Analysis and design of a novel variable-inductor-based LED driver for DC lighting grids

This paper presents a novel variable inductor (VI) based LED driver for DC grid lighting applications. The proposed driver requires only a series inductor and a transformer as major components to drive the LED lamp from a half-bridge inverter. By introducing a VI as the series inductor, the LED current can be controlled independently from any other parameter, which makes it possible to drive and regulate several LED branches from the same half-bridge output. Other advantages of the proposed converter include inherent open circuit and short circuit protections, ZVS for the bridge transistor and ZCS for the output rectifier diodes, simple dynamics, possibility of analog and PWM dimming, constant switching frequency operation and high efficiency. The converter is thoroughly analyzed and modelled for both steady-state and dynamic operation. As another novelty of this paper, the dynamic response of the VI has been studied and taken into account to obtain the complete transfer function of the VI-controlled system. In addition, some housekeeping issues that usually arise when dealing with VI, e.g. how to drive the VI bias winding, are solved in this work. Experimental results provided from a 50 W laboratory prototype demonstrate the correctness of the performed analysis and the good possibilities of the proposed converter.