High efficiency power converter

• US 7,564,702 B2
• Filed: 09/14/2007
• Issued: 07/21/2009
• Est. Priority Date: 01/24/1997
• Status: Expired due to Fees

• Current Assignee: SynQor Incorporated
• Original Assignee: SynQor Incorporated
• Inventors: Schlecht, Martin F.
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US11/901,263
• Publication Number:
  US 20080151580A1
• Time in Patent Office: 676 Days
• Field of Search: 363 15- 17, 363/21.06, 363/21.14, 363/56.01, 363/56.02, 363/95, 363/97, 363/98, 363/131, 363/132
• US Class Current: 363/21.06
• CPC Class Codes: H02J 1/102 being switching converters H02J1/108, H02J1/12 take precedence
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: H02M 3/3372 of the parallel type
• CPC Class Codes: H02M 3/3374 with preregulator, e.g. current injected push-pull
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A power converter nearly losslessly delivers energy and recovers energy from capacitors associated with controlled rectifiers in a secondary winding circuit, each controlled rectifier having a parallel uncontrolled rectifier. First and second primary switches in series with first and second primary windings, respectively, are turned on for a fixed duty cycle, each for approximately one half of the switching cycle. Switched transition times are short relative to the on-state and off-state times of the controlled rectifiers. The control inputs to the controlled rectifiers are cross-coupled from opposite secondary transformer windings.

Claims

1. A DC-DC power converter system providing plural regulated DC outputs, each having a regulated voltage, comprising:

a) a DC input providing an input voltage that varies over a range that is more than plus or minus a few percent;

b) a non-regulating isolating step-down converter through which power from the DC input flows first before flowing through any regulation stage, the non-regulating isolating step-down converter providing a non-regulated, isolated DC output having a non-regulated voltage and comprising;

i) at least one transformer that is not driven into saturation, the at least one transformer having plural windings including at least one primary winding and at least one secondary winding;

ii) plural power MOSFET switches in circuit with the at least one primary winding, the plural power MOSFET switches causing power to flow into the at least one primary winding;

iii) control circuitry coupled to the plural MOSFET switches, the control circuitry determining when the power MOSFET switches are turned on and off in a switching cycle at a switching frequency; and

iv) plural controlled rectifiers in circuit with the at least one secondary winding, each having a parallel uncontrolled rectifier, each controlled rectifier being turned on for an on-state time and off for an off-state time in synchronization with a voltage waveform of the at least one primary winding to provide the non-regulated, isolated DC output, the voltage waveform of the at least one primary winding having a fixed duty cycle and transition times which are short relative to the on-state and the off-state times of the controlled rectifiers; and

c) plural non-isolating down-converter switching regulators, each receiving power from the non-regulated, isolated DC output and each providing one of the regulated DC outputs having a regulated voltage.

2. A DC-DC power converter system as claimed in claim 1 wherein the DC input is a rectified source of power.

3. A DC-DC power converter system as claimed in claim 2 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

4. A DC-DC power converter system as claimed in claim 3 further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

5. A DC-DC power converter system as claimed in claim 4 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

6. A DC-DC power converter system as claimed in claim 4 wherein the input voltage is within the range of 36-75 volts.

7. A DC-DC power converter system as claimed in claim 4 wherein the non-regulated voltage of the non-regulated, isolated DC output is associated with the input voltage according to a turns ratio of the at least one transformer.

8. A DC-DC power converter system as claimed in claim 4 wherein the non-regulated voltage of the non-regulated, isolated DC output drops with increasing current flow through the non-regulating isolating step-down converter.

9. A DC-DC power converter system as claimed in claim 4 wherein power flow through the non-regulating isolating step-down converter is substantially uninterrupted.

10. A DC-DC power converter system as claimed in claim 4 wherein each of the at least one transformer has only one primary winding.

11. A DC-DC power converter system as claimed in claim 2 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, and further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

12. A DC-DC power converter system as claimed in claim 1 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

13. A DC-DC power converter as claimed in claim 12 wherein the fixed duty cycle is approximately 50% of the switching cycle.

14. A DC-DC power converter system as claimed in claim 12 wherein the switching frequency is in the range of 100 kHz and above.

15. A DC-DC power converter system as claimed in claim 12 wherein the input voltage is within the range of 36-75 volts.

16. A DC-DC power converter system as claimed in claim 12 wherein the input voltage is about 48 volts.

17. A DC-DC power converter system as claimed in claim 12 wherein the non-regulated voltage of the non-regulated, isolated DC output is associated with the input voltage according to a turns ratio of the at least one transformer.

18. A DC-DC power converter system as claimed in claim 12 wherein the non-regulated voltage of the non-regulated, isolated DC output drops with increasing current flow through the non-regulating isolating step-down converter.

19. A DC-DC power converter system as claimed in claim 12 wherein power flow through the non-regulating isolating step-down converter is substantially uninterrupted.

20. A DC-DC power converter as claimed in claim 12 wherein energy is nearly losslessly delivered to and recovered from capacitors associated with the controlled rectifiers during transition times of the power MOSFET switches.

21. A DC-DC power converter system as claimed in claim 12 wherein each of the at least one transformer has only one primary winding.

22. A DC-DC power converter system as claimed in claim 12 further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

23. A DC-DC power converter system as claimed in claim 12 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

24. A DC-DC power converter system as claimed in claim 1 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, and further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

25. A DC-DC power converter system as claimed in claim 24 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

26. A DC-DC power converter system as claimed in claim 1 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

27. A DC-DC power converter system as claimed in claim 1 comprising plural transformers in the isolating step-down converter, each transformer not driven into saturation, each transformer having at least one primary winding and at least one secondary winding, the switching cycle comprising two substantial portions, a first portion and a second portion, power flowing to the isolated DC output from a first of the plural transformers during the first portion of the switching cycle and from a second of the plural transformers during the second portion of the switching cycle.

28. A DC-DC power converter system providing plural regulated DC outputs, each having a regulated voltage, comprising:

a) a DC input providing an input voltage that varies over a percentage range that is greater than a respective percentage range over which the regulated voltage of each regulated output varies;

b) a non-regulating isolating step-down converter through which power from the DC input flows first before flowing through any regulation stage, the non-regulating isolating step-down converter providing a non-regulated, isolated DC output having a non-regulated voltage and comprising;

i) at least one transformer that is not driven into saturation, the at least one transformer having plural windings including at least one primary winding and at least one secondary winding;

ii) plural power MOSFET switches in circuit with the at least one primary winding, the plural power MOSFET switches causing power to flow into the at least one primary winding;

iii) control circuitry coupled to the plural MOSFET switches, the control circuitry determining when the power MOSFET switches are turned on and off in a switching cycle at a switching frequency; and

iv) plural controlled rectifiers in circuit with the at least one secondary winding, each having a parallel uncontrolled rectifier, each controlled rectifier being turned on for an on-state time and off for an off-state time in synchronization with a voltage waveform of the at least one primary winding to provide the non-regulated, isolated DC output, the voltage waveform of the at least one primary winding having a fixed duty cycle and transition times which are short relative to the on-state and the off-state times of the controlled rectifiers; and

c) plural non-isolating down-converter switching regulators, each receiving power from the non-regulated, isolated DC output and each providing one of the regulated DC outputs having a regulated voltage.

29. A DC-DC power converter system as claimed in claim 28 wherein the DC input is a rectified source of power.

30. A DC-DC power converter system as claimed in claim 29 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

31. A DC-DC power converter system as claimed in claim 30 further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

32. A DC-DC power converter system as claimed in claim 31 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

33. A DC-DC power converter system as claimed in claim 31 wherein the input voltage is within the range of 36-75 volts.

34. A DC-DC power converter system as claimed in claim 31 wherein the non-regulated voltage of the non-regulated, isolated DC output is associated with the input voltage according to a turns ratio of the at least one transformer.

35. A DC-DC power converter system as claimed in claim 31 wherein the non-regulated voltage of the non-regulated, isolated DC output drops with increasing current flow through the non-regulating isolating step-down converter.

36. A DC-DC power converter system as claimed in claim 31 wherein power flow through the non-regulating isolating step-down converter is substantially uninterrupted.

37. A DC-DC power converter system as claimed in claim 31 wherein each of the at least one transformer has only one primary winding.

38. A DC-DC power converter system as claimed in claim 29 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, and further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

39. A DC-DC power converter system as claimed in claim 28 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

40. A DC-DC power converter as claimed in claim 39 wherein the fixed duty cycle is approximately 50% of the switching cycle.

41. A DC-DC power converter system as claimed in claim 39 wherein the switching frequency is in the range of 100 kHz and above.

42. A DC-DC power converter system as claimed in claim 39 wherein the input voltage is within the range of 36-75 volts.

43. A DC-DC power converter system as claimed in claim 39 wherein the input voltage is about 48 volts.

44. A DC-DC power converter system as claimed in claim 39 wherein the non-regulated voltage of the non-regulated, isolated DC output is associated with the input voltage according to a turns ratio of the at least one transformer.

45. A DC-DC power converter system as claimed in claim 39 wherein the non-regulated voltage of the non-regulated, isolated DC output drops with increasing current flow through the non-regulating isolating step-down converter.

46. A DC-DC power converter system as claimed in claim 39 wherein power flow through the non-regulating isolating step-down converter is substantially uninterrupted.

47. A DC-DC power converter as claimed in claim 39 wherein energy is nearly losslessly delivered to and recovered from capacitors associated with the controlled rectifiers during transition times of the power MOSFET switches.

48. A DC-DC power converter system as claimed in claim 39 wherein each of the at least one transformer has only one primary winding.

49. A DC-DC power converter system as claimed in claim 39 further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

50. A DC-DC power converter system as claimed in claim 39 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

51. A DC-DC power converter system as claimed in claim 28 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, and further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

52. A DC-DC power converter system as claimed in claim 51 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

53. A DC-DC power converter system as claimed in claim 28 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

54. A DC-DC power converter system as claimed in claim 28 comprising plural transformers in the isolating step-down converter, each transformer not driven into saturation, each transformer having at least one primary winding and at least one secondary winding, the switching cycle comprising two substantial portions, a first portion and a second portion, power flowing to the isolated DC output from a first of the plural transformers during the first portion of the switching cycle and from a second of the plural transformers during the second portion of the switching cycle.

57. A DC-DC power converter system as claimed in claim 52 further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

58. A DC-DC power converter system as claimed in claim 53 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

59. A DC-DC power converter system as claimed in claim 53 wherein the input voltage is within the range of 36-75 volts.

60. A DC-DC power converter system as claimed in claim 57 wherein the non-regulated voltage of the non-regulated, isolated DC output is associated with the input voltage according to a turns ratio of the at least one transformer.

61. A DC-DC power converter system as claimed in claim 57 wherein the non-regulated voltage of the non-regulated, isolated DC output drops with increasing current flow through the non-regulating isolating step-down converter.

62. A DC-DC power converter system as claimed in claim 57 wherein power flow through the non-regulating isolating step-down converter is substantially uninterrupted.

63. A DC-DC power converter system as claimed in claim 57 wherein each of the at least one transformer has only one primary winding.

55. A DC-DC power converter system providing plural regulated DC outputs, each having a regulated voltage, comprising:

a) a rectified source of power that is a DC input, the DC input providing an input voltage;

b) a non-regulating isolating step-down converter through which power from the DC input flows first before flowing through any regulation stage, the non-regulating isolating step-down converter providing a non-regulated, isolated DC output having a non-regulated voltage and comprising;

i) at least one transformer that is not driven into saturation, the at least one transformer having plural windings including at least one primary winding and at least one secondary winding;

ii) plural power MOSFET switches in circuit with the at least one primary winding, the plural power MOSFET switches causing power to flow into the at least one primary winding;

iii) control circuitry coupled to the plural MOSFET switches, the control circuitry determining when the power MOSFET switches are turned on and off in a switching cycle at a switching frequency; and

iv) plural controlled rectifiers in circuit with the at least one secondary winding, each having a parallel uncontrolled rectifier, each controlled rectifier being turned on for an on-state time and off for an off-state time in synchronization with a voltage waveform of the at least one primary winding to provide the non-regulated, isolated DC output, the voltage waveform of the at least one primary winding having a fixed duty cycle and transition times which are short relative to the on-state and the off-state times of the controlled rectifiers; and

c) plural non-isolating down-converter switching regulators, each receiving power from the non-regulated, isolated DC output and each providing one of the regulated DC outputs having a regulated voltage.

56. A DC-DC power converter system as claimed in claim 55 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

64. A DC-DC power converter system as claimed in claim 56 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

65. A DC-DC power converter system as claimed in claim 55 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, and further comprising a filter inductor directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

66. A DC-DC power converter system as claimed in claim 65 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

67. A DC-DC power converter system as claimed in claim 55 comprising multiple non-regulating isolating step-down converters providing plural non-regulated, isolated DC outputs, there being plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

68. A DC-DC power converter system as claimed in claim 55 comprising plural transformers in the isolating step-down converter, each transformer not driven into saturation, each transformer having at least one primary winding and at least one secondary winding, the switching cycle comprising two substantial portions, a first portion and a second portion, power flowing to the isolated DC output from a first of the plural transformers during the first portion of the switching cycle and from a second of the plural transformers during the second portion of the switching cycle.

69. A DC-DC power converter as claimed in claim 55 wherein the fixed duty cycle is approximately 50% of the switching cycle.

70. A DC-DC power converter system as claimed in claim 55 wherein the switching frequency is in the range of 100 kHz and above.

71. A DC-DC power converter system as claimed in claim 55 wherein the input voltage is within the range of 36-75 volts.

72. A DC-DC power converter system as claimed in claim 55 wherein the input voltage is about 48 volts.

73. A DC-DC power converter system as claimed in claim 55 wherein the non-regulated voltage of the non-regulated, isolated DC output is associated with the input voltage according to a turns ratio of the at least one transformer.

74. A DC-DC power converter system as claimed in claim 55 wherein the non-regulated voltage of the non-regulated, isolated DC output drops with increasing current flow through the non-regulating isolating step-down converter.

75. A DC-DC power converter system as claimed in claim 55 wherein power flow through the non-regulating isolating step-down converter is substantially uninterrupted.

76. A DC-DC power converter as claimed in claim 55 wherein energy is nearly losslessly delivered to and recovered from capacitors associated with the controlled rectifiers during transition times of the power MOSFET switches.

77. A DC-DC power converter system as claimed in claim 55 wherein each of the at least one transformer has only one primary winding.

78. A method of converting power from DC to DC to provide plural regulated DC outputs, each having a regulated voltage, comprising:

a) providing a DC input having an input voltage that varies over a range that is more than plus or minus a few percent;

b) flowing power from the DC input through a non-regulating isolating step-down converter first before any regulation stage, the non-regulating isolating step-down converter providing a non-regulated, isolated DC output having a non-regulated voltage, and in the isolating step-down converter;

i) causing plural power MOSFET switches to be turned on in a switching cycle at a switching frequency to cause power to flow into at least one transformer that is not driven into saturation, the at least one transformer having plural windings including at least one primary winding and at least one secondary winding; and

ii) turning plural controlled rectifiers on for an on-state time and off for an off-state time, the plural controlled rectifiers being in circuit with the at least one secondary winding, each controlled rectifier having a parallel uncontrolled rectifier, the plural controlled rectifiers being turned on and off in synchronization with a voltage waveform of the at least one primary winding to provide the non-regulated, isolated DC output, the voltage waveform of the at least one primary winding having a fixed duty cycle and transition times which are short relative to the on-state and the off-state times of the controlled rectifiers; and

c) applying power from the non-regulated, isolated DC output to plural non-isolating down-converter switching regulators, each providing one of the regulated DC outputs having a regulated voltage.

79. A method as claimed in claim 78 wherein:

the DC input is a rectified source of power;

the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting; and

a filter inductor is directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

80. A method as claimed in claim 78 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

81. A method as claimed in claim 78 wherein power flows through multiple non-regulating isolating step down converters providing plural non-regulated, isolated DC outputs, plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

82. A method of converting power from DC to DC to provide plural regulated DC outputs, each having a regulated voltage, comprising:

a) providing a DC input having an input voltage that varies over a percentage range that is greater than a respective percentage range over which the regulated voltage of each regulated output varies;

b) flowing power from the DC input through a non-regulating isolating step-down converter first before any regulation stage, the non-regulating isolating step-down converter providing a non-regulated, isolated DC output having a non-regulated voltage, and in the isolating step-down converter;

i) causing plural power MOSFET switches to be turned on in a switching cycle at a switching frequency to cause power to flow into at least one transformer that is not driven into saturation, the at least one transformer having plural windings including at least one primary winding and at least one secondary winding; and

ii) turning plural controlled rectifiers on for an on-state time and off for an off-state time, the plural controlled rectifiers being in circuit with the at least one secondary winding, each controlled rectifier having a parallel uncontrolled rectifier, the plural controlled rectifiers being turned on and off in synchronization with a voltage waveform of the at least one primary winding to provide the non-regulated, isolated DC output, the voltage waveform of the at least one primary winding having a fixed duty cycle and transition times which are short relative to the on-state and the off-state times of the controlled rectifiers; and

c) applying power from the non-regulated, isolated DC output to plural non-isolating down-converter switching regulators, each providing one of the regulated DC outputs having a regulated voltage.

83. A method as claimed in claim 82 wherein:

the DC input is a rectified source of power;

the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting; and

a filter inductor is directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

84. A method as claimed in claim 82 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

85. A method as claimed in claim 82 wherein power flows through multiple non-regulating isolating step down converters providing plural non-regulated, isolated DC outputs, plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.

86. A method of converting power from DC to DC to provide plural regulated DC outputs, each having a regulated voltage, comprising:

a) providing a rectified source of power that is a DC input, the DC input having an input voltage;

b) flowing power from the DC input through a non-regulated isolating step-down converter first before any regulation stage, the non-regulating isolating step-down converter providing a non-regulated, isolated DC output having a non-regulated voltage, and in the isolating step-down converter;

i) causing plural power MOSFET switches to be turned on in a switching cycle at a switching frequency to cause power to flow into at least one transformer that is not driven into saturation, the at least one transformer having plural windings including at least one primary winding and at least one secondary winding; and

ii) turning plural controlled rectifiers on for an on-state time and off for an off-state time, the plural controlled rectifiers being in circuit with the at least one secondary winding, each controlled rectifier having a parallel uncontrolled rectifier, the plural controlled rectifiers being turned on and off in synchronization with a voltage waveform of the at least one primary winding to provide the non-regulated, isolated DC output, the voltage waveform of the at least one primary winding having a fixed duty cycle and transition times which are short relative to the on-state and the off-state times of the controlled rectifiers; and

c) applying power from the non-regulated, isolated DC output to plural non-isolating down-converter switching regulators, each providing one of the regulated DC outputs having a regulated voltage.

87. A method as claimed in claim 86 wherein:

the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting; and

a filter inductor is directly connected to plural of the windings of the at least one transformer, all current that flows through the inductor flowing through a first of the plural windings during the first portion of the switching cycle and a second of the plural windings during the second portion of the switching cycle.

88. A method as claimed in claim 86 wherein the switching cycle substantially comprises two substantial portions, a first portion and a second portion, a first controlled rectifier of the plural controlled rectifiers being conductive during the first portion of the switching cycle and a second controlled rectifier of the plural controlled rectifiers being conductive during the second portion of the switching cycle, there being a short time, during a transition between the portions, when the first controlled rectifier and the second controlled rectifier are both off and their corresponding uncontrolled rectifiers are both conducting.

89. A method as claimed in claim 86 wherein power flows through multiple non-regulating isolating step down converters providing plural non-regulated, isolated DC outputs, plural of the non-isolating down-converter switching regulators receiving power from one of the non-regulated, isolated DC outputs.