Off-line converter with digital control

• US 6,456,475 B1
• Filed: 08/29/2001
• Issued: 09/24/2002
• Est. Priority Date: 11/16/1998
• Status: Expired due to Term

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Lund, Leif, Balakrishnan, Balu, Djenguerian, Alex
• Primary Examiner(s): HUYNH, KIM NGOC
• Application Number:
  US09/941,905
• Publication Number:
  US 20020030957A1
• Time in Patent Office: 391 Days
• Field of Search: 361/17, 361/71, 361/72, 361/78, 361/75, 361/79, 361/83, 361/86, 361/93.2, 361/94, 323/276, 323/280, 323/283
• US Class Current: 361/94
• CPC Class Codes: B29C 2045/824 Accumulators
• CPC Class Codes: B29C 45/82 Hydraulic or pneumatic circuits
• CPC Class Codes: F16D 31/02 using pumps with pistons or plungers working in cylinders
• CPC Class Codes: H02H 7/1213 for DC-DC converters
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• 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

A circuit protects a power conversion system with a feedback control loop from a fault condition. The circuit has an oscillator having an input for generating a signal with a frequency and a timer connected to the oscillator input and to the feedback control loop. The timer disables the oscillator after a period following the opening of the feedback control loop to protect the power conversion system.

Claims

1. A circuit for protecting a power supply from fault conditions, comprising:

a switching device coupled to receive a switching signal and operable to control power delivered to an output of the power supply;

a feedback input for receiving a feedback signal representative of the output of the power supply, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal; and

a timer coupled to the switching device and the feedback input, the timer operable to disable the switching device to prevent power delivery to the output after detection of a fault condition.

2. The circuit of claim 1 wherein the feedback signal cycles periodically between the first and second states when the power supply operates normally.

3. The circuit of claim 1 wherein the existence of a fault condition is indicated by the feedback signal maintaining either the first state or the second state for at least a predetermined period.

4. The circuit of claim 1 wherein the timer disables the switching device after a first period of existence of the fault condition and wherein the timer enables the switching device after a second period.

5. The circuit of claim 4 wherein the switching device is alternately enabled for the first period and disabled for the second period when the fault condition exists.

6. The circuit of claim 5 wherein the switching device is enabled upon removal of the fault condition.

7. The circuit of claim 6 further comprising a capacitor that is charged at a first rate from a first threshold to a second threshold to generate the first period, the capacitor further being discharged from the second threshold to the first threshold at a second rate to generate the second period.

8. The circuit of claim 7 wherein the capacitor is discharged to a voltage below the first threshold each time the feedback signal changes state.

9. The circuit of claim 7 wherein the capacitor is discharged to a voltage below the first threshold each time the feedback signal enters the first state.

10. The circuit of claim 1 wherein the switching device is a power transistor.

11. The circuit of claim 1 wherein the timer comprises a digital counter.

12. The circuit of claim 11 further comprising an oscillator coupled to the counter, the oscillator having a predetermined frequency.

13. The circuit of claim 12, wherein the oscillator has a control input for changing the predetermined frequency, further comprising a first current source coupled to the oscillator control input to generate a first frequency.

14. The circuit of claim 13 further comprising a second current source coupled to the oscillator control input to generate a second frequency.

15. The circuit of claim 14 wherein the counter has an output coupled to the first and second current sources.

16. The circuit of claim 1 wherein the fault condition includes one or more of an output overload fault condition, an output short circuit fault condition and an open feedback control loop fault condition.

17. A method for protecting a power supply from fault conditions, comprising:

in response to a switching signal, enabling or disabling the delivery of power to an output of the power supply;

receiving a feedback signal representative of the output of the power supply, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal;

timing the feedback signal to detect whether a fault condition exists in the power supply; and

preventing the switching signal from enabling power delivery to the output in response to the detection of a fault condition.

18. The method of claim 17 wherein the feedback signal cycles periodically between the first and second states when the power supply operates normally.

19. The method of claim 17 wherein the existence of a fault condition is indicated by the feedback signal maintaining either the first state or the second state for at least a predetermined period.

20. The method of claim 17 wherein the switching signal is prevented from enabling power delivery to the output after a first period of existence of the fault condition and the switching signal is allowed to enable power delivery after a second period.

21. The method of claim 20, further comprising altematingly allowing the switching signal to enable power delivery to the output for the first period and preventing the switching signal from enabling power delivery to the output for the second period.

22. The method of claim 21 further comprising allowing the switching signal to enable power delivery to the output upon removal of the fault condition.

23. The method of claim 17 wherein the timing step includes counting periods of time digitally.

24. A circuit for protecting a power supply from fault conditions, comprising:

switching means coupled to receive a switching signal for controlling the delivery of power to an output of the power supply;

a feedback input for receiving a feedback signal representative of the output of the power supply, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal;

timing means coupled to the switching means and the feedback input for detecting a fault condition in the power supply and

means for disabling the switching means in response to the detection of a fault condition.

25. The circuit of claim 24 wherein the feedback signal cycles periodically between the first and second states when the power supply operates normally.

26. The circuit of claim 24 wherein the existence of a fault condition is indicated by the feedback signal maintaining either the first state or the second state for at least a predetermined period.

27. The circuit of claim 24 wherein the switching means is disabled after a first period of existence of the fault condition and further comprising means for enabling the switching means after a second period.

28. The circuit of claim 27, further comprising means for alternatingly enabling the switching means for the first period and disabling the switching means for the second period.

29. The circuit of claim 28 further comprising means for enabling the switching means upon removal of the fault condition.

30. The circuit of claim 24 wherein the timing means includes a digital counter.

31. The circuit of claim 30 further comprising means for oscillating at a first frequency when the switching means is enabled and at a second frequency when the switching means is disabled.

32. The circuit of claim 24 further comprising:

means for charging a capacitor at a first rate from a first threshold to a second threshold to generate the first period; and

means for discharging the capacitor from the second threshold to the first threshold at a second rate to generate the second period.

33. The circuit of claim 32 further comprising means for discharging the capacitor to a voltage below the first threshold each time the feedback signal changes state.

34. The circuit of claim 32 further comprising means for discharging the capacitor to a voltage below the first threshold each time the feedback signal enters the first state.

35. A fault protected power supply, comprising:

a energy transfer element having a input winding and an output winding, the output winding coupled to a secondary output;

a switching device coupled to the input winding of the energy transfer element for controlling delivery of power to the secondary output in response to a switching signal;

an oscillator for generating a signal with a predetermined frequency;

a feedback signal representative of the secondary output, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal; and

a timer coupled to the oscillator and coupled to receive the feedback signal, the timer operable to disable the switching device when the feedback signal indicates that the power supply is in a fault condition.

36. The power supply of claim 35 further comprising means for changing the frequency of the oscillator.

37. The power supply of claim 35 wherein the timer is further operable to alternatively enable and disable the switching device when the fault condition is present.

38. A method for protecting a power supply, comprising:

in response to a switching signal, enabling or disabling power delivery to a secondary output of the power supply;

generating an oscillating signal with a predetermined frequency;

timing a feedback signal representative of the secondary output with the oscillating signal to detect a fault condition, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal; and

in response to the detection of a fault condition, preventing the switching signal from enabling power delivery to the secondary output.

39. The method of claim 38 further comprising:

when the fault condition is present, alternately allowing the switching signal to enable power delivery and preventing the switching signal from enabling power delivery.

40. An automatically restartable power supply, comprising:

a energy transfer element having a input winding and an output winding, the output winding coupled to a secondary output;

a switching device coupled to the input winding of the energy transfer element for controlling the delivery of power to the secondary output in response to a switching signal;

a feedback signal representative of the secondary output, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal;

a capacitor;

means for charging the capacitor at a first rate from a first threshold to a second threshold to generate a first period and discharging the capacitor from the second threshold to the first threshold at a second rate to generate a second period;

means coupled to the switching device, the capacitor and the feedback signal, for alternately enabling the switching device during the first period and disabling the switching device during the second period when the feedback signal indicates that the power supply is in a fault condition; and

means for enabling the switching device when the feedback signal indicates the power supply is no longer in a fault condition.

41. A method for automatically restarting a power supply after the occurrence of a fault, comprising:

in response to a switching signal, enabling or disabling the delivery of power to a secondary output of the power supply;

receiving a feedback signal representative of the secondary output, the feedback signal cycling between a first state and a second state when the power supply operates normally and not cycling between the first and second states when the power supply is in a fault condition, the switching signal cycling separately from the cycling of the feedback signal;

generating a first period;

generating a second period;

when the feedback signal indicates that the power supply is in a fault condition, alternately allowing the switching signal to enable power delivery to the secondary output during the first period and preventing the switching signal from enabling power delivery to the secondary output during the second period; and

allowing the switching signal to enable power delivery to the secondary output when the feedback signal indicates the power supply is no longer in a fault condition.