Battery life is critical in portable applications. LED drive if practical, it must have high efficiency. The efficiency measurement of LED driver is different from the efficiency of typical power supply. Typical power efficiency measurement is defined as the output power divided by the input power. And for the LED driver, the output power is not the relevant parameters. It is important to generate the input power values that are needed for the expected LED brightness. This can be determined simply by dividing the LED power by the input power. Note: if this definition is efficient, the power dissipation in the current sense resistor will result in power dissipation. By the formula shown in Figure 3, we can see that the smaller current sensing voltage will produce a higher efficiency of the LED driver. Figure 4 shows that the choice of reference voltage 0.25V power supply and selection of 1V reference voltage of the power supply, the efficiency of the two to improve the situation. A lower current sense voltage supply is more effective, regardless of the input voltage or LED current, as long as other conditions are the same, the lower reference voltage can improve the efficiency and extend the battery life.