Patent Publication Number: US-7915993-B2

Title: Inductor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation in Part application of application Ser. No. 11/156,361, filed on Jun. 20, 2005, which is a Continuation in Part application of application Ser. No. 10/937,465, filed on Sep. 8, 2004. This application has a reference to application Ser. No. 11/156,361 and application Ser. No. 10/937,465, and application Ser. No. 11/156,361 has a reference to application Ser. No. 10/937,465. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an inductor and, more particularly, to an inductor with at least two different reductions in inductance. 
     2. Description of the Prior Art 
     An inductor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor&#39;s ability to store magnetic energy is measured by its inductance. Typically an inductor is a conducting wire shaped as a coil, the loops helping to create a strong magnetic field inside the coil due to Faraday&#39;s Law of Induction. Inductance is an effect resulting from the magnetic field that forms around a current-carrying conductor which tends to resist changes in the current. The number of loops, the size of each loop, and the material it is wrapped around all affect the inductance. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability such as ferrite magnet. 
     In electromagnetism, permeability is the degree of magnetization that a material obtains in response to an applied magnetic field. The permeability of a magnetic material is the ability of the material to increase the flux intensity or flux density within the material when electric current flows through a conductor wrapped around the magnetic materials providing the magnetization force. In general, when electric current flows through a conventional inductor, only one permeability can be obtained. Therefore, the usage of the conventional inductor is limited. 
     Furthermore, for those of ordinary skill in the art, an inductive coil is usually not suitable for current measurement due to the variation of resistance with temperature. Specifically, an inductive coil is generally made with copper coils. Since the copper has a relative high temperature coefficient of resistance (TCR), as the current passes through the copper coils, the coils experience a temperature rise. A higher temperature in turn causes a higher resistance in the coils with a positive TCR. The variation of the resistance in turn causes a change in the current conducted in the coils. For these reasons, in order to measure a direct current conducted in the coils, a separate resistor that is serially connected to the coils is often required. 
     Therefore, a need still exists in the art of design to provide a novel and improved inductor with at least two different reductions in inductance. In order simplify the implementation configuration with reduced cost; it is desirable to first eliminate the requirement of using a separate resistor for current measurement. It is desirable that the improved inductor configuration can be simplified to achieve lower production costs, high production yield while capable of providing inductor that more compact with lower profile such that the inductor can be conveniently integrated into miniaturized electronic devices. It is further desirable the new and improved inductor can improve the production yield with simplified configuration. 
     SUMMARY OF THE INVENTION 
     An objective of the invention is to provide an inductor with at least two different reductions in inductance. 
     Another objective of the invention is to provide a new inductive coil composed of alloys of low TCR such as Cu—Mn—Ni, Cu—Ni, Ni—Cr, and Fe—Cr alloys such that a high degree of current measurement accuracy can be maintained. With low value TCR the error of current measurement due to temperature variations are maintained at a very low level without requiring using a separate resistor. 
     According to one embodiment, an inductor of the invention comprises a first core, a second core, a protruding structure, at least two gaps and a conducting wire. The first core has a protruding portion. The second core is disposed opposite to the first core. The protruding structure protrudes from the protruding portion of the first core and toward the second core. The at least two gaps are between the protruding portion of the first core and the second core. The conducting wire winds around at least one of the first and second cores. The conducting wire is composed of a metallic alloy having temperature coefficients of resistance (TCR) 700 ppm/° C. or lower, wherein the conducting wire has a specific resistance value of 1.42 μΩm or lower. When electric current flows through the conducting wire, magnetic flux varies at the at least two gaps so as to generate at least two different reductions in inductance. 
     According to another embodiment, an inductor of the invention comprises a first core, a second core, at least one protruding structure, at least two gaps and a conducting wire. The first core has a protruding portion. The second core is disposed opposite to the first core. The at least one protruding structure protrudes from the protruding portion of the first core and toward the second core. The at least two gaps are between the protruding portion of the first core and the second core. The conducting wire winds around at least one of the first and second cores. The conducting wire has a specific resistance value of 1.42 μΩm or lower. When electric current flows through the conducting wire, magnetic flux varies at the at least two gaps so as to generate at least two different reductions in inductance. 
     According to another embodiment, an inductor of the invention comprises a first core, a second core, at least two gaps and a conducting wire. The first core has a protruding portion. The second core is disposed opposite to the first core. The at least two gaps are between the protruding portion of the first core and the second core. The conducting wire winds around at least one of the first and second cores. The conducting wire has a specific resistance value of 1.42 μΩm or lower. When electric current flows through the conducting wire, magnetic flux varies at the at least two gaps so as to generate at least two different reductions in inductance. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective illustrating an inductor according to one embodiment of the invention. 
         FIG. 2  is a side view illustrating the inductor shown in  FIG. 1 . 
         FIG. 3  is a perspective view illustrating the first core shown in  FIG. 1 . 
         FIG. 4  illustrates three types of the protruding structure in different shapes. 
         FIG. 5  illustrates a saturation current curve of the inductor shown in  FIG. 1 . 
         FIG. 6  illustrates a performance of the B-H curve which is the characteristic of the magnetic material of the inductor shown in  FIG. 1 . 
         FIG. 7  is a side view illustrating an inductor according to another embodiment of the invention. 
         FIG. 8  illustrates some types of the protruding structure in different shapes. 
         FIG. 9  is a side view illustrating an inductor according to another embodiment of the invention. 
         FIG. 10  is a side view illustrating an inductor according to another embodiment of the invention. 
         FIG. 11  is a side view illustrating an inductor according to another embodiment of the invention. 
         FIG. 12  is a side view illustrating an inductor according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 to 3 ,  FIG. 1  is a perspective illustrating an inductor  1  according to one embodiment of the invention,  FIG. 2  is a side view illustrating the inductor  1  shown in  FIG. 1 , and  FIG. 3  is a perspective view illustrating the first core  10  shown in  FIG. 1 . As shown in  FIGS. 1 and 2 , the inductor  1  comprises a first core  10 , a second core  12 , a protruding structure  14  and a conducting wire  16 . The first core has a protruding portion  100 . The second core  12  is disposed opposite to the first core  10 . The protruding structure  14  protrudes from the protruding portion  100  of the first core  10  and toward the second core  12 . In this embodiment, a volume of the protruding structure  14  is smaller than or equal to three percent of the first core. The protruding portion  100  is located at one side of the first core  10 , there is a first gap G 1  between the protruding portion  100  of the first core  10  and the second core  12 , and there is a second gap G 2  between the protruding structure  14  and the second core  12 . The conducting wire  16  passes through the hollow of the first core  10  and winds around the second core  12 . It should be noted that, in another embodiment, the conducting wire  16  can also wind around the first core  10 , and it depends upon practical applications. 
     As shown in  FIG. 3 , there are two longitudinal protruding structures  14  protruding from opposite sides of the first core  10 . In this embodiment, the first core  10  and the protruding structures  14  are formed integrally. A material of the first core  10 , the second core  12  or the protruding structure  14  can be iron powder, ferrite, permanent magnet or other magnetic materials. Since the first core  10  and the protruding structures  14  are formed integrally, the material of the first core  10  is the same as that of the protruding structures  14 . However, in another embodiment, the protruding structures  14  can be individual components attached on the first core  10 , and it depends upon practical applications. If the protruding structures  14  are individual components, the material of the protruding structures  14  may be the same as or different from the first core  10 . Furthermore, the first gap G 1  can be an air gap, a magnetic gap or a non-magnetic gap, the second gap G 2  can be also an air gap, a magnetic gap or a non-magnetic gap, and it depends upon practical applications. 
     In this embodiment, the first core  10  has a first permeability μ1, the second core  12  has a second permeability μ2, the first gap G 1  has a third permeability μ3, the second gap G 2  has a fourth permeability μ4, each of the protruding structures  14  has a fifth permeability μ5, and there is a relation between the first through fifth permeabilities as follows, μ1≧μ2≧μ5≧μ4≧μ3. For example, if the materials of the first core  10 , the second core  12  and the protruding structures  14  are the same, and the first gap G 1  and the second gap G 2  are the same, the relation between the first through fifth permeabilities will be μ1=μ2=μ5&gt;μ4=μ3. 
     As shown in  FIGS. 2 and 3 , in this embodiment, a shape of the protruding structure  14  is rectangle, and a major axis of the protruding structure  14  is perpendicular to that of the protruding portion  100 . However, referring to  FIG. 4 ,  FIG. 4  illustrates three types of the protruding structure  14  indifferent shapes. In another embodiment, the shape of the protruding structure  14  can be also trapezoid, taper or arc, as shown in  FIG. 4 . In other words, the shape of the protruding structure  14  can be designed based on practical applications. 
     In this embodiment, the first gap G 1  may be larger than or equal to 0.01 mm and lower than or equal to 0.3 mm, and the second gap G 2  may be lower than or equal to 0.15 mm. Furthermore, as shown in  FIG. 3 , the protruding structure  14  has a length L, a width W and a thickness T. The length L will affect an initial inductance of the inductor  1 , and the thickness T relates to the first gap G 1  and the second gap G 2 . The length L, the width W and the thickness T can be determined based on practical applications. Preferably, the width W of the protruding structure  14  may be lower than or equal to 1.5 mm. 
     In this embodiment, the conducting wire  16  may be composed of a metallic alloy having temperature coefficients of resistance (TCR) 700 ppm/° C. or lower, wherein the conducting wire  16  has a specific resistance value of 1.42 μΩm or lower. A metallic alloy of low TCR may be Cu—Mn—Ni metallic alloy, Ni—Cr metallic alloy, Cu—Ni metallic alloy, Fe—Cr metallic alloy or the like. The table 1 below shows some examples of metallic alloys with achievable low TCR for each of these metallic alloys. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Specific resistance 
                   
               
               
                 Material system 
                 value (micro ohm-m) 
                 TCR (ppm/deg) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Cu—Mn—Ni system 
                 0.44 
                 ±10 
               
               
                 Cu—Ni system 
                 0.49 
                 ±20 
               
               
                   
                 0.3 
                 180 
               
               
                   
                 0.15 
                 420 
               
               
                   
                 0.1 
                 650 
               
               
                   
                 0.43 
                 700 
               
               
                 Ni—Cr system 
                 1.08 
                 200 
               
               
                   
                 1.12 
                 260 
               
               
                 Fe—Cr system 
                 1.42 
                 80 
               
               
                   
               
            
           
         
       
     
     Referring to  FIGS. 5 and 6 ,  FIG. 5  illustrates a saturation current curve of the inductor  1  shown in  FIG. 1 , and  FIG. 6  illustrates a performance of the B-H curve which is the characteristic of the magnetic material of the inductor  1  shown in  FIG. 1 . When electric current flows through the conducting wire  16 , magnetic flux varies at the gaps G 1  and G 2  so as to generate two different reductions in inductance. The invention utilizes the protruding structures  14  to form the second gap G 2 , so as to generate first inductance dropped indicated by the arrow A 1  in  FIG. 5 . Afterwards, due to saturation flux density of the material and the first gap G 1 , the state indicated by the arrow A 2  in  FIG. 5  can be obtained. Finally, second inductance dropped indicated by the arrow A 3  in  FIG. 5  is achieved. As shown in  FIG. 6 , when electric current flows through the inductor  1  of the invention, two different permeabilities indicated by the two arrows A 4  and A 5  can be obtained. 
     Referring to  FIG. 7 ,  FIG. 7  is a side view illustrating an inductor  3  according to another embodiment of the invention. As shown in  FIG. 3 , the main difference between the inductor  3  and the aforesaid inductor  1  is that the protruding structure  14  contacts the second core  12 . In other words, in this embodiment, the aforesaid second gap G 2  substantially tends to zero. 
     Referring to  FIG. 8 ,  FIG. 8  illustrates some types of the protruding structure  14  in different shapes. As shown in  FIG. 8 , the protruding structure(s)  14  may be single on one side or four on opposite sides symmetrically, and the shape of the protruding structure  14  may be arc, circular or rectangle. Furthermore, the length of the protruding structure  14  shown in  FIG. 8  can be shorter than that of the protruding structure  14  shown in  FIG. 3 . That is to say, the number, arrangement and shape of the protruding structures  14  of the invention do not be limited to the aforesaid description with related figures and can be determined based on practical applications. 
     Referring to  FIGS. 9 to 11 ,  FIG. 9  is a side view illustrating an inductor  5  according to another embodiment of the invention,  FIG. 10  is a side view illustrating an inductor  7  according to another embodiment of the invention, and  FIG. 11  is a side view illustrating an inductor  9  according to another embodiment of the invention. As shown in  FIG. 9 , the first and second cores  10  and  12  are EE-shaped. As shown in  FIG. 10 , the first and second cores  10  and  12  are EI-shaped. As shown in  FIG. 11 , the first and second cores  10  and  12  are TI-shaped. In other words, the shapes of the first and second cores  10  and  12  of the invention can be also determined based on practical applications. 
     Referring to  FIG. 12 ,  FIG. 12  is a side view illustrating an inductor  8  according to another embodiment of the invention. As shown in  FIG. 12 , there are two protruding structures  14   a  and  14   b  protruding from the protruding portion  100  of the first core  10 . In this embodiment, there is a first gap G 1  between the protruding portion  100  of the first core  10  and the second core  12 , there is a second gap G 2  between the protruding structure  14   a  and the second core  12 , and there is a third gap G 3  between the protruding structure  14   b  and the second core  12 . As shown in  FIG. 12 , since the thickness of the protruding structure  14   a  is larger than that of the protruding structure  14   b , the second gap G 2  is smaller than the third gap G 3 . In other words, if there are at least two protruding structures with different thickness protruding from the protruding portion  100  of the first core  10 , there will be at least two different gaps between the protruding structures and the second core  12  correspondingly. The number of protruding structures with different thickness can be determined based on practical applications. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.