A >78%-Efficient Light Harvester over 100-to-100klux with Reconfigurable PV-Cell Network and MPPT Circuit.

Abstract

Energy harvesting is an attractive solution to extend system lifetime for internet of everything (IoE) nodes. Ambient light is a common energy source that can be harvested by photovoltaic (PV) cells. However, light intensity varies widely depending on location, ranging from ∼10s of lux in dim indoor conditions to ∼100klux under direct sunlight. Designing a fully integrated light harvester that spans such a wide range of light intensity with high efficiency is challenging, especially since typically low PV cell voltage requires a high upconversion ratio and PV-cell voltage/current characteristics change significantly with light intensity. Boost DC-DC converters are a typical energy-harvesting solution with high conversion efficiency, but they require a large off-chip inductor and hence cannot be fully integrated, increasing system size [1–3]. Recently, switched-capacitor (SC) DC-DC converters have been actively researched to enable fully-integrated energy harvesting using on-chip capacitors [4–6]. However, their efficiency has typically been limited to the 40-to-55% range at low input power levels (≤1µW) due to conduction/switching losses.