Coupled inductor filter and what is good for

The video titled “The Coupled Inductors (Ripple Steering) Filter” by Sam Ben-Yaakov explores the concept, history, and application of coupled inductors in power supply filters. The presentation begins by introducing the basic concept of a coupled inductor filter, or ripple steering filter, which was first patented in 1933. This filter uses two inductors magnetically coupled to steer and attenuate ripple. The video highlights its evolution, from initial theoretical studies to practical analysis in a 1999 academic paper by Hamill and Crane. Through simulations, the presenter demonstrates the filter’s behavior, including the creation of a “notch” or resonant point that effectively blocks ripple frequencies. Comparisons between a simple LC filter and the coupled inductor filter show that the latter provides greater ripple attenuation, particularly when tuned to a specific resonant frequency.

The video emphasizes the sensitivity of the coupled inductor filter to its coupling coefficient, showing through simulations that even slight changes in the coefficient can significantly affect performance. The coupling coefficient is identified as the most critical parameter, more so than the resonant capacitor value, which exhibits lower sensitivity to changes. Practical applications, such as integrating the coupled inductor filter into a buck converter to reduce ripple, are demonstrated. While the filter achieves notable attenuation at the resonant frequency, it is highly sensitive to variations in operating conditions, such as changes in the coupling coefficient. The presentation concludes by acknowledging the filter’s effectiveness but warns about its sensitivity and complexity, suggesting it may not always be practical for all applications.

Resource: EPCI Blog