Method for wide-range CCT tuning that follows the black body line using two independently controlled current channels and three CCTs
An interface currents channeling circuit may be used to convert two current channels of a conventional two-channel driver into three driving currents for the three strings of LEDs. By doing so, the same two channel driver can be used for applications requiring just two LED arrays as well as three LED arrays.
1. A light-emitting diode (LED) lighting system comprising:
a converter printed circuit board (PCB) having a current converter configured to receive a different input driving current from each channel of a multi-channel LED driver and provide a greater number of output driving currents than a number of the input driving currents, each channel having a positive output and a negative output; and
a light emitting diode (LED) PCB configured to receive the output driving currents from the converter PCB, the LED PCB including LED arrays in which each of the LED arrays is configured to receive a different one of the output driving currents and having a different correlated color temperature (CCT), a first LED array and a second LED array of the LED arrays each configured to emit light at opposing ends of a desired tunable CCT range and a third of the LED arrays configured to emit light between the opposing ends of the desired tunable CCT range.
2. The system of claim 1 , wherein the output driving currents are provided via separate electrical connections that include a different negative output coupled to each of the LED arrays and a single positive output coupled to an anode end of each of the LED arrays.
3. The system of claim 1 , wherein the converter PCB comprises:
a first current generator configured to provide a first of the output driving currents based on a first of the input driving currents, the first of the input driving currents having a first input current level, the first of the output driving currents having a first output current level equal to a combination of the first input current level and a second input current level if the first input current level is greater than the second input current level;
a second current generator configured to provide a second of the output driving currents based on a second of the input driving currents, the second of the input driving currents having the second input current level, the second of the output driving currents having a second output current level independent of at least one of the first input current level and the second input current level independent of whether the first input current level is greater than the second input current level, the first input output current level and the second output current level being different if the first input current level is not the same as the second input current level; and
a controller configured to provide a third of the output drive currents, the third of the output drive currents having a third output current level equal to a constant output current level if the first input current level is greater than the second input current level.
4. The system of claim 3 , wherein:
the first output driving current level is the constant output current level if the first input current level is not greater than the second input current level, and
the third output current level is equal to another combination of the first level and the second current level if the first current level is not greater than the second current level, the other combination different from the combination.
5. The system of claim 4 , wherein:
the constant output current level is approximately zero.
6. The system of claim 4 , wherein:
the combination is the first current level minus the second current level, and
the other combination is the second current level minus the first current level.
7. The system of claim 3 , wherein:
the second output current level is about two times the lesser of the first input current level and the second input current level independent of whether the first input current level is greater than the second input current level.
8. The system of claim 3 , wherein:
the first current generator comprises a first pair of operational amplifiers (opamps) and a first transistor, an output of a first opamp of the first pair of opamps coupled with a non-inverting input of a second opamp of the first pair of opamps, an output of the second opamp of the first pair of opamps coupled with a control terminal of the first transistor, an inverting input of the first opamp of the first pair of opamps configured to receive a first voltage based on the first of the input driving currents, and
the second current generator comprises a second pair of opamps and a second transistor, an output of a first opamp of the second pair of opamps coupled with a non-inverting input of a second opamp of the second pair of opamps, an output of the second opamp of the second pair of opamps coupled with a control terminal of the second transistor, an inverting input of the first opamp of the second pair of opamps configured to receive a first voltage based on the first of the input driving currents.
9. The system of claim 8 , wherein:
the first voltage is provided to the inverting input of the first opamp of the first pair of opamps through a first resistor divider, and the output of the first opamp of the first pair of opamps is coupled with the inverting input of the first opamp of the first pair of opamps through a first feedback resistor, and
the second voltage is provided to the inverting input of the first opamp of the second pair of opamps through a second resistor divider, and the output of the first opamp of the second pair of opamps is coupled with the inverting input of the first opamp of the second pair of opamps through a second feedback resistor.
10. The system of claim 9 , wherein:
the first resistor divider and the second resistor divider have about the same resistor ratio, and
the first feedback resistor and the second feedback resistor have about the same resistance.
11. The system of claim 8 , wherein:
the controller comprises:
a first shunt regulator having a first reference input to which the output of the second opamp of the first pair of opamps is supplied through a first controller resistor divider, and
a second shunt regulator having a second reference input to which the output of the second opamp of the second pair of opamps is supplied through a second controller resistor divider, and
an output of each of the first shunt regulator and the second shunt regulator is connected to a control terminal of a third transistor.
12. The system of claim 11 , wherein:
the first controller resistor divider and the second controller resistor divider have about the same resistor ratio.
13. A method of operating a light-emitting diode (LED) lighting system, the method comprising:
receiving, at a converter printed circuit board (PCB), a different input driving current from each channel of a multi-channel LED driver and providing a greater number of output driving currents than a number of the input driving currents, each channel having a positive output and a negative output;
receiving, at a light emitting diode (LED) PCB, the output driving currents from the converter PCB, the LED PCB including LED arrays each receiving a different one of the output driving currents and having a different correlated color temperature (CCT); and
driving a first and second of the LED arrays on the LED PCB to each emit light at opposing ends of a desired CCT tunable range and a third of the LED arrays to emit light between the opposing ends of the desired CCT tunable range.
14. The method of claim 13 , further comprising providing the output driving currents via separate electrical connections that include a different negative output coupled to each of the LED arrays and a single positive output coupled to an anode end of each of the LED arrays.
15. The method of claim 13 , further comprising, in the converter PCB:
providing a first of the output driving currents based on a first of the input driving currents, the first of the input driving currents having a first input current level, the first of the output driving currents having a first output current level equal to a combination of the first input current level and a second input current level if the first input current level is greater than the second input current level;
providing a second of the output driving currents based on a second of the input driving currents, the second of the input driving currents having the second input current level, the second of the output driving currents having a second output current level independent of at least one of the first input current level and the second input current level independent of whether the first input current level is greater than the second input current level, the first of the output current levels and the second of the output current levels being different if the first input current level is not the same as the second input current level; and
providing a third of the output drive currents, the third of the output drive currents having a third output current level equal to a constant output current level if the first input current level is greater than the second input current level.
16. The method of claim 15 , wherein:
the first output driving current level is the constant output current level if the first input current level is not greater than the second input current level, and
the third output current level is equal to another combination of the first input current level and the second input current level if the first current level is not greater than the second current level, the other combination different from the combination.
17. The method of claim 16 , wherein:
the constant output current level is approximately zero.
18. The method of claim 16 , wherein:
the combination is the first current level minus the second current level, and
the other combination is second current level minus the first current level.
19. The method of claim 15 , wherein:
the second output current level is two times the lesser of the first input current level and the second input current level independent of whether the first input current level is greater than the second input current level.