Secondary controller for use in synchronous flyback converter

Patent metadata

Field	Value
Publication number	US-2016268909-A1
Application number	US-201615158965-A
Country	US
Kind code	A1
Filing date	May 19, 2016
Priority date	Jan 22, 2013
Publication date	Sep 15, 2016
Grant date	—

Abstract

A secondary controller for use in a power converter includes a drive circuit coupled to a secondary side of the power converter. The drive circuit is coupled to generate a first signal to enable a first switch coupled to a primary side of the primary converter. The first signal is generated in response to a feedback signal representative of an output of the power converter. A control circuit is coupled to receive the first signal and an input signal representative of a secondary winding voltage of the power converter. The control circuit is coupled to generate a second signal to control a second switch coupled to the secondary side of the power converter in response to the first signal and the input signal.

First claim

What is claimed is:

1 . A secondary controller for use in a power converter, the secondary controller comprising:
a drive circuit coupled to a secondary side of the power converter, wherein the drive circuit is coupled to generate a first signal to enable a first switch coupled to a primary side of the primary converter, wherein the first signal is generated in response to a feedback signal representative of an output of the power converter; and a control circuit coupled to receive the first signal and an input signal representative of a secondary winding voltage of the power converter, wherein the control circuit is coupled to generate a second signal to control a second switch coupled to the secondary side of the power converter in response to the first signal and the input signal.

2 . The secondary controller of claim 1 , wherein the control circuit is coupled to turn on the second switch when the input signal is less than a threshold and turn off the second switch in response to at least one of a plurality of events, wherein the plurality of events includes the input signal reaching the threshold and includes the first signal having a level to enable the first switch.

3 . The secondary controller of claim 1 , wherein the control circuit further comprises a comparator coupled to receive the input signal and is coupled to generate a compare signal in response to the input signal and a threshold, wherein the control circuit is coupled to generate the second signal in response to the first signal and the compare signal.

4 . The secondary controller of claim 3 , wherein the control circuit includes a latch coupled to be set in response to the first signal and coupled to be reset in response to the second signal, and wherein the control circuit is coupled to generate the second signal in response to an output of the latch.

5 . The secondary controller of claim 4 , further comprising a delay circuit coupled to receive the first signal and coupled to generate a delayed first signal, wherein the latch is coupled to the delay circuit to be set in response to the delayed first signal.

6 . The secondary controller of claim 4 , wherein the control circuit includes a logic gate coupled to generate the second signal in response to the first signal, the compare signal, and the latch output.

7 . The secondary controller of claim 6 , wherein the logic gate is an AND gate.

8 . The secondary controller of claim 4 , further comprising a one-shot circuit coupled to the latch and coupled to receive the second signal, wherein the one-shot circuit is coupled to reset the latch in response to the second signal.

9 . The secondary controller of claim 8 , wherein the one-shot circuit is coupled to reset the latch in response to a falling edge of the second signal.

10 . The secondary controller of claim 1 , wherein the input signal is generated by a winding sense circuit that is coupled to a secondary winding of an energy transfer element of the power converter.

11 . The secondary controller of claim 1 , further comprising an oscillator coupled to generate a clock signal coupled to be received by the drive circuit, wherein the drive circuit is coupled to generate the first signal in response to the clock signal.

12 . The secondary controller of claim 1 , wherein the second switch is a synchronous rectifier.

13 . A method of controlling a power converter, the method comprising:
generating a first signal to control a first switch coupled to a primary winding of an energy transfer element to enable a transfer of energy through the energy transfer element from an input of the power converter to an output of the power converter; comparing a threshold to an input signal representative of a voltage of a secondary winding of the energy transfer element; generating, in a secondary controller galvanically isolated from the first switch, a second signal to enable a second switch coupled to the secondary winding in response to said comparing the threshold to the input signal; and generating the second signal to disable the second switch in response to at least one of a plurality of events, wherein the plurality of events includes the input signal reaching the threshold and includes the first signal having a level to enable the first switch.

14 . The method of claim 13 , wherein generating the second signal to enable the second switch comprises setting a latch in response to the first signal, and wherein generating the second signal to disable the second switch comprises resetting the latch.

15 . The method of claim 14 , wherein setting the latch comprises delaying the first signal such that the latch is set in response to the delayed first signal.

16 . The method of claim 14 , wherein resetting the latch comprises detecting a falling edge of a second signal that enables and disables the second switch, wherein the latch is reset in response to said detecting the falling edge of the second signal.

17 . The method of claim 13 , further comprising generating the first signal in response to a clock signal and in response to an output of the power converter.

Assignees

• Power Integrations Inc

Inventors

• Liu Sheng
• Djenguerian Alex B

Classifications

• 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

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• H02M1/14

  Arrangements for reducing ripples from DC input or output · CPC title

• H02M3/33515 Primary

  with digital control · CPC title