Resonant gate drive for synchronous rectifiers

• US 6,169,683 B1
• Filed: 10/07/1999
• Issued: 01/02/2001
• Est. Priority Date: 10/07/1999
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Farrington, Richard
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Vu, Bao Q.
• Application Number:
  US09/414,247
• Time in Patent Office: 453 Days
• Field of Search: 363/50, 363/53, 363/89, 363/127, 363/125, 363/81
• US Class Current: 363/127
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• CPC Class Codes: Y02B 70/10 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

Abstract

An externally-driven synchronous rectifier circuit (18) comprises first and second synchronous rectifiers (SQ1, SQ2), and first and second synchronous rectifier recovery switches (SQ3, SQ5), and a pair of resonant inductors (LR1, LR2). The resonant inductors (LR1, LR2) store the energy normally loss during charging and discharging the input capacitance of the first and second synchronous rectifiers (SQ1, SQ2). The recovery switches (SQ3, SQ5) transfer the stored energy from the at least one inductor (L_R) to the output terminal (Vout) creating a more energy efficient circuit (18).

Claims

1. An externally driven synchronous rectifier circuit for a DC-to-DC power converter comprising:

a primary transformer having a primary and secondary winding, said secondary winding having a first terminal and a second terminal;

a first synchronous rectifier operably coupled to said first terminal of said secondary winding;

a second synchronous rectifier operably coupled to said second terminal of said secondary winding;

an external drive circuit operably coupled to said first and second synchronous rectifiers to provide timing signals to turn on and off said first and second synchronous rectifiers;

an energy recovery circuit coupled to said first and second synchronous rectifiers and configured for storing energy associated with charging and discharging the input capacitance said first and second synchronous rectifiers; and

an output voltage terminal coupled to said energy recovery circuit for receiving rectified voltage waveforms.

2. The externally driven synchronous rectifier circuit of claim 1 wherein said external drive circuit includes a second transformer with a primary winding and a secondary winding, said secondary winding having first and second terminals through which said timing signals are delivered to said first and second synchronous rectifiers.

3. The externally driven synchronous rectifier circuit of claim 2 further comprising:

a first switch having a gate, said first switch coupled to a voltage source;

a second switch having a gate, said second switch coupled to a voltage source;

a first resistor coupled in series between said gate of said first switch and said first terminal of said secondary winding of said second transformer; and

a second resistor coupled in series between said gate of said second switch and said second terminal of said secondary winding of said second transformer.

4. The externally driven synchronous rectifier circuit of claim 1 wherein said first and second synchronous rectifiers are Field Effect Transistors devices with first, second and third terminals.

5. The externally driven synchronous rectifier circuit of claim 2 wherein said energy recovery circuit further comprises:

a first resonant inductor with first and second terminals;

a first set of diodes connected to a first terminal of said first synchronous rectifier circuit and arranged to direct current through said first resonant inductor via said first set of diodes;

a second resonant inductor with first and second terminals; and

a second set of diodes connected to a first terminal of said second synchronous rectifier circuit and arranged to direct current through said first resonant inductor via said second set of diodes.

6. The externally driven synchronous rectifier circuit of claim 5 further comprising:

a first recovery switch operably coupled to first resonant inductor and to said first terminal of said secondary winding of said second transformer for obtaining timing signal therefrom;

a second recovery switch operably coupled to second resonant inductor and to said second terminal of said secondary winding of said second transformer for obtaining timing signal therefrom.

7. The externally driven synchronous rectifier circuit of claim 1 further comprising:

a center tap connected to said secondary winding of said second transformer; and

an output inductor with a first terminal coupled to said center tap and a second terminal coupled to said output terminal.

8. The externally driven synchronous rectifier circuit of claim 7 wherein said output inductor further comprises an auxiliary winding configured to provide a correct charging pulse for said first and second synchronous rectifiers.

9. The externally driven synchronous rectifier circuit of claim 8 wherein said auxiliary winding is coupled to the positive end of said output terminal and whereby the number of turns of said auxiliary winding are reduced for low voltage synchronous rectifier circuits.

10. The externally driven synchronous rectifier circuit of claim 9 further comprising:

an auxiliary winding diode coupled to said first and second recovery switches; and

an auxiliary capacitor coupled in series with said auxiliary winding diode.

11. The externally driven synchronous rectifier circuit of claim 8 further comprising a second auxiliary winding whereby said energy recovery circuit is adaptable as a half-wave rectifier.

12. An energy recovery mechanism for an externally driven synchronous rectifier circuit having a primary transformer, first and second synchronous rectifiers, an output terminal, and an external driving circuit configured to provide the timing signals for driving said first and second synchronous rectifiers, said mechanism comprising:

first and second resonant inductors each having first and second terminals;

first and second recovery switches coupled to corresponding first terminals of said first and second resonant inductors;

a first set of diodes arranged to direct current into said second terminal of said first resonant inductor;

a second set of diodes arranged to direct current into said second terminal of said second resonant inductor; and

wherein said first and second recovery switches are further coupled to said external driving circuit for causing current to enter said first and second resonant inductors to recover energy used in charging and discharging said first and second synchronous rectifiers.

13. The energy recovery circuit of claim 12 further comprising:

a storage inductor coupled to said first and second recovery switches; and

an output diode coupled in series with said storage inductor, said output diode further configured to prevent energy from returning back to said first and second recovery switches.

14. The energy recovery circuit of claim 12 further comprising first and second resistors coupled to said first and second recovery switches and configured to effect the timing operation of said first and second recovery switches.

15. The energy recovery circuit of claim 12 further comprising:

a third recovery switch operably disposed between said first synchronous rectifier and one of said first set of diodes; and

a fourth recovery switch operably disposed between said second synchronous rectifier and the other of said first set of diodes;

whereby the voltage across said first and synchronous rectifiers can be limited to a voltage other than that of the supply voltage by the operation of said third and fourth recovery switches.

16. The energy recovery circuit of claim 12 wherein said first and second recovery switches are MOSFETs.

17. A method of energy recovery for an energy recovery circuit utilized with a self-driven synchronous rectifier circuit having a first and second synchronous rectifier and an output terminal, said energy recovery circuit having a first and second switch and an at least one storage inductor, said method comprising the steps of:

capturing the energy of said synchronous rectifiers in said storage inductor; and

transferring the stored energy from said storage inductor to said output terminal.

18. The method of claim 17 wherein said step of capturing the energy of the capacitance of said synchronous rectifiers includes capturing the charging energy of said synchronous rectifiers.

19. The method of claim 17 wherein said step of capturing the energy of the capacitance of said synchronous rectifiers includes capturing the discharging energy of said synchronous rectifiers.