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Critical conduction mode boost power factor (PF) correction converter is widely used in low-to-medium power applications for its advantages of high PF, zero-current turn- on of the switch, and no reverse recovery in diode. Nevertheless, the switching frequency varies continually with the input voltage phase angle with traditional constant on -time control. This makes the electromagnetic interference (EMI) spectra display great differences and complicates the design of EMI filter. An optimal switching frequency variation range control strategy is proposed in this article. The optimal harmonics amounts for the lowest switching frequency variation range without and with a limited PF are both figured out. In addition, a lower output voltage ripple is obtained. A prototype has been built and tested in the lab to demonstrate the validity of the theoretical analysis.

Critical conduction mode (CRM) buck power factor correction (PFC) is widely used in low-power applications because of its several advantages. However, the switching frequency is dependent on the electrical angle of the input voltage, and the variation range of the switching frequency is large, especially at high input voltages. This makes the conducted electromagnetic interference (EMI) spectra appearing great differences and complicates the design of the EMI filter. For this issue, a novel constant frequency control scheme is proposed by varying the on-time of the switch. Compared with the original control, the proposed method realizes a constant switching frequency operation in a line cycle. Consequently, the design of the power devices especially the magnetic components can be simplified. Meanwhile, a higher efficiency and a lower output voltage ripple are achieved. The proposed strategy also yields a higher PF at low input voltages and a lower PF at high input voltages. A 120-W prototype with 90–264-VAC input and 90-V output is built in the lab. The experimental waveforms of input voltage, input current, inductor current, and output voltage ripple, the measured input current harmonic contents, the PF and efficiency curves regarding the input voltage, and the common-mode (CM) and differential-mode (DM) noises’ spectra of the converter are presented to show the validity of the proposed scheme.

Buck power factor correction converter is widely used in low-power applications due to its specific advantages. In discontinuous conduction mode operation, the inductor current is zero during part of the switching cycle, leading to a useless period in the whole switching cycle of the power transmission. As a result, the peak value and the root-mean-square (RMS) value of the inductor current as well as the switch current are large. In addition, the current stress of the power devices is high, and so does the switching loss. A new method called adequate usage rate control of switching cycles to improve the effect of the energy transfer is proposed. Compared with the fixed duty ratio control, the critical inductance is increased, and the peak and rms current values of the main power components are reduced. Therefore, the efficiency of the converter is increased. The method brings about higher PF at low input voltages and lower PF at high input voltages. Meanwhile, a reduction of the output ripple voltage is achieved. A prototype is fabricated in the laboratory, and the experimental results are presented to verify the effectiveness of the proposed method.

The discontinuous conduction mode boost power factor correction converter features zero-current turn- on for the switch, no reverse recovery in diode, and constant frequency operation. With traditional constant duty ratio control, the power transfer in each switching cycle exhibits great difference during a half-line cycle. Consequently, the peak and root mean square values of the inductor current are large, the same goes for the switch and diode. This increases not only the current stress of the power components but also the conduction and switching turn- off loss, and lowers the efficiency of the converter. Introducing third and fifth harmonics into the input current and varying the duty cycle correspondingly can reduce the aforementioned power transfer difference, and provide huge space for the increment of boundary inductance as well. An optimum boundary inductance control concerning limited power factor (PF) is proposed in this paper. For the maximum boundary inductance of the converter within wide input voltage range, the optimum harmonics amounts are analyzed and figured out. The proposed method brings about efficiency improvement, output voltage ripple reduction, and PF increase as well, especially at high input voltages. A prototype has been built and the experimental results are presented to show the validity of the scheme.