change the voltage
A device that is mostly used to change the voltage in an alternating current (AC); however, it can also be used to maintain the same voltage but act as an electrical isolator. The most common type is the laminated core transformer, which is found in myriad power supplies. Made of steel laminations wrapped with two coils of wire, the ratio of windings between the "primary" input coil and the "secondary" output coil determines the voltage change. For example, if the primary has 1,000 windings and the secondary 100, an input of 120 volts is changed to 12v.