What is a characteristic of auto-transformers?

Auto-transformers are distinctive due to their ability to use a single winding for both the primary and secondary sides of the transformer. This configuration allows them to effectively step up or step down voltages while utilizing a portion of the winding only once. As a result, the overall design requires significantly less copper compared to standard transformers, which have two separate windings for primary and secondary operations. This reduction in material not only makes auto-transformers more economical but also more compact.

The efficiency and lower cost of materials in auto-transformers stem from their physical design, where part of the winding is common to both the input and output, leading to a lesser amount of conductive material needed for their construction. This unique operation is advantageous in many applications where space and material costs are critical considerations.