Abstract:
Various techniques directed to the design and construction of transformers are disclosed. In one aspect, a method according to embodiments of the present invention includes loading parameters of a transformer included in a power supply design, calculating primary winding parameters of the transformer in response to the loaded parameters of the transformer, calculating secondary winding parameters of the transformer in response to the loaded parameters of the transformer. Shield winding parameters of the transformer may be calculated in response to the loaded parameters of the transformer. The calculation of secondary winding parameters may include allocating pins of a secondary winding of the transformer.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     Embodiments of the invention relate generally to the design of circuits, and more specifically, to the design of a transformer construction in power supply.  
         [0003]     2. Background Information  
         [0004]     Power supplies are used to provide power to electronic devices to enable the electronic devices to operate. Power supplies can come in a variety of designs, depending on the needs of the electronic devices. Sometimes the electronic devices are powered directly from the power supplies and sometimes the electronic devices are powered from batteries, which are charged by the power supplies.  
         [0005]     One of the items often included in power supplies is a transformer. A voltage is usually applied to the transformer from one part of the power supply circuit (often referred to as the primary) and the transformer transfers energy from that part of the power supply circuitry to another part of the power supply circuitry (often referred to as the secondary). The transformer provides the electrical isolation and also shifts the voltage level between the primary and secondary.  
         [0006]     The design and construction of power supplies as well as the transformers that are used in the power supplies can be a very complicated and complex task due to many factors and variables. The complexity is further increased if transformer shielding is to be added to the construction process. For example, the design and construction of transformers is often done through experimentation, on a trial and error basis in order for the power supply designer to realize a power supply having the desired specifications with regard to electrical and electromagnetic interference (EMI) performance.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention detailed illustrated by way of example and not limitation in the accompanying Figures.  
         [0008]      FIG. 1  is a diagram illustrating an embodiment of a block diagram of power supply design including an embodiment of a transformer design that is generated by an embodiment of a power supply software design tool run on a computer in accordance with the teachings of the present invention.  
         [0009]      FIG. 2  is diagram illustrating an embodiment of design results of a power supply design including an embodiment of a transformer design that is generated by an embodiment of a power supply software design tool run on a computer in accordance with the teachings of the present invention.  
         [0010]      FIG. 3  is a block diagram of one embodiment of a computer system that may be used with an embodiment a power supply design tool and a transformer construction design tool in accordance with the teachings of the present invention.  
         [0011]      FIG. 4  is a diagram illustrating an embodiment of the output of an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0012]      FIG. 5  is a diagram illustrating an embodiment of additional output of an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0013]      FIG. 6  is a diagram illustrating an embodiment of still more of the output of an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0014]      FIG. 7  is a flowchart diagram illustrating one embodiment of a flow of events in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0015]      FIG. 8  is a flowchart diagram illustrating one embodiment of a flow of events of an initialization of an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0016]      FIG. 9  is a flowchart diagram illustrating one embodiment of a flow of events in a calculation of primary winding parameters in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0017]      FIG. 10  is a flowchart diagram illustrating one embodiment of a flow of events in a calculation of bias winding parameters in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0018]      FIG. 11  is a flowchart diagram illustrating one embodiment of a flow of events in a calculation of secondary winding parameters in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
         [0019]      FIG. 12  is a flowchart diagram illustrating one embodiment of a flow of events in a calculation of shield winding parameters in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0020]     Embodiments of a transformer construction design tool that may be integrated with a power supply design tool are disclosed. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. Well-known methods related to the implementation have not been described in detail in order to avoid obscuring the present invention.  
         [0021]     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.  
         [0022]      FIG. 1  is a diagram illustrating an embodiment an output  101  generated by power supply design tool including a transformer design tool in accordance with the teachings of the present invention. In one embodiment, output  101  may be a report generated by a computer program such as for example PI Expert™ power supply design software from Power Integrations of San Jose, Calif. In other embodiments, it is appreciated that other programs may be utilized to generate a report similar to output  101  in accordance with the teachings of the present invention.  
         [0023]     As shown in the depicted embodiment, output  101  includes an example block diagram of an example designed power supply  103  with design warnings  139 . Design warnings  139  provide a power supply designer with descriptions of potential concerns regarding power supply  103  and possible fixes regarding the potential concerns. In the illustrated example, the “Block Diagram” tab of output  101  is selected, which displays the design of power supply  103 . The design of power supply  103  includes a transformer  111 , which in the illustrated example includes a primary winding  113 , secondary windings  115 ,  117 ,  119  and  121 , and a bias winding  123 . In other transformer designs or embodiments, a different number of windings may be designed in accordance with the teachings of the present invention.  
         [0024]     In operation, an alternating current (AC) input voltage Vin is generated from an AC source  105  is rectified with a rectifier circuit  107  and filter capacitor  109 . The rectified input voltage Vin is applied to one end of the primary winding  113  of transformer  111 . A power supply controller  125  is coupled to the other end of the primary winding  111 . In the illustrated embodiment, power supply controller  125  is from the TOPSwitch® family of integrated circuit power supply controllers from Power Integrations of San Jose, Calif. In other embodiments, other power supply controllers may be utilized in power supply designs in accordance with the teachings of the present invention. When operating, power supply controller  125  includes a power switch that is switched on and off to control or regulate the transfer of energy in transformer  111  from the primary winding  111  to the secondary windings  115 ,  117 ,  119  and  121 , and a bias winding  123 . As a result, regulated voltages and/or currents are provided outputs  127 ,  129 ,  131 ,  133  and  135  of power supply  103 . In the illustrated embodiment, feedback is provided to power supply controller  125  through feedback/secondary Zener circuitry  137  from bias winding  123  through output  135 .  
         [0025]      FIG. 2  is diagram that illustrates an example of output  101  generated by a power supply design tool in which the “Design Results” tab is selected. With the “Design Results” tab selected, the design results  241  report corresponding to the design of power supply  103  of  FIG. 1  is displayed. As shown in the depicted embodiment, design results includes a report summarizing various features of the design of power supply  103  including a listing of power supply inputs, power supply outputs, device variables and the like. As illustrated, the design results also provides descriptions as well as other helpful information that will assist a power supply designer when designing a power supply in accordance with the teachings of the present invention.  
         [0026]      FIG. 3  is a block diagram illustrating one embodiment of a machine  301 , such as for example a personal computer, a personal digital assistant, or any other suitable computing equivalent capable to run software such as for example the power supply design tool including a transformer design tool in accordance with the teachings of the present invention. In one embodiment, machine  301  is a computer that includes a processor  303  coupled to a bus  307 . In one embodiment, memory  305 , storage  311 , display controller  309 , communications interface  313 , input/output controller  315  and audio controller  327  are also coupled to bus  307 .  
         [0027]     In one embodiment, machine  301  interfaces to external systems through communications interface  313 . Communications interface  313  may include an analog modem, digital modem, a network interface card, a wireless network interface, an optical carrier interface, token ring interface, satellite transmission interface, or any other interfaces for coupling a device to other devices.  
         [0028]     In one embodiment, a carrier wave signal  323  is received/transmitted by communications interface  313  to communicate with a wireless antenna  111 . In one embodiment, wireless antenna provides a wireless interface to a network  313 . In one embodiment, carrier wave signal  325  is received/transmitted by communications interface  313  to communicate with network  113 . In one embodiment, communications signals  323  and/or  325  may be used to interface machine  301  with another computer system, a network hub, router or the like. In one embodiment, communications signals  323  and  325  may be considered as carrier-wave signals and are considered to be machine readable media, which may be transmitted through wires, cables, optical fibers or through the atmosphere, or the like.  
         [0029]     In one embodiment, processor  303  may be a conventional microprocessor, such as for example but not limited to an Intel x86 or Pentium family microprocessor, a Motorola family microprocessor, or any other suitable equivalent. Memory  305  may be a machine readable medium such as dynamic random access memory (DRAM) and may include static random access memory (SRAM). Display controller  309  controls in a conventional manner a display  319 , which in one embodiment may be a cathode ray tube (CRT), a liquid crystal display (LCD), an active matrix display, a plasma display, a projector display, a television monitor or the like. The input/output device  317  coupled to input/output controller  315  may be a keyboard, disk drive, printer, scanner and other input and output devices, including a television remote, mouse, trackball, track pad, joystick, pointing device or the like. In one embodiment, audio controller  327  controls in a conventional manner audio output  331 , which may include for example audio speakers, headphones, an audio receiver, amplifier or the like. In one embodiment, controller also controls in a conventional manner audio input  329 , which may include for example a microphone or input(s) from an audio or musical device, or the like.  
         [0030]     Storage  311  in one embodiment may include machine readable or accessible media such as for example but not limited to a magnetic hard disk, a floppy disk, an optical disk, a flash memory drive, a smart card or any other suitable storage media equivalent for the storage for data. In one embodiment, storage  311  may include removable media, read-only media, readable/writable media or the like. Some of the data may be written by a direct memory access process into memory  305  during execution of software in computer system  301 . It is appreciated that software may reside in storage  311 , memory  305  or may be transmitted or received via modem or communications interface  313 . For the purposes of the specification, the term “machine readable medium” shall be taken to include any medium that is capable of storing data, information or encoding a sequence of instructions for execution by processor  303  to cause processor  303  to perform the methodologies of the present invention. The term “machine readable medium” shall be taken to include, but is not limited to solid-state memories, optical and magnetic disks, carrier wave signals, and the like.  
         [0031]      FIG. 4  is a diagram illustrating an embodiment of the output  401  of an embodiment of a transformer construction design tool, which in one embodiment may be integrated with a power supply design tool in accordance with the teachings of the present invention. In one embodiment, the transformer construction design tool is a software tool that may be operated on a computer such as for example machine  301 . For example, in one embodiment, the transformer construction design tool software includes instructions, which may be accessed from in storage  311 , memory  305  and/or the carrier wave signals of communications signals  323  and/or  325 . When processor  303  accesses the instructions, an embodiment of the transformer construction design tool is executed by machine  301  in accordance with the teachings of the present invention.  
         [0032]     In one embodiment, the transformer construction design tool is integrated or may used with a power supply design tool, such as for example the power supply design tool example described in connection with  FIGS. 1 and 2  above. In particular, in one embodiment, the transformer construction design tool provides more detailed information to a power supply designer on how to construct the transformer design included in the design of power supply  103  describe above in  FIGS. 1 and 2  in accordance with the teachings of the present invention. In one embodiment, the information regarding the design of power supply  103  may be provided as input to the transformer construction design tool through a data file stored locally on machine  301  in storage  311 , or remotely in a network storage device accessed through communications interface  313  in accordance with the teachings of the present invention. In one embodiment, the information regarding the design of power supply  103  may be provided as input to the transformer construction design tool through an input/output device  317  to machine  301  through input/output controller  315  in accordance with the teachings of the present invention.  
         [0033]     To illustrate, output  401  includes a diagram  403  of a transformer to be constructed in accordance with the teachings of the present invention. In one embodiment, output  401  may be output as on display, such as for example display  319 , or output may be printed on a printer connected to machine  301  through for example communications interface  313  or input/output controller  315  or the like. In one embodiment, the information of output  401  may be stored for example in a file stored in a local hard drive such as for example storage  311 , or for example an network storage device accessed via communications interface  313 .  
         [0034]     As shown in the depicted embodiment, output  401  includes a diagram  403  of a transformer to be constructed in accordance with the teachings of the present invention. Associated with the transformer in output  401  is specific detailed information that can be used when constructing the transformer illustrated in diagram  403 . For example, as illustrated in the depicted embodiment, output  401  may include a core information report  405 , a bobbin information report  407 , a primary winding report  409 , a bias winding report  411  and a shield information report  413  in  FIG. 4 . Each of the reports includes detailed information or parameters helpful to a power supply designer to construct the designed transformer in accordance with the teachings of the present invention.  
         [0035]     For example, in one embodiment, core information report  405  includes information regarding core type, core material, gap length, gapped effective inductance and primary inductance. Bobbin information report  407  includes a bobbin reference number, number of primary pins, number of secondary pins, as well as margins on the left and right. Primary winding report  409  includes parameters for the associated sections regarding number of turns, wire size, filar, layers, start pin and termination pin. For the purposes of this disclosure the term filar may be interpreted as a representation of the number of parallel strands of wire. Bias winding report  411  includes parameters and associated values regarding number of turns, wire size, filar, layers, start pin and termination pin. Shield information report  413  includes parameters associated with the primary shield, secondary shield and cancellation shield windings regarding number of turns, wire size, filar, layers, start pin and termination pin, if applicable.  
         [0036]      FIG. 5  is a diagram illustrating additional information that may be reported in an embodiment of the output  401 , which is generated by an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. As shown in the diagram of  FIG. 5 , one embodiment of output  401  may also include a secondary winding report  515  and a winding instruction report  517  in accordance with the teachings of the present invention. In the depicted embodiment, secondary winding report  515  includes parameters for the associated outputs regarding number of turns, wire size, filar, layers, start pin and termination pin. Winding instructions report  517  include one embodiment of specific detailed instructions on exactly how to wind each of the specific windings in the sections of the transformer including for example, primary section  1 , bias winding, secondary winding, each of the shield windings (primary shield, secondary shield and cancellation shield) and primary section  2 . In one embodiment, winding instruction report  517  may also include instructions on how to construct the core as well as how varnish the transformer.  
         [0037]      FIG. 6  is a diagram illustrating still more information that may reported in an embodiment of the output  401 , which is generated by an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. As shown in the diagram of  FIG. 6 , one embodiment of output  401  may also include comments report  619  regarding the transformer construction, a materials report  621  and an electrical test specification report  623  in accordance with the teachings of the present invention. In the depicted embodiment, comments report  619  may include helpful suggestions regarding the construction of the specific transformer that is described. Materials report  621  provides a detailed list of the materials that will used to construct the transformer and the electrical test specifications report  623  provides a list of parameters, conditions and specifications of the specific transformer to be constructed in accordance with the teachings of the present invention.  
         [0038]      FIG. 7  is a flowchart diagram illustrating one embodiment of a process or flow of events  701  in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. In one embodiment, a software power supply design tool executed on a computer is run prior to the processing illustrated in the flow of events  701  such that a power supply design is generated by the power supply design tool. In one embodiment, the generated power supply design includes a transformer to be designed and constructed in accordance with the teachings of the present invention. In one embodiment, the generated power supply design is stored on a computer-readable medium, such as for example a storage device like storage element  311  or memory  305  or a storage device accessible in network  313  in  FIG. 3 . In another embodiment, the generated power supply design may be output from the computer via printer connected to the computer via communications interface  313  or input/output controller  315  or a display  319  via display controller  309 . In one embodiment, the processing described in  FIG. 7  and subsequent figures may be performed with a software tool executed by the same or a different computer that executes the power supply design tool program that generated the power supply design in accordance with the teachings of the present invention.  
         [0039]     In the embodiment illustrated in  FIG. 7 , processing begins at block  703  with initialization of the transformer construction design tool. After initialization, block  705  shows that primary winding parameters of the designed transformer are calculated. Next, processing may continue with block  707 , which shows that bias winding parameters are calculated. After bias winding parameters are calculated, block  719  shows that secondary winding parameters are calculated. Next, processing may continue with block  711 , which shows that shield winding parameters are then calculated. As will be discussed, a variety of operations are performed during the calculation of the parameters of the various transformer windings. For instance, in various embodiments, the allocation of the respective windings on the appropriate number of pins on a given transformer bobbin is determined in accordance with the teachings of the present invention. This allocation of the respective windings on the appropriate number of pins may be performed on one or more of the primary, bias, secondary and/or shield windings in accordance with the teachings of the present invention.  
         [0040]     After the parameters of the windings have been calculated, processing may continue with block  713 , which shows that a material list is then generated. In one embodiment, calculation results of all of the transformer sections may be reviewed in block  713  and a material list is generated with a unique identifier for each material. Next, processing may continue with block  715 , which shows that winding instructions and comments are generated. In one embodiment, the winding instructions generated in block  715  are generated based at least in part on the particular shield case as calculated in block  711 . Block  717  shows that the output or a report of an embodiment of a transformer construction design tool may then be displayed or generated. After the output is displayed, block  719  shows that control may then returned back to block  705  if there is a user event with a parameter change. If there is a “User Exit” user event, processing is then complete in the flow of events  701  in accordance with the teachings of the present invention.  
         [0041]      FIG. 8  is a flow diagram illustrating one embodiment of a flow of events of the initialization in block  703  in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. In one embodiment, initialization in includes clearing all engine structures of the design tool, as shown with block  803 . Block  805  shows that parameters of the transformer design are then loaded. In one embodiment, the parameters that are loaded include for example parameters of the transformer that may be stored in a file in or on storage  311  generated by a power supply design tool in accordance with the teachings of the present invention. In another embodiment, the parameters of the transformer may be loaded into the transformer construction design tool through other suitable techniques, such as for example in a communications signal  323  and/or  325  received through communications interface  313  or through an input device  317  through input/output controller  315 . After the parameters are loaded, block  807  shows that the parameters are then organized or sorted, for example by voltage, by the transformer construction design tool in accordance with the teachings of the present invention. In one embodiment, negative output is separated from other output such that negative output doesn&#39;t participate in the sorting of block  807 .  
         [0042]      FIG. 9  is a flow diagram illustrating one embodiment of a flow of events occurring during the calculation of primary winding parameters of block  705  in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. Block  903  shows that it is determined whether the primary wire size is acceptable. For example, in one embodiment, the biggest primary wire size is  20  American Wire Gauge (AWG). If the wire gauge is not acceptable, block  905  shows that an equivalent wire size and filar is calculated. In one embodiment, the equivalent wire size is calculated based on one or more of a specific winding, a topology of the power supply and a switching frequency of the power supply designed by the power supply design program. Block  907  shows that it is determined if there is a split or sandwich primary construction. Block  909  shows that primary pin allocation is calculated. Block  911  shows that in one embodiment additional pins are allocated if necessary to ensure that the maximum number of wires terminating on or coupled to a pin is practical or within a predetermined maximum number of wires allowable to be coupled to a pin. In one embodiment, the order in which windings are windings are coupled to each pin of the transformer is also determined. In one embodiment, the identity of the particular windings of the transformer that are to be terminated on particular pins of the transformer are determined during the processing within blocks  909  and/or  911  in accordance with the teachings of the present invention. Block  913  shows that the total number of pins on the primary side is then determined. In one embodiment, the total number of pins required is based at least in part on the number of wires terminated on a pin.  
         [0043]      FIG. 10  is a flow diagram illustrating one embodiment of a flow of events during a calculation of bias winding parameters of block  707  in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. Block  1003  checks if the wire size and percentage of the bobbin window width that the Bias winding occupies is acceptable. In one embodiment, if one of the parameters is not acceptable block  1005  will calculate an optimum or improved wire size and filar. In one embodiment, the transformer construction design tool also tries to optimize bias layers. In one embodiment, optimum bias layers are between 0.5 and 1.0. Block  1007  shows that the transformer construction design tool also determines bias winding pin allocation in accordance with the teachings of the present invention.  
         [0044]      FIG. 11  is a flow diagram illustrating one embodiment of a flow of events during a calculation of secondary winding parameters of block in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. Block  1103  shows that all outputs of the transformer are identified or calculated. Block  1105  shows that secondary pins are then allocated by voltage. In one embodiment, pin allocation is based on stacked outputs sorted by voltage, with stacked outputs being outputs where the start of one winding is connected to the finish of a previous winding or rectified output of a previous winding. In one embodiment, there is a maximum wires per pin allowed and an extra pin is allocated if the number of wires allocated to a pin exceeds the predetermined limit. In one embodiment, the first secondary pin is based on the last pin on the primary side. Block  1107  shows that the ground pin is then defined and block  1109  then shows that secondary pin allocation is determined by current.  
         [0045]     In one embodiment, the secondary pin allocation by current of block  1109  begins by determining whether the number of total stack outputs is greater than one, as shown with block  1111 . If not, the outputs are independent or it is a single output and the secondary pin allocation by current isn&#39;t required. However, if the total of stack outputs is greater than one, then block  1113  shows that pin allocation data is then loaded from the allocation by voltage determined in block  1105 . Block  1115  shows that ground pins are then moved on the middle of the secondary bobbin part. In block  1117 , all valid outputs are then assigned to odd (e.g. physically located above ground pin) or even parts (e.g. physically located below the ground pin) from the ground pin. Next, all valid outputs are considered and it is determined if additional secondary pins are needed by checking if the number of wires per pin exceeds a predetermined limit or the maximum wires per pin allowed. If additional pins are required, then they are inserted at the defined location. Block  1121  shows that negative output pins are assigned if negative output exists. Block  1123  shows that the new secondary start and termination pins are then assigned. Block  1125  shows that it is checked if the new secondary pin allocation is out of sync, i.e. if during the process of extra pin allocation the first secondary pin or combination of any of the secondary pins have shifted. If this is so, then all of the pins are shifted in the correct direction so as to synchronize the first secondary pin with the calculated value during the process of output pin allocation by voltage, as shown with block  1127 . Then, the calculation of secondary winding parameters of the transform design is completed in accordance with the teachings of the present invention.  
         [0046]      FIG. 12  is a flowchart diagram illustrating one embodiment of a flow of events during a calculation of shield winding parameters of block  711  in an embodiment of a transformer construction design tool in accordance with the teachings of the present invention. Block  1203  shows that initialization occurs when the calculation of shield winding parameters begins with the clearing of shield structures. As will be shown, in one embodiment, all shield calculations are based on a particular shield “case” of the transformer to be constructed. In one embodiment, these shield cases are derived through complex consideration of electrical parameters that may include variables like type of device used, number of turns, layers, filar, output power, output voltage or current, whether split (sandwich) primary type of construction is used or not used and the type of secondary winding used (wire or foil). Depending on the combination existing in a particular design a shield case is intelligently assigned to it.  
         [0047]     For instance, block  1207  determines whether the shield design of the transformer to be constructed falls under a first shield case where there is a split (sandwich) primary with no foil technique. If so, the primary shield is calculated in block  1219  according to this first shield case. In one embodiment, the user is also advised that the design may be able to perform better with the addition of a flux band around the core.  
         [0048]     If the shield design of the transformer to be constructed does not fall under the first shield case, then block  1209  determines whether the shield design of the transformer to be constructed falls under a second shield case where there is a split (sandwich) primary with a foil technique. If so, the primary shield is calculated in block  1221  according to this second shield case. In one embodiment, this design of primary shield may or may not vary from the first case. In one embodiment, the user is also advised that the design may be able to perform better with the addition of a flux band around the core.  
         [0049]     If the shield design of the transformer to be constructed does not fall under the first or the second shield case, then block  1211  determines whether the shield design of the transformer to be constructed falls under a third shield case where there is no split (sandwich) primary and no foil technique. If so, the primary shield is calculated in block  1223  and the cancellation shield is calculated in block  1225  according to this third shield case. In one embodiment, the primary shield design may also be different than the design used in the first or the second case.  
         [0050]     If the shield design of the transformer to be constructed does not fall under the first or second or the third shield case, then block  1213  determines whether the shield design of the transformer to be constructed falls under a fourth shield case where there is no split (sandwich) primary but there is a foil technique. If so, the secondary shield is calculated in block  1227  and the cancellation shield is calculated in block  1229  according to this third fourth case. In one embodiment, the cancellation shield design may be different than the design used in the first or the second case. In one embodiment, the user may also be advised that the design may be able to perform better with the addition of a flux band around the core.  
         [0051]     If the shield design of the transformer to be constructed does not fall under the first, second, third or fourth shield cases, then block  1215  determines whether the shield design of the transformer to be constructed falls under a sixth shield case where there is no split (sandwich) primary but there is a foil technique and the secondary shield layer is more than one. If so, the primary shield is calculated in block  1231  and the cancellation shield is calculated in block  1233  according to this sixth case.  
         [0052]     If the shield design of the transformer to be constructed does not fall under the first, second, third, fourth or sixth shield case, then block  1217  determines whether the shield design of the transformer to be constructed falls under a seventh shield case where there is no split (sandwich) primary but there is a foil technique and there is no bias winding. If so, the secondary shield is calculated in block  1235 , the primary shield is calculated in block  1237  and the cancellation shield is calculated in block  1239  according to this seventh case.  
         [0053]     If the shield design of the transformer to be constructed does not fall under the first, second, third, fourth, sixth or seventh shield case, then it is assumed that the shield design of the transformer to be constructed falls under a fifth shield case where there is a primary side bias and no shield windings. In this fifth case, and after the flow events described above with regard to all of the first, second, third fourth, sixth and seventh cases, pin  1  is checked and all pins are shifted as required per block  1241 . In one embodiment, the number of wires on pin  1  is checked against a maximum limit. Afterwards, the calculation of shield winding parameters is complete in accordance with the teachings of the present invention.  
         [0054]     It is appreciated that the operations that have been described above as multiple discrete blocks performed in turn in a manner that may be helpful in understanding various embodiments according to the teachings of the present invention. However, the order in which the blocks are described above should not be construed to imply that these operations are necessarily order dependent or that the operations be performed in the order in which the blocks are presented. Of course, the process blocks described provide examples to describe embodiments of the present invention and other embodiments may be employed in accordance with the teachings of the present invention.  
         [0055]     In the foregoing detailed description, the methods and apparatuses of the present invention have been described with reference to a specific exemplary embodiment thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present invention. The present specification and figures are accordingly to be regarded as illustrative rather than restrictive.