A Switched-Mode Time-Sharing Solution for Piezoelectric Energy Harvesting and Vibration Sensing

In piezoelectric energy harvesting (PEH), utilizing the synchronized switch interface circuits can significantly enhance the energy harvesting capability. Vibration sensing and synchronization are necessary functions for carrying out the synchronized switching actions. Those functions were usually implemented with an external displacement sensor in the early designs, which is not friendly for self-contained applications. This paper proposes a compact time-sharing solution for energy harvesting and vibration sensing by making full use of a modified buck-boost design. The circuit works in a strong discontinuous conduction mode (DCM). It is based on the principle that, under DCM operation, the voltage levels of the piezoelectric source side and the storage side are proportional to the actively switch- on and passively freewheeling intervals, respectively. Compared with the other self-powered synchronized switch PEH solutions, which rely on analog peak detectors, this self-sensing solution not only provides synchronized triggering signals for carrying out the switching actions but also tells more information about the driven vibration, such as its frequency and displacement magnitude. With the detailed vibration information, such a time-sharing solution offers more design convenience towards future multi-functional battery-free IoT applications.