Active PFC has become quite common in AC/DC switch mode power supplies. For power supplies with output power ratings higher than 300 W, the harmonics, and consequently reactive power, loaded from the grid should be lower than the value specified in IEC61000-4-3. To meet this requirement, the input stage cannot be a simple rectifier bridge with a capacitor, but requires active PFC. A typical active PFC circuit is made with a boost converter as shown here.