The role of parasitic inductance in high-power planar transformer design and converter integration

Planar transformers provide a distinct advantage over the traditional transformer. However, when the planar transformer is integrated into a power circuit, the interconnect parasitic effects arise that are not shown in a traditional wire-wound transformer. For typical soft-switching converters, a specific leakage inductance is generally needed to charge and discharge the device output capacitances to achieve zero-voltage turn on. This designated leakage inductance value needs to be large enough to extend the zero-voltage switching range. However, it was found that this hard-to-come-by leakage inductance in a planar structure may be overshadowed by the circuit interconnect parasitic inductance. This paper presents a design integration that incorporates the planar transformer and a full-bridge dc/dc converter. Through design calculation, finite element analysis, and experimental verification, it was proven that the role of the parasitic inductance is indeed far exceeding the transformer leakage inductance. Thus, for any design optimization, it is necessary to take into account the parasitic inductance in the integrated structure.