Offline UPS, also known as UPS Line Interactive, are identified with the abbreviation VI (Voltage Independent) since the output voltage is not independent from the input voltage, but there is a stabilization that reduces the variations.
In this way, in normal operating conditions, the UPS protects the connected equipment from overvoltages or undervoltages by means of a rectifier circuit and, in the event of a blackout, an inverter comes into play and the group exchanges the load on the voltage generated by the inverter.
Line Interactive technology is particularly recommended for the protection of computers, surveillance systems, modems, switches and routers.
Online UPS, usually called "double conversion", are identified with the abbreviation VFI (Voltage and Frequency Independent). This technology ensures that the UPS always generates an output power supply, perfectly sinusoidal, independent from the input one, clean and stable in both frequency and voltage. In this way, the UPS output is powered thanks to the rectifier that switches the UPS input voltage from alternating to direct and by the inverter which transforms the direct voltage back into alternating. UPSs with online technology are ideal for powering servers, surveillance systems, healthcare equipment and MV / LV cabinets.