A boost converter is commonly used for power factor correction (PFC) in a two-stage off-line power converter. Traditionally, power factor correction blocks using a boost converter are designed to have a fixed output voltage greater than the maximum peak line voltage. Interestingly enough, higher power conversion efficiency of the power factor correction stage can be obtained by reducing the output voltage according to line voltage and load condition.

Altering the output voltage, however, results in a wider input voltage range for the second stage DC-DC converter. This design note explains how the greatest AC to DC power conversion efficiency can be achieved by selecting an optimized output voltage level for a power factor correction block.