Design-oriented model and critical inductance method for long life isolated power converters

For moderate-to-high power converters, electrolytic capacitor is an indispensable component. Life of electrolytic capacitor is critical compared with its semi-conductor 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.