I would like to build a toroidal transformer.

What are the formulas for dimensioning the various components?

EDIT: I try to explain myself better...

I would like to create a toroidal transformer for a power supply:

  • primary: 230V @ 50Hz
  • secondary: 2 x 12V
  • power: 150VA

Now, for Laminated E cores transformers I have formulas for calculating the N spires needed for primary and secondary based on required input and output voltages... but for toroidal cores I didn't find any specific formula on Google and on my books...

My question is: does anyone know the specific formulas to dimension a toroidal transformer for power conversion, knowing the desired input/output voltages and output power in VA?

  • 1
    \$\begingroup\$ What type of transformer - mains, RF, etc.? \$\endgroup\$ – Leon Heller May 9 '12 at 17:51
  • \$\begingroup\$ For power supply \$\endgroup\$ – byterussian May 9 '12 at 17:56

There is no real difference between the formulas for designing a toroidal transformer vs. an E-I transformer. The core cross-sectional area is \$\pi r^2\$ rather than the L \$\times\$ W of the center post, but the exact shape of the core does not matter much.

You'll need the core volume calculation for losses, but that's a straightforward lookup of a datasheet listing or lookup of a mensuration formula.


Its very important to specify RF toroid like perhaps a center tapped balun for biasing a class AB amplifier, or a AC line power toroid like the xfrmr for my semi-audiophile old record player amp which fed a old fashioned linear regulator.

To a crude first approximation, you're going to be buying your core from somebody unless you're making your own, and that mfgr will have helpful data sheets and books, for free or for sale. Amidon and Palomar have excellent RF design books for their products. For another perspective MFJ's "Ferromagnetic Core Design & Application Handbook" will set you back about $20.

  • \$\begingroup\$ Question edited... \$\endgroup\$ – byterussian May 10 '12 at 1:20

To build 150VA toroidal transformer you need a toroidal core by the following size. OD(outer diameter)-75mm, ID(Inner Diameter)-40mm,Height- 50mm.

Primary turn - 830, magnet wire size diameter- 0.61mm VA 230*0.67A =155VA secondary turn- 87 , -------------------------- 1.83mm VA 24*6.44A =155VA


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