In this work an LLC converter is used to achieve energy transfer with very low capacitance between windings. In typical non-resonant switching converters decreasing capacitance between windings usually comes with unwanted effect of increasing leakage inductance. However, some resonant converters like LLC work with transformers that are intentionally designed to have high leakage inductance – winding are more loosely coupled so capacitance between them can be lower.
Description of the design and experiments are in the attached archive.
The results are quite good. About 2.2pF capacitance is roughly about 10% of typical capacitance achieved in many isolating converter (at cost of size). Custom bobbin has been 3d printed and EF16 core modified to build the main part - high leakage transformer. Input voltage is 12V, output 5V, power 1W (or slightly more).