A buck-type power-factor-correction circuit

A buck-type power-factor-correction (PFC) circuit is proposed for low dc voltage applications. To achieve a high power factor, a conventional buck converter is cascaded by an auxiliary flyback conversion circuit to continue drawing current from the ac line source at the vicinity of zero crossing. The PFC circuit consists of only an active power switch, and thus has a high efficiency and can easily be accomplished by a simple control circuit with pulse width modulation. A laboratory circuit designed for a 48 V, 30 W dc load is built and tested to verify the theoretical analyses. Experimental results demonstrate that a power factor of 0.99 and a circuit efficiency of 92.5% can be achieved.