Switch mode power supply controllers

• US 20070274107A1
• Filed: 06/01/2006
• Published: 11/29/2007
• Est. Priority Date: 05/23/2006
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Cambridge Semiconductor Limited (Power Integrations Incorporated)
• Inventors: Lalithambika, Vinod A., Garner, David M., Coulson, David Robert, Kumar, Jayaraman, de Silva, Devarahandi Indika Mahesh
• Granted Patent: US 7,447,049 B2
• Time in Patent Office: Days
• US Class Current: 363/21.120
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

This invention relates to SMPS controllers employing primary side sensing to detect a point of zero magnetic flux, at which the output voltage of the SMPS may be sampled accurately on the primary side. We describe a switch mode power supply (SMPS) controller for regulating the output voltage of an SMPS is response to a feedback signal from an auxilliary winding of a magnetic energy storage device forming part of an output circuit of the SMPS, the SMPS controller comprising: a reference level input to receive an output reference level signal; an input to receive said feedback signal, said feedback signal being responsive to a voltage on said auxilliary winding of said magnetic energy storage device; an integrator to integrate a difference between said feedback signal and a first fixed reference level signal; a first comparator to compare an output of said integrator with a second fixed reference level signal and to provide an output responsive to said comparison for regulating said SMPS output voltage.

Claims

1. A switch mode power supply (SMPS) controller for regulating the output voltage of an SMPS is response to a feedback signal from a winding of a magnetic energy storage device forming part of an output circuit of the SMPS, the SMPS controller comprising:

a reference level input to receive an output reference level signal;

an input to receive said feedback signal, said feedback signal being responsive to a voltage on said winding of said magnetic energy storage device;

an integrator to integrate a difference between said feedback signal and a first fixed reference level signal;

a first comparator to compare an output of said integrator with a second fixed reference level signal and to provide an output responsive to said comparison for regulating said SMPS output voltage.

2. An SMPS controller as claimed in claim 1 further comprising:

a second comparator to compare a signal derived from said feedback signal with a third reference level signal derived from said output voltage reference level signal, at a time when said first comparator indicates that said integrator output is substantially equal to said second fixed reference level signal; and

a controller output coupled to an output of said second comparator to provide a regulation signal for controlling said SMPS to regulate said SMPS output voltage.

3. An SMPS controller as claimed in claim 2 wherein said second comparator includes a sample-hold circuit to sample and hold an output of said first comparator at said time when said first comparator indicates that said integrator output is substantially equal to said second fixed reference level signal.

4. An SMPS controller as claimed in claim 3 wherein said first and second fixed reference level signals are configured such that said sample and hold time indicates that a magnetic flux in said energy storage device is exactly zero.

5. An SMPS controller as claimed in claim 1 further comprising a second integrator, responsive to said output from said first comparator to begin integrating a waveform of said feedback signal, and having an output to provide a signal responsive to a value of said feedback signal at a point of approximately zero flux in said magnetic energy storage device.

6. An SMPS controller as claimed in claim 5 further comprising a zero-crossing detector to detect a zero crossing of said feedback signal and to stop said second integrator integrating response to a zero-crossing of said feedback signal

7. An SMPS controller as claimed in any claim 1 wherein said first and second reference level signals are substantially equal to one another.

8. An SMPS controller as claimed in claim 7 wherein said first and second reference level signals are substantially equal to zero.

9. An SMPS controller as claimed in claim 1 wherein said integrator is configured to begin integrating responsive to a switching control drive signal, said drive signal controlling a switching device of said SMPS switching power to said magnetic energy storage device to transfer energy between an input and an output of said SMPS.

10. An SMPS controller as claimed in claim 9 wherein said integrator is configured to be reset responsive to said drive signal indicating that said switching device has switched on power to said magnetic energy storage device.

11. An SMPS controller as claimed in any claim 1 said magnetic energy storage device comprises a transformer, and wherein said winding comprises an auxilliary winding of said transformer.

12. An SMPS comprising the SMPS controller of any claim 1.

13. A method of regulating the output voltage of an SMPS in response to a feedback signal from a winding of a magnetic energy storage device forming part of an output circuit of the SMPS, the method comprising:

receiving an output reference level signal;

receiving a feedback signal, said feedback signal being responsive to a voltage on said magnetic energy storage device winding;

integrating a difference between said feedback signal and a first fixed reference level signal;

comparing an output of said integration with a second fixed reference level signal and providing an output responsive to said comparison; and

regulating said SMPS using said output of said comparing.

14. A method as claimed in claim 13 further comprising:

comparing a signal derived from said feedback signal with a third reference level signal derived from said output voltage reference level signal at a time when said comparing of said integration output and said second fixed reference level signal indicates that said integrator output is substantially equal to said second fixed reference level signal; and

regulating said SMPS output voltage responsive to said comparing of said signals derived from said feedback signal and said third reference level signal.

15. A method as claimed in claim 14 wherein said time of comparing comprises a time when a magnetic flux in said energy storage device is exactly zero.

16. A method as claimed in claim 13 further comprising:

integrating a waveform of said feedback signal beginning at a time determined by said output of said comparing; and

regulating said SMPS using an output of said waveform integrating.

17. A method as claimed in claim 13 wherein said integrating comprises integrating beginning at a time when a switching device controlling switching of power to said magnetic energy storage device switches on.

18. A method of regulating the output of an SMPS operating in a discontinuous conduction mode, the SMPS including a magnetic energy storage device having at least one winding, the method comprising:

integrating a feedback signal from said at least one winding of said SMPS from a first point in time of known, substantially zero magnetic flux in the said magnetic energy storage device to determine a second time at which said magnetic flux is again substantially zero; and

determining an error signal by integrating a waveform of said feedback signal from said second time to a third later time; and

using said error signal to regulate said SMPS.

19. A method as claimed in claim 18 further comprising identifying a zero-crossing of said feedback signal waveform to determine said third time.

20. A method as claimed in claim 18 further comprising identifying a peak or tough in said feedback signal waveform to determine said first point in time.

21. An SMPS controller for regulating the output of an SMPS operating in a discontinuous conduction mode, the SMPS including a magnetic energy storage device having at least one winding, the system comprising:

a first integrator to integrate a feedback signal from said at least one winding of said SMPS from a first point in time of known, substantially zero magnetic flux in the said magnetic energy storage device to determine a second time at which said magnetic flux is again substantially zero; and

a second integrator to integrate a waveform of said feedback signal from said second time to a third later time and to output an error signal for controlling said SMPS.