Input filter design for switching regulators

A small signal average model is derived to study analytically the complex interaction among input filter, output filter and control loop, which frequently causes degradation of switch regulator performance. Analytically based design guidelines are formulated, and key design parameters are identified. It is shown that minimization of the forward transfer characteristics and the output impedance of the input filter at filter resonance are key to designing an input filter for a switching regulator with given output filter parameters and specified line and load conditions.