EXPERT TECHNICAL REPORT
Highly efficient - yet compact - power conversion is fundamental to continued profitable growth of the telecommunications and data processing industries and of many others. Power conversion sub-systems furnish electrical energy in a form needed by these end-use equipments - 50volts DC for telecommunications, 5volts DC or 3volts DC for computers - are but typical examples. For safety reasons, transformers must invariably be incorporated, to galvanically isolate the end equipments from the 230volts or 117volts, 50 or 60 Hz AC mains, as well as to adapt the output voltage to the proper level. In such units, size is directly related to switching frequency, higher frequencies translating into smaller volume, and also into higher efficiency, if the right transformer design is chosen. In the past, operating frequencies much above 20kHz were precluded by the non-availability of suitable switching transistors. Now, with power MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistor) capable of converting power at frequencies well above 200kHz, the major obstacles to ongoing performance improvements in power supplies are the limitations inherent in conventional "wire-wound-on-a-bobbin" transformers and companion inductors.
Transformers made of the planar principle eliminate virtually all the shortcomings of old-fashioned wire wound types. In a planar design, the windings are made so of copper foil lead frames or printed circuit boards. (a flat copper spirals laminated into thin dielectric substrates). These windings are then sandwiched, along with appropriate insulators, between large area, yet thin, state-of-the-art ferrite cores. This construction technique yields a host of benefits :
Planar magnetics is probably the most cost effective solution for high frequency high power density power conversion equipments available today.