Power converter adaptively driven

Abstract

A drive circuit for a converter and a method of driving a converter. The converter includes an inverter and a synchronous rectifier. The drive circuit includes: (1) a modulation circuit for generating a drive waveform for controlling the inverter and the synchronous rectifier employing a negative feedback loop, (2) a modification circuit, coupled to the modulation circuit, for sensing an operating condition of the converter and shifting a portion of the drive waveform as a function of the operating condition, the modification circuit thereby creating a variable drive waveform from the drive waveform without employing negative feedback and (3) a transmission circuit, coupled to the modification circuit, for applying the variable drive waveform to the converter, thereby allowing a variable nonconcurrent change in state of the inverter and the synchronous rectifier according to the function of the operating condition.

What is claimed is:  
     
       1. A drive circuit for a converter, said converter including an inverter and a synchronous rectifier, said drive circuit comprising: 
       a modulation circuit for generating a drive waveform for controlling said inverter and said synchronous rectifier employing a negative feedback loop;  
       a modification circuit, coupled to said modulation circuit, for sending an operating condition of said converter and shifting a portion of said drive waveform as a function of said operating condition, said modification circuit thereby creating a variable drive waveform from said drive waveform without employing negative feedback; and  
       a transmission circuit, coupled to said modification circuit, for applying said variable drive waveform to said converter, thereby allowing a variable nonconcurrent change in state of said inverter and said synchronous rectifier according to said function of said operating condition.  
     
     
       2. The drive circuit as recited in claim  1  wherein said modification circuit delays said portion of said waveform to produce said variable drive waveform. 
     
     
       3. The drive circuit as recited in claim  1  wherein said operating condition is an output current level of said converter. 
     
     
       4. The drive circuit as recited in claim  1  further comprising another transmission circuit and wherein said modification circuit creates a nonvariable drive waveform, said another transmission circuit applying said nonvariable drive waveform to said inverter and said transmission circuit applying said variable drive waveform to said synchronous rectifier. 
     
     
       5. The drive circuit as recited in claim  1  wherein said modification circuit comprises a plurality of delay circuits having different delays associated therewith and a delay selection circuit adapted to act on a selected one of said plurality of delay circuits to create said variable drive waveform. 
     
     
       6. The drive circuit as recited in claim  1  wherein said modification circuit increases a delay of said portion of said drive waveform as an output current level of said converter increases. 
     
     
       7. The drive circuit as recited in claim  1  wherein said drive waveform is adapted to cause a switching component within said synchronous rectifier to transition from a conducting to a nonconducting state. 
     
     
       8. The drive circuit as recited in claim  1  wherein said function of said operating condition is discontinuous. 
     
     
       9. The drive circuit as recited in claim  1  wherein said converter comprises an isolation transformer coupled between said inverter and said synchronous rectifier, said converter being an isolated, buck-derived converter. 
     
     
       10. The drive circuit as recited in claim  1  wherein said modification circuit comprises an RC circuit having a variable time constant associated therewith. 
     
     
       11. A method of driving a converter, said converter including an inverter and a synchronous rectifier, said method comprising the steps of: 
       generating a drive waveform for controlling said inverter and said synchronous rectifier employing a negative feedback loop;  
       sensing an operating condition of said converter and shifting a portion of said drive waveform as a function of said operating condition, thereby creating a variable drive waveform from said drive waveform without employing negative feedback; and  
       applying said variable drive waveform to said converter, thereby allowing a variable nonconcurrent change in state of said inverter and said synchronous rectifier according to said function of said operating condition.  
     
     
       12. The method as recited in claim  11  wherein said step of sensing and shifting comprises the step of delaying said portion of said drive waveform to produce said variable drive waveform. 
     
     
       13. The method as recited in claim  11  wherein said operating condition is an output current level of said converter. 
     
     
       14. The method as recited in claim  11  wherein said step of applying further comprises the steps of: 
       applying a nonvariable drive waveform to said inverter; and  
       applying said variable drive waveform to said synchronous rectifier.  
     
     
       15. The method as recited in claim  11  wherein said step of sensing and shifting comprises the step of acting on a selected one of a plurality of delay circuits to create said variable drive waveform. 
     
     
       16. The method as recited in claim  11  wherein said step of sensing and shifting comprises the step of increasing a delay of said portion of said drive waveform as an output current level of said converter increases. 
     
     
       17. The method as recited in claim  11  wherein said step of applying causes a switching component within said synchronous rectifier to transition from a conducting to a nonconducting state. 
     
     
       18. The method as recited in claim  11  wherein said function of said operating condition is discontinuous. 
     
     
       19. The method as recited in claim  11  wherein said converter comprises an isolation transformer coupled between said inverter and said synchronous rectifier, said converter being an isolated, buck-derived converter. 
     
     
       20. The method as recited in claim  11  wherein said step of sensing and shifting is performed by a modification circuit including an RC circuit having a variable time constant associated therewith. 
     
     
       21. A drive circuit for isolated, buck-derived converter, said converter including an inverter, a synchronous rectifier and an isolation transformer coupled between said inverter and said synchronous rectifier, said drive circuit comprising: 
       a modulation circuit for generating a drive waveform for controlling said inverter and said synchronous rectifier employing a negative feedback loop;  
       a modification circuit, coupled to said modulation circuit, for sensing an output current level of said converter and delaying a portion of said drive waveform as a function of said output current level, said waveform modification circuit thereby creating a fixed and a variable drive waveform from said drive waveform without employing negative feedback; and  
       a first and second transmission circuit, coupled to said modification circuit, for applying said fixed drive waveform to said inverter and said variable drive waveform to said synchronous rectifier, thereby allowing a variable change of state of said synchronous rectifier to lag a change of state of said inverter according to said function of said output current level.  
     
     
       22. The drive circuit as recited in claim  21  wherein said modification circuit comprises a plurality of delay circuits having different delays associated therewith and a delay selection circuit adapted to act on a selected one of said plurality of delay circuits to create said variable drive waveform. 
     
     
       23. The drive circuit as recited in claim  21  wherein said modification circuit increases a delay of said portion of said drive waveform as an output current level of said converter increases. 
     
     
       24. The drive circuit as recited in claim  21  wherein said drive waveform is adapted to cause a switching component within said synchronous rectifier to transition from a conducting to a nonconducting state. 
     
     
       25. The drive circuit as recited in claim  21  wherein said function of said operating condition is discontinuous. 
     
     
       26. The drive circuit as recited in claim  21  wherein said modification circuit comprises an RC circuit having a variable time constant associated therewith. 
     
     
       27. For use with a DC- DC converter including an isolation transformer having a primary winding coupled to an input of said converter and a secondary winding coupled to an output of said converter, said converter further including an inverter interposed between said input and said primary winding and a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches, a circuit coupled to and configured to control said inverter and said synchronous rectifier, comprising:    
       
         a modulation circuit configured to generate an inverter drive waveform for controlling said inverter to regulate an output characteristic of said converter; and  
       
       
         a modification circuit configured to advance a synchronous rectifier drive waveform for at least one of said first and second switches of said synchronous rectifier relative to said inverter drive waveform for said inverter as said converter transitions from a substantially full load operating condition to a partial load operating condition. 
       
     
     
       28. The circuit as recited in claim  27  further comprising a transmission circuit configured to apply said inverter and synchronous rectifier drive waveforms to said inverter and said first and second switches of said synchronous rectifier, respectively. 
     
     
       29. The circuit as recited in claim  27  wherein said converter further comprises an active clamp interposed between said input and said primary winding. 
     
     
       30. The circuit as recited in claim  27  wherein said modification circuit comprises a timing network. 
     
     
       31. The circuit as recited in claim  30  wherein said modification circuit further comprises a comparator and a controllable switch appended to said timing network and configured to vary a time constant associated therewith. 
     
     
       32. The circuit as recited in claim  27  wherein said modification circuit is configured to continuously and variably advance said synchronous rectifier drive waveform for said at least one of said first and second switches of said synchronous rectifier. 
     
     
       33. The circuit as recited in claim  27  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       34. For use with a DC- DC converter including an isolation transformer having a primary winding coupled to an input of said converter and a secondary winding coupled to an output of said converter, said converter further including an inverter interposed between said input and said primary winding and a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches, a method for controlling said inverter and said synchronous rectifier, comprising:    
       
         generating an inverter drive waveform for controlling said inverter to regulate an output characteristic of said converter; and  
       
       
         advancing a synchronous rectifier drive waveform for at least one of said first and second switches of said synchronous rectifier relative to said inverter drive waveform for said inverter as said converter transitions from a substantially full load operating condition to a partial load operating condition. 
       
     
     
       35. The method as recited in claim  34  further comprising applying said inverter and synchronous rectifier drive waveforms to said inverter and said first and second switches of said synchronous rectifier, respectively. 
     
     
       36. The method as recited in claim  34  wherein said converter further comprises an active clamp interposed between said input and said primary winding. 
     
     
       37. The method as recited in claim  34  wherein said advancing is performed by a modification circuit comprising a timing network. 
     
     
       38. The method as recited in claim  37  wherein said modification circuit further comprises a comparator and a controllable switch appended to said timing network and configured to vary a time constant associated therewith. 
     
     
       39. The method as recited in claim  34  wherein said advancing is continuously variable. 
     
     
       40. The method as recited in claim  34  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology;  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       41. A DC- DC converter having an input and output, comprising:    
       
         an isolation transformer having a primary winding and a secondary winding;  
       
       
         an inverter interposed between said input and said primary winding;  
       
       
         a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches; and  
       
       
         a circuit coupled to and configured to control said inverter and said synchronous rectifier, including:  
       
       
         a modulation circuit configured to generate an inverter drive waveform for controlling said inverter to regulate an output characteristic of said converter, and  
       
       
         a modification circuit configured to advance a synchronous rectifier drive waveform for at least one of said first and second switches of said synchronous rectifier relative to said inverter drive waveform for said inverter as said converter transitions from a substantially full load operating condition to a partial load operating condition. 
       
     
     
       42. The converter as recited in claim  41  wherein said circuit further comprises a transmission circuit configured to apply said inverter and synchronous rectifier drive waveforms to said inverter and said first and second switches of said synchronous rectifier, respectively. 
     
     
       43. The converter as recited in claim  41  further comprising an active clamp interposed between said input and said primary winding. 
     
     
       44. The converter as recited in claim  41  wherein said modification circuit comprises a timing network. 
     
     
       45. The converter as recited in claim  44  wherein said modification circuit further comprises a comparator and a controllable switch appended to said timing network and configured to vary a time constant associated therewith. 
     
     
       46. The converter as recited in claim  41  wherein said modification circuit is configured to continuously and variably advance said synchronously rectifier drive waveform for said at least one of said first and second switches of said synchronous rectifier. 
     
     
       47. The converter as recited in claim  41  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       48. For use with a DC- DC converter including an isolation transformer having a primary winding coupled to an input of said converter and a secondary winding coupled to an output of said converter, said converter further including an inverter interposed between said input and said primary winding and a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches, a circuit coupled to and configured to control said inverter and said synchronous rectifier, comprising:    
       
         a modulation circuit configured to generate inverter and synchronous rectifier drive waveforms for controlling said inverter and said first and second switches of said synchronous rectifier, respectively; and  
       
       
         a modification circuit configured to vary said synchronous rectifier drive waveform for at least one of said first and second switches of said synchronous rectifier relative to said inverter drive waveform for said inverter as a function of an operating condition of said converter. 
       
     
     
       49. The circuit as recited in claim  48  further comprising a transmission circuit configured to apply said inverter and synchronous rectifier drive waveforms to said inverter and said first and second switches of said synchronous rectifier, respectively. 
     
     
       50. The circuit as recited in claim  48  wherein said converter further comprises an active clamp interposed between said input and said primary winding. 
     
     
       51. The circuit as recited in claim  48  wherein said modification circuit comprises a timing network. 
     
     
       52. The circuit as recited in claim  51  wherein said modification circuit further comprises a comparator and a controllable switch, appended to said timing network, configured to vary a time constant associated therewith. 
     
     
       53. The circuit as recited in claim  48  wherein said modification circuit is configured to continuously vary said synchronous rectifier drive waveform for said at least one of said first and second switches of said synchronous rectifier, respectively. 
     
     
       54. The circuit as recited in claim  48  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       55. For use with a DC- DC converter including an isolation transformer having a primary winding coupled to an input of said converter and a secondary winding coupled to an output of said converter, said converter further including an inverter interposed between said input and said primary winding and a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches, a method for controlling said inverter and said synchronous rectifier, comprising:    
       
         generating inverter and synchronous rectifier drive waveforms for controlling said inverter and said first and second switches of said synchronous rectifier, respectively; and  
       
       
         varying said synchronous rectifier drive waveform for at least one of said first and second switches of said synchronous rectifier relative to said inverter drive waveform for said inverter as a function of an operating condition of said converter. 
       
     
     
       56. The method as recited in claim  55  further comprising applying said inverter and synchronous rectifier drive waveforms to said inverter and said first and second switches of said synchronous rectifier, respectively. 
     
     
       57. The method as recited in claim  55  wherein said converter further comprises an active clamp interposed between said input and said primary winding. 
     
     
       58. The method as recited in claim  55  wherein said varying is performed by a modification circuit comprising a timing network. 
     
     
       59. The method as recited in claim  57  wherein said modification circuit further comprises a comparator and a controllable switch, appended to said timing network, configured to vary a time constant associated therewith. 
     
     
       60. The method as recited in claim  55  wherein said varying is continuous. 
     
     
       61. The method as recited in claim  55  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       62. A DC- DC converter having an input and output, comprising:    
       
         an isolation transformer having a primary winding and a secondary winding;  
       
       
         an inverter interposed between said input and said primary winding;  
       
       
         a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches; and  
       
       
         a circuit coupled to and configured to control said inverter and said synchronous rectifier, including:  
       
       
         a modulation circuit configured to generate inverter and synchronous rectifier drive waveforms for controlling said inverter and said first and second switches of said synchronous rectifier, respectively, and  
       
       
         a modification circuit configured to vary said synchronous rectifier drive waveform for at least one of said first second switches of said synchronous rectifier relative to said inverter drive waveform for said inverter as a function of an operating condition of said converter. 
       
     
     
       63. The converter as recited in claim  62  wherein said circuit further comprises a transmission circuit configured to apply said inverter and synchronous rectifier drive waveforms to said inverter and said first and second switches of said synchronous rectifier, respectively. 
     
     
       64. The converter as recited in claim  62  further comprising an active clamp interposed between said input and said primary winding. 
     
     
       65. The converter as recited in claim  62  wherein said modification circuit comprises a timing network. 
     
     
       66. The converter as recited in claim  65  wherein said modification circuit further comprises a comparator and a controllable switch, appended to said timing network, configured to vary a time constant associated therewith. 
     
     
       67. The converter as recited in claim  62  wherein said modification circuit is configured to continuously vary said synchronous rectifier drive waveform for said at least one of said first and second switches of said synchronous rectifier. 
     
     
       68. The converter as recited in claim  62  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       69. For use with a DC- DC converter including an isolation transformer having a primary winding coupled to an input of said converter and a secondary winding coupled to an output of said converter, said converter further including an inverter interposed between said input and said primary winding and a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches, a circuit coupled to and configured to control said inverter and said synchronous rectifier, comprising:    
       
         a modulation circuit configured to generate drive waveforms for controlling said inverter and said first and second switches of said synchronous rectifier, respectively; and  
       
       
         a modification circuit, including:  
       
         an inverter modification sub - circuit configured to develop an inverter drive waveform for said inverter as a function of said drive waveform and an operating condition of the converter,    
         a first synchronous rectifier modification sub - circuit configured to develop a first synchronous rectifier drive waveform for said first switch of said synchronous rectifier as a function of said drive waveform and said operating condition of said converter,    
         a second synchronous rectifier sub - circuit configured to develop a second synchronous rectifier drive waveform for said second switch of said synchronous rectifier as a function of said drive waveform and said operating condition of said converter, at least one of said first and second synchronous rectifier drive waveforms varying from said inverter drive waveform.   
     
     
       70. The circuit as recited in claim  69  further comprising a transmission circuit, including: 
         an inverter transmission sub - circuit, coupled to said inverter modification sub - circuit, configured to apply said inverter drive waveform to said inverter;    
         an first synchronous rectifier transmission sub - circuit, coupled to said first synchronous rectifier modification sub - circuit, configured to apply said first synchronous rectifier drive waveform to said first switch of said synchronous rectifier; and    
         a second synchronous rectifier transmission sub - circuit, coupled to said second synchronous rectifier modification sub - circuit, configured to apply said second synchronous rectifier drive waveform to said second switch of said synchronous rectifier.   
     
     
       71. The circuit as recited in claim  69  wherein said converter further comprises an active clamp interposed between said input and said primary winding. 
     
     
       72. The circuit as recited in claim  69  wherein at least one of said inverter modification sub- circuit, said first synchronous rectifier modification sub - circuit and said second synchronous rectifier modification sub - circuit comprise a timing network.   
     
     
       73. The circuit as recited in claim  72  wherein said at least one of said inverter modification sub- circuit, said first synchronous rectifier modification sub - circuit and said second synchronous rectifier modification sub - circuit further comprise a comparator and a controllable switch, appended to said timing network, configured to vary a time constant associated therewith.   
     
     
       74. The circuit as recited in claim  69  wherein said at least one of said first and second synchronous rectifier drive waveforms continuously vary from said inverter drive waveform. 
     
     
       75. The circuit as recited in claim  69  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       76. For use with a DC- DC converter including an isolation transformer having a primary winding coupled to an input of said converter and a secondary winding coupled to an output of said converter, said converter further including an inverter interposed between said input and said primary winding and a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches, a method for controlling said inverter and said synchronous rectifier, comprising:    
       
         generating drive waveforms for controlling said inverter and said first and second switches of said synchronous rectifier; and  
       
       
         developing an inverter drive waveform, a first synchronous rectifier drive waveform and a second synchronous rectifier drive waveform for said inverter, said first switch of said synchronous rectifier and said second switch of said synchronous rectifier, respectively, as a function of said drive waveform and an operating condition of the converter, at least one of said first and second synchronous rectifier drive waveforms varying from said inverter drive waveform. 
       
     
     
       77. The method as recited in claim  76  further comprising applying said inverter drive waveform, said first synchronous rectifier drive waveform and said second synchronous rectifier drive waveform to said inverter, said first switch of said synchronous rectifier and said second switch of said synchronous rectifier, respectively. 
     
     
       78. The method as recited in claim  76  wherein said converter further comprises an active clamp interposed between said input and said primary winding. 
     
     
       79. The method as recited in claim  76  wherein said developing said inverter drive waveform, said first synchronous rectifier drive waveform and said second synchronous rectifier drive waveform are performed by an inverter modification sub- circuit, a first synchronous rectifier modification sub - circuit and a second synchronous rectifier modification sub - circuit, respectively, and at least one of said inverter modification sub - circuit, said first synchronous rectifier modification sub - circuit and said second synchronous rectifier modification sub - circuit comprise a timing network.   
     
     
       80. The method as recited in claim  79  wherein said at least one of said inverter modification sub- circuit, said first synchronous rectifier modification sub - circuit and said second synchronous rectifier modification sub - circuit further comprise a comparator and a controllable switch, appended to said timing network, configured to vary a time constant associated therewith.   
     
     
       81. The method as recited in claim  76  wherein said at least one of said first and second synchronous rectifier drive waveforms vary continuously. 
     
     
       82. The method as recited in claim  76  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology. 
       
     
     
       83. A DC- DC converter having an input and an output comprising:    
       
         an isolation transformer having a primary winding and a secondary winding;  
       
       
         an inverter interposed between said input and said primary winding;  
       
       
         a synchronous rectifier, interposed between said secondary winding and said output, having first and second switches; and  
       
       
         a circuit coupled to and configured to control said inverter and said synchronous rectifier, including:  
       
       
         a modulation circuit configured to generate drive waveforms for controlling said inverter and said first and second switches of said synchronous rectifier, and  
       
       
         a modification circuit, including:  
       
         an inverter modification sub - circuit configured to develop an inverter drive waveform for said inverter as a function of said drive waveform and an operating condition of the converter,    
         a first synchronous rectifier modification sub - circuit configured to develop a first synchronous rectifier drive waveform for said first switch of said synchronous rectifier as a function of said drive waveform and said operating condition of said converter, and    
         a second synchronous rectifier modification sub - circuit configured to develop a second synchronous rectifier drive waveform for said second switch of said synchronous rectifier as a function of said drive waveform and said operating condition of said converter, at least one of said first and second synchronous rectifier drive waveforms varying from said inverter drive waveform.   
     
     
       84. The converter as recited in claim  83  wherein said circuit further comprises a transmission circuit, including: 
         an inverter transmission sub - circuit, coupled to said inverter modification sub - circuit, configured to apply said inverter drive waveform to said inverter;    
         an first synchronous rectifier transmission sub - circuit, coupled to said first synchronous rectifier modification sub - circuit, configured to apply said first synchronous rectifier drive waveform to said first switch of said synchronous rectifier; and    
         a second synchronous rectifier transmission sub - circuit, coupled to said second synchronous rectifier modification sub - circuit, configured to apply said second synchronous rectifier drive waveform to said second switch of said synchronous rectifier.   
     
     
       85. The converter as recited in claim  83  further comprising an active clamp interposed between said input and said primary winding. 
     
     
       86. The converter as recited in claim  83  wherein at least one of said inverter modification sub- circuit, said first synchronous rectifier modification sub - circuit and said second synchronous rectifier modification sub - circuit comprise a timing network.   
     
     
       87. The converter as recited in claim  86  wherein at least one of said inverter modification sub- circuit, said first synchronous rectifier modification sub - circuit and said second synchronous rectifier modification sub - circuit further comprise a comparator and a controllable switch, appended to said timing network, configured to vary a time constant associated therewith.   
     
     
       88. The converter as recited in claim  83  wherein said at least one of said first and second synchronous rectifier drive waveforms continuously vary from said inverter drive waveform. 
     
     
       89. The converter as recited in claim  83  wherein said converter is a buck- derived converter employing a topology selected from the group consisting of:    
       
         a forward topology,  
       
       
         a flyback topology,  
       
         a push - pull topology, and    
       
         a bridge topology.