What Is an Uninterruptible Power Supply?

Definition: Uninterruptible Power Supply

An Uninterruptible Power Supply (UPS) is a device that provides emergency power to a load when the input power source, typically the main electricity supply, fails. A UPS differs from an auxiliary or emergency power system in that it will provide near-instantaneous protection from input power interruptions by supplying energy stored in batteries or a flywheel. The on-battery runtime of a UPS is relatively short but sufficient to start a standby power source or properly shut down the protected equipment.

Understanding Uninterruptible Power Supplies

Uninterruptible Power Supplies are critical for ensuring the continuous operation of computers, data centers, telecommunications equipment, and other electrical equipment where an unexpected power disruption could cause injuries, fatalities, business disruption, or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 volt-ampere rating) to large units powering entire data centers, buildings, or even cities.

Key Features and Benefits

Power Protection

UPS systems provide protection from power variances and outages. They maintain a steady flow of power to connected devices and help prevent data loss, hardware damage, and operational interruptions.

Surge Protection

Besides providing backup power, many UPS systems also protect against power surges, which can damage electronic equipment.

Voltage Regulation

UPS devices often include technology to regulate voltage, compensating for under-voltage and over-voltage conditions, ensuring that equipment operates within safe voltage limits.

Data Integrity

By allowing for safe shutdown procedures, UPS systems help maintain data integrity, preventing the corruption of critical data during unexpected power failures.

Types of UPS Systems

Standby UPS

Also known as offline UPS, it provides basic power protection. It switches to battery power when it detects a power loss. Ideal for home use or small office computers.

Line-Interactive UPS

This type of UPS includes a voltage regulator that adjusts low or high voltage conditions without using the battery, which extends the battery life. Line-interactive UPS systems are used for small business and consumer devices.

Double-Conversion (Online) UPS

Provides the most comprehensive level of power protection. The UPS continuously converts incoming AC power to DC power and then back to AC. It operates on isolated battery power, which shields connected devices from power anomalies.

How a UPS Works

A UPS typically uses a rectifier to convert AC power to DC to charge the batteries and a power inverter to convert the stored DC power back to AC power to run connected equipment. It also incorporates a bypass circuit that allows the mains power to supply the loads directly when it is available and switches to battery power almost instantaneously upon detecting a power failure.

Frequently Asked Questions Related to Uninterruptible Power Supply