Current controlled buck converter system analysis, the external ramp causes sub-harmonic oscillations

This paper presents a system analysis of the standard current mode buck converter and underlines an unwanted missing pulse behavior, caused by the external ramp itself, that will always appear at some output load current, depending on inductor and capacitor values. The missing pulse will force the converter to work at a sub-harmonic switching frequency in place of the designed one. This effect nullifies all efforts to keep under control the electromagnetic emissions of the circuit, that, otherwise, could be reduced by insertion of a tuned filter. In this paper some different solutions to this problem are analyzed and compared, paying attention to the possible undesired effects that they might cause to the system. Eventually the paper introduces a method to solve definitively the missing pulse oscillations also for high switching frequency working systems.