Wireless power transfer system having wireless power transfer system-charger

A method of transferring wireless power using magnetic induction, the method comprising:

• selecting a coil among a plurality of coils partially overlapping each other;
• sensing a current flowing through the selected coil;
• receiving an amount of power requested by a wireless power receiver;
• and
• controlling an output voltage of a DC-DC converter based on the current flowing through the selected coil and the amount of power requested by the wireless power receiver,
• wherein the controlling the output voltage of the DC-DC converter includes:
• dividing the output voltage of the DC-DC converter to generate a divided output voltage;
• and
• adjusting a level of the output voltage of the DC-DC converter with a feedback signal based on the divided output voltage, and
• wherein the dividing the output voltage includes damping the output voltage by a first resistor connected to an output terminal of the DC-DC converter, a second resistor connected to ground, and a third resistor connected to a controller.

A wireless power transmitter, comprising:

• a plurality of coils partially overlapping each other;
• a DC-DC converter connected to the plurality of coils;
• a voltage divider connected to the DC-DC converter;
• and
• a controller connected to the voltage divider,
• wherein the controller is configured to:
• select a coil among the plurality of coils,
• sense a current flowing through the selected coil,
• receive an amount of power requested by a wireless power receiver, and
• adjust an output voltage of the DC-DC converter based on the current flowing through the selected coil and the amount of power requested by the wireless power receiver, and
• wherein the voltage divider comprises:
• a first resistor connected between an output terminal of the DC-DC converter and a port of the DC-DC converter;
• a second resistor connected between the port of the DC-DC converter and ground;
• and
• a third resistor connected between a controller and the port of the DC-DC converter.