UPS is the essential part of the PC for providing uninterrupted power to run the system and to protect data. In the event of a power failure or voltage drop, PC will draw power from the UPS and will run for a prescribed time depending on the capacity of the battery. The change over time from the mains to battery power is a fraction of a second, so that the computer will not shut down. This is essential to protect the data in the computer. Basically there are two types of UPS. These are Offline UPS and Online UPS. Off line UPS passes the input AC to the output sockets if the AC power is available. The advantage of the Online UPS is that, it clean up the AC waveform by converting it into DC then reconverting this DC to fresh AC.
Offline UPS always monitor the voltage level in the mains, and if there is a voltage drop or mains failure, it switches on the inverter to give AC power to the device until the mains supply returns to normal. The switch over time from AC to inverter AC is less than five milli seconds so that the functioning of the gadget is not affected.
Online UPS on the other hand uses an Inverter which always on to give sine wave AC in the output socket. The incoming AC is first converted into DC by a transformer to charge the battery as well as to give power to the inverter transformer. The inverter transformer converts the DC to AC continuously to power the load. If power fails, the battery backup circuit switches on and takes the load. Online UPS is more efficient than the Offline UPS and uses a “Constant duty Inverter”. It also has a “Static bypass” system that transfers the load to the AC power if the inverter system fails.