Wireless Power Charging

A method of measuring current through a wireless power transmit coil, comprising:

• turning a sampling circuit on in response to a control signal to receive a signal from an inverter, the inverter being coupled between a voltage and a ground and configured to drive current through a transmission coil in accordance with inverter control signals;
• filtering the sampled signal from the sampling circuit in a filter circuit;
• turning a biasing circuit on according to the control signal when the sampling circuit is turned on to bias the filtered sampled signal, wherein the biasing occurs only when the sampling circuit is turned on;
• and
• amplifying the biased signal to provide a transmit coil current signal,
• wherein the filter circuit is not affected by the bias circuit when the bias circuit and the sampling circuit are turned off.

A method of operating a wireless power transmitter, comprising:

• operating a wireless power system that includes the wireless power transmitter providing power to a wireless power receiver at a first frequency;
• determining a zero-voltage switching (ZVS) deadtime at first frequency;
• lowering the first frequency until the ZVS deadtime is above a maximum ZVS deadtime;
• and
• setting a minimum operating frequency from the first frequency.

A wireless power transmitter, comprising:

• an inverter that includes an upper transistor in series with a lower transistor and coupled between an input voltage and a ground, the upper transistor being driven according to a UG signal and the lower transistor being driven according to a LG signal;
• a TX coil coupled to a switching node where the upper transistor and the lower transistor are connected;
• a capacitor coupled between the switching node and ground;
• an analog front end coupled to receive the input voltage, ground, and a switching voltage at the switching node, the analog front end providing signals that indicate the level of the switching node;
• and
• a processor with a ZVS control process, the processor executing instructions to
• operate the wireless power transmitter to provide power to a wireless power receiver at a first frequency;
• determine a zero-voltage switching (ZVS) deadtime at the first frequency;
• lower the first frequency until the ZVS deadtime is above a maximum ZVS deadtime;
• and
• set a minimum operating frequency from the first frequency that is above the maximum ZVS deadtime.