Topics in the analysis and design of multiple-output current-mode controlled DC-to-DC converters.

Abstract

This paper discusses several of the important issues related to the analysis and design of multiple-output current-mode controlled DC-to-DC converters. First, a technique is developed for predicting the regulation of these converters. The method allows regulation tradeoffs with respect to different components or feedback configurations to be made analytically rather than experimentally. The final model is completely normalized such that the results can be applied in general to any converter of a given topology regardless of the number of outputs or the specific values of those outputs. Plotting these general results offers the designer a simple tool to predict regulation. The results for an example topology are plotted and then applied to predict the regulation of a specific converter of the example topology. Experimental verification is then provided using a prototype of the example converter. In addition to this steady state analysis, the general small signal model for a multiple-output current-mode controlled converter is developed. Since a converter with multiple outputs can have a variety of feedback schemes, several small signal models are described. Once these models have been developed, the small signal characteristics of each converter configuration are derived. Because of the widespread use of coupled inductors in industry, their effect on these models is also investigated. As an example of how to use these models, the small signal model of a specific example converter is derived and used to characterize the small signal behavior of that converter. Finally, the small signal model of the example converter is extended to cover errors in the turns ratio of the coupled inductor as well as the effects of its parasitic resistance and leakage inductance. The theoretical results from this new model are then plotted and compared with the results from the prototype converter. Using these results, it is shown that a turns ratio mismatch introduces two new zeros into the frequency response of the control-to-output transfer function. Furthermore, by adjusting this turns ratio it is possible to steer the effects of this mismatch to any output of the converter.