Online UPS, it is getting power AC is converting to DC, then
the DC source stored to Battery at power supply on mode when
power fail, the DC sorce is changed to AC by inverter so
output power is having without noise.
OFFline UPS is having automatic voltage regulator, it
getting power from supply, it is regulated by AVR, then
power stored to battery so the change over time approx 2ms
to 5ms so change over noise comes.
Online UPS is unterrupted power suppy to the load,
Offline UPS can't ensure uninterrupted power supply, it
depends on the tolerance of the load. For any sophisticated
equipment (medical equipment), Online UPS is recommended.
A standby UPS or "offline UPS" draws current from the AC
outlet and switches to battery within a few milliseconds
after detecting a power failure.
The line interactive UPS "interacts" with the AC power line
to smooth out the waveforms and correct the rise and fall of
The "Online UPS" is the most advanced and most costly UPS.
The inverter is continuously providing clean power from the
battery, and the computer equipment is never receiving power
directly from the AC outlet. However, online units contain
cooling fans, which do make noise and may require some
location planning for the home user or small office.