This paper presents a low power DC-DC buck-boost topology functioning battery-less on the basis of a novel technique using a combination of both: singular optimal control plus an analog circuit control law. The very low power consumptions along with the optimal energy harvested, makes possible to perform FFT calculations on-line and on-chip for vibration analysis applied to wind-turbines maintenance operation using an ST microcontroller and transmitting up to 500 m. The complete functioning circuit is shown along with real measurements.