Operating an Inductive Energy Transfer System

Abstract

A receiver device in an inductive energy transfer system can include a touch sensing device. If the input surface of the touch sensing device is touched, a transmitter device can periodically stop transferring energy to allow the touch sensing device to sense touch samples while inductive energy transfer is inactive. Additionally or alternatively, a transmitter device can produce an averaged duty cycle by transferring energy to the receiver device for one or more periods at a first duty cycle step and for one or more periods at different second first duty cycle step. Additionally or alternatively, a transmitter device can reduce a current level received by a DC-to-AC converter if the current received by the DC-to-AC converter equals or exceeds a threshold. Additionally or alternatively, a transmitter device can ping a receiver device and transfer energy only after a response signal is received from the receiver device.

What is claimed is: 
     
         1 . A method for operating an inductive energy transfer system that includes a transmitter device and a receiver device, the transmitter device including a current sense circuit operatively connected to an input of a DC-to-AC converter and a processing device operatively connected to the current sense circuit, the method comprising:
 during inductive energy transfer from the transmitter device to the receiver device, the current sense circuit measuring a current input into the DC-to-AC converter;   the processing device determining if the measured current equals or exceeds a threshold; and   if the measured current equals or exceeds the threshold, reducing the current input into the DC-to-AC converter by modifying an operation of the DC-to-AC converter.   
     
     
         2 . The method as in  claim 1 , wherein modifying an operation of the DC-to-AC converter comprises decreasing a duty cycle of the energy transfer. 
     
     
         3 . The method as in  claim 1 , wherein modifying an operation of the DC-to-AC converter comprises decreasing a voltage level input into the DC-to-AC converter. 
     
     
         4 . The method as in  claim 1 , wherein modifying an operation of the DC-to-AC converter comprises decreasing an operating frequency of the DC-to-AC converter. 
     
     
         5 . The method as in  claim 1 , further comprising not responding to a request to increase the duty cycle. 
     
     
         6 . The method as in  claim 3 , further comprising changing a sampling time of the current measurement. 
     
     
         7 . The method as in  claim 2 , further comprising changing the given amount used to decrease the duty cycle of the energy transfer. 
     
     
         8 . A transmitter device for an inductive energy transfer system, comprising:
 a DC-to-AC converter operatively connected between a current sense circuit and a transmitter coil; and   a processing device operatively connected to the current sense circuit, wherein the processing device is configured to periodically receive a current measurement from the current sense circuit and configured to reduce a current level input into the DC-to-AC converter if the current measurement equals or exceeds a threshold by modifying an operation of the DC-to-AC converter.   
     
     
         9 . The transmitter device as in  claim 8 , wherein modifying an operation of the DC-to-AC converter comprises reducing an energy transfer duty cycle. 
     
     
         10 . The transmitter device as in  claim 8 , wherein modifying an operation of the DC-to-AC converter comprises reducing a voltage level input into the DC-to-AC converter. 
     
     
         11 . The transmitter device as in  claim 8 , wherein modifying an operation of the DC-to-AC converter comprises modifying an operating frequency of the DC-to-AC converter.