Reduced voltage stress asymmetrical DC-to-DC converter using first and second transformers having differing turns ratios

• US 5,754,413 A
• Filed: 09/06/1996
• Issued: 05/19/1998
• Est. Priority Date: 02/23/1996
• Status: Expired due to Fees

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Miftakhutdinov, Rais K., Fraidlin, Simon, Meleshin, Valery I., Nemchinov, Alexey V.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): JARDIEU, DEREK
• Application Number:
  US08/709,564
• Time in Patent Office: 620 Days
• Field of Search: 363/16, 363/17, 363/132
• US Class Current: 363/16
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer

Abstract

A voltage stress (e.g., reverse voltage stress) in rectifying diodes of, for instance, an asymmetrical DC-to-DC converter is reduced by using a transformer circuit having multiple power transformers with a composite static transfer characteristic. More specifically, the static transfer characteristic is selected to be monotonic in combination with the transformer circuit including two transformers, having independent isolated cores, coupling an input to output of the converter. A primary to secondary winding ratio of each of the two transformers is selected in such a way as to achieve a reduction in reverse voltage in at least one of the rectifying diodes. The reduction in the reverse voltage and, hence, improved efficiency of the rectifier is directly translatable into an increase in a power density of the converter.

Claims

1. For use in a power converter having a power train couplable to a source of electrical power and further having a rectifier subject to stress during a reverse voltage condition, a transformer circuit, comprising:

a first transformer having a primary winding coupled to said power train and a secondary winding coupled to said rectifier, said first transformer further having a first turns ratio (N₁), said first transformer passing a first portion of electrical power through said converter; and

a second transformer having a primary winding coupled to said power train and a secondary winding coupled to said rectifier, said second transformer further having a second turns ratio (N₂), said second transformer passing a second portion of electrical power through said converter, N₁ being different from N₂ to thereby reduce said stress on said rectifier during said reverse voltage condition.

2. The transformer circuit as recited in claim 1 wherein N₁ and N₂ are selected as a function of an input voltage to said converter.

3. The transformer circuit as recited in claim 1 wherein said power train is coupled to a control circuit and drive circuit for controlling an activation of at least one power switch associated with said power train.

4. The transformer circuit as recited in claim 1 wherein said rectifier comprises at least one rectifying diode.

5. The transformer circuit as recited in claim 1 wherein said rectifier is coupled to an output filter for providing a filtered output voltage at an output of said converter.

6. The transformer circuit as recited in claim 1 wherein said power train comprises a first and second alternately-conducting power switch having a duty cycle (D) and (1-D), respectively, N₁ and N₂ being selected as a function of D and 1-D.

7. The transformer circuit as recited in claim 6 wherein said inductor is connected to a diode.

8. The transformer circuit as recited in claim 6 wherein said primary winding of said first transformer and said primary winding of said second transformer are connected to an inductor thereby enhancing zero voltage switching (ZVS) across at least one of said first and second power switches.

9. The transformer circuit as recited in claim 8 wherein said inductor comprises a winding thereby providing a regulated voltage in said converter.

10. For use in a power converter having a power train couplable to a source of electrical power and further having a rectifier subject to stress during a reverse voltage condition, a method for reducing said stress on said rectifier with a transformer circuit, comprising the steps of:

passing a first portion of electrical power through a first transformer containing a primary winding coupled to said power train and a secondary winding coupled to said rectifier, said first transformer having a first turns ratio (N₁), and

passing a second portion of electrical power through a second transformer containing a primary winding coupled to said power train and a secondary winding coupled to said rectifier, said second transformer having a second turns ratio (N₂), N₁ being different from N₂ to thereby reduce said stress on said rectifier during said reverse voltage condition.

11. The method as recited in claim 10 further comprising the step of selecting N₁ and N₂ as a function of an input voltage to said converter.

12. The method as recited in claim 10 further comprising the step of controlling an activation of at least one power switch associated with said power train with a control circuit and drive circuit.

13. The method as recited in claim 10 wherein said rectifier comprises at least one rectifying diode.

14. The method as recited in claim 10 further comprising the step of filtering an output voltage of said converter with an output filter.

15. The method as recited in claim 10 wherein said power train comprises a first and second alternately-conducting power switch having a duty cycle (D) and (1-D), respectively, the method for reducing further comprising the step of selecting N₁ and N₂ as a function of D and 1-D.

16. The method as recited in claim 15 further comprising the step of enhancing zero voltage switching (ZVS) across at least one of said first and second power switches with an inductor connected to said primary winding of said first transformer and said primary winding of said second transformer.

17. The method as recited in claim 16 further comprising the step of providing a regulated voltage in said converter with a winding coupled to said inductor.

18. The method as recited in claim 16 wherein said inductor is connected to a diode.

19. A power converter, comprising:

a power train couplable to a source of electrical power;

a rectifier subject to stress resulting from a reverse voltage condition therein;

a transformer circuit, comprising;

a first transformer having a primary winding coupled to said power train and a secondary winding coupled to said rectifier, said first transformer further having a first turns ratio (N₁), said first transformer passing a first portion of electrical power through said converter, and

a second transformer having a primary winding coupled to said power train and a secondary winding coupled to said rectifier, said second transformer further having a second turns ratio (N₂), said second transformer passing a second portion of electrical power through said converter, N₁ being different from N₂ to thereby reduce said stress on said rectifier during said reverse voltage condition.

20. The converter as recited in claim 19 wherein N₁ and N₂ are selected as a function of an input voltage to said converter.

21. The converter as recited in claim 19 wherein said rectifier comprises at least one rectifying diode.

22. The converter as recited in claim 19 wherein said rectifier is coupled to an output filter for providing a filtered output voltage at an output of said converter.

23. The converter as recited in claim 19 wherein said power train comprises a first and second alternately-conducting power switch having a duty cycle (D) and (1-D), respectively, N₁ and N₂ being selected as a function of D and 1-D.

24. The converter as recited in claim 21 wherein said primary winding of said first transformer and said primary winding of said second transformer are connected to an inductor thereby enhancing zero voltage switching (ZVS) across at least one of said first and second power switches.

25. The converter as recited in claim 24 wherein said inductor comprises a winding thereby providing a regulated voltage in said converter.

26. The converter as recited in claim 24 wherein said inductor is connected to a diode.