LED is a device that is driven by the current, and its brightness is proportional to the forward current. There are two ways to control the forward current. The first method is to use the V-I LED curve to determine the voltage required to produce the desired forward current to the LED. In fact, the method generally uses a voltage power supply and a ballast resistor. As follows, this method has a number of deficiencies. Any change in the forward voltage of the LED can cause the change of the LED current. If the nominal forward voltage is 3.6V, the current of LED in Figure 1 is 20mA. If the voltage is changed to 4.0V, this is the specific voltage change caused by the temperature or the manufacturing change, then the forward current is reduced to 14mA. Positive voltage change 11% will lead to a greater positive current change, up to 30%. In addition, according to the available input voltage, the voltage drop and power consumption of the ballast resistance will waste power and reduce the battery life. The second method is also the preferred LED current adjustment method is the use of constant current power supply to drive LED. AZXX