A Bipolar-Input Thermoelectric Energy-Harvesting Interface With Boost/Flyback Hybrid Converter and On-Chip Cold Starter

This paper presents a bipolar-input thermoelectric energy-harvesting interface based on boost/flyback hybrid converter (BFHC). Two-type ring oscillators are combined to form as a complementary group with bipolar-input voltage operating range for self-start. With the technique of combining the boost converter and flyback converter together, the system is able to convert the energy with bipolar-input voltages. The open-circuit voltage maximum power point tracking (MPPT) method is adopted in this harvester to extract as much energy as possible from the thermoelectric generator. By dynamically adjusting the switching frequency according to the input power, the system achieves a high conversion efficiency with a wide input range. Implemented in 180-nm CMOS process, the harvester achieves a peak conversion efficiency of 84% at $V_{{\text {TEG}}}=260$ mV and 79% at $V_{{\text {TEG}}}=-300$ mV. In addition, the harvester can self-startup with minimum voltages of 129 mV with a positive input voltage and −140 mV with a negative input voltage.