Transformers are mainly used as power converters. The two variants, i.e. the step up and the step down converters function on the same line, but in opposite directions. While the step up transformer converts a low AC voltage to a higher strata, the step down transformer does the opposite. To put it simply, if a country uses 110v current, the step up transformer will convert the power to 220v current, and the step down transformer will do just the opposite. However both conduct A.C.
There are various places where this conversion is necessary. A step down transformer basically functions like a battery eliminator. As a layman would say, they power up any device that usually runs on main power, with a battery instead. This means that the converters are everywhere around us. Be it a laptop, a television, a radio, or any other comparatively small device, all are powered with a step down transformer. At times they are used to lower the voltage and then are connected to a step up transformer. This combination is suitable for factories and places where there is mass usage of current. Since the current output available with this mediator is only AC, it has to be smoothened to function accordingly.
These transformers follow the principle of magnetic induction between its coils to convert the voltage level. There is an iron core, and two insulated coils are wound around the core. When current flows through one coil, the core gets magnetized. At this point the coil through which the electricity is flowing becomes the primary or the input. The core then induces voltage in the other coil making it the secondary or the output. The ratio between the input and output is 2:1, which means if the input has 200 turns, the output will have 100 turns. This is also the determining factor of the voltage drop. This simply means that if the input is 500v, then the output is250v.
All transformers have a name plate rating. It is best to operate at voltages to the limit mentioned on the name plate. Using a step down transformer below the limit can put it to a wide number of uses. But going above limit is dangerous and can cause electrical failures.