A low-dropout voltage regulator is such a regulator that can work at a very small input-output differential voltage, that means this voltage regulators can regulate the output voltage even when the output voltage is extremely getting ready to the input voltage. If you use a standard linear regulator(for example a 78XX), you need a minimum difference between input and output voltage of about 2V, so if you want 5V, you have to provide minimum 7V as its input. If input goes below that voltage the regulation can not work. This 2V margin is named dropout voltage, you'll realize it within the datasheet of several part. Low-dropout voltage regulators have much lower dropout voltage about 0.5V-1.5V. So why do we need this? As for the linear voltage regulators, the lower the difference between input and output the higher the efficiency it will have because the power dissipation of the device is usually the difference between input and output voltage increased by the current its sup...