Owing to the widely used brushless DC motors (BDCMs) in high-efficiency applications, many position sensorless control methods based on voltage source inverters had been developed in the literature. Recently, current source inverters (CSIs) are receiving more and more attention because of their inherent short-circuit protection characteristics. But no position sensorless control for buck-type CSI with square-wave current had been found in the literature. In this study, the buck-type CSI-fed BDCM drive is designed and its application to the square-current position sensorless control is first proposed. The provided simulation and experimental results verify the effectiveness of the proposed CSI-based position sensorless control.