Off-line single-stage SEPIC-Buck converter for dimmable LED lighting with reduced storage capacitor

This paper presents an analysis and design of a Light Emitting Diode (LED) driver aiming to substitute the electrolytic capacitors. Considering the low lifetime of electrolytic capacitors compared to LEDs, this topology aims for reducing the storage capacitance and replaces it by a longer lifetime capacitor, increasing the overall system life span. A Proportional Integral (PI) controller is designed to reduce the output current ripple. Consequently, it reduces the bus voltage which allows working with reduced bus capacitances. The input current distortion limit must be observed. The power factor correction (PFC) stage is based on a Single Ended Primary Inductance Converter (SEPIC) operating under discontinuous conduction mode (DCM) because of its low input current distortion characteristic making it possible to eliminate the electromagnetic interference (EMI) filter. The power control (PC) stage is performed by a Buck converter using its output current source behavior, suitable for LED application. A 107 W LED driver prototype is implemented resulting in 15.2% total harmonic distortion (THD), 50% current ripple on the LED and an efficiency of 90.1% using a 35μF bus film capacitor. Furthermore a dimming strategy is proposed and implemented by an LED parallel active switch.