Toroidal transformers are assembled on a ring shaped core, usually with a rectangular cross section, although a more expensive circular type is available. The core is constructed from strips of silicon steel wound in to a coil. The closed ring eliminates any air gaps which are present in ‘E’ ‘I’ laminated cores.
Toroidal transformers are usually more efficient, although more expensive, than laminated ‘E’ ‘I’ types of a similar power level, other advantages include less mechanical hum, making their usage superior in audio applications such as amplifiers, as well as size and weight being around half that of ‘E’ ‘I’ laminated transformers.
When fitting a toroidal transformer, it is important not to allow both ends of the mounting bolt to simultaneously come into contact with metalwork, as this would make a loop of conductive material flowing through the hole in the toroid, thus allowing a dangerously large current to flow through the bolt.