Abstract
This paper presents a step-up DC-DC converter that uses a stepwise
gate-drive technique to reduce the power FET gate-drive energy by 82%,
allowing positive efficiency down to an input voltage of ±0.5 mV—the
lowest input voltage ever achieved for a DC-DC converter as far as we
know. Below ±0.5 mV the converter automatically hibernates, reducing
quiescent power consumption to just 255 pW. The converter has an
efficiency of 63% at ±1 mV and 84% at ±6 mV. The input impedance is
programmable from 1 Ω to 600 Ω to achieve maximum power extraction. A
novel delay line circuit controls the stepwise gate-drive timing,
programmable input impedance, and hibernation behavior. Bipolar input
voltage is supported by using a flyback converter topology with two
secondary windings. A generated power good signal enables the load when
the output voltage has charged above 2.7 V and disables when the output
voltage has discharged below 2.5 V. The DC-DC converter was used in a
thermoelectric energy harvesting system that effectively harvests energy
from small indoor temperature fluctuations of less than 1°C. Also, an
analytical model with unprecedented accuracy of the stepwise gate-drive
energy is presented.