Using input current and output voltage ripple to estimate the output filter condition of switch mode DC/DC converters

This paper presents a fault diagnostic technique that is able to estimate the output filter condition of DC/DC boost and buck-boost converters. More than half of the breakdowns in these equipments are mainly due to the output filter capacitor. So, the development of fault diagnostic techniques that can avoid unexpected breakdowns is of paramount importance. The aging of the output filter capacitors is expressed by the increase of their internal resistance, that changes considerable with temperature. The proposed technique uses both input current and output voltage ripple to estimate capacitors internal resistance; for that, a very simple analytical relationship between both waveforms is used. The temperature effect is also considered for evaluating the capacitors condition.