Fixed frequency series-parallel mode (SPM) active clamp flyback converter

Patent metadata

Field	Value
Publication number	US-9923472-B1
Application number	US-201715405901-A
Country	US
Kind code	B1
Filing date	Jan 13, 2017
Priority date	Sep 7, 2016
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

A flyback converter can include a series-parallel mode (SPM) active clamp circuit. The active clamp circuit, coupled in parallel with the primary coil, may include multiple networks in parallel. The first network, comprising a switch, one or more snubber capacitors, and one or more diodes, may be configured to absorb and retain the leakage energy from the leakage inductance of the flyback converter. The second network, comprising another switch and a diode, may be configured to create a circulating circuit for the flow of current through the primary coil in a reverse direction and clamp the current to a threshold level. With the active clamp circuit, the flyback converter may first re-capture the leakage energy in the active clamp circuit and then recover it back to the power source.

First claim

The invention claimed is:

1. A power conversion apparatus, comprising:
a primary coil configured to receive an input voltage;
a secondary coil electromagnetically coupled to the primary coil and configured to provide an output voltage;
a first switch coupled to the primary coil and configured to control a flow of current through the primary coil based on a first control signal;
a second switch configured to control, based on a second control signal, a flow of current through a snubber network of an active clamp circuit, the snubber network comprising two or more capacitors configured to charge in series and discharge in parallel, the snubber network coupled in parallel with the primary coil and configured to absorb a leakage energy from a leakage inductance associated with the primary coil and the secondary coil by charging the two or more capacitors;
a third switch configured to control, based on a third control signal, a flow of current through a reverse circulating network of the active clamp circuit, the reverse circulating network coupled in parallel with the primary coil and configured to clamp the current through the primary coil in a reverse direction to a threshold level; and
a controller coupled to the first, the second and the third switches, the controller configured to generate the first, the second and the third control signals.

2. The power conversion apparatus of claim 1 , wherein the snubber network of the active clamp circuit further comprises first and second capacitors coupled in series with the second switch.

3. The power conversion apparatus of claim 2 , wherein the snubber network of the active clamp circuit further comprises a first diode coupled in series with the second switch, whereby the first diode is configured to retain the absorbed leakage energy in the first and second capacitors by disconnecting the first and second capacitors from the primary coil.

4. The power conversion apparatus of claim 3 , wherein the snubber network of the active clamp circuit further comprises a second diode coupled in parallel with the first capacitor and the first diode, whereby the second diode is configured to conduct a discharging current of the second capacitor.

5. The power conversion apparatus of claim 3 , wherein the snubber network of the active clamp circuit further comprises a third diode coupled in parallel with the second capacitor and the first diode, whereby the third diode is configured to conduct a discharging current of the first capacitor.

6. The power conversion apparatus of claim 1 , wherein the reverse circulating network of the active clamp circuit further comprises a fourth diode coupled in series with the third switch.

7. The power conversion apparatus of claim 1 , wherein the first control signal is generated to achieve zero voltage switching of the first switch.

8. The power conversion apparatus of claim 1 , wherein the second control signal is generated to achieve zero voltage switching of the second switch.

9. The power conversion apparatus of claim 1 , further comprising a diode configured to achieve zero voltage switching of the third switch, the diode coupled between the snubber network and the reverse circulating network.

10. A method for operating a power conversion apparatus, the power conversion apparatus comprising primary and secondary coils, the primary coil configured to receive an input voltage, the secondary coil electromagnetically coupled with the primary coil and configured to provide an output voltage, the method comprising:
generating, with a controller, first, second and third control signals;
controlling, with a first switch and based on the first control signal, a flow of current through the primary coil in a forward direction;
controlling, with a second switch and based on the second control signal, a flow of current through the primary coil and a snubber network of an active clamp circuit, the snubber network comprising two or more capacitors configured to charge in series and discharge in parallel, so as to recover an absorbed leakage energy from the primary coil until the flow of current in the reverse direction reaches a threshold level; and
controlling, with a third switch and based on the third control signal, a flow of current through a reverse circulating network of the active clamp circuit coupled in parallel with the primary coil so as to clamp the current through the primary coil in the reverse direction to the threshold level.

11. The method of claim 10 , wherein the snubber network of the active clamp circuit further comprises first and second capacitors coupled in series with the second switch.

12. The method of claim 11 , wherein the snubber network of the active clamp circuit further comprises a first diode coupled in series with the second switch, whereby the first diode is configured to retain the absorbed leakage energy in the first and second capacitors by disconnecting the first and second capacitors from the primary coil.

13. The method of claim 12 , wherein the snubber network of the active clamp circuit further comprises a second diode coupled in parallel with the first capacitor and the first diode, whereby the second diode is configured to conduct a discharging current of the second capacitor.

14. The method of claim 12 , wherein the snubber network of the active clamp circuit further comprises a third diode coupled in parallel with the second capacitor and the first diode, whereby the third diode is configured to conduct a discharging current of the first capacitor.

15. The method of claim 10 , wherein the reverse circulating network of the active clamp circuit further comprises a fourth diode coupled in series with the third switch.

16. The method of claim 10 , wherein the first control signal is generated to achieve zero voltage switching of the first switch.

17. The method of claim 10 , wherein the second control signal is generated to achieve zero voltage switching of the second switch.

18. The method of claim 10 , wherein the power conversion apparatus further comprises a diode configured to achieve zero voltage switching of the third switch, the diode coupled between the snubber network and the reverse circulating network.

19. A method of actively clamping a power conversion circuit, the power conversion circuit comprising primary and secondary coils, the primary coil configured to receive an input voltage from a power source, the secondary coil electromagnetically coupled with the primary coil and configured to provide an output voltage, the method comprising:
turning on a first switch so as to store energy in a primary coil;
turning off the first switch and turning on second and third switches so as to transfer a leakage energy associated with the primary and secondary coils to a first and second capacitors by charging the first and second capacitors in series;
retaining the leakage energy in the first and second capacitors by disconnecting the first and second capacitors from the primary coil by using a first diode;
transferring the leakage energy from the first and second capacitors to the primary coil by discharging the first and second capacitors in parallel through second and third diodes;
turning off the second switch so as to clamp a flow of current through the primary coil in a reverse direction by using the third switch and a fourth diode; and
turning off the third switch so as to transfer the leakage energy from the primary coil to the power source.

20. The method of claim 19 , wherein the second switch is t

Assignees

• Apple Inc

Inventors

• Phadke Vijay G

Classifications

• H02M2001/342

  Electricity · mapped topic

• H02M3/33507 Primary

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M1/34 Primary

  Snubber circuits · CPC title

• H02M1/342

  Active non-dissipative snubbers · CPC title

• H02M1/0058

  by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero (using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826) · CPC title