a method of controlling an oxygen generation device of the kind including a ceramic membrane through which an electrical current is passed whilst ambient air is supplied to one side of the membrane , the membrane allowing oxygen in the supplied air to diffuse therethrough by ionic transport when the membrane is at or above an operating temperature , at a rate dependant upon the electrical current , there being a plenum or the like to recover the oxygen at a second side of the membrane , the method comprising regulating the electrical current passing through the membrane by switching the electrical current on and off and varying the proportion of current - on time in a given time interval in dependence upon a feedback signal .