4-1. Efficiency of LDO regulators

The efficiency of an LDO regulator can be calculated as follows:

Input power (P_IN) and output power (P_OUT) can be calculated using Equation 2 and Equation 3, respectively:

When the quiescent current (I_B) of an LDO regulator is negligibly smaller than the input current (I_IN), Equation 2 can be approximated as follows:

Substituting Equations 3 and 4 into Equation 1, we obtain:

In the case of series regulators, I_IN = I_OUT.
Hence,

So, the efficiency of an LDO regulator can be calculated as the ratio of input voltage (V_IN) to output voltage (V_OUT).
Therefore, an LDO regulator can be used to compose a high-efficiency power supply, depending on the input and output voltage conditions.