This document summarizes research on modifying the design of a magnetic core type E used in a Cuk converter to increase efficiency. Three models of the magnetic core were tested by varying the placement of air gaps. Model 1 had air gaps on all feet, Model 2 on the left and right feet, and Model 3 on the middle and right feet. Model 3 performed best, achieving 94% efficiency with a 0.19mm gap on the middle foot and 0.254mm gap on the right foot. The document analyzes the equivalent circuits and magnetic properties of each core design to determine the optimal air gap configuration and maximize load current.