Abstract:
A transformer network circuit utilizing multiple smaller transformer cores, instead of a single, relatively larger core, for transferring electrical power while maintaining a smaller overall core mass.

Description:
CLAIM OF PRIORITY 
     Priority is claimed to U.S. Provisional patent application Ser. No. 61/662,992, filed on Jun. 22, 2012; which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present application is related generally to small-size step-up transformers. 
     BACKGROUND 
     Transformers can be used to step up, or step down, a voltage or a current, from primary windings to secondary windings. A core of the transformer can saturate, based on the amplitude of the electrical current through the windings, time of electrical current flow, and number of turns. Saturation of the core can result in reduced impedance of primary windings and a resulting increase in electrical current through the primary windings. This increased electrical current can result in undesirable heat generation and damage to components. A larger core may be used to avoid core saturation. In some applications, use of a larger core is undesirable, such as if small overall size is preferred, or due to a high cost of a larger core. 
     SUMMARY 
     It has been recognized that it would be advantageous to avoid transformer core saturation while minimizing transformer size increase. The present invention is directed to a transformer network that satisfies these needs. The apparatus comprises an LC switching circuit including a center connection, a top connection, and a bottom connection; primary windings comprising top primary windings and bottom primary windings; and secondary windings having a first end and a second end. 
     The center connection of the LC switching circuit can be electrically connected to a first end of the top primary windings and to a first end of the bottom primary windings. The top primary windings can be wrapped in a first direction around a first transformer core. The bottom primary windings can be wrapped in a second direction around the first transformer core. The first direction is opposite to the second direction. 
     The top primary windings can be wrapped in the first direction around at least one additional transformer core then a second end of the top primary windings can be electrically connected to the top connection of the LC switching circuit. The bottom primary windings can be wrapped in the second direction around the additional transformer core(s), then a second end of the bottom primary windings can be electrically connected to the bottom connection of the LC switching circuit. 
     The secondary windings can be wrapped around at least one of the transformer cores. The first end and the second end of the secondary windings can be configured to be electrically connected across a load. 
     Use of multiple cores, instead of a single larger core, can allow a relatively larger amount of electrical power transfer from primary to secondary windings without core saturation. The multiple cores can have a smaller overall mass or volume than a single core designed for the same power transfer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a transformer network, in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic of primary windings and transformer cores of a transformer network, in accordance with an embodiment of the present invention; 
         FIGS. 3   a - d  are schematics of transformer cores and secondary windings in series on a transformer network, in accordance with an embodiment of the present invention; 
         FIG. 4  is a schematic of transformer cores and secondary windings in parallel on a transformer network, in accordance with an embodiment of the present invention; 
         FIG. 5  is a schematic of transformer cores and secondary windings in parallel on a transformer network, in accordance with an embodiment of the present invention; 
         FIG. 6  is a schematic of secondary windings in parallel, primary windings, and transformer cores, of a transformer network, in accordance with an embodiment of the present invention. 
       DEFINITIONS 
       As used herein, terms related to direction of windings, such as “the top primary windings wrapped in a first direction” or “the bottom primary windings wrapped in a second direction” refers to a direction of winding wraps in a direction of electrical current flow around a core of a transformer. The winding direction relates to a direction of the magnetic field that will be produced by electrical current through the windings. Thus, if electrical current through windings wrapped in the first direction creates a magnetic field in one direction in the core (up for example), then electrical current through windings wrapped in the second direction can create a magnetic field in an opposite direction in the core (down for example). 
     
    
    
     DETAILED DESCRIPTION 
     As illustrated in  FIG. 1 , a transformer network  10  is shown comprising an LC switching circuit  9  including a center connection  3 , a top connection  1 , and a bottom connection  2 ; primary windings  15  comprising top primary windings  4  and bottom primary windings  5 ; and secondary windings  7  having a first end  7   f  and a  7   s  second end. The center connection  3  can be electrically connected to a first end  4   f  of the top primary windings  4  and to a first end  5   f  of the bottom primary windings  5 . The top connection  1  of the LC switching circuit  9  can be electrically connected to a second end  4   s  of the top primary windings  4 . The bottom connection  2  of the LC switching circuit  9  can be electrically connected to a second end  5   s  of the bottom primary windings  5 . The primary windings  15  and the secondary windings  7  can be wrapped around a transformer core  6 . 
     As shown on the schematic  20  of top primary windings sections  4   a - 4   c  and transformer cores  6   a - 6   c  in  FIG. 2 , the top primary windings section  4   a  can be wrapped in a first direction  21  around a first transformer core  6   a . The bottom primary windings section  5   a  can be wrapped in a second direction  22  around the first transformer core  6   a.    
     The first direction  21  can be opposite to the second direction  22 . The top primary windings sections  4   b - 4   c  can be wrapped in the first direction  21  around at least one additional transformer cores  6   b - 6   c , then the second end  4   s  of the top primary windings  4  can be electrically connected to the top connection  1  of the LC switching circuit  9  ( FIG. 1 ). The bottom primary windings  5   b - 5   c  can be wrapped in the second direction  22  around the additional transformer core(s)  6   b - 6   c , then the second end  5   s  of the bottom primary windings  5  can be electrically connected to the bottom connection  2  of the LC switching circuit  9 . The secondary windings  7  can be wrapped around at least one of the transformer core(s)  6   a - 6   c.    
     Use of multiple transformer cores, instead of a single larger transformer core, can allow a relatively larger amount of electrical power transfer from primary to secondary windings without core saturation. The multiple transformer cores can have a smaller overall mass or volume than a single core designed for the same power transfer, which can result in a lower overall power supply size, weight, and cost. 
     The transformer networks described herein can especially be useful for step up transformers in which there is a relatively large voltage difference between primary and secondary windings. A turn ratio of the primary windings  15  to secondary windings  7  on one, some, or all of the transformer cores  6  can be greater than 1:10 in one embodiment or greater than 1:100 in anther embodiment. For example, in the circuit  60  of  FIG. 6 , N 15a :N 7a &gt;1:10, N 15b :N 7b &gt;1:10, N 15c :N 7c &gt;1:10, and/or N 15d :N 7d &gt;1:10. Alternatively, in the circuit  60  of  FIG. 6 , N 15a :N 7a &gt;1:100, N 15b :N 7b &gt;1:100, N 15c :N 7c &gt;1:100, and/or N 15d :N 7d &gt;1:100. A peak voltage of the secondary windings  7  can be at least 100 volts higher than a peak voltage of the primary windings  15  in one embodiment, or at least 1000 volts higher in another embodiment. 
     As shown in  FIG. 1 , secondary windings  7  of the transformer network  10  can have a first end  7   f  and a second end  7   s . The first end  7   f  and a second end  7   s  can be configured to be electrically connected across a load. The first end  7   f  and a second end  7   s  can be electrically connected to the load  8 . In one embodiment, the load  8  can be a high voltage multiplier circuit, such as a Cockcroft-Walton multiplier for example. The high voltage multiplier circuit can provide at least 1000 volts between an anode  18   b  and a cathode  18   a  of an x-ray tube  18 . 
     The LC switching circuit  9  of  FIG. 1  can comprise a direct current source  11 , an inductor  13 , a capacitor  14 , a first electronic switch  16 , a second electronic switch  17 , a center connection  3 , a top connection  1 , and a bottom connection  2 . The direct current source  11  can be electrically connected to a common connection  12  at one end and to a first connection  13   f  of an inductor  13  at an opposing end. A second connection  13   s  of the inductor  13  can be electrically connected to the center connection  3 . A capacitor  14  can have a first end  14   f  electrically connected to the top connection  1 , and at an opposing end, a second end  14   s  electrically connected to the bottom connection  2 . The capacitor  14  can be electrically connected in parallel with the primary windings  15 . The first electronic switch  16  can be electrically connected to the common connection  12  at one end and to the top connection  1  at an opposing end. The second electronic switch  17  can be electrically connected to the common connection  12  at one end and to the bottom connection  2  at an opposing end. 
     For normal operation of the LC switching circuit  9 , the first electronic switch  16  is closed and the second electronic switch  17  is open, thus allowing electrical current to flow from the direct current source  11  through the top primary windings  4  to ground or the common connection  12 . The first electronic switch  16  can then open and the second electronic switch  17  can close, thus allowing electrical current to flow from the direct current source  11  through the bottom primary windings  5  to the common connection  12 . This process can then be continually repeated. Allowing electrical current to alternately flow through the top primary windings  4  then through the bottom primary windings  5  (which is wound in an opposite direction) can result in a changing magnetic field of the transformer cores  6   a - 6   c . This changing magnetic field can induce an alternating current in the secondary windings  7 . The inductor  13  can impede the change in quantity of direction of electrical current flow, thus smoothing out the changes in electrical current which can result in a sine wave electrical current output in the secondary winding  7 . 
     As shown in  FIGS. 3   a - d , the secondary windings  7  can be wrapped in series. As shown on circuit  30   a  of  FIG. 3   a , an end  7   d  of a secondary winding  7   a  on one core  6   a  can be a connected to a beginning  7   e  of a secondary winding  7   b  on another core  6   b . Wrapping the secondary windings  7  in series can be beneficial for having the same electrical current through each section of secondary windings  7  and for allowing addition of voltage across the multiple secondary windings sections  7   a - 7   c . Thus total voltage V T  between the first end  7   f  of the secondary windings  7  and the second end  7   s  of the secondary windings  7  can be: V T =V1+V2+V3. 
     As shown on circuit  40  in  FIG. 4 , the secondary windings sections  7   a - 7   c  can be wrapped in parallel with the transformer cores  6   a - 6   c . Thus, the first end  7   f  of the secondary windings  7  can be a starting connection for all secondary windings sections  7   a - 7   c , and the second end  7   s  of the secondary windings  7  can be a terminal point for all secondary windings sections  7   a - 7   c . Wrapping the secondary windings sections  7   a - 7   c  in parallel can be beneficial for having the same voltage across each section of secondary windings  7 , but electrical current will be summed (I T =I1+I2+I3). If secondary windings sections  7   a - 7   c  are wrapped in parallel, typically the same number of turns N of secondary windings sections  7   a - 7   c  would be used on each core  6   a - 6   c . An alternative to having all secondary windings sections  7   a - 7   c  in parallel, or all in series, would be a combination of series and parallel. 
     For all transformer cores  6   a - 6   c  that have secondary windings sections  7   a - 7   c , the secondary windings sections  7   a - 7   c  can all be wrapped in a single direction  31 . The single direction  31  of wrapping the secondary windings  7  can be the same as the first direction  21  or the second direction  22 . 
     As shown in  FIGS. 3   a - 3   c , the secondary windings sections  7   a - 7   c  can be wrapped around the transformer cores  6   a - 6   c  in any order. For example, on circuit  30   a  in  FIG. 3   a , secondary windings sections  7   a - 7   c  wrap transformer core  6   a  first, transformer core  6   b  second, and transformer core  6   c  third. On circuit  30   b  in  FIG. 3   b , secondary windings sections  7   a - 7   c  wrap transformer core  6   b  first, transformer core  6   a  second, and transformer core  6   c  third. On circuit  30   c  in  FIG. 3   c , secondary windings sections  7   a - 7   c  wrap transformer core  6   a  first, transformer core  6   c  second, and transformer core  6   b  third. 
     The secondary windings sections  7   a - 7   c  need not be wrapped on all transformer cores  6   a - 6   c . For example, as shown on circuit  30   d  of  FIG. 3   d , the secondary windings section  7   b  and  7   c  can be wrapped around additional cores  6   c  and  6   b , but not around the first transformer core  6   a . Alternatively, but not shown, the secondary windings sections  7   b  and  7   c  can be wrapped around only one of the additional cores  6   c  and  6   b , and/or the first transformer core  6   a . It can be beneficial to leave at least one core unwrapped by secondary windings  7  in order to allow at least one core to avoid saturation during periods of high electrical current, and thus maintain a higher impedance in the primary windings. Wrapping the secondary windings  7  on only some of the cores is shown on the series configuration in  FIG. 3   d , but this also applies to the parallel configuration, as shown on circuit  50  in  FIG. 5 , wherein one of the additional transformer cores  6   b  is free of secondary windings  7 . 
       FIGS. 2-5  show the first transformer core  6   a  plus two additional transformer cores  6   b - 6   c . The total number of transformer cores  6  can be more than 2, more than 3, or more than 4. For example, circuit  60  of  FIG. 6  shows four transformer cores  6   a - 6   d , with primary windings  15   a - 15   d , top primary windings sections  4   a - 4   d , bottom primary windings sections  5   a - 5   d , and secondary windings sections  7   a - 7   d . The secondary windings sections  7   a - 7   d  are arranged in parallel in this figure.