Fault diagnosis on switch-mode power supplies operating in discontinuous mode

This paper addresses the subject of fault diagnosis on switchmode power supplies operating in discontinuous mode, focusing particularly in the output filtering electrolytic capacitors. The failure of these capacitors leads to an increase of their equivalent series resistance (ESR), and consequently the efficiency decreases and the output voltage ripple increases. The method of diagnostics used is based on the relation between the values of the output voltage ripple and the capacitor current ripple. Several theoretical, simulated and experimental results are presented for a buck-type switch-mode power supply.