LDO stands for Low Dropout Regulator, which is a type of DC linear voltage regulator that can operate even when the supply voltage is very close to the output voltage. The main difference between LDO and non-LDO regulators is their schematic topology. Instead of an emitter follower topology, low-dropout regulators consist of an open collector or open drain topology, where the transistor may be easily driven into saturation with the voltages available to the regulator. LDO regulators are used when the required output voltage differs from the input voltage, and they provide a simple and inexpensive solution for power supply regulation. The advantages of an LDO regulator over other DC-to-DC voltage regulators include the absence of switching, which reduces noise and simplifies circuit design. LDO regulators are characterized by their drop-out voltage, quiescent current, load regulation, line regulation, maximum current, speed, voltage variations in the output because of sudden transients in the load current, output capacitor, and its equivalent series resistance. Dropout voltage is defined as the voltage drop across the regulator where the device can no longer regulate the output voltage.