How to use a mains transformer (for instance 110-230 Volt and 50-60 Hz) in an electronic project. Do's and dont's with mains transformers in home brew electronics.
Saturation of the core means that the core gets more or less permanenty magnetised. In that case the magnetic field is not built up (and decreased) quickly enough (50 Hz -60 Hz), the permanent field acts as a sort of "brake" for quick magnetic changes and the power cannot be well transferred from the primary to the secundary coil. The core gets heated up more or less, it gives loss of energy. On high(er) frequencies (16 Khz and more) transformers with a ferrite core give very good results with low loss of energy in the core.