Solar Energy-Harvesting Buck–Boost Converter With Battery-Charging and Battery-Assisted Modes

In this article, a buck-boost converter is described which harvests energy from a solar cell and performs dc-dc conversion with only one inductor. If the harvested energy is larger than the system load, the buck-boost converter charges a battery with the residual energy, which is called the battery-charging mode. If system load is larger than the harvested energy, the load is supplied by both the harvested energy and the battery, which is called the battery-assisted mode. The optimum control scheme has been found to be the integral charging scheme for the maximized power efficiency (PE). The buck-boost converter implemented in a 180-nm complementary metal-oxide-semiconductor (CMOS) process operates at 97 kHz and shows the steady-state output ripple smaller than 25 mV with the maximum PE of 89.4% for 28-mW output power.