Power conversion apparatus and methods with reduced current and voltage switching

• US 6,442,047 B1
• Filed: 08/25/2000
• Issued: 08/27/2002
• Est. Priority Date: 10/08/1999
• Status: Expired due to Fees

• Current Assignee: Lambda Electronics, Inc. (TDK Corporation)
• Original Assignee: Lambda Electronics, Inc. (TDK Corporation)
• Inventors: Cohen, Isaac
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/648,837
• Time in Patent Office: 732 Days
• Field of Search: 363/17, 363/16, 363/98, 363/127, 363/132
• US Class Current: 363/17
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• 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 3/3376 with automatic control of output voltage or current
• 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 conversion apparatus, e.g., a DC-to-DC converter, includes a transformer having primary and secondary windings. A first switching circuit has an input port configured to be coupled across a DC power source and an output port coupled to the primary winding of the transformer. A switch control circuit is operatively associated with the switching circuit and causes the switching circuit to alternately apply first and second polarity voltages to the primary winding. A second switching circuit is operative to transfer energy to a load from the secondary winding via a first capacitor responsive to application of the first polarity voltage to the primary winding and to transfer energy to the load from the secondary winding via a second capacitor responsive to application of the second polarity voltage to the primary winding. The first switching circuit may be operated such that switches therein may be operated under reduced current and/or reduced voltage conditions. Related power conversion methods are also discussed.

Claims

1. A power conversion apparatus, comprising:

a transformer having primary and secondary windings;

a first switching circuit having an input port configured to be coupled across a DC power source and an output port coupled to the primary winding of the transformer;

a switch control circuit, operatively associated with the first switching circuit, that causes the first switching circuit to alternately apply first and second polarity voltages to the primary winding;

first and second capacitors;

an output inductor configured to be coupled to a load; and

a second switching circuit coupled to secondary winding, the first and second capacitors and the output inductor and operative to transfer energy to the load from the secondary winding via respective ones of the first capacitor and the second capacitor responsive to respective ones of the application of the first polarity voltage to the primary winding and the application of the second polarity voltage to the primary winding.

2. An apparatus according to claim 1, wherein the first switching circuit comprises at least one switch, and wherein the switch control circuit constrains the at least one switch to operate when current in the at least one switch falls to a predetermined level.

3. An apparatus according to claim 2, wherein the switch control circuit operates the at least one switch responsive to a current through the transformer.

4. An apparatus according to claim 2, wherein the switch control circuit operates the at least one switch responsive to a current through the switch.

5. An apparatus according to claim 2, wherein the switch control circuit estimates a time when current in the at least one switch will reach the predetermined level and operates the at least one switch based on the estimated time.

6. An apparatus according to claim 1:

wherein the first switching circuit comprises first and second half bridges; and

wherein the switch control circuit controls a time delay between operations of the first and second half-bridges.

7. An apparatus according to claim 6, wherein the switch control circuit controls the time delay such that the first and second half-bridges operate under substantially zero current switching conditions.

8. An apparatus according to claim 6, wherein the switch control circuit maintains a fixed time delay between operations of the first and second half-bridges.

9. An apparatus according to claim 6, wherein the switch control circuit varies the time delay responsive to a sensed current.

10. An apparatus according to claim 6, wherein the switch control circuit varies the time delay responsive to an input voltage applied to the first switching circuit.

11. An apparatus according to claim 6, wherein the switching control circuit varies a frequency at which the first and second half-bridges operate responsive to an output voltage applied to the load.

12. An apparatus according to claim 1, wherein the first switching circuit comprises at least one switch, and wherein the switch control circuit constrains the at least one switch to operate when voltage across the at least one switch falls to a predetermined level.

13. An apparatus according to claim 12, wherein the switch control circuit constrains the at least one switch to operate when voltage across the at least one switch falls to substantially zero volts.

14. An apparatus according to claim 1:

wherein the first switching circuit comprises a first half-bridge including first and second switches and a second half-bridge including third and fourth switches; and

wherein the switch control circuit, in transitioning the first switching circuit from a first state in which the second and third switches are closed and the first and fourth switches are open and a second state in which the first and third switches are closed and the second and fourth switches are open, opens the second switch before closing the first switch such that a voltage across the first switch is reduced before the first switch closes.

15. An apparatus according to claim 14, wherein the switch control circuit opens the second switch a sufficient time before closing the first switch to allow the voltage across the first switch to fall to substantially zero volts before the first switch closes.

16. An apparatus according to claim 14, wherein the switch control circuit, in transitioning the first switching circuit from the second state to a third state in which the first and fourth switches are closed and the first and third switches are open, opens the third switch before closing the fourth switch such that a voltage across the fourth switch is reduced before the fourth switch closes.

17. An apparatus according to claim 16, wherein the switch control circuit opens the third switch a sufficient time before closing the fourth switch to allow the voltage across the fourth switch to fall to substantially zero volts before the fourth switch is closed.

18. An apparatus according to claim 1, wherein the second switching circuit comprises a plurality of diodes.

19. A power conversion apparatus, comprising:

a transformer having primary and secondary windings;

first and second half-bridges configured to be coupled across a DC power source and coupled to respective first and second terminals of the primary winding of the transformer;

an output circuit coupled to the secondary winding of the transformer and including first and second capacitors and at least one inductor configured to be coupled to a load, the output circuit operative to transfer energy to the load from the secondary winding via the first capacitor responsive to application of a first polarity voltage to the primary winding of the transfer and to transfer energy to the load from the secondary winding via the second capacitor responsive to application of a second polarity voltage to the primary winding of the transformer; and

a switch control circuit, operatively associated with the first and second half-bridges, that varies a frequency at which the first and second half-bridges operate responsive to an output voltage produced by the output circuit.

20. An apparatus according to claim 19, wherein the switch control circuit is operative to control a time delay between operations of the first and second half-bridges.

21. An apparatus according to claim 20, wherein the switch control circuit controls the time delay such that the first and second half-bridges operate under substantially zero current switching conditions.

22. An apparatus according to claim 20, wherein the switch control circuit maintains a fixed time delay between operations of the first and second half-bridges.

23. An apparatus according to claim 20, wherein the switch control circuit varies the time delay responsive to a sensed current.

24. An apparatus according to claim 20, wherein the switch control circuit varies the time delay responsive to an input voltage applied to the first and second half-bridges.

25. An apparatus according to claim 19, wherein the output circuit comprises a switching circuit, coupled to the secondary winding, the first and second capacitors, and the at least one output inductor, and operative to transfer energy to the load from the secondary winding via the first capacitor responsive to application of the first polarity voltage to the primary winding and to transfer energy to the load from the secondary winding via the second capacitor responsive to application of the second polarity voltage to the primary winding.

26. An apparatus according to claim 25, wherein the switching circuit comprises one of a passive diode network and an active switching network.

27. A power conversion apparatus, comprising:

a transformer having primary and secondary windings;

a switching circuit coupled to the primary winding of the transformer and configured to be coupled to a DC power source, the switching circuit operative to couple the DC power source to the primary winding of the transformer with a first polarity in a first state and to couple the DC power source to the primary winding of the transformer with a second polarity in a second state; and

an output circuit coupled to the secondary winding of the transformer and including first and second capacitors and at least one inductor configured to be coupled to a load, the output circuit operative to transfer energy to the load from the secondary winding via the first capacitor responsive to the first state of the switching circuit and to transfer energy to the load from the secondary winding via the second capacitor responsive to the second state of the switching circuit.

28. An apparatus according to claim 27:

wherein the output circuit, when the switching circuit is in the first state, delivers current from the secondary winding to the first capacitor responsive to current in the secondary winding exceeding a first level and reduces current in the secondary winding responsive to discharge of the first capacitor; and

wherein the output circuit, when the switching circuit is in the second state, delivers current from the secondary winding to the second capacitor responsive to current in the secondary winding exceeding a second level and reduces current in the secondary winding responsive to discharge of the second capacitor.

29. An apparatus according to claim 28, wherein respective capacitances of the first and second capacitors are such that respective discharge currents produced from respective ones of the first and second capacitors in response to respective ones of the first and second states of the switching circuit are sufficient to cause the output circuit to block current flow in the secondary winding.

30. An apparatus according to claim 28:

wherein the output circuit, when the first switching circuit is in the first state, delivers current from the secondary winding to the first capacitor responsive to current in the secondary winding exceeding a current demand of the load and then discharges current from the first capacitor through the at least one output inductor to supply current to the load;

wherein the output circuit, when the switching circuit is in the second state, delivers current from the secondary winding to the second capacitor responsive to current in the secondary winding exceeding a current demand of the load and then discharges the second capacitor through the at least one output inductor to supply current to the load.

31. An apparatus according to claim 30, wherein respective capacitances of the first and second capacitors are such that respective peak discharge currents produced from respective ones of the first and second capacitors responsive to respective ones of the first and second states of the switching circuit are greater than or equal to a current delivered to the load via the at least one inductor.

32. An apparatus according to claim 27, wherein the switching circuit short circuits the primary winding in an interval occurring between respective periods in which the switching circuit is in respective ones of the first and second states.

33. An apparatus according to claim 32, wherein the switching circuit short circuits the primary winding when a current in the transformer meets a predetermined criterion.

34. An apparatus according to claim 33, further comprising a sensor that senses a current in at least one of the primary and secondary windings, wherein the switching circuit short is responsive to the sensor such that the switching circuit short circuits the primary winding when the sensed current meets a predetermined criterion.

35. An apparatus according to claim 33, further comprising a switch control circuit that predicts a time at which current in at least one of the primary winding and the secondary winding meets a predetermined criterion and that causes the switching circuit to short the primary winding based on the predicted time.

36. An apparatus according to claim 32, wherein the switching circuit short circuits the primary winding responsive to lapse of a predetermined time interval following transition to either one of the first and second states.

37. An apparatus according to claim 27, wherein the switching circuit varies a frequency at which the switching circuit alternates between the first and second states to control an output voltage applied to the load.

38. An apparatus according to claim 27, wherein the switching circuit comprises:

first and second input terminals configured to be coupled to first and second terminals of a DC power source;

a first switch that selectively couples the first input terminal to a first terminal of the primary winding;

a second switch that selectively couples the second input terminal to the first terminal of the primary winding;

a third switch that selectively couples the first input terminal to a second terminal of the primary winding;

a fourth switch that selectively couples the second input terminal to the second terminal of the primary winding; and

a switch control circuit that controls the first, second, third and fourth switches.

39. An apparatus according to claim 38:

wherein the switch control circuit, when the switching circuit is in the first state, couples the first input terminal to the first terminal of the primary winding via the first switch and couples the second input terminal to the second terminal of the primary winding via the fourth switch; and

wherein the switch control circuit, when the switching circuit is in the second state, couples the first input terminal to the second terminal of the primary winding via the third switch and couples the second input terminal to the first terminal of the primary winding via the second switch.

40. An apparatus according to claim 27, wherein the switching circuit comprises a first switching circuit, and wherein the output circuit comprises a second switching circuit that controls current flow between the secondary winding, the first and second capacitors and the at least one output inductor.

41. An apparatus according to claim 40, wherein second switching circuit controls current flow between the secondary winding, the first and second capacitors and the at least one output inductor such that:

when the first switching circuit is in the first state, the second switching circuit clamps the first capacitor when current in the secondary winding is less than a first level, conducts current from the secondary winding to the first capacitor responsive to current in the secondary winding exceeding a second level, and reduces current flow in the secondary winding responsive to discharge of the first capacitor; and

when the first switching circuit is in the second state, the second switching circuit clamps the second capacitor when current in the secondary winding is less than a third level, conducts current from the secondary winding to the second capacitor when current in the secondary winding exceeds a fourth level, and reduces current flow in the secondary winding responsive to discharge of the second capacitor.

42. An apparatus according to claim 41:

wherein the second switching circuit, when the first switching circuit is in the first state, clamps the first capacitor when current in the secondary winding is less than current in the at least one output inductor and conducts current from the secondary winding to the first capacitor responsive to current in the secondary winding exceeding current in the at least one output inductor; and

wherein the second switching circuit, when the first switching circuit is in the second state, clamps the second capacitor when current in the secondary winding is less than current in the at least one output inductor and conducts current from the secondary winding to the second capacitor responsive to current in the secondary winding exceeding current in the at least one output inductor.

43. An apparatus according to claim 40:

wherein the output circuit comprises first and second output terminals configured to be coupled to the load;

wherein the at least one inductor comprises an inductor that couples a first terminal of the first capacitor to the first output terminal;

wherein a second terminal of the first capacitor is coupled to a first terminal of the secondary winding;

wherein a first terminal of the second capacitor is coupled to the second output terminal;

wherein a second terminal of the second capacitor is coupled to the first terminal of the secondary winding;

wherein the second switching circuit comprises;

a first switch that selectively couples the first terminal of the secondary winding to the first terminal of the first capacitor;

a second switch that selectively couples a second terminal of the secondary winding to the first terminal of the first capacitor;

a third switch that selectively couples the first terminal of the secondary winding to the first terminal of the second capacitor; and

a fourth switch that selectively couples the second terminal of the secondary winding to the first terminal of the second capacitor.

44. An apparatus according to claim 43, wherein the first capacitor is connected in parallel with the first switch and wherein the second capacitor is connected in parallel with the third switch.

45. An apparatus according to claim 43, wherein the first, second, third and fourth switches comprise respective first, second, third and fourth diodes.

46. An apparatus according to claim 40:

wherein the output circuit comprises an output port configured to be coupled to the load;

wherein the second switching circuit comprises a full bridge rectifier having a rectifier input port coupled to first and second terminals of the secondary winding of the transformer and a rectifier output port connected in series with the at least one output inductor and the output port;

wherein the first capacitor is coupled between a first terminal of the rectifier output port and the first terminal of the secondary winding; and

wherein the second capacitor is coupled between a second terminal of the rectifier output port and the first terminal of the secondary winding.

47. An apparatus according to claim 46, wherein the full-bridge rectifier comprises a passive diode bridge.

48. An apparatus according to claim 47, wherein the full bridge rectifier comprises an active bridge rectifier.

49. An apparatus according to claim 40:

wherein the secondary winding of the transformer comprises first and second secondary windings, each of which is magnetically coupled to the primary winding;

wherein the output circuit comprises an output port configured to be coupled to a load;

wherein the at least one output inductor comprises a first output inductor that couples the first capacitor to the output port and a second output inductor that couples the second capacitor to the output port;

wherein a first terminal of the first capacitor is coupled to a first terminal of the first secondary winding;

wherein a first terminal of the second capacitor is coupled to a second terminal of the second secondary winding; and

wherein the second switching circuit comprises;

a first switch that selectively couples the first terminal of the first secondary winding to the first output inductor and a second terminal of the first capacitor;

a second switch that selectively couples a second terminal of the first secondary winding to the first output inductor and the second terminal of the first capacitor;

a third switch that selectively couples a first terminal of the second secondary winding to the second output inductor and a second terminal of the second capacitor; and

a fourth switch that selectively couples a second terminal of the second secondary winding to the second output inductor and the second terminal of the second capacitor.

50. An apparatus according to claim 49, wherein the first terminal of the first capacitor and the first terminal of the second capacitor are coupled to a first terminal of the output port of the output circuit and the first output inductor and the, second output inductor are coupled to a second terminal of the output port of the output circuit.

51. An apparatus according to claim 49, wherein the first, second, third and fourth switches comprise respective first, second, third and fourth diodes.

52. An apparatus according to claim 40:

wherein the secondary winding of the transformer comprises first and second secondary windings, each of which is magnetically coupled to the primary winding;

wherein t he output circuit comprises an output port configured to be coupled to a load;

wherein the at least one output inductor comprises a first output inductor that couples a first terminal of the first capacitor to a first terminal of the output port and a second output inductor that couples a first terminal of the second capacitor to a second terminal of the first capacitor and to a first terminal of the first secondary winding;

wherein a second terminal of the second capacitor is coupled to a second terminal of the output port and to a first terminal of the second secondary winding;

wherein first terminal of the second capacitor is coupled to a second terminal of the second secondary winding; and

wherein the second switching circuit comprises;

a first switch that selectively couples a second terminal of the first secondary winding to the first terminal of the first capacitor ;

a second switch that selectively couples the first terminal of the first secondary winding to the first terminal of the first capacitor;

a third switch that selectively couples a second terminal of the second secondary winding to the first terminal of the second capacitor; and

a fourth switch that selectively couples the first terminal of the second secondary winding to the first terminal of the second capacitor.

53. A power supply, comprising:

a rectifier circuit configured to receive and AC input voltage and operative to generate a DC voltage therefrom;

a transformer having primary and secondary windings;

a first switching circuit coupled to the rectifier circuit and having an output port coupled to the primary winding of the transformer,

a switch control circuit, operatively associated with the first switching circuit, that causes the first switching circuit to alternately apply the DC voltage with first and second polarities to the primary winding;

first and second capacitors;

an output inductor configured to be coupled to a load; and

a second switching circuit coupled to secondary winding, the first and second capacitors and the output inductor and operative to transfer energy to the load from the secondary winding via the first capacitor responsive to application of the DC voltage with the first polarity voltage to the primary winding and to transfer energy to the load from the secondary winding via the second capacitor responsive to application of the DC voltage with the second polarity to the primary winding.

54. An apparatus according to claim 53:

wherein the first switching circuit comprises first and second half bridges; and

wherein the switching control circuit varies a frequency at which the first and second half-bridges operate responsive to an output voltage applied to the load.

55. An apparatus according to claim 53:

wherein the first switching circuit comprises first and second half bridges; and

wherein the switch control circuit controls a time delay between operations of the first and second half-bridges.

56. An apparatus according to claim 55, wherein the switch control circuit controls the time delay such that the first and second half-bridges operate under substantially zero current switching conditions.

57. An apparatus according to claim 53, wherein the first switching circuit comprises at least one switch, and wherein the switch control circuit constrains the at least one switch to operate when voltage across the at least one switch falls to a predetermined level.

58. An apparatus according to claim 57, wherein the switch control circuit constrains the at least one switch to operate when voltage across the at least one switch falls to substantially zero volts.

69. A method according to claim 58, wherein the step of alternately applying first and second polarity voltages to a primary winding comprises operating a switching circuit coupled to a DC power source and to the primary winding such that at least one switch of the switching circuit is constrained to operate when voltage across the at least one switch falls to a predetermined level.

70. A method according to claim 69, wherein the step of operating a switching circuit comprises constraining the at least one switch to operate when voltage across the at least one switch falls to substantially zero volts.

59. A method of converting power, the method comprising:

alternately applying first and second polarity voltages to a primary winding of a transformer;

transferring energy to a load from a secondary winding of the transformer via a first capacitor responsive to application of the first polarity voltage to the primary winding; and

transferring energy to the load from the secondary winding via a second capacitor responsive to application of the second polarity voltage to the primary winding.

60. A method according to claim 59, wherein the step of alternately applying first and second polarity voltages to a primary winding comprises operating a switching circuit coupled to a DC power source and to the primary winding such that at least one switch of the switching current is constrained to operate when current in the at least one switch falls to a predetermined level.

61. A method according to claim 60, wherein the step of operating a switching circuit comprises the step of operating the at least one switch responsive to a current through the transformer.

62. A method according to claim 60, wherein the step of operating a switching circuit comprises estimating a time when current in the at least one switch will reach the predetermined level and operating the at least one switch based on the estimated time.

63. A method according to claim 59, wherein the step of alternately applying first and second polarity voltages to a primary winding comprises controlling a frequency at which first and second half-bridges of a switching circuit that couples a DC power source to the primary operate.

64. A method according to claim 63, wherein the step of alternately applying first and second polarity voltages to a primary winding further comprises controlling a time delay between operations of the first and second half-bridges.

65. A method according to claim 64, wherein the step of controlling a time delay comprises controlling the time delay such that the first and second half-bridges operate under substantially zero current switching conditions.

66. A method according to claim 64, wherein the step of controlling a time delay comprises maintaining a fixed time delay between operations of the first and second half-bridges.

67. A method according to claim 64, wherein the step of controlling a time delay comprises varying the time delay responsive to a sensed current.

68. A method according to claim 64, wherein the step of controlling a time delay comprises varying the time delay responsive to an input voltage applied to the switching circuit.

71. A method according to claim 59, wherein the step of alternately applying first and second polarity voltages to a primary winding comprises:

operating a switching circuit coupled to a DC power source and to the primary winding, the switching circuit including a first half-bridge including first and second switches and a second half-bridge including third and fourth switches; and

transitioning the switching circuit from a first state in which the second and third switches are closed and the first and fourth switches are open and a second state in which the first and third switches are closed and the second and fourth switches are open by opening the second switch before closing the first switch such that a voltage across the first switch is reduced before the first switch closes.

72. A method according to claim 71, wherein the step of opening the second switch before closing the first switch such that a voltage across the first switch is reduced before the first switch closes comprises opening the second switch a sufficient time before closing the first switch to allow the voltage across the first switch top fall to substantially zero volts before the first switch closes.

73. A method according to claim 71, wherein the step of alternately applying first and second polarity voltages to a primary winding comprises transitioning the switching circuit from the second state to a third state in which the first and fourth switches are closed and the first and third switches are open by opening the third switch before closing the fourth switch such that a voltage across the fourth switch is reduced before the fourth switch closes.

74. A method according to claim 73, wherein the step of opening the third switch before closing the fourth switch such that a voltage across the fourth switch is reduced before the fourth switch closes comprises opening the third switch a sufficient time before closing the fourth switch to allow the voltage across the fourth switch to fall to substantially zero volts before the fourth switch is closed.