Design considerations of a single-stage LED lamp driver with power factor correction

Abstract

Light emitting diodes (LEDs) with their current performances have become the most convenient solution to replace conventional lighting sources. LEDs are current driven devices with low equivalent dynamic resistance. This causes instabilities and bifurcations in the driver. Therefore, this paper provides the analysis and design considerations of the stability boundaries of the LED lamp model in comparison with resistive loads. Single stage power factor correction converters are cost effective solution to drive LED lamps with a near unity power factor and high efficiency. Unfortunately the single stage converters suffer from two main problems: the increased voltage stresses and bifurcations during line cycle. The proposed LED lamp driver is based on a modified SEPIC converter which is well known by its reduced voltage stresses. If the system is operated in discontinuous conduction mode (DCM), the input current will follow automatically the input voltage profile. This paper describes the fast-scale instability in a power-factor-correction (PFC) modified SEPIC converter operating in DCM for driving LED lamps. This work provides a convenient mean of designing a high performance LED lamp driver and predicting stability boundaries which can facilitate the selection of practical parameters values for maintaining stable operation. In this paper, it will be shown that, with improper choice of system parameters, the converter can suffer from fast-scale instability for some intervals of time during the line cycle. Simulation results of exact cycle-by-cycle system equations are presented to demonstrate the effectiveness of the proposed design method. Then, a laboratory prototype is built to verify the feasibility of the proposed LED lamp driver and design considerations.