Resonant converters with synchronous rectifier feedback

Patent metadata

Field	Value
Publication number	US-9787200-B2
Application number	US-201615061717-A
Country	US
Kind code	B2
Filing date	Mar 4, 2016
Priority date	Nov 4, 2013
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

A method comprises detecting a signal representing a drain-to-source voltage of a switch of a synchronous rectifier of an inductor-inductor-capacitor (LLC) resonant converter, comparing the signal with a predetermined threshold, generating a first logic state if the drain-to-source voltage is greater than the predetermined threshold, generating a second logic state if the drain-to-source voltage is less than the predetermined threshold and in response to the first logic state and the second logic state, adjusting a switching frequency of the LLC resonant converter such that the switching frequency moves back and forth across a boundary of body diode conduction, wherein a frequency difference between the switching frequency and a resonant frequency of the LLC resonant converter is less than or equal to one frequency adjustment step.

First claim

What is claimed is:

1. A method comprising: detecting a signal representing a drain-to-source voltage of a switch of a synchronous rectifier of an inductor-inductor-capacitor (LLC) resonant converter; comparing the signal with a predetermined threshold; generating a first logic state if the drain-to-source voltage is greater than the predetermined threshold; generating a second logic state if the drain-to-source voltage is less than the predetermined threshold; and in response to the first logic state and the second logic state, adjusting a switching frequency of the LLC resonant converter such that the LLC resonant converter moves back and forth across a boundary of body diode conduction, wherein, after the switching frequency of the LLC resonant converter has been adjusted, a frequency difference between the switching frequency and a resonant frequency of the LLC resonant converter is less than or equal to one frequency adjustment step and based upon the logic state, configuring the resonant converter such that a switching frequency of the resonant converter moves back and forth within a frequency band.

2. The method of claim 1 , wherein:
the predetermined threshold is a body diode voltage of the switch.

3. The method of claim 2 , wherein:
the body diode voltage is approximately equal to −0.6 V.

4. The method of claim 3 , further comprising:
increasing the switching frequency of the LLC resonant converter until a first logic state change occurs when the resonant frequency is greater than the switching frequency.

5. The method of claim 4 , further comprising:
after the first logic state change occurs, reducing the switching frequency of the LLC resonant converter until a second logic state change occurs.

6. The method of claim 5 , further comprising:
after the second logic state change occurs, increasing the switching frequency of the LLC resonant converter until a logic state change similar to the first logic state change occurs.

7. The method of claim 1 , further comprising:
reducing the switching frequency of the LLC resonant converter until a third logic state change occurs when the switching frequency is greater than the resonant frequency.

8. The method of claim 7 , further comprising:
after the third logic state change occurs, increasing the switching frequency of the LLC resonant converter until a fourth logic state change occurs.

9. The method of claim 8 , further comprising:
after the fourth logic state change occurs, reducing the switching frequency of the LLC resonant converter until a logic state change similar to the third logic state change occurs.

10. The method of claim 1 , wherein the LLC resonant converter comprises:
a power stage comprising:
an input switch network coupled to a power source, wherein the input switch network comprises a plurality of power switches;
a resonant tank coupled to the plurality of power switches;
an isolation device coupled to the resonant tank; and
an output stage coupled to the isolation device through the synchronous rectifier;
a comparator coupled to the synchronous rectifier; and
a control circuit coupled to the power switches, wherein the control circuit generates a plurality of gate drive signals for the power switches.

11. The method of claim 10 , further comprising:
a diode coupled between an input of the comparator and a drain of the switch, wherein:
a cathode of the diode is coupled to the drain of the switch; and
an anode of the diode is coupled to the input of the comparator; and

a bias voltage source coupled to the input of the comparator through a bias resistor.

12. A method comprising: detecting a drain voltage of a transistor of a resonant converter, wherein the resonant converter comprises: an input switch network coupled to a power source, wherein the input switch network comprises a plurality of power switches; a resonant tank coupled to the plurality of power switches; a transformer coupled to the resonant tank; and an output stage coupled to the transformer, wherein the output stage comprises the transistor; comparing the drain voltage with a predetermined voltage threshold, wherein: the drain voltage is coupled to a negative input of a comparator; and the predetermined voltage threshold is coupled to a positive input of the comparator; generating a logic state based upon an output of the comparator; and adjusting, by a control circuit, a switching frequency of the resonant converter based upon a result of comparing the drain voltage with a predetermined voltage threshold, wherein the control circuit is configured such that the resonant converter moves back and forth across a boundary between body diode conduction and transistor conduction, and based upon the logic state, configuring the resonant converter such that a switching frequency of the resonant converter moves back and forth within a frequency band.

13. The method of claim 12 , further comprising:
when a resonant frequency of the resonant converter is greater than the switching frequency of the resonant converter, increasing the switching frequency of the resonant converter until a first logic state change occurs; and
after the first logic state change occurs, adjusting the switching frequency of the resonant converter such that the switching frequency of the resonant converter moves back and forth at the boundary between body diode conduction and transistor conduction.

14. The method of claim 12 , further comprising:
when the switching frequency of the resonant converter is greater than a resonant frequency of the resonant converter, reducing the switching frequency of the resonant converter until a second logic state change occurs; and
after the second logic state change occurs, adjusting the switching frequency of the resonant converter such that the switching frequency of the resonant converter moves back and forth at the boundary between body diode conduction and transistor conduction.

15. The method of claim 12 , further comprising:
when a resonant frequency of the resonant converter is greater than the switching frequency of the resonant converter, increasing the switching frequency of the resonant converter until the switching frequency is equal to a predetermined upper limit.

16. The method of claim 12 , further comprising:
when the switching frequency of the resonant converter is greater than a resonant frequency of the resonant converter, reducing the switching frequency of the resonant converter until the switching frequency is equal to a predetermined lower limit.

17. A method comprising:
detecting a signal across a drain and a source of a transistor of a resonant converter, wherein the resonant converter comprises:
a power stage comprising:
an input switch network coupled to a power source, wherein the input switch network comprises a plurality of power switches;
a resonant tank coupled to the plurality of power switches;
an isolation device coupled to the resonant tank; and
an output stage coupled to the isolation device through a rectifier, wherein the rectifier comprises the transistor, and wherein a drain of the transistor is coupled to the isolation device and a source of the transistor is coupled to ground; and

a control circuit coupled to the power switches, wherein the control circuit generates a plurality of gate drive signals for the power switches;

comparing the signal with a predetermined threshold to generate a logic state; and
based upon the logic state, configuring the resonant converter such that a switching frequency of the resonant converter moves back and forth wi

Assignees

• Futurewei Technologies Inc

Inventors

• Fu Dianbo
• Dai Heping
• Ye Liming
• Chen Daoshen

Classifications

• H02M2001/0058

  Electricity · mapped topic

• Y02B70/1433

  Cross-Sectional Technologies · mapped topic

• H02M3/33576

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

• H02M3/33546 Primary

  with automatic control of the output voltage or current (H02M3/33561 takes precedence) · CPC title

• Y02B70/1491

  Cross-Sectional Technologies · mapped topic