A Prognostic Sensor for Voltage Regulated Switch-Mode Power Supplies

This paper outlines a non-invasive method for the detection of failure precursors for optical isolators used in switch-mode power supplies (SMPS). The method relies on the transfer characteristics of the closed loop operation of the power supply circuit to evaluate gain, rather than direct measurement of current at the isolator terminals. With voltage regulation, a power supply will continue to operate within specifications well beyond the onset of opto-isolator wear, but then fail suddenly when the damage accumulation reaches a threshold. We show that it is possible to detect the onset of degradation of the isolator before performance is adversely affected, and track the progression of a fault to provide greater lead time for field replacement. The method presented is simple to implement on many commercial off-the-shelf (COTS) supplies, and offers the advantage of longer maintenance cycles at lower cost. We show how this method can improve the accuracy of remaining useful life (RUL) prediction, reduce the occurrence of No Trouble Found (NTF), and improve manufacturing of highly reliable SMPS.