Abstract:
A variable coupled inductor includes a first core, two conducting wires, a second core and a magnetic structure. The first core includes two first protruding portions, a second protruding portion and two grooves, wherein the second protruding portion is located between the two first protruding portions and each of the grooves is located between one of the first protruding portions and the second protruding portion. Each of the conducting wires is disposed in one of the grooves. The second core is disposed on the first core. A first gap is formed between each of the first protruding portions and the second core and a second gap is formed between the second protruding portion and the second core. The magnetic structure is disposed between the second protruding portion and the second core and distributed symmetrically with respect to a centerline of the second protruding portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of Taiwan Application No. 101130231, filed Aug. 21, 2012, which is incorporated by reference herein in their entirety. 
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to a variable coupled inductor and, in particular, to a variable coupled inductor can improve efficiency in both light-load and heavy-load situations. 
     II. Description of the Prior Art 
     A coupled inductor has been developed for a period of time; however, it is not often used in the circuit board. As a more powerful microprocessor needs a high current in a small circuit board, a variable coupled inductor has been gradually used in the circuit board. A variable coupled inductor can be used to reduce the total space of the circuit board consumed by traditional coupled inductors. Currently, a coupled inductor can reduce the ripple current apparently, wherein a smaller capacitor can be used to save the space of the circuit board. As the DC resistance (direct current resistance, DCR) of the coupled inductor is low, efficiency is better in a heavy-load situation. However, as the flux generated by each of the dual conducting wires will be cancelled each other when the dual conducting wires are coupled, the inductance becomes low and the efficiency becomes worse in a light-load situation. 
     SUMMARY OF THE INVENTION 
     One objective of present invention is to provide a variable coupled inductor that can increase the efficiency in both heavy-load and light-load situations to solve the above-mentioned problem. 
     In one embodiment, a variable coupled inductor is provided, wherein variable coupled inductor comprises a first core comprising a first protrusion, a second protrusion, a third protrusion, a first conducting-wire groove and a second conducting-wire groove, wherein the second protrusion is disposed between the first protrusion and the third protrusion, the first conducting-wire groove is located between the first protrusion and the second protrusion, and the second conducting-wire groove is located between the second protrusion and the third protrusion; a first conducting wire disposed in the first conducting-wire groove; a second conducting wire disposed in the second conducting-wire groove; a second core disposed over the first core, wherein a first gap is formed between the first protrusion and the second core, a second gap is formed between the second protrusion and the second core and a third gap is formed between the third protrusion and the second core; and a magnetic structure disposed between the second protrusion and the second core, wherein the magnetic structure is symmetric with respect to the central line of the second protrusion. 
     The present invention proposes that the magnetic structure is disposed between the second projection in the middle of the first core and the second core, wherein the magnetic structure is symmetric with respect to the central line CL of the second protrusion  102 . Therefore, the initial-inductance of the variable coupled inductor can be enhanced and light-load efficiency can be improved by means of the magnetic structure. 
     In one embodiment, the material of the variable coupled inductor of the present invention can be a ferrite material to achieve a high-saturation current, and copper sheet is used as an electrode to reduce the DC resistance, so that the efficiency in heavy-load is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the accompanying advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  illustrates a variable coupled inductor in three dimensions in accordance with one embodiment of present invention; 
         FIG. 2  illustrates the variable coupled inductor in  FIG. 1  where the second core is removed; 
         FIG. 3  illustrates the first core and the magnetic structure of the variable coupled inductor in  FIG. 2 ; 
         FIG. 4  illustrates a side view of the variable coupled inductor in  FIG. 1  where the second conducting wire is removed; 
         FIG. 5  illustrates the relationships between the measured inductances and the currents in the variable coupled inductor in  FIG. 1 ; 
         FIG. 6  illustrates a three dimensional view of the first core and the magnetic structure in accordance with one embodiment of present invention; 
         FIG. 7  illustrates a three dimensional view of the first core and the magnetic structure in accordance with another embodiment of present invention; and 
         FIG. 8  illustrates a three dimensional view of the first core and the magnetic structure in accordance with yet another embodiment of present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 1  to  FIG. 4 .  FIG. 1  is a three dimensional view of a variable coupled inductor  1  according to one embodiment of the present invention.  FIG. 2  is a three dimensional view of a variable coupled inductor  1  where the second core  14  is removed in  FIG. 1 .  FIG. 3  is a three dimensional view of a first core  10  and a magnetic structure  16  in  FIG. 2 .  FIG. 4  is a lateral view of a variable coupled inductor  1  wherein two conducting wires  12  are removed in  FIG. 1 . As illustrated in  FIG. 1  to  FIG. 4 , the variable coupled inductor  1  comprises a first core  10 , two conducting wires  12 , a second core  14  and a magnetic structure  16 . The first core  10  comprises two first protrusions  100 , a second protrusion  102  and two conducting-wire grooves  104 , wherein the second protrusion  102  is located between the two first protrusions  100 , and each of the two conducting-wire groove  104  is located between corresponding one of the two first protrusions  100  and the second protrusion  102 , respectively. In other words, the second protrusion  102  is located in the middle portion of the first core  10 . Each of the two conducting wire  12  is disposed in one of the two conducting-wire grooves  104 , respectively. The second core  14  is disposed over the first core  10  so that a first gap G 1  is formed between each first protrusion  100  and the second core  14  and a second gap G 2  is formed between the second protrusion  102  and the second core  14 . A magnetic structure  16  is disposed between the second protrusion  102  and the second core  14 , and the magnetic structure  16  is symmetric with respect to the central line CL of the second protrusion  102 , as illustrated in  FIG. 3  and  FIG. 4 . 
     As the second protrusion  102  is located in the middle portion of the first core  10  and the magnetic structure  16  is disposed between the second protrusion  102  and the second core  14 , the magnetic structure  16  is located in the middle portion of the variable coupled inductor  1  after the variable coupled inductor  1  is fabricated. Furthermore, two ends of the magnetic structure  16  are respectively in full contact with the first core  10  and the second core  14 . In this embodiment, magnetic structure  16  is, but not limit to, in a long-strip shape. In this embodiment, the material of the first core  10 , the second core  14  and the magnetic structure  16  can be iron powder, ferrite, permanent magnet or other magnetic material. Because the first core  10  and the magnetic structure  16  are integrally formed, the material of the first core  10  is the same as that of the magnetic structure  16 . In another embodiment, the magnetic structure  16  and the second core  14  are also formed integrally, in such case, the material of the second core  14  is the same as that of the magnetic structure  16 . In another embodiment, the magnetic structure  16  can be also an independent device, in such case, the material of the magnetic structure  16  and the material of the first core  10 , or the second core  14 , can be the same or different. It should be noted that if the magnetic structure  16  is not in full contact with the first core  10  and the second core  14  due to manufacturing tolerance, magnetic glue can be filled in the gap (e.g., insulating resin and magnetic adhesive made of magnetic powder). 
     In this embodiment, the vertical distance D 1  of the first gap G 1  is smaller that the vertical distance D 2  of the second gap G 2 . The first gap G 1  can be an air gap, a magnetic gap and a non-magnetic gap, and the second gap G 2  can be also an air gap, a magnetic gap and a non-magnetic gap. The first gap G 1  and the second gap G 2  can be designed according to the practical application. It should be noted that the air gap is a gap filled with air for isolating and it does not contain other material; because air has a larger magnetic reluctance, it can increase degree of saturation of the inductor. The magnetic gap is formed by filling the magnetic material in the gap to reduce the magnetic reluctance and to further increase the inductance; non-magnetic gap is formed by filling the non-magnetic material, except the air, in the gap to enhance the function that the air gap can not achieve, such as by filling a bonding glue to combine different magnetic materials. Preferably, the first gap G 1  can be a non-magnetic gap, and the second gap G 2  can be an air gap or a non-magnetic gap. 
     In this embodiment, the variable coupled inductor  1  has a total high H after the variable coupled inductor  1  is fabricated; the vertical distance D 1  of the first gap G 1  can be in a range between 0.0073H and 0.0492H and the vertical distance D 2  of the second gap G 2  can be in a range between 0.0196H and 0.1720H. Furthermore, as illustrated in  FIG. 4 , each of the first gap G 1  and the second gap G 2  lies within a height covered by the vertical distance D 3  between the bottom surface of the conducting-wire groove  104  and the second core  14 . In other words, when looking at the side view shown in  FIG. 4 , each top point of the first gap G 1  and the second gap G 2  is not higher than the top point of vertical distance D 3  between the bottom surface of the conducting-wire groove  104  and the second core  14 ; and each bottom point of the first gap G 1  and the second gap G 2  is not lower than the bottom point of vertical distance D 3  between the bottom surface of the conducting-wire groove  104  and the second core  14 . In practical applications, the first gap G 1  generates a major inductance and the second gap G 2  generates a leakage inductance. 
     In this embodiment, the magnetic structure  16  has a first magnetic permeability μ 1 , the first gap G 1  has a second magnetic permeability μ 2 , and the second gap G 2  has a third magnetic permeability μ 3 , wherein the relationship between the first magnetic permeability μ 1 , the second magnetic permeability μ 2  and the third magnetic permeability μ 3  is μ 1 &gt;μ 2 ≧μ 3 . In general, magnetic permeability is inversely proportional to the magnetic reluctance (i.e. the greater the magnetic permeability, the smaller the magnetic reluctance). The first magnetic permeability μ 1  of the magnetic structure  16  is larger than each of the second magnetic permeability μ 2  of the first gap G 1  and the third magnetic permeability μ 3  of the second gap G 2 , wherein the first gap G 1  and the second gap G 2  are located in two sides of the magnetic structure  16 , respectively. In other words, the magnetic reluctance of the magnetic structure  16  is smaller than that of the first gap G 1 ; and the magnetic reluctance of the magnetic structure  16  is smaller than that of the second gap G 2 . 
     For example, the magnetic structure  16  can be manufactured by LTCC (low temperature co-fired ceramic, LTCC) printing; in such case, the first magnetic permeability μ 1  of the magnetic structure  16  is about between 50 and 200, and each of the second magnetic permeability μ 2  of the first gap G 1  and the third magnetic permeability μ 3  of the second gap G 2  is about 1. Because the first magnetic permeability μ 1  of the magnetic structure  16  is larger than each of the second magnetic permeability μ 2  of the first gap G 1  and the third magnetic permeability μ 3  of the second gap G 2 , the initial flux will passes through the magnetic structure  16  when a current passes through variable coupled inductor  1 . It should be noted that the first magnetic permeability μ 1  of the magnetic structure  16  is larger than each of the second magnetic permeability μ 2  of the first gap G 1  and the third magnetic permeability μ 3  of the second gap G 2  to achieve the effect of the variable inductance coupling regardless of the material of the first core  10  and the second core  14  (i.e. regardless of the magnetic permeability of the first core  10  and the second core  14 ). 
     Furthermore, the first core  10  has a fourth magnetic permeability μ 4 , and the second core  14  has a fifth magnetic permeability μ 5 . For example, in another embodiment, when the magnetic structure  16 , the first core  10  and the second core  14  are all made of ferrite material, the first magnetic permeability μ 1 , the fourth magnetic permeability μ 4  and the fifth magnetic permeability μ 5  are the same. When the material of the magnetic structure  16  is ferrite material, the initial-inductance characteristic of the variable coupled inductor  1  can be enhanced and the efficiency of the variable coupled inductor  1  in a light-load situation can be improved as well. It should be noted that the relationship between the first magnetic permeability μ 1 , the second magnetic permeability μ 2 , the third magnetic permeability μ 3 , the fourth magnetic permeability μ 4  and the fifth magnetic permeability μ 5  is: μ 1 ≧μ 4 &gt;μ 2 ≧μ 3  and μ 1 ≧μ 5 &gt;μ 2 ≧μ 3 , regardless of the material of the magnetic structure  16 , the first core  10  and the second core  14 . 
     In summary, the present invention proposes that the magnetic structure  16  having a high magnetic permeability (i.e. the first magnetic permeability μ 1  described above) is disposed between the second projection  102  in the middle of the first core  10  and the second core  14 , and the magnetic structure  16  is symmetric with respect to the central line CL of the second protrusion  102 . Therefore, by using the magnetic structure  16 , the initial-inductance of the variable coupled inductor  1  can be enhanced and efficiency can be improved in a light-load situation. 
     Please refer to  FIG. 5  and Table 1.  FIG. 5  illustrates the relationship between the inductances and the currents measured in the variable coupled inductor  1  in  FIG. 1 , and table 1 lists the inductances and the currents in different measurements. As illustrated in  FIG. 5 , point A is a conversion point between light-load and heavy-lead situations (In this embodiment, the current at point A is, but not limited to, 10A.,) and the current at the point B is the maximum current to be expected to achieve (In this embodiment, the current at point B is, but not limited to, 50A.). Herein, Light-load is called when the current is below the point A. From  FIG. 5  and Table 1, the inductance of the variable coupled inductor  1  in a light-load situation is apparently enhanced, so that the variable coupled inductor  1  of the present invention can effectively improve light-load efficiency. It should be noted that, in this embodiment, the total height H of the variable coupled inductor  1  is about 4.07 mm, the vertical distance D 1  of the first gap G 1  is between 0.03 mm and 0.2 mm, and the vertical distance D 2  of the second gap G 2  is between 0.08 mm and 0.7 mm. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 current (A) 
                 inductance (nH) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 599.6 
               
               
                   
                 5 
                 269.8 
               
               
                   
                 10 
                 159.35 
               
               
                   
                 11 
                 154.38 
               
               
                   
                 12 
                 150.52 
               
               
                   
                 13 
                 147.55 
               
               
                   
                 14 
                 145.29 
               
               
                   
                 15 
                 143.61 
               
               
                   
                 20 
                 138.05 
               
               
                   
                 25 
                 134.3 
               
               
                   
                 30 
                 131.45 
               
               
                   
                 35 
                 129.3 
               
               
                   
                 40 
                 127.4 
               
               
                   
                 45 
                 125.5 
               
               
                   
                 50 
                 123.6 
               
               
                   
                 55 
                 121.7 
               
               
                   
                 60 
                 119.8 
               
               
                   
                   
               
             
          
         
       
     
     In this embodiment, the magnetic structure  16  has a first surface area A 1 , and the second protrusion  102  has a second surface area A 2 . As illustrated in  FIG. 3 , the length of the magnetic structure  16  and the length of the second protrusion  102  are both X; the width of the magnetic structure  16  is Y 1 , and the width of the second protrusion  102  is Y 2 ; the first surface area Al of the magnetic structure  16  is X*Y 1 ; the second surface area A 2  of the second protrusion  102  is X*Y 2 . If the current at point A is defined as a first current I 1 , and the current at point B is defined as a second current I 2 , the relationship between the first current I 1 , the second current I 2 , the first surface area A 1  and the second surface area A 2  can represented as 1.21 (I 1 /I 2 )≧A 1 /A 2 ≧0.81 (I 1 /I 2 ). Furthermore, a first inductance L 1  can be measured at the first current I 1 , and a second inductance L 2  can be measured at the second current  12 ; the relationship between the first inductance L 1  and the second inductance L 2  can represented as 0.8L 1 ≧L 2 ≧0.7L 1 . In other words, the present invention proposes that the first inductance L 1  at the first current I 1  (i.e. the current at the conversion point between light-load and heavy-lead described above) and the second inductance L 2  at the second current  12  (i.e. the maximum current to be expected to achieve) can be adjusted by adjusting the first surface area A 1  and the second surface A 2 . 
     It should be noted that the first current I 1  can be defined as follows. A third inductance L 3  is measured when the first current I 1  plus 1 amp is applied and 5.5 nH≧L 1 -L 3 ≧4.5 nH. For example, the first current I 1  of this embodiment is 10A, and the corresponding first inductance L 1  is 159.35 nH; the first current I 1  plus 1 equals 11A, and the corresponding third inductance L 3  is 154.38 nH, wherein L 1 -L 3 =4.97 nH is obtained and 5.5 nH≧4.97 nH≧4.5 nH is satisfied. As defined above, when the current passes through the variable coupled inductor  1  in accordance with present invention, the corresponding current (i.e. the first current I 1  described above) at point A in  FIG. 4  can be derived by measuring the inductance. 
     Please refer to  FIG. 6 .  FIG. 6  is a three dimensional view of a first core  10  and a magnetic structure  16 ′ according to another embodiment of the present invention. The main difference between the magnetic structure  16  described above and the magnetic structure  16 ′ is that the length X 3  of the magnetic structure  16 ′ is smaller than the length X of the magnetic structure  16 , and the width Y 3  of the magnetic structure  16 ′ is larger than the width Y 1  of the magnetic structure  16 . In this embodiment, the surface area X 3 *Y 3  of the magnetic structure  16 ′ is equal to the surface area X*Y 1  of the magnetic structure  16 . Furthermore, the magnetic structure  16 ′ is still symmetric with respect to the central line CL of the second protrusion  102 . It should be noted that the magnetic structure  16 ′ and the first core  10  can be integrally formed or the magnetic structure  16 ′ and the second core  14  can be integrally formed. Alternatively, the magnetic structure  16 ′ can be an independent device. 
     Please refer to  FIG. 7 .  FIG. 7  is a three dimensional view of a first core  10  and a magnetic structure  16 ″ according to another embodiment of the present invention. The main difference between the magnetic structure  16  described above and the magnetic structure  16 ″ is that the magnetic structure  16 ″ comprises two segments  160 , and the length and the width of each segment  160  are respectively X 4  and Y 4 . In this embodiment, the surface area (X 4 *Y 4 )*2 of the magnetic structure  16 ″ is equal to the surface area X*Y 1  of the magnetic structure  16 . Furthermore, the magnetic structure  16 ″ is still symmetric with respect to the central line CL of the second protrusion  102 . It should be noted that the magnetic structure  16 ″ and the first core  10  can be integrally formed or the magnetic structure  16 ″ and the second core  14  can be integrally formed. Alternatively, the magnetic structure  16 ″ can be an independent device. 
     Please refer to  FIG. 8 .  FIG. 8  is a three dimensional view of a first core  10  and a magnetic structure  16 ″′ according to another embodiment of the present invention. The main difference between the magnetic structure  16  described above and the magnetic structure  16 ″′ is that the magnetic structure  16 ″′ comprises four segments  162 , and the length and the width of each segment are X 5  and Y 5  respectively. In this embodiment, the surface area (X 5 *Y 5 )*4 of the magnetic structure  16 ″′ is equal to the surface area X*Y 1  of the magnetic structure  16 . Furthermore, the magnetic structure  16 ″′ is still symmetric with respect to the central line CL of the second protrusion  102 . It should be noted that the magnetic structure  16 ″′ and the first core  10  can be integrally formed or the magnetic structure  16 ″′ and the second core  14  can be integrally formed. Alternatively, the magnetic structure  16 ″′ can be an independent device. 
     In other words, the number of the segments and appearance of the magnetic structure can be designed in many ways as long as the same surface area is maintained. The magnetic structure is symmetric with respect to the central line CL of the second protrusion  102  regardless of the number of the segments and appearance of the magnetic structure 
     In conclusion, the present invention proposes that the magnetic structure is disposed between the second projection  102  in the middle of the first core  10  and the second core, and the magnetic structure is symmetric with respect to the central line CL of the second protrusion  102 . Therefore, the initial-inductance of the variable coupled inductor can be enhanced and light-load efficiency can be improved by means of the magnetic structure. Furthermore, the material of the variable coupled inductor of the present invention can be a ferrite material to achieve a high-saturation current, and copper sheet is used as an electrode to reduce the DC resistance, so efficiency is better in heavy-load. In other words, the variable coupled inductor of the present invention can improve efficiency in both light-load and heavy-load situations. 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.