Emitter Switching for Power BJT Based LED Drivers

Abstract

In recent years, the LED lighting developed rapidly because of its superior efficiency, eco-friendliness, and longer lifetime compared to the fluorescent and its incandescent counterparts. As the core of LED systems, LED drivers need to be well designed in order to properly drive the LEDs with high efficiency, high reliability, long lifetime, and last but not least low cost. The major objective of this thesis project was to design an emitter switching power Bipolar Junction Transistor (BJT) based LED driver using the low-cost switch mode driving topology that can achieve high efficiency and low power dissipation. Using power BJT instead of power MOSFETs was because of the low cost feature. At the same time, there was a topology investigation on the low-cost high-quality driver. BIFRED was chosen due to the single switch structure. An average model of the BIFRED was built to facilitate the analysis and design. In order to make the power BJT has the same switching performance as power MOSFETs, there was a literature study of the characteristic of the power BJT. Aiming at overcoming the disadvantage of power BJTs, the emitter switching technology was investigated. Next was the design of the emitter switching power BJT-based LED driver. The hardware of the LED driver was experimentally tested, and it showed a good performance with high efficiency of the driver and low power dissipation in power BJT.