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Toroid, Toroidal Cores, Transformers and Unicore

Therma FM, Ltd. was established as a trading and consulting company in the field of metallurgy and metallurgical material in 1998. In 2005 it was extended to the production and non-production activities:

  • production of magnetic circuits for electrical machines
  • processing of metal scrap from machining so called baling
  • trading in metal plates and strips for electrical engineering (isotropic and anisotropic)
  • sale of steel logs
  • technical advice in the field of metallurgy

In 2005 Therma FM, Ltd. moved to the production site in Pržno near Frýdlant nad Ostravicí which provides sufficient capacity for the company´s further development in all mentioned fields of its activities.

The manufacture of toroidal cores is the main activity of our company, which responds primarily to the demand of toroidal transformers. These require specific components.

The sale of CRGO material and recycling scrap metals are closely connected with the specialisation of our company.

Nowadays Therma FM produces magnetic circuits, toroidal cores, unicore cores, wound divided cores and beside this it sells CRGO materials or special amorphous and nanocrystalline materials.


A transformer is a power converter that transfers electrical energy from one circuit to another through inductively coupled conductors - the transformers coils.

Toroidal transformers

Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or permalloy wound into a coil or powdered iron. A strip construction ensures that the grain boundaries are optimally aligned, improving the transformers efficiency by reducing the cores reluctanceToroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level.

Toroidal cores

Toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of inductive components.

Toroid, High Quality, High Performace, Toroidal Power Transformers and Chokes

What is a Toroid? Toroid is the core shape of the common mode chokes. A continuous circular path aids in maximizing the magnetic coupling between the windings. This minimizes leakage inductance. A toroid is inexpensive compared to the other type (E cores).

The toroids have a simple coil wound around a cylindrical structure, which is then bent into a doughnut shape. This merges the poles and creates an external magnetic field with regular polarities. A toroid coil also has the magnetic flux largely kept inside the coil to lessen magnetic radiation from the coil and sensitivity to the external fields.