What is a key characteristic of an autotransformer?

An autotransformer is defined by its unique construction that includes a single winding that serves multiple functions—both as the primary and secondary winding. This single winding is tapped at different points to provide different voltage levels. This design allows for efficient voltage transformation, either stepping up or stepping down the voltage depending on how the taps are utilized.

The characteristic of utilizing a single winding distinguishes autotransformers from traditional transformers, which require separate windings for primary and secondary functions. Understanding this key feature helps clarify why autotransformers are often used in applications where size and efficiency are crucial, as they can be more compact and have less copper loss due to their design.

In contrast, the requirement for two separate windings pertains more to conventional transformers, which cannot operate without them. Similarly, the mention of operating with a steel core is not a defining characteristic of an autotransformer specifically, as both autotransformers and conventional transformers can use various core materials. Lastly, while autotransformers can function to step down voltage, they are also capable of stepping up voltage depending on how they are configured.