Technologies for Improving Performance of Indoor Dimmable Light-Emitting Diode (LED) Drivers

Abstract

With the rapid transformation taking place in lighting technology, light-emitting diode (LED) becomes the new promising light source for the future world. In the recent years, indoor application becomes the new battlefield for the industry, so higher price-performance ratio is the key in today and future LED lighting applications. This thesis comprises of a comprehensive overview of the latest technologies in LED lighting and presents several novel techniques to significantly improve the overall performance for indoor dimmable LED systems. More importantly, all the proposed novel technologies can be practically implemented with very high reliability and low cost. The first contribution is a topology and control innovation for indoor dimmable lighting applications. The proposed LED driver delivers a high quality constant current (CC) output for LED driving and another constant voltage (CV) auxiliary output simultaneously for the use of active cooling, digital lighting controller, etc. To decouple the two outputs and avoid the loading interaction, a novel nonlinear ramp control scheme is proposed, resulting in significant overall system cost saving. Secondly, a new adjustable off-time power factor correction (PFC) control method is proposed for a low power dimmable single stage Flyback LED driver to achieve high power factor (PF, >0.90) and low total harmonic distortion (THD, <20%) even down to half load condition for universal AC input (120V~277Vac). It has several unique advantages, such as: 1) wider LED output operating window; and 2) high accuracy of current control in deep dimming application. The third contribution is the modeling of the cascode switching Flyback converter for fast startup in deeply dimmed phase-cut LED driver. The structure’s inherent instability issue is modeled and analyzed quantitatively. Three solutions are proposed to stabilize the structure and suppress the unstable voltage oscillation. The final contribution is the conducted common mode (CM) noise path modeling and EMI reduction method for two-wire input LED lighting system. The model demonstrates 1) the potential resonance issue caused by the CM inductor and the parasitic capacitors in the system; 2) the impact of modeled design elements on EMI result; and 3) the harmful parasitic coupling paths using Miller Theorem.