Online & Offline UPS

On-line UPS

This system is basically a double conversion system. In this system, the Mains power is first converted to DC voltage of appropriate value and fed to the inverter that converts it back to AC power. Thus in this system, the load is always powered by the inverter. The battery is connected to the DC bus. Thus this is truly a No-Break system. The load being totally isolated from the Mains power, DMRR as well as CMRR noise is filtered out and the load gets clean power.

Off-Line UPS

This system is basically an OFF-LINE UPS system. In this system, the output waveform is synchronized with the Mains waveform. Thus the change over the inverter mode is faster (about 2ms)compared to the common OFF-LINE UPS. Compounded with automatic Voltage Regulator (AVR). This may be a cost-effective solution for a stand-alone computer where power conditions are less severe. For LAN application though, it is questions. Firstly, whenever mains power is available, it is directly given to the load though it is controlled to some extent by the built-in AVR. Thus the load is not completely isolated from the mains. The Differential mode noise (DMRR) can be greatly attenuated in this systems, however the Common Mode noise (CMRR) is still passed on to the computer. Moreover, if this is such a good system that it can replace an ON-LINE UPS system, one wonders why the same companies who manufacture LINE-INTERACTIVE system, also manufacture the ON-LINE systems.