Analysis, design, and experimentation of the active hybrid‐series‐parallel PWM dimming scheme for high‐efficient off‐line LED drivers

Abstract

This study presents a high power factor (PF) light-emitting diode (LED) driver featuring a pulse width modulation (PWM) dimming technique. The integrated buck-flyback-buck converter (IBFBC) is built by connecting a buck converter to the integrated buck-flyback converter's output. The IBFBC ensures a constant output current regulation as well as high PF at all dimming ratios. The purpose of the output buck converter is to clear up the discontinuous power operation created by the PWM dimming. This occurs when the buck converter absorbs the output power, at LED switched-off, and sends it back to the input. Thus, the IBFBC maintains the operational enhancement shown by the hybrid-series-parallel (HSP)-PWM technique, ensuring greater efficiency. This study explains the operating principles of the IBFBC using circuit diagrams as well as an average model for the entire converter. Moreover, the study presents a mathematical analysis of the IBFBC power flow. It provides guidance on how to select the optimum value for the output buck inductance. A 230V, 50Hz input, 160V output, 100W AC–DC converter operating at 100 kHz has been implemented. The prototype is fully tested to demonstrate the active HSP-PWM technique. An efficiency ranging 50–86% corresponding to the dimming ratio of 5–100% is reached, where 5% dimming refers to an output power of 4W.