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Optimization design of novel zero-crossing point detection method for boundary current mode PFC converter

This paper presents a novel boundary current mode boost-type PFC converter for driving the light emitting diode lightings. In the PFC converter, a novel method for zero-crossing point of inductor current detecting is proposed. In conventional boundary current mode PFC converter, the zero-crossing point is detected by observing the inductor voltage. The detection of zero-crossing point is delayed by the effect of the parasitic capacitance of main components in the PFC converter. The PFC converter operates under the discontinuous current mode when zero-crossing point detection is delayed. 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 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, differential amplifier circuit and the RS-FF. This paper shows the process of select the optimization parameters of the differentiation circuit and differential amplifier circuit. By optimizing the parameters of the differentiation circuit and the differential amplifier circuit, it is able to detect the zero-crossing point accurately and the converter can be expected to operate under the boundary current mode with high accurate. Simulation results show that near unity power factor and low input current THD can be achieved in the proposed PFC converter. The high-order harmonics can be reduced to meet the lighting system limitation (IEC 61000-3-2 Class C).