Korea Advanced Institute of Science and Technology (KAIST) and Samsung Electronics Co Ltd co-developed a receiving circuit for wireless chargers based on magnetic resonance and announced it at ISSCC 2013 (lecture number: 4.1).
The circuit uses a resonance frequency of 6.78MHz. Its maximum output is 6W, which is more than 10 times higher than before, and its maximum transmission efficiency is as high as 86% (with an output of 3.4W). The circuit is targeted at mobile devices such as smartphones.
Commonly-used receiving circuits for wireless chargers based on magnetic resonance consist of a rectifier circuit and a step-down converter circuit. On the other hand, KAIST and Samsung realized one-step AC-DC conversion by developing a switching converter called "Resonant Regulating Rectifier (3R)." As a result, they reduced power consumption and simplified the constitution of receiving circuit.
The 3R consists of a full-bridge rectifier circuit and three LD-MOSFETs. It eliminates the need for inductors by using the inductance of a resonance coil. It is made by using 0.35μm BCD (Bipolar-CMOS-DMOS) process, and its chip area is 5.52mm2.
The 3R realizes a high operation efficiency with switching operation that uses the continuous conduction mode (CCM) and the discontinuous conduction mode (DCM), in which the current becomes zero.