Methods and apparatus for providing a sufficiently stable power to a load in an energy transfer system

• US 20020123779A1
• Filed: 05/01/2002
• Published: 09/05/2002
• Est. Priority Date: 10/19/1999
• Status: Active Grant

• Current Assignee: Abiomed, Inc. (Johnson & Johnson)
• Original Assignee: Abiomed, Inc. (Johnson & Johnson)
• Inventors: Zarinetchi, Farhad, Keville, Stephen J.
• Granted Patent: US 7,155,291 B2
• Time in Patent Office: Days
• US Class Current: 607/60
• CPC Class Codes: A61M 2205/8243 by induction
• CPC Class Codes: A61M 60/165 implantable in, on, or around the heart
• CPC Class Codes: A61M 60/178 drawing blood from a ventricle and returning the blood to the arterial system via a cannula external to the ventricle, e.g. left or right ventricular assist devices
• CPC Class Codes: A61M 60/196 replacing the entire heart, e.g. total artificial hearts [TAH]
• CPC Class Codes: A61M 60/216 including a rotating member acting on the blood, e.g. impeller
• CPC Class Codes: A61M 60/873 specially adapted for wireless or transcutaneous energy transfer [TET], e.g. inductive charging
• CPC Class Codes: A61N 1/00 Electrotherapy; Circuits therefor A61N2/00 takes precedence; irradiation apparatus A61N5/00
• CPC Class Codes: A61N 1/3787 from an external energy source
• CPC Class Codes: H02J 2310/23 The load being a medical device, a medical implant, or a life supporting device
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/80 involving the exchange of data, concerning supply or distribution of electric power, between transmitting devices and receiving devices
• CPC Class Codes: H02J 50/90 involving detection or optimisation of position, e.g. alignment
• CPC Class Codes: Y10S 323/911 Medical electronics

Abstract

Methods and apparatus for providing a sufficiently stable power to a load in an energy transfer system that transfers energy from one side of a physical boundary to another side of the boundary. In one example, a power supply and a primary winding are located on a first side of a physical boundary (e.g., external to a body), and a secondary winding and the load are located on a second side of the physical boundary (e.g., internal to the body). A primary voltage across the primary winding is regulated so as to provide a sufficiently stable output power to the load notwithstanding changes in the load and/or changes in a relative position of the primary winding and the secondary winding. One aspect of the invention relates to energy transfer methods and apparatus for use in connection with the human body. In particular, one example of the invention includes a transcutaneous energy transfer (TET) system for transferring power from a power supply external to the body to a device implanted in the body.

Claims

1. An apparatus for use in a transcutaneous energy transfer system that includes a power supply, a primary winding and a secondary winding, the apparatus comprising:

a control circuit, coupled to the power supply and the primary winding, to monitor a primary amplitude of a primary voltage across the primary winding and to control the primary amplitude based only on the monitored primary amplitude and a reference voltage.

2. The apparatus of claim 1, in combination with the primary winding.

3. The combination of claim 2, further including the secondary winding.

4. The apparatus of claim 1, wherein the control circuit regulates the primary amplitude such that the primary voltage has essentially a constant frequency.

5. The apparatus of claim 1, wherein the reference voltage is fixed during normal operation of the energy transfer system.

6. The apparatus of claim 1, wherein the control circuit includes:

at least one capacitor coupled to the primary winding to form a primary resonant circuit with the primary winding;

an excitation circuit coupled to the power supply and the primary resonant circuit to provide power to the primary resonant circuit; and

an excitation control circuit coupled to the excitation circuit and the primary winding to control the excitation circuit based only on the monitored primary amplitude and the reference voltage.

7. The apparatus of claim 6, wherein:

the excitation circuit outputs pulses to the primary resonant circuit to provide the power to the primary resonant circuit; and

the excitation control circuit controls a width of the pulses output by the excitation circuit such that the primary amplitude is approximately equal to a predetermined amplitude that is proportional to the reference voltage.

8. The apparatus of claim 7, in combination with the primary winding.

9. The combination of claim 8, further including the secondary winding.

10. The apparatus of claim 1, wherein the reference voltage varies based on the primary amplitude during normal operation of the energy transfer system.

11. The apparatus of claim 10, wherein the reference voltage varies based on surges in the monitored primary amplitude during the normal operation of the energy transfer system.

12. The apparatus of claim 11, wherein the control circuit includes:

a reference control circuit to control the varying reference voltage based on the surges in the monitored primary amplitude.

13. The apparatus of claim 12, wherein the reference control circuit includes:

a surge detector to detect the surges in the monitored primary amplitude;

a timer circuit coupled to the surge detector; and

an output circuit coupled to the timer circuit,

wherein the timer circuit controls the output circuit to output the varying reference voltage based on the detected surges in the monitored primary amplitude.

14. The apparatus of claim 13, wherein the timer circuit controls the output circuit such that the output circuit outputs the varying reference voltage as an essentially triangular waveform.

15. The apparatus of claim 13, wherein the timer circuit controls the output circuit such that the output circuit outputs the varying reference voltage as an essentially saw-tooth waveform.

16. The apparatus of claim 13, wherein the control circuit further includes:

at least one capacitor coupled to the primary winding to form a primary resonant circuit with the primary winding;

an excitation circuit coupled to at least the power supply and the primary resonant circuit to provide power to the primary resonant circuit; and

an excitation control circuit, coupled to the excitation circuit, the primary winding, and the reference control circuit, to control the excitation circuit based only on the monitored primary amplitude and the varying reference voltage.

17. The apparatus of claim 16, wherein:

the excitation circuit outputs pulses to the primary resonant circuit to provide the power to the primary resonant circuit; and

the excitation control circuit controls a width of the pulses output by the excitation circuit such that the primary amplitude is approximately equal to a predetermined amplitude that is proportional to the varying reference voltage.

18. The apparatus of claim 16, wherein the surge detector is coupled to the excitation circuit so as to control the power provided by the excitation circuit to the primary resonant circuit based on at least the detected surges in the monitored primary amplitude.

19. The apparatus of claim 18, in combination with the primary winding.

20. The combination of claim 19, further including the secondary winding.

21. In a transcutaneous energy transfer system including a power supply, a primary winding and a secondary winding, a method comprising acts of:

monitoring a primary amplitude of a primary voltage across the primary winding; and

regulating the primary amplitude based only on the monitored primary amplitude and a reference voltage.

22. The method of claim 21, wherein the act of regulating includes an act of maintaining an essentially constant frequency of the primary voltage.

23. The method of claim 21, wherein the act of regulating includes an act of comparing a sample of the monitored primary amplitude to a fixed reference voltage. the sample being proportional to the monitored primary amplitude.

24. The method of claim 21, wherein the energy transfer system further includes at least one capacitor coupled to the primary winding to form a primary resonant circuit with the primary winding, and wherein the act of regulating the primary amplitude includes an act of controlling power provided to the primary resonant circuit based only on the monitored primary amplitude and the reference voltage.

25. The method of claim 24, wherein the act of controlling power includes an act of controlling a width of pulses provided to the primary resonant circuit such that the primary amplitude is approximately equal to a predetermined amplitude that is proportional to the reference voltage.

26. The method of claim 21, wherein the act of regulating includes an act of making a comparison of a sample of the monitored primary amplitude and a varying reference voltage, the sample being proportional to the monitored primary amplitude.

27. The method of claim 26, wherein the act of making a comparison includes an act of generating the varying reference voltage based on surges in the monitored primary amplitude during normal operation of the energy transfer system.

28. The method of claim 27, wherein the act of generating the varying reference voltage includes an act of generating the varying reference voltage as an essentially triangular waveform based on the surges in the monitored primary amplitude.

29. The method of claim 27, wherein the act of generating the varying reference voltage includes an act of generating the varying reference voltage as an essentially triangular waveform based on the surges in the monitored primary amplitude.

30. The method of claim 27, wherein the energy transfer system further includes at least one capacitor coupled to the primary winding to form a primary resonant circuit with the primary winding, and wherein the act of regulating the primary amplitude further includes act of controlling power provided to the primary resonant circuit based on at least the comparison.

31. The method of claim 30, wherein the act of controlling power includes an act of controlling a width of pulses provided to the primary resonant circuit such that the primary amplitude is approximately equal to a predetermined amplitude that is proportional to the varying reference voltage.

32. The method of claim 30, wherein the act of controlling power includes an act of controlling the power based on the comparison and the surges in the monitored primary amplitude.

33. An energy transfer system for transferring power from a power supply located on a first side of a physical boundary to a variable load located on a second side of the physical boundary, the energy transfer system comprising:

a primary winding electrically coupled to the power supply to generate a magnetic field based on input power provided by the power supply, the magnetic field permeating the physical boundary;

a secondary winding, magnetically coupled to the primary winding via the magnetic field, to receive at least a portion of the magnetic field, the secondary winding electrically coupled to the variable load to provide output power to the variable load based on the received magnetic field; and

at least one control circuit, electrically coupled to at least the primary winding, to regulate a primary voltage across the primary winding such that a sufficiently stable output power is provided to the variable load notwithstanding at least one of changes in the load and changes in a relative position of the primary winding and the secondary winding.

34. The system of claim 33, wherein the at least one control circuit regulates a load voltage across the variable load based on at least one of the changes in the variable load and the changes in the relative position of the primary winding and the secondary winding.

35. The system of claim 33, wherein the at least one control circuit regulates the primary voltage based on at least one of the changes in the load and the changes in the relative position of the primary winding and the secondary winding.

36. The system of claim 35, wherein:

the power is transferred from the power supply to the variable load via a power channel, wherein the magnetic field that couples the primary and secondary windings forms a portion of the power channel; and

the at least one control circuit obtains information related to at least one of the changes in the variable load and the changes in the relative position of the primary winding and the secondary winding via the power channel.

37. The system of claim 36, wherein the power channel has essentially a constant frequency.

38. The system of claim 33, wherein the at least one control circuit includes:

at least one capacitor coupled to the primary winding to form a primary resonant circuit with the primary winding;

an excitation circuit coupled to at least the power supply and the primary resonant circuit to provide the input power to the primary resonant circuit; and

an excitation control circuit coupled to the excitation circuit and the primary winding to control the excitation circuit so as to regulate the primary voltage.

39. The system of claim 38, wherein the excitation control circuit controls the excitation circuit based on a comparison of a reference voltage and a primary amplitude of the primary voltage.

40. The system of claim 39, wherein:

the excitation circuit outputs pulses to the primary resonant circuit to provide the input power to the primary resonant circuit; and

the excitation control circuit controls a width of the pulses output by the excitation circuit such that the primary amplitude is approximately equal to a predetermined amplitude that is proportional to the reference voltage.

41. The system of claim 33, wherein the power is transferred from the power supply to the variable load via a power channel, wherein the magnetic field that couples the primary and secondary windings forms a portion of the power channel, and wherein the at least one control circuit includes:

a first control circuit electrically coupled to the primary winding to regulate the primary voltage based on at least one of the changes in the variable load and the changes in the relative position of the primary winding and the secondary winding; and

a second control circuit electrically coupled to the secondary winding to provide a detectable indication on the power channel that indicates when a load voltage across the variable load exceeds a predetermined threshold load voltage.

42. The system of claim 41, wherein the first control circuit regulates the primary voltage based on the detectable indication.

43. The system of claim 42, wherein the first control circuit regulates the primary voltage such that the load voltage approximates the predetermined threshold load voltage notwithstanding at least one of the changes in the variable load and changes in the relative position of the primary winding and the secondary winding.

44. The system of claim 42, wherein the first control circuit includes a detector circuit coupled to the primary winding to detect the detectable indication on the power channel.

45. The system of claim 44, wherein the first control circuit increases a primary amplitude of the primary voltage if the detector circuit does not detect the detectable indication and decreases the primary amplitude if the detector circuit detects the detectable indication.

46. The system of claim 44, wherein:

the detectable indication includes at least one surge in the primary amplitude; and

the detector circuit includes a surge detector.

47. The system of claim 46, wherein the second control circuit includes:

a comparator to make a comparison of the load voltage to the predetermined threshold load voltage; and

a surge generator coupled to the comparator to generate the at least one surge based on the comparison.

48. The system of claim 47, wherein the surge generator includes a shunt circuit that diverts the output power provided by the secondary winding away from the variable load when an input signal to the shunt circuit reaches a shunt activation level, the comparator providing the input signal having the shunt activation level when the load voltage exceeds the predetermined threshold load voltage.

49. The system of claim 48, wherein the first control circuit regulates the primary voltage such that the input signal to the shunt circuit approximates and substantially remains below the shunt activation level.

50. The system of claim 48, wherein the first control circuit regulates the primary voltage such that the shunt circuit has a duty cycle of less than approximately 1%.

51. The system of claim 46, wherein the first control circuit regulates the primary voltage based on a varying reference voltage that is derived from the detectable indication.

52. The system of claim 51, wherein the first control circuit includes a reference control circuit to generate the varying reference voltage, the reference control circuit including:

the detector circuit to detect the detectable indication on the power channel and to provide a detected indication signal;

a timer circuit coupled to the detector circuit to receive the detected indication signal; and

an output circuit coupled to the timer circuit,

wherein the timer circuit controls the output circuit to output the varying reference voltage based on the detected indication signal.

53. The system of claim 52, wherein the timer circuit controls the output circuit such that the output circuit outputs the varying reference voltage as an essentially tri angular waveform.

54. The system of claim 52, wherein the timer circuit controls the output circuit such that the output circuit outputs the varying reference voltage as an essentially saw-tooth waveform.

55. The system of claim 52, wherein the varying reference voltage has a frequency in a range of from approximately 5 Hz to approximately 40 Hz.

56. The system of claim 52, wherein the first control circuit further includes:

at least one capacitor coupled to the primary winding to form a primary resonant circuit with the primary winding;

an excitation circuit coupled to at least the power supply and the primary resonant circuit to provide the input power to the primary resonant circuit; and

an excitation control circuit, coupled to the excitation circuit, the primary winding, and the reference control circuit, to control the excitation circuit based on the primary voltage and the varying reference voltage.

57. The system of claim 56, wherein:

the excitation circuit outputs pulses to the primary resonant circuit to provide the input power to the primary resonant circuit; and

the excitation control circuit controls a width of the pulses output by the excitation circuit such that a primary amplitude of the primary voltage is approximately equal to a predetermined amplitude that is proportional to the varying reference voltage.

58. The system of claim 57, wherein the detector circuit is coupled to the excitation circuit so as to control the input power provided by the excitation circuit to the primary resonant circuit based on at least the detectable indication.

59. The system of claim 58, wherein:

the detectable indication includes at least one surge in the primary amplitude; and

the detector circuit includes a surge detector.

60. The system of claim 59, wherein the second control circuit includes:

a comparator to make a comparison of the load voltage to the predetermined threshold load voltage; and

a surge generator coupled to the comparator to generate the at least one surge based on the comparison.

61. The system of claim 60, wherein the surge generator includes a shunt circuit that diverts the output power provided by the secondary winding away from the variable load when an input signal to the shunt circuit reaches a shunt activation level, the comparator providing the input signal having the shunt activation level when the load voltage exceeds the predetermined threshold load voltage.

62. The system of claim 61, wherein the first control circuit regulates the primary voltage such that the input signal to the shunt circuit approximates and substantially remains below the shunt activation level.

63. The system of claim 61, wherein the first control circuit regulates the primary voltage such that the shunt circuit has a duty cycle of less than approximately 1%.

64. In an energy transfer system that includes a primary winding electrically coupled to a power supply located on a first side of a physical boundary, the energy transfer system further including a secondary winding electrically coupled to a variable load located on a second side of the physical boundary, a method of transferring power from the power supply to the variable load comprising an act of:

regulating a primary voltage across the primary winding so as to provide a sufficiently stable output power to the variable load notwithstanding at least one of changes in the variable load and changes in a relative position of the primary winding and the secondary winding.

65. The method of claim 64, wherein the act of regulating a primary voltage includes an act of regulating the primary voltage based on at least one of the changes in the variable load and the changes in the relative position of the primary winding and the secondary winding.

66. The method of claim 65, wherein the power is transferred from the power supply to the variable load via a power channel, wherein a magnetic field that couples the primary and secondary windings forms a portion of the power channel, and wherein the act of regulating includes an act of:

obtaining information related to at least one of the changes in the variable load and the changes in the relative position of the primary winding and the secondary winding via the power channel.

67. The method of claim 66, wherein the power channel has essentially a constant frequency.

68. The method of claim 64, wherein the act of regulating includes an act of regulating the primary voltage based on a comparison of a reference voltage and the primary voltage.

69. The method of claim 68, wherein the energy system further includes at least one capacitor coupled to the primary winding to form a primary resonant circuit, and wherein the act of regulating includes an act of:

controlling a width of pulses input to the primary resonant circuit so as to regulate the input power to the primary resonant circuit.

70. The method of claim 69, wherein the act of controlling a width of pulses includes an act of controlling the width of the pulses such that a primary amplitude of the primary voltage is approximately equal to a predetermined amplitude that is proportional to the reference voltage.

71. The method of claim 64, wherein the power is transferred from the power supply to the variable load via a power channel, wherein a magnetic field that couples the primary and secondary windings forms a portion of the power channel, and wherein the method further includes an act of:

generating a detectable indication on the power channel that indicates when a load voltage across the variable load exceeds a predetermined threshold load voltage.

72. The method of claim 71, wherein the act of regulating includes an act of regulating the primary voltage based on the detectable indication.

73. The method of claim 72, wherein the act of regulating includes an act of regulating the primary voltage such that the load voltage approximates the predetermined threshold load voltage notwithstanding at least one of the changes in the variable load and the changes in the relative position of the primary winding and the secondary winding.

74. The method of claim 72, further including an act of detecting the detectable indication on the power channel.

75. The method of claim 74, wherein the act of regulating includes acts of:

increasing a primary amplitude of the primary voltage if the detector circuit does not detect the detectable indication; and

decreasing the primary amplitude if the detector circuit detects the detectable indication.

76. The method of claim 75, wherein:

the act of generating a detectable indication includes an act of generating at least one surge in the primary amplitude; and

the act of detecting the detectable indication includes an act of detecting the at least one surge in the primary amplitude.

77. The method of claim 76, wherein the act of generating at least one surge includes acts of:

making a comparison of the load voltage to the predetermined threshold load voltage; and

generating the at least one surge based on the comparison.

78. The method of claim 77, wherein the act of generating the at least one surge based on the comparison includes acts of:

diverting the output power provided by the secondary winding away from the variable load when an activation signal is generated; and

generating the activation signal when the load voltage exceeds the predetermined threshold load voltage.

79. The method of claim 78, wherein the act of regulating the primary voltage includes an act of regulating the primary voltage such that the load voltage approximates and substantially remains below the predetermined threshold load voltage.

80. The method of claim 78, wherein the act of regulating includes an act of regulating the primary voltage such that the activation signal has a duty cycle of less than approximately 1%.

81. The method of claim 73, wherein the act of regulating the primary voltage includes an acts of:

generating a varying reference voltage based on the detectable indication; and

regulating the primary voltage based on the varying reference voltage.

82. The method of claim 81, wherein the act of generating the varying reference voltage includes an act of generating the varying reference voltage as an essentially triangular waveform.

83. The method of claim 81, wherein the act of generating the varying reference voltage includes an act of generating the varying reference voltage as an essentially saw-tooth waveform.

84. The method of claim 81, wherein the act of generating the varying reference voltage includes an act of generating the varying reference voltage such that the varying reference voltage has a frequency in a range of from approximately 5 Hz to approximately 40 Hz.

85. The method of claim 81, wherein the energy system further includes at least one capacitor coupled to the primary winding to form a primary resonant circuit, and wherein the act of regulating includes an act of:

controlling a width of pulses input to the primary resonant circuit so as to control the input power to the primary resonant circuit based on at least the varying reference voltage.

86. The method of claim 85, wherein the act of controlling a width of pulses includes an act of controlling the width of the pulses such that the primary amplitude is approximately equal to a predetermined amplitude that is proportional to the varying reference voltage.

87. The method of claim 86, wherein the act of controlling the input power includes an act of regulating the primary amplitude based on at least the detectable indication.

88. The method of claim 87, wherein:

the act of generating a detectable indication includes an act of generating at least one surge in the primary amplitude; and

the act of detecting the detectable indication includes an act of detecting the at least one surge in the primary amplitude.

89. The method of claim 88, wherein the act of generating at least one surge includes acts of:

making a comparison of the load voltage to the predetermined threshold load voltage; and

generating the at least one surge based on the comparison.

90. The method of claim 89, wherein the act of generating the at least one surge based on the comparison includes acts of:

diverting the output power provided by the secondary winding away from the variable load when an activation signal is generated; and

generating the activation signal when the load voltage exceeds the predetermined threshold load voltage.

91. The method of claim 90, wherein the act of regulating the primary amplitude includes an act of regulating the primary amplitude such that the load voltage approximates and substantially remains below the predetermined threshold load voltage.

92. The method of claim 90, wherein the act of regulating includes an act of regulating the primary amplitude such that the activation signal has a duty cycle of less than approximately 1%.

93. An apparatus for use in an energy transfer system, the energy transfer system including a power supply electrically coupled to a primary winding, and a secondary winding magnetically coupled to the primary winding, the primary and secondary windings for transferring power from the power supply to a load that is electrically coupled to the secondary winding, the primary winding and the secondary winding not having a fixed spatial relationship to each other, the apparatus comprising:

a secondary circuit, electrically coupled to the secondary winding, to monitor a measurable quantity associated with the load and to provide a detectable indication based on the monitored measurable quantity; and

a primary circuit, electrically coupled to the primary winding, to monitor the detectable indication provided by the secondary circuit and to regulate a primary voltage across the primary winding based on the detectable indication so as to regulate a load voltage across the load.

94. The apparatus of claim 93, wherein the primary circuit regulates the primary voltage such that the secondary circuit has a relatively small activation duty cycle to provide the detectable indication, so as to reduce a power dissipation in the secondary circuit.

95. The apparatus of claim 94, wherein the primary circuit regulates the primary voltage such that the secondary circuit has an activation time of less than approximately 100 microseconds.

96. The apparatus of claim 95, wherein the primary circuit regulates the primary voltage such that the secondary circuit has an activation cycle in a range of from approximately 2 milliseconds to 3 milliseconds between consecutive activations of the secondary circuit to provide the detectable indication.

97. The apparatus of claim 94, wherein the primary circuit regulates the primary voltage such that activation duty cycle of the secondary circuit is less than approximately 1%.

98. The apparatus of claim 94, wherein the primary circuit regulates the primary voltage such that the activation duty cycle of the secondary circuit is less than approximately 0.5%.

99. The apparatus of claim 94, wherein the primary circuit regulates the primary voltage such that the activation duty cycle of the secondary circuit is less than approximately 0.1%.

100. The apparatus of claim 93, wherein the secondary circuit is activated to provide the detectable indication when the measurable quantity associated with the load exceeds a predetermined threshold level.

101. The apparatus of claim 100, wherein the primary circuit regulates the primary voltage such that the measurable quantity approximates and substantially remains below the predetermined threshold level.

102. The apparatus of claim 101, in combination with the primary winding and the secondary winding.

103. The apparatus of claim 101, wherein the power is transferred from the power supply to the load via a power channel, wherein a magnetic field that couples the primary and secondary windings forms a portion of the power channel, and wherein the secondary circuit generates the detectable indication on the power channel that indicates when the measurable quantity exceeds the predetermined threshold level.

104. The apparatus of claim 103, wherein the primary circuit monitors the power channel and regulates the primary voltage based on the detectable indication.

105. The apparatus of claim 104, wherein the primary circuit regulates the primary voltage such that the measurable quantity approximates and substantially remains below the predetermined threshold level notwithstanding at least one of variations in the load and variations in a relative position of the primary winding and the secondary winding.

106. The apparatus of claim 105, wherein the primary circuit includes a detector circuit coupled to the primary winding to detect the detectable indication on the power channel.

107. The apparatus of claim 106, wherein the primary circuit increases a primary amplitude of the primary voltage if the detector circuit does not detect the detectable indication and decreases the primary amplitude if the detector circuit detects the detectable indication.

108. The apparatus of claim 106, wherein:

the detectable indication includes at least one surge in the primary voltage; and

the detector circuit includes a surge detector.

109. The apparatus of claim 108, wherein the secondary circuit includes:

a comparator to make a comparison of the measurable quantity and the predetermined threshold level; and

a surge generator coupled to the comparator to generate the at least one surge based on the comparison.

110. The apparatus of claim 109, wherein the surge generator includes a shunt circuit that diverts the output power provided by the secondary winding away from the load when an input signal to the shunt circuit reaches a shunt activation level, the comparator providing the input signal having the shunt activation level when the measurable quantity exceeds the predetermined threshold level.

111. The apparatus of claim 110, wherein the primary circuit regulates the primary voltage such that the input signal to the shunt circuit approximates and substantially remains below the shunt activation level.

113. The method of claim 112, wherein the act of regulating includes an act of regulating the primary voltage such that the secondary circuit has a relatively small activation duty cycle to provide the detectable indication, so as to reduce a power dissipation in the secondary circuit.

114. The method of claim 113, wherein the act of regulating the primary voltage includes an act of regulating the primary voltage such that the secondary circuit has an activation time of less than approximately 100 microseconds.

115. The method of claim 113, wherein the act of regulating the primary voltage includes an act of regulating the primary voltage such that the secondary circuit has an activation duty cycle of less than approximately 1%.

116. The method of claim 113, wherein the act of regulating the primary voltage includes an act of regulating the primary voltage such that the secondary circuit has an activation duty cycle of less than approximately 0.5%.

117. The method of claim 113, wherein the act of regulating the primary voltage includes an act of regulating the primary voltage such that the secondary circuit has an activation duty cycle of less than approximately 0.1%.

118. The method of claim 112, wherein the act of activating a secondary circuit to provide a detectable indication based on the comparison includes an act of activating the secondary circuit to provide the detectable indication when the measurable quantity associated with the load exceeds a predetermined threshold level.

119. The method of claim 118, wherein the act of regulating a primary voltage includes an act of regulating the primary voltage such that the measurable quantity approximates and substantially remains below the predetermined threshold level.

120. The method of claim 119, wherein the act of regulating the primary voltage includes an act of regulating the primary voltage such that the measurable quantity approximates and substantially remains below the predetermined threshold level notwithstanding at least one of changes in the load and changes in a relative position of the primary winding and the secondary winding.

121. The method of claim 119, wherein the power is transferred from the power supply to the load via a power channel, wherein a magnetic field that couples the primary and secondary windings forms a portion of the power channel, and wherein the method further includes an act of:

generating the detectable indication on the power channel that indicates when the measurable quantity exceeds the predetermined threshold level.

122. The method of claim 121, wherein the act of regulating the primary voltage includes acts of:

monitoring the power channel;

detecting the detectable indication; and

regulating the primary voltage based on the detected indication.

123. The method of claim 122, wherein the act of regulating includes acts of:

increasing a primary amplitude of the primary voltage if the detector circuit does not detect the detectable indication; and

decreasing the primary amplitude if the detector circuit detects the detectable indication.

124. The method of claim 123, wherein:

the act of generating the detectable indication includes an act of generating at least one surge in the primary amplitude; and

the act of detecting the detectable indication includes an act of detecting the at least one surge in the primary amplitude.

125. The method of claim 124, wherein the act of generating at least one surge includes acts of:

making a comparison of the load voltage to the predetermined threshold load voltage; and

generating the at least one surge based on the comparison.

126. The method of claim 125, wherein the act of generating the at least one surge based on the comparison includes acts of:

diverting the output power provided by the secondary winding away from the load when an activation signal is generated; and

generating the activation signal when the measurable quantity exceeds the predetermined threshold level.

128. The system of claim 127, further including a second control circuit, electrically coupled to the secondary winding, to encode the power channel with at least some of the information.

129. The system of claim 128, wherein the second control circuit encodes the power channel with information related to a proximity of the load voltage across the variable load to a predetermined threshold load voltage.

130. The system of claim 129, wherein the first control circuit regulates a primary amplitude of a primary voltage across the primary winding based on the information obtained via the power channel such that the load voltage approximates the predetermined threshold load voltage.

131. The system of claim 127, wherein the power channel has essentially a constant frequency.

132. The system of claim 131, wherein the frequency of the power channel is approximately 300 kHz.

134. The method of claim 133, further including an act of encoding the power channel with at least some of the information.

135. The method of claim 134, wherein the act of encoding includes an act of encoding the power channel with information related to a proximity of the load voltage across the variable load to a predetermined threshold load voltage.

136. The method of claim 135, wherein the act of regulating the load voltage includes an act of regulating a primary amplitude of a primary voltage across the primary winding based on the information obtained via the power channel such that the load voltage approximates the predetermined threshold load voltage.

137. The method of claim 133, wherein the power channel has essentially a constant frequency.

138. The method of claim 137, wherein the frequency of the power channel is approximately 300 kHz.

112. In a transcutaneous energy transfer system that includes a power supply electrically coupled to a primary winding and a secondary winding magnetically coupled to the primary winding, the primary and secondary windings for transferring power from the power supply to a load that is electrically coupled to the secondary winding, the primary winding and the secondary winding not having a fixed spatial relationship to each other, a method comprising acts of:

making a comparison of a measurable quantity associated with the load and a predetermined threshold level;

activating a secondary circuit to provide a detectable indication based on the comparison; and

regulating a primary voltage across the primary winding based on the detectable indication.

127. An energy transfer system for transferring power from a power supply located on a first side of a physical boundary to a variable load located on a second side of the physical boundary, the energy transfer system comprising:

a primary winding electrically coupled to the power supply to generate a magnetic field based on input power provided by the power supply;

a secondary winding magnetically coupled to the primary winding to receive at least a portion of the magnetic field generated by the primary winding, the secondary winding providing output power to the variable load based on the received magnetic field, the magnetic field forming a portion of a power channel between the primary winding and the secondary winding to transfer at least some of the power from the power supply to the variable load; and

a first control circuit, electrically coupled to the primary winding, to regulate a load voltage across the variable load based on information related to the variable load that is obtained via the power channel.

133. In an energy transfer system for transferring power from a power supply located on a first side of a physical boundary to a variable load located on a second side of the physical boundary, the energy transfer system including a primary winding electrically coupled to the power supply to generate a magnetic field based on input power provided by the power supply, the energy transfer system further including a secondary winding magnetically coupled to the primary winding to receive at least a portion of the magnetic field generated by the primary winding, the secondary winding providing output power to the variable load based on the received magnetic field, the magnetic field forming a portion of a power channel between the primary winding and the secondary winding to transfer at least some of the power from the power supply to the variable load, a method comprising acts of:

monitoring the power channel to obtain information related to the variable load; and

regulating a load voltage across the variable load based on the information obtained via the power channel.