Power management for sub-mW energy harvester with adaptive hybrid energy storage

Energy harvesting with its ubiquitous availability is intensively investigated to extend the wireless sensor nodes lifetime. While the harvested power is often less than 1 mW, the commercial-off-the-shelf power management circuits designed for conventional battery applications operate in much higher power. A designated power management module for sub-mW energy harvester is proposed in this article to increase the energy conversion efficiency and extend the energy storage lifetime for small input power. The proposed module consists of discrete component-based pulse-width modulation (PWM) controlled synchronous boost converter structured impedance matching circuit and supercapacitor/micro- battery hybrid energy storage. The synchronous boost converter-based power management circuit achieves 79% conversion efficiency at the input power of 0.5 mW. The power loss during the energy conversion is significantly reduced and thus allows wireless sensor nodes to be powered from a minimum of 120 Lux fluorescent light with a photovoltaic cell smaller than a credit card. The supercapacitor/micro-battery energy storage provides lifetime of more than 73 h when no external energy is available. The experimental results with 25 energy harvester-powered wireless sensor nodes demonstrate that the practical ultra-low-power design makes sub-1-mW energy harvester power management applicable.