ABSTRACT As new ideas unfold and technology become advanced with business increasingly being dependent on technology for their fundamental operation; the need for system availability is of paramount importance. Uninterruptible power supply [INVERTER] maintain continuous supply of electric power to certain essential equipment that cannot be shut down unexpectedly. They are generally associated with telecommunication equipment, computer system and other facilities such as airport traffic controls system where even brief commercial power interruption could cause injuries or fatalities, serious business disruption in data loss. The 500watts UPs is designed to be used in such situation. With its conversion design, providing clean square wave power to the critical load and with the battery, this UPs [Inverter] is ideal for small business and home PC that need adequate protection against power failure. TABLE OF CONTENTS Title page Approval page Dedication Acknowledgement Abstract Table of contents CHAPTER ONE PROJECT OVERVIEW 1.1 Introduction 1.2 Scope and specification 1.3 System Architecture CHAPTER TWO LITERATURE REVIEW 2.1 Introduction 2.2 Current Trends in UPs 2.3 Implementation option 2.4 Preference Technique CHAPTER THREE 3.1 Working Principles of an Inverter 3.2 Working Principle of some Device in an Inverter 3.3 Table of Components used 3.4 Conclusion. REFERENCES