Don't Miss

What Is Toroidal Transformer?

By on March 26, 2009


Here is a good explanation taken from Wikipedia:

“Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or perm alloy wound into a coil, powdered iron, or ferrite. A strip construction ensures that the grain boundaries are optimally aligned, improving the transformer’s efficiency by reducing the core’s reluctance. The closed ring shape eliminates air gaps inherent in the construction of an E-I core. The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed, and also provides screening to minimize the core’s magnetic field from generating electromagnetic interference.


Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher cost and limited power capacity (see “Classification” above).


Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to a megahertz, to reduce losses, physical size, and weight of switch-mode power supplies. A drawback of toroidal transformer construction is the higher cost of windings. As a consequence, toroidal transformers are uncommon above ratings of a few kVA. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings.”


For your information I’ve seen Toroidal transformer in Computer subwoofer speaker system but not on any Monitors or even Computer SMPS.



  1. jim

    April 6, 2009 at 5:34 pm

    some old type UPS(Tvs) is also using this type of transformers..

  2. admin

    April 6, 2009 at 8:42 pm

    Hi Jim,

    Thanks for the info.


  3. Francesco

    March 18, 2011 at 6:51 pm

    Dear Mr. Jestine, I was approaching your ebooks and I will buy them soon because I'm very interested in them.

    I would like to know how can I check a Toroidal transformer, please.

    I just ordered a Peak Atlas LCR (that can measure Inductance and passive components), but I don't know if I need a Blue Ring Tester too.

    May you help me to choose the right tools, please?

    Many thanks
    Best Regards

  4. admin

    March 20, 2011 at 11:01 am

    HI Francesco,

    You can check the transformer by measuring the input and output resistance. If there is ac input and no ac output then you know the transformer have problem. If you have the blue ring tester then you can check the winding to see if it is shorted or not. Voltage testing is the best.


  5. Waleed Rishmawi

    July 10, 2011 at 3:53 pm

    good article. I have seen transformers like this one in amplifiers. it took me a while to figure them out.these transformers are heavy. still get them in my shop but very hard to find replacement. i have not encoutered a bad transformer but someday...

  6. Amir mukhtar

    August 12, 2011 at 3:41 am

    Sir Jestine,
    This is very interesting and valuable topic in tranformer's Era.
    Actually, Topic already given astonish informations about the toroidal transformer. Despite, above transformer quality is more useful and safe in order to accuracy and precision measures with respect to E-I Core transformer.
    for example: Toroidal transformer is mostly used in Low wattage servo AVR stabilizer System. Because, its accuracy depends on precision control 380 degrees movement and rotation.

    To Sum UP, Servo AVR (Toroidal transformer based) is safe and accurate solution for home electrical equipments with respect to E-I, Type devices.Also, its upto the user what they wants and its need with in the budget.

    thanks you
    Amir Mukhtar

  7. Raymundo Saura

    February 9, 2014 at 12:59 am

    thanks for sharing

  8. Stephen Wilson-Floyd

    August 25, 2018 at 4:15 am

    We have a torodial transformer for a massage chair that is non working. Is there a service that rewinds single transformers for $100 or less. Thanks.

    • Jestine Yong

      August 25, 2018 at 11:47 am

      Hi Stephen,

      Sorry we do not have info about the rewinding service.



Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.