Power converter and control method therefor

Patent metadata

Field	Value
Publication number	US-9800166-B2
Application number	US-201615216701-A
Country	US
Kind code	B2
Filing date	Jul 22, 2016
Priority date	Jul 23, 2015
Publication date	Oct 24, 2017
Grant date	Oct 24, 2017

Abstract

A power converter and a control method therefor are provided. The power converter includes a transformer, synchronous rectifier and a control circuit. A primary side of the transformer receives an input voltage, and a secondary side of the transformer generates a sensing signal. The synchronous rectifier is coupled to the secondary side of the transformer. The control circuit receives the sensing signal and detects a changing slope of the sensing signal, and accordingly generates a control signal to control the synchronous rectifier to be turned on or turned off, so as to regulate an output voltage of the power converter.

First claim

What is claimed is:

1. A power converter, comprising:
a synchronous rectifier configured to be coupled to a secondary side of a transformer, the transformer having a primary side receiving an input voltage and the secondary side for generating a sensing signal; and
a control circuit coupled to the synchronous rectifier, receiving the sensing signal from the secondary side, detecting a changing slope of the sensing signal according to a first time point and a second time point, determining a time length from the second time point to a time point that the sensing signal reaches a zero-crossing point according to the changing slope and generating a control signal to control the synchronous rectifier to be turned off according to the time length, so as to regulate an output voltage of the power converter.

2. The power converter according to claim 1 , wherein the sensing signal comprises a sensing current, and during a discharge period of the secondary side of the transformer, the control circuit calculates the changing slope of the sensing current respectively according to the sensing current at the first time point, the sensing current at the second time point, and a time difference between the first time point and the second time point, so as to turn off the synchronous rectifier when a secondary side current of the transformer reaches the zero-crossing point.

3. The power converter according to claim 1 , wherein the sensing signal comprises a sensing voltage, and during a discharge period of the secondary side of the transformer, the control circuit calculates the changing slope of the sensing voltage respectively according to the sensing voltage at the first time point, the sensing voltage at the second time point, and a time difference between the first time point and the second time point, so as to turn off the synchronous rectifier when a secondary side current of the transformer reaches the zero-crossing point.

4. The power converter according to claim 1 , wherein the sensing signal is an inductor current of the secondary side of the transformer.

5. The power converter according to claim 1 , wherein the sensing signal is a drain voltage of the synchronous rectifier.

6. The power converter according to claim 1 , wherein the control circuit comprises:
a first amplifier configured to receive a first inversed sensing signal of the sensing signal and to amplify the first inversed sending signal using a first gain to generate a first amplified signal; and
a second amplifier configured to receive a second inversed sensing signal of the sensing signal and to amplify the second inversed sensing signal using a second gain to generate a second amplified signal, wherein the second gain is different from the first gain.

7. The power converter according to claim 6 , wherein the control circuit further comprises:
a first comparator, coupled to the first amplifier and the second amplifier, and configured to compare the first amplified signal and the second amplified signal to generate a first comparison result;
a second comparator configured to compare the first inversed sensing signal and the second inversed sensing signal to generate a second comparison result; and
a third comparator configured to compare the first comparison result and the second comparison result to generate a determination signal,
wherein the determination signal is used to determine the time length from the second time point to the time point that the sensing signal reaches the zero-crossing point.

8. The control method according to claim 7 , wherein the step of configuring the control circuit to determine the time length from the second time point to the time point that the sensing signal reaches the zero-crossing point according to the changing slope further comprises:
configuring the control circuit to compare the first amplified signal and the second amplified signal to generate a first comparison result by a first comparator;
configuring the control circuit to compare the first inversed sensing signal and the second inversed sensing signal to generate a second comparison result by a second comparator; and
configuring the control circuit to compare the first comparison result and the second comparison result to generate a determination signal by a third comparator,
wherein the determination signal is used to determine the time length from the second time point to the time point that the sensing signal reaches the zero-crossing point.

9. A control method for a power converter, wherein the power converter includes a synchronous rectifier configured to be coupled to a transformer, the control method includes:
configuring a control circuit to receive a sensing signal generated by a secondary side of the transformer according an input voltage received by a primary side of the transformer;
configuring the control circuit to detect a changing slope of the sensing signal according to a first time point and a second time point;
configuring the control circuit to determine a time length from the second time point to a time point that the sensing signal reaches a zero-crossing point according to the changing slope; and
configuring the control circuit to generate a control signal to control the synchronous rectifier to be turned off according to the time length, so as to regulate an output voltage of the power converter.

10. The control method according to claim 9 , wherein the sensing signal comprises a sensing current, and
the step for configuring the control circuit to detect a changing slope of the sensing signal further includes:
configuring the control circuit to calculate the changing slope of the sensing current respectively according to the sensing current at the first time point, the sensing current at the second time point, and a time difference between the first time point and the second time point during a discharge period of the secondary side of the transformer, so as to turn off the synchronous rectifier when a secondary side current of the transformer reaches the zero-crossing point.

11. The control method according to claim 9 , wherein the sensing signal comprises a sensing voltage, and
the step for configuring the control circuit to detect a changing slope of the sensing signal further includes:
configuring the control circuit to calculate the changing slope of the sensing voltage respectively according to the sensing voltage at the first time point, the sensing voltage at the second time point, and a time difference between the first time point and the second time point during a discharge period of the secondary side of the transformer, so as to turn off the synchronous rectifier when a secondary side current of the transformer reaches the zero-crossing point.

12. The control method according to claim 9 , wherein configuring the control circuit to receive the sensing signal includes configuring the control circuit to receive an inductor current of the secondary side of the transformer.

13. The control method according to claim 9 , wherein configuring the control circuit to receive the sensing signal includes configuring the control circuit to receive a drain voltage of the synchronous rectifier.

14. The control method according to claim 9 , wherein the step of configuring the control circuit to determine the time length from the second time point to the time point that the sensing signal reaches the zero-crossing point according to the changing slope comprises:
configuring the control circuit to receive a first inversed sensing signal of the sensing signal and to amplify the first inversed sending signal using a first gain to generate a first ampli

Assignees

• Semiconductor Components Ind Llc

Inventors

• Chang Yung-I
• Huang Kuo-Hsien

Classifications

• H02M2001/0009

  Electricity · mapped topic

• H02M2001/0058

  Electricity · mapped topic

• Y02B70/1491

  Cross-Sectional Technologies · mapped topic

• H02M3/33592 Primary

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

• Y02B70/1475

  Cross-Sectional Technologies · mapped topic