If not, the sum of the initial value of the turn-off delay time and the preset incremental time is determined as the first turn-off delay time.

[0116] Determine whether the first shutdown delay time is less than 0;

[0117] If yes, determining that the value of the first activation delay time is 0;

[0118] If not, it is determined that the value of the first turn-on delay time is the same as the value of the first turn-off delay time.

[0119] That is, when the rectified current is determined to be a negative value, the first turn-off delay time T lag1 =T lag1 Initial-△T,

[0120] When the rectified current is determined to be a non-negative value, the first turn-off delay time T lag1 =T lag1 Initial + △T,

[0121] T lag1 Initial is the initial value of the shutdown delay time, which can be -T s / 2, where T s Represents the control period of the digital controller on the synchronous rectifier.

[0122] When determining the first turn-off delay time T lag1 After that, T lag1 The relationship between the value of and 0 is determined to determine the first opening delay time T lag2 If T lag1 <0, then T lag2 =0, if T lag1 ≥0, then T lag2 =T lag1 , thus ending the synchronous rectification control method within a single control cycle, until entering the next switching cycle, the same adaptive synchronous rectification control method is performed on the original basis. After multiple cycles, T lag1 Can be approached T successively lag1 ', to achieve a more ideal synchronous rectification control.

[0123] Step S104: Generate a synchronous rectification control signal based on the first turn-off delay time and the first turn-on delay time.

[0124] Step S105: Based on the synchronous rectification control signal, the synchronous rectification tube is controlled by the driving circuit.

[0125] Step S106 , entering the next control cycle to perform synchronous rectification control on the synchronous rectifier tube again until the error between the first turn-off delay time and the second turn-off delay time is within a preset range.

[0126] The second turn-off delay time is: the turn-off delay time of the rectified current zero-crossing relative to the primary switch tube.

[0127] In summary, the synchronous rectification control method disclosed in the present invention, when T lag1 ≤T lag1 ', T lag1 Gradually increase △T in each control cycle of the digital controller. After multiple control cycles, T lag1 Can be approached T successively lag1 ', until T lag1 >T lag1 ', before the synchronous rectifier is turned off, i is detected rec is a negative value, T lag1 Reduce △T, then T lag1 In T lag1 'Change within the range of ±△T, T lag1 With T lag1 The error of ' will be controlled within the range of △T. The value of △T is limited by the accuracy of the synchronous rectification control signal issued by the digital controller. The △T accuracy of common digital controllers can reach picoseconds to nanoseconds. s For example, this value is very small and can be ignored. Therefore, the present invention can achieve relatively ideal synchronous rectification control through adaptive adjustment in multiple cycles. In addition, the method proposed in the present invention does not depend on the parameters of the converter and the working mode of the converter, so it has the advantages of strong adaptability and good scalability.

[0128] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0129] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0130] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A synchronous rectification control circuit, It is characterized in that include: A current detection resistor, wherein the current detection resistor is connected to the output end of the synchronous rectifier tube of the main power circuit of the DC converter; A comparator, wherein an input terminal of the comparator is connected to the current detection resistor; a switch connected to an output terminal of the comparator; A driving circuit, wherein the driving circuit is connected to a control end of the synchronous rectifier; a digital controller, the digital controller being connected to the switch and the drive circuit respectively, and being used for outputting a synchronous rectifier tube shutdown enable signal to the switch to turn on the switch in a current control cycle, so that the current detection resistor collects the rectified current output by the synchronous rectifier tube at the shutdown moment, and obtains the determination result of the negative value determination of the rectified current output by the comparator, and determines the first shutdown delay time and the first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube based on the determination result and the preset incremental time, and generates a synchronous rectification control signal based on the first shutdown delay time and the first turn-on delay time, and performs synchronous rectification control on the synchronous rectifier tube through the drive circuit, and enters the next control cycle to perform synchronous rectification control on the synchronous rectifier tube again until the error between the first shutdown delay time and the second shutdown delay time is within a preset range; Among them, the second shutdown delay time is: the shutdown delay time of the rectifier current zero crossing relative to the primary switch tube, and the value of the preset incremental time is limited by the accuracy of the synchronous rectification control signal output by the digital controller.

2. The synchronous rectification control circuit according to claim 1, It is characterized in that The switch is a MOS tube.

3. A DC converter, It is characterized in that include: A DC converter main power circuit and a synchronous rectification control circuit as claimed in claim 1; The DC converter main power circuit comprises: a primary switch tube, a synchronous rectifier tube and a resonant circuit, wherein the resonant circuit is respectively connected to the output end of the primary switch tube and the input end of the synchronous rectifier tube; The current detection resistor in the synchronous sorting control circuit is connected to the output end of the synchronous rectifier tube, and the driving circuit in the synchronous sorting control circuit is connected to the control end of the synchronous rectifier tube.

4. The DC converter according to claim 3, It is characterized in that The resonant circuit comprises: a first transformer and a first resonant branch, wherein the first resonant branch comprises a first inductor and a first capacitor connected in series; The primary side of the first transformer is connected to the primary side switch tube through the first resonant branch, and the secondary side of the first transformer is connected to the synchronous rectifier tube.

5. The DC converter according to claim 3, It is characterized in that The resonant circuit comprises: a second transformer, a second resonant branch and a third resonant branch; The second resonant branch comprises a second inductor and a second capacitor connected in series; The third resonant branch comprises a third inductor and a third capacitor connected in series; The primary side of the second transformer is connected to the primary side switch tube through the second resonant branch, and the secondary side of the second transformer is connected to the synchronous rectifier tube through the third resonant branch.

6. A synchronous rectification control method, It is characterized in that A digital controller applied to the synchronous rectification control circuit of claim 1, the method comprising: In the current control cycle, a synchronous rectifier tube shutdown enable signal is output to the switch to turn on the switch, so that the current detection resistor collects the rectified current output by the synchronous rectifier tube at the shutdown moment; Obtaining a determination result of a negative value determination of the rectified current output by the comparator; Based on the determination result and the preset incremental time, determine a first turn-off delay time and a first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube, wherein the value of the preset incremental time is limited by the accuracy of the synchronous rectification control signal output by the digital controller; generating the synchronous rectification control signal based on the first turn-off delay time and the first turn-on delay time; Based on the synchronous rectification control signal, the synchronous rectification tube is synchronously controlled by the driving circuit; Entering the next control cycle, the synchronous rectifier tube is again subjected to synchronous rectification control until the error between the first turn-off delay time and the second turn-off delay time is within a preset range, wherein the second turn-off delay time is: the turn-off delay time of the rectifier current zero-crossing relative to the primary switch tube.

7. The synchronous rectification control method according to claim 6, It is characterized in that The determining, based on the determination result and the preset incremental time, a first turn-off delay time and a first turn-on delay time of the synchronous rectifier tube relative to the primary switch tube comprises: Determining whether the determination result indicates that the rectified current is a negative value; If yes, determining the difference between the initial value of the shutdown delay time and the preset incremental time as the first shutdown delay time; If not, the sum of the initial value of the turn-off delay time and the preset incremental time is determined as the first turn-off delay time.

8. The synchronous rectification control method according to claim 7, It is characterized in that Also includes: Determine whether the first shutdown delay time is less than 0; If yes, determining that the value of the first activation delay time is 0; If not, it is determined that the value of the first turn-on delay time is the same as the value of the first turn-off delay time.

9. The synchronous rectification control method according to claim 7 or 8, It is characterized in that The initial value of the shutdown delay time is -T s / 2, where T s Represents the control period of the digital controller on the synchronous rectifier.

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