Novel Power Feed-Forward Regulation for Dual Stage PFC+DCDC Converters

Inhalt:
Current power adaptor and charger trends include supporting USB-PD, extended power range (5 V to 48 V), and at the same time overall size reduction. For output power greater than 75 W active power factor correction is required. In that case, a dual stage converter consisting of a boost PFC followed by an isolated DC-DC converter is the most common used configuration. However, one of the biggest and most expensive components in the converter is the intermediate high voltage bulk capacitor between these two stages. This capacitor is used to hold the voltage (V(bus)) within certain range for proper operation of the following DC-DC stage. While power feed-forward is a known method to improve the Vbus control, the current methods come across with practical implementation issues. In this paper, an innovative and practical power feed-forward concept, from the DC-DC stage to the boost PFC stage to ensure the Vbus voltage stability during load transients, will be presented. It enables best-in-class regulated Vbus voltage even with very small bulk capacitor that ensures minimum adaptor size and lower cost. The concept has been implemented and tested in a 140 W prototype USB-PD EPR adaptor, the practical results will be presented and analyzed in this paper.