Apparatus, System and Method for Cascaded Power Conversion

• US 20100026208A1
• Filed: 07/29/2008
• Published: 02/04/2010
• Est. Priority Date: 07/29/2008
• Status: Active Grant

• Current Assignee: Chemtron Research LLC (Intellectual Ventures LLC)
• Original Assignee: Exclara, Inc. (Million Star Technology Ltd.)
• Inventors: Rodriguez, Harry, Shteynberg, Anatoly, Lehman, Bradley M.
• Granted Patent: US 8,344,638 B2
• Time in Patent Office: Days
• US Class Current: 315/297
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• 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 45/385 using flyback topology
• CPC Class Codes: H05B 47/165 following a pre-assigned programmed sequence; Logic control [LC]

Abstract

An apparatus, method and system are provided for power conversion to supply power to a load such as a plurality of light emitting diodes. An exemplary apparatus comprises: a first power converter stage having a first power switch and a first inductive element; a second power converter stage having a second power switch and a second inductive element; a plurality of sensors; and a controller. The second power converter stage provides an output current to the load. The controller is adapted to use a sensed input voltage to determine a switching period, and is further adapted to turn the first and second power switches into an on-state at a frequency substantially corresponding to the switching period while maintaining a switching duty cycle within a predetermined range.

Claims

1. An apparatus for power conversion, the apparatus couplable to a load, the apparatus comprising:

a first power converter stage comprising a first power switch and a first inductive element;

a second power converter stage coupled to the first power converter stage, the second power converter stage comprising a second power switch and a second inductive element, the second power converter stage couplable to provide an output current to the load;

a first sensor adapted to sense a first parameter; and

a controller coupled to the first power switch, the second power switch, and the first sensor, the controller adapted to determine a switching period, the controller adapted to turn the first and second power switches into an on-state at a frequency substantially corresponding to the switching period while maintaining a switching duty cycle within a predetermined range.

2. The apparatus of claim 1, wherein the controller is adapted to determine the switching period as a switching interval which maintains voltage stress of the first power switch and the second power switch below corresponding predetermined levels.

3. The apparatus of claim 1, wherein the controller is adapted to maintain the switching duty cycle within the predetermined range to maintain voltage stress of the first power switch and the second power switch below corresponding predetermined levels.

4. The apparatus of claim 1, wherein the controller is further adapted to turn the first and second power switches into the on-state and into an off-state substantially concurrently.

5. The apparatus of claim 1, wherein the switching duty cycle is substantially constant.

6. The apparatus of claim 1, wherein the first sensor is coupled to the second power converter stage and wherein the first parameter is a current level corresponding to the output current or a second inductive element current.

7. The apparatus of claim 6, wherein the first power converter stage is couplable to receive an input voltage, and wherein the apparatus further comprises:

a second sensor coupled to the first power converter stage, the second sensor adapted to sense an input voltage level.

8. The apparatus of claim 7, wherein the controller is further adapted to turn the first and second power switches into the on-state and into an off-state with a switching period determined in response to the first parameter.

9. The apparatus of claim 7, wherein the controller is further adapted to turn the first and second power switches into an off-state when the first parameter has increased to a first threshold.

10. The apparatus of claim 9, wherein the controller is further adapted to determine the first threshold as substantially related to a predetermined reference current level, a predetermined current variance level, a minimum input voltage level, and a sensed input voltage level.

11. The apparatus of claim 9, wherein the controller is further adapted to determine the first threshold (I_MAX) as substantially proportional to a predetermined reference current level (I_REF) plus an offset term comprising a predetermined current variance level (Δ

I_L2) multiplied by the square of a minimum RMS input voltage (V²<sub>LOW—

RMS</sub>) and divided by twice the square of an RMS value of the sensed input voltage (2*V²_{IN RMS}) (I_MAX∝

I_REF+(Δ

I_L2*V²_{LOW RMS}/2*V²_{IN RMS})).

12. The apparatus of claim 9, wherein the controller is further adapted to turn the first and second power switches into an on-state when the first parameter has decreased to a second threshold.

13. The apparatus of claim 12, wherein the controller is further adapted to determine the second threshold as substantially related to a predetermined reference current level, a predetermined current variance level, a minimum input voltage level, and a sensed input voltage level.

14. The apparatus of claim 12, wherein the controller is further adapted to determine the second threshold (I_MIN) as substantially proportional to a predetermined reference current level (I_REF) minus an offset term comprising a predetermined current variance level (Δ

I_L2) multiplied by the square of a minimum RMS input voltage (V²<sub>LOW—

RMS</sub>) and divided by twice the square of an RMS value of the sensed input voltage (2*V²<sub>IN—

RMS</sub>) (I_MIN ∝

_REF−

(Δ

I_L2*V²<sub>LOW—

RMS</sub>/2*V²<sub>IN—

RMS</sub>)).

15. The apparatus of claim 12, further comprising:

a memory storing a look up table, the look up table comprising a plurality of first and second thresholds corresponding to a plurality of input voltage levels.

16. The apparatus of claim 15, wherein the controller is further adapted to determine the first threshold and the second threshold by accessing the look up table using the sensed input voltage

17. The apparatus of claim 7, wherein the switching period corresponds to a first threshold and to a second threshold, and wherein the controller is further adapted to turn the first and second power switches into an off-state when the first parameter has increased to the first threshold and into the on-state when the first parameter has decreased to the second threshold.

18. The apparatus of claim 7, wherein the controller is further adapted to determine the switching period in response to the sensed input voltage level.

19. The apparatus of claim 18, further comprising:

a memory storing a look up table, the look up table comprising a plurality of switching period values corresponding to a plurality of input voltage levels.

20. The apparatus of claim 18, wherein the controller is further adapted to determine the switching period by accessing the look up table using the sensed input voltage.

21. The apparatus of claim 7, wherein the controller is further adapted to determine the switching period based on a maximum switching period, a minimum input voltage, and the sensed input voltage.

22. The apparatus of claim 7, wherein the controller is further adapted to determine the switching period T as substantially proportional to a maximum switching period multiplied by the square of a minimum RMS input voltage and divided by the square of an RMS value of the sensed input voltage (T ∝

T_MAX*V²<sub>LOW—

RMS</sub>/V²<sub>IN—

RMS</sub>).

23. The apparatus of claim 7, wherein the controller is further adapted to determine the switching period T as substantially proportional to a minimum switching period multiplied by the square of a maximum RMS input voltage and divided by the square of an RMS value of the sensed input voltage (T ∝

T_MAX*V²<sub>HIGH—

RMS</sub>/V²<sub>IN—

RMS</sub>).

24. The apparatus of claim 7, wherein the controller is further adapted to determine the switching period T as substantially proportional to a selected switching period (T₁) multiplied by the square of a selected RMS input voltage (V_1—

_RMS) and divided by the square of an RMS value of the sensed input voltage (T ∝

T₁*V²<sub>1—

RMS</sub>/V²<sub>IN—

RMS</sub>).

25. The apparatus of claim 6, wherein the controller is further adapted to decrease the duty cycle when the output current is above a first predetermined level.

26. The apparatus of claim 6, wherein the controller is further adapted to increase the duty cycle when the output current is below a second predetermined level.

27. The apparatus of claim 1, further comprising:

a memory storing a predetermined parameter, wherein the predetermined parameter comprises at least one of the following parameters;

a minimum switching period, a maximum switching period, a maximum duty ratio, a minimum duty ratio, a desired output current level, a desired inductor current level, a maximum input voltage, a minimum input voltage, a minimum RMS input voltage, a desired inductor ripple current, a desired output ripple current, and a maximum voltage stress level.

28. The apparatus of claim 1, wherein the first power converter stage comprises a flyback configuration, or a buck configuration, or a double-buck configuration.

29. The apparatus of claim 1, wherein the second power converter stage comprises a buck configuration, or a boost configuration, or a buck-boost configuration.

30. The apparatus of claim 1, wherein the first inductive element comprises a transformer and the second inductive element comprises an inductor.

31. The apparatus of claim 1, wherein the first inductive element comprises at least one first inductor and the second inductive element comprises a second inductor.

32. The apparatus of claim 1, wherein the first sensor and second sensors are referenced to a common reference.

33. The apparatus of claim 32, wherein the common reference is a ground potential.

34. The apparatus of claim 1, wherein the load comprises at least one light emitting diode.

35. The apparatus of claim 1, wherein the controller is further adapted to operate the first power converter stage in a discontinuous conduction mode and to operate the second power converter stage in a continuous conduction mode.

36. The apparatus of claim 1, wherein the first power converter stage is couplable to receive an input voltage having a predetermined range of voltages.

37. The apparatus of claim 36, wherein the predetermined range of voltages is substantially from to 90 V RMS to 264 V RMS.

38. The apparatus of claim 36, wherein the first power converter stage further comprises a rectifier couplable to receive an AC input voltage

39. The apparatus of claim 1, wherein the first power converter stage further comprises a diode, and wherein the controller is adapted to determine the switching period as a switching interval which maintains voltage stress of the diode below a predetermined level or is adapted to maintain the switching duty cycle within the predetermined range to maintain voltage stress of the diode below the predetermined level.

40. The apparatus of claim 1, wherein the first power converter stage is couplable to receive an input voltage, wherein the first sensor is coupled to the first power converter stage, and wherein the first sensor is adapted to sense an input voltage level.

41. A method of providing power conversion for a load using a power converter comprising a first power converter stage coupled to a second power converter stage, the first power converter stage comprising a first inductive element and a first power switch and the second power converter stage comprising a second inductive element and a second power switch, the method comprising:

sensing a first parameter comprising an input voltage;

sensing a second parameter, the second parameter comprising an output current or a second inductive element current;

using the sensed input voltage, determining a switching period;

turning the first and second power switches into an on-state substantially concurrently and at a frequency substantially corresponding to the switching period; and

turning the first and second power switches into an off-state substantially concurrently while maintaining a switching duty cycle within a predetermined range.

42. The method of claim 41, wherein the switching duty cycle is substantially constant.

43. The method of claim 41, wherein the switching period corresponds to a first threshold and to a second threshold, wherein the step of turning the first and second power switches into the off-state further comprises turning the first and second power switches into the off-state when the first parameter has increased to the first threshold;

and wherein the step of turning the first and second power switches into the on-state further comprises turning the first and second power switches into the on-state when the first parameter has decreased to the second threshold.

44. The method of claim 41, further comprising:

using a predetermined reference current level, a predetermined current variance level, a minimum input voltage level, and the sensed input voltage level, determining the first threshold and the second threshold.

45. The method of claim 41, further comprising:

using the sensed input voltage level, accessing a memory to determine the first threshold and the second threshold.

46. The method of claim 41, further comprising:

using a sensed input voltage level, accessing a memory to determine the switching period.

47. The method of claim 41, further comprising:

using a maximum switching period, a minimum input voltage, and the sensed input voltage, determining the switching period.

48. The method of claim 41, further comprising:

decreasing the duty cycle when the output current is above a first predetermined level; and

increasing the duty cycle when the output current is below a second predetermined level.

49. The method of claim 41, further comprising:

operating the first power converter stage in a discontinuous conduction mode; and

operating the second power converter stage in a continuous conduction mode.

50. The method of claim 41, further comprising:

receiving an input voltage having a predetermined range of voltages.

51. A system for power conversion, the system couplable to receive an input voltage, the system comprising:

a plurality of light emitting diodes;

a first power converter stage having a flyback configuration and comprising a first power switch and a transformer;

a first sensor coupled to the first power converter stage, the first sensor adapted to sense an input voltage level of the first power converter stage;

a second power converter stage having a buck configuration and coupled to the first power converter stage, the second power converter stage comprising a second power switch and an inductor, the second power converter stage coupled to the plurality of light emitting diodes to provide an output current to the plurality of light emitting diodes;

a second sensor coupled to the second power converter stage, the second sensor comprising a sense transformer and adapted to sense an output current level or a second inductive element current level; and

a controller coupled to the first power switch, the second power switch, the first sensor and the second sensor, the controller adapted to use the sensed input voltage to determine a switching period, the controller adapted to turn the first and second power switches into an on-state at a frequency substantially corresponding to the switching period while maintaining a switching duty cycle within a predetermined range.

52. An apparatus for power conversion, the apparatus couplable to a plurality of light emitting diodes and couplable to receive an input voltage, the apparatus comprising:

a first power converter stage comprising;

a first power switch;

a first diode;

a flyback transformer having a primary coupled to the first power switch and to the input voltage and having a secondary coupled to the first diode;

a first capacitor coupled to the first transformer secondary and to the first diode; and

a first sensor adapted to determine an input voltage level;

a second power converter stage coupled to the first power converter stage, the second power converter stage couplable to provide an output current to the plurality of light emitting diodes, the second power converter stage comprising;

an inductor coupled to the first diode and couplable to the plurality of light emitting diodes;

a second power switch coupled to the secondary of the first transformer;

an isolation transformer coupled to a gate of the second power switch;

a second diode coupled to the second inductor;

a second capacitor coupled to the inductor and couplable to the plurality of light emitting diodes; and

a sense transformer coupled to the second power switch; and

a controller coupled to the first power switch, the first sensor, the isolation transformer and the sense transformer, the controller adapted to use the sensed input voltage to determine a switching period, and the controller adapted to turn the first and second power switches into an on-state at a frequency substantially corresponding to the switching period while maintaining a switching duty cycle within a predetermined range.