Volume 5, Issue 6, June – 2020 International Journal of Innovative Science and Research Technology ISSN No:-2456-2165 IJISRT20JUN1114 www.ijisrt.com 1567 Comparision of Voltage Stress Across the MOSFET Switch of a Flyback Converter with Various Snubbers Soumya Dept. of EEE BMSCE Bengaluru, India A.N Nagashree Dept. of EEE BMSCE Bengaluru, India R.S Geetha Dept. of EEE BMSCE Bengaluru, India Abstract:- A Flyback converter is a simple switch-mode power supply that can be used to generate a DC output from either an AC or DC input. The converter switch is the most critical part of any converter. The voltage stress across the switch is a major issue as the high voltage spikes occur due to interaction between its output capacitance and the leakage inductance of the transformer. These spikes can be reduced with various snubbers like conventional tertiary winding, Resistor Capacitor and Diode(RCD) snubber, energy regenerative snubber and an active clamp snubber. This paper aims to analyze and compare the voltage stress across the MOSFET switch of Flyback converter with various snubber circuits. Keywords:- Active clamp snubber; Energy regenerative snubber; Flyback converter; RCD snubber; Tertiary winding reset. I. INTRODUCTION Flyback converter is the simplest isolated DC-DC converter topology widely used in low power applications due to its cost effectiveness and electrical isolation characteristics [1]. Its main power circuit comprises of a MOSFET as a switch, a transformer, an output diode and an output filter capacitor. The transformer winding polarities of flyback converter are designed in such a way that when the current passes through only one winding at a time [1]. The application of transformer is an efficient method to provide the electrical isolation between input and output of a dc-dc converter [1]. A steady current builds-up in every cycle, within the magnetizing inductance of the transformer. This steady buildup of current results in saturation of the transformer core [1]. Therefore, it needs to be reset always for each pulse and this problem can be solved by using a tertiary winding [1]. In Flyback converters, switching voltage spikes appears across the converter switches during its turn off time that can be reduced with the addition of snubber circuit [1]. A snubber normally comprises of a capacitor that is greater than the output capacitance of the switch that helps to discharge the output capacitor. A snubber circuit also serves to reduce turn-off switching losses [1]. The main focus in this paper is to compare voltage stress on the converter switch using different snubber circuits. This paper is organized as follows: Section I consists of an introduction, Section Ⅱ explains the working of Flyback converter, Section Ⅲ discusses about various types of snubber and its working, Section Ⅳ discusses the simulation results of the Flyback converter with various types of snubbers. II. FLYBACK CONVERTER Flyback converter is the most popular DC-DC converter topology for the applications involving 150W of power or less as it is simple and cost effective. The basic topology of a Flyback circuit is shown in Fig. 1. Fig 1:- Conventional Flyback converter [2] During switch on condition the energy is incorporated into the primary winding and due to the dot convention of the transformer as shown in Fig. 1, the energy from the secondary winding does not get supplied to the load [3]. During this period, the output capacitor supplies the energy to the load. During turn OFF condition, no current flows in the transformer’s primary. Simultaneously, the transformer’s secondary voltage polarity changes. Therefore, the energy is carried from the transformer to the output. Thus, the operation of converter is determined by the dot-ends of the inductor [3]. The amount of output DC voltage depends on the on-time of the switch during a switching period. For longer on time of the switch, larger output DC voltage is obtained. The transformer must be reset to equalize the negative volt-seconds and positive volt-seconds. If this condition is not satisfied, then a large amount of energy will be stored in the transformer during a switching cycle [3]. Due to this, the net accumulation of energy causes the transformer saturation and also leads to the short circuit of primary resulting in the failure of the switch.