Spinal cord stimulator system

1. A method, comprising:

receiving, by a charger during a charging of an implantable medical device, a signal from the implantable medical device, wherein the signal causes a sensor of the charger to produce an output;

comparing, by the charger, a pattern of the output produced by the sensor with a predefined pattern;

determining, by the charger and based on the comparing, that the implantable medical device no longer needs to be charged; and

performing, by the charger, an action in response to the determining.

2. The method of claim 1 , wherein the performing the action comprises communicating, to a user of the charger, a tactile feedback signal or an audible feedback signal via the charger.

3. The method of claim 1 , wherein the performing the action comprises terminating the charging of the implantable medical device.

4. The method of claim 1 , wherein the signal causes the output of the sensor of the charger to go up and down.

5. The method of claim 1 , wherein the predefined pattern comprises a sine wave.

6. The method of claim 1 , wherein the determining comprises:

counting a number of times the output produced by the sensor rises above a threshold value; and

determining that the implantable medical device no longer needs to be charged when the counted number of times exceeds a predetermined number.

7. The method of claim 1 , wherein the charging of the implantable medical device is performed via a charging coil of the charger, and wherein the method further comprises:

sensing an electrical current flowing through the charging coil or a voltage across the charging coil via a transformer of the sensor.

8. The method of claim 1 , wherein the implantable medical device is charged via a receiving coil of the implantable medical device, and wherein the method further comprises:

determining, by the implantable medical device, that a rechargeable battery of the implantable medical device has been sufficiently charged; and

in response to the determining that the rechargeable battery has been sufficiently charged, electrically shorting the receiving coil to ground repeatedly, thereby producing the signal.

9. A system, comprising:

a charging coil configured to charge a rechargeable battery of an implantable medical device;

a sensor circuit coupled to the charging coil, wherein the sensor circuit is configured to detect an electrical current flowing through the charging coil or a voltage across the charging coil; and

a controller coupled to the sensor circuit and to the charging coil, wherein the controller is configured to:

compare an output of the sensor circuit with a predefined pattern; and

determine, based on a match between the output of the sensor circuit and the predefined pattern, that the rechargeable battery no longer needs to be charged.

10. The system of claim 9 , wherein the controller is further configured to play a tactile feedback signal or an audible feedback signal in response to a determination that the rechargeable battery no longer needs to be charged.

11. The system of claim 9 , wherein the controller is further configured to terminate a charging of the rechargeable battery in response to a determination that the rechargeable battery no longer needs to be charged.

12. The system of claim 9 , wherein the predefined pattern comprises a pattern that goes up and down.

13. The system of claim 12 , wherein the predefined pattern comprises a sine wave.

14. The system of claim 9 , wherein:

the controller counts a number of times the output produced by the sensor circuit rises above a threshold value; and

the controller determines that the rechargeable battery no longer needs to be charged only when the number of times exceeds a predetermined number.

15. The system of claim 9 , wherein: the sensor circuit comprises a transformer that includes a primary coil and a secondary coil that is electromagnetically coupled to the primary coil; and

the primary coil is coupled to the charging coil in series.

16. The system of claim 15 , wherein the sensor circuit further comprises a rectifier that rectifies an AC voltage from the secondary coil into a DC voltage.

17. The system of claim 15 , wherein the sensor circuit further comprises a voltage divider and a zener diode.

18. The system of claim 9 , wherein:

the charging coil, the sensor circuit, and the controller are parts of a charger; and

the system further comprises the implantable medical device that includes a receiving coil inductively coupled to the charging coil; and

the implantable medical device is configured to electrically short the receiving coil to ground repeatedly in response to a determination that the rechargeable battery no longer needs to be charged.

19. A system, comprising:

an implantable medical device that includes:

a rechargeable battery;

a receiving coil; and

a first controller, wherein the first controller is configured to electrically short the receiving coil to ground repeatedly in response to a determination that the rechargeable battery has been sufficiently charged; and

a charger that charges the implantable medical device, wherein the charger includes:

a charging coil that is inductively coupled to the receiving coil;

a sensor circuit coupled to the charging coil, wherein the sensor circuit is configured to detect an electrical current flowing through the charging coil or a voltage across the charging coil; and

a second controller coupled to the sensor circuit and to the charging coil, wherein the second controller is configured to:

compare an output of the sensor circuit with a predefined pattern; and

based on a match between the output of the sensor circuit and the predefined pattern, communicate a feedback signal to a user of the charger or terminate charging of the implantable medical device.

20. The system of claim 19 , wherein the sensor circuit comprises a transformer, the transformer including:

a primary coil that is coupled to the charging coil in series; and

a secondary coil that is electromagnetically coupled to the primary coil.