Alignment indication for transcutaneous energy transfer

1. A system for transcutaneous energy transfer, comprising:

an implantable medical device having componentry for providing a therapeutic output, said implantable medical device having an internal power source and a secondary coil operatively coupled to said internal power source, said implantable medical device adapted to be implanted in a patient;

an external power source having a primary coil, said external power source providing energy to said implantable medical device when said primary coil of said external power source is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current;

wherein said current is compared with a predetermined value associated with an expected alignment between said primary coil and said secondary coil;

wherein said internal power source has an internal impedance and wherein said predetermined value is adjusted as a function of said internal impedance of said internal power source;

wherein said internal impedance of said internal power source increases over time; and

wherein said predetermined value decreases as said internal impedance increases.

2. A system for transcutaneous energy transfer, comprising:

an implantable medical device having componentry for providing a therapeutic output, said implantable medical device having an internal power source and a secondary coil operatively coupled to said internal power source, said implantable medical device adapted to be implanted in a patient;

an external power source having a primary coil, said external power source providing energy to said implantable medical device when said primary coil of said external power source is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current;

wherein said current is compared with a predetermined value associated with an expected alignment between said primary coil and said secondary coil; and

wherein said internal power source has a voltage and wherein said predetermined value is adjusted as a function of said voltage of said internal power source.

3. A system for transcutaneous energy transfer, comprising:

an implantable medical device having componentry for providing a therapeutic output, said implantable medical device having an internal power source and a secondary coil operatively coupled to said internal power source, said implantable medical device adapted to be implanted in a patient;

an external power source having a primary coil, said external power source providing energy to said implantable medical device when said primary coil of said external power source is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current;

wherein said current is compared with a predetermined value associated with an expected alignment between said primary coil and said secondary coil;

wherein said internal power source has an internal impedance and wherein said predetermined value is adjusted as a function of said internal impedance of said internal power source; and

wherein said predetermined value decreases as a voltage of said internal power source decreases.

4. The system as in claim 3 wherein said internal power source is a battery.

5. A system for transcutaneous energy transfer, comprising:

an implantable medical device having componentry for providing a therapeutic output, said implantable medical device having an internal power source and a secondary coil operatively coupled to said internal power source, said implantable medical device adapted to be implanted in a patient;

an external power source having a primary coil, said external power source providing energy to said implantable medical device when said primary coil of said external power source is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current; and

wherein said external power source automatically varies its power output in order to generate a predetermined current in said internal power source.

6. The system as in claim 5 wherein said predetermined current in said internal power source varies as a function of a voltage of said internal power source.

7. The system as in claim 6 wherein said predetermined current in said internal power source declines as said voltage of said internal power source increases during a charging cycle.

8. The system as in claim 5 wherein said predetermined current in said internal power source comprises a maximum amount of current for charging said internal power source.

9. The system as in claim 8 wherein said predetermined current in said internal power source declines over time as an internal impedance of said internal power source increases.

10. An external power system for transcutaneous energy transfer to an implantable medical device having componentry for providing a therapeutic output and a secondary coil operatively coupled to said componentry and an internal power source operatively coupled to said secondary coil and said componentry, said implantable medical device adapted to be implanted in a patient, comprising:

a primary coil providing energy to said implantable medical device when said primary coil is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current generated through said internal power source with a predetermined value associated with an expected alignment between said primary coil and secondary coil;

wherein said internal power source has an internal impedance and wherein said predetermined value is adjusted as a function of said internal impedance of said internal power source;

wherein said internal impedance of said internal power source increases over time; and

wherein said predetermined value decreases as said internal impedance increases.

11. An external power system for transcutaneous energy transfer to an implantable medical device having componentry for providing a therapeutic output, a secondary coil operatively coupled to said componentry and an internal power source operatively coupled to said secondary coil and said componentry, said implantable medical device adapted to be implanted in a patient, comprising:

a primary coil providing energy to said implantable medical device when said primary coil is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current generated through said internal power source with a predetermined value associated with an expected alignment between said primary coil and secondary coil; and

wherein said internal power source has a voltage and wherein said predetermined value is adjusted as a function of said voltage of said internal power source.

12. An external power system for transcutaneous energy transfer to an implantable medical device having componentry for providing a therapeutic output, a secondary coil operatively coupled to said componentry and an internal power source operatively coupled to said secondary coil and said componentry, said implantable medical device adapted to be implanted in a patient, comprising:

a primary coil providing energy to said implantable medical device when said primary coil is placed in proximity of said secondary coil of said implantable medical device and thereby generating a current through said internal power source;

an alignment indicator, operatively coupled to said internal power source, measuring said current and reporting an alignment between said primary coil and said secondary coil based on said current generated through said internal power source with a predetermined value associated with an expected alignment between said primary coil and secondary coil;

wherein said internal power source has an internal impedance and wherein said predetermined value is adjusted as a function of said internal impedance of said internal power source; and

wherein said predetermined value decreases as said voltage of said internal power source decreases.

13. The external power system as in claim 12 wherein said internal power source is a battery.