Soft switching flyback converter with primary control
First Claim
1. A flyback converter, comprising:
- a transformer, including;
a primary winding, including a first end to receive an input voltage signal, and a second end, anda secondary winding, including a first end to provide an output voltage signal, and a second end;
a first switch, including a first terminal coupled with the second end of the primary winding, a second terminal coupled with a first constant voltage node, and a first control terminal to receive a first switching control signal;
a second switch, including a first terminal coupled with the second end of the secondary winding, a second terminal coupled with a second constant voltage node, and a second control terminal to receive a second switching control signal;
a first control circuit to provide the first switching control signal to turn on the first switch for a non-zero first time period in a converter cycle to allow current to flow in a first direction in the primary winding in response to a first switch voltage across the first switch transitioning below a first threshold; and
a second control circuit to provide the second switching control signal to turn on the second switch for a non-zero second time period following the first time period in the converter cycle, the second control circuit operative to provide the second switching control signal to again turn on the second switch for a non-zero third time period in the converter cycle in response to a second switch voltage across the second switch transitioning below a second threshold to cause current flow in a second direction in the primary winding to at least partially discharge a capacitance of the first switch to cause the first switch voltage to transition below the first threshold to initiate a subsequent converter cycle and allow the first switch to operate at or near a zero-voltage switching (ZVS) condition.
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Accused Products
Abstract
Disclosed examples include synchronous rectifiers and flyback converters, integrated circuits and operating methods, in which a first switch is turned on to allow current to flow for a first time period in a first direction in a transformer primary winding responsive to a first switch voltage transitioning below a first threshold, and a second switch is turned on for a second time period after the first time period to transfer energy from a secondary transformer winding to drive a load. In the same converter cycle, the second switch is again turned on for a third time period in response to a second switch voltage transitioning below a second threshold at one of a series of troughs of a resonant ringing voltage waveform across the second switch, to cause current flow in a second direction in the primary winding to discharge a capacitance of the first switch to cause the first switch voltage to transition below the first threshold to initiate a subsequent converter cycle.
29 Citations
20 Claims
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1. A flyback converter, comprising:
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a transformer, including; a primary winding, including a first end to receive an input voltage signal, and a second end, and a secondary winding, including a first end to provide an output voltage signal, and a second end; a first switch, including a first terminal coupled with the second end of the primary winding, a second terminal coupled with a first constant voltage node, and a first control terminal to receive a first switching control signal; a second switch, including a first terminal coupled with the second end of the secondary winding, a second terminal coupled with a second constant voltage node, and a second control terminal to receive a second switching control signal; a first control circuit to provide the first switching control signal to turn on the first switch for a non-zero first time period in a converter cycle to allow current to flow in a first direction in the primary winding in response to a first switch voltage across the first switch transitioning below a first threshold; and a second control circuit to provide the second switching control signal to turn on the second switch for a non-zero second time period following the first time period in the converter cycle, the second control circuit operative to provide the second switching control signal to again turn on the second switch for a non-zero third time period in the converter cycle in response to a second switch voltage across the second switch transitioning below a second threshold to cause current flow in a second direction in the primary winding to at least partially discharge a capacitance of the first switch to cause the first switch voltage to transition below the first threshold to initiate a subsequent converter cycle and allow the first switch to operate at or near a zero-voltage switching (ZVS) condition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An integrated circuit (IC) to operate a flyback converter, comprising:
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a first switch, including a first terminal to couple with a primary winding of a transformer, a second terminal to couple with a first constant voltage node, and a first control terminal to receive a first switching control signal; a second switch, including a first terminal to couple with a secondary winding of the transformer, a second terminal to couple with a second constant voltage node, and a second control terminal to receive a second switching control signal; a first control circuit to provide the first switching control signal to turn on the first switch for a non-zero first time period in a converter cycle to allow current to flow in a first direction in the primary winding in response to a first switch voltage across the first switch transitioning below a first threshold; and a second control circuit to provide the second switching control signal to turn on the second switch for a non-zero second time period following the first time period in the converter cycle, the second control circuit operative to provide the second switching control signal to again turn on the second switch for a non-zero third time period in the converter cycle in response to a second switch voltage across the second switch transitioning below a second threshold to cause current flow in a second direction in the primary winding to at least partially discharge a capacitance of the first switch to cause the first switch voltage to transition below the first threshold to initiate a subsequent converter cycle and allowing the first switch to operate at or near a zero-voltage switching (ZVS) condition. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A method of operating a flyback converter having a first switch coupled with a primary winding of a converter transformer and a second switch coupled with a secondary winding of the converter transformer, the method comprising, in each of a series of converter cycles:
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turning on the first switch for a non-zero first time period to allow current to flow in a first direction in the primary winding in response to a first switch voltage across the first switch transitioning below a first threshold; turning off the first switch after the first time period; turning on the second switch for a non-zero second time period after the first time period; turning off the second switch after the second time period; turning on the second switch again for a non-zero third time period in response to a second switch voltage across the second switch transitioning below a second threshold to cause current flow in a second direction in the primary winding to at least partially discharge a capacitance of the first switch to cause the first switch voltage to transition below the first threshold to initiate a subsequent converter cycle and allowing the first switch to operate at or near a zero-voltage switching (ZVS) condition. - View Dependent Claims (18, 19, 20)
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Specification