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

This paper presents a novel zero-crossing point detection method for boundary current mode PFC converter. In the conventional boundary current mode, the zero-crossing point is detected by observing the inductor voltage. When the digital controller is used in the conventional method, the detection of the zero-crossing point is delayed due to the delay time caused by the processing of DSP. And the detection of the zero-crossing point is also delayed by the effect of the parasitic capacitance of main components in the PFC converter. As a result, the boost converter operates under the discontinuous mode. The harmonic currents occur and the power factor becomes low when the boost converter operates under the discontinuous mode. In order to make the boost converter to operate under the boundary current mode, it is necessary to reduce the delay time caused by the DSP's processing and the parasitic capacitance. The proposed zero-crossing detection circuit is formed by the differentiation circuit and the differential amplifier circuit and the RS-FF. In the proposed method, the delay time of zero-crossing point detection can be reduced and the boost converter can operate under the boundary current mode with high accurate. Simulation results show that compared with the conventional method, the zero-crossing point detection delay time characteristics are improved in the proposed method.