Patent Publication Number: US-2023155477-A1

Title: Resonance conversion device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 110142627, filed on Nov. 16, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a resonance conversion device, and more particularly to a resonance conversion device capable of achieving zero current cutoff under different loads. 
     Description of Related Art 
     An LLC resonance converter has the advantages of soft switching and high conversion efficiency, and adopts variable frequency operation to adjust the voltage gain. Therefore, the LLC resonance converter can achieve the function of stable voltage output. Based on the analysis of its soft switching characteristics, the synchronous rectification switch located on the secondary side of the LLC resonance converter is designed to have zero current cutoff to reduce the switching loss during transition and improve the conversion efficiency of the converter. 
     As shown in  FIG.  1   , in order to prevent a first synchronous rectification switch and a second synchronous rectification switch from being turned on at the same time, causing safety concerns such as a short circuit in the secondary side loop, the first synchronous rectification switch and the second synchronous rectification switch are designed to be turned on with a delay based on a dead time length DT. 
     However, under a condition where the load is large, the current value of the current IQ 1  flowing through the first synchronous rectification switch and the current value of the current IQ 2  flowing through the second synchronous rectification switch are also larger. Therefore, the current IQ 1  flowing through the first synchronous rectification switch and the current IQ 2  flowing through the second synchronous rectification switch are discharged to 0 ampere within a dead time length DT. Hence, the current IQ 1  flowing through the first synchronous rectification switch and the current IQ 2  flowing through the second synchronous rectification switch have current differences ST 1  to ST 4  that are not equal to 0 ampere within the dead time length DT. The first synchronous rectification switch and the second synchronous rectification switch cannot achieve zero current cutoff. The current differences ST 1  to ST 4  increase the switching loss, and thus the conversion efficiency cannot be optimized. 
     SUMMARY 
     The disclosure provides a resonance conversion device capable of achieving zero current cutoff under different loads. 
     The resonance conversion device of the disclosure includes an LLC synchronous resonance converter, a synchronous rectification controller, and a dead time adjustment circuit. The LLC synchronous resonance converter includes a resonance tank, a main transformer, and multiple synchronous rectification switches. The synchronous rectification controller is coupled to the LLC synchronous resonance converter and controls the multiple synchronous rectification switches. The multiple synchronous rectification switches are turned on with a delay based on a dead time length. The dead time adjustment circuit is coupled to the LLC synchronous resonance converter and the synchronous rectification controller. The dead time adjustment circuit inductively couples an electric energy at an output of the LLC synchronous resonance converter to the resonance tank, and provides a dead time control signal according to a resonance voltage variation of the resonance tank so that the synchronous rectification controller adjusts the dead time length according to the dead time control signal. 
     Based on the above, the dead time adjustment circuit inductively couples the electric energy at the output of the LLC synchronous resonance converter to the resonance tank, and provides the dead time control signal according to the resonance voltage variation of the resonance tank so that the synchronous rectification controller adjusts the dead time length according to the dead time control signal. The dead time adjustment circuit can provide a corresponding dead time length according to different loads. Therefore, the disclosure can achieve zero current cutoff under different loads. In this way, the conversion efficiency of the LLC synchronous resonance converter can be optimized under different loads. 
     In order to make the aforementioned features and advantages of the disclosure comprehensible, embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram showing that a first synchronous rectification switch and a second synchronous rectification switch cannot achieve zero current cutoff. 
         FIG.  2    is a schematic diagram of a resonance conversion device according to the first embodiment of the disclosure. 
         FIG.  3    is a schematic diagram of achieving zero current cutoff according to an embodiment of the disclosure. 
         FIG.  4    is a schematic diagram of a resonance conversion device according to the second embodiment of the disclosure. 
         FIG.  5    is a schematic diagram of a circuit of a resonance conversion device according to an embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Some embodiments of the disclosure accompanied with drawings are described in detail as follows. The reference numerals used in the following description are regarded as the same or similar elements when the same reference numerals appear in different drawings. These embodiments are only a part of the disclosure, and do not disclose all the possible implementation modes of the disclosure. To be more precise, the embodiments are only examples in the scope of the claims of the disclosure. 
     Please refer to  FIG.  2   , which is a schematic diagram of a resonance conversion device according to the first embodiment of the disclosure. In the embodiment, the resonance conversion device  100  includes an LLC synchronous resonance converter  110 , a synchronous rectification controller  120 , and a dead time adjustment circuit  130 . The LLC synchronous resonance converter  110  includes power switches Q 1  and Q 2 , a resonance tank  111 , a main transformer TR 1 , synchronous rectification switches Q 3  and Q 4 , and an output capacitor CO. The power switch Q 1  performs a switching operation in response to a control signal GD 1 . The power switch Q 2  performs a switching operation in response to a control signal GD 2 . The synchronous rectification controller  120  is coupled to the LLC synchronous resonance converter  110 , and controls the synchronous rectification switches Q 3  and Q 4 . In the embodiment, the synchronous rectification controller  120  provides control signals GD 3  and GD 4 . The synchronous rectification switch Q 3  performs a switching operation in response to the control signal GD 3 . The synchronous rectification switch Q 4  performs a switching operation in response to the control signal GD 4 . In addition, under the control of the synchronous rectification controller  120 , the synchronous rectification switches Q 3  and Q 4  are turned on with a delay based on a dead time length DT. 
     In the embodiment, the dead time adjustment circuit  130  is coupled to the LLC synchronous resonance converter  110  and the synchronous rectification controller  120 . The dead time adjustment circuit  130  inductively couples an electric energy at an output of the LLC synchronous resonance converter  110  (i.e., output power VO) to the resonance tank  111 , and provides a dead time control signal SS according to resonance voltage variation of the resonance tank  111 . Therefore, the synchronous rectification controller  120  adjusts the dead time length DT according to the dead time control signal SS. The electrical energy at the output of the LLC synchronous resonance converter  110 , a voltage of the resonance tank  111 , and the dead time length DT are in a positive correlation. Taking the embodiment as an example, when the electric energy at the output of the LLC synchronous resonance converter  110  is greater, the voltage of the resonance tank  111  is greater. The dead time adjustment circuit  130  provides a dead time control signal SS for extending the dead time length DT. Therefore, the dead time length DT is extended. Moreover, when the electric energy at the output of the LLC synchronous resonance converter  110  is smaller, the voltage of the resonance tank  111  is smaller. The dead time adjustment circuit  130  provides a dead time control signal SS for shortening the dead time length DT. Therefore, the dead time length DT is shortened. 
     It is worth mentioning here that the electric energy at the output of the LLC synchronous resonance converter  110  is related to a load of the LLC synchronous resonance converter  110 . The dead time adjustment circuit  130  inductively couples the electric energy at the output of the LLC synchronous resonance converter  110  to the resonance tank  111 , and adjusts the dead time length DT according to the resonance voltage variation of the resonance tank  111 . The dead time adjustment circuit  130  can control the synchronous rectification controller  120  to provide a corresponding dead time length DT according to different loads. Therefore, the synchronous rectification switches Q 3  and Q 4  can achieve zero current cutoff under different loads. In this way, the conversion efficiency of the LLC synchronous resonance converter  110  can be optimized under different loads. 
     Please refer to  FIGS.  2  and  3    at the same time.  FIG.  3    is a schematic diagram of achieving zero current cutoff according to an embodiment of the disclosure. In the embodiment, when the load of the LLC synchronous resonance converter  110  increases, the electric energy at the output of the LLC synchronous resonance converter  110  is greater. The current value of the current IQ 1  flowing through the synchronous rectification switch Q 3  and the current value of the current IQ 2  flowing through the synchronous rectification switch Q 4  are also greater. Therefore, compared to  FIG.  1   , the dead time length DT shown in  FIG.  3    is extended. Based on the extension of the dead time length DT, the current IQ 1  flowing through the synchronous rectification switch Q 3  and the current IQ 2  flowing through the synchronous rectification switch Q 4  can resonate to 0 ampere within a sufficient dead time length DT. In this way, under large load, the synchronous rectification switches Q 3  and Q 4  can achieve zero current cutoff. Moreover, when the load of the LLC synchronous resonance converter  110  decreases, the dead time length DT shown in  FIG.  3    is shortened. 
     Please refer to the embodiment of  FIG.  2    again. In the embodiment, the first terminal of the power switch Q 1  is coupled to an input power VIN. The second terminal of the power switch Q 1  is coupled to a connection node ND. The control terminal of the power switch Q 1  receives the control signal GD 1 . The first terminal of the power switch Q 2  is coupled to the connection node ND. The second terminal of the power switch Q 2  is coupled to a ground terminal GND 1 . The control terminal of the power switch Q 2  receives the control signal GD 2 . The resonance tank  111  is coupled between the connection node ND and the ground terminal GND 1 . The resonance tank  111  includes a resonance inductor LR, a magnetizing inductor LM, and a resonance capacitor CR. The resonance inductor LR, the magnetizing inductor LM, and the resonance capacitor CR are coupled in series with each other. Furthermore, the resonance inductor LR is coupled between the connection node ND and the first terminal of the magnetizing inductor LM. The resonance capacitor CR is coupled between the second terminal of the magnetizing inductor LM and the ground terminal GND 1 . 
     In the embodiment, the main transformer TR 1  includes a primary side winding NP and secondary side windings NS 1  and NS 2 . The primary side winding NP is coupled in parallel to the magnetizing inductor LM. The first terminal of the secondary side winding NS 1  is coupled to the first terminal of the synchronous rectification switch Q 3 . The second terminal of the secondary side winding NS 1  is coupled to the first terminal of the secondary side winding NS 2  and a ground terminal GND 2 . The second terminal of the synchronous rectification switch Q 3  is configured as the output of the LLC synchronous resonance converter  110 . The output is configured to provide the output power VO. The control terminal of the power switch Q 3  receives the control signal GD 3 . The second terminal of the secondary side winding NS 2  is coupled to the first terminal of the synchronous rectification switch Q 4 . The second terminal of the synchronous rectification switch Q 4  is coupled to the second terminal of the synchronous rectification switch Q 3 . The control terminal of the power switch Q 4  receives the control signal GD 4 . The output capacitor CO is coupled between the output of the LLC synchronous resonance converter  110  and the ground terminal GND 2 . The control signals GD 1  and GD 2  may be provided by a power switch controller (not shown). In some embodiments, the power switch controller and the synchronous rectification controller  120  may be integrated in a single controller. 
     In the embodiment, the LLC synchronous resonance converter  110  takes a half-bridge LLC synchronous resonance converter as an example. The disclosure is not limited thereto. In some embodiments, the LLC synchronous resonance converter  110  may be a full-bridge LLC synchronous resonance converter with four power switches. 
     Please refer to  FIG.  4   , which is a schematic diagram of a resonance conversion device according to the second embodiment of the disclosure. In the embodiment, the resonance conversion device  200  includes an LLC synchronous resonance converter  110 , a synchronous rectification controller  120 , and a dead time adjustment circuit  230 . The implementation modes of the LLC synchronous resonance converter  110  and the synchronous rectification controller  120  have been fully described in the embodiment of  FIG.  2    and thus are not repeated here. In the embodiment, the dead time adjustment circuit  230  includes a coupled inductor  231 , an auxiliary circuit  232 , a detection circuit  233 , and a dead time controller  234 . The coupled inductor  231  is coupled to an output of the LLC synchronous resonance converter  110 . The coupled inductor  231  uses inductive coupling to provide an inductive electric energy PC corresponding to electric energy at the output of the LLC synchronous resonance converter  110 . The auxiliary circuit  232  is coupled to the coupled inductor  231  and a resonance tank  111 . The auxiliary circuit  232  inductively couples the received inductive electric energy PC to the resonance tank  111 . 
     In the embodiment, the detection circuit  233  is coupled to the resonance tank  111 . Furthermore, a magnetizing inductor LM and a resonance capacitor CR form a series element group. The detection circuit  233  is coupled in parallel with the series element group. The detection circuit  233  provides a detection result of resonance voltage variation of the series element group. The dead time controller  234  is coupled to the detection circuit  233  and the synchronous rectification controller  120 . The dead time controller  234  correspondingly provides a dead time control signal SS in response to the detection result. 
     Please refer to  FIG.  5   , which is a schematic diagram of a circuit of a resonance conversion device according to an embodiment of the disclosure. In the embodiment, the resonance conversion device  300  includes an LLC synchronous resonance converter  110 , a synchronous rectification controller  120 , and a dead time adjustment circuit  330 . The implementation modes of the LLC synchronous resonance converter  110  and the synchronous rectification controller  120  have been fully described in the embodiment of  FIG.  2    and thus is not repeated here. In the embodiment, the dead time adjustment circuit  330  includes a coupled inductor  331 , an auxiliary circuit  332 , a detection circuit  333 , and a dead time controller  334 . 
     In the embodiment, the coupled inductor  331  includes inductors L 1  and L 2 . The inductor L 1  is coupled between an output of the LLC synchronous resonance converter  110  and a ground terminal GND 2 . The inductor L 2  is coupled to the auxiliary circuit  332  and provides inductive electric energy. Furthermore, the coupled inductor  331  receives the electric energy at the output of the LLC synchronous resonance converter  110  through the first inductor L 1 , and inductively couples the energy on the inductor L 1  to the inductor L 2  by means of voltage synchronous induction. Therefore, the inductor L 2  provides inductive electric energy. 
     In the embodiment, the auxiliary circuit  332  includes an auxiliary resistor RX and an auxiliary transformer TR 2 . The auxiliary resistor RX is coupled to the coupled inductor  331 , and establishes a first induced voltage VX according to the inductive electric energy. Specifically, the auxiliary resistor RX is coupled in parallel to the inductor L 2  of the coupled inductor  331 . Therefore, the auxiliary resistor RX can absorb the inductive electric energy to establish the first induced voltage VX. 
     The auxiliary transformer TR 2  is coupled to the coupled inductor  331 . The auxiliary transformer TR 2  transforms the first induced voltage VX to generate a second induced voltage. The auxiliary transformer TR 2  includes auxiliary windings N 1  and N 2 . The auxiliary winding N 1  may be regarded as the primary side winding of the auxiliary transformer TR 2 . The auxiliary winding N 2  may be regarded as the secondary side winding of the auxiliary transformer TR 2 . The auxiliary winding N 2  is coupled in parallel to the auxiliary resistor RX and receives the first induced voltage VX. The auxiliary winding N 1  generates a second induced voltage. Moreover, the auxiliary winding N 1  is coupled in series with the primary side winding NP of the main transformer TR 1  to form a winding string. It should be noted that the winding string is designed to be coupled in parallel with the magnetizing inductor LM of the resonance tank  111 . The voltage difference across the winding string changes based on a change of the second induced voltage. Therefore, the change of the second induced voltage generated by the auxiliary winding N 1  is related to the resonance voltage variation. 
     In the embodiment, the electric energy at the output of the LLC synchronous resonance converter  110 , the second induced voltage, and the voltage difference across the magnetizing inductor LM are in a positive correlation. For example, when the electric energy at the output of the LLC synchronous resonance converter  110  is increased, the second induced voltage is correspondingly raised. Therefore, the voltage difference across the magnetizing inductor LM is correspondingly increased. Moreover, when the electric energy at the output of the LLC synchronous resonance converter  110  is reduced, the second induced voltage is correspondingly lowered. Therefore, the voltage difference across the magnetizing inductor LM is correspondingly reduced. 
     In the embodiment, the detection circuit  333  includes a detection resistor RR and a detection unit  3331 . The detection resistor RR is coupled in parallel with the series element group formed by the magnetizing inductor LM and the resonance capacitor CR. Moreover, the detection resistor RR provides a resonance voltage value. The detection unit  3331  is coupled to the detection resistor RR and provides a change of the resonance voltage value to provide a detection result. 
     In the embodiment, the dead time controller  334  receives the detection result provided by the detection unit  3331 , and in response to the detection result, provides a dead time control signal SS corresponding to the detection result. If the detection result indicates that the resonance voltage value is raised, the dead time controller  334  provides a dead time control signal SS for extending the dead time length DT. If the detection result indicates that the resonance voltage value is lowered, the dead time controller  334  provides a dead time control signal SS for shortening the dead time length DT. 
     It should be noted that in the embodiment, the coupled inductor  331  is disposed on the secondary side of the resonance conversion device  300 . Therefore, the dead time adjustment circuit  330  can receive the electric energy at the output of the LLC synchronous resonance converter  110 . In addition, the auxiliary circuit  332  couples the electric energy at the output of the LLC synchronous resonance converter  110  to the resonance tank  111 . Therefore, the detection circuit  333  and the dead time controller  334  may be disposed on the primary side of the resonance conversion device  300 . In this way, the volume of the secondary side of the resonance conversion device  300  may be reduced. In the embodiment, the number of turns of the auxiliary windings N 1  and N 2  has a relatively low number of turns, respectively, for example, less than 5 turns. Therefore, the auxiliary circuit  332  itself also has a smaller volume. 
     In summary, the dead time adjustment circuit inductively couples the electric energy at the output of the LLC synchronous resonance converter to the resonance tank, and provides a dead time control signal according to the resonance voltage variation of the resonance tank. The synchronous rectification controller adjusts the dead time length according to the dead time control signal. The dead time adjustment circuit can provide the corresponding dead time length according to different loads. Therefore, the disclosure can achieve zero current cutoff under different loads. In this way, the conversion efficiency of the LLC synchronous resonance converter can be optimized under different loads. In addition, the dead time adjustment circuit judges the resonance voltage variation on the primary side of the resonance conversion device, and provides a dead time control signal accordingly. Therefore, the volume of the secondary side of the resonance conversion device may be reduced. 
     Although the disclosure has been described with reference to the above embodiments, the described embodiments are not intended to limit the disclosure. People of ordinary skill in the art may make some changes and modifications without departing from the spirit and the scope of the disclosure. Thus, the scope of the disclosure shall be subject to those defined by the attached claims.