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

Patent metadata

Field	Value
Publication number	US-9774270-B2
Application number	US-201615042885-A
Country	US
Kind code	B2
Filing date	Feb 12, 2016
Priority date	Jun 15, 2015
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

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 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 a 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, 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;
switch the second switch off at a predetermined time interval or when a voltage across the first capacitor and a voltage across the second capacitor each falls to a predetermined voltage level; and
switch the first switch on, so as to achieve zero voltage switching.

2. The apparatus of claim 1 , wherein the second switch is configured to be turned on when a current is flowing through its body diode.

3. The apparatus of claim 1 , wherein a capacitance value of the first capacitor is equal to a capacitance value of the second capacitor.

4. The apparatus of claim 1 , wherein the first and second capacitors are configured to be disconnected from the primary winding of the transformer due to presence of the first diode.

5. The apparatus of claim 1 , wherein the first diode is configured to block reverse current from flowing through the second switch back into the primary winding of the transformer.

6. The apparatus of claim 1 , wherein the predetermined voltage level comprises half of an output reflected voltage.

7. The apparatus of claim 6 , wherein the second switch is configured to be switched off when there is a first predetermined minimum amount of reverse current in the primary winding of the transformer.

8. The apparatus of claim 7 , wherein transfer of leakage energy stored in the first and second capacitors to the primary winding of the transformer is started only after all the energy stored in the transformer is delivered to a load.

9. A method of operating a power conversion circuit that comprises 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, so as to store energy in a primary winding of the transformer;
switching the first switch off, so as to charge the first and second capacitors in series;
disconnecting 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;
switching the second switch off when a voltage across the first capacitor and a voltage across the second capacitor each falls to a predetermined voltage level; and
switching the first switch on, so as to achieve zero voltage switching.

10. The method of claim 9 , wherein the second switch is turned on when a current is flowing through its body diode.

11. The method of claim 9 , wherein a capacitance value of the first capacitor is equal to a capacitance value of the second capacitor.

12. The method of claim 9 , wherein the first and second capacitors are disconnected from the primary winding of the transformer due to presence of a first diode connected in series between the first and second capacitors.

13. The method of claim 9 , wherein a first diode connected in series between the first and second capacitors blocks reverse current from flowing through the second switch back into the primary winding of the transformer.

14. The method of claim 9 , wherein the predetermined voltage level comprises half of an output reflected voltage.

15. The method of claim 14 , wherein the second switch is switched off when there is a first predetermined minimum amount of reverse current in the primary winding of the transformer.

16. The method of claim 9 , wherein transfer of leakage energy stored in the first and second capacitors to the primary winding of the transformer is started after all energy stored in the transformer is delivered to the load.

17. A method of operating a power conversion circuit that comprises 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 predetermined time interval, so as to store energy in a primary winding of the transformer;
switching the first switch off, so as to charge the first and second capacitors in series;
switching the second switch on when current is flowing through its body diode;
disconnecting 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
switching the second switch off at a predetermined amount of time before next predetermined switching on of the first switch, wherein the amount of time is predetermined so as to achieve zero voltage switching of the first switch.

18. The method of claim 17 , wherein 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.

19. The method of claim 17 , wherein energy stored in the first and second capacitors is retained when power is being delivered to the load.

20. The method of claim 17 , wherein transfer of leakage energy stored in the first and second capacitors to the primary winding of the transformer is started after all energy stored in the transformer is delivered to the load.

Assignees

• Apple Inc

Inventors

• Phadke Vijay

Classifications

• H02M1/34 Primary

  Snubber circuits · CPC title

• H02M1/083 Primary

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

• H02M3/335

  using semiconductor devices only · CPC title

• H02M3/33523

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

• H02M2001/342

  Electricity · mapped topic