An autotransformer can be used as

An autotransformer can be used as

Right Answer is:

Both step up and step down


An autotransformer is a type of transformer that uses a single tapped winding rather than the two separate and electrically isolated windings used by mutual transformers.

Because autotransformers don’t have separate windings, unlike mutual transformers there is no electrical isolation between the primary and secondary circuits.

  • For example, if 230 V is applied between points A and B which involves 115 turns of the autotransformer winding, then the volts per turn (230/115) will be 2.
  • By a suitable selection of taps, one may select the number of turns to supply the necessary voltage to the other components.
  • A selection of 55 turns will provide a voltage of 110 V while a selection of 160 turns can provide 320 V.
  • Thus, an autotransformer can function as a step-up or step-down transformer.
  • In the step-up version, the voltage induced in the additional winding is added to the supply voltage.
  • In the step-down version, the induced voltage reduces the supply voltage.
  • It is possible to design an autotransformer to a required secondary output, which is variable in fractions or multiples of applied voltage.
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