This application note describes the LED driving system using a half-bridge LLC resonant converter for high power LED lighting applications, such as outdoor or street lighting. Due to the existence of the non-isolation DC-DC converter to control the LED current and the light intensity, the conventional PWM DC-DC converter has the problem of low-power conversion efficiency. The half-bridge LLC converter can perform the LED current control and the efficiency can be significantly improved. Moreover, the cost and the volume of the whole LED driving system can be reduced.