A special subset of linear regulators are the low drop-out regulators. The drop-out is the minimum voltage across the regulator (input to output) to maintain regulation. The classification of linear regulators based on the drop-out voltage is shown on this slide along with representative part numbers in each group. A common misconception is that if a standard regulator is changed to a low drop-out regulator, the result is to save power. That is true only provided that the input voltage is reduced accordingly, because power dissipation depends on input-output multiplied by the current and if the difference Vin-Vout stays the same, so does the power. In practice an LDO achieves low power only by allowing a lower Vin to be used for the same output voltage.