High efficiency and total harmonic distortion improvement by zero current prediction technique for transformer-free buck power factor corrector

Power factor correction (PFC) can shape the input current of off-line power supplies to be in-phase with the input AC voltage to maximize the available real power from the AC source for high power factor (PF). Boundary current mode (BCM) operation is the easiest way to get good power factor performance. However, the zero current detection in conventional PFC based on the voltage across the auxiliary winding which is suffer from the delay of zero current detection timing. Therefore, this paper proposed a high efficiency and total harmonic distortion (THD) improvement for transformer-free buck power factor corrector with zero current prediction mechanism. The chip fabricated in 0.5μm 800V ultra-high voltage (UHV) process can be powered on directly by the AC source owing to the 800V ultra-high voltage device. The output voltage of buck PFC is set at 80V and the PF is high to 0.98 without additional component compared with traditional buck PFC. The maximum efficiency of proposed buck PFC converter is 98.4% when input voltage is 110V AC.