The present invention provides a LED driver for control the brightness of the LED. An energy-transferred element and a switch are connected in series with the LED for controlling the current of the LED. A diode is coupled to the energy-transferred element for freewheeling the energy of the energy-transferred element through the LED. A control circuit is developed to generate a control signal for switching the switch in response to the LED current. The LED current is further adjusted in response to a voltage signal of the LED. The value of the voltage signal is correlated to the LED temperature. Therefore the LED current can be programmed in accordance with the LED temperature.