A wireless power transfer system-charger comprising: a power supply ; a transformer unit for converting a voltage supplied by the power supply into a direct current (DC) voltage; and a controller for adjusting a level of the DC voltage of the transformer unit , whereby the transformer unit includes: a DC-DC converter ; and a divider for dividing an output voltage (Vout) of the DC-DC converter ; characterized in that the transformer unit further includes: a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier , wherein the controller includes an output control port (OCP) as an output terminal connected to the divider for adjusting the divided voltage (Vd). a power supply ; a transformer unit for converting a voltage supplied by the power supply into a direct current (DC) voltage; and a controller for adjusting a level of the DC voltage of the transformer unit , whereby the transformer unit includes: a DC-DC converter ; and a divider for dividing an output voltage (Vout) of the DC-DC converter ; characterized in that the transformer unit further includes: a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier , wherein the controller includes an output control port (OCP) as an output terminal connected to the divider for adjusting the divided voltage (Vd). a DC-DC converter ; and a divider for dividing an output voltage (Vout) of the DC-DC converter ; characterized in that the transformer unit further includes: a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier , wherein the controller includes an output control port (OCP) as an output terminal connected to the divider for adjusting the divided voltage (Vd). a control unit for controlling an error (Vc) of the output voltage (Vout) of the DC-DC converter based on a divided voltage (Vd), wherein the controller is connected to the divider to adjust a target value of the output voltage (Vout) of the DC-DC converter according to a wireless charging state, wherein the divider includes a plurality of resistors (R1, R2, R3) for dividing the output voltage (Vout) of the DC-DC converter and supplying the divided voltage (Vd) to the error amplifier , wherein the controller includes an output control port (OCP) as an output terminal connected to the divider for adjusting the divided voltage (Vd). <EOS>