4-1. Efficiency of LDO regulators

𝜂 = 𝑃𝑂𝑈𝑇 / 𝑃𝐼𝑁 ・・・(1)

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

𝑃𝐼𝑁 = 𝑉𝐼𝑁 × (𝐼𝐼𝑁 + 𝐼𝐵) ・・・(2)  𝑃𝑂𝑈𝑇 = 𝑉𝑂𝑈𝑇 × 𝐼𝑂𝑈𝑇 ・・・(3)

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

𝑃𝐼𝑁 = 𝑉𝐼𝑁 × 𝐼𝐼𝑁 ・・・(4)

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

𝜂 = (𝑉𝑂𝑈𝑇 × 𝐼𝑂𝑈𝑇) / (𝑉𝐼𝑁 × 𝐼𝐼𝑁)

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

𝜂 = 𝑉𝑂𝑈𝑇 / 𝑉𝐼𝑁

In the case of series regulators, IIN = IOUT.

LDO regulator

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

Chapter4 Efficiency and power loss calculation for LDO

4-2. Calculating the power dissipation and junction temperature of an LDO regulator

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