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