A self-powered power conditioning circuit for battery-free energy scavenging applications

A controllable power conditioning circuit is proposed for battery-free energy harvesting applications. The circuit is designed for piezoelectric energy harvester applications and it has only 11 transistors and consist a simple feedback loop and switched capacitor that conditionally allows the power to be applied to the load (circuit to be powered in this case). The area- and power-efficient digital design that does not include any inductors makes the topology easy to apply to any low-power sensor applications. The power conditioning circuit relies on a digital Schmitt trigger that controls the voltage threshold values of the power supply where the load circuit would operate within. The hysteresis (hence the threshold) levels were set to 435 and 710 mV and the overall energy conversion efficiency is around 65 %. The theory of the piezoelectric harvester was also studied.