Linear Technology’s LTC3331 delivers up to 50 mA of continuous output current to extend battery life when harvesting energy is available. Thanks to a simple 10-mA shunt, a rechargeable battery with harvested energy can be charged while a low-battery disconnect function protects the battery from deep discharge. The device needs a mere 200 nA of supply current from the battery when providing regulated power to the load from harvested energy, and only 950 nA when powered from the battery under no-load conditions. Integrated into the LTC3331 are a high-voltage energy-harvesting power supply, battery charger, and synchronous buck-boost dc-dc converter powered by a rechargeable battery. The power supply consists of a full-wave bridge rectifier accommodating ac or dc inputs and a high-efficiency buck converter. It harvests energy from piezoelectric (ac), solar (dc), or magnetic (ac) sources. When harvested energy is unavailable, the rechargeable battery input powers a buck-boost converter that operates over the full battery-voltage range up to 4.2 V (the LTC3331 automatically transitions to the battery when the harvesting source is no longer available). Energy-harvesting inputs operate from 3 to 19 V ac or dc. Undervoltage lockout threshold settings are programmable between 3 and 18 V. Packaging is a 5- by 5-mm QFN.