PFC with high efficiency at low load

• US 8,644,041 B2
• Filed: 01/14/2010
• Issued: 02/04/2014
• Est. Priority Date: 01/14/2009
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Pansier, Frans
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): AHMED, YUSEF A
• Application Number:
  US13/144,154
• Publication Number:
  US 20110267856A1
• Time in Patent Office: 1,482 Days
• Field of Search: 363/21.12, 363/21.14, 363 2116- 2118, 363/40, 363/41, 363/81, 363/82, 363/89, 323/299
• US Class Current: 363/89
• CPC Class Codes: H02M 1/4225 using a non-isolated boost converter
• 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

A Power Factor Corrector (PFC), typically used as the first stage of switched mode power supplies, particularly suited for Universal Mains inputs, is disclosed, along with methods for controlling a switched mode power supply having power factor correction. In order to increase efficiency, particularly under low load conditions, without undue degradation of the Power Factor, the switching of the PFC circuit is confined to one or more operating windows within each half-cycle. In example embodiments, the operating window comprises a small time window centered around the peak of the mains voltage. The higher the power level, the wider the switching window.

Claims

1. A method of operating a switched mode power supply having power factor correction and supplied from an AC supply stage,

the method comprising

defining an operating window entirely within a half-cycle of the AC supply, and

switching the power supply within the half-cycle only during the operating window and with an on-time of each switching cycle, wherein the operating window is an operating window such that a peak of the AC supply is included within the operating window, characterized in that, an output characteristic of the power supply is controlled by controlling the width of the operating window, wherein the switched mode power supply is supplied with an input voltage and outputs an output voltage, wherein the on-time of each switching cycle is controlled in dependence on the ratio between the output voltage and the input voltage such that the on-time is increased when the ratio between the output voltage and the input voltage exceeds a ratio threshold.

2. A method as claimed in claim 1, wherein the output characteristic is one of output power, output current and output voltage.

3. A method as claimed in claim 1, wherein the operating window is symmetrical about the peak of the AC supply.

4. A method as claimed in claim 1, wherein the on-time is one of constant and varied within the operating window.

5. A method as claimed in claim 4, wherein the on-time is varied between either successive half-cycles or between successive cycles.

6. A method as claimed in claim 1, wherein a peak switched current is one of constant and varied throughout the operating window.

7. A method as claimed in claim 6, wherein the peak switched current is varied between either successive half-cycles or between successive cycles.

8. A method as claimed in claim 1, wherein an average switched current is one of constant and varied throughout the operating window.

9. A method as claimed in claim 8, wherein the respective on-time, peak switched current or average switched current is varied between either successive half-cycles or between successive cycles.

10. A method as claimed in claim 1, wherein the switching frequency is constant throughout the operating window.

11. A method as claimed in claim 1, wherein an output characteristic is controlled by controlling the switching frequency, and wherein the switching frequency is constrained not to exceed a predetermined clamping frequency and further control is provided by controlling the width of the operating window.

12. A method as claimed in claim 1, wherein a sample-and-hold function is carried out at one of the peak of the half-cycle of the AC supply, and at least one of the end and the start of the operating window.

13. A method as claimed in claim 12, wherein an output from the sample-and-hold function is used for determining the width of the operating window for a subsequent half-cycle of the AC supply.

14. A method as claimed in claim 1, wherein the at least one operating window comprises a first side-window and a second side-window, such that the first side-window lies to one side of a peak of the AC supply and the second side-window lies to the other side of the peak of the AC supply.

15. A control circuit for a switched mode power supplied configured to operate according to a method as claimed in claim 1.

16. A switched mode power supply comprising a control circuit as claimed in claim 15.