In applications where there is no need for isolation between primary and secondary windings, the autotransformer is an economical alternative in addition to the benefits of size and weight reduction.

In autotransformers, a single coil shares the duty as both primary and secondary winding. The location of a tap defines the step-down or step-up ratio.

The amount of copper and iron used is less than in an ordinary double-wound transformer.

The savings can be considerable in fractional step-up or step-down (buck boost) configurations and close to 50% reduction in size at a 1:2 ratio, e.g. 120V to 240V.