Switched mode power supply control system

A d.c switched mode power supply (SMPS) is controlled by an output voltage regulator that can operate in one of two modes; a static first mode where a feedback signal supply is derived in response to the supply output voltage and a dynamic second mode where the feedback signal is derived in response to the output of an auxiliary winding of a coupling transformer. The mode may be selected according to the level of the feedback signal(s) which may be assessed using comparators and thresholds values. The feedback signal may be digitised and may be sampled at a time dependant upon the operative mode, when the transformer input current is at a peak for the first mode and at a fixed backwards offset time from when the transformer out put current is zero in the second mode. When in the first mode regulation may also be in response to a current sense signal. The controlled supply may operate in either continuous conduction mode or discontinuous conduction mode and the regulator may be implemented in a digital processor.