Auto Transformer Working Principle

An auto transformer is a special transformer that does not require isolation between the primary and secondary. To put it simply, its primary and secondary windings are on the same winding. Namely, it is a transformer with only one winding and its output and input share a set of coils.

Working Principle

When the auto transformer is used as a step-down transformer, a part of the turns is extracted from the winding as the secondary winding. And when it comes to a step-up transformer, the voltage is only applied to some turns of the winding. Because the direct current cannot be directly boosted, it needs to pass through electronic components.

In a word, no matter it is buck or boost, the autotransformer only needs one winding to complete stepping up and stepping down volatge. Therefore, compared with ordinary isolation transformers with the same capacity, auto transformers provide some advantages, including small size and high efficiency. Most importantly, the combination of the primary winding and the secondary winding is the most outstanding feature of the autotransformer. Therefore, with the rapid development of power system today, auto transformers feature large capacity, low loss and low cost and are widely used in human life and industrial production.

According to the autotransformer structure, it can be classified into fixed type and adjustable type.

Auto transformer consists of two windings connected in series to form the primary winding bd, the number of turns is N1, and some of the windings are used as the secondary winding cd of the transformer, and the number of turns is N2, which is called the common winding and is shared by the primary and secondary sides. The winding bc that belongs to the primary winding and is connected in series with the common winding is called a series winding, whose number of turns is N1-N2.