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ITGlossary · UPS technology
UPS (Uninterruptible Power Supply)
A device that provides backup power and protects equipment from power disturbances.
Technical level:Basic
A UPS sits between the wall outlet and the equipment and, when the mains fails or goes out of tolerance, powers the load from its batteries. At the same time it filters spikes and noise and, depending on the type, stabilises the voltage. There are three main topologies: offline (standby), line-interactive and online double conversion, offering increasing levels of protection.
Runtime depends on the batteries and the load. A small line-interactive UPS at full load typically provides a few minutes, roughly 3–10, and considerably more at half load. That is enough to save your work and shut computers down safely. For longer runtimes, external battery packs or a generator are used.
To size a UPS correctly, calculate the consumption in W, not only in VA, and leave a margin of about 20–30%.
Related terms
- BypassA path that feeds the load directly from the mains, without protection, when the UPS is overloaded, faulty or under maintenance.
- Cold Start FunctionA feature that allows a UPS to be started directly from the battery without utility power.
- InverterThe component inside a UPS that converts DC power from batteries back to usable AC power.
- Pure Sine WaveUPS output with the same waveform as the mains, needed for PFC power supplies, motors and sensitive equipment, unlike a stepped approximation.
- Auto RestartA UPS feature that automatically restarts the system after utility power returns following a shutdown.
- Double Conversion EfficiencyThe share of input power that an online UPS delivers to its output, lower at light load and highest at medium to high load.