A New Soft Switching Step-Down/Up Converter with Inherent PFC Performance 835 JPE 9-6-2 A New Soft Switching Step-Down/Up Converter with Inherent PFC Performance Masoud Jabbari † and Hosein Farzanehfard * †* Dept. of Electrical and Computer Eng., Isfahan University of Technology (IUT), Isfahan, Iran ABSTRACT In this paper a new buck-boost type DC-DC converter is presented. Its voltage gain is positive, all active elements operate under soft-switching condition independent of loading, magnetic isolation and self output short-circuit protection exist, and very fast dynamic operation is achievable by a simple bang-bang controller. This converter also exhibits appropriate PFC characteristics since its input current is inherently proportional to the source voltage. When the voltage source is off-line, it is sufficient to add an inductor after the rectifier, then near unity power factor is achievable. All essential guidelines to design the converter as a DC-DC and a PFC regulator are presented. Simulation and experimental results verify the developed theoretical analysis. Keywords: DC-DC converter, PFC, Resonant converters, Soft switching 1. Introduction Soft switching techniques are mainly developed to reduce switching losses. Under soft switching condition, switching frequency can be increased and thereby converter size can be reduced as well. These converters are often obtained by modifying hard switching topologies or sometimes by presenting novel circuits. Soft switching condition is commonly attained by switching under zero voltage (ZV) or zero current (ZC) condition [1-3] . PFC converters are presented to reduce line current harmonics and are classified as single-stage and two-stage topologies [4-6] . Single-stage topologies are more economical for low power applications [4-9] . Two-stage topologies are formed by a PFC preregulator which is followed by a DC-DC converter. The preregulator which is often a boost converter, enhances the input power factor and the second stage provides tight output voltage regulation with a fast dynamic response. However, number of elements is increased, efficiency is decreased, and two control loops are required. Among various presented topologies, only a few are soft switched [7-13] . To have a universal voltage gain or to decrease power processing, PFC (pre-) regulators based on buck-boost, SEPIC and Cuk converter are also developed [14-24] . A new soft-switching step down/up converter is presented in this paper. The converter is resonant type, has a positive voltage gain, and exhibits inherent PFC characteristics. Its topology is derived from our previous work, switch-resonator converters [25] . For DC-DC purposes, the proposed converter can be attractive as a soft-switched alternative for SEPIC or Cuk converter. Manuscript received Dec. 24, 2008; revised Aug. 27, 2009 † Corresponding Author: Jabbari.Masoud@Gmail.com Tel: +98-913-314-8874, Isfahan Univ. of Tech. * Dept. of Electrical and Computer Eng., Isfahan Univ. of Tech.