Novel power conditioning circuits for piezoelectric micro power generators

by Han, Jifeng

Advanced low power devices promote the development of micro power

generators (MPGs) to replace the batteries to power them. Due to the trend in

decreasing integrated circuit (IC) supply voltages, power supply designers are facing

more and more serious challenges. The objective of this research is to design a power

conditioning circuit (PCC) for use in conjunction with low voltage

microelectromechanical systems (MEMS)-based Palouse Piezoelectric Power (P3)

micro heat engine power generation systems. The PCC enables maximum power

extraction from a piezoelectric MPG. The proposed PCC includes a rectifier stage and

a regulator stage. The rectifier stage is based on the synchronous rectification

technique. The dc-dc regulator is a charge pump-based step-down converter.

Interleaved discharge (ID) is proposed to reduce the output voltage ripple

significantly, without sacrificing the converter efficiency. The proposed step-down

charge pump is analyzed with state-space averaging.

In order to facilitate the PSpice simulation of the lead zirconate titanate (PZT)

membrane, a simplified PZT model was developed. Both the rectifier and the charge

pump are simulated with PSpice. Simulations show that the interleaved discharge method takes full advantage of the step-down charge pump structure, and provides

flexibilities to the design of step-down charge pumps. The designed 200mW 5V/1.2V

charge pump has an efficiency of 92.2%, with reduced output ripple. Proof-of-concept

demonstration of the proposed PCC includes a 4-stage completely passive charge

pump driving an analog wristwatch, proving proper operation of the entire P3 micro

power system.

A maximum output power of 18.8mW has been extracted from a single

piezoelectric MPG, with 92% efficiency in the rectifier stage. Arbitrary waveform

generator representation (AWGR) of the piezoelectric membrane is also presented.

AWGR facilitates ongoing tests and demonstrates the feasibility of cascading many

MPGs to extract additional power.