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.
For moderate-to-high power converters, electrolytic capacitor is an indispensable component. Life of electrolytic capacitor is critical compared with its semiconductor counterparts. This study proposes a new model to analyse the converter life and to design the circuit to lower the current ripple in the electrolytic capacitor in order to reach for longer converter life. Two-stage power converter (a power factor correction converter followed by a DC-DC converter) is the typical practice for AC-DC converter. Forward converter and Flyback converters are the common choices for the downstream converter for this power range. Comparison between two modes of operation, discontinuous conduction mode and continuous conduction mode (CCM), for the two converter topologies shows a typical CCM Forward converter to have almost 300 times longer life than a CCM Flyback converter. Another focus of the work is to analyse the effect of circuit parameters on the converter life. A critical inductance is established to guide the design for long life converters.
Engineers are always looking for more reliable or longer life power converters. Electrolytic capacitor is the critical component to be considered. Using the powerful calculation tools like Mathcad and Matlab and allowable life model, this paper aims at proposing a method to optimize the circuit design to lower the current ripple through the electrolytic capacitor in order to reach for longer capacitor life. Comparison between two modes of operation and the two converter topologies, Forward and Flyback, are made as well. This work provides a guideline to design power converters for long life application like LED driver. I.
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