There is an additional feature on some online UPS's where there is buck/boost circuitry. If there is a brown out, and it is just above the cutoff voltage, the equipment will keep running on the low voltage on a normal UPS. With the buck/boost feature, the voltage will be brought up or down to a normal level as required.
Gregg > Big part of the problem though relies on the inverter switching at the > moment of power failure, so the most expensive UPS's run on battery > all the time and the charging circuit is always on. These are the > online UPS's.
