Auto Transformer

Auto-transformers are used strictly in a step-up or step-down application. They are very similar to isolation transformers with one important exception. In an auto-transformer the primary and secondary windings are electrically common to each other. The advantage of using an auto-transformer over an isolation transformer is its smaller size, it’s lighter and cost less. The major disadvantage is that there is no isolation between the primary and secondary which allows noise on the power line to be directly coupled to the load. Another disadvantage is that auto-transformers provide no regulation. It is also important to note that the greater the change in voltage the less cost effective the auto-transformer is. Some common applications for auto transformers are motors, heaters, and other non sensitive loads