Abstract:
A self-coupled transformer boostbuck circuit includes a first transformer having a first winding, a second winding and a third winding, a first switch having a first voltage output at its one end, a second switch, a second transformer, a third switch having a second voltage output at its one end, a fourth switch, a fifth switch having a third voltage output at its one end, and a sixth switch.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a boostbuck circuit and more particularly, to a self-coupled transformer boostbuck circuit that provides multiple voltage outputs. 
     2. Description of the Related Art 
     In a regular LLC resonant converter, the secondary wide has +12V, +5V and +3.3V voltage outputs drawn from the middle part. However, when the load at one voltage output of the LLC resonant converter is changed, the other voltage output will be affected to cause cross regulation. For example, when the load at the +12V output is changed, the voltage outputs +5V and +3.3V will be relatively changed; when the load at the +5V is changed, the voltage outputs +12V and +3.3V will be relatively changed. Thus, these three voltage outputs affect one another, causing a cross regulation error. 
     Therefore, it is desirable to provide a boostbuck circuit that eliminates the aforesaid problem. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a self-coupled transformer boostbuck circuit that provides multiple voltage outputs. 
     It is another object of the present invention to provide a self-coupled transformer boostbuck circuit that uses a self-coupled transformer to execute voltage boosting and dropping, providing multiple voltage outputs. 
     To achieve these and other objects, the self-coupled transformer boostbuck circuit of the first embodiment of the present invention comprises a first transformer, the first transformer having a primary side and a secondary side, the primary side comprising a first winding, the secondary side comprising a second winding and a third winding, the second winding and the third winding being connected in series, the connection between the second winding and the third winding being connected to ground potential, the first winding having one end coupled to the output terminal of the LLC converter; a first switch, the first switch having one end coupled to one end of the second winding that has an opposite end providing with an opposite end of the first switch a first voltage output (V 1 ); a second switch, the second switch having one end coupled to one end of the third winding opposite to the second winding and an opposite end coupled to one end of the first switch opposite to the second winding; a second transformer, the second transformer comprising a first winding, a second winding, a third winding, a fourth winding, a fifth winding and a sixth winding that are connected in series, the first winding of the second transformer having one end coupled to the second winding of the first transformer, the sixth winding of the second transformer having an opposite end coupled to one end of the third winding opposite to the second winding, the connection between the third winding and fourth winding of the second transformer being connected to ground potential; a third switch, the third switch having one end coupled to the connection between the first winding and second winding of the second transformer and an opposite end providing a second voltage output (V 2 ); a fourth switch, the fourth switch having one end coupled to the connection between the second winding and third winding of the second transformer; a fifth switch, the fifth switch having one end coupled to the connection between the fourth winding and fifth winding of the second transformer and an opposite end coupled to an opposite end of the fourth switch and providing a third voltage output (V 3 ); and a sixth switch, the sixth switch having one end coupled to the connection between the fifth winding and sixth winding of the second transformer and an opposite end connected to the second voltage output end of the third switch such that the second voltage output and the third voltage output are not affected by variation of the first voltage output. 
     To achieve these and other objects, the self-coupled transformer boostbuck circuit of the second embodiment of the present invention comprises a first transformer, the first transformer having a primary side and a secondary side, the primary side comprising a first winding, the secondary side comprising a second winding, a third winding, a fourth winding and a fifth winding, the second winding and the third winding and the fourth winding and the fifth winding being connected in series, the first winding having one end coupled to the output terminal of the LLC converter; a second transformer, the second transformer comprising a first winding, a second winding, a third winding, a fourth winding, a fifth winding and a sixth winding, the first winding of the second transformer having one end coupled to the second winding of the first transformer, the sixth winding of the second transformer having one end coupled to an opposite end of the fifth winding of the first transformer, the connection between the third winding and fourth winding of the second transformer being connected to ground potential; a first switch, the first switch having one end coupled to the first winding of the second transformer and an opposite end providing a first voltage output (V 1 ); a second switch, the second switch having one end coupled to one end of the second winding of the second transformer and the second winding of the first transformer and an opposite end providing a second voltage output (V 2 ); a third switch, the third switch having one end coupled to the connection between the second winding and third winding of the second transformer and an opposite end providing a third voltage output (V 3 ); a fourth switch, the fourth switch having one end coupled to the connection between the fourth winding and fifth winding of the second transformer and an opposite end connected to an opposite end of the third switch; a fifth switch, the fifth switch having one end coupled to an opposite end of the fifth winding of the second transformer and the connection between the fourth winding and fifth winding of the first transformer and an opposite end coupled to an opposite end of the second switch; and a sixth switch, the sixth switch having one end coupled to an opposite end of the sixth winding of the second transformer and an opposite end coupled to an opposite end of the first switch such that the second voltage output and the third voltage output are not affected by variation of the first voltage output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit block diagram of a self-coupled transformer boostbuck circuit in accordance with a first embodiment of the present invention. 
         FIG. 2  is a circuit block diagram of a self-coupled transformer boostbuck circuit in accordance with a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a circuit block diagram of a self-coupled transformer boostbuck circuit in accordance with a first embodiment of the present invention. As illustrated, the self-coupled transformer boostbuck circuit comprises a first transformer  10 , a first switch  20 , a second switch  30 , a second transformer  40 , a third switch  50 , a fourth switch  60 , a fifth switch  70 , and a sixth switch  80 . 
     The first transformer  10  has a primary side and a secondary side. The primary side comprises a first winding  11 . The secondary side comprises a second winding  12  and a third winding  13 . The second winding  12  and the third winding  13  are connected in series. The connection between the second winding  12  and the third winding  13  is connected to ground potential (GND). The first winding  11  has one end coupled to the output terminal of a LLC resonant converter  90 . The LLC resonant converter  90  is a known AC/DC converter, no further detailed description is necessary in this regard. The first transformer  10  can be, but not limited to, a flyback transformer. The flyback transformer is of the known design, no further detailed description is necessary in this regard. Further, the first winding  11  of the first transformer  10  has a number of turns N 1 ; the second winding  12  and third winding  13  of the first transformer  10  have a same number of turns N 2 . 
     The first switch  20  has one end coupled to one end of the second winding  12 . A first voltage output V 1  is provided between the other end of the second winding  12  and the other end of the first switch  20 . The first switch  20  can be, but not limited to a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The second switch  30  has one end coupled to the other end of the third winding  13 , and the other end coupled to the other end of the first switch  20 . The second switch  30  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The second transformer  40  comprises a first winding  41 , a second winding  42 , a third winding  43 , a fourth winding  44 , a fifth winding  45 , and a sixth winding  46  that are connected in series. The first winding  41  has one end coupled to the second winding  12  of the first transformer  10 . The other end of the sixth winding  46  is coupled to the other end of the third winding  13  of the first transformer  10 . The connection between the third winding  43  and the fourth winding  44  is connected to ground potential. The second transformer  40  can be, but not limited to, a self-coupled transformer. The first winding  41  and sixth winding  46  of the second transformer  40  have a same number of turns N 5 . The second winding  42  and fifth winding  45  of the second transformer  40  have a same number of turns N 4 . The third winding  43  and fourth winding  44  of the second transformer  40  have a same number of turns N 3 . 
     The third switch  50  has one end coupled to the connection between the first winding  41  and second winding  42  of the second transformer  40 , and the other end providing a second voltage output V 2 . The third switch  50  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The fourth switch  60  has one end coupled to the connection between the second winding  42  and third winding  43  of the second transformer  40 . The fourth switch  60  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The fifth switch  70  has one end coupled to the connection between the fourth winding  44  and fifth winding  45  of the second transformer  40 , and the other end coupled to the other end of the fourth switch  60  and providing a third voltage output V 3 . The fifth switch  70  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The sixth switch  80  has one end coupled to the connection between the fifth winding  45  and sixth winding  46  of the second transformer  40 , and the other end coupled to the other end of the third switch  50 . The sixth switch  80  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     After shunt by ratio of winding of the related windings, the second voltage V 2  is obtained subject to the equation: 
               V   ⁢           ⁢   2     =           N   ⁢           ⁢   3     +     N   ⁢           ⁢   4           N   ⁢           ⁢   3     +     N   ⁢           ⁢   4     +     N   ⁢           ⁢   5         ×   V   ⁢           ⁢   1.           
Therefore, by means of accurately controlling the number of turns N 3  of the third winding  43  and fourth winding  44  of the second transformer  40 , the number of turns N 4  of the second winding  42  and fifth winding  45  of the second transformer  40  and the number of turns N 5  of the first winding  41  and sixth winding  46  of the second transformer  40 , the desired stable second voltage V 2  is obtained, preventing the aforesaid cross regulation problem.
 
     After shunt by ratio of winding of the related windings, the third voltage V 3  is obtained subject to the equation: 
               V   ⁢           ⁢   3     =         N   ⁢           ⁢   3         N   ⁢           ⁢   3     +     N   ⁢           ⁢   4     +     N   ⁢           ⁢   5         ×   V   ⁢           ⁢   1.           
Therefore, by means of accurately controlling the number of turns N 3  of the third winding  43  and fourth winding  44  of the second transformer  40 , the number of turns N 4  of the second winding  42  and fifth winding  45  of the second transformer  40  and the number of turns N 5  of the first winding  41  and sixth winding  46  of the second transformer  40 , the desired stable third voltage V 3  is obtained, preventing the aforesaid cross regulation problem. Therefore, the self-coupled transformer boostbuck circuit is superior to the technique conventional LLC resonant converter.
 
       FIG. 2  is a circuit block diagram of a self-coupled transformer boostbuck circuit in accordance with a second embodiment of the present invention. As illustrated, the self-coupled transformer boostbuck circuit is used in a LLC resonant converter, comprising a first transformer  110 , a second transformer  120 , a first switch  130 , a second switch  140 , a third switch  150 , a fourth switch  160 , a fifth switch  170 , and a sixth switch  180 . 
     The first transformer  110  has a primary side and a secondary side. The primary side comprises a first winding  111 . The secondary side comprises a second winding  112  and a third winding  113 , a fourth winding  114 , and a fifth winding  115 . The second winding  112 , the third winding  113 , the fourth winding  114  and the fifth winding  115  are connected in series. The first winding  111  has one end coupled to the output terminal of the LLC resonant converter  190 . The LLC resonant converter  190  is a known AC/DC converter, no further detailed description is necessary in this regard. The first transformer  110  can be, but not limited to, a flyback transformer. The flyback transformer is of the known design, no further detailed description is necessary in this regard. Further, the first winding  111  of the first transformer  110  has a number of turns N 1 ; the second winding  112  and fifth winding  115  of the first transformer  110  have a same number of turns N 2 ; the third winding  113  and the fourth winding  114  of the first transformer  110  have a same number of turns N 3 . 
     The second transformer  120  comprises a first winding  121 , a second winding  122 , a third winding  123 , a fourth winding  124 , a fifth winding  125 , and a sixth winding  126 . The first winding  121  has one end coupled to the second winding  112  of the first transformer  110 . The sixth winding  126  has one end coupled to the other end of the fifth winding  115  of the first transformer  110 . The connection between the third winding  123  and the fourth winding  124  is connected to ground potential. The second transformer  120  can be, but not limited to, a self-coupled transformer. The first winding  121  and sixth winding  126  of the second transformer  120  have a same number of turns N 4 . The second winding  122  and fifth winding  125  of the second transformer  120  have a same number of turns N 5 . The third winding  123  and fourth winding  124  of the second transformer  120  have a same number of turns N 6 . 
     The first switch  130  has one end coupled to the other end of the first winding  121 , and the other end providing a first voltage output V 1 . The first switch  130  can be, but not limited to a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The second switch  140  has one end coupled to the other end of the second winding  122  of the second transformer  120  and the other end of the second winding  112  of the first transformer  110 , and the other end providing a second voltage output V 2 . The second switch  140  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The third switch  150  has one end coupled to the connection between the second winding  122  and third winding  123  of the second transformer  120 , and the other end providing a third voltage output V 3 . The third switch  150  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The fourth switch  160  has one end coupled to the connection between the fourth winding  124  and fifth winding  125  of the second transformer  120 , and the other end coupled to the other end of the third switch  150 . The fourth switch  160  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The fifth switch  170  has one end coupled to the other end of the fifth winding  125  of the second transformer  120  and the connection between the fourth winding  114  and fifth winding  115  of the first transformer  110 , and the other end coupled to the other end of the second switch  140 . The fifth switch  170  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     The sixth switch  180  has one end coupled to the other end of the sixth winding  126  of the second transformer  120 , and the other end coupled to the other end of the first switch  130 . The sixth switch  180  can be, but not limited to, a rectifier or power switch for synchronous rectification. In case of a power switch, it can be a N-pass MOSFET (metal-oxide semiconductor field-effect) transistor, N-pass junction field-effect transistor, P-pass MOSFET transistor or P-pass junction field-effect transistor for the advantage of low cost. 
     After shunt by ratio of winding of the related windings, the first voltage V 1  is obtained subject to the equation: 
               V   ⁢           ⁢   1     =       (         N   ⁢           ⁢   4         N   ⁢           ⁢   5     +     N   ⁢           ⁢   6         +         N   ⁢           ⁢   2     +     N   ⁢           ⁢   3         N   ⁢           ⁢   3         )     ×   V   ⁢           ⁢   2.           
Therefore, by means of accurately controlling the number of turns N 2  of the second winding  112  and fifth winding  115  of the first transformer  110 , the number of turns N 3  of the third winding  113  and fourth winding  114  of the first transformer  110  and the number of turns N 4  of the first winding  121  and sixth winding  126  of the second transformer  120 , the number of turns N 5  of the second winding  122  and fifth winding  125  of the second transformer  120  and the number of turns N 6  of the third winding  123  and fourth winding  124  of the second transformer  120 , the desired stable first voltage V 1  is obtained, preventing the aforesaid cross regulation problem.
 
     After shunt by ratio of winding of the related windings, the third voltage V 3  is obtained subject to the equation: 
               V   ⁢           ⁢   3     =         N   ⁢           ⁢   6         N   ⁢           ⁢   5     +     N   ⁢           ⁢   6         ×   V   ⁢           ⁢   2.           
Therefore, by means of accurately controlling the number of turns N 5  of the second winding  122  and fifth winding  125  of the second transformer  120  and the number of turns N 6  of the third winding  123  and fourth winding  124  of the second transformer  120 , the desired stable third voltage V 3  is obtained, preventing the aforesaid cross regulation problem.
 
     By means of the application of the self-coupled transformer boostbuck circuit to boost and drop the voltage, multiple voltage outputs are provided without cross regulation, eliminating the drawbacks of conventional LLC resonant converter. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.