A flexible thermoelectric generator with a fully electrical, low startup voltage and high efficiency DC-DC converter

The growing demand of wearable and low cost sensor devices, pushed the development of key enabling technologies able to transfer the well know materials on cheap substrates, keeping the capabilities of developed systems to integrate energy harvesting, sensing and communication functions. A flexible thermoelectric generator (TEG) with a fully electrical, low startup voltage and high efficiency DC-DC converter is presented in this paper. The proposed generator has been produced by screen printing technology on 80 microns thick common paper and thin Kapton foil and integrates about 280 thermocouples, for an output voltage of about 75 mV with 5 K of thermal gradient, useful for wearable-oriented applications. To increase the voltage provided by TEG, a DC-DC converter is designed. It operates with an input voltage (V_in) range from 40mV up to 400mV. By means the pulse width modulation (PWM), the DC-DC converter achieves an automatic control, ensuring an 1V output voltage. It is composed of two control section: the feedforward control circuit operates with an input voltage ranging from 40mV up to 150mV. As the output voltage of TEG is higher than 150mV, the feedback control circuit starts to operate, achieving an automatic control of the output voltage of the boost converter. The DC-DC converter is implemented in 65nm CMOS technology and its peak efficiency is 85%.