Single stage AC/DC converter high frequency AC distribution systems

• US 6,288,919 B1
• Filed: 12/16/1999
• Issued: 09/11/2001
• Est. Priority Date: 12/16/1999
• Status: Expired due to Term

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: Chippower.Com, Inc.
• Inventors: Jain, Praveen Kumar
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US09/464,950
• Time in Patent Office: 635 Days
• Field of Search: 363/89, 363/127
• US Class Current: 363/89
• CPC Class Codes: H02M 7/1557 with automatic control of the output voltage or current
• CPC Class Codes: H02M 7/217 using semiconductor devices only
• 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 AC/DC converter for outputting high current, low voltage output from a high frequency AC source is described. The AC/DC converter includes two resonant components, a resonant circuit having a capacitor and an inductor. Both of the resonant components are connected in series and form a series resonant circuit. The converter further includes a transformer having a primary winding with a center tap to a secondary winding. The resonant circuit and the primary winding are connected in series. The center tap is connected to an output filter and a load, while the other two ends of the secondary winding are connected to two controlled switches, respectively. A drain of each of the two controlled switches is connected to opposite ends of the secondary winding, while each of the sources of the two controlled switches are interconnected. Two anti-parallel diodes are respectively connected across the two controlled switches. Two capacitors are also respectively connected across the two controlled switches. The on-time of the controlled switches is regulated to control the output voltage of the converter. The advantage is an inexpensive converter adapted to output high currents at low voltages with very little ripple and very low slew rate.

Claims

1. An AC/DC converter, comprising:

a) resonant components connected in series to form a series resonant circuit;

b) a transformer having a primary winding with a first predetermined number of turns and a center tap to a secondary winding with a second predetermined number of turns, the resonant circuit and the primary winding of the transformer being connected in series, and the center tap of the secondary winding being connected to an output filter and a load;

c) two controlled switches regulated to control output voltage of the AC/DC converter, the two controlled switches being, respectively connected to two ends of the secondary winding, a drain of each of the two controlled switches being respectively connected to opposite ends of the secondary winding, and respective sources of the two controlled switches being interconnected; and

d) means respectively connected across the two controlled switches for providing a current path around the two controlled switches.

2. An AC/DC converter as claimed in claim 1 wherein the means connected across the two controlled switches comprises an anti-parallel diode and a capacitor respectively connected across each of the two controlled switches.

3. An AC/DC converter as claimed in claim 2 wherein the turns ratio of the transformer at the center tap is such that the two anti-parallel diodes are always reversed biased for any given output voltage.

4. An AC/DC converter as claimed in claim 3 wherein gating pulses of the two controlled switches are synchronized with a high frequency AC source voltage so that leading edges of the gating pulses are synchronized with a zero crossing of the source voltage.

5. An AC/DC converter as claimed in claim 2 wherein the turns ratio of the transformer at the center tap is such that the two anti-parallel diodes are always forward biased whenever a primary voltage is either positive or negative.

6. An AC/DC converter as claimed in claim 5 wherein gating pulses of the two controlled switches are synchronized with a high frequency AC source voltage so that the leading edge of the pulse is delayed by a given time duration from a zero crossing of the source voltage.

7. An AC/DC converter as claimed in claim 2 wherein the anti-parallel diodes connected across the controlled switches are integral parts of the controlled switches.

8. An AC/DC converter as claimed in claim 2 wherein the capacitors connected across the controlled switches are integral parts of the controlled switches.

9. An AC/DC converter as claimed in claim 1 wherein each controlled switch comprises several controlled switches connected in parallel.

10. An AC/DC converter as claimed in claim 1 wherein the output filter is a capacitor.

11. An AC/DC converter as claimed in claim 1 wherein the output filter capacitor is connected across the center tap of the transformer and the sources of the two controlled switches.

12. An AC/DC converter as claimed in claim 1 wherein depending on a turns-ratio of the transformer at the center tap, there are two distinct modes of operation for the AC/DC converter.

13. An AC/DC converter as claimed in claim 1 wherein the series resonant circuit comprises two resonant components and a first of the resonant components comprises an inductor.

14. An AC/DC converter as claimed in claim 13 wherein a second resonant component comprises a capacitor connected in series with the inductor.

15. An Ac/DC converter as claimed in claim 13 wherein the inductor is an integral part of the output transformer.

16. An AC/DC converter as claimed in claim 1 wherein a leakage inductor of the transformer is an integral part of the resonant circuit.

17. An AC/DC converter as claimed in claim 1 wherein the two controlled switches are reversed and a diode is added in series with each controlled switch to block conduction of body diodes of the controlled switches.

18. An AC/DC converter as claimed in claim 1 wherein the two controlled switches are reversed and another controlled switch is added in series with each of the two controlled switches to block conduction of body diodes of the respective two controlled switches.

19. An AC/DC converter as claimed in claim 1 wherein a source of each of the two controlled switches is connected to a source of an additional switch, and a drain of the additional switch is connected to a negative pole of a capacitor in the output filter, and two additional diodes respectively connect gate signals to the gate and source of the additional switch.

20. An AC/DC converter as claimed in claim 1 wherein the controlled switches do not include integral anti-parallel body diodes.

21. An AC/DC converter as claimed in claim 20 wherein the controlled switches include integral capacitors.

22. An AC/DC converter as claimed in claim 1 wherein a second stage inductance/capacitance filter at the output reduces ripple in an output voltage.

23. An AC/DC converter as claimed in claim 1 wherein the controlled switches are the MOSFETs.

24. An AC/DC converter as claimed in claim 1 wherein the controlled switches are the CHFETs.

25. An AC/DC converter as claimed in claim 1 wherein the AC input voltage is a sinusoidal waveform.

26. An AC/DC converter as claimed in claim 1 wherein the AC input voltage is a trapezoidal waveform.

27. An AC/DC converter as claimed in claim 1 wherein the AC input voltage is a square waveform.

28. An AC/DC converter as claimed in claim 1 wherein the AC input voltage is a quasi-square waveform.

29. An AC/DC converter as claimed in claim 1 wherein the AC input voltage is a unidirectional voltage waveform.

30. A method of converting high frequency alternating current (AC) to high amperage, low voltage direct current (DC), comprising the steps of:

a) supplying high frequency AC input voltage to a resonance circuit having a resonance frequency approximate the frequency of the input voltage, the resonance circuit being connected to a transformer having a primary winding with a first number of turns and a center tap to a secondary winding with a second, fewer number of turns;

b) rectifying a current output by the transformer by controlling at least two switches having respective drains connected to opposite ends of the secondary winding and interconnected sources, and means connected across the switches to provide a current path around the switches;

c) regulating an output voltage of the AC/DC converter by controlling an on-time of the at least two switches; and

d) filtering the output current using an output filter connected across the center tap of the transformer and the sources of the at least two switches to provide an output voltage with a small current ripple.

31. A method as claimed in claim 30 wherein the means connected across the switches to provide a current path around the switches comprises an anti-parallel diode and a capacitor connected across each of the at least two switches.

32. A method as claimed in claim 31 wherein the number of second turns in the secondary winding is such that the anti-parallel diodes are always back biased, and the output voltage of the converter is controlled by controlling an on-time of the at least two switches.

33. A method as claimed in claim 32 wherein gating pulses of the at least two switches are synchronized with a high frequency AC source voltage so that leading edges of the gating pulses are synchronized with a zero crossing of the source voltage.

34. A method as claimed in claim 31 wherein the number of second turns in the secondary winding is such that the anti-parallel diodes are always forward biased, and the output voltage of the converter is controlled by controlling conduction through the at least two switches and the anti-parallel diodes.

35. A method as claimed in claim 31 wherein the output voltage V_o of the converter is characterized by:

36. A method as claimed in claim 31 wherein the resonance circuit comprises a series connected inductance and a capacitor to form a series resonant circuit.

37. A method as claimed in claim 30 wherein the output filter comprises a capacitor connected across the center tap of the transformer and the sources of the at least two switches.

38. A method as claimed in claim 30 wherein the at least two switches are the MOSFETs.

39. A method as claimed in claim 30 wherein the at least two switches are the CHFETs.

40. A method as claimed in claim 30 wherein the AC input voltage is a sinusoidal waveform.

41. A method as claimed in claim 30 wherein the AC input voltage is a trapezoidal waveform.

42. A method as claimed in claim 30 wherein the AC input voltage is a square waveform.

43. A method as claimed in claim 30 wherein the AC input voltage is a quasi-square waveform.

44. A method as claimed in claim 30 wherein the AC input voltage is a unidirectional voltage waveform.

45. A method as claimed in claim 30 wherein gating pulses of the two controlled switches are synchronized with a high frequency AC source voltage so that the leading edge of the pulse is delayed by a given time duration from a zero crossing of the source voltage.