The issue of variable-step size maximum power point tracking algorithms has been addressed in literature. However, most of the addressed algorithms actually tune the variable-step size according to two variables: the photovoltaic (PV) array voltage (VPV) and the PV array current (IPV). Therefore both PV array current and voltage have to be measured. Recently, maximum power point trackers that based on single variable (IPV or VPV) have a great attention due to their simplicity and ease in implementation, when compared to the other tracking techniques. In this paper, a single current sensor based variable step size maximum power point tracker has been proposed. This method uses only the relationship between the PV array measured current and the converter duty cycle (D) to automatically adapt the step change in the duty cycle to reach the maximum power point of the PV array. Detailed analysis and flowchart of the proposed algorithm are included. Moreover, PSIM simulation and experimental results are presented to verify the performance of the suggested algorithm.