Design of high efficiency wireless charging pad based on magnetic resonance coupling

In this paper, a design of wireless power charging pad based on magnetic resonance coupling is introduced. For highly efficient operation of the overall charging pad system, the efficiency of RF TX is very important so that the 6.78MHz, 30W, 91% class-E power amplifier (PA) is designed and the power tracking technique, whose function is easily embedded in the AC-to-DC power converter conventionally used for consumer electronics, is applied for the power control. Compared to the conventional approach employing the additional DC-to-DC converter for the power control, it presents maximally 20% higher efficiency over the wide output power region. To charge various mobile devices on a single 320×220mm² TX pad, a uniform field resonator is designed. The receiving unit consists of a general full-bridge rectifier and a 5V DC-DC converter coupled to the internal battery charger in the mobile device. The overall AC60Hz-to-DCLoad efficiency of the implemented wireless power charging pad is 42-51% for various charging conditions; from single device to multiple devices of Samsung Galaxy-S2, Galaxy-Tab7, and NX-100 Digital Camera. The DC-to-DC efficiencies, generally used term to present the system efficiency, are higher than 60% for the whole cases.