A Time-Based Direct MPPT Technique for Low-Power Photovoltaic Energy Harvesting

This letter introduces a maximum power point tracking (MPPT) technique for photovoltaic (PV) energy harvesting (EH) systems to enhance the end-to-end efficiency ( η _E-E ) when the output power of PV cell ( P _PV,MAX ) is low. A ripple-based PV cell current sensing and a time-domain multiplication are proposed to monitor the PV cell power delivered to the charger, which reduces the controller power consumption ( P _CTR ). The PV EH system with the proposed MPPT method is implemented in a 180-nm CMOS process. The P _CTR is 1.34 μ W. The measured η _E-E at low P _PV,MAX (13 μ W) is 88%. The measured peak η _E-E is 94.4% at 82 μ W.