How Do Toroidal Core Inductors Work?

A. Structure

Toroidal inductors and transformers are wound with a toroidal or circular core and copper wire. They are passive electronic components consisting of a torus or ring core made of ferromagnetic material such as laminated iron, powdered iron, or ferrite, around which a wire is wound. Toroidal inductors have high coupling results before winding and early saturation.

B. How it works?

In an inductor wound on a straight bar core, the flux lines emanating from one end of the core must travel through the air to re-enter the core at the other end. This reduces the magnetic field since most of the magnetic field path is in the air rather than the higher permeability core material and is a source of EMI. Higher magnetic fields and inductances can be achieved by forming an iron core in a closed magnetic circuit. The flux lines form a closed loop within the core without leaving the core material.

A frequently used shape is a ring or toroidal ferrite core. Due to their symmetry, toroidal cores allow minimal magnetic flux to escape the core, so they radiate less electromagnetic interference than other shapes. Toroidal core coils are made from a variety of materials, primarily ferrite, powdered iron, and laminated cores.

C. Magnetic field calculation

The magnetic field of a toroidal inductor can be calculated using the following formula, namely:
B=(µ0NI/2/πr)

Note:

'I' represents the point flow of the entire toroid, 'r' is the average radius of the toroid, 'n' is the number of turns per unit length, N=2rn is the average number of turns per unit length of the toroid.