Subharmonic Behavior In Current-Mode Control (Part 1): The Causes And Cure At High Duty Cycles

by Ernie Wittenbreder, Technical Witts, Flagstaff, Ariz, How2Power Today, May 16 2016

Focus:
In peak and average current-mode control there are well known problems that can cause subharmonic behavior associated with operation above 50% duty cycle. Less well known and less reported are the subharmonic operating states associated with low duty cycle operation. This article series will address the subharmonic issues of peak current-mode control at both high and low duty cycles. The issues described here for peak current-mode control apply as well to average current-mode control. In this first part of the article series, the causes and mechanisms of subharmonic behavior at high duty cycles are explained using the familiar buck converter. Then the use of slope compensation to correct this problem is explained. This discussion may be helpful for new power designers and a welcome refresher for more-experienced power designers.

What you’ll learn:

• How to understand the causes of subharmonic behavior in current-mode controlled power converters operating at high duty cycles

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