An LDO, or low dropout regulator, is a low dropout linear regulator that uses a transistor or field effect tube (FET) operating in its saturation region to subtract excess voltage from the applied input voltage to produce a regulated output voltage.
The four main elements are Dropout, Noise, Power Supply Rejection Ratio (PSRR), and Quiescent Current Iq.
The main components: starting circuit, constant current source bias unit, enabling circuit, adjusting element, reference source, error amplifier, feedback resistor network and protection circuit, etc.