Transformers are electronic devices that transfer the voltage (electrical energy) from one circuit to another.They do this using the magnetic induction process.Step-up transformers increase the voltage, whilst step-down transformers reduce the voltage.The most basic of transformers consist of two wire coils: a primary for the AC input, and a secondary that leads to the AC output.These coils are not connected electrically but are wound around an iron ‘core’.This ‘core’ increases the strength of the magnetic field.