Single inductor control of multi-color LED systems
A circuit for driving multiple light emitting diodes (LEDs) includes at least two sets of LEDs, each set comprised of one or more LEDs in series. The circuit further includes a single inductor connected in series with the two sets of LEDs. At least one set of LEDs is connected to a shunting transistor connected in parallel with the set of LEDs. The duty cycle of the shunting transistor is controlled by a single controller connected to the shunting transistor and the inductor.
1. A circuit for driving multiple sets of light emitting diodes (LEDs), the circuit comprising:
a first set of LEDs comprised of one or more LEDs in series;
a second set of LEDs comprised of one or more LEDs in series, wherein the first set of LEDs is configured to produce different color or color spectrum than the second set of LEDs;
a single inductor connected in series with the first and second sets of LEDs;
a first shunting transistor connected in parallel with the second set of LEDs; and
a single controller connected to the single inductor and the first shunting transistor, wherein the controller is configured to set a first duty cycle of the first shunting transistor, and wherein the first set of LEDs is not connected in parallel with a shunting transistor.
2. The circuit of claim 1 , wherein the controller is configured to set the first duty cycle based on a measurement of the luminosity of the first set of LEDs.
3. The circuit of claim 1 , further comprising:
a resistor connected to the inductor and the controller, wherein the controller is configured to determine a current through the first set of LEDs by measuring the voltage developed across the resistor.
4. The circuit of claim 1 , wherein the single inductor is the primary inductance of a flyback transformer.
5. The circuit of claim 1 , further comprising:
a third set of LEDs comprised of one or more LEDs in series, wherein the third set of LEDs is configured to produce different color or color spectrum than the first and second sets of LEDs, and wherein the third set of LEDs is connected in series to the single inductor; and
a second shunting transistor connected in parallel with the third set of LEDs, wherein the controller is connected to the second shunting transistor, and wherein the controller is configured to set a second duty cycle of the second shunting transistor.
6. The circuit of claim 5 , wherein the first duty cycle is different than the second duty cycle.
7. The circuit of claim 1 , wherein the one or more LEDs of the first set of LEDs are configured to produce red color, wherein the one or more LEDs of the second set of LEDs are configured to produce blue color, and wherein the one or more LEDs of the third set of LEDs are configured to produce green color.
8. The circuit of claim 1 , wherein the single controller is a switching power supply controller.
9. The circuit of claim 8 , wherein the controller is configured to set the second duty cycle based on the determined current.
10. The circuit of claim 1 , wherein the single inductor has an inductance value of at least one millihenry.
11. A circuit for driving multiple sets of light emitting diodes (LEDs), the circuit comprising:
a first set of LEDs comprised of one or more LEDs in series;
a second set of LEDs comprised of one or more LEDs in series;
a third set of LEDs comprised of one or more LEDs in series, wherein the first set of LEDs is configured to produce different color or color spectrum than the second and third sets of LEDs, wherein the second set of LEDs is configured to produce different color or color spectrum than the first and third sets of LEDs;
a single inductor connected in series with the first, second, and third sets of LEDs;
a first shunting transistor connected in parallel with the second set of LEDs;
a second shunting transistor connected in parallel with the third set of LEDs; and
a single controller connected to the first shunting transistor and the second shunting transistor, wherein the controller is configured to control a first duty cycle of the first shunting transistor and a second duty cycle of the second shunting transistor; and wherein the first set of LEDs is not connected in parallel with a shunting transistor.
12. The circuit of claim 11 , wherein the controller is configured to set the first and second duty cycles based on a measurement of the luminosity of the first set of LEDs.
13. The circuit of claim 11 , wherein the single inductor has an inductance value of at least one millihenry.
14. The circuit of claim 11 , further comprising:
a resistor connected to the inductor and the controller, wherein the controller is configured to determine a current through the first set of LEDs by measuring the voltage developed across the resistor.
15. The circuit of claim 11 , wherein the single inductor is the primary inductance of a flyback transformer.
16. The circuit of claim 11 , further comprising:
a first capacitor connected to the first shunting transistor and the controller; and
a second capacitor connected to the second shunting transistor and the controller.
17. The circuit of claim 11 , wherein the single controller is a switching power supply controller.
18. A method of building a circuit for driving multiple sets of LEDs, the method comprising:
connecting a single inductor in series to a first set of LEDs comprised of one or more LEDs in series;
connecting the first set of LEDs in series to a second set of LEDs comprised of one or more LEDs in series, wherein the first set of LEDs is configured to produce different color or color spectrum than the second set of LEDs;
connecting a first shunting transistor in parallel with the second set of LEDs, wherein the first set of LEDs is not connected in parallel with a shunting transistor; and
connecting a single controller to the first shunting transistor, wherein the controller is configured to control a first duty cycle of the first shunting transistor.
19. The method of claim 18 , wherein the controller is configured to determine the current through the first set of LEDs, wherein the first duty cycle is set based on the determined current.
20. The method of claim 19 , further comprising:
connecting a resistor to the inductor and the controller, wherein the controller is configured to determine the current through the first set of LEDs by measuring the voltage developed across the resistor.
21. The method of claim 18 , wherein the controller is configured to set the first duty cycle based on a measurement of the luminosity of the first set of LEDs.
22. The method of claim 18 , further comprising:
connecting the second set of LEDs in series to a third set of LEDs comprised of one or more LEDs in series, wherein the third set of LEDs is configured to produce different color or color spectrum than the first and second sets of LEDs;
connecting a second shunting transistor in parallel with the third set of LEDs; and
connecting the controller to the second shunting transistor, wherein the controller is configured to control a second duty cycle of the second shunting transistor.
23. The method of claim 18 , wherein the inductor has an inductance value of at least one millihenry.
24. The method of claim 18 , further comprising:
connecting a switching transistor to the controller, wherein the controller is configured to control the switching transistor, which controls the current through the inductor.