From the appearance of toroidal is a ring structure (round), EI-type is a heart structure (square), from the practicality, EI-type is the most common transformer, toroidal is belong to the special transformer, EI-type magnetic circuit is disconnected, toroidal is the magnetic circuit is closed, toroidal compared to EI-type for the high utilization of the window, high efficiency, temperature rise is low, EI-type collection of the skeleton of the limitations of the volume is difficult to change, and the EI-type can arbitrarily better core size, change the volume, toroidal leakage is small, and EI leakage is large, EI-type is the most conventional transformer suitable for large quantities of suitable for large-scale transformer. Toroidal can be arbitrarily better core size, change the volume, toroidal magnetic leakage is small, and EI-type magnetic leakage is large, EI-type is the most conventional transformer suitable for mass production, the cost advantage is higher than the toroidal.