Regulating the output of a switch mode power supply

摘要

A switch mode power supply (SMPS) output voltage is regulated using primary side sensing of a magnetic energy storage device such as transformer 1. An integrator 6 integrates the difference between a feedback signal from a winding 4 and first reference Vref1 and the result is compared with second reference Vref2 in a comparator 7 whose output is then used to regulate the output. The reference levels may be set so that the output of comparator 7 may control sample-hold circuit 12,13 to sample the feedback signal at a time when the flux in the storage device is zero and may also control a second integrator (fig 4) that integrates the feedback signal when the flux is zero. Integrator 6 may begin integrating and be reset in response to a switch 5 control signal. The circuit provides an area correlator that compares an area under a feedback signal between timing signals with a reference area to generate feedback information and is particularly used in a discontinuous conduction mode (DCM) SMPS.