Methods and apparatus for simulating resistive loads
View Patent ↗Methods and apparatus for simulating resistive loads, and facilitating series, parallel, and/or series-parallel connections of multiple loads to draw operating power. Current-to-voltage characteristics of loads are altered in a predetermined manner so as to facilitate a predictable and/or desirable behavior of multiple loads drawing power from a power source. Exemplary loads include LED-based light sources and LED-based lighting units. Altered current-to-voltage characteristics may cause a load to appear as a substantially linear or resistive element to the power source, at least over some operating range. In connections of multiple such loads, the voltage across each load is relatively more predictable. In one example, a series connection of multiple loads with altered current-to-voltage characteristics may be operated from a line voltage without requiring a transformer.
1. An apparatus, comprising:
at least one load having a nonlinear or variable current-to-voltage characteristic; and
a converter circuit coupled to the at least one load and configured such that the apparatus has a substantially linear current-to-voltage characteristic over at least some range of operation,
wherein a first current conducted by the apparatus when the apparatus draws power from a power source is independent of a second current conducted by the load; and
wherein the apparatus has a terminal voltage V T and conducts a terminal current I T when the apparatus draws power from a power source, and wherein the converter circuit is configured such that the apparatus has an effective resistance of between approximately 0.1 (V T /I T ) to 10.0(V T /I T ) at least at a nominal operating point V T =V nom in the at least some range of operation.
2. The apparatus of claim 1 , wherein the nominal operating point is approximately 5 Volts.
3. The apparatus of claim 2 , wherein the at least some range of operation includes terminal voltages in a range of from approximately 4.5 Volts to 9 Volts.
4. The apparatus of claim 1 , wherein the nominal operating point is approximately 24 Volts.
5. The apparatus of claim 4 , wherein the at least some range of operation includes terminal voltages in a range of from approximately 21 Volts to 30 Volts.
6. The apparatus of claim 1 , wherein the converter circuit comprises a variable current source.
7. The apparatus of claim 6 , wherein the variable current source includes at least one operational amplifier.
8. The apparatus of claim 6 , wherein the variable current source includes at least one current mirror.
9. The apparatus of claim 6 , wherein the converter circuit further comprises a voltage regulator to provide an operating voltage for the at least one load.
10. The apparatus of claim 9 , wherein the voltage regulator comprises a zener diode.
11. The apparatus of claim 6 , wherein the converter circuit further comprises at least one of a fixed current source and a fixed voltage source coupled to the variable current source.
12. The apparatus of claim 6 , wherein the converter circuit comprises a single integrated circuit.
13. The apparatus of claim 1 , wherein the at least one load comprises at least one LED.
14. The apparatus of claim 13 , wherein the at least one LED includes at least one non-white LED.
15. The apparatus of claim 13 , wherein the at least one LED includes at least one white LED.
16. The apparatus of claim 1 , wherein the at least one load comprises at least one LED-based lighting unit, and wherein the at least one LED-based lighting unit comprises:
at least one first LED to generate first radiation having a first spectrum; and
at least one second LED to generate second radiation having a second spectrum different than the first spectrum.
17. The apparatus of claim 16 , wherein the at least one first LED includes at least one non-white LED.
18. The apparatus of claim 16 , wherein the at least one first LED includes at least one white LED.
19. The apparatus of claim 18 , wherein the at least one second LED includes at least one second white LED.
20. The apparatus of claim 1 , wherein the converter circuit does not include any energy storage device.
21. The apparatus of claim 20 , wherein the at least one load comprises at least one LED, and wherein the apparatus comprises a single integrated circuit.
22. The apparatus of claim 20 , wherein the at least one load comprises at least one LED-based lighting unit, wherein the at least one LED-based lighting unit comprises at least one LED and control circuitry for the at least one LED, and wherein the converter circuit and the control circuitry for the at least one LED are implemented as a single integrated circuit to which the at least one LED is coupled.
23. An apparatus, comprising:
at least one load having a nonlinear or variable current-to-voltage characteristic; and
a converter circuit coupled to the at least one load and configured such that the apparatus has a substantially linear current-to-voltage characteristic over at least some range of operation,
wherein a first current conducted by the apparatus when the apparatus draws power from a power source is independent of a second current conducted by the load;
wherein the apparatus has a terminal voltage V T and conducts a terminal current I T when the apparatus draws power from a power source, and wherein the converter circuit is configured such that the apparatus has an effective resistance of between approximately 1.0(V T /I T ) to 4.0(V T /I T ) at a nominal operating point.
24. The apparatus of claim 23 , wherein the converter circuit comprises a variable current source.
25. The apparatus of claim 24 , wherein the variable current source includes at least one operational amplifier and/or at least one current mirror.
26. The apparatus of claim 24 , wherein the converter circuit further comprises at least one of a fixed current source and a fixed voltage source coupled to the variable current source.
27. The apparatus of claim 24 , wherein the converter circuit comprises a single integrated circuit.
28. The apparatus of claim 23 , wherein the at least one load comprises at least one LED.
29. The apparatus of claim 23 , wherein the at least one load comprises at least one LED-based lighting unit, and wherein the at least one LED-based lighting unit comprises:
at least one first LED to generate first radiation having a first spectrum; and
at least one second LED to generate second radiation having a second spectrum different than the first spectrum.
30. The apparatus of claim 29 , wherein the converter circuit does not include any energy storage device.
31. The apparatus of claim 29 , wherein the at least one load comprises at least one LED, and wherein the apparatus comprises a single integrated circuit.
32. The apparatus of claim 29 , wherein the at least one load comprises at least one LED-based lighting unit, wherein the at least one LED-based lighting unit comprises at least one LED and control circuitry for the at least one LED, and wherein the converter circuit and the control circuitry for the at least one LED are implemented as a single integrated circuit to which the at least one LED is coupled.