APC Back-UPS 1250 User Manual download pdf (Page 4)

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1.0 Introduction

1.1 Overview

This equipment is a high performance line interactive uninterruptible power source

(UPS) designed to provide clean, reliable AC power to computer loads. The UPS's line

interactive circuit topology, illustrated below, offers excellent efficiency, on-line voltage

regulation and fast utility fault response.

The UPS’s DC-to-AC inverter is always connected to the output and when operating on-

line, a portion of the inverter circuitry is put to work “in reverse” to continuously

maintain optimum float charge on the battery. The inverter circuitry also acts to protect

the load from surges and EMI/RFI noise as part of an advanced hybrid surge suppres-

sion and filtering network. A unique mode of operation, named SmartBoost, serves to

regulate the load voltage by compensating for brownouts or sags. This is accomplished

without the need to draw power from the UPS’s battery. In anticipation of utility failure,

the UPS continuously monitors the line and prepares the inverter frequency for

synchronous transfer of the load. Upon occurrence of utility voltage failure such as a

blackout, severe brownout or an overvoltage condition, the UPS transfers the load to

power derived from the battery. Transfer to the "on-battery" mode of operation takes

place typically within 2 milliseconds. The inverter's output voltage waveshape is a low

distortion sine wave. Resynchronization and retransfer to on-line operation is auto-

matic upon recovery of the line voltage to within normal limits.

Line interactive UPS block diagram

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APC Back-UPS 1250 User Manual Page 4