In this paper, an improved one-cycle control is proposed for an AC/DC boost converter with power factor correction (PFC) using logic and analogy circuits. The proposed improved one-cycle control method realizes features that are similar to those of the conventional one-cycle method without using a sense input voltage and a multiplier. It can also promote the stability of the converter. The adjustable maximum duty cycle limit of the converter is designed to limit the maximum duty cycle by adopting the logic and analogy circuits. According to the analysis of the modified one-cycle control method, the suitable circuit component parameters of the converter can be designed for the one-cycle control AC/DC PFC boost converter. Finally, a modified one-cycle control AC/DC PFC boost converter with input ACs of 90, 110, 220, and 260 V, an output DC of 400 V, and an output power of 500 W was built to verify the accuracy and feasibility of its performance.