An Uninterruptible Power Supply (UPS), also known as an Uninterruptible Power Source or a battery backup is a device which maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available.
There are two distinct types of Uninterruptible Power Supply (UPS): off-line UPS and line-interactive UPS (also called on-line UPS).
An off-line UPS remains idle until a power failure occurs, and then switches from utility power to its own power source, almost instantaneously.
An on-line UPS continuously powers the protected load from its reserves (usually lead-acid batteries), while simultaneously replenishing the reserves from the AC power.
The on-line type of UPS, in addition to providing protection against complete failure of the utility supply, provides protection against all common power problems, and for this reason it is also known as a power conditioner and a line conditioner.
While not limited to safeguarding any particular type of equipment, an Uninterruptible Power Supply (UPS) is typically used to protect computers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss.
