PRIMARY-SIDE BASED CONTROL OF SECONDARY-SIDE CURRENT FOR A TRANSFORMER

• US 20100244726A1
• Filed: 03/31/2009
• Published: 09/30/2010
• 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.
• Granted Patent: US 8,288,954 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• 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 the controller is configured to 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 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 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.

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 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 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 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.

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; and

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.

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.