<p> Analysis of the Integrated SEPIC-Flyback Converter as a Single- Stage Single-Switch Power-Factor-Correction LED Driver</p><p>Abstract This paper proposes a new isolated single-stage single-switch power-factor-correction (S4 PFC) driver for supplying light emitting diodes (LEDs) without electrolytic capacitor. In the proposed LED driver, the switch turns on under zero current switching (ZCS) condition. Also, it turns on at a voltage less than its nominal voltage stress and, therefore, the switch capacitive turn-on loss decreases too much extent. The leakage energy is absorbed, so there are no voltage spikes across the switch when the switch turns off. In this paper, operating principles of the proposed driver are discussed and design considerations are presented. Also, a laboratory prototype for supplying a 21W/30V LED module from 220Vrms/50Hz AC mains is implemented and experimental results are presented to verify the theoretical analysis. Exisiting method: In recent decades, some regulations for limiting input current harmonics of power supplies have been approved, which impose power factor requirements on AC-DC power converters. To meet these requirements, designers have to use power-factor-correction (PFC) techniques that improve the low frequency harmonic contents of power supplies. Earlier methods for improving the power factor, suggested applying a basic DC-DC converter (such as boost or flyback converters) for AC-DC stage.This method suffers from significant twice-line-frequency voltage ripple across the output capacitor. In this situation, to achieve a regulated DC output voltage, a second stage is required which results in lower efficiency because of processing the power twice. Proposed method: A family of single-stage isolated PFC power supplies are introduced based on buck and boost PFC cells. Also, an integrated boost-flyback PFC converter is proposed.In this converter, there are voltage spikes across the switch when it turns off. This converter is improved by employing Further Details Contact: A Vinay 9030333433, 08772261612 Email: [email protected] | www.takeoffprojects.com an extra winding on the flyback transformer to reduce the bulk capacitor voltage.Reference presents a single-stage PFC converter which integrates a buck-boost converter with a buck converter. However, it uses two active switches and, therefore, its complexity is high. An integrated buck-flyback converter is proposed as a LED driver, in which the switch has voltage spikes.Another single-stage PFC converter is introduced which is an integrated double-buck converter. This converter suffers from zero-crossing distortion in line current and its switch also needs a floating driver. In this paper, a new isolated single-stage single-switch PFC (S4 PFC) converter for LED driver applications is proposed, which is composed of a single-ended primary inductor converter (SEPIC) with a flyback converter and uses no electrolytic capacitors. Block diagram of propsed method:</p><p>Fig. 2. Simplified circuit diagram of the proposed LED driver. Drawbacks of existing method:  By using the parallel PFC structure improves the efficiency, but its complexity and cost are high.  To achieve a regulated DC output voltage, a second stage is required which results in lower efficiency because of processing the power twice. Advantages of proposed method:  This converter is improved by employing an extra winding on the flyback transformer to reduce the bulk capacitor voltage  The proposed single-ended primary inductor converter (SEPIC) with a flyback converter and uses no electrolytic capacitors.</p>