A converter circuit to be connected to an electrical energy source capable of showing major fluctuations in delivered power includes a chopper circuit with a variable duty cycle and connectable to the electrical energy source, an output circuit adapted for connection to the chopper circuit, a control loop for tracking an MPP of the energy source connected to an output of the energy source, and a control unit configured to command, at predefined intervals, changes in the chopper circuit's duty cycle as a function of the control loop's set-value signal. The control loop includes means for analog storage of pieces of information corresponding to output voltages from the energy source for at least three successive duty cycles, and an analog comparison unit delivering an output, as a function of the stored pieces of information, and a set-value signal for increasing or reducing of the duty cycle by the control unit.