Primary-side based control of secondary-side current for a transformer

• US 8,288,954 B2
• Filed: 03/31/2009
• Issued: 10/16/2012
• Est. Priority Date: 12/07/2008
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): HAMMOND, DEDEI KHALIEAH
• Application Number:
  US12/415,830
• Publication Number:
  US 20100244726A1
• Time in Patent Office: 1,295 Days
• Field of Search: None
• US Class Current: 315/219
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges

Abstract

A power control system includes a transformer and a controller regulates a current on a secondary-side of the transformer based on a primary-side signal value. In at least one embodiment, the secondary-side current is a current out of a filter coupled to a rectifier and the secondary-side of the transformer and into a load. In at least one embodiment, the primary-side signal value is a sample of a current in the primary-side windings of the transformer. In at least one embodiment, the primary-side signal value represents a sample value of a primary-side transformer current. Proper timing of sampling the primary-side signal value substantially eliminates contributions of a transformer magnetizing current from the primary-side transformer current sample. Sampling the primary-side signal value when contributions of the transformer magnetizing current are substantially eliminated allows at least an average of the secondary-side current to be determined from the primary-side signal value.

Claims

1. An apparatus comprising:

a controller to regulate a load current to a load coupled to a secondary-side of a transformer to an approximately average value based on an observed primary-side signal value, wherein (i) the controller is configured to (a) generate one or more duty cycle modulated switch control signals to control a voltage on a primary-side of the transformer based on the primary-side signal value and (b) compensate for imbalances in a primary-side interface of the transformer and (ii) the load current represents a current into the load and out of a filter coupled to a rectifier coupled to the secondary-side of the transformer.

2. The apparatus of claim 1 wherein the load comprises a light emitting diode.

3. The apparatus of claim 1 wherein the primary-side signal value represents a current in the primary-side of the transformer.

4. The apparatus of claim 3 wherein the primary-side signal value is a voltage signal.

5. The apparatus of claim 1 wherein the controller is configured to generate the one or more switch control signals based on a value of the primary-side signal value occurring at a sampling time during a period of at least one of the switch control signals.

6. The apparatus of claim 5 wherein the primary-side signal value represents a current in the primary-side of the transformer and the sampling time is when an average value of the current in the primary-side is reached.

7. The apparatus of claim 5 wherein the primary-side signal value represents a current in the primary-side of the transformer and the sampling time corresponds to a midpoint during a pulse of at least one of the one or more switch control signals.

8. The apparatus of claim 5 wherein the sampling time occurs when a magnetizing current of the transformer is approximately zero.

9. The apparatus of claim 1 wherein the one or more switch control signals control a plurality of switches coupled to one or more windings of the primary side of the transformer, wherein the one or more windings and the switches are configured in a push-pull configuration and the controller is configured to generate a plurality of the one or more switch control signals to control conductivity of the switches.

10. The apparatus of claim 1 wherein the one or more switch control signals control a plurality of switches coupled to one or more windings of the primary side of the transformer, wherein the one or more windings and the switch are configured in a half-bridge configuration and the controller is configured to generate the one or more switch control signals to control conductivity of the switches.

11. The apparatus of claim 1 wherein the controller is configured to determine at least one of the one or more switch control signals independently of a value of an input voltage at the primary-side and independently of inductance values on the primary and secondary sides of the transformer.

12. The apparatus of claim 1 wherein the controller is further configured to control power factor correction of a switching power converter.

13. The apparatus of claim 1 wherein the controller is further configured to receive lighting data and the approximately average value of the current on the secondary-side of the isolation transformer is determined by the lighting data.

14. The apparatus of claim 13 wherein the lighting data is received from a dimmer.

15. The apparatus of claim 1 wherein the controller is further configured to generate multiple sets of one or more switch control signals to drive primary-sides of a plurality of transformers, wherein, for each of the transformers, the controller is configured to regulate an output current on a secondary-side of the transformer to an approximately average value based on a primary-side signal value, wherein the controller is configured to generate one or more switch control signals to control a voltage on a primary-side of the transformer based on the primary-side signal value.

36. The apparatus of claim 1 wherein the controller is further configured to generate switch control signals to control a push-pull circuit of the primary-side interface of the transformer.

37. The apparatus of claim 36 wherein the controller is configured to compensate for imbalances in a primary-side interface of the transformer by decreasing or increasing a duty cycle of a first of the switch control signals relative to a duty cycle of a second of the switch control signals.

16. A method comprising:

regulating a load current to a load coupled to a secondary-side of a transformer to an approximately average value based on an observed primary-side signal value, wherein regulating the output current comprises (i) generating one or more duty cycle modulated switch control signals to control a voltage on a primary-side of the transformer based on the primary-side signal value and (b) compensating for imbalances in a primary-side interface of the transformer and the load current represents a current into the load and out of a filter coupled to a rectifier coupled to the secondary-side of the transformer.

17. The method of claim 16 wherein the load comprises a light emitting diode.

18. The method of claim 16 wherein the primary-side signal value represents a current in the primary-side of the transformer.

19. The method of claim 18 primary-side signal value is a voltage signal.

20. The method of claim 16 further comprising:

sampling the primary-side signal value at a sampling time during a period of at least one of the switch control signals.

21. The method of claim 20 wherein the primary-side signal value represents a current in the primary-side of the transformer and the sampling time is when an average value of the current in the primary-side is reached.

22. The method of claim 20 wherein the primary-side signal value represents a current in the primary-side of the transformer and the sampling time corresponds to a midpoint during a pulse of at least one of the one or more switch control signals.

23. The method of claim 20 wherein the sampling time occurs when a magnetizing current of the transformer is approximately zero.

24. The method of claim 16 wherein the one or more switch control signals control a plurality of switches coupled to one or more windings of the primary side of the transformer, wherein the one or more windings and the switches are configured in a push-pull configuration and the method further comprises:

generating a plurality of the one or more switch control signals to control conductivity of the switches.

25. The method of claim 16 wherein the one or more switch control signals control a plurality of switches coupled to one or more windings of the primary side of the transformer, wherein the one or more windings and the switch are configured in a half-bridge configuration and the method further comprises:

generating the one or more switch control signals to control conductivity of the switches.

26. The method of claim 16 further comprising:

determining at least one of the one or more switch control signals independently of a value of an input voltage at the primary-side and independently of inductance values on the primary and secondary sides of the transformer.

27. The method of claim 16 further comprising:

controlling power factor correction of a switching power converter.

28. The method of claim 16 further comprising:

receiving lighting data; and

determining the approximately average value of the current on the secondary-side of the isolation transformer using the lighting data.

29. The apparatus of claim 28 wherein the lighting data is received from a dimmer.

30. The method of claim 16 further comprising:

generating multiple sets of one or more switch control signals to drive primary-sides of a plurality of transformers; and

for each of the transformers, regulating an output current on a secondary-side of the transformer to an approximately average value based on a primary-side signal value, wherein regulating the output current comprises generating one or more switch control signals to control a voltage on a primary-side of the transformer based on the primary-side signal value.

38. The method of claim 16 the method further comprising:

generating switch control signals to control a push-pull circuit of the primary-side interface of the transformer.

39. The apparatus of claim 38 wherein generating the switch control signals further comprises:

decreasing or increasing a duty cycle of a first of the switch control signals relative to a duty cycle of a second of the switch control signals.

31. An electronic system comprising:

a controller, wherein the controller is configured to;

receive a feedback signal from a primary-side of a transformer, wherein the feedback signal represents a current in the primary-side of the transformer;

generate control signals for circuitry coupled to the primary-side of the transformer to regulate a load current on a secondary-side of the transformer to an approximately average value based on the feedback signal from the primary-side of the transformer without using a feedback signal from a secondary-side of the transformer and

compensate for imbalances in a primary-side interface of the transformer.

32. The electronic system of claim 31 wherein the controller is further configured to:

process the feedback signal to eliminate influence of a magnetizing current of the transformer.

33. The electronic system of claim 31 wherein the controller is configured to generate the one or more switch control signals based on a value of the primary-side signal value occurring at a sampling time during a period of at least one of the switch control signals.

34. The electronic system of claim 33 wherein the primary-side signal value represents a current in the primary-side of the transformer and the sampling time is when an average value of the current in the primary-side is reached.

35. The electronic system of claim 33 wherein the primary-side signal value represents a current in the primary-side of the transformer and the sampling time corresponds to a midpoint during a pulse of at least one of the one or more control signals.

40. The electronic system of claim 31 wherein the controller is further configured to generate switch control signals to control a push-pull circuit of the primary-side interface of the transformer.

41. The apparatus of claim 40 wherein the controller is configured to compensate for imbalances in a primary-side interface of the transformer by decreasing or increasing a duty cycle of a first of the switch control signals relative to a duty cycle of a second of the switch control signals.