Toroidal inductors and transformers

Several small toroidal inductors. The major scale is in inches.		A small toroidal transformer.

Toroidal inductors and transformers are a kind of electronic component. They typically consist of a circular, ring-shaped magnetic centre. The magnet is usually considered a monopole, although the central axis will have a dipole, and have the advantage of being wound continuously in a single direction, thus there is no inductive interference between windings as in a solenoid that is wound back and forth.

Toroidal Inductors And Transformers Media

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  Traditional transformers wound on rectangular-shaped cores.

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  Interior of a linear power supply with toroidal mains transformer.

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  Fig. 1. Coordinate system. The Z-axis is the nominal axis of symmetry. The X-axis chosen arbitrarily to line up with the starting point of the winding. ρ is called the radial direction. θ is called the circumferential direction.

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  Fig. 2. An axially symmetric toroidal inductor with no circumferential current.

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  Fig. 3. Toroidal inductor with circumferential current

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  Fig. 4. Circumferential current countered with a return wire. The wire is white and runs between the outer rim of the inductor and the outer portion of the winding.

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  Fig. 5. Circumferential current countered with a return winding.

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  Fig. 6. Circumferential current countered with a split return winding.

References

• Griffiths, David. Introduction to Electrodynamics (1989)Prentice-Hall. ISBN 0-13-481367-7.
• Halliday. Physics, part two (1962)John Wiley & Sons.
• Hayt, William. Engineering Electromagnetics (1989)McGraw-Hill. ISBN 0-07-027406-1.
• Purcell, Edward M.. Electricity and Magnetism. Berkeley Physics Course II (1965)McGraw-Hill. ISBN 978-0-07-004859-1.
• Reitz, John R.. Foundations of Electromagnetic Theory (1993)Addison-Wesley. ISBN 0-201-52624-7.

Other websites

• Approximate inductance of a toroid includes formula, but assumes circular windings