Control circuit for a synchronous rectification circuit, LLC resonant converter and associated method

Patent metadata

Field	Value
Publication number	US-9379630-B2
Application number	US-201414313369-A
Country	US
Kind code	B2
Filing date	Jun 24, 2014
Priority date	Jun 24, 2013
Publication date	Jun 28, 2016
Grant date	Jun 28, 2016

Abstract

A control circuit for a synchronous rectification circuit, a LLC resonant converter and a control method. The control circuit has a first comparing circuit, a second comparing circuit, a blanking circuit, a first logic circuit and a second logic circuit. The blanking circuit is configured to provide a first blanking signal and a second blanking signal to avoid one or more repeated conduction of a first synchronous rectifier and a second synchronous rectifier respectively, and the first blanking signal and the second blanking signal are logic complementary.

First claim

I claim:

1. A control circuit for a synchronous rectification circuit, wherein the synchronous rectification circuit has a first synchronous rectifier and a second synchronous rectifier, and wherein each of the first synchronous rectifier and the second synchronous rectifier has a drain, a source and a gate, the control circuit comprises:
a first comparing circuit having an input terminal and an output terminal, wherein the input terminal of the first comparing circuit is configured to receive a first drain-source voltage signal of the first synchronous rectifier, and wherein the first comparing circuit is configured to compare the first drain-source voltage signal with a threshold voltage and to provide a first comparing signal at the output terminal;
a second comparing circuit having an input terminal and an output terminal, wherein the input terminal of the second comparing circuit is configured to receive a second drain-source voltage signal of the second rectifier, and wherein the second comparing circuit is configured to compare the second drain-source voltage signal with the threshold voltage and to provide a second comparing signal at the output terminal;
a blanking circuit having a first input terminal, a second input terminal, a first output terminal and a second output terminal, wherein the first input terminal of the blanking circuit is coupled to the output terminal of the first comparing circuit for receiving the first comparing signal, and wherein the second input terminal of the blanking circuit is coupled to the output terminal of the second comparing circuit for receiving the second comparing signal, and wherein the blanking circuit is configured to conduct a logic operation to the first comparing signal and the second comparing signal so as to provide a first blanking signal and a second blanking signal respectively at the first output terminal and the second output terminal, and wherein the first blanking signal and the second blanking signal are logic complementary;
a first logic circuit having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the first logic circuit is coupled to the output terminal of the first comparing circuit for receiving the first comparing signal, and wherein the second input terminal of the first logic circuit is coupled to the first output terminal of the blanking circuit for receiving the first blanking signal, and wherein the first logic circuit is configured to conduct a logic operation to the first comparing signal and the first blanking signal so as to provide a first driving signal at the output terminal of the first logic circuit, and wherein the first driving signal is coupled to the gate of the first synchronous rectifier to control an on and off switching of the first synchronous rectifier; and
a second logic circuit having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the second logic circuit is coupled to the output terminal of the second comparing circuit for receiving the second comparing signal, and wherein the second input terminal of the second logic circuit is coupled to the second output terminal of the blanking circuit for receiving the second blanking signal, and wherein the second logic circuit is configured to conduct a logic operation to the second comparing signal and the second blanking signal so as to provide a second driving signal at the output terminal of the second logic circuit, and wherein the second driving signal is coupled to the gate of the second synchronous rectifier to control an on and off switching of the second synchronous rectifier.

2. The control circuit of claim 1 , wherein:
the first blanking signal is active beginning at each falling edge of the first comparing signal and ending at each falling edge of the second comparing signal; and wherein:
the second blanking signal is active beginning at each falling edge of the second comparing signal and ending at each falling edge of the first comparing signal.

3. The control circuit of claim 2 , wherein the threshold voltage comprises a first threshold voltage and a second threshold voltage; and wherein the first threshold voltage and the second threshold voltage are negative; and wherein the first threshold voltage is larger than the second threshold voltage; and wherein the first drain-source voltage signal is negative; and wherein:
when the first blanking signal is inactive, the first synchronous rectifier is turned off once the first drain-source voltage signal is larger than the first threshold voltage; and wherein
when the first blanking signal is inactive, the first synchronous rectifier is turned on once the first drain-source voltage signal is smaller than the second threshold voltage.

4. The control circuit of claim 2 , wherein the threshold voltage comprises a first threshold voltage and a second threshold voltage; and wherein the first threshold voltage and the second threshold voltage are negative; and wherein the first threshold voltage is larger than the second threshold voltage; and wherein the second drain-source voltage signal is negative; and wherein:
when the second blanking signal is inactive, the second synchronous rectifier is turned off once the second drain-source voltage signal is larger than the first threshold voltage; and wherein
when the second blanking signal is inactive, the second synchronous rectifier is turned on once the second drain-source voltage signal is smaller than the second threshold voltage.

5. The control circuit of claim 2 , wherein:
the first synchronous rectifier remains off when the first blanking signal is active; and wherein
the second synchronous rectifier remains off when the second blanking signal is active.

6. The control circuit of claim 1 , wherein the blanking circuit further comprises:
a first inverter having an input terminal and an output terminal, wherein the input terminal of the first inverter is configured to receive the first comparing signal, and wherein the output terminal of the first inverter is configured to provide a first inverted signal of the first comparing signal;
a second inverter having an input terminal and an output terminal, wherein the input terminal of the second inverter is configured to receive the second comparing signal, and wherein the output terminal of the second inverter is configured to provide a second inverted signal of the second comparing signal; and
a trigger having a first input terminal, a second input terminal, a first output terminal and a second output terminal, wherein the first input terminal of the trigger is coupled to the output terminal of the first inverter, and wherein the second input terminal of the trigger is coupled to the output terminal of the second inverter, and wherein the first output terminal of the trigger is configured to provide the first blanking signal, and wherein the second output terminal of the trigger is configured to provide the second blanking signal, and wherein the first inverted signal of the first comparing signal is configured to set the first blanking signal, and wherein the second inverted signal of the second comparing signal is configured to reset the first blanking signal.

7. The control circuit of claim 1 , wherein the first comparing circuit comprises a first hysteresis comparator.

8. The control circuit of claim 1 , wherein the second comparing circuit comprises a second hysteresis comparator.

9. A LLC resonant converter comprising the control circuit of claim 1 , wherein the LLC resonant converter further comprises:
a bridge circuit having an input terminal and an output terminal, wherein the input terminal of the bridge circuit

Assignees

• Chengdu Monolithic Power Sys

Inventors

• Miao Lei

Classifications

• H02M2001/0058

  Electricity · mapped topic

• Y02B70/1433

  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

• H02M7/217

  using semiconductor devices only · CPC title