METHODS AND APPARATUS FOR SIMULATING RESISTIVE LOADS
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 . A lighting system, comprising:
a plurality of lighting nodes coupled in series to draw power from a power source, each lighting node of the plurality of lighting nodes comprising:
at least one lighting unit having a significantly nonlinear or variable current-to-voltage characteristic; and
a converter circuit coupled to the at least one lighting unit and configured such that the lighting node has a substantially linear current-to-voltage characteristic over at least some range of operation.
2 . The lighting system of claim 1 , wherein the power source is an A.C. power source, wherein the lighting system further comprises a rectifier and a filter, and wherein the plurality of lighting nodes is coupled to the filter to draw the power when the rectifier is coupled to the A.C. power source.
3 . The lighting system of claim 2 , wherein the lighting system does not include a voltage transformer between the filter and the plurality of lighting nodes.
4 . The lighting system of claim 1 , wherein the power source is an A.C. power source, and wherein the lighting system does not include any voltage transformation circuitry or voltage transformation components between the power source and the plurality of lighting nodes.
5 . The lighting system of claim 1 , wherein the plurality of lighting nodes also are coupled in series to receive data based on a serial data protocol.
6 . The lighting system of claim 1 , wherein each converter circuit is configured such that respective node voltages of the plurality of lighting nodes are substantially similar over the at least some range of operation when the plurality of lighting nodes draws power from the power source.
7 . The lighting system of claim 6 , wherein the power source has a terminal voltage, and wherein each converter circuit is configured such that the plurality of lighting nodes share the terminal voltage in substantially equal amounts to provide the respective node voltages.
8 . The lighting system of claim 1 , wherein each lighting node has a node voltage V and conducts a node current I when the plurality of lighting nodes draws power from the power source, and wherein each converter circuit is configured such that each lighting node has an effective resistance of between approximately 0.1(V/I) to 10.0(V/I) at least at a nominal node voltage V=V nom .
9 . The lighting system of claim 8 , wherein each converter circuit is configured such that the effective resistance is between approximately 1.0(V/I) to 4.0(V/I) at least at the nominal node voltage V=V nom .
10 . The lighting system of claim 8 , wherein each converter circuit comprises a variable current source.
11 . The lighting system of claim 10 , wherein each converter circuit further comprises a voltage regulator to provide an operating voltage for the at least one lighting unit.
12 . The lighting system of claim 1 , wherein for each lighting node, the at least one 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.
13 . The lighting system of claim 12 , wherein the at least one first LED includes at least one non-white LED.
14 . The lighting system of claim 12 , wherein the at least one first LED includes at least one white LED.
15 . The lighting system of claim 14 , wherein the at least one second LED includes at least one second white LED.
16 . The lighting system of claim 1 , wherein for each lighting node:
the at least one lighting unit comprises at least one LED and control circuitry for the at least one LED; and
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.
17 . A lighting method, comprising:
A) coupling a plurality of lighting nodes in series to draw power from a power source, each lighting node including at least one lighting unit; and
B) converting a nonlinear or variable current-to-voltage characteristic of the at least one lighting unit of each lighting node to a substantially linear current-to-voltage characteristic.
18 . A lighting system, comprising:
a plurality of lighting nodes coupled in series to draw power from a power source, each lighting node of the plurality of lighting nodes having a node voltage and comprising:
at least one lighting unit having a significantly nonlinear or variable current-to-voltage characteristic; and
a converter circuit coupled to the at least one lighting unit to provide an operating voltage for the at least one lighting unit,
wherein each converter circuit is configured such that respective node voltages of the plurality of lighting nodes are substantially similar over at least some range of operation when the plurality of lighting nodes draws power from the power source.
19 . The lighting system of claim 18 , wherein the power source has a terminal voltage, and wherein each converter circuit is configured such that the plurality of lighting nodes share the terminal voltage in substantially equal amounts to provide the respective node voltages.
20 . The lighting system of claim 18 , wherein each converter circuit is configured such that the plurality of lighting nodes have identical current-to-voltage characteristics over the at least some range of operation.
21 . The lighting system of claim 18 , wherein each converter circuit is configured such that each lighting node has a substantially linear current-to-voltage characteristic over the at least some range of operation.
22 . The lighting system of claim 21 , wherein each converter circuit is configured such that the plurality of lighting nodes have identical current-to-voltage characteristics over the at least some range of operation.
23 . The lighting system of claim 18 , wherein each lighting node has the node voltage V and conducts a node current I when the plurality of lighting nodes draws power from the power source, and wherein each converter circuit is configured such that each lighting node has an effective resistance of between approximately 0.1(V/I) to 10.0(V/I) at least at a nominal node voltage V=V nom .
24 . The lighting system of claim 23 , wherein each converter circuit is configured such that the effective resistance is between approximately 1.0(V/I) to 4.0(V/I) at least at the nominal node voltage.
25 . The lighting system of claim 23 , wherein each converter circuit comprises a variable current source.
26 . The lighting system of claim 25 , wherein each converter circuit further comprises a voltage regulator to provide an operating voltage for the at least one lighting unit.
27 . The lighting system of claim 18 , wherein for each lighting node, the at least one 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.
28 . The lighting system of claim 27 , wherein the at least one first LED includes at least one non-white LED.
29 . The lighting system of claim 27 , wherein the at least one first LED includes at least one white LED.
30 . The lighting system of claim 29 , wherein the at least one second LED includes at least one second white LED.
31 . The lighting system of claim 18 , wherein for each lighting node:
the at least one lighting unit comprises at least one LED and control circuitry for the at least one LED; and
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.
32 . A lighting method, comprising:
A) coupling a plurality of lighting nodes in series to draw power from a power source, each lighting node including at least one lighting unit; and
B) converting a nonlinear or variable current-to-voltage characteristic of the at least one lighting unit of each lighting node such that respective node voltages of the plurality of lighting nodes are substantially similar over at least some range of operation when the plurality of lighting nodes draws power from the power source.