WIRELESS INDUCTIVE POWER TRANSFER

摘要

A wireless power transfer system includes a power receiver and a power transmitter providing power using an inductive power signal. The power transmitter comprises a resonance circuit (201) comprising a capacitive impedance (503) and an inductive impedance (501). A driver (203) generates a drive signal for the resonance circuit. A frequency modification circuit (505) controls the resonance frequency of the resonance circuit (201) by slowing a state change for at least one of the capacitive impedance (503) and the inductive impedance (501) for a fractional time interval of at least some cycles of the drive signal. The frequency modification circuit (505) is arranged to align at least one of a start time and an end time for the fractional time interval to transitions of a timing signal. In the power transmitter, the driver (203) generates the timing signal to have transitions synchronized to the drive signal. The slowing may be by impeding current flow between the capacitive and inductive impedance (503, 501).