NCP1631PFCGEVB(#2): 390V @ 300W, 95 ~ 265VAC in

Interleaved PFC is an emerging solution that becomes particularly popular in applications where a strict form factor has to be met like for instance, in slim notebook adapters or in LCD TVs. Interleaving consists in paralleling two “small” stages in lieu of a bigger one, which may be more difficult to design.

Practically, two 150−W PFC stages are combined to form our 300−W PFC pre−regulator. This approach has several merits like the ease of implementation, the use of more but smaller components or a better heat distribution.

Also, Interleaving extends the power range of Critical Conduction Mode (CrM) that is an efficient and cost−effective technique (no need for low trr diodes). Even, as reported by NCP1631EVB/D [3], when associated to the Frequency Clamped Critical conduction Mode (FCCrM), this technique yields particularly high efficiency levels (about 95% over a large load range at 90 Vrms in a 300−W application).

Furthermore, if the two stages are operated out−of−phase, the current ripple is significantly reduced. In particular, the input current looks like that of a Continuous Conduction Mode (CCM) one and the rms current within the bulk capacitor is dramatically reduced. These characteristics are detailed in application note AND8355 [1].

This paper gives the main equations that are useful to design an interleaved PFC stage driven by the NCP1631.