High-voltage and high-frequency design of planar transformer with minimum coupling capacitance

Abstract

This paper investigates the design of a planar transformer operating at 6.78 MHz and with a target maximum isolation voltage of 40 kV using 2D FEM simulations as a tool. In addition, minimal coupling capacitance must be ensured for the target application of auxiliary power supply for medium voltage converters with high EMI immunity. The design space for a transformer with target inductance and coupling capacitance of 1 μH and 10 pF is explored with varying number of winding layers and turns. From the simulation design space, five designs are prototyped for experimental validation. Overall, the prototypes show good coherence with the simulated values with inductance and coupling factors within an error margin of maximum 7%. Results show that different designs can achieve the same transformer efficiency although with different isolation voltages.