An Ultra-Low-Power CMOS Supercapacitor Storage Unit for Energy Harvesting Applications

Abstract

This work presents an ultra-low-power CMOS supercapacitor storage unit suitable for a plethora of low-power autonomous applications. The proposed unit exploits the unregulated voltage output of harvesting circuits (i.e., DC-DC converters) and redirects the power to the storage elements and the working loads. Being able to adapt to the input energy conditions and the connected loads' supply demands offers extended survival to the system with the self-startup operation and voltage regulation. A low-complexity control unit is implemented which is composed of power switches, comparators and logic gates and is able to supervise two supercapacitors, a small and a larger one, as well as a backup battery. Two separate power outputs are offered for external load connection which can be controlled by a separate unit (e.g., microcontroller). Furthermore, user-controlled parameters such as charging and discharging supercapacitor voltage thresholds, provide increased versatility to the system. The storage unit was designed and fabricated in a 0.18 um standard CMOS process and operates with ultra-low current consumption of 432 nA at 2.3 V. The experimental results validate the proper operation of the overall structure.

On Search for Unconventional Energy Sources for Harvesting

“…However, most often, electricity in harvesters is generated irregularly and its storage is necessary. The basic solution here is the use of capacitors, supercapacitors, and batteries [20]. Here, electricity is stored directly and immediately available.…”

Energy Harvesting and Energy Storage Systems

“…An ultra-low-power CMOS supercapacitor storage unit for energy harvesting applications was presented by Gogolou et al [7]. The ultra-low current consumption of only 432 nA at 2.3 V proves that the proposed storage unit is ideal for energy harvesting systems, even for cases with a small input power range.…”