If transformers are used in the range of several Kilohertz or higher usual core materials made of iron-silicon-alloys are not applicable due to high eddy current losses. Nanoperm has a very thin hysteresis curve which means low losses and it is very stable over a wide temperature range. The high saturation induction of 1,2 T is about three times higher compared to ferrites. The usage of Nanoperm cores allows a high efficiency with low installation space. Due to permeabilities of about 90.000 at 10 kHz the stray inductance is very low if the windings are applied evenly. This makes them ideal for the usage with frequency converters even if they are built up with SiC and GaN semiconductors.