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Reasons to Choose a Toroid Over E-I Cores

When comparing a toroid to other similarly powered transformers, a toroid is considered highly efficient. The equation used for efficiency is Efficiency = Pout/Pin. Pin is the power input of a transformer, whereas the Pout is the measured output power that is delivered to a load. The difference between Pout and Pin is consumed by losses experienced inside the core and the windings. Toroids efficiently run at higher flux densities than E-I laminates. Their ideal magnetic circuit reduces the number of turns of wire wrapped around the core in cross-sectional areas. Custom coil winding of toroids creates efficiency rates that are consistently close to 95%. E-I laminates are less efficient than toroids, at around 90%.


Recently, more attention has been paid to the energy efficiency of electronics. To meet the modern standard of electrical products, a toroidal transformer serves as a critical tool for meeting strict standards. Toroids are known to do a better job of reducing losses than other transformers.

Another benefit to strongly consider is a toroids low stray field. An E-I core is difficult to align with the grain structure of a stamped lamination that has a flux path over the entirety of the magnetic path. E-I cores have higher core losses and they are less efficient at standard operations when compared to toroidal transformers.

Discontinuity in E-I winding causes leakage flux. Concentrating windings in small regions of laminates leaves portions of the flux path open. As a result of this winding style, transitions go from windings to bare laminates. At these moments, flux escapes the confined core. A winding transition is also known to create high leakage inductance from E-I cores.


Toroidal cores do not have this problem (air gaps). Custom coil winding creates perfect symmetry between winding and the core, which reduces flux leakage. Toroids are known to provide predictable and strong performances. They are free from discontinuities.

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