A ±0.5-mV-Minimum-Input DC-DC Converter with Stepwise Adiabatic Gate-Drive and Efficient Timing Control for Thermoelectric Energy Harvesting

Abstract

<p>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. </p>

An Analytical Model for Stepwise Adiabatic Driver Energy Consumption

“…The number of rising/falling steps in a stepwise driver is defined as N. A stepwise driver has N -1 CTank capacitors, N rising-edge switches SR, and N falling-edge switches SF. In an application such as in [1], the falling-edge switches need to be much lower resistance than the rising-edge switches to enable fast falling transitions. If the resistance of the switches can be equal, then SR,k and SF,N−k (for k = 1 to N − 1) can be one and same device as in [9].…”

“…With the developments of the Internet of Things and low-power battery-operated or battery-free devices, numerous techniques have been employed to reduce power consumption of electrical circuits. One such technique is adiabatic charging of capacitive loads that must be charged/discharged periodically, such as large power FETs in DC-DC converters [1], clock lines [2], capacitive touch sensors [3], or others [4], [5]. Inherently, a capacitive load does not consume energy itself when driven with a periodic changing voltage; however, traditional drivers dissipate energy in the process of driving the voltage due to the intrinsic properties of the driver.…”