Robust Self-Regulated Rectifier for Parallel-Resonant Rx Coil in Multiple-Receiver Wireless Power Transmission System

This paper presents a small, low-cost self-regulated rectifier for parallel-resonant receivers (Rxs) in the wireless power transmission (WPT) system to maintain the individual rectifier voltages of each Rx to be constant. The problem of the conventional rectifier-low-dropout regulator (LDO) for parallel-resonant Rx coil is analyzed. Specifically, although the LDO attempts to reduce the excessive voltage by increasing its dropout resistance, this increases the power delivered to the Rx coil and rectifier due to the current source behavior of parallel-resonant Rx coil. To solve the problem, the proposed regulation reduces the total resistance seen by Rx coil so that the power delivered to Rx coil itself is reduced, which is fundamentally different from conventional regulation where excessive received power had to be dissipated at LDO. The proposed regulation does not require complex analog or digital control blocks and abrupt switch transitions, allowing noiseless operation and the low-cost smaller volume with off-the-shelf components. The regulation is demonstrated with commercially available off-the-shelf components for applications of multiple distributed receivers. The proposed method increased the overall efficiency from 20.9% to 43.0% at 2.8-W load power in three individual Rxs.