A low-input-voltage wireless power transfer for biomedical implants

Wireless power transfer is an essential technology to increase implants’ longevity. A pair of inductivelycoupled coils operating at radio-frequency is extensively used to deliver electrical power to implants wirelessly. In this system, a power conditioning circuit is required convert the induced time-varying AC power harvested by the receiving coil to a stable DC power that is needed for powering circuits and sensors. Most existing power conditioning circuits require the induced voltage of the receiving coil to be significantly higher than the turn-on voltage of the diodes used in the rectifier for the efficient AC to DC conversion. This requirement results in larger coil size, shorter operating distance or more stringent geometrical alignment between the two coils. In this paper, a low-input-voltage wireless power transfer has been demonstrated. In this system, the opencircuit voltage of the induced 5 kHz AC input is as low as ~ 190 mV, and it has been converted to 5 V DC over a 25 kΩ resistor. Both the output voltage and the power drawn into the receiving coil can be regulated by the duty cycle of a control signal. The described system has the potential to reduce the size of the receiving coil, increase the operating distance between the transmitting and the receiving coil, and yet to achieve the desired DC output for implants.