Due to the widely used brushless DC motors (BDCMs) in high-efficiency applications, many square-wave-current sensorless control methods based on voltage source inverters (VSI) had been developed in the literature. Recently, current source inverters (CSI) are receiving more and more attentions due to their inherent short-circuit protection characteristics. But no CSI-based sensorless control had been found in the literature. In this paper, the buck-type current source inverter fed BDCM is studied and the position senosorless control is proposed. The provided simulation and experimental results support the validity of the proposed CSI-based position sensorless control.