Three stage power source for electric ARC welding

1. A three stage power source for an electric arc welding process, said power source comprising an input stage having an AC input and a first fixed DC output signal; a second stage in the form of an unregulated DC to DC converter having an input connected to said first fixed DC output signal, a network of switches switched at a high frequency with a given duty cycle to convert said input into a first internal AC signal, an isolation transformer with a primary winding driven by said first internal high frequency AC signal and a secondary winding for creating a second internal high frequency AC signal and a rectifier to convert said second internal AC signal into a second fixed DC output signal of said second stage; with a magnitude related to said duty cycle of said switches; and a third stage to convert said second fixed DC output signal to a welding output for welding wherein said input stage has a regulated DC to DC converter including a boost converter having a main inductance, a main rectifier, and a power switch having an active soft switching circuit, said active soft switching circuit of said input stage comprising:

an auxiliary switching device and a tank circuit closed by said auxiliary switching device, said tank circuit comprising a resonant inductance coupled in series with said auxiliary switching device, and a resonant capacitance coupled in parallel with said power switch, said resonant capacitance having a first resonant capacitor portion coupled in parallel with said resonant inductance and a second resonant capacitor portion coupled in parallel with said auxiliary switching device.

2. A three stage power source as defined in claim 1 wherein said regulated DC to DC converter is a power factor correcting converter.

3. A three stage power source as defined in claim 1 wherein said regulated DC to DC converter is said boost converter.

4. A three stage power source as defined in claim 1 wherein said tank circuit is activated by said auxiliary switch.

5. A three stage power source as defined in claim 1 wherein said auxiliary switch is operated in unison with said power switch.

6. A three stage power source as defined in claim 1 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

7. A three stage power source as defined in claim 1 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

8. A three stage power source as defined in claim 1 , wherein said given duty cycle is adjustable.

9. A three stage power source as defined in claim 2 wherein said regulated DC to DC power factor correcting converter includes said boost converter.

10. A three stage power source as defined in claim 2 wherein said tank circuit is activated by said auxiliary switch.

11. A three stage power source as defined in claim 2 wherein said auxiliary switch is operated in unison with said power switch.

12. A three stage power source as defined in claim 2 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

13. A three stage power source as defined in claim 2 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

14. A three stage power source as defined in claim 3 wherein said auxiliary switch operated in u nison with said power switch.

15. A three stage power source as defined in claim 3 wherein said tank circuit is activated by said auxiliary switch.

16. A three stage power source as defined in claim 3 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

17. A three stage power source as defined in claim 3 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

18. A three stage power source as defined in claim 5 wherein said main rectifier is a boost diode soft switched by said soft switching circuit.

19. A three stage power source as defined in claim 5 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

20. A three stage power source as defined in claim 5 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

21. A three stage power source as defined in claim 5 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

22. A three stage power source as defined in claim 9 wherein said tank circuit is activated by said auxiliary switch.

23. A three stage power source as defined in claim 9 wherein said auxiliary switch is operated in unison with said power switch.

24. A three stage power source as defined in claim 9 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

25. A three stage power source as defined in claim 9 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

26. A three stage power source as defined in claim 11 wherein said main rectifier is a boost diode soft switched by said soft switching circuit.

27. A three stage power source as defined in claim 11 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

28. A three stage power source as defined in claim 11 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

29. A three stage power source as defined in claim 11 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

30. A three stage power source as defined in claim 14 wherein said main rectifier is a boost diode soft switched by said soft switching circuit.

31. A three stage power source as defined in claim 14 wherein said tank circuit closed is activated by said auxiliary switch.

32. A three stage power source as defined in claim 14 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

33. A three stage power source as defined in claim 14 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

34. A three stage power source as defined in claim 14 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

35. A three stage power source as defined in claim 18 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

36. A three stage power source as defined in claim 18 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

37. A three stage power source as defined in claim 18 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

38. A three stage power source as defined in claim 23 wherein said main rectifier is a boost diode soft switched by said soft switching circuit.

39. A three stage power source as defined in claim 23 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

40. A three stage power source as defined in claim 23 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

41. A three stage power source as defined in claim 23 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

42. A three stage power source as defined in claim 26 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

43. A three stage power source as defined in claim 26 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

44. A three stage power source as defined in claim 26 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

45. A three stage power source as defined in claim 30 wherein said tank circuit is activated by said auxiliary switch.

46. A three stage power source as defined in claim 30 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

47. A three stage power source as defined in claim 31 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

48. A three stage power source as defined in claim 32 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

49. A three stage power source as defined in claim 32 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

50. A three stage power source as defined in claim 38 wherein said regulated DC to DC converter has a positive and a negative output lead with said resonant capacitance joining said leads and a diode clamping the positive end of said auxiliary switch to said positive output lead.

51. A three stage power source as defined in claim 38 wherein said third stage is a chopper with a power switch having a passive soft switching circuit.

52. A three stage power source as defined in claim 38 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

53. A three stage power source comprising an input first stage having an AC input and a first fixed DC output signal, a second stage in the form of an unregulated DC to DC converter having an input connected to said first fixed DC output signal, a network of switches switched at a high frequency with a given duty cycle to convert said input into a first internal AC signal, an isolation transformer with a primary winding driven by said first internal high frequency AC signal and a secondary winding for creating a second internal AC signal and a rectifier to convert said second internal AC signal into a second fixed DC output signal of said second stage, with the magnitude related to said duty cycle of said switches, wherein said input first stage includes a boost converter having a main inductance, a main rectifier, and a power switch having an active soft switching circuit and a third stage to convert said second fixed DC output signal of said second stage into a current suitable for welding, said active soft switching circuit of said input first stage including:

an auxiliary switching device and a tank circuit closed by said auxiliary switching device, said tank circuit comprising a resonant inductance coupled in series with said auxiliary switching device, and a resonant capacitance coupled in parallel with said power switch, said resonant capacitance having a first resonant capacitor portion coupled in parallel with said resonant inductance and a second resonant capacitor portion coupled in parallel with said auxiliary switching device.

54. A power source as defined in claim 53 wherein said input first stage includes a rectifier and a power factor correcting converter.

55. A power source as defined in claim 53 wherein said power switch is in said boost converter.

56. A power source as defined in claim 53 wherein said auxiliary switch is operated in unison with said power switch.

57. A power source as defined in claim 53 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

58. A power source as defined in claim 54 wherein said power factor correcting converter includes said boost converter operated by said power switch.

59. A power source as defined in claim 54 wherein said auxiliary switch is operated in unison with said power switch.

60. A power source as defined in claim 54 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

61. A power source as defined in claim 55 wherein said auxiliary switch is operated in unison with said power switch.

62. A power source as defined in claim 55 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

63. A power source as defined in claim 56 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

64. A power source, as defined in claim 56 wherein said power switch comprises a main boost switch.

65. A power source as defined in claim 58 wherein said auxiliary switch is operated in unison with said power switch.

66. A power source as defined in claim 58 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

67. A power source as defined in claim 59 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

68. A power source as defined in claim 61 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

69. A power source as defined in claim 64 wherein said second resonant capacitor portion is coupled in parallel with said auxiliary switch by a forward poled diode.

70. A power source as defined in claim 64 wherein said second resonant capacitor portion is substantially less than ½ the capacitance of said first resonant capacitor portion.

71. A power source as defined in claim 65 wherein said given duty cycle is greater than 80% to hold conduction losses of said second stage at a low level.

72. A power source as defined in claim 69 wherein said second resonant capacitor portion is substantially less than ½ the capacitance of said first resonant capacitance capacitor portion.

73. A three stage power source comprising an input first stage having an AC input and a first fixed DC output signal with a DC to DC converter including a boost converter having a main inductance, a main rectifier, and a power switch with an active soft switching circuit, a second stage in the form of an unregulated DC to DC inverter having a plurality of power switches, said plurality of switches operated by a pulse-width-modulated control set at a given duty cycle, and a third stage to convert a second fixed DC output of said unregulated inverter into a current suitable for welding, said active soft switching circuit of said input first stage including an auxiliary switching device and a tank circuit closed by said auxiliary switching device, said tank circuit comprising a resonant inductance coupled in series with said auxiliary switching device, and a resonant capacitance coupled in parallel with said power switch, said resonant capacitance having a first resonant capacitor portion coupled in parallel with said resonant inductance and a second resonant capacitor portion coupled in parallel with said auxiliary switching device.

74. A power source as defined in claim 73 wherein said DC to DC converter is said boost converter.

75. A power source as defined in claim 73 wherein said DC to DC converter is driven by a power factor correcting control.

76. A power source as defined in claim 73 wherein said given duty cycle of said pulse-width-modulated control is greater than 80%.

77. A power source, as defined in claim 73 wherein said power switch comprises a main boost switch.

78. A three stage power source as defined in claim 73 , wherein said pulse-width-modulated control is a phase shift pulse-width-modulated control.

79. An active soft switching circuit as defined in any one of claims 1 , 53 and 73 , wherein the series combination of said resonant inductance and said auxiliary switching device form a first leg of said tank circuit with a first intermediate node between said resonant inductance and said auxiliary switch, wherein said first and second resonant capacitor portions form a second leg of said tank circuit with a second intermediate node between said first and second resonant capacitor portions, and wherein said tank circuit further comprises a first diode coupled between said first and second intermediate nodes and a second diode coupled between said second intermediate node and said cathode of said main rectifier.

80. A power source as defined in claim 74 wherein said DC to DC converter is driven by a power factor correcting control.

81. A power source as defined in claim 74 wherein said given duty cycle of said pulse-width-modulated control is greater than 80%.

82. A power source as defined in claim 75 wherein said given duty cycle of said pulse-width-modulated control is greater than 80%.

83. A three stage power source, as defined in claim 75 wherein said power switch comprises a main boost switch.

84. A power source as defined in claim 76 wherein said duty cycle is greater than 90%.

85. A power source as defined in claim 77 wherein said second resonant capacitor is coupled in parallel with said auxiliary switch by a forward poled diode.

86. A power source as defined in claim 77 wherein said second resonant capacitor portion is substantially less than ½ the capacitance of said first resonant capacitor portion.

87. An active soft switching circuit as defined in claim 79 , wherein said first resonant capacitor portion is larger than said second resonant capacitor portion.

88. The active soft switching circuit as defined in claim 79 , wherein said second resonant capacitor portion controls a rate of increase of a voltage across said auxiliary switching device when said auxiliary switching device is turned off.

89. The active soft switching circuit as defined in claim 79 , wherein said second resonant capacitor portion controls a rate of increase of a voltage across said auxiliary switching device when said auxiliary switching device is turned off.

90. A power source as defined in claim 80 wherein said given duty cycle of said pulse-width-modulated control is greater than 80%.

91. A power source as defined in claim 81 wherein said duty cycle is greater than 90%.

92. A power source as defined in claim 82 wherein said duty cycle is greater than 90%.

93. A power source as defined in claim 83 wherein said second resonant capacitor portion is coupled in parallel with said auxiliary switch by a forward poled diode.

94. A power source as defined in claim 83 wherein said second resonant capacitor portion is substantially less than ½ the capacitance of said first resonant capacitor portion.

95. A power source as defined in claim 85 wherein said second resonant capacitance is substantially less than ½ the capacitance of said first resonant capacitance.

96. The active soft switching circuit as defined in claim 87 , wherein said second resonant capacitor portion controls a rate of increase of a voltage across said auxiliary switching device when said auxiliary switching device is turned off.

97. A power source as defined in claim 90 wherein said duty cycle is greater than 90%.

98. A power source as defined in claim 93 wherein said second resonant capacitor portion is substantially less than ½ the capacitance of said first resonant capacitor portion.