A 3.4mW photovoltaic energy-harvesting charger with integrated maximum power point tracking and battery management

Energy harvesting is an attractive technique to take advantage of renewable energy and make systems, such as wireless sensor nodes, less dependent on external power sources. A photovoltaic (PV) energy-harvesting charger can convert energy from solar panels to charge batteries or super capacitors. To manage the variation in illumination, maximum power point tracking (MPPT) is essential to lock the output power of solar panels on the maximum power points [1, 2]. For any generic solar cell, its output current is determined by the output voltage in an exponential relation. Without knowing the characteristics of the solar cell in advance, it is necessary to monitor a feedback parameter to reach its maximum power point. Current measurement is needed at the output of the boost converter [1] or in the output path of the solar cell [2]. Motivated by the topology in [2], we propose a mixed-signal integration to avoid power hungry digital signal processing. In this paper, we report a charger with an integrated MPPT controller that can provide fast tracking for wide-range illumination levels while keeping high conversion efficiency. Also, a battery management unit is implemented and integrated on the same IC.