When voltage falls outside a specific range or fails entirely, a mechanical switch transfers the load to the internal battery and inverter.

Similar to Off-line, but includes an autotransformer (AVR - Automatic Voltage Regulation). This allows the UPS to boost or lower incoming voltage without switching to battery power.

Better protection against brownouts than Off-line models, with a reduced frequency of battery use, extending battery life. 3. On-line (Double Conversion) Scheme