U cores, with rectangular crosssections, are easy to produce and are relatively inexpensive. for this reason they are very popular in low cost applications such as interference fi lters and output chokes in radio and TV equipment. There is no real optimization for transformer winding designs and the core is rather bulky. Large U cores like U93 and U100 are suitable for very high throughput Powers. They can be stacked to form transformers, capable of handling several kW's in applications such as industrial HF welding.