Active Power Factor Correction Supplies for IT Equipment
During the past thirty years, people have become more aware of the amount of energy used by IT equipment and devices. For many years, desktop computers and workstations inefficiently consumed power, partly due to the design of the power supplies which transformed AC power (from the wall outlet) to DC power (used by computers). This voltage transformation was relatively inefficient as reflected in low power factor ratings.
In 1992, the U.S. Environmental Protection Agency (EPA), in collaboration with advocates in the IT industry, developed the ENERGY STAR® program to prompt the development of energy-efficient products. Today this program is recognized as an international standard.
To comply with ENERGY STAR standards, manufacturers of desktop and workstation computers incorporate Active Power Factor Correction (Active PFC) as part of the engineering designs, enabling energy efficiencies of 95% or higher. Computers with Active PFC power supplies require sine wave AC power, as supplied by utility companies, for trouble-free operation. For this reason, sine wave UPS systems have become the best choice for backup power.
Simulated or stepped sine wave power, provided by entry-level UPS systems, may be problematic or incompatible with Active PFC devices. Sine wave power varies continuously from positive to negative. Simulated sine wave power mimics a sine wave by using a squared-off approximation. Due to this approximation, simulated sine wave power momentarily creates a zero power gap. When power is interrupted, a computer with an Active PFC power supply may not recognize incoming simulated sine wave power due to the zero output present in the approximated wave. This could cause the system to unexpectedly shut down or sustain system component stress.