Battery-free power management circuit for impact-type micro wind piezoelectric energy harvester

A battery-free power management circuit (PMC) for an impact-type piezoelectric energy harvester for micro wind is presented in this paper. As the energy generated by micro wind is intermittent, sleep mode is adopted for the PMC to save power. A new energy sensing circuit is designed to detect the energy level generated by the piezoelectric cantilever and then to control the operation modes, sleep or active mode, of the PMC accordingly. The energy sensing circuit also provides the power supply for the PMC so as to realize the battery-free PMC. Besides, based on the analysis of the output capacitor of full bridge rectifier, the output capacitor is removed to obtain maximum power from piezoelectric material. The PMC is prototyped with discrete components, and it dissipates the power of 1.8 mW in active mode and only 40 μW in sleep mode. The efficiency of the proposed PMC is about 76% for the wind speed of 3.5 m/s.