High-frequency transformers operate using the same basic principles as standard transformers. The primary difference is that, as their name implies, they operate at much higher frequencies — while most line voltage transformers operate at 50 or 60 Hz, high-frequency transformers use frequencies from 20 KHz to over 1MHz.Operating at a higher frequency has many benefits, the first of which is size.For any given power rating, the higher the frequency, the smaller the transformer can be.