METHOD FOR CONTROLLING A SWITCHING REGULATOR AND RELATED SWITCHING REGULATOR

• US 20100164443A1
• Filed: 12/31/2008
• Published: 07/01/2010
• Est. Priority Date: 12/31/2008
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: PASQUA, Alfio, GIOMBANCO, Salvatore, TUMMINARO, Salvatore, ADRAGNA, Claudio
• Granted Patent: US 8,179,699 B2
• Time in Patent Office: Days
• US Class Current: 323/247
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

An embodiment of a power-supply controller comprises a switching-control circuit, an error amplifier, and a signal generator. The switching-control circuit is operable to control a switch coupled to a primary winding of a transformer, and the error amplifier has a first input node operable to receive a feedback signal, a second input node operable to receive a comparison signal, and an output node operable to provide a control signal to the switching-control circuit. The signal generator is operable to generate either the feedback signal or the comparison signal in response to a compensation signal that is isolated from a secondary winding of the transformer and that is proportional to a load current through a conductor disposed between the secondary winding and a load.

Claims

1. A primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage a logic flag for flagging demagnetization phases of said switching regulator and a control voltage that fixes the maximum current level that may circulate in the primary side of the regulator in function of the difference between a reference voltage and said feedback voltage, said feedback control circuit further comprises:

circuit means for generating a signal representative of the ratio between the duration of a demagnetization phase and the respective switching period from signals in the primary side of the converter;

an auxiliary block input with said control voltage and with said representative signal and adapted to adjust said difference between the reference voltage and the feedback voltage in order to compensate eventual voltage differences between the regulated output voltage and the voltage effectively provided to a load supplied by the regulator.

2. The switching regulator of claim 1, wherein said circuit means is a filter capacitor that is coupled to a current generator and to a resistor through a switch controlled by said logic flag, such to be discharged on said resistor during demagnetization phases and charged by said current generator during magnetization phases.

3. The switching regulator of claim 1, wherein said circuit means is an integrator that generates said representative signal as the integral average of said logic flag over a switching period.

4. The switching regulator of claim 1, wherein said circuit means comprises:

a first counter that counts externally provided clock pulses when said logic flag is high and is reset when said logic flag is low;

a second counter that counts said externally provided clock pulses when said logic flag is low and is reset when said logic flag is high;

a processor input with the countings of said counters first and second, that generates said representative signal of said ratio.

5. The switching regulator of claim 4, wherein said circuit means further comprises a digital-to-analog converter downstream said processor that generates an analog replica of said representative signal.

6. The switching regulator of claim 1, wherein said circuit means comprises:

a first monostable flip-flop input with said logic flag, that generates a first pulse signal in correspondence of trailing or leading edges of said logic flag;

a second monostable flip-flop input with said logic flag, that generates a second pulse signal in correspondence of leading or trailing edges of said logic flag;

a circuit block connected in cascade to said first monostable flip-flop, that generates a third pulse signal as a delayed replica of said first pulse signal;

a linear voltage ramp generator, reset at each assertion of said third pulse signal;

a first sample-and-hold circuit that samples the voltage generated by said ramp generator at each assertion of said first pulse signal;

a second sample-and-hold circuit that samples the voltage generated by said ramp generator at each assertion of said second pulse signal;

a divider that generates said representative signal as the ratio between the sampled voltages of said second sample-and-hold circuit and of said first sample-and-hold circuit.

7. The switching regulator of claim 6, wherein said sample-and-hold circuits first and second are switched capacitors first and second respectively, charged with said voltage ramp when said first and second pulse signals are asserted, respectively, and said circuit block is a third monostable flip-flop that generates a pulse in correspondence of each trailing edge of said second signal.

8. The switching regulator of claim 1, wherein said feedback control circuit comprises:

a voltage divider coupled to the winding of the primary side for generating a scaled replica of said output voltage;

an error amplifier generating said control voltage representative of the difference between the reference voltage and said feedback voltage;

a logic circuit that flags magnetization and demagnetization phases of said switching regulator and generates said logic flag.

9. The switching regulator of claim 8, wherein said auxiliary block is input with said reference voltage and generates an adjusted reference voltage input to the error amplifier instead of said reference voltage.

10. The switching regulator of claim 2, wherein said auxiliary block is coupled to said voltage divider such to adjust said feedback voltage in function of the ratio between said threshold voltage and the charge voltage of said filter capacitor.

11. The switching regulator of claim 2, wherein said auxiliary block comprises:

a divider input with said threshold voltage and the charge voltage of said filter capacitor, generating a quotient signal representative of said ratio;

an operational amplifier in cascade to said divider and input with said reference voltage, generating said adjusted reference voltage.

12. The switching regulator of claim 11, wherein said auxiliary block further comprises a low-pass filter that generates a low-pass replica of said quotient signal that is input to said operational amplifier.

13. The switching regulator of claim 10, wherein said auxiliary block comprises:

a divider input with said threshold voltage and the charge voltage of said filter capacitor, generating a quotient signal representative of said ratio;

an adjustable current generator controlled by said quotient signal, that absorbs a current proportional to said quotient signal from the middle node of said resistive voltage divider.

14. The switching regulator of claim 13, wherein said adjustable current generator of the auxiliary block is coupled to said middle node of the resistive voltage divider through an auxiliary resistor.

15. A method of controlling a primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage, a logic flag for flagging demagnetization phases of said switching regulator and a control voltage that fixes the maximum current level that may circulate in the primary side of the regulator in function of the difference between a reference voltage and said feedback voltage, the method comprising the steps of:

generating a signal representative of the ratio between the duration of a demagnetization phase and the respective switching period, from signals in the primary side of the converter;

adjusting the difference between said reference voltage and the feedback voltage in function of said representative signal.

16. The method of claim 15, comprising the steps of

discharging a filter capacitor during demagnetization phases through a resistor and charging it with a constant current during the remaining part of switching periods flagged by said logic flag;

adjusting the difference between said reference voltage and said feedback signal in function of the ratio between said control voltage and the charge voltage of said filter capacitor.

17. A method of generating a signal representative of a current delivered by a primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage, a logic flag for flagging demagnetization phases of said switching regulator and a control voltage that fixes the maximum current level that may circulate in the primary side of the regulator in function of the difference between a reference voltage and said feedback voltage, the method using only signals available at the primary side and comprising the steps of:

discharging a filter capacitor during demagnetization phases through a resistor and charging it with a constant current during the remaining part of switching periods flagged by said logic flag;

generating said representative signal as a voltage proportional to the ratio between said control voltage and the charge voltage of said filter capacitor.

18. A method of generating a signal representative of a current delivered by a primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage and a logic flag for flagging demagnetization phases of said switching regulator, the method using only signals available at the primary side and comprising the step of

generating said representative signal by integrating said logic flag over a switching period and scaling the resulting voltage by a factor corresponding to the duration of said switching period.

19. A method of generating a signal representative of a current delivered by a primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage and a logic flag for flagging demagnetization phases of said switching regulator, the method using only signals available at the primary side and comprising the steps of:

generating counting values first and second of externally provided clock pulses while said logic flag is high and while said logic flag is low, respectively;

generating said representative signal as the ratio between said counting values first and second.

20. A method of generating a signal representative of a current delivered by a primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage and a logic flag for flagging demagnetization phases of said switching regulator, the method using only signals available at the primary side and comprising the steps of:

generating a linear voltage ramp reset at the beginning of each demagnetization phase;

sampling said linear voltage ramp at the beginning and at the end of said demagnetization phase, generating corresponding voltages first and second;

generating said representative signal as the ratio between said voltages second and first.

21. Circuit means for generating a signal representative of a current delivered by a primary-sensing flyback switching regulator, having a primary side generating a primary voltage magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side including a feedback control circuit that generates a feedback voltage representative of said output voltage and a logic flag for flagging demagnetization phases of said switching regulator, the circuit means comprising:

a first monostable flip-flop input with said logic flag, that generates a first pulse signal in correspondence of trailing or leading edges of said logic flag;

a second monostable flip-flop input with said logic flag, that generates a second pulse signal in correspondence of leading or trailing edges of said logic flag;

a circuit block connected in cascade to said first monostable flip-flop, that generates a third pulse signal as a delayed replica of said first pulse signal;

a linear voltage ramp generator, reset at each assertion of said third pulse signal;

a first sample-and-hold circuit that samples the voltage generated by said ramp generator at each assertion of said first pulse signal;

a second sample-and-hold circuit that samples the voltage generated by said ramp generator at each assertion of said second pulse signal;

a divider that generates said representative signal as the ratio between the sampled voltages of said second sample-and-hold circuit and of said first sample-and-hold circuit.

22. The circuit means of claim 21, wherein said sample-and-hold circuits first and second are switched capacitors first and second respectively, charged with said voltage ramp when said first and second pulse signals are asserted, respectively, and said circuit block is a third monostable flip-flop that generates a pulse in correspondence of each trailing edge of said second signal.

23. Circuit means for generating a signal representative of a current delivered by a primary-sensing switching regulator, having a primary side generating a control voltage, magnetically coupled to a secondary side that generates a regulated output voltage on output terminals of the regulator, the primary side comprising a feedback control circuit that generates said control voltage and a logic flag for detecting demagnetization phases of said switching regulator, the circuit means comprising:

a first counter that counts externally provided clock pulses when said logic flag is high and is reset when said logic flag is low;

a second counter that counts said externally provided clock pulses when said logic flag is low and is reset when said logic flag is high;

a processor input with the countings of said counters first and second, that generates said representative signal of said ratio.

24. A power-supply controller, comprising:

a switching-control circuit operable to control a switch coupled to a primary winding of a transformer;

an error amplifier having a first input node operable to receive a first feedback signal from an auxiliary winding of the transformer, a second input node operable to receive a comparison signal, and an output node operable to provide a control signal to the switching-control circuit; and

a comparison-signal generator operable to generate the comparison signal in response to a first compensation signal that is isolated from a secondary winding of the transformer and that is proportional to a load current through a conductor disposed between the secondary winding and a load.

25. The power-supply controller of claim 24 wherein the switching-controller circuit comprises a comparator having a first input node operable to receive the control signal from the error amplifier, a second input node operable to receive a second feedback signal that is proportional to a current through the primary winding, and an output node operable to be coupled to a control node of the switch.

26. The power-supply controller of claim 24 wherein the feedback, comparison, and control signals respectively comprise feedback, comparison, and control voltages.

27. The power-supply controller of claim 24 wherein the first compensation signal is operable to have a first level while a non-zero current flows through the secondary winding and to have a second level while a substantially zero current flows through the secondary winding.

28. The power-supply controller of claim 24 wherein the first compensation signal is proportional to a ratio of a time during which current flows through the secondary winding to a period during which the switching-controller circuit activates and deactivates the switch.

29. The power-supply controller of claim 24, further comprising a compensation circuit operable to generate the first compensation signal from a second compensation that is isolated from the secondary winding and that is proportional to the load current.

30. The power-supply controller of claim 29 wherein the compensation circuit is operable to generate the first compensation signal from the second compensation signal and from a reference signal.

31. The power-supply controller of claim 29 wherein the compensation circuit is operable to generate the first compensation signal from the second compensation signal and from a reference current.

32. The power-supply controller of claim 29 wherein the first and second compensation signals respectively comprise first and second compensation voltages.

33. The power-supply controller of claim 24 wherein the comparison-signal generator is operable to generate the comparison signal in response to a reference signal.

34. The power-supply controller of claim 24 wherein the comparison-signal generator is operable to generate the comparison signal in response to a reference voltage.

35. The power-supply controller of claim 24 wherein the comparison-signal generator is operable to generate the comparison signal in response to the control signal.

36. The power-supply controller of claim 24 wherein the comparison-signal generator is operable to generate the comparison signal in response to the control signal and a reference signal.

37. The power-supply controller of claim 24 wherein the comparison-signal generator is operable to generate the comparison signal equal to a difference between a reference voltage and a ratio of the control signal to the first compensation signal.

38. The power-supply controller of claim 24 wherein the load current substantially equals a current flowing through the secondary winding.

39. A power-supply controller, comprising:

a switching-control circuit operable to control a switch coupled to a primary winding of a transformer;

an error amplifier having a first input node operable to receive a first feedback signal, a second input node operable to receive a reference signal, and an output node operable to provide a control signal to the switching-control circuit; and

a feedback-signal generator operable to generate the first feedback signal in response to a first compensation signal that is isolated from a secondary winding of the transformer and that is proportional to a load current through a conductor disposed between the secondary winding and a load.

40. The power-supply controller of claim 39 wherein the switching-controller circuit comprises a comparator having a first input node operable to receive the control signal from the error amplifier, a second input node operable to receive a second feedback signal that is proportional to a current through the primary winding, and an output node operable to be coupled to a control node of the switch.

41. The power-supply controller of claim 39 wherein the feedback, reference, and control signals respectively comprise feedback, reference, and control voltages.

42. The power-supply controller of claim 39 wherein the first compensation signal is operable to have a first level while a non-zero current flows through the secondary winding and to have a second level while a substantially zero current flows through the secondary winding.

43. The power-supply controller of claim 39 wherein the first compensation signal comprises a substantially DC compensation voltage.

44. The power-supply controller of claim 39 wherein the first compensation signal is proportional to a ratio of a time during which current flows through the secondary winding to a period during which the switching-controller circuit activates and deactivates the switch.

45. The power-supply controller of claim 39, further comprising a compensation circuit operable to generate the first compensation signal from a second compensation that is isolated from the secondary winding and that is proportional to the load current.

46. The power-supply controller of claim 45 wherein the compensation circuit is operable to generate the first compensation signal from the second compensation signal and from a reference signal.

47. The power-supply controller of claim 45 wherein the compensation circuit is operable to generate the first compensation signal from the second compensation signal and from a reference current.

48. The power-supply controller of claim 45 wherein the first and second compensation signals respectively comprise first and second compensation voltages.

49. The power-supply controller of claim 39 wherein the feedback-signal generator is operable to generate the first feedback signal in response to a signal from an auxiliary winding of the transformer.

50. The power-supply controller of claim 39 wherein the feedback-signal generator is operable to generate the first feedback signal in response to a voltage across an auxiliary winding of the transformer.

51. The power-supply controller of claim 39 wherein the feedback-signal generator is operable to generate the first feedback signal in response to the control signal.

52. The power-supply controller of claim 39 wherein the feedback-signal generator is operable to generate the feedback signal in response to the control signal and a signal from an auxiliary winding of the transformer.

53. The power-supply controller of claim 39 wherein the feedback-signal generator is operable to generate the feedback signal inversely proportional to a ratio of the control signal to the first compensation signal.

54. The power-supply controller of claim 39 wherein the load current substantially equals a current flowing through the secondary winding.

55. A power supply, comprising:

a transformer having primary, secondary, and auxiliary windings;

a switch serially coupled to the primary winding; and

a power-supply controller, comprising

a switching-control circuit operable to control the switch,

an error amplifier having a first input node operable to receive a first feedback signal from the auxiliary winding, a second input node operable to receive a comparison signal, and an output node operable to provide a control signal to the switching-control circuit, and

a comparison-signal generator operable to generate the comparison signal in response to a first compensation signal that is isolated from the secondary winding of the transformer and that is proportional to a load current through a conductor disposed between the secondary winding and a load.

56. The power supply of claim 55 wherein the switch comprises a transistor.

57. A power supply, comprising:

a transformer having primary, secondary, and auxiliary windings;

a switch serially coupled to the primary winding; and

a power-supply controller, comprising

a switching-control circuit operable to control the switch,

an error amplifier having a first input node operable to receive a first feedback signal, a second input node operable to receive a reference signal, and an output node operable to provide a control signal to the switching-control circuit, and

a feedback-signal generator operable to generate the first feedback signal in response to a first compensation signal that is isolated from a secondary winding and that is proportional to a load current through a conductor disposed between the secondary winding and a load.

58. The power supply of claim 57 wherein the switch comprises a transistor.

59. A system, comprising:

a load;

a conductor having a first node coupled to the load and having a second node; and

a power supply comprising

a transformer having a primary winding, a secondary winding coupled to the second node of the conductor, and an auxiliary winding,

a switch serially coupled to the primary winding, and

a power-supply controller, comprising

a switching-control circuit operable to control the switch,

an error amplifier having a first input node operable to receive a first feedback signal from the auxiliary winding, a second input node operable to receive a comparison signal, and an output node operable to provide a control signal to the switching-control circuit, and

a comparison-signal generator operable to generate the comparison signal in response to a first compensation signal that is isolated from the secondary winding of the transformer and that is proportional to a current through the conductor.

60. The system of claim 59 wherein the load and the power-supply controller are disposed on a same integrated-circuit die.

61. The system of claim 59 wherein the load, the power-supply controller, and the switch are disposed on a same integrated-circuit die.

62. The system of claim 59 wherein the load, the conductor, and the power supply are disposed on a same integrated-circuit die.

63. The system of claim 59 wherein the load comprises a controller.

64. The system of claim 59 wherein the load and the power-supply controller are disposed on separate integrated-circuit dies.

65. The system of claim 59 wherein the load and the conductor are disposed on a same integrated-circuit die.

66. The system of claim 59 wherein:

the load is disposed on a first integrated-circuit die;

the power-supply controller is disposed on a second integrated-circuit die; and

the conductor is disposed between the first and second dies.

67. A system, comprising:

a load;

a conductor having a first node coupled to the load and having a second node; and

a power supply, comprising

a transformer having primary, secondary, and auxiliary windings,

a switch serially coupled to the primary winding, and

a power-supply controller, comprising

a switching-control circuit operable to control the switch,

an error amplifier having a first input node operable to receive a first feedback signal, a second input node operable to receive a reference signal, and an output node operable to provide a control signal to the switching-control circuit, and

a feedback-signal generator operable to generate the first feedback signal in response to a first compensation signal that is isolated from a secondary winding and that is proportional to a load current through a conductor disposed between the secondary winding and a load.

68. The system of claim 67 wherein the load and the power-supply controller are disposed on a same integrated-circuit die.

69. The system of claim 67 wherein the load, the power-supply controller, and the switch are disposed on a same integrated-circuit die.

70. The system of claim 67 wherein the load, the conductor, and the power supply are disposed on a same integrated-circuit die.

71. The system of claim 67 wherein the load comprises a controller.

72. The system of claim 67 wherein the load and the power-supply controller are disposed on separate integrated-circuit dies.

73. The system of claim 67 wherein the load and the conductor are disposed on a same integrated-circuit die.

74. The system of claim 67 wherein:

the load is disposed on a first integrated-circuit die;

the power-supply controller is disposed on a second integrated-circuit die; and

the conductor is disposed between the first and second dies.

75. A method, comprising:

generating a regulated output voltage with a secondary winding of a transformer;

generating a comparison signal in response to a first compensation signal that is isolated from, and that is proportional to a current through, the secondary winding;

generating a control signal in response to the comparison signal and in response to a first feedback signal from an auxiliary winding of the transformer; and

switching a current through a primary winding of the transformer in response to the control signal.

76. The method of claim 75, further comprising:

generating the first compensation signal having a first level while a non-zero current flows through the secondary winding; and

generating the first compensation signal having a second level otherwise.

77. The method of claim 75, further comprising generating the first compensation signal proportional to a ratio of a time during which current flows through the secondary winding to a period with which current is switched through the primary winding.

78. The method of claim 75, further comprising generating the first compensation signal from a second compensation signal that is isolated from the secondary winding and that is proportional to the current through the secondary winding.

79. The method of claim 78 wherein generating the first compensation signal comprises generating the first compensation signal from the second compensation signal and from a reference signal.

80. The method of claim 75 wherein generating the comparison signal comprises generating the comparison signal in response to a reference signal.

81. The method of claim 75 wherein generating the comparison signal comprises generating the comparison signal in response to the control signal.

82. The method of claim 75 wherein generating the comparison signal comprises generating the comparison signal in response to the control signal and a reference signal.

83. The method of claim 75 wherein generating the comparison signal comprises generating the comparison signal equal to a difference between a reference voltage and a ratio of the control signal to the first compensation signal.

84. The method of claim 75 wherein the first compensation signal is proportional to an average current through the secondary winding.

85. A method, comprising:

generating a regulated output voltage with a secondary winding of a transformer;

generating a feedback signal in response to a first compensation signal that is isolated from, and that is proportional to a current through, the secondary winding;

generating a control signal in response to a reference signal and in response to the feedback signal; and

switching a current through a primary winding of the transformer in response to the control signal.

86. The method of claim 85, further comprising generating the first compensation signal proportional to a ratio of a time during which current flows through the secondary winding to a period with which current is switched through the primary winding.

87. The method of claim 85, further comprising generating the first compensation signal from a second compensation that is isolated from the secondary winding and that is proportional to the current through the secondary winding.

88. The method of claim 87 wherein generating the first compensation signal comprises generating the first compensation signal from the second compensation signal and from a reference signal.

89. The method of claim 85 wherein generating the feedback signal comprises generating the feedback signal in response to a signal from an auxiliary winding of the transformer.

90. The method of claim 85 wherein generating the feedback signal comprises generating the feedback signal in response to the control signal.

91. The method of claim 85 wherein generating the feedback signal comprises generating the first feedback signal in response to the control signal and a signal from an auxiliary winding of the transformer.

92. The method of claim 85 wherein generating the feedback signal comprises generating the feedback signal inversely proportional to a ratio of the control signal to the first compensation signal.