The operating principle of the UPS is shown in Figure 6.
Operating principle diagram
The UPS is composed of mains input, TVSS and EMI/RFI filters, rectifier/PFC, inverter, battery
charger, DC-to-DC converter, battery, dynamic bypass and UPS output.
Transient Voltage Surge Suppression (TVSS) and EMI/RFI Filters
The Liebert GXT4 has surge protection and filters that protect the connected load from power surges
and sags, electromagnetic interference (EMI) and radio frequency interference (RFI). These features
can minimize any surges or interference present in the mains power. The filters also prevent surges
or interference generated by the UPS from adversely affecting other devices connected on the same
branch as the UPS.
Rectifier/Power Factor Correction (PFC) Circuit
In normal operation, the Liebert GXT4's rectifier/power factor correction (PFC) circuit converts mains
power to regulated DC power for use by the inverter while ensuring that the wave shape of the input
current used by the UPS is near ideal. Extracting this sine wave input current achieves two
• Efficient power use by the UPS
• Reduced reflected harmonics
This results in cleaner power being available to other devices in the building that are not protected by
In normal operation, the Liebert GXT4's inverter utilizes the DC output of the PFC circuit to produce
precise, regulated sine wave AC power. When mains power fails, the inverter receives DC power from
the battery through the DC-to DC converter. In either operation mode, the UPS inverter is online,
continuously generating clean, precise, regulated AC output power.
The battery charger utilizes energy from the mains power and precisely regulates it to continuously
float charge the batteries. The batteries are being charged whenever the Liebert GXT4 is plugged in,
even when the UPS is not turned On.
Outlet Group 1
Outlet Group 2
(3000 VA Only)