SWITCH MODE POWER SUPPLY SYSTEMS

摘要

This invention generally relates to methods and apparatus for sensing the output current in a switch mode power supply (SMPS), in particular using primary side sensing. A module for estimating the output current of a switch mode power supply (SMPS), said SMPS including a transformer (21) with at least a primary winding coupled to an input of the SMPS and a secondary winding coupled to an output of the SMPS and having a power switching device (31) to switch power to said primary winding of said transformer responsive to a drive signal (DRIVE), the module comprising: a current sense input to receive a current sense signal (CS) sensing a current (IP) in said primary winding of said transformer; a voltage sense input to receive a voltage sense signal (VS) from said primary or an auxiliary winding of said transformer; a drive signal input to receive said drive signal; a signal averager coupled to said drive signal input and to said current sense input to average said current sense signal over a period when said drive signal is controlling said power switching device to apply power to said primary winding and to provide an averaged current sense signal; a timing signal generator (27) coupled to said voltage sense input to generate a timing signal (To) indicating a duration of a period during which said secondary winding is providing power to said SMPS output; a multiplier coupled to an output of said signal averager and to an output of said timing signal generator to multiply said averaged current sense signal by a fraction (Tl) of a total cycle period of said SMPS during which said secondary winding is providing power to said SMPS output, indicated by said timing signal; and an output coupled to an output of said multiplier to provide a signal estimat ing said output current of said SMPS.