Soft switching flyback converter

Patent metadata

Field	Value
Publication number	US-2016233779-A1
Application number	US-201615007262-A
Country	US
Kind code	A1
Filing date	Jan 27, 2016
Priority date	Feb 6, 2015
Publication date	Aug 11, 2016
Grant date	—

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.

First claim

The following is claimed:

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, 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.

2 . The flyback converter of claim 1 , wherein the second switch voltage undergoes resonant ringing including a series of peaks and troughs while the second switch is off; and wherein the second control circuit is operative to provide the second switching control signal to turn on the second switch for the third time period in response to the second switch voltage transitioning below the second threshold at or near a particular one of the troughs.

3 . The flyback converter of claim 2 , wherein the second control circuit selects the particular one of the troughs at which to again turn on the second switch for the third time period at least partially according to a converter output signal.

4 . The flyback converter of claim 3 , wherein the second control circuit selects the particular one of the troughs at which to again turn on the second switch for the third time period to selectively adjust a switching frequency and a duration of the converter cycle to at least partially regulate the converter output signal according to a setpoint signal.

5 . The flyback converter of claim 4 , wherein the second control circuit directly senses the converter output signal.

6 . The flyback converter of claim 4 , wherein the second control circuit computes the converter output signal according to one or more sensed conditions on the secondary side of the transformer.

7 . The flyback converter of claim 1 , wherein the first control circuit selectively adjusts the first time period to regulate a converter output signal.

8 . The flyback converter of claim 1 , comprising:
a third switch, including a first terminal coupled to receive the input voltage signal, a second terminal coupled with the first end of the primary winding, and a third control terminal to receive a third switching control signal; a first diode, including a first anode connected to the second end of the primary winding, and a first cathode connected to the first terminal of the third switch; and a second diode, including a second anode connected to the first constant voltage node, and a second cathode connected to the first end of the primary winding; wherein the first control circuit is operative to provide the third switching control signal to turn on the third switch when the first switch is on, and to turn off the third switch when the first switch is off.

9 . The flyback converter of claim 8 , wherein the second switch voltage undergoes resonant ringing including a series of peaks and troughs while the second switch is off; and wherein the second control circuit is operative to provide the second switching control signal to turn on the second switch for the third time period in response to the second switch voltage across the second switch transitioning below the second threshold at or near a particular one of the troughs.

10 . The flyback converter of claim 9 , wherein the second control circuit selects the particular one of the plurality of troughs at which to again turn on the second switch for the third time period at least partially according to a converter output signal.

11 . An integrated circuit (IC) to operate a flyback converter, comprising:
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.

12 . The IC of claim 11 , wherein the second switch voltage undergoes resonant ringing including a series of peaks and troughs while the second switch is off; and wherein the second control circuit is operative to provide the second switching control signal to turn on the second switch for the third time period in response to the second switch voltage transitioning below the second threshold at or near a particular one of the troughs.

13 . The IC of claim 12 , wherein the second control circuit selects the particular one of the troughs at which to again turn on the second switch for the third time period at least partially according to a converter output signal.

14 . The IC of claim 13 , wherein the second control circuit selects the particular one of the troughs at which to again turn on the second switch for the third time period to selectively adjust a switching frequency and a duration of the converter cycle to at least partially regulate the converter output signal according to a setpoint signal.

15 . The IC of claim 11 , wherein the first control circuit selectively adjusts the first time period to regulate a converter output signal

Assignees

• Texas Instruments Inc

Inventors

• Cohen Isaac

Classifications

• H02M3/33576

  having at least one active switching element at the secondary side of an isolation transformer · CPC title

• H02M3/33507

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

• H02M3/33592 Primary

  having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer · 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

• Y02B70/10

  Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes · CPC title