Study of contactless inductive charging platform with core array structure for portable products

In this research, contactless power transmission technique is applied in the charging of lithium battery for portable electronic products and the concept of common charging platform is proposed. The charging platform is comprised of several pot type cores with array structure, allowing circuit to be charged within a permitted region of displacement on the charging platform. However, a larger air gap exists in contactless structure compared to other contact structures, i.e. poor power transmission efficiency. In order to overcome the weakness, phase-locked loop (PLL) is applied to enable the operation frequency of circuit to be maintained above primary resonant frequency and microprocessor is utilized to improve the transmission efficiency when charging platform is standby. In addition, printed-circuit-board (PCB) is utilized on the secondary to reduce the thickness of the secondary circuit, forming PCB coil. Experimental results show that the transmission efficiency between contactless inductive structures is 55% under the condition of charging current 200 mA and air gap 2.5 mm.