Power electronic converters used in motor drives exhibit non-linear behaviour due to dead time and other circuit imperfections. Motors and their mechanical loads are often characterized by significant non-linearities as well. Since the parameters describing the system are not always accurately known, improved motion control performance may be attempted by using non-linear adaptive control methods. In this paper, the focus is on a de motor fed by a full-bridge dc-dc converter. A linearizing adaptive motion controller is derived for the overall system, under the assumption that the parameters describing the converter, the motor and its load are all unknown. The controller guarantees global stability and asymptotic tracking.