The first step to understanding POWER SUPPLIES ICs! | ⑤The Importance of POWER SUPPLIES ICs What is Efficiency?

Efficiency is an important parameter that indicates the performance of POWER SUPPLIES POWER SUPPLIES, expressing the ratio of output power to input power.
The higher the efficiency, the less power is consumed during power conversion, resulting in an excellent POWER SUPPLIES with low loss and low heat generation.
The efficiency of an LDO or SWITCHING POWER SUPPLIES can be calculated using the following formula.

Efficiency η [%] = (output power / input power) × 100 = (output voltage Vout × output current Iout) / (input voltage Vin × output current Iin) × 100 ... (Equation 1)

Figure 1. Parameters required for calculating POWER SUPPLIES efficiency

As can be seen from equation (1), measured values of input and output currents and input and output voltages are required to calculate the efficiency.
Each voltage/current is measured using a multimeter, but if the measurement is made at a location far away from the object being measured, the value will include losses caused by CABLES and wiring, and the calculated efficiency may be lower than the actual efficiency.
Therefore, it is important to measure each voltage/current in close proximity to the object being measured.

Figure 2. Example of correct efficiency measurement

Figure 3. Example of an incorrect efficiency measurement

In the case of an LDO, when Iout is sufficiently larger than the LDO's self-consumption current, the relationship Iin ≒ Iout holds true.
Therefore, equation (1)

Efficiency η [%] = (output power / input power) × 100 = (output voltage Vout / input voltage Vin) × 100 ... (Equation 2)

This shows that the efficiency is simply the ratio of the output voltage to the input voltage.
In other words, the greater the difference between the input and output voltages of an LDO, the less efficient it becomes.

Figure 4. Example of LDO efficiency calculation

On the other hand, unlike LDOs, SWITCHING POWER SUPPLIES do not have the relationship Iin ≠ Iout, and although it depends on input/output and other specifications, they can achieve efficiency of 90% or more even if the difference between the input and output voltage is large.

Figure 5. Example of SWITCHING POWER SUPPLIES efficiency simulation results