A High-Efficiency Charger With Adaptive Input Ripple MPPT for Low-Power Thermoelectric Energy Harvesting Achieving 21% Efficiency Improvement

A high-efficiency charger for low-power thermoelectric energy harvesting with a method for improving the efficiency, which is called the adaptive input ripple (AIR) maximum power point tracking (MPPT) technique, is introduced in this paper. On the basis of the key finding that the end-to-end efficiency (η
_E-E
) is highly dependent on the amplitude of the input ripple of the charger (ΔV
_IN
) in the low-power region, the proposed AIR MPPT technique adjusts Δ
_VIN
to maximize η
_E-E
. Moreover, the minimum input power that allows the charger to maintain operation is enhanced by the proposed AIR MPPT technique. The proposed charger is implemented with 180-nm complementary metal oxide-semiconductor technology. An improvement of 21% in η
_E-E
is achieved with the proposed technique. Furthermore, the proposed technique enhances the minimum power by 7.5 μW. The startup power and minimum power of the prototype are 37 and 6 μW, respectively. The maximum η
_E-E
is 82%.