Efficient power harvesting from the mobile phone audio jack for mHealth peripherals

A tremendous opportunity currently exists to enable practical and portable mHealth tools by taking advantage of the ubiquity of mobile phones across the world. To this end, we describe the design of a circuit to efficiently harvest energy from the standard audio jack of a mobile phone to power mHealth peripherals, lowering cost, reducing size, and improving the practicality of portable medical devices. This design not only obviates the need to charge or change an extra battery but also is universally compatible with all phones. The audio output channels of several popular phones were characterized in order to determine the range of design parameters. Using these data, different power harvesting topologies are presented, simulated, and compared. A PCB implementation was used to measure and confirm the performance. Compared with prior art, which have achieved 21% and 47% efficiency, this design is able to achieve greater than 77% efficiency by using a tunable impedance matching network.