Synchronous rectifier circuit, control circuit and control method thereof

Patent metadata

Field	Value
Publication number	US-11606039-B2
Application number	US-202117145526-A
Country	US
Kind code	B2
Filing date	Jan 11, 2021
Priority date	Jan 16, 2020
Publication date	Mar 14, 2023
Grant date	Mar 14, 2023

Abstract

A method of controlling a synchronous rectifier circuit can include: adjusting a falling amplitude of a drive voltage of a synchronous rectifier switch in the synchronous rectifier circuit in a pull-down mode; adjusting a shielding time during which the synchronous rectifier switch is in a turn-off shielding mode and is not to be turned off; turning off the synchronous rectifier switch after a drain-source voltage of the synchronous rectifier switch reaches a turn-off threshold; and where the falling amplitude of the drive voltage in the pull-down mode and the shielding time for a current period are adjusted according to an operation state of the synchronous rectifier switch in a previous period.

First claim

What is claimed is:

1. A method of controlling a synchronous rectifier circuit, the method comprising:
a) adjusting a falling amplitude of a drive voltage of a synchronous rectifier switch in the synchronous rectifier circuit in a pull-down mode;
b) adjusting a shielding time during which the synchronous rectifier switch is in a turn-off shielding mode and is not to be turned off;
c) turning off the synchronous rectifier switch after a drain-source voltage of the synchronous rectifier switch reaches a turn-off threshold; and
d) wherein the falling amplitude of the drive voltage in the pull-down mode and the shielding time for a current period are adjusted according to an operation state of the synchronous rectifier switch in a previous period.

2. The method of claim 1 , wherein the adjusting the falling amplitude of the drive voltage comprises:
a) adjusting a pull-down threshold; and
b) controlling the drive voltage to be decreased to the pull-down threshold in the pull-down mode.

3. The method of claim 1 , wherein the adjusting the falling amplitude of the drive voltage comprises adjusting a pull-down time for the pull-down mode, and the drive voltage is decreased during the pull-down time.

4. The method of claim 1 , further comprising:
a) detecting whether a body diode of the synchronous rectifier switch is in a conduction state after the synchronous rectifier switch is turned off to generate a status signal; and
b) detecting a change rate of a current flowing through the synchronous rectifier switch.

5. The method of claim 4 , further comprising:
a) adjusting the falling amplitude of the drive voltage in the pull-down mode for a next period according to the status signal, the change rate of the current, and the falling amplitude of the drive voltage in the pull-down mode for a current period; and
b) adjusting the shielding time for a next period according to the status signal, the change rate of the current, and the shielding time for the current period.

6. The method of claim 4 , further comprising increasing the falling amplitude of the drive voltage in the pull-down mode for a next period and increasing the shielding time for a next period, when the body diode is detected to be in the conduction state after the synchronous rectifier switch is turned off.

7. The method of claim 4 , further comprising:
a) comparing the change rate of the current for a current period against the change rate of the current for the previous period to generate a comparison result, when the body diode is detected not to be in the conduction state after the synchronous rectifier switch is turned off; and
b) adjusting the falling amplitude of the drive voltage in the pull-down mode and the shielding time for the next period according to the comparison result.

8. The method of claim 7 , further comprising:
a) comparing a timing time during which the drain-source voltage of the synchronous rectifier switch rises from a first threshold to a second threshold in the current period against that in the previous period to generate the comparison result; and
b) adjusting the falling amplitude of the drive voltage in the pull-down mode according to the comparison result.

9. The method of claim 8 , wherein when a difference between the timing time for the current period and the timing time for the previous period is greater than a preset time, the falling amplitude of the drive voltage in the pull-down mode is gradually decreased in each subsequent cycle until the falling amplitude of the drive voltage in the pull-down mode is decreased to zero or the body diode of the synchronous rectifier switch is detected to be in the conduction state again after the synchronous rectifier switch is turned off.

10. The method of claim 7 , further comprising:
a) detecting whether the drain-source voltage of the synchronous rectifier switch reaches the turn-off threshold within the shielding time for the current period to generate a detection result; and
b) adjusting the shielding time for the next period according to the detection result.

11. The method of claim 10 , wherein when the drain-source voltage of the synchronous rectifier switch does not exceed the turn-off threshold within the shielding time, the shielding time is gradually decreased in each subsequent cycle until the shielding time is decreased to zero or the body diode of the synchronous rectifier switch is detected to be in the conduction state again after the synchronous rectifier switch is turned off.

12. The method of claim 1 , wherein when the drain-source voltage of the synchronous rectifier switch reaches a first threshold, the synchronous rectifier switch enters the pull-down mode; and when the drain-source voltage of the synchronous rectifier switch reaches a second threshold, the synchronous rectifier switch enters the turn-off shielding mode.

13. A control circuit for a synchronous rectifier circuit, the control circuit comprising:
a) a sampling circuit configured to obtain a drain-source voltage of a synchronous rectifier switch in the synchronous rectifier circuit; and
b) a drive control circuit configured to adjust a drive voltage of the synchronous rectifier switch according to the drain-source voltage, and to adjust a shielding time during which the synchronous rectifier switch is controlled not to be turned off in a turn-off shielding mode.

14. The control circuit of claim 13 , wherein the drive control circuit comprises:
a) a drive pull-down circuit configured to adjust a falling amplitude of the drive voltage of the synchronous rectifier switch in a pull-down mode; and
b) a turn-off shielding circuit configured to adjust the shielding time and to disable a turn-off signal.

15. The control circuit of claim 14 , wherein the falling amplitude of the drive voltage in the pull-down mode and the shielding time for a current period are adjusted according to an operation state of the synchronous rectifier switch in a previous period.

16. The control circuit of claim 14 , wherein the drive pull-down circuit is configured to adjust a pull-down threshold and control the drive voltage to be decreased to the pull-down threshold in the pull-down mode.

17. The control circuit of claim 14 , wherein the drive pull-down circuit is configured to adjust a pull-down time for the pull-down mode, and the drive voltage is decreased during the pull-down time.

18. The control circuit of claim 14 , wherein the drive control circuit further comprises an adaptive drive regulation circuit, configured to control the drive voltage of the synchronous rectifier switch to be maintained at a first threshold after the pull-down mode ends.

19. The control circuit of claim 13 , wherein the drive control circuit further comprises a drive turn-off circuit, configured to generate a turn-off signal when the drain-source voltage reaches a turn-off threshold, in order to turn off the synchronous rectifier switch.

20. The control circuit of claim 14 , further comprising a signal detection circuit configured to detect whether a body diode of the synchronous rectifier switch is in a conduction state after the synchronous rectifier switch is turned off, and to detect a change rate of a current flowing through the synchronous rectifier switch, thereby adjusting the falling amplitude of the drive voltage in the pull-down mode and the shielding time for the next period.

Assignees

• Silergy Semiconductor Technology Hangzhou Ltd

Inventors

• Chen Chaojun
• Deng Jian
• Jin Jin

Classifications

• H02M1/08

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

• H02M3/01 Primary

  Resonant DC/DC converters · 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

• H02M3/33592 Primary

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