Power converter

• US 20030090914A1
• Filed: 05/03/2002
• Published: 05/15/2003
• Est. Priority Date: 11/09/2001
• Status: Active Grant

• Current Assignee: Minebea Electronics Co Ltd (Minebea Mitsumi, Inc.)
• Original Assignee: Minebea Electronics Co Ltd (Minebea Mitsumi, Inc.)
• Inventors: Zhang, Xiaoyang, Jansen, Arian
• Granted Patent: US 6,671,189 B2
• Time in Patent Office: Days
• US Class Current: 363/21.12
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer
• 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

The invention is a power converter having a transformer with a primary side winding and a secondary side winding. Both the primary side and the secondary side have switches which are switched on and off alternately. When the primary master switch is switched on, the transformer charges. When the primary master switch is switched off, the intrinsic capacitance of the secondary slave switch discharges generating the zero voltage switching condition for the secondary slave switch. The secondary slave switch is switched on at a time determined in accordance with the waveform generated by the transformer. When the secondary slave switch is switched on, the transformer discharges and ultimately the charge from an output capacitor flows into the transformer as a backflow which charges the transformer. The secondary slave switch is switched off at a time determined in accordance with a current flowing through said secondary switch. The intrinsic capacitance of primary master switch discharges generating the zero voltage switching condition for primary master switch which is then switched on and the cycle repeats.

Claims

1. A power converter comprising:

a transformer having a primary side and a secondary side, said transformer generating a waveform;

a primary side switch;

a secondary side switch;

wherein switching of said secondary side switch is accomplished in accordance with the waveform of said transformer.

2. A power converter according to claim 1, further comprising a secondary control unit, said secondary control unit being configured to control switching of said secondary side switch.

3. A power converter according to claim 2, wherein said switching of said secondary side switch is performed during a zero voltage switching condition.

4. A power converter according to claim 3, wherein said secondary side switch further comprises an intrinsic output capacitance, and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

5. A power converter according to claim 1, further comprising a primary control unit, said primary control unit being configured to control switching of said primary side switch.

6. A power converter according to claim 5, wherein said switching of said primary side switch is performed during a zero voltage switching condition.

7. A power converter according to claim 6, wherein said primary side switch further comprises an intrinsic output capacitance, and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

8. A power converter according to Claim 1 further comprising a secondary sense winding located on said secondary side of said transformer and configured to detect said waveform of said transformer.

9. A power converter according to claim 1, further comprising a secondary current sense detecting a secondary current in said secondary side switch.

10. A power converter according to claim 9, wherein said secondary side switch is switched off in accordance with said secondary current in said secondary side switch.

11. A power converter according to claim 1, further comprising a primary current sense for detecting a primary current in said primary switch.

12. A power converter comprising

a transformer having a primary side and a secondary side, said transformer generating

a waveform;

a primary side switch;

a secondary side switch;

a master control unit controlling said primary side switch; and

a slave control unit controlling said secondary side switch, wherein said master control unit and said slave control unit operate independently and wherein said slave control unit follows said waveform of said transformer.

13. A power converter according to claim 12, wherein said secondary side switch is switched during a zero voltage switching condition.

14. A power converter according to claim 13, wherein said secondary side switch further comprises an intrinsic output capacitance, and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

15. A power converter according to claim 12, wherein said primary side switch is switched during a zero voltage switching condition.

16. A power converter according to claim 15, wherein said primary side switch further comprises an intrinsic output capacitance, and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

17. A power converter according to claim 12, further comprising a secondary sense winding located on said secondary side of said transformer and configured to detect said waveform of said transformer.

18. A power converter according to claim 12, further comprising a secondary current sense detecting a secondary current in said secondary side switch.

19. A power converter according to claim 18, wherein said secondary side switch is switched off in accordance with said secondary current in said secondary side switch.

20. A power converter according to claim 12, further comprising a primary current sense for detecting a primary current in said primary switch.

21. A power converter comprising:

an input terminal;

an output terminal;

a transformer having a primary side and a secondary side, said transformer further comprising a primary side winding connected to said input terminal and a secondary side winding connected to said output terminal;

a primary side switch;

a secondary side switch;

a slave control unit controlling switching of said secondary side switch; and

a master control unit controlling switching of said primary side switch, said primary side switch and said secondary side switch being configured to be switched on and off alternately;

wherein said switching of said secondary side switch is accomplished depending on a secondary current detected in said secondary side switch, and wherein said primary side switch and said secondary side switch are switched on during a zero voltage switching condition.

22. A power converter according to claim 21 further comprising a secondary current sense detecting said secondary current in said secondary side switch.

23. A power converter according to claim 22, wherein said slave control unit further comprises a comparator and a set/reset flip flop, wherein said secondary current sense conveys an output signal into said comparator when said secondary current becomes negative, wherein said comparator compares said output signal of said secondary current sense to a current reference level and outputs a switching signal to said set/reset flip flop when said output signal of said secondary current sense exceeds said current reference level, and wherein said set/reset flip flop switches said secondary side switch when said switching signal is received.

24. A power converter according to claim 23, wherein said current reference level is given by the following equation:

I_reverse=(Vin+Vo*N)*{square root}{square root over ( )}[(Cds₁+Cds₂/N²)/L_T1C]

wherein I_reverse is said current reference level, L_T1C is an inductance of said secondary side winding of said transformer, Cds1 is an intrinsic capacitance of said primary side switch, Cds2 is an intrinsic capacitance of said secondary side switch, Vin is an input voltage, Vo is an output voltage and N is a winding ratio between said primary and said secondary side windings.

25. A power converter according to claim 23 wherein said switching signal is a reset signal switching said secondary side switch off.

26. A power converter according to claim 21, further comprising a secondary waveform sensor detecting a waveform generated by said transformer, said secondary waveform sensor being a sense winding on said secondary side of the transformer.

27. A power converter according to claim 26 wherein said secondary side switch is switched on in accordance with said waveform of said transformer.

28. A power converter according to claim 21 further comprising an output capacitor.

29. A power converter according to claim 21, wherein said secondary side switch further comprises an intrinsic output capacitance and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

30. A power converter according to claim 21, wherein said primary side switch further comprises an intrinsic capacitance and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

31. A power converter according to claim 21 further comprising an output feedback circuitry connected between said output terminal and said master control unit, said output feed back circuitry generating an output feedback signal.

32. A power converter according to claim 31, wherein said master control unit further comprises an on-timer, a time-delay circuitry, a zero voltage detector and an error-amplifier, wherein said output feedback signal is fed into said error-amplifier, said error-amplifier producing an amplified error signal, and wherein said amplified error signal is fed into said on-timer, said on-timer controlling switching of said primary side switch.

33. A power converter according to claim 21 further comprising a primary current sense for detection of a primary current in said primary side switch.

34. A power converter comprising:

a transformer having a primary side and a secondary side;

a primary side switch;

a secondary side switch;

a slave control unit controlling switching of said secondary side switch; and

a master control unit controlling switching of said primary side switch;

wherein said switching of said secondary side switch is accomplished depending on a secondary current detected in said secondary side switch, and wherein said primary side switch and said secondary side switch are switched on during a zero voltage switching condition.

35. A power converter according to claim 34 further comprising a secondary current sense detecting said secondary current in said secondary side switch.

36. A power converter according to claim 35, wherein said slave control unit further comprises a comparator and a set/reset flip flop, wherein said secondary current sense conveys an output signal into said comparator when said secondary current becomes negative, wherein said comparator compares said output signal of said secondary current sense to a current reference level and outputs a switching signal to said set/reset flip flop when said output signal of said secondary current sense exceeds said current reference level, and wherein said set/reset flip flop switches said secondary side switch when said switching signal is received.

37. A power converter according to claim 36, wherein said current reference level is given by the following equation:

I_reverse=(Vin+Vo*N)*{square root}{square root over ([(Cds₁+Cds₂/N²)/L_T1C] )}

wherein I_reverse is said current reference level, L_T1C is an inductance of a secondary winding of said transformer, Cds1 is an intrinsic capacitance of said primary side switch, Cds2 is an intrinsic capacitance of said secondary side switch, Vin is an input voltage, Vo is an output voltage and N is a winding ratio between a primary side winding and said secondary side winding of said transformer.

38. A power converter according to claim 36 wherein said switching signal is a reset signal switching said secondary side switch off.

39. A power converter according to claim 34, further comprising a secondary waveform sensor detecting a waveform generated by said transformer, said secondary waveform sensor being a sense winding on said secondary side of the transformer.

40. A power converter according to claim 39 wherein said secondary side switch is switched on in accordance with said waveform of said transformer.

41. A power converter according to claim 39, wherein said slave control unit is configured to switch said secondary side switch on within a predetermined time delay after said slave unit detects a zero level of said waveform.

42. A power converter according to claim 34 further comprising an output capacitor.

43. A power converter according to claim 34, wherein said secondary side switch further comprises an intrinsic output capacitance and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

44. A power converter according to claim 34, wherein said primary side switch further comprises an intrinsic capacitance and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

45. A power converter according to claim 34, further comprising an output terminal and an output feedback circuitry connected between said output terminal and said master control unit, said output feedback circuitry generating an output feedback signal.

46. A power converter according to claim 45, wherein said master control unit further comprises an on-timer, a time-delay circuitry, a zero voltage detector and an error-amplifier, wherein said output feedback signal is fed into said error-amplifier, said error-amplifier producing an amplified error signal, and wherein said amplified error signal is fed into said on-timer, said on-timer controlling switching of said primary side switch.

47. A power converter according to claim 34 further comprising a primary current sense for detection of a primary current in said primary side switch.

48. A variable frequency flyback converter, comprising:

a transformer having a primary side and a secondary side;

a primary side switch; and

a secondary side switch;

wherein said primary side switch and said secondary side switch are configured to be switched at a full zero voltage switching condition and wherein said secondary side switch is configured to act as a synchronous rectifier.

49. A power converter according to claim 48, wherein said secondary side switch further comprises an intrinsic output capacitance and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

50. A power converter according to claim 48, wherein said primary side switch further comprises an intrinsic capacitance and wherein said zero voltage switching condition is generated when said intrinsic output capacitance is discharged.

51. A method of power conversion comprising the steps of:

providing a transformer having a primary side comprising a primary side switch and a secondary side comprising a secondary side switch;

zero voltage switching of said primary side switch;

zero voltage switching of said secondary side switch; and

controlling said switching of said secondary side switch by switching said secondary side switch in accordance with a waveform generated by said transformer.

52. A method of power conversion according to claim 51, further comprising a step of switching said secondary side switch off in accordance with a back flow current flowing through said secondary side switch.

53. A method of power conversion according to claim 52, further comprising the step of detecting said back flow current by a secondary current sense.

54. A method of power conversion according to claim 51, further comprising the step of detecting said waveform of said transformer by a secondary sense winding.

55. A method of power conversion according to claim 51 further comprising the step of regulating output power by varying a duty cycle of said primary side switch.

56. A method of power conversion comprising the steps of:

providing a transformer having a primary side comprising a primary side switch and a secondary side comprising a secondary side switch;

zero voltage switching of said primary side switch;

controlling said zero voltage switching of said primary side switch with a primary control unit;

zero voltage switching of said secondary side switch; and

controlling said zero voltage switching of said secondary side switch with a secondary control unit independently from said primary control unit.