In an autotransformer, how does the connection differ from a conventional transformer?

An autotransformer is characterized by its use of a single winding that serves both as the primary and secondary winding. This design allows a portion of the winding to function as the primary side connected to the power source, while another portion can provide the desired output voltage as the secondary side. This unique configuration enables the autotransformer to step up or step down voltage with greater efficiency and less material since it does not require an entirely separate winding for the secondary side, as is the case in conventional transformers.

This implementation results in a more compact design and lowers the weight and cost compared to conventional transformers, which utilize two distinct windings. As a result, the autotransformer is often used in applications where the voltage difference between input and output is small, taking advantage of its efficiency and reduction in losses.

In contrast, the other options refer to features and designs not applicable to autotransformers, such as having an additional coil for isolation, requiring two separate power supplies, or only operating on AC power, which does not capture the specific defining characteristics of an autotransformer as stated in the correct answer.