Design and application of high-frequency and low-profile power transformers

A new design and fabrication method for planar windings is presented. This method can automatically series-connect each layer of the winding, and virtually eliminate external soldering or conductive vias, thus reducing the DC resistance and increasing the reliability. Compared with the previously reported folding method for winding fabrication, this method maximizes the use of window height and minimizes the wastage of copper area in manufacturing. Practical examples of low-profile transformers and inductors were constructed and tested in an active-clamped DC-DC converter with self-driven synchronous rectifiers. Experimental results are presented to show that such transformers/inductors are particularly useful for the design of low-profile and high-power-density converter modules. Finally, a new and easy-to-implement algorithm is presented for minimum core volume design of high-frequency planar transformers. Given a set of specifications, such as transformer efficiency, converter topology, output power and voltage, etc., the PC-based program can search for a core with minimum volume, and provide such transformer parameters as core and winding geometry, etc. Unlike the conventional design, the new design approach considers the high frequency effect, and offers more flexibility in design.