Switch mode power supply control systems

• US 7,504,815 B2
• Filed: 07/06/2006
• Issued: 03/17/2009
• Est. Priority Date: 07/06/2005
• Status: Expired due to Fees

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Cambridge Semiconductor Limited (Power Integrations Incorporated)
• Inventors: Moyse, Philip John, Coulson, David Robert, Jacques, Russell, Garner, David M.
• Primary Examiner(s): Han; Jessica
• Assistant Examiner(s): Pham; Emily
• Application Number:
  US11/481,485
• Publication Number:
  US 20070041224A1
• Time in Patent Office: 985 Days
• Field of Search: 323282-284, 323/351
• US Class Current: 323/351
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/157 with digital control
• 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
• CPC Class Codes: H02M 3/33515 with digital control
• 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

Abstract

We describe a switch mode power supply (SMPS) controller employing a combination of pulse frequency and pulse width modulation. The controller employs a “gear box” control scheme using two complementary control loops, one for real-time control of the SMPS using PFM and a second using a PWM control scheme which monitors the switching frequency and, at defined operating points, adjusts the pulse width up or down through a set of pre-determined values. This can be considered analogous to the gearbox of a motor vehicle with the SMPS pulse width, switching frequency and output power roughly corresponding to the vehicle'"'"'s gear ratio, engine speed and road speed respectively.

Claims

1. A switch mode power supply controller employing a combination of pulse frequency modulation and pulse width modulation to control a power switching device, the controller having:

an input to receive an output voltage dependent feedback signal;

an output for driving said power switching device; and

a control system to provide a switching control signal to said output responsive to said feedback signal from said input, said switching control signal having a switching cycle including an ON portion for switching on said power switching device, and wherein said control system is configured to select one of a plurality of discrete pulse widths for said ON portion of said switching cycle using at least one stored pulse width, and to vary a duration of said switching cycle responsive to said feedback signal; and

wherein the control system is configured to determine said switching cycle duration and to select one of said at least one stored pulse width responsive to said determined duration; and

wherein said control system has a plurality of operating power ranges each defining a range of average power transferred per switching cycle by said power switching device, each said range being defined by a combination of one of said at least one stored pulse width and a range of durations of said switching cycle, adjacent ones of said operating power ranges overlapping across a range of power levels.

2. A switch mode power supply controller as claimed in claim 1 wherein said control system is configured to select one of a plurality of stored pulse widths for said ON portion of said switching cycle.

3. A switch mode power supply controller as claimed in claim 1 wherein said at least one stored pulse width comprises a maximum pulse width and a minimum pulse width, and wherein said control system is configured to select a said discrete pulse width between said stored maximum and minimum pulse widths.

4. A switch mode power supply controller as claimed in claim 1 wherein said ON portion of said switching cycle is followed by a OFF portion for switching off said power device, and wherein said control system is configured to end said OFF portion of said switching cycle and restart said ON portion of said switching cycle responsive to said feedback signal.

5. A switch mode power supply controller as claimed in claim 4 wherein said feedback signal comprises a variable level signal, and wherein said control system is configured to compare said feedback signal level with a reference level to determine a timing of said switching cycle restart.

6. A switch mode power supply controller as claimed in claim 1 wherein said control system is configured to select an increased said pulse width responsive to said determined duration being less than a lower threshold and a decreased pulse width responsive to said determined duration being greater than an upper threshold.

7. A switch mode power supply controller as claimed in claim 6 wherein said upper threshold duration defines a switching cycle frequency of greater than 20 KHz.

8. A switch mode power supply controller as claimed in claim 1 further comprising a data store to store values of one or more of n, m, p and q where n defines a minimum duration of a said switching cycle, m defines a number of said stored pulse widths for selection, p defines a minimum duration of a said pulse width, and q defines a minimum duration of a said pulse width.

9. A switch mode power supply controller as claimed in claim 1 further comprising a look-up table storing said one or more pulse widths.

10. A switch mode power supply controller as claimed in claim 1 wherein said pulse widths are stored, embodied as hardware for a set of pulse generators, to generate pulses having said pulse widths.

11. A switch mode power supply including the switch mode power supply controller in claim 1.

12. A method of operating a switch mode power supply controller employing a combination of pulse frequency modulation and pulse width modulation to control a power switching device, the controller having:

an input to receive an output voltage dependent feedback signal;

an output for driving said power switching device; and

a control system to provide a switching control signal to said output responsive to said feedback signal from said input, said switching control signal having a switching cycle including an ON portion for switching on said power switching device; and

wherein said control system has a plurality of operating power ranges each defining a range of average power transferred per switching cycle by said power switching device, each said range being defined by a combination of one of at least one stored pulse width and a range of durations of said switching cycle, adjacent ones of said operating power ranges overlapping across a range of power levels, the method comprising;

selecting one of a plurality of discrete pulse widths for said ON portion of said switching cycle using at least one stored pulse width;

varying a duration of said switching cycle responsive to said feedback signal to regulate an output of said switch mode power supply;

determining said switching cycle duration; and

selecting a next highest or next lowest one of said at least one stored pulse width responsive to said determining when the power switching device is operating at a power level within the corresponding overlapping range of power levels.

13. A method as claimed in claim 12 wherein said selecting one of a plurality of discrete pulse widths comprises selecting one of a plurality of stored pulse widths for said ON portion of said switching cycle.

14. A method as claimed in claim 12 wherein said at least one stored pulse width comprises a maximum pulse width and a minimum pulse width, and wherein said selecting one of a plurality of discrete pulse widths comprises selecting a said discrete pulse width between said stored maximum and minimum pulse widths.

15. A carrier medium carrying processor control code to implement the method of claim 12.

16. A switch mode power supply controller employing a combination of pulse frequency modulation and pulse width modulation to control a power switching device, the controller having a plurality of operating power ranges each defining a range of average power transferred per switching cycle by said power switching device, each said range being defined by a combination of:

one of a plurality of pre-determined pulse widths, and a range of durations of said switching cycle, wherein adjacent ones of said operating power ranges overlap across a range of power levels to provide hysteresis.

17. A pulse width and frequency modulation (PWFM) SMPS (switch mode power supply) controller configured to control a drive signal to a power switching device of said SMPS by PWFM in response to a feedback signal responsive to an output condition of said SMPS, wherein said controller has a variable gearing ratio, said gearing ratio determining a range of available pulse widths for said PWFM, associated with a frequency of said PWFM, determining an operating power range for said SMPS, and wherein adjacent ones of said available pulse widths determined by said variable gearing ratio are able to deliver an overlapping range of power levels.

18. A PWFM SMPS controller as claimed in claim 17 configured to control said gearing ratio such that as said frequency is reduced said gearing ratio adjusts to select a said range of available pulse widths determining a reduced operating power range for said SMPS and vice-versa.

19. A PWFM SMPS controller as claimed in claim 17 configured to control said frequency responsive to said feedback signal using a pulse width selected from said range of available pulse widths.

20. A PWFM SMPS as claimed in claim 17 wherein said output condition comprises a condition selected from the group comprising an output current of said SMPS, an output voltage of said SMPS and an output load of said SMPS.

21. A PWFM SMPS controller as claimed in claim 17 wherein said variable gearing ratio comprises a plurality of substantially fixed said gearing ratios.

22. A PWFM SMPS controller as claimed in claim 17 wherein said variable gearing ratio comprises a substantially continuously variable said gearing ratio.

23. A PWFM SMPS controller as claimed in claim 17 wherein a said range of available pulse widths is determined by at least one stored pulse width.