Load change detection for switched mode power supply with low no load power

• US 9,136,769 B2
• Filed: 03/05/2013
• Issued: 09/15/2015
• Est. Priority Date: 10/10/2012
• Status: Active Grant

• Current Assignee: MyPAQ Holdings Ltd. (Transpacific IP Group Limited)
• Original Assignee: Flextronics America LLC (Flextronics International Limited)
• Inventors: Schroeder gen Berghegger, Ralf
• Primary Examiner(s): Nguyen, Matthew
• Assistant Examiner(s): DANG, TRINH Q
• Application Number:
  US13/786,032
• Publication Number:
  US 20140098576A1
• Time in Patent Office: 924 Days
• Field of Search: 363/21.01, 363/21.02, 363/21.04, 363/21.03, 363/21.16, 363/16
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0003 Details of control, feedback or regulation circuits
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/335 using semiconductor devices only
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H02M 3/33538 of the forward type H02M3/3353, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33546 with automatic control of the output voltage or current H02M3/33561 takes precedence
• CPC Class Codes: H02M 3/33553 with galvanic isolation between input and output of both the power stage and the feedback loop
• 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 pulse scheme is used for load change detection in a switching mode power supply with low no-load power consumption. The pulse scheme includes a measurement pulse for determining a load condition or a no-load condition at the output. Generation of the measurement pulse results in sufficient energy transfer to the secondary side to accurately measure the output voltage via a reflected voltage on the primary side. Once in no-load operation mode, a reference pulse having a lower energy transfer than the measurement pulse is used to determine a baseline reflected voltage value that corresponds to a no-load condition. Successive detection pulses are then generated and corresponding reflected voltage measured and compared to the baseline reflected voltage. A change in the reflected value that exceeds a threshold value is indicative of a change in the no-load condition.

Claims

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

a. configuring the switching mode power converter comprising a transformer having a primary winding coupled to an input supply voltage and a secondary winding coupled to an output, a switch coupled in series to the primary winding, and a controller coupled to the switch;

b. generating one or more measurement pulses by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to each of the one or more measurement pulses until a no-load condition at the output is determined, wherein the measured reflected voltage is proportional to an output voltage of the switching mode power converter;

c. after the no-load condition is determined, generating a reference pulse by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to the reference pulse, wherein the measured reflected voltage corresponding to the reference pulse comprises a baseline reflected voltage;

d. generating one or more detection pulses by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to each of the one or more detection pulses;

e. comparing the reflected voltage corresponding to each of the one or more detection pulses to the baseline reflected voltage until a difference between the baseline reflected voltage and the reflected voltage corresponding to one of the one or more detection pulses exceeds a threshold value whereupon a change in the no-load condition is determined.

2. The method of claim 1 wherein generating each measurement pulse results in sufficient energy transfer to a secondary side of the switching mode power converter so as to accurately determine the output voltage according to the measured reflected voltage.

3. The method of claim 1 wherein there is an off time between generating the reference pulse and generating a first detection pulse during which the reflected voltage settles to almost zero.

4. The method of claim 1 wherein there is an off time between generating successive detection pulses during which the reflected voltage settles to almost zero.

5. The method of claim 1 wherein when the no-load condition is determined, the switching mode power converter is set to a no-load mode of operation.

6. The method of claim 1 wherein when the change in the no-load condition is determined, the switching mode power converter is set to a normal load mode of operation.

7. The method of claim 1 wherein when the change in the no-load condition is determined, the method further comprises generating another measurement pulse, measuring the reflected voltage corresponding to the other measurement pulse and determining if there is a load condition or the no-load condition at the output according to the measured reflected voltage corresponding to the other measurement pulse.

8. The method of claim 1 wherein the reflected voltage comprises a voltage across the primary winding.

9. The method of claim 1 wherein the switching mode power converter further comprises an auxiliary winding electrically coupled to the controller and magnetically coupled to the secondary winding, wherein the reflected voltage comprises a voltage across the auxiliary winding.

10. The method of claim 2 wherein generating the reference pulse results in energy transfer to the secondary side of the switching mode power converter, wherein an energy transfer corresponding to the reference pulse is less than an energy transfer corresponding to the measurement pulse.

11. The method of claim 10 wherein the energy transfer corresponding to the reference pulse is insufficient to accurately determine the output voltage according to the measured reflected voltage.

12. A method of controlling a switching mode power converter, the method comprising:

a. configuring the switching mode power converter comprising a transformer having a primary winding coupled to an input supply voltage and a secondary winding coupled to an output, a switch coupled in series to the primary winding, and a controller coupled to the switch;

b. generating a measurement pulse by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to the measurement pulse, wherein the measured reflected voltage corresponding to the measurement pulse is proportional to an output voltage of the switching mode power converter;

c. determining a load condition or a no-load condition at the output according to the measured reflected voltage corresponding to the measurement pulse;

d. if the load condition is determined, then periodically generating additional measurement pulses until the no-load condition is determined;

e. if the no-load condition is determined, then;

i. generating a reference pulse by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to the reference pulse, wherein the measured reflected voltage corresponding to the reference pulse comprises a baseline reflected voltage;

ii. generating a detection pulse by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to the detection pulse;

iii. comparing the reflected voltage corresponding to the detection pulse to the baseline reflected voltage, and if a difference between the reflected voltage corresponding to the detection pulse and the baseline reflected voltage is less than a threshold value, then it is determined that the no-load condition remains and a subsequent detection pulse is generated and compared, and if the difference is greater than or equal to the threshold value, then it is determined that there is a change in the no-load condition.

13. The method of claim 12 wherein generating the measurement pulse results in sufficient energy transfer to a secondary side of the switching mode power converter so as to accurately determine the output voltage according to the measured reflected voltage.

14. The method of claim 12 wherein there is an off time between generating the reflected pulse and generating the detection pulse during which the reflected voltage settles to almost zero.

15. The method of claim 12 wherein there is an off time between generating successive detection pulses during which the reflected voltage settles to almost zero.

16. The method of claim 12 wherein if the no-load condition is determined, the switching mode power converter is set to a no-load mode of operation.

17. The method of claim 12 wherein if the load condition is determined, then the switching mode power converter is set to a normal load mode of operation.

18. The method of claim 12 wherein if the change in the no-load condition is determined, then the switching mode power converter is set to a normal load mode of operation.

19. The method of claim 12 wherein if the change in the no-load condition is determined, then the method further comprises generating another measurement pulse, measuring the reflected voltage corresponding to the other measurement pulse and determining if there is the load condition or the no-load condition at the output according to the measured reflected voltage corresponding to the other measurement pulse.

20. The method of claim 12 wherein the reflected voltage comprises a voltage across the primary winding.

21. The method of claim 12 wherein the switching mode power converter further comprises an auxiliary winding electrically coupled to the controller and magnetically coupled to the secondary winding, wherein the reflected voltage comprises a voltage across the auxiliary winding.

22. The method of claim 13 wherein generating the reference pulse results in energy transfer to the secondary side of the switching mode power converter, wherein the energy transfer corresponding to the reference pulse is less than the energy transfer corresponding to the measurement pulse.

23. The method of claim 22 wherein the energy transfer corresponding to the reference pulse is insufficient to accurately determine the output voltage according to the measured reflected voltage.

24. A switching mode power converter comprising:

a. a transformer having a primary winding coupled to an input supply voltage and a secondary winding coupled to an output;

b. a switch coupled in series to the primary winding; and

c. a controller coupled to the switch, wherein the controller is configured to turn the switch ON and OFF,

wherein the controller is configured to generate one or more measurement pulses by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to each of the one or more measurement pulses until a no-load condition at the output is determined, wherein the measured reflected voltage is proportional to an output voltage of the switching mode power converter, and after the no-load condition is determined, generate a reference pulse by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to the reference pulse, wherein the measured reflected voltage corresponding to the reference pulse comprises a baseline reflected voltage, and generate one or more detection pulses by selectively turning ON and OFF the switch and measuring a reflected voltage corresponding to each of the one or more detection pulses, and compare the reflected voltage corresponding to each of the one or more detection pulses to the baseline reflected voltage until a difference between the baseline reflected voltage and the reflected voltage corresponding to one of the one or more detection pulses exceeds a threshold value whereupon a change in the no-load condition is determined.