Patent 7,825,537 B2 characteristic of said time varying electric current) responsive to the ‘feedback signal’ to achieve and maintain operation at the ‘resonant’ frequency of the coupled inductor system,” where “the ‘feedback signal’ from the sense coil constitutes ‘at least one parameter indicative of an efficiency of power transfer from said base unit to said target unit.’” Pet. 55.
As discussed above with respect to elements 1.3 and 1.4, Flowerdew teaches that “[a]pplication of a variable frequency is predicated on the basis that the high efficiency achieved by driving a resonant system is needed for effective operation.” Ex. 1007, 13:30–35 (cited by Pet. 55).
Petitioner also directs us to Flowerdew’s teaching that a “‘free running’ state, where no secondary unit 304 is present, can be detected and the power output reduced to a predetermined level or applied periodically to determine whether an item has been placed on the charging surface.” Id. at 13:18–21 (cited by Pet. 67).
Petitioner contends that “[i]t would have been obvious to modify Flowerdew in accordance with Jang’s suggestion to regulate the drive frequency based on a feedback loop that compares a measurement of the current through a primary coil to a constant reference value.” Pet. 68.
As discussed above, the Baarman Provisional Application teaches that “[u]sing feedback from the secondary, such as the sensed voltage and/or current, ... the duty cycle may be adjusted to provide additional or less power to meet the desired goal.” Ex. 1009, 16 (cited by Pet. 8).