Planar Transformers Electromagnetic Modeling Considering Capacitive Couplings up to 100 MHz

Planar transformer technology provides a serious alternative to wound transformers for improving the efficiency and power density of isolated converters. The flat shape of its coil turns and the interleaving of its windings allow an excellent control of the skin and proximity effects. The major drawback of planar technology is the strong capacitive couplings between the windings. These couplings are detrimental to the increased switching frequency induced by the new wide-bandgap transistors, and to electromagnetic compatibility. Using fundamental equations, material properties, and geometric dimensions, the present work proposes a semianalytical electromagnetic model of planar transformers able to account for capacitive couplings. Compared with current models, it allows rapid estimation of all its sizing parameters: losses, leakage inductance, bandwidth, and interwinding impedance. This novel model was experimentally validated over a wide frequency range (1 kHz up to 100 MHz) using transformers with both series and parallel connected windings.