Design of Transformer-Based Boost Converter for High Internal Resistance Energy Harvesting Sources With 21 mV Self-Startup V oltage and 74% Power Ef ficiency

Abstract

Thin-film thermoelectric generators (TEG) or graphene-based microbial fuel cells (MFC) are emerging energy harvesting sources with promising power density and sustain- ability. Nevertheless, convent ional transformer-based boost converters commonly used to achieve autonomous low voltage startup encounter low ef ficiency and potential startup problems with these novel power sources due to their high internal resis- tance. In this paper, an improved design of transformer-based boost converter addressing th ese issues is demonstrated with prototype chip fabricated using a standard 0.13 µm CMOS process. The self-start oscillation does not rely on the conventional LC resonant principle, but instead is dependent on the MOS transistor’s active-over-leakage current ratio and the mutual cou- pling between the two identical transformer coils. Circuit design techniques to regulate output vol tage and to track system’s max- imum power point (MPP) of this b oost converter are presented. Measurement results con firmed that the proposed circuit works with either low threshold voltage or native MOS transistors. It needs minimum self-startup voltage of 21 mV (at 5.8 µW input power) and minimum startup power of 1.3 µW (at 35 mV input voltage) respectively. The m aximum output power is 2 mW and peak power conversion ef ficiency is 74% at a regulated output voltage of 1 V.