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Why a Donut Shape is Ideal

Many electrical engineers will argue that a donut shape is ideal for transformers used in audio amplifiers. Transformers are essential features of many electronics because they transfer and transform electrical energy. Considering that basic functions cannot work without transformers properly functioning, it is ideal for a transformer to meet 100% efficiency. The end goal is to have no energy loss in transferring power from an input to an output. Transformer winding must be ideal as well, meaning that winding should have zero resistance with no core losses. The voltage ratio of a transformer, from primary to secondary winding, must be equal to the number of turns to the ratio of the windings.

Toroid

Toroid and Toroidal Transformers

An ideal transformer should have practical applications including easy approximations for design construction, but that is not always attainable. When comparing a toroid transformer to other shapes (EL, C, R), a toroid typically emerges as being the transformer that comes closest to being ideal.

An EI core is shaped like an E made from magnetic steel. It is inserted into one side of the winding bobbin with an extra I shape section that is butted against the other end. There are gaps between core layers and the E’s and I’s, which creates chatter and a hum. Winding on these transformers only cover the center leg of the core.

C cores are constructed from C shaped laminations that are formed with strips of magnetic steel. When looking closely, the C sort of resembles a U. After joining the two parts, there will be gaps found in the magnetic circuit, which makes for lower core efficient when compared to toroidal cores. C cores perform better than EI variants, but not nearly as accurate as toroids.

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