Automatic On-Off Charger for an Implantable Medical Device

Abstract

An external charger for an implantable medical device is disclosed which can automatically detect an implant and generate a charging field. The technique uses circuitry typically present in an external charger, such as control circuitry, a Load Shift Keying (LSK) demodulator, and a coupling detector. An algorithm in the control circuitry periodically issues charging fields of short duration in a standby mode. If the coupling detector detects the presence of a conductive material, the algorithm issues a listening window during which a charging field is generated. If an LSK reply signal is received at the LSK demodulator, the external charger can charge the implant in a normal fashion. If a movement signature is detected at the LSK demodulator indicative of a predetermined user movement of the external charger, a charging field is issued for a set timing period, to at least partially charge the IPG battery to restore LSK communications.

What is claimed is: 
     
         1 . A charger, comprising:
 a coil; and   control circuitry configured to automatically provide power to an implantable medical device (IMD) in the charger's vicinity by:
 evaluating a voltage across the coil or a current through the coil during one or more periodic activations of the coil; and 
 energizing the coil to provide power to the IMD when the voltage or the current indicates that the IMD is possibly in the charger's vicinity. 
   
     
     
         2 . The charger of  claim 1 , wherein the control circuitry comprises a coupling detector that compares the voltage across the coil to a threshold voltage. 
     
     
         3 . The charger of  claim 2 , wherein the threshold voltage is dependent upon one or more charging parameters. 
     
     
         4 . The charger of  claim 2 , wherein the control circuitry determines that the IMD is possibly in the charger's vicinity when the voltage across the coil is less than the threshold voltage for a plurality of consecutive periodic activations of the coil. 
     
     
         5 . The charger of  claim 1 , wherein the control circuitry is further configured to generate a user alert when the voltage or the current indicate that the IMD is possibly in the charger's vicinity. 
     
     
         6 . The charger of  claim 1 , wherein the control circuitry is further configured to de-energize the coil at the end of a first time period unless a verification that the IMD is in the charger's vicinity is received. 
     
     
         7 . The charger of  claim 6 , wherein the verification is an LSK signal reflected to the charger by the IMD. 
     
     
         8 . The charger of  claim 6 , wherein the verification is an indication of a predefined movement of the charger by a user. 
     
     
         9 . The charger of  claim 6 , wherein the control circuitry is further configured to modify the evaluation of the voltage or the current when the coil is de-energized a predetermined number of consecutive times. 
     
     
         10 . A method, comprising:
 automatically providing power to an implantable medical device (IMD) from a coil in a charger by:
 evaluating a voltage across the coil or a current through the coil during one or more periodic activations of the coil; and 
 energizing the coil to provide power to the IMD when the voltage or the current indicates that the IMD is possibly in the charger's vicinity. 
   
     
     
         11 . The method of  claim 10 , wherein evaluating the voltage across the coil comprises comparing the voltage across the coil to a threshold voltage. 
     
     
         12 . The method of  claim 11 , wherein the threshold voltage is dependent upon one or more charging parameters. 
     
     
         13 . The method of  claim 11 , wherein the coil is energized when the voltage across the coil is less than the threshold voltage for a plurality of consecutive periodic activations of the coil. 
     
     
         14 . The method of  claim 10 , further comprising generating a user alert when the voltage or the current indicate that the IMD is possibly in the charger's vicinity. 
     
     
         15 . The method of  claim 10 , further comprising de-energizing the coil at the end of a first time period unless a verification that the IMD is in the charger's vicinity is received. 
     
     
         16 . The method of  claim 15 , wherein the verification is an LSK signal reflected to the charger by the IMD. 
     
     
         17 . The method of  claim 15 , wherein the verification is an indication of a predefined movement of the charger by a user. 
     
     
         18 . The method of  claim 15 , further comprising modifying the evaluation of the voltage or the current when the coil is de-energized a predetermined number of consecutive times. 
     
     
         19 . A charger, comprising:
 a coil;   means for evaluating a voltage across the coil or a current through the coil during one or more periodic activations of the coil; and   means for automatically energizing the coil to provide power to the IMD when the voltage or the current indicates that the IMD is possibly in the charger's vicinity.   
     
     
         20 . The charger of  claim 19 , wherein the means for evaluating the voltage across the coil comprise means for comparing the voltage across the coil to a threshold voltage.