Effects of Switching Frequency Modulation on the Power Converter´s Output Voltage

Frequency modulation of the switching signal controlling the electromagnetic interference (EMI) performance of a switching power converter (SPC) is a quite well-known theme that has been previously discussed. Generic spread spectrum clock generation methods have been theoretically analyzed and finally applied to an SPC´s emissions reduction (whereas the previous real applications were focused on digital signals operated by a clock line). From this point of view, a more general denomination of these methods is necessary and spread spectrum switching generation is here proposed. Effects on EMI emissions reduction are clearly worthy when selecting the modulation parameters in a convenient way. However, most references are focused on reducing the EMI emissions generated by the SPC without taking into account the influence of such frequency modulation methods on the output voltage of the power supply. This paper aims at this point because, in fact, this is the main purpose of a power converter: supplying energy at an ideally constant voltage. Continuous conduction mode of a buck converter is theoretically studied and compared to the practical results obtained from a real power supply. In a first approximation, open-loop configuration was selected as the operation mode before closing the loop, where influence of the modulation is also present but is much more complicated to analyze.