A 93.7%-Efficiency 5-Ratio Switched-Photovoltaic DC-DC Converter

Abstract

Ambient light can enable near-perpetual operation of sensing and internet of everything (loE) nodes. A step-up DC-DC converter with a large off-chip inductor (L) [1] or area-consuming on-chip capacitors (C) [2], [3] is typically used to upconvert the low output voltage of a photovoltaic (PV) cell to the required supply level. Instead of using area-consuming energy storage elements (i.e., L or C) to step up the PV voltage, the number of PV cells connected in series can be reconfigured using a switch matrix (SM) to match the maximum power point (MPP) voltage of the cells with the battery voltage (VBAT) under varying light intensity [4]. Unfortunately, manufacturing tolerances, aging, and environmental factors (e.g., shading, dust, and debris) introduce practical mismatches among the PV cells that limit the current, and hence the output power, of a series string to its worst-performing cell, as exemplified in Fig. 1 (top left). In this case, the voltage across the strong cells increases above the MPP value while the weak cells voltages decrease until all PV currents reach the same value, lowering the harvesting efficiency (e.g., by 20% for $\Delta\mathrm{l}$= 23% in Fig. 1 which is a typical $3\sigma$ PV-manufacturing tolerance).