A life prediction scheme for electrolytic capacitors in power converters without current sensor

Predicting the expected life of switching power supply is essential since unexpected failure of the subsystem can produce enormous loss. Electrolytic capacitor is the weakest among various power components in a power converter. Monitoring the Equivalent Series Resistance (ESR) variation of the electrolytic capacitor, achieving by voltage and current ripple, can estimate the converter life. Currently, Hall Effect sensor or others are current sensing options but all of them add series impedance to the capacitor and deteriorate capacitor voltage waveform. A sensor-less current waveform prediction method is proposed. Popular current mode control with the switch current signal is used. Repetitive sampling on the switch current allows capacitors current waveforms prediction without any current sensor at capacitor nodes. Together with the voltage waveform acquired, the ESR value can be calculated.