Uninterruptible Power Supply (UPS) is a secondary power source. 

Uninterruptible power supplies have been recently seen in homes, offices, industrial enterprises. They are widely used to protect various devices. The main purpose of the UPS is to ensure correct operation of the load in case of sudden voltage fluctuations, as well as providing short-term autonomous operation of the connected equipment with a complete power outage.

Modern UPS are divided into three types:

- Backup (offline);

- Line-interactive;

- With double energy conversion (online).

The main task of the UPS is to provide power to consumers when the external power is cut off. This is possible by automatically switching to the battery and converting the energy accumulated in the batteries (DC - direct current) into a sinusoidal voltage (AC - alternating current) of the desired value in the required range. And at restoration of an input voltage there is an automatic switching of a mode of work from AKB on an electric system.

          Normal mode (Network)                         Emergency mode (Battery)

In addition, some UPS technologies perform correction or conversion of incoming voltage during operation from the network, while ensuring reliable protection of sensitive electrical equipment from external interference, distortion, bursts, voltage drops and frequency oscillations, feeding a clean filtered signal to the load.