What is the difference between double wound transformer and an auto transformer?

A double wound transformer has two separate windings (primary and secondary) that are magnetically coupled, allowing for electrical isolation between the input and output circuits. In contrast, an auto transformer has a single winding that acts as both the primary and secondary, with part of the winding shared between them, which means it provides no electrical isolation. This design makes auto Transformers more compact and efficient for certain applications, but they are less versatile in terms of voltage transformation and safety.