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.