UPSes To The Rescue

UPS Types

  • Standby UPS (entry-level);
  • Line-Interactive UPS (entry-level, mainstream);
  • Standby-Ferro UPS (mainstream to high-end);
  • Double-Conversion Online UPS; Delta Conversion Online UPS (high-end, industrial).

A standby UPS will only switch to the battery if the main power fails, which is why it is called standby. Most commercially-used UPS solutions are based on a line-interactive design. This means that the AC/DV inverter, which is used to charge the battery and to provide the failover power, is always connected to the active circuit. The other designs include a transformer for maximum reliability and filtering (Standby-Ferro, at the expense of efficiency). They implement a rectifier in front of the battery (double conversion online UPS) or even a transformer before the battery (delta conversion). All these designs are suitable for enterprise or industrial applications. If you are interested in more details on UPS implementations, I recommend reading Neil Rasmussen's document on the Different Types of UPS Systems.

Most UPS devices in the upper end of the entry level and in the mainstream are based on a line-interactive design. The battery is always connected to the power circuit through the AC/DV inverter.

Patrick Schmid
Editor-in-Chief (2005-2006)

Patrick Schmid was the editor-in-chief for Tom's Hardware from 2005 to 2006. He wrote numerous articles on a wide range of hardware topics, including storage, CPUs, and system builds.