USRE37889EExpiredUtility
Low loss synchronous rectifier for application to clamped-mode power converters
Est. expiryApr 29, 2013(expired)· nominal 20-yr term from priority
Inventors:Allen F. Rozman
H02M 3/33569Y02B70/10H02M 3/33592H02M 7/217
58
PatentIndex Score
16
Cited by
9
References
60
Claims
Abstract
A synchronous rectifier for use with a clamped-mode power converter uses in one embodiment a hybrid rectifier with a MOSFET rectifying device active in one first cyclic interval or the conduction/nonconduction sequence of the power switch and a second rectifying device embodied in one illustrative embodiment as a low voltage bipolar diode rectifying device active during an alternative interval to the first conduction/nonconduction interval. The gate drive to the MOSFET device is continuous at a constant level for substantially all of the second interval which enhances efficiency of the rectifier. The bipolar rectifier device may also be embodied as a MOSFET deice. The subject rectifier may be used in both forward and flyback power converters.
Claims
exact text as granted — not AI-modifiedI claim:
1. In a power converter, comprising:
an input for accepting a DC voltage;
a power transformer including a primary and secondary winding;
a power switch for periodically connecting the input to the primary winding;
an output for accepting a load to be energized;
clamping means for limiting a voltage and extending the voltage's duration across the secondary winding at a substantially constant amplitude during substantially an entire extent of a clamping interval of a cyclic period of the power converter;
a rectifier circuit connecting the secondary winding to the output; and including:
a synchronous rectification device with a control terminal connected to be responsive to a signal across the secondary winding such that the synchronous rectification device conducts a load current during substantially the entire extent of the clamping interval; and
a rectifying device connected for enabling conduction of the load current during a second interval other than the clamping interval.
2. In a power converter, comprising
an input for accepting a DC voltage;
a power transformer including a primary and secondary winding;
a power switch for periodically connecting the input to the primary winding during a second interval of a cyclic period;
an output for accepting a load to be energized;
clamping means for limiting a voltage and extending the voltage's duration across the secondary winding at a substantially constant amplitude during substantial an entire extent of a clamping interval of a cyclic period of the power converter; a rectifier circuit connecting the secondary winding to the output; and including:
a first synchronous rectification device with a control terminal connected to be responsive to a signal across the secondary winding such that the synchronous rectification deice conducts a load current during substantially the entire extent of the clamping interval, and
a second synchronous rectification device with a control terminal connected to be responsive to a signal across he secondary winding such that the second synchronous rectification device conducts the load current during substantially and entire extent of the second interval other than the clomping interval.
3. In a power converter as claimed in claim 1 or 2 , comprising:
the converter connected to operate as a forward type converter.
4. In a power converter as claimed in claim 1 or 2 , comprising:
the converter connected to operate as a flyback type converter.
5. A switching mode power converter, comprising:
a power transformer including a magnetizing inductance requiring periodic recycling;
a first power stage for converting a DC input in a periodic pulsed voltage applied to a primary winding of the transformer, including;
a clamping circuit for limiting a voltage of the transformer during the periodic recycling at a substantially constant amplitude and extending the voltage duration to maintain a constant voltage for substantially an entire extent of periodic recycling;
a second power stage for rectifying an output of a secondary winding of the transformer and applying it to a lead to be energized, including;
a synchronous rectifier including a first rectifying device with a control gate connected to be responsive to a signal across the secondary winding such that the synchronous rectification device conducts a load current during the periodic recycling when the clamping circuit is active, and
a second rectifying device connected for enabling conduction of the load current when the first rectifying device is nonconducting.
6. A switching mode power converter as claimed in claim 5 , further comprising:
the second rectifying device comprises a diode.
7. A switching mode power converter as claimed in claim 5 , further comprising:
the second rectifying device comprises a rectifying device with a control gate connected to be responsive to a signal of the secondary winding.
8. A switching mode power converter as claimed in claim 6 or 7 , further comprising:
The secondary winding tapped and separated into first and second winding segments, and the first rectifying device is connected to the first winding segment and the second rectifying device is connected to the second winding segment.
9. A switching mode power converter as claimed in claim 6 or 7 , further comprising:
the converter connected to operate as a forward type converter.
10. A switching mode power converter as claimed in claim 6 or 7 , further comprising:
the converter connected to operate as a flyback type converter.
11. A method of operating a power converter, comprising:
providing a power transformer having a plurality of windings;
limiting a voltage across at least one of said plurality of windings with a clamping circuit during a clamping interval of said power converter; and
rectifying said voltage with a synchronous rectification device having a control terminal responsive to a signal across at least one of said plurality of windings such that said synchronous rectification device is active for substantially all of said clamping interval.
12. The method as claimed in claim 11 wherein said clamping circuit is directly connected to said power transformer.
13. The method as claimed in claim 11 wherein said clamping circuit is coupled to a primary winding of said power transformer.
14. The method as claimed in claim 11 wherein said power transformer has a center- tapped secondary winding.
15. The method as claimed in claim 11 further comprising connecting a primary winding of said power transformer to an input of said power converter during a first cyclic interval of said power converter.
16. The method as claimed in claim 11 further comprising a further synchronous rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
17. The method as claimed in claim 11 further comprising a rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
18. The method as claimed in claim 11 wherein said clamping circuit comprises a switching device connected in series with a capacitor.
19. The method as claimed in claim 18 further comprising controlling said switching device with a control circuit.
20. The method as claimed in claim 11 wherein said power converter operates in one of:
a forward mode,
a flyback mode, and
a forward/flyback mode.
21. A method of operating a power converter, comprising:
providing a power transformer having a plurality of windings;
coupling a synchronous rectification device, having a control terminal, to at least one of said plurality of windings;
coupling a clamping circuit to said at least one of said plurality of windings; and
limiting a voltage applied to said control terminal with said clamping circuit such that said synchronous rectification device is active for substantially all of a clamping interval.
22. The method as claimed in claim 21 wherein said clamping circuit is directly connected to said power transformer.
23. The method as claimed in claim 21 wherein said clamping circuit is coupled to a primary winding of said power transformer.
24. The method as claimed in claim 21 wherein said power transformer has a center- tapped secondary winding.
25. The method as claimed in claim 21 further comprising connecting a primary winding of said power transformer to an input of said power converter during a first cyclic interval of said power converter.
26. The method as claimed in claim 21 further comprising a further synchronous rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
27. The method as claimed in claim 21 further comprising a rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
28. The method as claimed in claim 21 wherein said clamping, circuit comprises a switching device connected in series with a capacitor.
29. The method as claimed in claim 28 further comprising controlling said switching device with a control circuit.
30. The method as claimed in claim 21 wherein said power converter operates in one of:
a forward mode,
a flyback mode, and
a forward/flyback mode.
31. A method of operating a power converter, comprising:
providing a power transformer having a plurality of windings;
coupling a synchronous rectification device, having a control terminal, to at least one of said plurality of windings;
coupling a clamping circuit to said at least one of said plurality of windings; and
limiting a voltage applied to said control terminal with said clamping circuit such that said synchronous rectification device conducts a load current for substantially all of a clamping interval.
32. The method as claimed in claim 31 wherein said clamping circuit is directly connected to said power transformer.
33. The method as claimed in claim 31 wherein said clamping circuit is coupled to a primary winding of said power transformer.
34. The method as claimed in claim 31 wherein said power transformer has a center- tapped secondary winding.
35. The method as claimed in claim 31 further comprising connecting a primary winding of said power transformer to an input of said power converter during a first cyclic interval of said power converter.
36. The method as claimed in claim 31 further comprising a further synchronous rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
37. The method as claimed in claim 31 further comprising a rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
38. The method as claimed in claim 31 wherein said clamping circuit comprises a switching device connected in series with a capacitor.
39. The method as claimed in claim 38 further comprising controlling said switching device with a control circuit.
40. The method as claimed in claim 31 wherein said power converter operates in one of:
a forward mode,
a flyback mode, and
a forward/flyback mode.
41. A method of operating a power converter, comprising:
providing a power transformer having a plurality of windings;
coupling a synchronous rectification device, having a control terminal responsive to a drive signal, to at least one of said plurality of windings;
coupling a clamping circuit to said at least one of said plurality of windings; and
limiting said drive signal applied to said control terminal with said clamping circuit such that said drive signal is continuous for substantially all of a clamping interval.
42. The method as claimed in claim 41 wherein said clamping circuit is directly connected to said power transformer.
43. The method as claimed in claim 41 wherein said clamping circuit is coupled to a primary winding of said power transformer.
44. The method as claimed in claim 41 wherein said power transformer has a center- tapped secondary winding.
45. The method as claimed in claim 41 further comprising connecting a primary winding of said power transformer to an input of said power converter during a first cyclic interval of said power converter.
46. The method as claimed in claim 41 further comprising a further synchronous rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
47. The method as claimed in claim 41 further comprising a rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
48. The method as claimed in claim 41 wherein said clamping circuit comprises a switching device connected in series with a capacitor.
49. The method as claimed in claim 48 further comprising controlling said switching device with a control circuit.
50. The method as claimed in claim 41 wherein said power converter operates in one of:
a forward mode,
a flyback mode, and
a forward/flyback mode.
51. A method of operating a power converter, comprising:
accepting a DC voltage at an input of said power converter;
providing current to a load coupled to an output of said power converter;
transforming a voltage from said input to said output with a power transformer having at least one primary winding and at least one secondary winding;
periodically connecting said input to said at least one primary winding during a first cyclic interval of said power converter;
limiting said voltage across said at least one secondary winding with a clamping circuit during a clamping interval of said power converter; and
rectifying said voltage with a synchronous rectification device having a control terminal responsive to a signal across said at least one secondary winding such that said synchronous rectification device is active for substantially all of said clamping interval.
52. The method as claimed in claim 51 wherein said clamping circuit is directly connected to said power transformer.
53. The method as claimed in claim 51 wherein said clamping circuit is coupled to said at least one primary winding of said power transformer.
54. The method as claimed in claim 51 wherein said at least one secondary winding has a center- tap.
55. The method as claimed in claim 51 further comprising a voltage limiting device coupled to said synchronous rectification device.
56. The method as claimed in claim 51 further comprising a further synchronous rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
57. The method as claimed in claim 51 further comprising rectification device, coupled to said power transformer, that is active during a first cyclic interval of said power converter.
58. The method as claimed in claim 51 wherein said clamping circuit comprises a switching device connected in series with a capacitor.
59. The method as claimed in claim 58 further comprising controlling said switching device with a control circuit.
60. The method as claimed in claim 51 wherein said power converter operates in one of:
a forward mode,
a flyback mode, and
a forward/flyback mode.Join the waitlist — get patent alerts
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