Subharmonic Behavior In Current Mode Control (Part 2): The Causes And Cures At Low Duty Cycles
by Ernie Wittenbreder, Technical Witts, Flagstaff, Ariz., How2Power Today, Jul 15 2016
Focus:
Part 1 discussed the subharmonic behavior that occurs in power converters operating under
current-mode control at high duty cycles and how this problem can be remedied with slope
compensation. At low duty cycles we often do not expect to see subharmonic behavior. So when it
arises we may take the step of designing in slope compensation after the fact, which often
resolves the problem, but not always. So now what do we do? This second and final part of the
article answers that question. The causes of subharmonic behavior at low duty cycles are
explained along with techniques to counteract them. This discussion culminates in the
description of circuits that generate a precise analog of the inductor current, which is then
combined with slope compensation to eliminate the subharmonic behavior.
What you’ll learn:
- How to understand the causes of subharmonic behavior at sub 50% duty cycles in current-mode controlled power converters
- How to understand the causes of subharmonic behavior at sub 50% duty cycles in current-mode controlled power converters
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