Discontinuous conduction mode (DCM) using sensed current for a switch-mode converter

• US 7,719,248 B1
• Filed: 04/28/2008
• Issued: 05/18/2010
• Est. Priority Date: 05/02/2007
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John Laurence
• Primary Examiner(s): Laxton; Gary L
• Application Number:
  US12/110,714
• Time in Patent Office: 750 Days
• Field of Search: 323/205, 323/207, 323/222, 323/282, 323/283, 323/284, 323/285
• US Class Current: 323/283
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• CPC Class Codes: H03M 3/476 Non-linear conversion systems
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A switch-mode converter controller and method utilizes a comparator for receiving and comparing a sensed current and a peak current that is determined by a product of a multiplying factor, that is greater than or equal to two, and a target current. A finite state machine (FSM) is configured to operate the switch-mode converter in a discontinuous conduction mode (DCM). Responsive to the comparator, the FSM turns on the switch and observes an on-time duration of the switch until the sensed current reaches the peak current; calculates a switching period responsive to the peak current and the observed on-time duration; and varies the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current. The FSM can also be configured to alternatively operate the switch-mode converter in a continuous conduction mode (CCM).

Claims

1. A switching converter controller for controlling a switch-mode converter which has a switch and an inductor coupled to the switch wherein the switch-mode converter receives an input voltage and provides an output voltage and wherein a sensed current is observed from the switch-mode converter, comprising:

a comparator for receiving and comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current, wherein further the multiplying factor is greater than or equal to two; and

a finite state machine, configured to operate the switch-mode converter in a discontinuous conduction mode (DCM), responsive to comparisons made by the comparator, for;

turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;

calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration; and

varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

2. The switching converter controller of claim 1, wherein a flyback signal is observed from the switch-mode converter and wherein the finite state machine responsive to comparisons made by the comparator, turns off the switch and observes an off-time duration of the switch based on the flyback signal.

3. The switch-mode converter controller of claim 2, further comprising:

a flyback time detector coupled to the switch-mode converter wherein the flyback time detector detects and generates the flyback signal; and

wherein the finite state machine further comprises a flyback detector logic unit coupled to the flyback time detector for receiving and using the flyback signal to observe the off-time duration of the switch.

4. The switching converter controller of claim 1, wherein the finite state machine calculates an off-time duration for the switch based on the input voltage and the output voltage of the switch-mode converter and turns off the switch for the calculated off-time duration.

5. The switching converter controller of claim 1 further comprising a multiplying factor function generator coupled to the finite state machine wherein the multiplying factor function generator provides the multiplying factor to the finite state machine and the multiplying factor function generator sets the multiplying factor to a higher value when the target current is set to a lower value.

6. The switch-mode converter controller of claim 1, wherein the finite state machine is configured to alternatively operate the switch-mode converter in a continuous conduction mode (CCM).

7. The switch-mode converter controller of claim 6, wherein:

when the switch-mode converter is operating in CCM, the comparator receives and compares the sensed current value representative of the sensed current and a target current value representative of the target current; and

the finite state machine, responsive to the comparisons made by the comparator, operates the switch-mode converter in the continuous conduction mode (CCM).

8. The switch-mode converter controller of claim 7, wherein the switch-mode converter operates in CCM when the target current is set greater than or equal to a minimum CCM target current and wherein the switch-mode converter operates in DCM when the target current is set less than the minimum CCM target current.

9. A method for controlling a switch-mode converter which has a switch and an inductor coupled to the switch wherein the switch-mode converter receives an input voltage and provides an output voltage and wherein a sensed current is observed from the switch-mode converter, comprising:

in configuring to operate the switch-mode converter in a discontinuous conduction mode (DCM) and responsive to comparisons made by the comparing;

comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current wherein further the multiplying factor is greater than or equal to two;

turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;

calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration; and

varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

10. The method of claim 9, further comprising:

observing a flyback signal from the switch-mode converter;

responsive to comparisons made by the comparing, turning off the switch and observing an off-time duration of the switch based on the flyback signal.

11. The method of claim 9, further comprising:

calculating an off-time duration for the switch based on the input voltage and the output voltage of the switch-mode converter; and

turning off the switch for the calculated off-time duration.

12. The method of claim 9, further comprising:

setting the multiplying factor to a higher value when the target current is set to a lower value.

13. The method of claim 9, further comprising:

alternatively operating the switch-mode converter in a continuous conduction mode (CCM).

14. The method of claim 13, further comprising:

when the switch-mode converter is operating in CCM, receiving and comparing the sensed current value representative of the sensed current and a target current value representative of the target current; and

responsive to the comparisons made by the comparing, operating the switch-mode converter in the continuous conduction mode (CCM).

15. The method of claim 14 further comprising:

operating the switch-mode converter in CCM when the target current is set greater than or equal to a minimum CCM target current; and

operating the switch-mode converter in DCM when the target current is set less than the minimum CCM target current.

16. A power factor corrector (PFC), comprising:

a switch-mode boost stage having a switch and an inductor coupled to the switch wherein the switch-mode boost stage receives a rectified line input voltage and provides a link output voltage and wherein a sensed current is observed from the switch-mode boost stage;

a target current generator for receiving the link output voltage and for generating a target current proportionate to the rectified line input voltage;

a comparator for receiving and comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current, wherein further the multiplying factor is greater than or equal to two; and

a finite state machine, configured to operate the switch-mode converter in a discontinuous conduction mode (DCM), responsive to comparisons made by the comparator, for;

turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;

calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration; and

varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

17. The PFC of claim 16, wherein a flyback signal is observed from the switch-mode converter and wherein the finite state machine responsive to comparisons made by the comparator, turns off the switch and observes an off-time duration of the switch based on the flyback signal.

18. The PFC of claim 17, further comprising:

a flyback time detector coupled to the switch-mode converter wherein the flyback time detector detects and generates the flyback signal; and

wherein the finite state machine further comprises a flyback detector logic unit coupled to the flyback time detector for receiving and using the flyback signal to observe the off-time duration of the switch.

19. The PFC of claim 16, wherein the finite state machine calculates an off-time duration for the switch based on the rectified line input voltage and the link output voltage of the switch-mode converter and turns off the switch for the calculated off-time duration.

20. The PFC of claim 16 further comprising a multiplying factor function generator coupled to the finite state machine wherein the multiplying factor function generator provides the multiplying factor to the finite state machine and the multiplying factor function generator sets the multiplying factor to a higher value when the target current is set to a lower value.

21. The PFC of claim 16, wherein the finite state machine is configured to alternatively operate the switch-mode converter in a continuous conduction mode (CCM).

22. The PFC of claim 16, wherein the finite state machine selects operating the switch-mode converter in CCM based in one part of a cycle of the rectified line input voltage and in DCM based in another part of the cycle of the rectified line input voltage.

23. The PFC of claim 21, wherein:

when the switch-mode converter is operating in CCM, the comparator receives and compares the sensed current value representative of the sensed current and a target current value representative of the target current; and

the finite state machine, responsive to the comparisons made by the comparator, operates the switch-mode converter in the continuous conduction mode (CCM).

24. The PFC of claim 23, wherein the switch-mode converter operates in CCM when the target current is set greater than or equal to a minimum CCM target current and wherein the switch-mode converter operates in DCM when the target current is set less than the minimum CCM target current.

25. A method for power factor correction (PFC), comprising:

coupling a switch and an inductor together to form a switch-mode boost stage that receives a rectified line input voltage and provides a link output voltage;

observing a sensed current from the switch-mode boost stage;

receiving the link output voltage;

generating a target current proportionate to the rectified line input voltage; and

in configuring to operate the switch-mode converter in a discontinuous conduction mode (DCM) and responsive to comparisons made by the comparing;

comparing a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current wherein further the multiplying factor is greater than or equal to two;

turning on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;

calculating a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration; and

varying the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

26. The method of claim 25, further comprising:

observing a flyback signal from the switch-mode converter;

responsive to comparisons made by the comparing, turning off the switch and observing an off-time duration of the switch based on the flyback signal.

27. The method of claim 25, further comprising:

calculating an off-time duration for the switch based on the rectified line input voltage and the link output voltage of the switch-mode converter; and

turning off the switch for the calculated off-time duration.

28. The method of claim 25, further comprising:

setting the multiplying factor to a higher value when the target current is set to a lower value.

29. The method of claim 25, further comprising:

alternatively operating the switch-mode converter in a continuous conduction mode (CCM).

30. The method of claim 29, further comprising:

when the switch-mode converter is operating in CCM, receiving and comparing the sensed current value representative of the sensed current and a target current value representative of the target current; and

responsive to the comparisons made by the comparing, operating the switch-mode converter in the continuous conduction mode (CCM).

31. The method of claim 29, further comprising:

operating the switch-mode converter in CCM when the target current is set greater than or equal to a minimum CCM target current; and

operating the switch-mode converter in DCM when the target current is set less than the minimum CCM target current.

32. An integrated circuit which incorporates a switch-mode converter controller for controlling a switch-mode converter which has a switch and an inductor coupled to the switch wherein the switch-mode converter receives an input voltage and provides an output voltage and wherein a sensed current is observed from the switch-mode converter, and wherein the switch-mode converter controller includes a comparator and a finite state machine, the integrated circuit configured to:

in configuring to operate the switch-mode converter in a discontinuous conduction mode (DCM) and responsive to comparisons made by the comparing;

compare a sensed current value representative of the sensed current and a peak current value representative of a peak current, wherein the peak current is determined by a product of a multiplying factor and a target current wherein further the multiplying factor is greater than or equal to two;

turn on the switch and observing an on-time duration of the switch until the sensed current reaches the peak current;

calculate a switching period of a switch control signal for controlling the switch wherein the switching period is responsive to the peak current and the observed on-time duration; and

vary the switching period responsive to the on-time duration and the multiplying factor such that an average of the sensed current equals the target current.

33. The integrated circuit of claim 32, further configured to:

alternatively operate the switch-mode converter in a continuous conduction mode (CCM).

34. The integrated circuit of claim 33 further configured to:

operate the switch-mode converter in CCM when the target current is set greater than or equal to a minimum CCM target current; and

operate the switch-mode converter in DCM when the target current is set less than the minimum CCM target current.

35. The integrated circuit of claim 33 wherein:

the switch-mode converter controller is configured to operate as a power factor correction controller for a power factor corrector;

the switch-mode converter is a switch-mode boost stage which receives a rectified line input voltage as the input voltage and provides a link output voltage as the output voltage and wherein the sensed current is observed from the switch-mode boost stage; and

the power factor correction controller further includes a target current generator for receiving the link output voltage as the input voltage and for generating a target current proportionate to the rectified line input voltage.