UPS Topology – Line interactive vs Online double conversion

There are two main UPS topologies, line interactive and online double conversion. We are going to explain these and assist you to select which one would be best for your application.

This information is broken down into two parts; the layman definition, written by myself (I have a marketing and sales, non-technical background) and a technical definition, which we will be explained by our technical manager.

Layman definition

Line-interactive, the load is always running off the mains power, when the power is cut there is a short change-over time to the batteries (approx. 6ms) Line-interactive the power always go through and AVR and Surge protection before the load, thus the power is still being “cleaned”.

Online, the load is always running off the batteries, so we always have a controlled frequency (50Hz) and AC output (230V AC). There is no change over time with online for it is already on the batteries.

Overall, short change over does not affect most equipment (CCTV, basic computer equipment) , however online UPS is preferred for more expensive and sensitive equipment like servers and medical scanners.

Below is a diagram to demonstrate the difference between how a line interactive UPS “cleans the power” vs and online UPS. Please note if you are after a more technical diagram we do have this below.

comical description of line interactive vs online topology

Technical definition

Line-Interactive, during normal operation the mains supply is fed via an automatic voltage regulator (AVR) to feed the load. The AVR regulates the mains supply voltage, boosting if low or bucking if high. The mains supply is used to charge the batteries. When the AC goes out of the specified range, the load is switched to the inverter that draws its power from the batteries.

Online double conversion, converts the power twice, so during normal operation the mains supply is converted from AC to DC, the DC is then converted to AC that feeds the load. When the mains supply goes out of a specified range, there is no switching, and the UPS simply draws its power from the batteries.

image explaining line interactive vs online topology

Topology Comparison

Line InteractiveOnline Double Conversion
Normal OperationAVR supplies LoadInverter supplies load
Total Cost of OwnershipLower initial cost & Lower operating costHigher initial cost                  & Higher operating cost                          (Energy & Heat generation)
Energy Efficiency during Normal Operation96% – 98%85% – 95%
Response to unstable or highly distorted mains supplyExtreme voltage distortion can require frequent battery usageAccepts extreme voltage distortion without going to battery
Output Frequency regulationOutput frequency varies within a rangeOutput fixed to a configurable frequency


If you require any further assistance in selecting the correct UPS for your application, please contact one of our technicians 1300882447 or [email protected]

Why Us


We offer our clients many years of experience in power related products and have more than 50 000 Uninterruptible Power Supply units in the market.

Don’t Be Antisocial


1/17 Sunblest Crescent,
Mount Druitt NSW 2770

8 / 35 Garden Road,
Clayton, VIC 3168

1 / 14 Dellamarta Rd,
Wangara, WA 6065


© 2023 PSS Distributors. All right reserved.