ADVANTAGES OF HIGH PACKING DENSITY
Toroidal transformer cores are the ideal shape, which minimizes the amount of core material and allows symmetrical distribution of the winding around the entire core. This, along with higher operating flux densities, permit fewer copper wire turns than required on an equivalent laminated core. These inherent characteristics result in considerable weight and volume savings, as well as other advantages.
Referring to Faraday’s equation for induced voltage in a transformer winding:
E_RMS = 4.44 x N x AC x F x B x 10^-8
where:

F = frequency
N =number of turns
B = flux density (gauss)
AC = core cross section area (cm²)

Toroidal transformers can operate at flux densities up to 16.5 kilogauss, approximately 40% higher than the conventional laminated power transformer. Operation of any core beyond its maximum rated flux density will result in increased Wfe losses in addition to waveform distortion.
The weight of a transformer is comprised of the following items:

1. Copper (windings)
2. Steel (core
3. Insulation materials
4. Mounting hardware or potting material

The obvious trade-off for weight reduction is between the amount of copper wire and the size of the core. A well-designed transformer will be a balance of copper and steel needed to obtain reasonable AC regulation, temperature rise, and minimum physical size. See Toroidal Transformers, Figure 3 for a comparison of Toroidal vs. Laminated weights.

The physical dimensions (volume) of a transformer can be varied for any given design. The core of the toroid transformer is made of a strip of grain oriented silicon steel. The strip width determines the height of the core while the inside and outside diameters determine the physical dimensions and the cores’ cross-section area. The cost to produce a custom vs. standard toroid core is relatively low. Most toroidal transformers have a diameter to height ratio of 3:1, but ratios of 2:1 (high profile) and 7:1 (low profile) are possible. See Toroidal Transformers, Figure 2, for a comparison of the standard Toroid vs. Laminated volumes.

OTHER ADVANTAGES OF HIGH PACKING DENSITY
EMI fields are very low because of the unique construction of the Toroid transformer. These transformers are wound on a ring shaped core, a configuration that provides maximum containment of magnetic fields. Unlike laminated transformers, toroid transformers do not have air gaps within the core. Air gaps cause a discontinuity in the magnetic path giving rise to increased radiated fields. Additionally, the even distribution of the primary winding over the secondary winding, uniformly around the entire core, ensures that the magnetic fields generated in the windings can be cancelled. Reductions of up to eight times, relative to the laminated transformer, can be expected. Further reduction is possible with a metal bellyband around the outside of the transformer, or full containment of the transformer within a steel enclosure.

Audible noise generated by a Toroid transformer is inherently low. The single strip of steel wound into a ring and welded at both ends is very solid and stable. The copper windings and insulation system completely envelope the core, further stabilizing the transformer and dampening the acoustical noise caused by magnetostriction phenomena.
Transformer noise can also be minimized by increasing DC ripple requirements in linear power supply applications. Low DC ripple require the transformer to deliver very large pulses of current in short periods of time. The high energy pulses further increase the magnetostriction action.