A Low-Power Piezoelectric Energy Harvesting Circuit for Wearable Battery-Free Power Supply

This paper presents the structure and principle of operation of a prototype low-power energy-harvesting circuit (with efficiency higher than 50 %) intended for AC-to-DC conversion, where the input signal is obtained from micro-power piezoelectric elements. The proposed electronic circuit prototype is intended to work as a wearable autonomous system that provides electrical energy obtained through mechanical vibrations in piezoelectric ceramic disks. The obtained electrical energy through a switching circuit is used to charge low-power supercapacitors. The electronic circuit consists of a bridge rectifier, a low-pass filter, a step-down (buck) synchronous converter, a power-controlling system, and a window detector to produce a power-good signal. The designed electronic circuit of the control system allows for tuning the level of the output voltage to around 1.8 V, and the output discharge current reaches values higher than 0.5 mA. To verify the effectiveness of the proposed scheme, simulation, and experimental testing of the proposed prototype was carried out, as the obtained results confirmed the preliminary theoretical analyses and the derived analytical expressions for the basic electrical parameters.