A control system provides a control signal to a nonlinear plant that generates a response signal responsive to the control signal. The control system includes a detector that detects a predetermined value of a plant quantity, valley switching logic, coupled to the detector, to change a state of a plant switch when the plant quantity is minimized, and a pulse-width modulator, coupled to the valley switching logic, to generate a control signal that controls the plant switch. The valley switching logic includes a nonlinear delta-sigma modulator that compensates for an error in a plant response signal by adjusting the duration of an on-time of a plant switch to cause an average value of the plant response signal to converge toward a target signal value.