Simple Analog-Based Accurate Variable On-Time Control for Critical Conduction Mode Boost Power Factor Correction Converters

In order to suppress the input current distortion of critical conduction mode (CRM) boost power factor correction (PFC) converters, variable on-time (VOT) control has been adopted in many analog commercial integrated chips (ICs). However, the quantitative VOT expression applicable to analog control has not been studied until now. According to the fitting functional form of VOT, this paper proposes a uniform and simple VOT expression, which can be directly implemented by analog circuits and provide accurate VOT control just as digital control. Only an inverse signal of the rectified input voltage is additionally introduced to achieve accurate VOT control, and the inherent voltage feedback loop of PFC is utilized to eliminate the effect of the input rms voltage and output power. With the proposed quantitative design consideration, the optimum input current total harmonics distortion (THD) is naturally obtained without trial-and-error design. The experimental results of a 160-W prototype are built to verify the effectiveness and advantages of the proposed VOT control.