Analysis and design of an asynchronous pulse‐width modulation technique for switch mode power supply

Abstract

This paper presents a new mathematical approach to design an asynchronous pulse width modulation (APWM) for the switched mode power supply (SMPS). Unlike the conventional APWM that utilises a Hysteretic comparator based Asynchronous Pulse Width Modulation (HAPWM) to provide the self-oscillating property, the proposed APWM is based on a Binary comparator based Asynchronous Pulse Width Modulation (BAPWM) and a delay cell. This way, compared to the HAPWM, the mathematical analysis of the modulator is significantly simplified. This was achieved by replacing the describing function (DF) -based graphical method with a ?linearised mathematical model. The introduced mathematical approach is extended to study the behaviour of the higher order self-oscillating modulators in terms of the harmonic distortion. To confirm the effectiveness of the analytical derivations, the BAPWMs are employed in a classic DC-DC buck converter and the system-level simulation results are provided. It is concluded that there is an acceptable degree of similarity between the simulation results and the deployed analytical calculations for different orders of the modulators. Finally, to validate these analytical and simulation results and also to compare the BAPWM performance with its HAPWM counterpart, both modulators are implemented using off-the-shelf components and their measurement results are presented.