<p>This invention relates to switch mode power supply (SMPS) controllers employing primary side sensing. We describe an (SMPS) controller which uses an area correlator, comprising an integrator, to compare an area under a feedback signal waveform between a start point defined by said first timing signal and an end point defined by said second timing signal with a reference area. An output of the area correlator provides an error signal for regulating the SMPS output.</p>
