Abstract—This paper investigates the insulation design for
printed, planar, coreless, and high-frequency transformers with
high isolation-voltage. By using finite element analysis on 2D
axial-symmetry, the transformer circuit parameters and electric
field distribution are modelled and estimated. Several transformers
are designed for an operating frequency of 6.78 MHz. The
high frequency, coreless design allows for using thicker insulation
material while ensuring a high transformer efficiency. The
inclusion of the coupling capacitance in the design optimisation
results in several design solutions with the same figure of merit,
but with different footprint and isolation voltages. Moreover,
high electric fields are identified around the sharp edges of the
PCB windings. Finally, the electrical and isolation performance
is verified experimentally. The measured electrical properties
are close to the simulated values, validating the chosen model.
Breakdown tests demonstrate the feasibility of isolation voltage
levels up to several tens of kilovolts. The majority of breakdowns
occurs at the outer edge of the PCB winding that was identified as
a high-field area. Additionally, a concept for grading the electric
field of PCB windings is also proposed. Based on the results, the
design aspects are discussed in detail for planar, high-frequency
isolation transformers with medium-voltage isolation level.
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