Modeling The Effects of Leakage Inductance On Flyback Converters (Part 3): The Small-Signal Model

by Christophe Basso, ON Semiconductor, Toulouse, France, How2Power Today, Jan 15 2016

Focus:
In the final part of this article series, the author studies the small-signal response of the CCM flyback converter operated in voltage mode as affected by the leakage inductance. The large-signal model of this converter, which was introduced in part 2, is transphormed or linearized in a step-by-step process into a simplified small-signal model. From this final circuit, the author extracts a control-to-output transfer function that shows how the leakage inductance affects the quality factor of the transfer function’s denominator. This new transfer function is compared against the one given in the literature for this type of flyback converter, and when leakage inductance is set to zero, both responses are shown to agree. Results are also verified with SPICE and SIMPLIS simulations. Then the new model is used to demonstrate the damping effects of leakage inductance on quality factor of the converter’s response. The lesser effects of leakage inductance under current-mode control are briefly discussed. The analysis performed in this series paves the way for a study of the more-complex active-clamp flyback converter.

What you’ll learn:

• How to derive a small-signal model of the voltage-mode-controlled CCM-operated flyback converter that accounts for effects of leakage inductor
• How to model the effects of leakage inductance on the voltage-mode-controlled CCM-operated flyback converter

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