A Quasi-Constant On-Time Control for SMPS with a Nonlinear Inductor Based on Power Switch Conduction Time Estimation

This article proposes a control method for switching-mode power supplies equipped with nonlinear inductors; the method is based on the estimation of the conduction time (Ton) of the power switch. The Ton value is tuned according to the inductor model to obtain quasi-constant on-time control. The method is devised for ferrite core power inductor, the nonlinearity is exploited up to saturation, condition where the differential inductance is reduced to half of its maximum value. This approach allows the calculation of the conduction time Ton such that the maximum current of the inductor always corresponds to the saturation value while also considering the inductor temperature. This method obtains the current peak versus Ton through a proper inductor model and a recursive algorithm for a given inductor temperature. The theoretical analysis was verified on a boost converter by comparing the simulations with experimental data with different loads, showing that the operating current can be increased by approximately 40% avoiding thermal runaway.