A micropower energy harvesting circuit with piezoelectric transformer-based ultra-low voltage start-up

This paper introduces the use of piezoelectric transformers (PTs) as key elements for ultra-low voltage start-up circuits for battery-less energy harvesting applications. Firstly, a step-up oscillator topology based on a PT and a JFET is presented. The circuit is able to start from voltages as low as 16 mV, and to boost the output voltage up to 1.32 V in a no load condition. In order to validate the proposed approach, a surrounding power management and conversion circuit is developed. This circuit is able to automatically enable a boost DC/DC converter once the start-up circuit has generated a sufficient voltage. The whole circuit self-starts with an input voltage of 30 mV, and the maximum conversion efficiency referred to the maximum power point (MPP) is higher than 40%, with an intrinsic current consumption as low as 1.3 µA.