Input Filter Damping Design for Control Loop Stability of DC-DC Converters

An input filter is often employed for EMI noise reduction between a dc-dc converter and its power source. However, its presence, in turn, often results in degradation of dynamic performance and instability of the system even if the filter attenuation is brilliantly designed. The detrimental interaction between an input filter and a switched mode converter is a function of the input filter parameters as well as the supply voltage. This paper addresses the instability problem in dc-dc converters under strong influence of input filter interaction and suggests a systematic design procedure to damp the input filter using R-C parallel damping in order to stabilize the whole filter- converter system without over sizing or under sizing. It is then possible to define a dc-dc converter´s stable operating region based on the input filter´s damping circuit parameters. A buck converter under voltage-mode control is used as an illustrative example. Computer simulations and experimental results validate theoretical results of this paper.