drive current for different levels of LED diming. For this aim, a step-down LED driver chip, XRP7613 is employed In the circuit design. The XRP7613 is a non-synchronous step down converter which can drive high power LEDs at up to 1.2A of continuous current. In order to control the LED brightness by linearly adjusting the LED current, the PWM/EN port of a XRP7613 chip with dividing resistance is designed in the driver circuit as shown in Fig. 2.