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.
LED lighting is rapidly replacing conventional lighting sources like incandescent bulbs, fluorescent tubes, and halogens because LED lighting reduces energy consumption. LED lighting has greater longevity, contains no toxic materials, and emits no harmful UV rays, which are 5 ~ 20 times longer than fluorescent tubes and incandescent bulbs. All metal halide and fluorescent lamps, including CFLs, n contain mercury.
The amount of current through an LED determines the light it emits. The LED characteristics determine the forward voltage necessary to achieve the required level of current. Due to the variation in LED voltage versus current characteristics, controlling only the voltage across the LED leads to variability in light output. Therefore, most LED drivers use current regulation to support brightness control. Brightness can be controlled directly by changing the LED current.