LDO is a low dropout voltage regulator and a linear voltage regulator. It can only be used in step-down scenarios, that is, the output voltage can only be smaller than the input voltage.
The advantage is that the load response is fast, very stable, and the ripple is relatively small; the
disadvantage is that the input voltage and the output voltage cannot be too different, the load cannot be too large, and the efficiency is low. Linear regulation means that the input and output voltage difference is multiplied. The upper average load current is the power consumed by the turn-on element of the linear regulator, that is, Pd = (VIN-VOUT) *ILOAD. High VIN/VOUT ratio and high load current will cause excessive extra power loss. .
Principle: The reason why the LDO can adjust the output voltage is because the amplifier will adjust the driving ability of the PNPmos tube (Q1) according to the increase and decrease of the load. At this time, the mos tube works in the variable resistance area. When the load becomes smaller, the output will be caused. When the voltage increases, the output voltage of the feedback amplifier circuit increases at this time, so |Vgs| becomes smaller, and the equivalent resistance of the regulator tube becomes larger, thereby pulling down the output voltage; in the same way, when the load becomes larger, the output voltage decreases. When it is small, the output voltage of the amplifying circuit decreases, so |Vgs| becomes larger, and the equivalent resistance of the regulator tube decreases. Thereby the output voltage is pulled high; therefore, the LDO can stabilize the output voltage at a certain value.
Vout =(1+R1/R2)Vref