Methods and apparatus for simulating resistive loads

• US 8,026,673 B2
• Filed: 08/09/2007
• Issued: 09/27/2011
• Est. Priority Date: 01/05/2007
• Status: Active Grant

• Current Assignee: Signify North America Corporation (Signify N.V.)
• Original Assignee: Philips Solid-State Lighting Solutions (Koninklijke Philips N.V.)
• Inventors: Lys, Ihor A.
• Primary Examiner(s): Philogene; Haissa
• Application Number:
  US11/836,568
• Publication Number:
  US 20080164827A1
• Time in Patent Office: 1,510 Days
• Field of Search: 315/291, 315/307, 315/169.1, 315/169.3, 315/312, 315/225, 315/209.R, 345/82, 345/102, 363/34, 363/56.01, 363/56.02
• US Class Current: 315/291
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix

Abstract

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.

Claims

1. An apparatus, comprising:

at least one load having a first current-to-voltage characteristic; and

a converter circuit coupled to the at least one load to alter the first current-to-voltage characteristic in a predetermined manner so as to facilitate a predictable behavior of the at least one load when the at least one load is connected in series with at least one other load to draw power from a power source,

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.

2. The apparatus of claim 1, wherein the converter circuit is configured such that the apparatus has a substantially linear current-to-voltage characteristic over at least some range of operation.

3. The apparatus of claim 2, wherein the first current-to-voltage characteristic is nonlinear or variable.

4. The apparatus of claim 1, 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.

5. The apparatus of claim 4, wherein the converter circuit is configured such that the effective resistance is between approximately 1.0(V_T/I_T) to 4.0(V_T/I_T) at least at the nominal operating point V_T=V_nom in the at least some range of operation.

6. The apparatus of claim 4, wherein the converter circuit comprises a variable current source.

7. 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.

8. 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.

9. The apparatus of claim 6, wherein the converter circuit comprises a single integrated circuit.

10. The apparatus of claim 1, wherein the at least one load comprises at least one LED.

11. The apparatus of claim 10, wherein the at least one LED includes at least one non-white LED.

12. The apparatus of claim 10, wherein the at least one LED includes at least one white LED.

13. 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.

14. The apparatus of claim 13, wherein the at least one first LED includes at least one non-white LED.

15. The apparatus of claim 13, wherein the at least one first LED includes at least one white LED.

16. The apparatus of claim 15, wherein the at least one second LED includes at least one second white LED.

17. The apparatus of claim 1, wherein the converter circuit does not include any energy storage device.

18. The apparatus of claim 17, wherein the at least one load comprises at least one LED, and wherein the apparatus comprises a single integrated circuit.

19. The apparatus of claim 17, 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.

20. An apparatus, comprising:

at least one light source having an operating voltage V_L, an operating current I_L, and a first current-to-voltage characteristic based on the operating voltage V_L and the operating current I_L; and

a converter circuit coupled to the at least one light source to provide the operating voltage V_L, the converter circuit configured such that the apparatus conducts a terminal current I_T and has a terminal voltage V_T when the apparatus draws power from a power source,

wherein;

the operating voltage V_L of the at least one light source is less than the terminal voltage V_T of the apparatus;

the terminal current I_T of the apparatus is independent of the operating current I_L or the operating voltage V_L of the at least one light source; and

the converter circuit alters the first current-to-voltage characteristic in a predetermined manner to provide a second current-to-voltage characteristic for the apparatus, based on the terminal voltage V_T and the terminal current I_T, that is significantly different from the first current-to-voltage characteristic; and

the second current-to-voltage characteristic facilitates a predictable behavior of the at least one light source when the at least one light source is connected in series with at least one other light source to draw power from the power source.

21. The apparatus of claim 20, wherein the first current-to-voltage characteristic of the light source is nonlinear or variable, and wherein the second current-to-voltage characteristic of the apparatus is substantially linear over a range of voltages above and below the terminal voltage V_T.

22. The apparatus of claim 20, 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.

23. The apparatus of claim 20, wherein the converter circuit is configured such that the effective resistance is between approximately 1.0(V_T/I_T) to 4.0(V_T/I_T) at least at the nominal operating point.

24. The apparatus of claim 22, wherein the converter circuit comprises a variable current source.

25. The apparatus of claim 24, wherein the at least one light source 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.

26. A method, comprising:

altering a first current-to-voltage characteristic of at least one load in a predetermined manner so as to facilitate a predictable behavior of the at least one load when the at least one load is connected in series with at least one other load to draw power from a power source, wherein a first current conducted from the power source is independent of a second current conducted by the at least one load.

27. The method of claim 26, wherein altering the first current-to-voltage characteristic comprises converting the first current-to-voltage characteristic to a substantially linear current-to-voltage characteristic.