Adaptive control for transition between multiple modulation modes in a switching power converter

• US 8,018,743 B2
• Filed: 03/05/2009
• Issued: 09/13/2011
• Est. Priority Date: 03/05/2009
• Status: Active Grant

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Yan, Liang, Poon, Clarita, Wang, Xiaoyan, Zheng, Junjie, Kesterson, John William
• Primary Examiner(s): Berhane; Adolf
• Assistant Examiner(s): Finch, III; Fred E
• Application Number:
  US12/398,878
• Publication Number:
  US 20100225293A1
• Time in Patent Office: 922 Days
• Field of Search: 323282-284, 363/21.04, 363/21.05, 363/21.1, 363/21.11, 363/21.12, 363/21.13, 363/21.18
• US Class Current: 363/21.18
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• 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: 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

In a switching power converter, PWM mode and PFM mode are separated into two independent control sections with the control voltage range in each control section determined independently. Each of the PWM and PFM modulation modes cannot operate continuously beyond its boundaries, thereby forming a control gap between the two control sections within which no continuous operation is allowed. In order to supply a load condition within the control gap, the power supply operates at the two boundaries of the control gap. Transition between PWM and PFM modes occurs fast, with low output voltage ripple. No limitation needs to be imposed on the control voltage range in each of the PWM and PFM control sections, because the control parameters in the PWM and PFM control sections need not be matched to one another, due to separation of the PWM and PFM modes by the control gap.

Claims

1. A method of operating a switching power converter, the method comprising:

operating the switching power converter in pulse frequency modulation mode in a first output current range higher than a first output current level and lower than a second output current level;

operating the switching power converter in pulse width modulation mode in a second output current range higher than a third output current level and lower than a fourth output current level, the third output current level being higher than the second output current level, and

wherein between the second output current level and the third output current level the switching power converter is operated at either a first operating point associated with the third output current level or a second operating point associated with the second output current level thereby forming a control gap, the first operating point corresponding to a first operating frequency and a first duty cycle of the switching power converter and the second operating point corresponding to a second operating frequency and a second duty cycle of the switching power converter.

2. The method of claim 1, further comprising:

transitioning from the pulse width modulation mode to the pulse frequency modulation mode if an output voltage of the switching power converter increases beyond a reference voltage plus a predetermined hysteresis voltage and an output current level of the switching power converter decreases below the third output current level.

3. The method of claim 1, further comprising:

transitioning from the pulse frequency modulation mode to the pulse width modulation mode if an output voltage of the switching power converter decreases beyond a reference voltage minus a predetermined hysteresis voltage and an output current level of the switching power converter increases above the second output current level.

4. The method of claim 1, wherein the control gap includes a first control gap corresponding to a third output current range higher than the second output current level and lower than a fifth output current level and a second control gap corresponding to a fourth output current range higher than the fifth output current level and lower than the third output current level, the fifth output current level associated with a third operating point of the switching power converter corresponding to a third operating frequency and a third duty cycle of the switching power converter.

5. The method of claim 1, wherein transitioning between the first operating point and the second operating point of the switching power converter occurs solely based on an output voltage level of the switching power converter without regard to an output current level of the switching power converter, if the output current level of the switching power converter is between the second output current level and the third output current level.

6. The method of claim 1, further comprising lowering a switching frequency of the switching power converter in pulse frequency modulation mode as an output current level of the switching power converter decreases.

7. A switching power converter comprising:

a switch configured to couple or de-couple an output of the switching power converter to or from an input voltage to the switching power converter; and

a controller coupled to the switch and configured to control the on or off state of the switch, the controller operating the switching power converter by;

operating the switching power converter in pulse frequency modulation mode in a first output current range higher than a first output current level and lower than a second output current level;

operating the switching power converter in pulse width modulation mode in a second output current range higher than a third output current level and lower than a fourth output current level, the third output current level being higher than the second output current level, and

wherein between the second output current level and the third output current level the controller operates the switching power converter at either a first operating point associated with the third output current level or a second operating point associated with the second output current level thereby forming a control gap, the first operating point corresponding to a first operating frequency and a first duty cycle of the switching power converter and the second operating point corresponding to a second operating frequency and a second duty cycle of the switching power converter.

8. The switching power converter of claim 7, wherein the controller transitions operation of the switching power converter from the pulse width modulation mode to the pulse frequency modulation mode if an output voltage of the switching power converter increases beyond a reference voltage plus a predetermined hysteresis voltage and an output current level of the switching power converter decreases below the third output current level.

9. The switching power converter of claim 7, wherein the controller transitions operation of the switching power converter from the pulse frequency modulation mode to the pulse width modulation mode if an output voltage of the switching power converter decreases beyond a reference voltage minus a predetermined hysteresis voltage and an output current level of the switching power converter increases above the second output current level.

10. The switching power converter of claim 7, wherein the control gap includes a first control gap corresponding to a third output current range higher than the second output current level and lower than a fifth output current level and a second control gap corresponding to a fourth output current range higher than the fifth output current level and lower than the third output current level, the fifth output current level associated with a third operating point of the switching power converter corresponding to a third operating frequency and a third duty cycle of the switching power converter.

11. The switching power converter of claim 7, wherein transitioning between the first operating point and the second operating point of the switching power converter occurs solely based on an output voltage level of the switching power converter without regard to an output current level of the switching power converter, if the output current level of the switching power converter is between the second output current level and the third output current level.

12. The switching power converter of claim 7, wherein the controller lowers a switching frequency of the switching power converter in the pulse frequency modulation mode as an output current level of the switching power converter decreases.

13. A method of operating a switching power converter, the method comprising:

operating the switching power converter in a first mode when the switching power converter is in a first output current range higher than a first output current level and lower than a second output current level;

operating the switching power converter in a second mode when the switching power converter is in a second output current range higher than a third output current level and lower than a fourth output current level, the third output current level being higher than the second output current level, and

wherein between the second output current level and the third output current level the switching power converter is operated at either a first operating point associated with the third output current level or a second operating point associated with the second output current level thereby forming a control gap, the first operating point corresponding to a first operating frequency and a first duty cycle of the switching power converter and the second operating point corresponding to a second operating frequency and a second duty cycle of the switching power converter.