Abstract: A control circuit for controlling a UV light source configured to emit UV light into a purifying chamber of a device for purifying a fluid, the control circuit comprising a driver configured to provide the UV light source with a drive current; a fluid flow sensor configured to determine whether a flow of a fluid through the purifying chamber is present and generate a flow signal indicative thereof; a light sensor configured to measure radiant flux of light emitted from the UV light source and to generate a radiant flux signal comprising data pertaining to the measured radiant flux; a memory comprising a reference radiant flux; and a processor configured to: activate the UV light source upon the flow signal being indicative of presence of flow of fluid through the purifying chamber, during the UV light source being active: determine the drive current for the driver based on the measured radiant flux comprised in the radiant flux signal and the reference radiant flux.