Chaos-modulated ramp IC for EMI reduction in PWM buck converters design and analysis of critical issues

Abstract

Various non-conventional methods have been employed in the past, to reduce the cost and weight of traditional conducted EMI filters and radiation screens for EMI suppression in switching power electronic converters. This paper points out various shortcomings of these methods which are mainly frequency modulation based, and describes the design of a ramp-generator IC based on a modified modulation scheme. This IC can be used on any voltage mode controlled converter and has a feature that enables the user to tune the same converter to various EMC norms. Test results from a prototype showing significant reduction in harmonic power level have been presented. Moreover, this paper discusses a theoretical formulation for calculating the output capacitor size to maintain ripple specifications, when operating under chaotic modulation.