Adaptive output current control for switching circuits

• US 7,639,517 B2
• Filed: 02/08/2007
• Issued: 12/29/2009
• Est. Priority Date: 02/08/2007
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Ng, David Roy, Dobkin, Robert C., Zhou, Xigen, Pietkiewicz, Steven M.
• Primary Examiner(s): Sterrett; Jeffrey L
• Application Number:
  US11/703,718
• Publication Number:
  US 20080192514A1
• Time in Patent Office: 1,055 Days
• Field of Search: 363/21.01, 363/21.04, 363/21.09, 363/21.12, 363/21.17, 363/97
• US Class Current: 363/21.17
• CPC Class Codes: H02M 3/335 using semiconductor devices only

Abstract

System and methodology for controlling output current of switching circuitry having an input circuit and an output circuit electrically isolated from each other. A value of the output current may be determined based on input voltage, input current and reflected output voltage representing the voltage in the input circuit which corresponds to the output voltage. A switching element in the input circuit is controlled to produce the determined value of output current.

Claims

1. A method of controlling an output current of switching circuitry having an input circuit for receiving an input voltage and an input current, and an output circuit for developing an output voltage, the output circuit electrically isolated from the input circuit, comprising the steps of:

determining a value of the output current in the output circuit based on the input voltage, the input current and a reflected output voltage obtained at the input circuit, and

controlling a switching element in the input circuit to produce the determined value of output current.

2. The method of claim 1, wherein the output current value is determined so as to reduce variation of the output current with a change in the input voltage and the output voltage.

3. The method of claim 1, wherein the switching element is controlled to operate the switching circuit in a boundary conduction mode.

4. The method of claim 1, wherein the switching element is controlled to operate the switching circuit in a continuous conduction mode.

5. The method of claim 1, wherein the switching element is controlled to operate the switching circuit in a discontinuous conduction mode.

6. The method of claim 1, wherein the switching circuitry includes an inductive element having a first winding isolated from a second winding.

7. A method of controlling an output current of switching circuitry having an input circuit for receiving an input current and an input voltage represented by a fixed parameter, and an output circuit for developing an output voltage, the output circuit electrically isolated from the input circuit, comprising the steps of:

determining a value of the output current in the output circuit based on the input current, the fixed parameter and a reflected output voltage obtained at the input circuit, and

controlling a switching element in the input circuit to produce the determined value of output current.

8. The method of claim 7, wherein the switching element is controlled to operate the switching circuit in a boundary conduction mode.

9. The method of claim 7, wherein the switching element is controlled to operate the switching circuit in a continuous conduction mode.

10. The method of claim 7, wherein the switching element is controlled to operate the switching circuit in a discontinuous conduction mode.

11. A system for controlling an output current of switching circuitry including an input circuit for receiving an input voltage and an input current, and an output circuit for producing an output voltage, the output circuit electrically isolated from the input circuit, the system comprising:

a switching control circuit for controlling a switching element in the input circuit so as to control the output current in the output circuit,

the switching control circuit being configured for determining a value of the output current based on the input voltage, the input current, and a reflected output voltage obtained at the input circuit, and for controlling the switching element to reduce variation of the output current with change in the input voltage and the output voltage.

12. The system of claim 11, wherein the switching control circuit further is configured to control the switching element to produce the output current that is proportional to the input voltage.

13. The system of claim 11, wherein the switching control circuit further is configured to control the switching element to produce the output current that is proportional to the input current.

14. The system of claim 11, wherein the switching control circuit further is configured to control the switching element to produce the output current that is inversely proportional to the reflected output voltage.

15. The system of claim 11, wherein the input circuit includes a primary winding of an inductive element, and the output circuit includes a secondary winding of the inductive element.

16. The system of claim 15, wherein the switching control circuit further is configured to control the switching element to produce the output current that is proportional to a turns-ratio of the inductive element.

17. The system of claim 11, wherein the switching control circuit is configured to operate the switching circuit in a boundary conduction mode.

18. The system of claim 11, wherein the switching control circuit is configured to operate the switching circuit in a continuous conduction mode.

19. The system of claim 11, wherein the switching control circuit is configured to operate the switching circuit in a discontinuous conduction mode.

20. A system for controlling an output current of switching circuitry including an input circuit for receiving an input current and an input voltage represented by a fixed parameter, and an output circuit for producing an output voltage, the output circuit electrically isolated from the input circuit, the system comprising:

a switching control circuit for controlling a switching element in the input circuit so as to control the output current in the output circuit,

the switching control circuit being configured for determining a value of the output current based on the input current, the fixed parameter and a reflected output voltage obtained at the input circuit, and for controlling the switching element to reduce variation of the output current with change in the input voltage and the output voltage.

21. The system of claim 20, wherein the switching control circuit is configured to operate the switching circuit in a boundary conduction mode.

22. The system of claim 20, wherein the switching control circuit is configured to operate the switching circuit in a continuous conduction mode.

23. The system of claim 20, wherein the switching control circuit is configured to operate the switching circuit in a discontinuous conduction mode.

24. A system for driving a light-emitting diode (LED), comprising:

a switching regulator for providing power supply to drive the LED, the switching regulator including an input circuit for receiving an input voltage and an input current, and an output circuit for developing an output voltage, electrically isolated from the input circuit; and

a control circuit for controlling current in the output circuit of the switching regulator, the control circuit being configured for producing the current in the output circuit based on the input voltage, the input current, and a reflected output voltage obtained at the input circuit.

25. The system of claim 24, wherein the input circuit includes a primary winding of an inductive element, and the output circuit includes a secondary winding of the inductive element.

26. The system of claim 24, wherein the control circuit is configured to operate the switching regulator in a boundary conduction mode.

27. The system of claim 24, wherein the control circuit is configured to operate the switching circuit in a continuous conduction mode.

28. The system of claim 24, wherein the control circuit is configured to operate the switching circuit in a discontinuous conduction mode.

29. A method of controlling switching circuitry of a type having an input circuit for receiving an input voltage and an output circuit for developing an output voltage, the output circuit electrically isolated from the input circuit, comprising the steps of:

determining a value of output current in the output circuit based on the input voltage and a reflected output voltage obtained at the input circuit, and

controlling a switching element in the input circuit to produce the determined value of output current.

30. The method of claim 29, wherein the output current value is determined so as to reduce variation of the output current with a change in the input voltage and the output voltage.

31. The method of claim 29, wherein the switching element is controlled to operate the switching circuit in a boundary conduction mode.

32. The method of claim 29, wherein the switching element is controlled to operate the switching circuit in a continuous conduction mode.

33. The method of claim 29, wherein the switching circuit includes an inductive element having a first winding isolated from a second winding.

34. A method of controlling switching circuitry operating in a discontinuous conduction mode and including an input circuit and an output circuit for producing an output voltage, the output circuit electrically isolated from the input circuit, comprising the steps of:

determining a value of output current in the output circuit based on a reflected output voltage obtained at the input circuit, and

controlling a switching element in the input circuit to produce the determined value of output current.

35. A system for controlling switching circuitry including an input circuit for receiving an input voltage and an output circuit for producing an output voltage, the output circuit electrically isolated from the input circuit, the system comprising:

a switching control circuit for controlling a switching element in the input circuit so as to control current in the output circuit,

the switching control circuit being configured for determining a value of the current in the output circuit based on the input voltage and a reflected output voltage obtained at the input circuit, and for controlling the switching element to reduce variation of the current in the output circuit with change in the input voltage and the output voltage.

36. The system of claim 35, wherein the switching control circuit further is configured to control the switching element to produce current in the output circuit that is proportional to the input voltage.

37. The system of claim 35, wherein the switching control circuit further is configured to control the switching element for producing current in the output circuit that is inversely proportional to the sum of the input voltage and the reflected output voltage.

38. The system of claim 35, wherein the input circuit includes a primary winding of an inductive element, and the output circuit includes a secondary winding of the inductive element.

39. The system of claim 35, wherein the switching control circuit further is configured to adjust switch current in the switching element for producing the current in the output circuit at a level corresponding to the determined value.

40. The system of claim 39, wherein the switching control circuit further is configured to adjust a peak level of the switch current in the switching element for producing the current in the output circuit at a level corresponding to the determined value.

41. The system of claim 40, wherein the switching control circuit includes a comparator for comparing the switch current with a reference value to switch the switching element when the switch current exceeds the reference value.

42. The system of claim 41, wherein the switching control circuit further includes a reference circuit for producing the reference value.

43. The system of claim 42, wherein the reference circuit is configured for producing the reference value inversely proportional to the input voltage.

44. The system of claim 43, wherein the reference circuit is configured for producing the reference value that is proportional to the sum of the input voltage and the reflected output voltage.

45. The system of claim 44, wherein the input circuit includes a primary winding of an inductive element, the output circuit includes a secondary winding of the inductive element, and the reference circuit is configured to provide the reference value proportional to a turns-ratio of the inductive element.

46. The system of claim 35, wherein the switching control circuit is configured to operate the switching circuit in a boundary conduction mode.

47. The system of claim 35, wherein the switching control circuit is configured to operate the switching circuit in a continuous conduction mode.

48. A system for controlling switching circuitry including an input circuit and an output circuit for developing an output voltage, the output circuit electrically isolated from the input circuit, the system comprising:

a switching control circuit for controlling a switching element in the input circuit to control current in the output circuit of the switching circuit,

the switching control circuit being configured to operate the switching circuit in a discontinuous conduction mode,

the switching control circuit being further configured to control the switching element for producing the current in the output circuit based on a reflected output voltage obtained at the input circuit.

49. The system of claim 48, wherein the switching control circuit further is configured to control the switching element for producing the current in the output circuit inversely proportional to the reflected output voltage.

50. The system of claim 48, wherein the input circuit includes a primary winding of an inductive element, and the output circuit includes a secondary winding of the inductive element.

51. The system of claim 50, wherein the switching control circuit is configured to control the switching element for producing the current in the output circuit directly proportional to inductance of the inductive element.

52. The system of claim 51, wherein the switching control circuit is configured to control the switching element for producing the current in the output circuit directly proportional to a switching frequency of the switching element.

53. The system of claim 52, wherein the switching control circuit is configured to adjust switch current in the switching element in accordance with the input voltage supplied to the switching circuit.

54. The system of claim 53, wherein the switching control circuit includes a comparator for comparing the switch current with a reference value to switch the switching element when the switch current exceeds the reference value.

55. The system of claim 54, wherein the switching control circuit includes a reference circuit for producing the reference value proportional to square root of the reflected output voltage.

56. The system of claim 55, wherein the reference circuit is configured for producing the reference value inversely proportional to square root of the inductance of the inductive element.

57. The system of claim 56, wherein the reference circuit is configured for producing the reference value inversely proportional to square root of the switching frequency of the switching element.