Design of a high-frequency planar power transformer in multilayer technology

Batch-type millimeter-size transformers for miniaturized power applications

“…The geometry is the same for the inductors (containing one coil of windings) and transformers (containing two sets of windings). A simple relation allows the calculation of the inductance of a ferrite core (1) where is the inductance factor and the number of turns. The factor contains the geometrical and magnetic properties of the ferrite core through the relation with (2) where and are, respectively, the effective area and the path length of the core, and is the effective permeability introduced to take into account the influence of an eventual air gap in a closed magnetic circuit.…”

“…These high frequencies necessitate the use of high-resistivity magnetic core materials, such as ferrites, for reducing eddy current losses in the inductors or transformers. During recent years, a large research effort has been developed in the field of so-called planar magnetics, where one integrates flat three-dimensional (3-D) ferrite cores with Cu windings realized in planar printed circuit board (PCB) technology [1]- [3]. This device geometry has lead to devices with reduced height and enhanced power density in a vast range of power (few Watt to many kW).…”

The Influence of Dielectric Thickness on the Power Bandwidth of Planar Transformers

“…These transformers are constructed by sandwiching layers of conductors, dielectrics and magnetic materials together [3]. The advantages of planar transformers are that the planar nature of the windings allow for more complex and efficient winding configurations, and also allows for excellent repeatability in manufacturing due to well defined geometry [4][5][6]. This characteristic allows parasitics to be intelligently controlled such that they have the least effect on the performance of the transformer.…”

“…Trade-off between leakage inductance, losses and stray capacitance has been investigated to some extent in [8], and in [4] the authors define a 'figure-of-trouble' product LC as being the product of leakage inductance and parasitic capacitance, since both quantities are dependent on the dielectric thickness of the windings in an opposing manner. In both papers, the trade-off has not been thoroughly investigated within the context of bandwidth, leaving room for further research in this direction.…”

“…The general view is that both stray capacitance and leakage inductance have an impact on the 'cutoff frequency' and 'bandwidth' of the transformer respectively [4,[21][22][23]. However, the bandwidth is yet to be described as functions of these intrinsic electromagnetic parasitic elements.…”