Simulation Demonstrates Impact Of Current-Loop Crossover Frequency On Stability

Focus:

For switching converters operating in current-mode control, many engineers mistakenly believe that the subharmonic oscillations that occur at half the switching frequency in the voltage loop are caused by a peak in the current loop response at this frequency. In reality, the instability observed as a peak in the voltage loop at Fsw/2 is simply due to a poor phase margin in the current loop (caused by a pair of right-half plain zeros) not because of a peak there. While this phenomenon was analyzed and explained many years ago through modeling of current-mode control, it can be difficult to find experimental results that demonstrate the underlying relationships between power supply crossover frequency, phase margin and the resulting instability. This 24-page article presents circuit models in SPICE and SIMPLIS that engineers can use to simulate these effects.

What you’ll learn:

• How to simulate the relationships between crossover frequency, phase margin and stability in current-mode controlled power converters
• How to predict subharmonic oscillations in a current-mode controlled converter using SPICE and SIMPLIS simulations

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Author & Publication:

Christophe Basso, ON Semiconductor, Toulouse, France, How2Power Today, Jan 15 2021

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