The preceding chapter introduced a fully integrated DC-DC converter featuring a 31–325 V DC input range. This chapter extends this DC-DC converter into a fully integrated AC-DC converter with a high power density. While the DC-DC converter covers a broad range of mains-rectified AC inputs, it cannot bridge the zero-crossing. Addressing this challenge mandates a sizeable buffer capacitor, imposing constraints on both integration and power density. Consequently, this chapter searches for topology techniques to minimize the size of the buffer capacitor. This chapter commences by discussing state-of-the-art AC-DC converters and their limitations. It subsequently delves into the challenges entailed in the complete integration of an AC-DC converter and proposes a topology to overcome these obstacles. Section 5.4 details the implementation of this topology, encompassing the control, buffer capacitor, and drivers. To conclude, this chapter demonstrates the measurement results obtained from a prototype and compares them with state-of-the-art approaches.