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

• US 8,581,505 B2
• Filed: 09/05/2012
• Issued: 11/12/2013
• 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 K
• Application Number:
  US13/604,434
• Publication Number:
  US 20120327690A1
• Time in Patent Office: 433 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 (i) 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 (ii) to generate one or more duty cycle modulated switch control signals to control a voltage on a 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 (iii) to compensate for imbalances in a primary-side interface of the transformer.

2. The apparatus of claim 1 wherein the controller is further configured to:

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

3. The apparatus of claim 1 wherein the controller is configured to generate the one or more duty cycle modulated 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.

4. The apparatus of claim 3 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.

5. The apparatus of claim 3 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 switch control signals.

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

7. The apparatus of claim 6 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.

8. The apparatus of claim 1 further comprising:

the transformer, coupled to the controller; and

a load coupled to the transformer.

9. The apparatus of claim 1 wherein the load comprises one or more light emitting diodes.

10. A method comprising:

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

generating 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

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

11. The method of claim 10 further comprising:

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

12. The method of claim 10 wherein generating control signals comprises generating 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.

13. The method of claim 10 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.

14. The method of claim 10 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.

15. The method of claim 10 wherein the controller is configured to generate switch control signals to control a push-pull circuit of the primary-side interface of the transformer.

16. The method of claim 15 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.

17. The method of claim 10 further comprising:

receiving the load current by a load.

18. The method of claim 17 wherein the load comprises one or more light emitting diodes.

19. An apparatus comprising:

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

means for generating 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

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

20. An apparatus comprising:

means for 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 the means for regulating the output current comprises;

means for 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

means for 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.