Power converter and method of entering skip at a fixed output power in a light load condition independent of magnetizing inductance

• US 10,050,536 B2
• Filed: 08/03/2016
• Issued: 08/14/2018
• Est. Priority Date: 03/29/2016
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Hari, Ajay Karthik, McCoy, Bryan Wayne
• Primary Examiner(s): Finch, III, Fred E
• Application Number:
  US15/227,822
• Publication Number:
  US 20170288552A1
• Time in Patent Office: 741 Days
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0035 using burst mode control
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static 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
• 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 converter has a power transistor and inductor coupled in a conduction path with the power transistor. A switching frequency of the power transistor is reduced during a light load condition. A pulse width of a drive signal to the power transistor is controlled to select a current through the inductor and power transistor corresponding to the switching frequency to maintain a fixed output power of the power converter, and further to vary the current through the inductor and power transistor to maintain the fixed output power of the power converter over a range of switching frequencies. A first number of pulses of the drive signal to the power transistor during a first time period sets the fixed output power of the power converter. No pulses of the drive signal are provided during a second time period after the first time period.

Claims

1. A method of maintaining a fixed output power during a light load condition in a power converter, comprising:

providing a range of programmable switching frequencies;

selecting a switching frequency of a power transistor;

reducing the switching frequency of the power transistor during the light load condition;

providing a relationship of a current through the power transistor according to a primary inductance of a transformer of the power converter that provides fixed output power of the power converter; and

controlling a pulse width of a drive signal to the power transistor to vary the current through the power transistor according to the relationship to maintain the fixed output power of the power converter during the light load condition.

2. The method of claim 1, further including measuring a value of the current through the power transistor to control the pulse width of the drive signal to the power transistor.

3. The method of claim 1, further including:

providing a first number of pulses of the drive signal to the power transistor during a first time period to set the fixed output power of the power converter; and

providing no pulses of the drive signal during a second time period after the first time period.

4. The method of claim 3, further including:

providing a second number of pulses of the drive signal to the power transistor during a third time period after the second time period to set the fixed output power of the power converter, wherein the second number of pulses is different from the first number of pulses; and

providing no pulses of the drive signal during a fourth time period after the third time period.

5. The method of claim 1, further including:

setting the switching frequency of the power transistor to different values in response to different loads on the power converter; and

varying the current through the power transistor to maintain the fixed output power of the power converter for the different values of the switching frequency.

6. The method of claim 1, wherein the current through the power transistor varies with the switching frequency.

7. A method of maintaining a fixed output power during a light load condition in a power converter, comprising:

providing a switching frequency of a power transistor for a full-load condition;

reducing the switching frequency of the power transistor during the light load condition;

providing a relationship of a current through the power transistor according to a primary inductance of a transformer of the power converter that provides fixed output power of the power converter; and

controlling a pulse width of a drive signal to the power transistor to set the current through the power transistor according to the relationship to maintain the fixed output power of the power converter.

8. The method of claim 7, further including controlling the pulse width of the drive signal to the transistor to vary the current through the power transistor to enter a fixed power delivery point at the same output power over a range of programmable switching frequencies.

9. The method of claim 7, further including measuring a value of the current through the power transistor to control the pulse width of the drive signal to the power transistor.

10. The method of claim 7, further including:

providing a first number of pulses of the drive signal to the power transistor during a first time period to set the fixed output power of the power converter; and

providing no pulses of the drive signal during a second time period after the first time period.

11. The method of claim 10, further including:

providing a second number of pulses of the drive signal to the power transistor during a third time period after the second time period to set the fixed output power of the power converter, wherein the second number of pulses is different from the first number of pulses; and

providing no pulses of the drive signal during a fourth time period after the third time period.

12. The method of claim 7, further including:

setting the switching frequency of the power transistor to different values in response to different loads on the power converter; and

varying the current through the power transistor to maintain the fixed output power of the power converter for the different values of the switching frequency.

13. The method of claim 7, wherein the current through the power transistor varies with the switching frequency.

14. The method of claim 7, further including providing a relationship of the current through the power transistor and the switching frequency.

15. A power converter providing a fixed output power during a light load condition, comprising:

a power transistor;

an oscillator having an input coupled for receiving a feedback signal from the output of the power converter and an output providing a switching frequency of the power transistor in response to the feedback signal; and

a controller for controlling a pulse width of a drive signal to the power transistor to select a current through the power transistor to maintain the fixed output power of the power converter during the light load condition.

16. The power converter of claim 15, further including a current sensing circuit coupled to the controller for measuring a value of the current through the power transistor to control the pulse width of the drive signal to the power transistor.

17. The power converter of claim 15, wherein the controller provides a first number of pulses of the drive signal to the power transistor during a first time period to set the fixed output power of the power converter, and provides no pulses of the drive signal during a second time period after the first time period.

18. The power converter of claim 17, wherein the controller provides a second number of pulses of the drive signal to the power transistor during a third time period after the second time period to set the fixed output power of the power converter, wherein the second number of pulses is different from the first number of pulses, and provides no pulses of the drive signal during a fourth time period after the third time period.

19. The power converter of claim 15, further including a feedback circuit coupled between an output of the power converter and the controller for setting the switching frequency of the power transistor to different values in response to different loads on the power converter, wherein the controller varies the current through the power transistor to maintain the fixed output power of the power converter.

20. The power converter of claim 15, further including a transformer with a primary side inductor coupled in a conduction path of the power transistor, wherein the primary side inductor includes a primary inductance.

21. The power converter of claim 20, wherein the controller includes a relationship of the current through the power transistor according to the primary inductance that provides fixed output power of the power converter.