Multiple receiver wireless power charger for mobile electronic devices in near field

In recent years, wireless power transfer technology has come to limelight because of its possibility of providing viable solutions to the challenges encountered by electronic device consumers when using traditional methods of charging batteries. This paper presents a multiple receiver wireless power transfer system for charging mobile phone batteries. The circuit consists of a transmitter and two receiver systems. A mathematical analysis of the circuit is carried out and simulated to understand its behavior with variation in coupling coefficient and load. In order to charge mobile phones without an extra communication module over a wide range of coupling coefficients, a variable frequency control algorithm is used. The transmitter circuit uses the algorithm to track the maximum input power of the system. The output voltage of the receiver circuit is controlled to meet the power requirement of the load as coupling coefficient varies by using a switch capacitor modeled as two back to back connected MOSFETs with their drain-to-source capacitance. The proposed converter circuit topology is simulated and the results are presented. The circuit operates over a wide range of coupling coefficient and the power requirement of the mobile phones are met without using an extra communication module. The resonance frequency of the circuit is 5.7MHZ and it is design to deliver 10W (5V, 2A) each to two mobile phones.