Differences Between Autotransformers and Isolation Transformers

There are various types of transformers. Some people might think autotransformers and isolation transformers are difficult to choose between them. What are their differences? Any advantages and disadvantages? Which one is suitable for me?


As the top manufacturer of toroidal power transformers in Taiwan, WEBB will discuss this topic today.


What is a Transformer?

In the beginning, let us learn about the regular transformer before talking about autotransformers and isolation transformers.

A transformer is a device that transfers AC currents from one circuit to another circuit, and doesn’t change the frequency. It is widely used in our daily life, from travel to manufacturing. It contains a magnetic core, primary winding, and secondary winding (2 or more windings). Operating on the base of Faraday's law, there are many kinds of transformers. We use them to change, stabilize and isolate AC current voltage.


What is an Autotransformer?

The regular transformer has two winding separated into two circuits, while in the autotransformer both circuits share the same winding. This means that the autotransformer has only one winding, which is primary and secondary at the same time. The common end of the windings has a tap to control the voltage. It is normally used for voltage regulation for connecting devices operating at different voltages.



  • Audio systems
  • Railways
  • Air conditioners
  • Induction motors
  • Most of equipment when using in different country need to change the voltage

Pros of Autotransformer

  • Compared to regular transformer and isolation transformer, it is cheaper, lighter and smaller because it has fewer windings and components inside.
  • Easier to move and transport due to its size and weight
  • Good at voltage control
  • Compared with regular transformer, the losses are lower.

Cons of Autotransformer

  • There is no isolation between both windings, which requires safety consideration.
  • If one wiring has malfunction, noise, and surge will affect the other side (the whole voltage output and input).


What is an Isolation Transformer?

The isolation transformer, also known as the insulation transformer, has two separate windings: the primary winding(input) and the secondary winding (output) of the circuit.
They are totally isolated from each other, and have an isolation space in between. The regular transformer also has two windings, but is connected to the same circuit.


Therefore, the isolation transformer windings will not interrupt or disturb each other. It reduces the current surge and noise from the wire to the connected device. Widely used in places where load and power supply need to be separated to ensure no electric spikes or surges would affect the precise equipment.



  • Computers and IT equipment
  • Medical equipment
  • Telecommunication equipment
  • Power supply industry
  • Lab

Pros of Isolation Transformer

  • More safe
  • Reduce electric surges and spikes
  • Reduce noise


Cons of Isolation Transformer

  • Higher cost compared to autotransformers, due to they use more copper coils and their size is bigger
  • It often causes an output distortion if used as a pulse transformer.



We have learned about both transformers. Their uses actually are different, the autotransformer change voltages for voltage regulation, and the isolation transformer separated the power supply and load for safety protection. WEBB suggest using isolation transformers for precise equipment needing stability, safety and protection. And choosing autotransformers for appliance needing alter voltage.


When it comes to selecting suitable transformers, one also needs to consider voltage, load requirement, number of phases, frequency, and installed location, then will know which one fits you. Still, wondering how to choose transformers for your equipment? Established in 1996, WEBB is the expert in providing reliable solutions and products, if you require more information about transformers or need a quote, please do not hesitate to contact us.