US Patent 7681090 Ripple correlation control based on limited sampling

A method for controlling a variable of a switching electrical circuit detects values for each of a first waveform and of a second waveform in the switching circuit at a beginning of and at a predetermined instant during a switching interval of a switching operation of the electrical circuit, both of the first and second waveforms are perturbed by the switching operation, and evaluates the variable based on the corresponding values of both the first waveform and the second waveform detected at the beginning and at the predetermined instant during the switching interval. The method further adjusts an operating point of the circuit based on a change in the variable between the two evaluations so as to maximize the variable.