Abstract:
Described are methods and systems for using a planar inductor that includes a magnetically conductive core, a first planar coil and a second planar coil. The first and second planar coils are attached to a first bridge, located about the core, and are composed of a conductive material. The first and second planar coils have at least one thermally conductive surface exposed to cooling fluid. The first planar coil, the first bridge and the second planar coil are formed from a first unitary section of conductive material. The second planar coil is positioned relative to the first planar coil in a spaced relationship, which is defined by a thickness of the first bridge. An upper surface of the first planar coil is oriented toward a lower surface of the second planar coil to define a first cooling channel between the first planar coil and the second planar coil.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Application No. 61/505,476, filed Jul. 7, 2011, the entirety of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to inductors and ignition transformers using planar magnetics. 
       BACKGROUND OF THE INVENTION 
       [0003]    Magnetic components such as inductors and transformers are used in power supply designs for various devices, including plasma cutting power supplies. High voltage ignition transformers form an integral part of the high voltage high frequency (“HVHF”) circuits used in plasma cutting systems. Traditionally, these types of transformers are fabricated using custom made plastic bobbins that ensure appropriate inter-winding spacing and clearance to meet regulatory and functional specifications. The windings are typically wound manually and need to be done precisely in order to meet the self inductance and coupling factor requirements of the application. 
         [0004]    Custom made plastic bobbins have a significant impact on the size and cost of a transformer. Furthermore, the windings can often have fractional turns and imprecise winding methods results in unit to unit start reliability variance. Further, the use of custom made bobbins can make it difficult to have manufacturer redundancy, resulting in supply chain vulnerability. 
         [0005]    Inductors and transformers can account for a significant portion of the power supply cost. Inductors and transformers can also account for a majority of a power supply&#39;s weight. The effort to reduce the cost of these components can be driven by the expectation of increase in the price of materials, such as copper and steel, due to the increase in global demand. For example, the price of copper has increased by more than 40% between 2010 and 2011. 
         [0006]    Planar technology has been used to improve on the current methods by reducing size and cost. One aspect of planar technology replaces copper wires with copper-clad printed circuit boards (“PCBs”). Using PCBs in lieu of copper wires can reduce the amount of copper used. In some examples, there is a reduction of more than 50% in the amount of copper used. However, using PCBs in lieu of copper wires still results in other issues, such as overheating and cost at high currents (e.g., 80 amps or higher). 
       SUMMARY OF THE INVENTION 
       [0007]    The invention uses planar coils composed of conductive materials to replace windings of wire. The planar coils are scalable and can be stacked to form a planar inductor. Two or more planar inductors can be used to form a transformer. 
         [0008]    The invention, in one aspect, features a planar inductor that includes a magnetically conductive core, a first planar coil and a second planar coil. The first planar coil is attached to a first bridge and is located about the core. The first planar coil is made out of a conductive material and has at least one thermally conductive surface exposed to cooling fluid. The second planar coil is also attached to the first bridge and is also located about the core. Like the first planar coil, the second planar coil is made out of a conductive material and has at least one thermally conductive surface exposed to cooling fluid. The first planar coil, the first bridge and the second planar coil are formed from a first unitary section of conductive material. The second planar coil is positioned relative to the first planar coil in a spaced relationship. The spaced relationship is defined by a thickness of the first bridge. An upper surface of the first planar coil is oriented toward a lower surface of the second planar coil to define a first cooling channel between the first planar coil and the second planar coil. 
         [0009]    Another aspect of the invention includes a method of manufacturing a planar inductor that includes cutting a section of thermally conductive material into a pattern to create a first planar coil, a second planar coil and a bridge that is disposed between the first and second planar coils. The method also bends the section of thermally conductive material at the bridge so that the second planar coil is positioned opposite and at least substantially in parallel to the first planar coil. At least two connection points a created during manufacturing for a combination of the first planar coil, the bridge and the second planar coil. 
         [0010]    Another aspect of the invention includes a method of manufacturing an ignition transformer that includes selecting two or more planar inductors that are created by cutting a section of thermally conductive material into a pattern to create a first planar coil, a second planar coil and a bridge disposed between the first and second planar coils, bending the section of thermally conductive material at the bridge such that the second planar coil is positioned opposite and at least substantially in parallel to the first planar coil, and creating at least two connection points for a combination of the first planar coil, the bridge and the second planar coil. The method further includes coupling the two or more planar inductors by placing the two or more planar inductors in a close proximity so that there is a fixed gap between the two or more planar inductors. 
         [0011]    Another aspect of the invention includes a method of using planar coils to form a planar inductor. The method includes utilizing a magnetically conductive core, utilizing a first planar coil, which is attached to a first bridge, and is located about the core, and utilizing a second planar coil, which is also attached to the first bridge, and is also located about the core. The first planar coil and the second planar coil are made up of a conductive material and have at least one thermally conductive surface exposed to cooling fluid. The first planar coil, the bridge and the second planar coil are formed from a first unitary section of conductive material, and the second planar coil is positioned relative to the first planar coil in a spaced relationship defined by a thickness of a bent portion of the first bridge. An upper surface of the first planar coil is oriented toward a lower surface of the second planar coil to define a first cooling channel between first planar coil and the second planar coil. 
         [0012]    Another aspect of the invention includes a combination heat exchanger inductor that has a magnetically conductive core, a substantially rigid, first planar coil located about the core, a substantially rigid, second planar coil located about the core, and a substantially rigid bridge contiguous with said first and second planar coils. The first planar coil is made of conductive material and has a first exposed thermally conductive surface. The second planar coil is made of conductive material and has a second thermally conductive surface. The bridge is made of said conductive material and is oriented at least substantially orthogonal to the first and second planar coils so that the bridge can provide a spaced relationship and define a cooling channel, while orienting the first and second thermally conductive surfaces opposite each other with the cooling channel. 
         [0013]    Another aspect of the invention includes a method of manufacturing an inductor that includes providing a magnetically conductive core, etching a conductive material to form a substantially rigid first planar coil that has first exposed thermally conductive surface and a second planar coil that has a second thermally conductive surface. The method also includes manipulating the conductive material to form a substantially rigid bridge contiguous with the first and second planar coils such that the bridge is oriented at least substantially orthogonal to the first and second planar coils in order to provide a spaced relationship and define a cooling channel, and to orient said first and second thermally conductive surfaces opposite each other with the cooling channel therebetween. 
         [0014]    Each of the aspects above can further employ one or more of the following advantages. 
         [0015]    In some embodiments, a third planar coil, attached to a second bridge is located about the core and is composed of the conductive material. The third planar coil can have at least one thermally conductive surface exposed to cooling fluid. A fourth planar coil, which attached to the second bridge and is located about the core, is composed of conductive material and has at least one thermally conductive surface exposed to cooling fluid. The third planar coil, the second bridge and the fourth planar coil are formed from a second unitary section of conductive material. The third planar coil is positioned relative to the second planar coil in a spaced relationship equal to the thickness of a bent portion of the first bridge or the thickness of a bent portion of the second bridge such that an upper surface of the second coil is oriented toward a lower surface of the third coil to define a second cooling channel between second planar coil and the third planar coil. The fourth planar coil is positioned relative to the third planar coil in a spaced relationship defined by a thickness of a bent portion of the second bridge such that an upper surface of the third coil is oriented toward a lower surface of the fourth coil to define a third cooling channel between third planar coil and the fourth planar coil. The magnetically conductive core can be an E-type core. 
         [0016]    In some embodiments, the number of cooling channels can be 2n−1, where n is the number of pairs of planar coils. Fluid cooling can be done using a fan that is oriented to direct an air flow to cool the planar inductor through the first cooling channel, below the first planar coil and above the second planar coil. 
         [0017]    In some embodiments, a first pair of planar coils can be positioned in a spaced relationship relative to a second part of planar coils such that the spaced relationship is equal to a thickness of a bent portion of the first pair bridge or a thickness of a bent portion of the second pair bridge. In some embodiments, the thickness of the bent portion of the first bridge and the thickness of the bent portion of the second bridge is the same. Te first unitary section of conductive material and the second unitary section of conductive material can be identical. The conductive material can be cooper or aluminum. 
         [0018]    In some embodiments, the second planar coil and the third planar coil are soldered together so that the first planar coil, the second planar coil, the third planar coil and the fourth planar coil are connected through the first bridge, a solder joint, and the second bridge. A first connector and a second connector can be added to a planar inductor in order to connect the planar inductor to a voltage source or a load. In some embodiments, the planar coils can be stacked to achieve a desired inductance value. 
         [0019]    In some embodiments, an ignition transformer can include a first and a second planar inductor. The first and the second planar inductor can be separated by a fixed gap to provide a predetermined inductance value for the ignition transformer. The fixed gap can be maintained using standoffs or spacers of a required height bobbin. 
         [0020]    In some embodiments, the planar inductor can have a first connector and a second connector and the another planar inductor can have a third connector and a fourth connector such that the first connector or the second connector are not attached to any device attached to the third connector or the fourth connector. 
         [0021]    In some embodiments, the first planar coil and the second planar coil are cut so that a magnetically conductive core can be used to hold multiple planar coils. An air bobbin can be used to hold two or more planar inductors in place. Connecting the combination of the first planar coil, the bridge and the second planar coil to a combination of a third planar coil, a second bridge and a fourth planar coil through the connection points can create a larger winding. 
         [0022]    Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
           [0024]      FIG. 1  shows a planar coil. 
           [0025]      FIG. 2  shows a stack of planar coils. 
           [0026]      FIG. 3  shows a front sectional view of a stack of planar coils forming a planar inductor. 
           [0027]      FIG. 4  shows a stack of planar coils with a magnetically conductive core. 
           [0028]      FIG. 5  shows a pair of planar coils connected with bridge that are created from a unitary section of conductive material. 
           [0029]      FIG. 6  shows a process for creating a planar inductor. 
           [0030]      FIG. 7  shows an ignition transformer. 
           [0031]      FIG. 8  shows a process for creating an ignition transformer. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0032]      FIG. 1  shows a planar coil  101 . The planar coil  101  has a coil width  105 , a turn width  109 , an inter-turn spacing  113 , and a turn number  117 . The coil width  105  is a distance from a center of the planar coil to a furthest edge of the planar coil  101 . The turn width  109  is a width of a turn of the planar coil  101 . The inter-turn spacing  113  is a gap between adjacent turns of the planar coil  101 . The turn number  117  is the number of turns the planar coil  101  takes. At or around the center of the planar coil  101  is a hole  121 . A magnetically conductive core (see below) can be inserted into the hole  121 . 
         [0033]    The planar coil  101  can be made from a conductive material, such as copper or aluminum. In some embodiments, the planar coil  101  is made solely of a conductive material. The conductive material is cut, etched, or similarly manipulated in order to achieve a desired shape and size. The conductive material can be cut, etched, or similarly manipulated to have the turn diameter  105 , the turn width  109 , the inter-turn spacing  113 , and the turn number  117 . The conductive material used for the planar coil  101  can be thermally conductive such that the surface of the planar coil  101  is thermally conductive. 
         [0034]    In other embodiments (not shown), the planar coil  101  can be supported on a printed circuit board (“PCB”). The planar coil  101  can be prefabricated before being bonded to a PCB substrate. A sheet of the conductive material can also be bonded to a PCB substrate and subsequently cut, etched or similarly manipulated to achieve the desired shape and size on a PCB. 
         [0035]      FIG. 2  shows a planar inductor made up of a stack of planar coils  201 . The stack of planar coils  201  can have similar properties exhibited by a coil of wire. For example, each individual planar coil (e.g., planar coils  205   a - c ) can represent a single turn in a coil of wire and thus using more planar coils  205   a - c  can yield more inductance like having more turns in a coil with a traditional inductor. Other properties of traditional wire-coil inductors can be realized with the stack of planar coils  201 . A length  209  can have similar effects to the inductance of the planar inductor as would the length of a coil of wire for a traditional inductor. A width  213  can be determined by measuring the distance from an outer edge of a planar coil  205   a  to the center of the planar coil  205   a . Gaps are present in the stack of planar coils  201  (e.g., gap  217   a - c ). These gaps are used as cooling channels. A cooling channel exists between every two planar coils. A cooling fluid, such as air, can be introduced into the cooling channel in order to cool the planar coils that form the cooling channel. In some embodiments, the cooling fluid can be any type of liquid or gas. 
         [0036]    In some embodiments, the planar coils  205   a - c  can be identical. In other embodiments, the planar coils  205   a - c  can have be different and have dissimilar shapes, sizes, thickness or compositions. 
         [0037]      FIG. 3  shows a front sectional view of the stack of planar coils  201 ′. Planar coils in the stack of planar coils  201 ′ are all connected. For example, planar coil  301   a  is connected to planar coil  301   b  through connection point  305   a , planar coil  301   b  is connected to planar coil  301   c  through connection point  305   b , planar coil  301   c  is connected to planar coil  301   d  through connection point  305   c , and so on. The purpose of connection points  350   a - c  is to make the stack of planar coils appear to be a single wire, much like traditional inductors which are made from a single wire. 
         [0038]    In some embodiments, there can be multiple types of connection points. For example, connection point  305   a  can be a wire or spacer and connection  305   b  can be a contiguous portion of a conductive material between two planar coils (e.g., planar coil  301   b  and planar coil  301   c ). The wire or spacer can be soldered to a planar coil. 
         [0039]      FIG. 4  shows a planar inductor  401 . The planar inductor  401  includes a magnetically conductive core  405 . The magnetically conductive core  405  is used to increase the inductance of the stack of planar coils  409 . The magnetically conductive core  405  can be made from any magnetically conductive materials, such as iron. The magnetically conductive core  405  can be used to support or hold a stack of planar coils  409 . The magnetically conductive core  405  can surround a stack of planar coils  409 , as depicted in  FIG. 4 . 
         [0040]    In some embodiments, the magnetically conductive core  405  can be an E-type conductive core, meaning the magnetically conductive core  405  is shaped like the capital letter “E.” As shown in  FIG. 4 , the magnetically conductive core  405  can be made from 4 E-type conductive cores (e.g.,  413   a - d ). The E-type conductive cores  413   a - d  can be made of different types of conductive material or can be made of the same conductive material. In some embodiments, only two E-type conductive cores are used. In other embodiments, any number of E-type conductive cores can be used. 
         [0041]      FIG. 5  shows a combined pair of planar coils  501 . The combined pair of planar coils  501  includes a first planar coil  505   a  and a second planar coil  505   b . The first planar coil  505   a  and the second planar coil  505   b  are connected through a bridge  509 . The bridge  509  can act as a connection point between the first planar coil  505   a  and the second planar coil  505   b . The combined pair of planar coils  501  can be fabricated from a unitary section of thermally and electrically conductive material. Fabrication can be done by etching, cutting (e.g., with a plasma arc torch or with a laser), milling or any other method that can manipulate the unitary section of thermally conductive material and be used to create the winding in the first planar coil  505   a  or the second planar coil  505   b.    
         [0042]    In some embodiments, the bridge  509  can be bent twice so that the first planar coil  505   a  and the second planar coil  505   b  are substantially parallel (e.g., the bends can be approximately 90 degree bends towards a common point). In other words, an upper surface of the first planar coil  505   a  is oriented toward a lower surface of the second planar coil  505   b . The portion of the bridge  509  between bends can define a thickness. The thickness determines how far apart the first planar coil  505   a  and the second planar coil  505   b  are from each other. The distance between the first planar coil  505   a  and the second planar coil  505   b  can define a spaced relationship for the planar inductor. The spaced relationship can be used as a distance between pairs of planar coils in a planar inductor. End point  513   a  and end point  513   b  can also be bent so that the combined pair of planar coils  501  can be connected to other pairs of planar coils. In some embodiments, instead of bending end point  513   a  or end point  513   b , connectors can be affixed to the end point  513   a  or the end point  513   b.    
         [0043]    By positioning the first planar coil  505   a  and the second planar coil  505   b  to be substantially parallel, a cooling channel is defined. A cooling fluid, such as air, can be introduced into the cooling channel in order to cool the first planar coil  505   a  and the second planar coil  505   b . In some embodiments, the cooling fluid can be any type of liquid or gas. In embodiments where multiple pairs of planar coils are used, a cooling channel can exist between adjacent pairs of planar coils. The number of cooling channels formed can be equal to one less than twice the number of pairs of planar coils. 
         [0044]    Manufacturing the combined pair of planar coils  501  has several advantages. First, the combined pair of planar coils  501  eliminates having to create some connection points. This is because the bridge  509  acts as a connection point. Eliminating some connection points can speed up the process of creating a planar inductor, use less materials (e.g., no need for additional wires and solder), and avoid some manufacturing defects (e.g., such as from an improperly connected wires). Second, the bridge  509  can be used to maintain a consistence gap between the first planar coil  505   a  and the second planar coil  505   b , which is important for cooling purposes. 
         [0045]      FIG. 6  shows a process  601  for creating planar inductors. In step  605 , a unitary section of thermally conductive material is selected. The unitary section of thermally conductive material is the basis for a pair of planar coils. A pair of planar coils and a bridge are fabricated from the selected section of thermally conductive material in step  609 . The pair of planar coils and bridge can resemble a configuration as shown in  FIG. 5 . As described above, fabrication can be done by cutting, etching or similarly manipulating the section of thermally conductive material. The bridge is bent in step  613 . The bridge is bent at two different locations so that the pair of planar coils is substantially parallel. In step  617 , if an additional planar coil is needed (e.g., another pair of planar coils is necessary to achieve a desired inductance), the process repeats itself starting at step  601 . When all additional pairs of planar coils are created, connection points will be added in step  625 . In some embodiments, pairs of planar coils are spaced the same as between the first planar coil and the second planar coil of a pair of planar coils. Step  625  is necessary only if there is more than one pair of planar coils, since the bridge acts as a connection point between pairs of planar coils. The decision to add connection points in step  625  is made at step  621 . Connection points can be a solder joint, wire, or metal spacer with a fastener between end points of planar coils belonging to different pairs of planar coils (e.g., end point  513   a  or end point  513   b ). After all the connection points have been added, connectors, such as termination wires, are added to unconnected ends of any planar coils in step  629 . In some embodiments, there are only two unconnected ends in the planar inductors. The connectors are available for connecting the inductor to the external world as per the requirements of the application. 
         [0046]      FIG. 7  shows an ignition transformer  701 . The ignition transformer  701  can be made by coupling a first planar inductor  705   a  and a second planar inductor  705   b . A fixed gap  709  is maintained between a first planar inductor  705   a  and a second planar inductor  705   b . The inductance of the first planar inductor  705   a  can be determined using turn diameters, turn widths, inter-turn spacings, and turn numbers of the first planar inductor  705   a . Similarly, the inductance of the second planar indictor  705   b  can be determined using turn diameters, turn widths, inter-turn spacings, and turn numbers of the second planar inductor  705   b . The coupling factor between the two coils is determined by the respective coil inductances and the fixed gap  709 . Transformers have four or more connectors (two per planar inductor) for connecting to a source or a load. 
         [0047]      FIG. 8  shows a process  801  for creating ignition transformers. In step  805 , a first planar inductor is created. In some embodiments, step  805  is or is similar to process  601 . In step  809 , a second planar inductor is created. In some embodiments, step  809  is or is similar to process  601 . A decision to make more planar inductors is made in step  813 . If more planar inductors are necessary, step  817  creates additional planar inductors. In some embodiments, step  817  is or is similar to process  601 . Step  813  is repeated as many times as needed (e.g., to create as many planar inductors as needed). The planar inductors created are coupled in step  821 . Coupling can be simply placing two or more planar inductors in close proximity to each other, such as by stacking them with an air gap in-between each planar inductor. Coupling can also be done using insulated stand-offs or spacers of a required height. Bobbins can also be used in a transformer. Bobbins can be selected for the affect on the inductance of the transformer or for achieving a desired distance between inductors. The spacing between inductors can also be used to form additional cooling channels to help cool the transformer (thereby meaning there are cooling channels between planar coils and between inductors). 
         [0048]    In some embodiments, cooling fans are used to direct air flow in between cooling channels to cool both planar inductors and ignition transformers. However, any type of fluid cooling can be used to cool inductors or transformers. In some embodiments, multiple types of fluid cooling can be used. 
         [0049]    While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The alternatives described herein are examples for illustration only and not to limit the alternatives in any way. The steps of the invention can be performed in a different order and still achieve desirable results. Other embodiments are within the scope of the following claims.