Method for operating in burst mode active clamp flyback converters and corresponding active clamp flyback converter apparatus

A system, comprising:

• an active clamp flyback converter having a transformer, a power switch and a clamp switch;
• and
• control circuitry coupled to the active clamp flyback converter, wherein the control circuitry, in operation:
• compares a control voltage of the active clamp flyback converter to a first voltage threshold, a second voltage threshold having a magnitude greater than a magnitude of the first voltage threshold, and a third voltage threshold having a magnitude greater than a magnitude of the second voltage threshold;
• counts a number of consecutive switching cycles during which the clamp switch remains off;
• and
• selectively transitions the active clamp flyback converter between a plurality of operational states based on the comparing of the control signal to the voltage thresholds and the count of the number of consecutive switching cycles during which the clamp switch remains off, the plurality of operational states including:
• a run state of operation of one or more consecutive switching cycles of the active flyback converter;
• an idle state of operation of one or more consecutive switching cycles of the active flyback converter;
• a first burst state of operation of one or more sets of consecutive switching cycles of the active flyback converter;
• and
• a second burst state of operation of one or more sets of consecutive switching cycles during which the power switch is turned on and off and the clamp switch is off.

A device, comprising:

• one or more comparators, which, in operation, compare a control voltage signal of an active clamp flyback converter to a first voltage threshold, a second voltage threshold and a third voltage threshold, wherein a magnitude of the second voltage threshold is greater than a magnitude of the first voltage threshold and a magnitude of the third voltage threshold is greater than a magnitude of the second voltage threshold;
• and
• logic circuitry coupled to the one or more comparators, wherein the logic circuitry, in operation:
• counts a number of consecutive switching cycles during which an off state of a clamp switch of the active clamp flyback converter is maintained;
• and
• selectively transitions the active clamp flyback converter between a plurality of operational states based on the comparing of the control voltage signal to the voltage thresholds and the count of the number of consecutive switching cycles during which the off state of the clamp switch is maintained, the plurality of operational states including:
• a run state of operation of one or more consecutive switching cycles;
• an idle state of operation of one or more consecutive switching cycles;
• a first burst state of operation of one or more sets of consecutive switching cycles;
• and
• a second burst state of operation of one or more sets of consecutive switching cycles during which signals are generated to turn the power switch on and off and to maintain an off state of the clamp switch.

A non-transitory computer-readable medium having contents which cause control circuitry to control operation of an active flyback converter device, the controlling comprising:

• selectively transitioning the active clamp flyback converter between a plurality of operational states by controlling a power switch and a clamp switch of the active clamp flyback converter, the plurality of operational states including:
• a run state of operation of one or more consecutive switching cycles;
• an idle state of operation of one or more consecutive switching cycles;
• a first burst state of operation of one or more sets of consecutive switching cycles;
• and
• a second burst state of operation of one or more sets of consecutive switching cycles during which the power switch is turned on and off and the clamp switch is off;
• comparing a control signal of an active clamp flyback converter to a plurality of three or more thresholds;
• and
• counting a number of consecutive switching cycles during which the clamp switch remains off, wherein the selectively transitioning is based on the comparing of the control signal to the plurality of three or more thresholds and the count of the number of consecutive switching cycles during which the clamp switch remains off.