A High Precision CV Control Scheme for Low Power AC-DC BUCK Converter Controller

This article presents a constant voltage control scheme to improve the transfer efficiency and output voltage accuracy for single-stage AC-DC converters. The proposed scheme also has the advantage of low cost because of the simple application and few peripheral devices. To realize above features, the peak current and frequency curves with high efficiency are selected by analyzing the power losses of the applied topology. A voltage self-compensation circuit is designed to improve the output accuracy, especially the output voltage below 5V. Furthermore, a multi-stage startup circuit is also proposed to reduce the output voltage overshoot. To verify the feasibility of the proposed constant voltage control scheme, a BUCK controller adopting the proposed control scheme has been designed and fabricated with 0.18 mu m BCD process. Using the proposed controller, the peak efficiency of the prototype can reach as high as 66.9%, 78.9% and 82.8% under 115Vac input and 3.3V@300mA, 5V@300mA and 12V@300mA respectively. The load regulation is counted to be within +/- 1%.