we describe a switch mode power supply current regulation system comprising : a current sense signal input sensing a primary current of the smps ; a voltage sense input to receive a voltage sense signal from a primary or auxiliary winding ; a switch drive signal input to receive a drive signal ; a timing signal generator coupled to said voltage sense input and to said drive signal input to generate a timing signal t 0 indicating a duration of a period for which current is flowing through said primary winding and a timing signal t 1 indicating a duration of a period for which current is flowing through said secondary winding ; and a regulator to provide an output current regulation signal responsive to an average of the current sense signal multiplied by a ratio of t 1 to t 0 , and wherein t 0 and / or t 1 are generated responsive to the voltage or current sense signal .