The Design, Characterization, and Deployment of a Bipolar ±0.5-mV-Minimum-Input DC-DC Converter with Stepwise Adiabatic Gate-Drive and Efficient Timing Control for Thermoelectric Energy Harvesting

Abstract

This work presents a step-up DC-DC converter that is optimized to extract power from thermoelectric generators that generate extremely low voltages from small temperature differentials. The DC-DC converter 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 the author knows. 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. To aid in efficiency optimization, an analytical model with unprecedented accuracy of the stepwise gate-driver energy consumption was developed. A test fixture that can accurately measure the efficiency, input impedance, and quiescent power consumption of the DC-DC converter was designed and utilized. Lastly, a method for characterizing the leakage current of capacitors was developed so that capacitors of the lowest leakage can be selected for the DC-DC converter output energy storage.