CHAPTER ONE

1.0     INTRODUCTION

The idea behind a UPS (Uninterruptible Power Supply) is pretty obvious from the name, in addition to filtering, enhancing or modifying the unity power, special circuit and batteries are used to prevent electrical machines from losing power during a disruption (blackout or voltage sag brownout). The units are all called different names depending on the next design, but all fit into general category of backup power.

          Before delving into details of how an uninterruptible power supply works, let’s take a quick look of the basic of the type of equipment. An electrical device plugged into the wall or into a surge suppressor has only one source of power. If there is a blackout, the electricity is out an the device obviously goes off immediately. A UPS changes this equation by providing its equipment two source of power.

          UPS are designed so that there is one source of power normally used called the primary power source and another source that kicks in if the primary is disrupted called the secondary power source. The power from the wall is always one of those sources and the battery contains within the UPS is the other. A switch is used to control each of these powers and the equipment of any given time. The switch changes from the primary of the secondary when it detects the primary has gone out. It switches back from the secondary power the primary power, source has returned.

          Contrary to what you might think, the wall A.C power is not always the primary power source and the battery the secondary source. Which source is primary and which is secondary depends on the type of UPS. Therefore, circuit is provided with this UPS to convert AC power to DC to change the battery. A device called an invert is also provided to change the battery stone DC electricity to AC to run your equipment.

          Furthermore, those components of the uninterruptible power supply and other one discussed in details in the section covering the various parts of the UPS. The size of the UPS is primary dictated by the size of the time your equipment can run on battery power switching down, higher units not only can power equipment for more time they can also handle a large total demand for power.

1.1     BACKGROUND

In this section we will take a brief look of the various parts that are made up of typical UPS. Focus is on small units more commonly used for home and smaller business.

INVERTER PART: That is inversion circuit, all UPS include cone circuit that manipulates electricity converting it from AC power produced by your utility company to DC power stored in the battery and back again for use by your equipment. The inverter section converts a DC voltage into an AC voltage with the help of an oscillator. This section also consists of two stages of switching circuits which comprises of a power transistor connected i in the common emitter configuration.

Since the oscillator has two outputs each of the switching circuits is coupled to the two outputs of the oscillator respectively. The two outputs one explained in detail in subsequent chapter. The exact type, netune size and quality of the circuit depend on the type of UPS and more specifically the model you have chosen. As with all things the better the unit, the high the quality of the components and as with all thins quality is often corrected to price but not always.