A step-up transformer is a transformer which has more turns of wire wound around its secondary winding than on the primary, thus increasing the input voltages applied to the primary coil. When voltage is applied to a primary coil or input, it magnetizes the iron core, inducing a voltage in the other secondary coil. Using a step up transformer to increase the voltage does not give you something for nothing. As the voltage goes up, the current goes down by the same proportion. The power equation shows that the overall power remains the same: Power=Voltage x Current.