The ER core design is derived from the original E core and, like ETD and EC cores, has a round centre pole and outer legs with a radius to accomodate round coil formers. These cores are mainly used for power transformers. The round centre pole allows the use of thicker wires while the shorter turn length keeps the copper losses low. Planar ER cores are very suitable to build small SMD or planar power and signal tranformers. For the 3 smallest sizes matching SMD coil formers and clips are available.
