An apparatus to receive power wirelessly from a transmitter , comprising: a receive coil configured to receive power wirelessly from the transmitter ; a circuit coupled to the receive coil , the circuit configured to reduce a received voltage when activated; a controller configured to activate the circuit when the received voltage is greater than or equal to a first threshold value and configured to deactivate the circuit when the received voltage decays to a second threshold value , wherein: the second threshold value is lower than the first threshold value; wherein the circuit comprises a first transistor coupled between a first terminal of the receive coil and a ground terminal and a second transistor coupled between a second terminal of the receive coil and a ground terminal and wherein the circuit is configured to change the impedance of the apparatus by activation and deactivation of the first transistor and the second transistor ; and wherein the circuit is further configured to generate a signal for indicating that the received voltage has reached the first threshold value when activated, the signal being generated according to a pulse width modulation process as a series of pulses configured to activate and deactivate the first transistor and the second transistor . a receive coil configured to receive power wirelessly from the transmitter ; a circuit coupled to the receive coil , the circuit configured to reduce a received voltage when activated; a controller configured to activate the circuit when the received voltage is greater than or equal to a first threshold value and configured to deactivate the circuit when the received voltage decays to a second threshold value , wherein: the second threshold value is lower than the first threshold value; wherein the circuit comprises a first transistor coupled between a first terminal of the receive coil and a ground terminal and a second transistor coupled between a second terminal of the receive coil and a ground terminal and wherein the circuit is configured to change the impedance of the apparatus by activation and deactivation of the first transistor and the second transistor ; and wherein the circuit is further configured to generate a signal for indicating that the received voltage has reached the first threshold value when activated, the signal being generated according to a pulse width modulation process as a series of pulses configured to activate and deactivate the first transistor and the second transistor . the second threshold value is lower than the first threshold value; wherein the circuit comprises a first transistor coupled between a first terminal of the receive coil and a ground terminal and a second transistor coupled between a second terminal of the receive coil and a ground terminal and wherein the circuit is configured to change the impedance of the apparatus by activation and deactivation of the first transistor and the second transistor ; and wherein the circuit is further configured to generate a signal for indicating that the received voltage has reached the first threshold value when activated, the signal being generated according to a pulse width modulation process as a series of pulses configured to activate and deactivate the first transistor and the second transistor . <EOS>