The importance of parasitic resistances as stabilizing agents for current-programmed converters

It is shown that parasitic resistances have a dramatic stabilizing effect on the inner, or current-programming, loop of certain current-mode controlled DC/DC power converters. In some regimes, typical values of parasitic resistance can extend the input voltage range for stable operation by as much as 80 V beyond that to which a lossless converter would be limited. Any calculation to predict stability must therefore include some model of the parasitic resistances. By consideration of the physical means of dissipation, it is demonstrated that the correct parasitic for use in predicting the stable operating range is series resistance at the natural frequency (that is, the frequency associated with the positive eigenvalue of the state-space averaged time-evolution operator). Calculations are shown to agree best with experiment when this value of parasitic resistance is used