Adaptive Capacitor Charging Circuit With Simplified Configuration for Efficient Piezoelectric Energy Harvesting

In this study, we present an adaptive capacitor charging circuit for efficient piezoelectric (PE) energy harvesting (EH), which simplifies the configuration for powering wireless sensor network (WSN) nodes. In the circuit, the PE harvester directly charges the storage capacitor through the rectifier, eliminating the energy loss in the dc–dc converter of conventional EH circuits. An adaptive control circuit is designed to optimize the average charging power. Theoretical analysis shows that the optimal average power of the novel circuit varies from 81.4% to 86.5% of the maximum power of the conventional EH circuit, without considering the power dissipation in the dc–dc converter. Moreover, the power losses of both the proposed and conventional circuits are estimated. When the excitation level is low, the net harvested power of the proposed circuit can be enhanced to as high as 180% of that of the conventional circuit. The experimental results validate that the power transferred to the load is increased by adopting the proposed interface. It is also proved that the circuit is adaptive to different harvesters and excitation conditions. In addition, the area of the proposed circuit is reduced, allowing it to be easily integrated into the WSN nodes.