A 115× Conversion-Ratio Thermoelectric Energy-Harvesting Battery Charger for the Internet of Things
Ming-Jie Chung, Tetsuya Hirose, Takahito Ono, Po-Hung Chen
Abstract
This article presents a high-conversion-ratio (HCR), high-voltage-tolerant (HVT) energy-harvesting battery charger using 0.18-μm standard CMOS for Internet of Things (IoT). To reduce conversion ratio (CR) of inductive power converter and optimize overall power efficiency, the proposed charger cascades a boost converter and reconfigurable charge pump. Different from the high-voltage device, the standard CMOS process has lower parasitic capacitance and on-resistance; therefore, it can reduce switching and conduction loss. The reconfigurable charge pump dynamically changes the number of pumping stages according to the output voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> ) by automatic configuration selector (ACS). To manage the limited power from a thermoelectric generator (TEG), the converter works under the discontinuous conduction mode (DCM). The zero-current detector (ZCD) employs an analog comparator with digital offset compensator and digital comparator to control off-time (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ) quickly and accurately. The self-idle constant on-time (SI-COT) and idle mode both control the mechanism, helping to further reduce static power dissipation. As a result, the proposed converter can achieve peak efficiency of up to 76% at a 92× conversion ratio with output power ranging from 10 μW to 1.9 mW. The available input voltage ranges are 40 to 400 mV, and the dual output voltage ranges are 1 to 1.6 V and 2 to 4.6 V for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BOOST</sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> , respectively.