Zero-crossing point detection using differentiation circuit for boundary current mode PFC converter

This paper presents a novel zero-crossing point detection method for boundary current mode boost-type PFC converter. In the conventional boundary current mode PFC converter, the zero-crossing point of inductor current is detected by observing the inductor voltage. The detection of the zero-crossing point is delayed due to the effect of the parasitic capacitance of main components in the PFC converter. As the digital controller is used in the conventional method, the detection of the zero-crossing point also delays due to the DSP´s processing. Since the two major reasons, PFC converter operates under the discontinuous current mode. The power factor becomes low and the harmonic currents occur when the PFC converter operates under the discontinuous current mode. Therefore, it is required to reduce the delay time caused by the parasitic capacitance and the DSP´s processing in order to make the PFC converter to operate under the boundary current mode. The proposed zero-crossing point detector is very suitable for the purpose. It is formed by the differentiation circuit, the differential amplifier circuit and RS-FF. Simulation results show that in the proposed method, the detection delay time characteristics are much improved compared with the conventional method. The PFC converter can operate under the boundary current mode with high accurate. Near unity power factor and lower input current THD are achieved in the proposed method.