Autotransformers are a type of electrical transformer that use a single continuous winding to perform both primary and secondary functions, rather than having separate coils for input and output. This shared winding design allows part of the same coil to act as both the input and output, with electrical connections made at different points along the winding to achieve the desired voltage transformation. As a result, autotransformers are generally more compact and require less copper and core material than conventional two-winding transformers.

One of the key advantages of autotransformers is their high efficiency. Because a portion of the electrical energy is transferred directly through the conductive connection rather than entirely through electromagnetic induction, energy losses are reduced. This makes them particularly suitable for applications where efficiency and cost savings are important. They also tend to have better voltage regulation, meaning the output voltage remains more stable under varying load conditions.

Autotransformers are commonly used in situations where the difference between input and output voltage is relatively small. Typical applications include voltage regulation in power distribution systems, starting motors, and adapting equipment to operate at different voltage levels. They are also widely used in laboratory settings and industrial environments where adjustable voltage is required, often in the form of variable autotransformers.

Despite their advantages, autotransformers have some limitations. Because the primary and secondary circuits are electrically connected, they do not provide isolation between input and output, which can be a safety concern in certain applications. For this reason, they are generally not used where electrical isolation is necessary to protect equipment or users.

Overall, autotransformers offer a simple, efficient, and cost-effective solution for voltage conversion in many electrical systems, particularly where compact size and high performance are priorities and full isolation is not required.