An Accurate and Practical Small-Signal Model for Current-Mode Control

Past models of current-mode control have sufferered from either insufficient accuracy to properly predict the effects of current-mode control, or from analytical complexity that renders them inaccessible to the power supply designer. This paper combines the accuracy of sampled-data modeling with the simplicity of conventional pole-zero representation. As a result, it offers a current-mode control model which is accurate to half the switching frequency, and practical for everyday use. All of the small-signal characteristics of current-mode control are predicted, including low-frequency effects, and high-frequency subharmonic oscillation which can occur even at duty cycles of less than 0.5. In addition to the conventional dominant pole response of other current-mode models, a pair of poles is produced at half the switching frequency, the Q of which determines the amount of subharmonic oscillation.