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ITGlossary · UPS technology
Online (Double Conversion) UPS
A UPS that continuously converts incoming AC to DC and back to AC, so the load is always fed by the inverter with clean, stable power.
Technical level:Intermediate
In a double-conversion UPS, the load is not fed directly from the mains during normal operation. The rectifier converts the incoming voltage to DC, which charges the batteries and feeds the inverter, and the inverter then produces a new, clean sine wave with stable amplitude and frequency.
Because the inverter runs all the time, switching to battery during an outage involves no transfer time. This topology protects against overvoltage, sags, noise and frequency deviations, which is why it is preferred for servers, medical and industrial equipment, and for operation on a generator. The trade-off is slightly lower efficiency and more heat than a line-interactive unit.
A practical tip: many models offer an ECO mode to save energy; enable it only if the load can tolerate a brief transfer.
Related articles
Related terms
- InverterThe component inside a UPS that converts DC power from batteries back to usable AC power.
- 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.
- Zero Transfer TimeA feature of online UPS systems, where the inverter feeds the load continuously so a power cut causes no gap at all.
- Transfer TimeThe brief power gap when a UPS switches from mains to battery, typically 2–10 ms for line-interactive models and zero for online ones.
- Static SwitchA thyristor-based switch with no moving parts that transfers the load between inverter and mains within a fraction of a cycle.
- AC EfficiencyIndicates how efficiently a UPS converts incoming AC power into usable output power during normal operation.