Planar transformer is an electric transformer or a magnetic transformer, has been constructed in conformity with integrated technology (in particular, on the basis of multilayer printed-circuit plates). The principle of operation the planar transformer is not distinguished accordingly from the suitable electric transformer. The distinctions of planar transformer are only in its design. As a result the working frequencies of planar transformers are over the frequency band in value from the power frequency (50 – 60 Hz) to MHz and GHz. The substantial merits of planar transformers are following: -- the comparison small sizes and a possibility of using in the compact and mobile devices; -- the splendid heat-transport thermal charakteristics; -- the small value of a scattering inductance; -- the high replication of the properties.