LLC resonant converter synchronous rectification control circuit

Abstract

The invention discloses a synchronous rectification control circuit of an LLC resonant converter, and belongs to the technical field of synchronous rectification. In the synchronous rectification control circuit, the input end of a half-cycle detection module is electrically connected with an auxiliary winding of an LLC main circuit transformer; a first input end of the active rectification module is electrically connected with an auxiliary winding of an LLC main circuit transformer, and a second input end and a third input end of the active rectification module are electrically connected with the half-cycle detection module; a first input end and a second input end of the inflection point detection module are electrically connected with the half-cycle detection module, and a third input end of the inflection point detection module is electrically connected with the active rectification module; the turn-off signal prediction module is electrically connected with the inflection point detection module; the first input end of the synchronous signal generation module is electrically connected with the turn-off signal prediction module, the second input end is electrically connected with the first synchronous rectifier tube, the third input end is electrically connected with the second synchronous rectifier tube, the first output end is electrically connected with the first synchronous rectifier tube, and the second output end is electrically connected with the second synchronous rectifier tube.

Description

Technical Field

[0001] The present invention belongs to the technical field of synchronous rectification, and particularly relates to a synchronous rectification control circuit for an LLC resonant converter. Background Art

[0002] LLC resonant converters are widely used in medium and high power DC-DC conversion applications due to their advantages such as high efficiency and high power density.

[0003] However, when it is applied to high current output, if diode rectification is used for output, due to its large forward conduction voltage drop, serious conduction losses will occur.

[0004] To solve this problem, synchronous rectification technology is often adopted. By replacing the output rectifier diode with a synchronous switch tube with low on-resistance, the conduction loss of the switch tube is used to replace the conduction loss of the diode, thereby optimizing the efficiency of the output rectification circuit. Therefore, the ideal conduction signal of the synchronous switch tube should be as consistent as possible with the conduction time of the diode, as Figure 1 the driving signal v g_SR_E shown (as Figure 1 shown, which shows the key waveform diagram of a traditional synchronous rectification control circuit based on the detection of the drain-source voltage of the synchronous rectifier tube provided by the present invention).

[0005] Existing synchronous rectification schemes mainly fall into two categories. One is to detect the change in the secondary output current through a current sensor to generate the driving signal for the synchronous rectifier tube; the other is to detect the change in the drain-source voltage of the synchronous rectifier tube to generate the driving signal for the synchronous rectifier tube. Since the first scheme often requires adding a current detection circuit, the volume and cost of the synchronous rectification driving circuit are relatively high, and the loss is large. Therefore, existing commercial synchronous rectification chips often adopt the second scheme.

[0006] However, in an actual circuit, due to the presence of parasitic inductance in the circuit (as Figure 2 shown, which shows the equivalent circuit model diagram of a synchronous rectifier tube considering the influence of parasitic inductance provided by the present invention), the actually detected drain-source voltage waveform v DS_SR_A differs significantly from the ideal drain-source voltage waveform v DS_SR_E (as Figure 1 shown), which in turn causes the actual driving signal v g_SR_A of the synchronous rectifier tube to turn off prematurely. This causes the output current to depend on the body diode of the synchronous rectifier tube for freewheeling during the △t time, increasing the conduction loss on the output side.

[0007] Therefore, it is difficult for current existing technologies to achieve precise synchronization between the driving signal of the synchronous rectifier tube and the LLC secondary output current waveform. Summary of the Invention

[0008] In order to solve the technical problem that it is difficult for current existing technologies to achieve precise synchronization between the driving signal of the synchronous rectifier and the waveform of the LLC secondary side output current, the present invention provides a synchronous rectification control circuit for an LLC resonant converter.

[0009] The present invention provides a synchronous rectification control circuit for an LLC resonant converter, including: a half-cycle detection module, an active rectification module, an inflection point detection module, a turn-off signal prediction module, and a synchronization signal generation module;

[0010] The input end of the half-cycle detection module is electrically connected to the auxiliary winding of the LLC main circuit transformer;

[0011] The first input end of the active rectification module is electrically connected to the auxiliary winding of the LLC main circuit transformer, the second input end of the active rectification module is electrically connected to the first output end of the half-cycle detection module, and the third input end of the active rectification module is electrically connected to the second output end of the half-cycle detection module;

[0012] The first input end of the inflection point detection module is electrically connected to the first output end of the half-cycle detection module, the second input end of the inflection point detection module is electrically connected to the second output end of the half-cycle detection module, and the third input end of the inflection point detection module is electrically connected to the output end of the active rectification module;

[0013] The input end of the turn-off signal prediction module is electrically connected to the output end of the inflection point detection module;

[0014] The first input end of the synchronization signal generation module is electrically connected to the output end of the turn-off signal prediction module, the second input end of the synchronization signal generation module is electrically connected to the drain of the first synchronous rectifier, the third input end of the synchronization signal generation module is electrically connected to the drain of the second synchronous rectifier, the first output end of the synchronization signal generation module is electrically connected to the gate of the first synchronous rectifier, and the second output end of the synchronization signal generation module is electrically connected to the gate of the second synchronous rectifier.

[0015] Compared with the existing technology, the present invention has at least the following beneficial technical effects:

[0016] In the present invention, the synchronous rectification control signal can be accurately obtained according to the change of the output current. By solving the problem of premature turn-off caused by parasitic parameters in the traditional synchronous rectification circuit, the additional conduction loss caused by diode freewheeling can be effectively reduced, thereby improving the overall efficiency of the converter. Description of the Drawings

[0017] The above characteristics, technical features, advantages and their implementation manners of the present invention will be further described below in a clear and understandable manner in conjunction with the accompanying drawings.

[0018] Figure 1 is a key waveform diagram of a synchronous rectification control circuit based on the detection of the drain-source voltage of a synchronous rectifier tube provided by the present invention;

[0019] Figure 2 is an equivalent circuit model diagram of a synchronous rectifier tube considering the influence of parasitic inductance provided by the present invention;

[0020] Figure 3 is a schematic structural diagram of a synchronous rectification control circuit of an LLC resonant converter provided by the present invention;

[0021] Figure 4 is a circuit principle block diagram of a synchronous rectification control circuit of an LLC resonant converter provided by the present invention;

[0022] Figure 5 is a key waveform diagram of a half-bridge LLC resonant converter operating in the continuous current mode provided by the present invention;

[0023] Figure 6 is a key waveform diagram of a half-bridge LLC resonant converter operating in the discontinuous current mode provided by the present invention. Specific Embodiments

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings and other embodiments can be obtained.

[0025] For the sake of simplicity of the drawings, only the parts related to the invention are schematically shown in each drawing, and they do not represent the actual structure of the product. In addition, for the sake of simplicity and easy understanding of the drawings, in some drawings, only one of the components with the same structure or function is schematically shown, or only one of them is marked. In this document, "one" not only means "only this one", but also means "more than one" situation.

[0026] It should also be further understood that the term "and / or" used in the specification and appended claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0027] In this text, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", and "linked" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0028] In addition, in the description of the present invention, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0029] Refer to the appended Figure 3 illustrates a schematic structural diagram of a synchronous rectification control circuit of an LLC resonant converter provided by the present invention;

[0030] Refer to the appended Figure 4 illustrates a circuit principle block diagram of a synchronous rectification control circuit of an LLC resonant converter provided by the present invention;

[0031] The synchronous rectification control circuit of the present invention is applicable to the occasion where the LLC topology operates at low voltage and high current, and is also applicable to both the current continuous mode and the current discontinuous mode. The following combines the main circuit topology with a half-bridge LLC input and a full-wave rectification output, and combines Figure 3 and Figure 4 to make a detailed description of the basic principle of realizing the synchronous rectification control circuit of the LLC resonant converter in the present invention.

[0032] The synchronous rectification control circuit of the present invention uses the traditional drain-source voltage detection method for the turn-on of the synchronous rectifier tube, but proposes a new solution to the problem of premature turn-off caused by the influence of the loop parasitic inductance on the traditional drain-source voltage detection. According to the basic relationship between the transformer winding voltage and the output current waveform of the LLC resonant converter, combined with Figure 3 and Figure 4 it can be known that when the output current decreases to zero, the voltage on the corresponding transformer winding begins to drop, that is, there is a corresponding voltage waveform inflection point. Therefore, by detecting this voltage inflection point, the change of the actual output current can be known. However, even the most accurate inflection point detection circuit, due to problems such as control circuit delay, will cause the finally generated turn-off signal to lag behind the moment when the output current decreases to zero. This will cause the output current to increase in the reverse direction, thereby bringing additional conduction losses, which is also not desired in synchronous rectification control.

[0033] To overcome the above problems, the present invention adopts a method based on predictive control. In fact, under steady-state operating conditions, the on-periods of the synchronous rectifier tubes in two consecutive cycles are almost the same, so the turn-off moment of the next cycle can be estimated based on the turn-off signal of the previous synchronous rectifier tube. Even under dynamic regulation, since this predictive control method only needs to estimate the next signal, it also has good dynamic performance. At the same time, by adding a compensation signal △vcp to the freewheeling period of the actual output current in the control circuit, the problem of the turn-off lag of the synchronous rectifier tube caused by the control circuit delay can be effectively compensated, and a high-precision synchronous rectification control signal corresponding to the change of the output current can be obtained.

[0034] A synchronous rectification control circuit for an LLC resonant converter provided by the present invention is applicable to both the continuous conduction mode (CCM for short) and the discontinuous conduction mode (DCM for short), and can effectively overcome the problem that the traditional commercial synchronous rectification chip causes the synchronous rectifier tube to turn off in advance due to parasitic parameters.

[0035] A synchronous rectification control circuit for an LLC resonant converter provided by the present invention includes: a half-cycle detection module 101, an active rectification module 102, an inflection point detection module 103, a turn-off signal prediction module 104, and a synchronization signal generation module 105;

[0036] The input end of the half-cycle detection module 101 is electrically connected to the auxiliary winding of the LLC main circuit transformer, and is used to receive the signal v that reflects the voltage change of the primary winding transmitted by the auxiliary winding of the LLC main circuit transformer aux ;

[0037] The first input end of the active rectification module 102 is electrically connected to the auxiliary winding of the LLC main circuit transformer, and is used to receive the signal v that reflects the voltage change of the primary winding transmitted by the auxiliary winding of the LLC main circuit transformer aux , the second input end of the active rectification module 102 is electrically connected to the first output end of the half-cycle detection module 101, and is used to receive the first output signal v of the half-cycle detection module 101 p , the third input end of the active rectification module 102 is electrically connected to the second output end of the half-cycle detection module 101, and is used to receive the second output signal v of the half-cycle detection module 101 n ;

[0038] The first input end of the inflection point detection module 103 is electrically connected to the first output end of the half-cycle detection module 101, and is used to receive the first output signal v of the half-cycle detection module 101 p, the second input terminal of the inflection point detection module 103 is electrically connected to the second output terminal of the half-cycle detection module 101, and is used to receive the second output signal v of the half-cycle detection module 101 n , the third input terminal of the inflection point detection module 103 is electrically connected to the output terminal of the active rectification module 102, and is used to receive the output signal v of the active rectification module 102 aux_rec ;

[0039] The input terminal of the turn-off signal prediction module 104 is electrically connected to the output terminal of the inflection point detection module 103, and is used to receive the output signal v of the inflection point detection module 103 sm ;

[0040] The first input terminal of the synchronization signal generation module 105 is electrically connected to the output terminal of the turn-off signal prediction module 104, and is used to receive the output signal v of the turn-off signal prediction module 104 g_SR_off , the second input terminal of the synchronization signal generation module 105 is electrically connected to the drain of the first synchronous rectifier tube S1, and is used to receive the drain-source voltage signal v of the first synchronous rectifier tube S1 ds_SR1 , the third input terminal of the synchronization signal generation module 105 is electrically connected to the drain of the second synchronous rectifier tube S2, and is used to receive the drain-source voltage signal v of the second synchronous rectifier tube S2 ds_SR2 , the first output terminal of the synchronization signal generation module 105 is electrically connected to the gate of the first synchronous rectifier tube S1, the second output terminal of the synchronization signal generation module 105 is electrically connected to the gate of the second synchronous rectifier tube S2, and the first output terminal and the second output terminal of the synchronization signal generation module 105 respectively output the first synchronous rectification drive signal v g_SR1 and the second synchronous rectification drive signal v g_SR2 to control the first synchronous rectifier tube S1 and the second synchronous rectifier tube S2 for the secondary side output of the LLC resonant converter.

[0041] In the present invention, according to the change of the output current, the synchronous rectification control signal can be accurately obtained. By solving the problem of premature turn-off caused by parasitic parameters in the traditional synchronous rectification circuit, the additional conduction loss caused by diode freewheeling can be effectively reduced, thereby improving the overall efficiency of the converter.

[0042] In a possible implementation manner, the half-cycle detection module 101 specifically includes: a first comparator Uc1, a second comparator Uc2, a first voltage source -V bias , a second voltage source V bias , a first resistor R1, a second resistor R2, a first control switch S p and a second control switch S n ;

[0043] The positive input terminal of the first comparator Uc1 is electrically connected to the auxiliary winding of the LLC main circuit transformer, and receives the signal v that reflects the voltage change of the primary winding transmitted from the auxiliary winding Na of the LLC main circuit transformer. aux , the negative input terminal of the first comparator Uc1 is electrically connected to the negative terminal of the first voltage source -V bias , the output terminal of the first comparator Uc1 is electrically connected to the first end of the first resistor R1; the positive terminal of the first voltage source -V bias is electrically connected to the secondary ground of the transformer; the second end of the first resistor R1 is respectively electrically connected to the first end of the first control switch S p and the control terminal of the second control switch S n to form the first output signal v p of the half-cycle detection module 101; the second end of the first control switch S p is electrically connected to the secondary ground of the transformer, and the control terminal of the first control switch S p is respectively electrically connected to the first end of the second control switch S n and the first end of the second resistor R2 to form the second output signal v n of the half-cycle detection module 101; the negative input terminal of the second comparator Uc2 is electrically connected to the auxiliary winding of the LLC main circuit transformer, and receives the signal v aux that reflects the voltage change of the primary winding transmitted from the auxiliary winding Na of the LLC main circuit transformer, the positive input terminal of the second comparator Uc2 is electrically connected to the positive terminal of the second voltage source V bias , the output terminal of the second comparator Uc2 is electrically connected to the second end of the second resistor R2; the negative terminal of the second voltage source V bias is electrically connected to the secondary ground of the transformer; the second end of the second control switch S n is electrically connected to the secondary ground of the transformer.

[0044] In a possible implementation manner, the active rectification module 102 specifically includes: a level inversion circuit, an operational amplifier U op1 , a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, and a first capacitor C1;

[0045] The level inversion circuit includes four switches, namely a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4;

[0046] The first end of the first switch S1 is electrically connected to the auxiliary winding of the LLC main circuit transformer and the first end of the third switch S3 respectively. The second end of the first switch S1 is electrically connected to the first end of the switch S2, the first end of the first capacitor C1, and the first end of the fourth resistor R4 respectively. The control end of the first switch S1 is electrically connected to the first output end of the half-cycle detection module 101. The second end of the second switch S2 is electrically connected to the first end of the fourth switch S4 and the secondary side ground of the transformer respectively. The control end of the second switch S2 is electrically connected to the second output end of the half-cycle detection module 101. The second end of the third switch S3 is electrically connected to the second end of the first capacitor C1, the second end of the fourth switch S4, and the first end of the fifth resistor R5 respectively. The control end of the third switch S3 is electrically connected to the second output end of the half-cycle detection module 101. The control end of the fourth switch S4 is electrically connected to the first output end of the half-cycle detection module 101. The second end of the fourth resistor R4 is electrically connected to the first end of the third resistor R3 and the non-inverting input terminal of the operational amplifier U op1 respectively. The second end of the third resistor R3 is electrically connected to the secondary side ground of the transformer. The second end of the fifth resistor R5 is electrically connected to the first end of the sixth resistor R6 and the inverting input terminal of the operational amplifier U op1 respectively. The output end of the operational amplifier U op1 is electrically connected to the second end of the sixth resistor R6, forming the output signal v aux_rec of the active rectification module 102;

[0047] The level inversion circuit is used to achieve the holding of the positive part and the inversion of the negative part of the auxiliary winding voltage signal v aux within the switching period.

[0048] In a possible implementation manner, the inflection point detection module 103 specifically includes: an inflection point detection circuit, a first RS flip-flop Urs1, a second RS flip-flop Urs2, and an OR gate Uc7;

[0049] The inflection point detection circuit includes a third comparator Uc3, a second capacitor C2, a seventh resistor R7, and an eighth resistor R8;

[0050] The first end of the seventh resistor R7 is electrically connected to the inverting input terminal of the third comparator Uc3 to receive the output signal v aux_rec; The second end of the seventh resistor R7 is electrically connected to the non-inverting input terminal of the third comparator Uc3, the eighth resistor R8, and the first end of the second capacitor C2 respectively; the second end of the eighth resistor R8 is electrically connected to the second end of the second capacitor C2 and is connected to the secondary ground of the transformer; the output terminal of the third comparator Uc3 is electrically connected to the reset terminals of the first RS flip-flop Urs1 and the second RS flip-flop Urs2 respectively; the set terminal of the first RS flip-flop Urs1 is electrically connected to the first output terminal of the half-cycle detection module 101, and the non-inverting output terminal of the first RS flip-flop Urs1 is electrically connected to the first terminal of the OR gate Uc7; the set terminal of the second RS flip-flop Urs2 is electrically connected to the second output terminal of the half-cycle detection module 101, and the non-inverting output terminal of the second RS flip-flop Urs2 is electrically connected to the second terminal of the OR gate Uc7; the output terminal of the OR gate Uc7 outputs a control signal v sm ;

[0051] The inflection point detection circuit is used to detect the moment when the transformer winding voltage changes. The moment when the transformer winding voltage changes corresponds to the moment when the secondary output current drops to zero.

[0052] In a possible implementation manner, the turn-off signal prediction module 104 specifically includes: a third capacitor C3, a fourth capacitor C4, a ninth resistor R9, a tenth resistor R 10 , an inverter Uc8, a delay circuit Uc9, an AND gate Uc10, a subtractor Uc11, a fourth comparator Uc4, a third voltage source Vcc, a current source Idc1, a fifth switch S5, and a sixth switch S6;

[0053] The control terminal of the fifth switch S5 is electrically connected to the output terminal of the inflection point detection module 103, the first terminal of the inverter Uc8, and the first terminal of the delay circuit Uc9 respectively. The first terminal of the fifth switch S5 is electrically connected to the first terminal of the current source Idc1, the first terminal of the sixth switch S6, and the first terminal of the third capacitor C3 respectively. The second terminal of the fifth switch S5 is electrically connected to the second terminal of the third capacitor C3 and the secondary ground of the transformer respectively. The second terminal of the current source Idc1 is connected to the secondary ground of the transformer. The second terminal of the inverter Uc8 is electrically connected to the first terminal of the AND gate Uc10. The second terminal of the delay circuit Uc9 is electrically connected to the second terminal of the AND gate Uc10. The output terminal of the AND gate Uc10 is electrically connected to the control terminal of the sixth switch S6. The second terminal of the sixth switch S6 is electrically connected to the first terminal of the fourth capacitor C4. The negative input terminal of the fourth comparator Uc4 is electrically connected to the positive input terminal of the subtractor Uc11. The second terminal of the fourth capacitor C4 is connected to the secondary ground of the transformer. The negative input terminal of the subtractor Uc11 is electrically connected to the first terminal of the ninth resistor R9 and the tenth resistor R 10 respectively. The output terminal of the subtractor Uc11 is electrically connected to the positive input terminal of the fourth comparator Uc4. The second terminal of the ninth resistor R9 is electrically connected to the positive terminal of the third voltage source Vcc. The negative terminal of the third voltage source Vcc is grounded. The second terminal of the tenth resistor R 10 is grounded. The output terminal of the fourth comparator Uc4 outputs the turn-off signal v of the synchronous rectifier tube g_SR_off ;

[0054] Among them, the current source Idc1, the third capacitor C3, and the fifth switch S5 together constitute a sawtooth wave generating circuit, and the sawtooth wave generating circuit is used to reflect the duration of the output current freewheeling;

[0055] By changing the ratio relationship between the ninth resistor R9 and the tenth resistor R 10 , the amplitude △vcp of the compensation signal is changed to adjust the early turn-off time.

[0056] In a possible implementation manner, the synchronization signal generation module 105 specifically includes: a fifth comparator Uc5, a sixth comparator Uc6, a third RS flip-flop Urs3, a fourth RS flip-flop Urs4, a voltage source V TH_on , a first driving module 1, and a second driving module 2;

[0057] The positive input terminal of the fifth comparator Uc5 is electrically connected to the drain of the first synchronous rectifier tube S1 to receive the drain voltage signal v of the first synchronous rectifier tube S1 ds_SR1 , and the negative input terminal of the fifth comparator Uc5 is respectively connected to the voltage source VTH_on The positive terminal is electrically connected to the negative input terminal of the sixth comparator Uc6, and the output terminal of the fifth comparator Uc5 is electrically connected to the set terminal of the third RS flip-flop Urs3; the positive input terminal of the sixth comparator Uc6 is electrically connected to the drain-source terminal of the second synchronous rectifier S2 to receive the drain-source voltage signal v of the second synchronous rectifier S2 ds_SR2 , and the output terminal of the sixth comparator Uc6 is electrically connected to the set terminal of the third RS flip-flop Urs3; the negative terminal of the voltage source V TH_on is connected to the secondary ground of the transformer; the reset terminal of the third RS flip-flop Urs3 is electrically connected to the output terminal of the turn-off signal prediction module 104 and the reset terminal of the fourth RS flip-flop Urs4 respectively, and the positive output terminal of the third RS flip-flop Urs3 is electrically connected to the input terminal of the first driving module 1; the positive output terminal of the fourth RS flip-flop Urs4 is electrically connected to the input terminal of the second driving module 2; the output terminal of the first driving module 1 is electrically connected to the gate of the first synchronous rectifier S1 to output the first synchronous rectification driving signal v g_SR1 ; the output terminal of the second driving module 2 is electrically connected to the gate of the second synchronous rectifier S2 to output the second synchronous rectification driving signal v g_SR2 ;

[0058] Among them, the fifth comparator Uc5 and the sixth comparator Uc6 are used to generate the synchronous rectifier turn-on signal, and the third RS flip-flop Urs3 and the fourth RS flip-flop Urs4 are used to generate the synchronous rectification driving signal.

[0059] In a possible implementation manner, the signal v reflecting the change of the primary winding voltage transmitted by the auxiliary winding of the LLC main circuit transformer is aux obtained by taking from the non-homonymous end of the secondary winding Ns1 or the homonymous end of the secondary winding Ns2.

[0060] In a possible implementation manner, the primary switching tube in the LLC main circuit adopts pulse frequency modulation (PFM).

[0061] In a possible implementation manner, the synchronous rectification control circuit of the LLC resonant converter is arranged in a half-bridge LLC topology or a full-bridge LLC topology.

[0062] Refer to the attached specification Figure 5 , which shows a key waveform diagram of a half-bridge LLC resonant converter provided by the present invention operating in the current continuous mode;

[0063] Refer to the attached specification Figure 6, which shows the key waveform diagram of a half-bridge LLC resonant converter operating in the current discontinuous mode provided by the present invention.

[0064] Figure 5 and Figure 6 are respectively the main waveforms of the first embodiment formed by the synchronous rectification control circuit of the present invention and the main circuit of the half-bridge LLC resonant converter operating in the current continuous mode and the discontinuous mode. According to the waveforms, it can be seen that the synchronous rectification control circuit is applicable to both the current continuous mode and the discontinuous mode.

[0065] In a possible implementation manner, the control process of the LLC resonant converter synchronous rectification control circuit includes:

[0066] S1: Comparing the drain-source voltage signal of the synchronous rectifier tube with the threshold voltage to generate a synchronous rectifier tube turn-on signal;

[0067] S2: Generating a synchronous rectifier tube turn-off signal by using an inflection point detection circuit according to the voltage of the auxiliary winding of the transformer;

[0068] S3: Generating a synchronous rectification drive signal according to the turn-on signal and the turn-off signal.

[0069] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0070] In the present invention, the synchronous rectification control signal can be accurately obtained according to the change of the output current. By solving the problem of premature turn-off caused by parasitic parameters in the traditional synchronous rectification circuit, the additional conduction loss caused by diode freewheeling can be effectively reduced, thereby improving the overall efficiency of the converter.

[0071] The technical features of the above embodiments can be combined arbitrarily. For the sake of brief description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0072] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. An LLC resonant converter synchronous rectification control circuit, characterized in that, Including: A half-cycle detection module, an active rectification module, an inflection point detection module, a turn-off signal prediction module, and a synchronization signal generation module; The input end of the half-cycle detection module is electrically connected to the auxiliary winding of the LLC main circuit transformer; The first input end of the active rectification module is electrically connected to the auxiliary winding of the LLC main circuit transformer, the second input end of the active rectification module is electrically connected to the first output end of the half-cycle detection module, and the third input end of the active rectification module is electrically connected to the second output end of the half-cycle detection module; The first input end of the inflection point detection module is electrically connected to the first output end of the half-cycle detection module, the second input end of the inflection point detection module is electrically connected to the second output end of the half-cycle detection module, and the third input end of the inflection point detection module is electrically connected to the output end of the active rectification module; The input end of the turn-off signal prediction module is electrically connected to the output end of the inflection point detection module; The first input end of the synchronization signal generation module is electrically connected to the output end of the turn-off signal prediction module, the second input end of the synchronization signal generation module is electrically connected to the drain of the first synchronous rectifier tube, the third input end of the synchronization signal generation module is electrically connected to the drain of the second synchronous rectifier tube, the first output end of the synchronization signal generation module is electrically connected to the gate of the first synchronous rectifier tube, and the second output end of the synchronization signal generation module is electrically connected to the gate of the second synchronous rectifier tube.

2. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein the half-cycle detection module specifically comprises: A first comparator, a second comparator, a first voltage source, a second voltage source, a first resistor, a second resistor, a first control switch, and a second control switch; The non-inverting input end of the first comparator is electrically connected to the auxiliary winding of the LLC main circuit transformer, the inverting input end of the first comparator is electrically connected to the negative end of the first voltage source, and the output end of the first comparator is electrically connected to the first end of the first resistor; the positive end of the first voltage source is electrically connected to the secondary ground of the transformer; the second end of the first resistor is electrically connected to the first end of the first control switch and the control end of the second control switch respectively; the second end of the first control switch is electrically connected to the secondary ground of the transformer, and the control end of the first control switch is electrically connected to the first end of the second control switch and the first end of the second resistor respectively; the inverting input end of the second comparator is electrically connected to the auxiliary winding of the LLC main circuit transformer, the non-inverting input end of the second comparator is electrically connected to the positive end of the second voltage source, and the output end of the second comparator is electrically connected to the second end of the second resistor; the negative end of the second voltage source is electrically connected to the secondary ground of the transformer; the second end of the second control switch is electrically connected to the secondary ground of the transformer.

3. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein the active rectification module specifically includes: A level inversion circuit, an operational amplifier, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a first capacitor; The level inversion circuit includes four switches, namely a first switch, a second switch, a third switch, and a fourth switch; The first end of the first switch is electrically connected to the auxiliary winding of the LLC main circuit transformer and the first end of the third switch respectively. The second end of the first switch is electrically connected to the first end of the switch, the first end of the first capacitor, and the first end of the fourth resistor respectively. The control end of the first switch is electrically connected to the first output end of the half-cycle detection module. The second end of the second switch is electrically connected to the first end of the fourth switch and the secondary ground of the transformer respectively. The control end of the second switch is electrically connected to the second output end of the half-cycle detection module. The second end of the third switch is electrically connected to the second end of the first capacitor, the second end of the fourth switch, and the first end of the fifth resistor respectively. The control end of the third switch is electrically connected to the second output end of the half-cycle detection module. The control end of the fourth switch is electrically connected to the first output end of the half-cycle detection module. The second end of the fourth resistor is electrically connected to the first end of the third resistor and the non-inverting input terminal of the operational amplifier respectively. The second end of the third resistor is connected to the secondary ground of the transformer. The second end of the fifth resistor is electrically connected to the first end of the sixth resistor and the inverting input terminal of the operational amplifier respectively. The output end of the operational amplifier is electrically connected to the second end of the sixth resistor. The level inversion circuit is used to hold the positive part and invert the negative part of the auxiliary winding voltage signal within the switching period.

4. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein the inflection point detection module specifically includes: An inflection point detection circuit, a first RS flip-flop, a second RS flip-flop, and an OR gate; The inflection point detection circuit includes a third comparator, a second capacitor, a seventh resistor, and an eighth resistor; The first end of the seventh resistor is electrically connected to the inverting input terminal of the third comparator. The second end of the seventh resistor is electrically connected to the non-inverting input terminal of the third comparator, the eighth resistor, and the first end of the second capacitor respectively. The second end of the eighth resistor is electrically connected to the second end of the second capacitor and is connected to the secondary ground of the transformer. The output end of the third comparator is electrically connected to the reset terminal of the first RS flip-flop and the reset terminal of the second RS flip-flop respectively. The set terminal of the first RS flip-flop is electrically connected to the first output end of the half-cycle detection module. The non-inverting output terminal of the first RS flip-flop is electrically connected to the first end of the OR gate. The set terminal of the second RS flip-flop is electrically connected to the second output end of the half-cycle detection module. The non-inverting output terminal of the second RS flip-flop is electrically connected to the second end of the OR gate. The output end of the OR gate outputs a control signal; The inflection point detection circuit is used to detect the moment when the transformer winding voltage changes. The moment when the transformer winding voltage changes corresponds to the moment when the secondary output current drops to zero.

5. The synchronous rectification control circuit of the LLC resonant converter according to claim 1, wherein the turn-off signal prediction module specifically comprises: A third capacitor, a fourth capacitor, a ninth resistor, a tenth resistor, an inverter, a delay circuit, an AND gate, a subtractor, a fourth comparator, a third voltage source, a current source, a fifth switch, and a sixth switch; The control terminal of the fifth switch is electrically connected to the output terminal of the inflection point detection module, the first terminal of the inverter, and the first terminal of the delay circuit respectively. The first terminal of the fifth switch is electrically connected to the first terminal of the current source, the first terminal of the sixth switch, and the first terminal of the third capacitor respectively. The second terminal of the fifth switch is electrically connected to the second terminal of the third capacitor and the secondary ground of the transformer respectively. The second terminal of the current source is connected to the secondary ground of the transformer. The second terminal of the inverter is electrically connected to the first terminal of the AND gate. The second terminal of the delay circuit is electrically connected to the second terminal of the AND gate. The output terminal of the AND gate is electrically connected to the control terminal of the sixth switch. The second terminal of the sixth switch is electrically connected to the first terminal of the fourth capacitor. The negative input terminal of the fourth comparator is electrically connected to the positive input terminal of the subtractor. The second terminal of the fourth capacitor is connected to the secondary ground of the transformer. The negative input terminal of the subtractor is electrically connected to the first terminals of the ninth resistor and the tenth resistor respectively. The output terminal of the subtractor is electrically connected to the positive input terminal of the fourth comparator. The second terminal of the ninth resistor is electrically connected to the positive terminal of the third voltage source. The negative terminal of the third voltage source is grounded. The second terminal of the tenth resistor is grounded. The output terminal of the fourth comparator outputs the turn-off signal of the synchronous rectifier tube. Wherein, the current source, the third capacitor and the fifth switch together constitute a sawtooth wave generating circuit, and the sawtooth wave generating circuit is used to reflect the output current freewheeling duration. By changing the ratio relationship between the ninth resistor and the tenth resistor, the amplitude of the compensation signal is changed to adjust the early turn-off time.

6. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein the synchronous signal generating module specifically comprises: A fifth comparator, a sixth comparator, a third RS flip-flop, a fourth RS flip-flop, a voltage source, a first driving module and a second driving module; The positive input terminal of the fifth comparator is electrically connected to the drain of the first synchronous rectifier tube. The negative input terminal of the fifth comparator is electrically connected to the positive terminal of the voltage source and the negative input terminal of the sixth comparator respectively. The output terminal of the fifth comparator is electrically connected to the set terminal of the third RS flip-flop. The positive input terminal of the sixth comparator is electrically connected to the drain of the second synchronous rectifier tube. The output terminal of the sixth comparator is electrically connected to the set terminal of the third RS flip-flop. The negative terminal of the voltage source is connected to the secondary ground of the transformer. The reset terminal of the third RS flip-flop is electrically connected to the output terminal of the turn-off signal prediction module and the reset terminal of the fourth RS flip-flop respectively. The positive output terminal of the third RS flip-flop is electrically connected to the input terminal of the first driving module. The positive output terminal of the fourth RS flip-flop is electrically connected to the input terminal of the second driving module. The output terminal of the first driving module is electrically connected to the gate of the first synchronous rectifier tube to output the first synchronous rectifier driving signal. The output terminal of the second driving module is electrically connected to the gate of the second synchronous rectifier tube to output the second synchronous rectifier driving signal. Among them, the fifth comparator and the sixth comparator are used to generate a synchronous rectifier turn-on signal, and the third RS flip-flop and the fourth RS flip-flop are used to generate a synchronous rectifier drive signal.

7. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein The signal reflecting the change in the primary winding voltage transmitted by the auxiliary winding of the LLC main circuit transformer is obtained from the opposite-named end of the secondary winding or the same-named end of the secondary winding.

8. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein, The primary switching tube in the LLC main circuit adopts pulse frequency modulation.

9. The LLC resonant converter synchronous rectification control circuit according to claim 1, characterized in that The synchronous rectification control circuit of the LLC resonant converter is arranged in a half-bridge-based LLC topology or in a full-bridge-based LLC topology.

10. The LLC resonant converter synchronous rectification control circuit according to claim 1, wherein The control process of the synchronous rectification control circuit of the LLC resonant converter includes: S1: Comparing the drain-source voltage signal of the synchronous rectifier with the threshold voltage to generate a synchronous rectifier turn-on signal; S2: Generating a synchronous rectifier turn-off signal by using an inflection point detection circuit according to the voltage of the transformer auxiliary winding; S3: Generating a synchronous rectifier drive signal according to the turn-on signal and the turn-off signal.

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