Systems and methods of operation for power converters having series-parallel mode active clamps

Patent metadata

Field	Value
Publication number	US-9893636-B2
Application number	US-201715585715-A
Country	US
Kind code	B2
Filing date	May 3, 2017
Priority date	Jun 15, 2015
Publication date	Feb 13, 2018
Grant date	Feb 13, 2018

Abstract

Systems and methods for operating improved flyback converters are disclosed, in which leakage energy is returned to the input power source rather than to the output load, while still achieving zero voltage switching (i.e., ZVS) operation. In some embodiments, the improved converters may transfer the energy stored in the leakage inductance to a snubber capacitor(s) at the instant of turning off of the control switch. Further, the improved converter embodiments may also retain the stored energy in the snubber capacitor(s) when the power is being delivered to the load by the secondary circuits. The improved converter embodiments may start the transfer of leakage energy stored in the snubber capacitor(s) to the primary winding once the energy stored in the transformer is delivered to the load. Finally, the improved converter embodiments may intelligently control their active clamp switches such that all leakage inductance energy is returned to the input source.

First claim

The invention claimed is:

1. A method of operating a power conversion circuit comprising a transformer, first and second capacitors, first and second switches, and a controller operating the first and second switches to produce a regulated output voltage for delivery to a load in an output system, the method comprising:
switching the first switch on at a first switching frequency, so as to store energy in a primary winding of the transformer;
charging the first and second capacitors in series by switching the first switch off;
switching the second switch on when current is flowing through a body diode of the second switch;
discharging the first and second capacitors in parallel by switching the second switch off to disconnect the first and second capacitors from the primary winding of the transformer once all leakage inductance energy has been transferred from the transformer to the first and second capacitors;
wherein the second switch is switched off at a first amount of time before the next switching on of the first switch, wherein the first amount of time is determined so as to achieve zero voltage switching of the first switch;
wherein at least one of the first switching frequency and the first amount of time is adaptive.

2. The method of claim 1 wherein the first switching frequency is adaptive and the method further comprises:
monitoring a dead time of the transformer;
increasing the first adaptable switching frequency when the dead time exceeds a first predetermined threshold value; and
decreasing the first adaptable switching frequency when the dead time is less than a second predetermined threshold value.

3. The method of claim 2 , further comprising decreasing a peak current limit level of the primary winding when the dead time exceeds the first predetermined threshold value.

4. The method of claim 3 , wherein decreasing a peak current limit level of the primary winding comprises decreasing the peak current limit level so as to maintain a constant output power level to the output system.

5. The method of claim 2 , further comprising increasing a peak current limit level of the primary winding when the dead time is less than the second predetermined threshold value.

6. The method of claim 5 , wherein increasing the peak current limit level of the primary winding comprises increasing a peak current limit level so as to maintain a constant output power level to the output system.

7. The method of claim 3 , wherein the first switching frequency is adaptive and is selected to avoid frequency bands associated with common mode noise of an electronic device being charged by the power conversion circuit.

8. The method of claim 1 , wherein the first amount of time is adaptive and a timing of switching the first switch off is based, at least in part, on one or more of the following values: an error signal value, an output loading value, and an input voltage value.

9. The method of claim 8 , wherein the first amount of time is adaptive and is determined so that the next switching on of the first switch immediately follows complete discharging of the first and second capacitors.

10. The method of claim 1 , wherein the discharging of the first and second capacitors is started when a voltage across the primary winding equals a voltage across at least one of the first and second capacitors.

11. The method of claim 1 , wherein the first amount of time is adaptive and is determined based, at least in part, on a measurement of a duration of reverse current flowing through the first switch after the first switch is switched on.

12. A power conversion apparatus, comprising:
a transformer, wherein the transformer has a primary winding and a secondary winding;
a first switch coupled to the primary winding so as to control a flow of current through the primary winding;
a second switch coupled to the primary winding, so as to control the flow of current through an active resonant clamp circuit,
wherein the active resonant clamp circuit is configured to absorb leakage energy from the primary winding, and comprises:
a first capacitor coupled to the primary winding;
a second capacitor coupled to the primary winding; and
a first diode connected in series between the first capacitor and the second capacitor; and
a controller coupled to the first switch and the second switch, configured to:
switch the first switch on at a first switching frequency, so as to store energy in the primary winding of the transformer;
switch the first switch off, so as to charge the first and second capacitors in series;
disconnect the first and second capacitors from the primary winding of the transformer once all leakage inductance energy has been transferred from the transformer to the first and second capacitors, so as to begin to discharge the first and second capacitors in parallel; and
switch the second switch off at a first amount of time before the next switching on of the first switch, wherein the first amount of time is determined so as to achieve zero voltage switching of the first switch;
wherein at least one of the first switching frequency and the first amount of time is adaptive.

13. The power conversion apparatus of claim 12 , wherein the first switching frequency is adaptive and the controller is further configured to:
monitor a dead time of the transformer;
increase the first adaptable switching frequency when the dead time exceeds a first predetermined threshold value; and
decrease the first adaptable switching frequency when the dead time is less than a second predetermined threshold value.

14. The power conversion apparatus of claim 13 , wherein the controller is further configured to decrease a peak current limit level of the primary winding when the dead time exceeds the first predetermined threshold value.

15. The power conversion apparatus of claim 14 , wherein the controller is further configured to peak a current limit level so as to maintain a constant output power level to an output system.

16. The power conversion apparatus of claim 13 , wherein the controller is further configured to increase a peak current limit level of the primary winding when the dead time is less than the second predetermined threshold value.

17. The power conversion apparatus of claim 16 , wherein the controller being configured to increase a peak current limit level of the primary winding comprises the controller being configured to increase the peak current limit level so as to maintain a constant output power level to an output system.

18. The power conversion apparatus of claim 13 , wherein the first switching frequency is adaptable and is selected to avoid frequency bands associated with common mode noise of an electronic device being powered by the power conversion apparatus.

19. The power conversion apparatus of claim 12 , wherein the first amount of time is adaptive and a timing of switching the first switch off is based, at least in part, on one or more of the following values: an error signal value, an output loading value, and an input voltage value.

20. The power conversion apparatus of claim 12 , wherein energy stored in the first and second capacitors is retained when power is being delivered to a load in an output system.

21. The power conversion apparatus of claim 12 , wherein the first amount of time is adaptive and is determined so that the next switching on of the first switch immediately follows the complete discharging of the first and second capacitors.

22. The pow

Assignees

• Apple Inc

Inventors

• Phadke Vijay

Classifications

• H02M1/083 Primary

  for the ignition at the zero crossing of the voltage or the current · CPC title

• H02M3/33523

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H02M3/335

  using semiconductor devices only · CPC title

• H02M1/34 Primary

  Snubber circuits · CPC title

• H02M3/33546

  with automatic control of the output voltage or current (H02M3/33561 takes precedence) · CPC title