Solid-state lighting apparatus and methods using current diversion controlled by lighting device bias states

1. A lighting apparatus comprising:

a string of light emitting diode (LED) sets coupled in series, each set comprising at least one LED;

a resistor coupled in series with the string; and

a plurality of current diversion circuits, respective ones of which are coupled to respective nodes of the string and to a terminal of the resistor and configured to operate responsive to bias state transitions of respective ones of the LED sets, wherein a first one of current diversion circuits is configured to conduct current to a first one of the LED sets while bypassing a second one of the LED sets and to be turned off responsive to a voltage at the terminal of the resistor.

2. The apparatus of claim 1 , wherein the first one of the current diversion circuits is configured to conduct current responsive to a forward biasing of the first one of the LED sets.

3. The apparatus of claim 1 , wherein a second one of the current diversion circuits is configured to conduct current responsive to a forward biasing of the second one of the LED sets.

4. The apparatus of claim 1 , wherein the first one of the current diversion circuits comprises a bipolar transistor providing a controllable current path between a node of the string and a terminal of a power supply, and wherein current through the resistor varies an emitter bias of the bipolar transistor.

5. The apparatus of claim 1 , wherein the bias states of the LED sets transition responsive to a power supply having a varying voltage such that the diversion circuits are incrementally turned on and off in response to increases and decreases in the varying voltage.

6. A lighting apparatus comprising:

a string of light emitting diode (LED) sets coupled in series, each set comprising at least one LED; and

a plurality of current diversion circuits, respective ones of which are coupled to respective nodes of the string and configured to operate responsive to bias state transitions of respective ones of the LED sets, wherein a first one of current diversion circuits is configured to conduct current to a first one of the LED sets while bypassing a second one of the LED sets and to be turned off responsive to a current through the second one of the LED sets, wherein each of the current diversion circuits comprises:

a transistor providing a controllable current path between a node of the string and a terminal of a power supply; and

a turn-off circuit coupled to a node of the string and to a control terminal of the transistor and configured to control the current path responsive to a control input.

7. The apparatus of claim 6 , wherein current through one of the LED sets provides the control input.

8. The apparatus of claim 6 , wherein the transistor comprises a bipolar transistor and wherein the turn-off circuit is configured to vary a base current of the bipolar transistor responsive to the control input.

9. A lighting apparatus comprising:

a rectifier circuit configured to be coupled to an AC power source and to generate a rectified AC voltage;

a resistor having a first terminal coupled to a first output node of the rectifier circuit;

a string of serially-connected LED sets, the string having a first end coupled to a second terminal of the resistor and a second end coupled to a second output node of the rectifier circuit, each LED set comprising at least one LED; and

a plurality of current diversion circuits, respective ones of which provide respective separate current paths from respective nodes of the string to the second terminal of the resistor and are configured to be selectively enabled and disabled responsive to bias state transitions of the LED sets as a magnitude of the rectified AC voltage varies.

10. The apparatus of claim 9 , wherein a first one of the current diversion circuits is configured to conduct current via a first one of the LED sets and is configured to be turned off responsive to current through a second one of the LED sets.

11. The apparatus of claim 10 , wherein the first one of the current diversion circuits is configured to conduct current responsive to a forward biasing of the first one of the LED sets.

12. The apparatus of claim 10 , wherein the second one of the current diversion circuit is configured to conduct current responsive to a forward biasing of the second one of the LED sets.

13. The apparatus of claim 9 , wherein each of the current diversion circuits comprises a bipolar transistor providing a controllable current path between a node of the string and the second terminal of the resistor and wherein current through the resistor varies an emitter bias of the bipolar transistor.

14. A lighting apparatus comprising:

a string of serially-connected LED sets, each LED set comprising at least one LED;

a resistor coupled having a terminal coupled to an end of the string; and

a plurality of transistors, respective ones of which are configured to provide respective separate controllable current paths between respective nodes of the string and the terminal of the resistor; and

a control circuit configured to control the transistors responsive to a voltage at the terminal of the resistor.

15. The apparatus of claim 14 , wherein a first one of the transistors is configured to conduct current via a first one of the LED sets and wherein the control circuit is configured to turn off the first one of the transistors responsive to current through a second one of the LED sets.

16. The apparatus of claim 15 , wherein an emitter of the first one of the transistors is biased by the voltage at the terminal of the resistor.

17. The apparatus of claim 15 , wherein the control circuit comprises a turn-off circuit coupled to a node of the string and to a control terminal of the first one of the transistors and configured to turn off the first one of the transistors responsive to a control input.

18. The apparatus of claim 17 , wherein the current through the second one of the LED sets provides the control input.

19. An apparatus comprising:

a plurality of current diversion circuits, respective ones of which are configured to be coupled to respective nodes of a string of serially-connected LED sets and to a terminal of a resistor coupled in series with the string, the current diversion circuits further configured to operate responsive to bias state transitions of respective ones of the LED sets, wherein a first one of current diversion circuits is configured to conduct current to a first one of the LED sets while bypassing a second one of the LED sets and to be turned off responsive to a voltage at the terminal of the resistor.

20. The apparatus of claim 19 , wherein the first one of the current diversion circuits is configured to conduct current responsive to a forward biasing of the first one of the LED sets.

21. The apparatus of claim 19 , wherein the second one of the current diversion circuit is configured to conduct current responsive to a forward biasing of the second one of the LED sets.

22. The apparatus of claim 19 , wherein each of the current diversion circuits comprises a bipolar transistor providing a controllable current path between a node of the string and the terminal of the resistor and wherein current through the resistor varies an emitter bias of the bipolar transistor.

23. The apparatus of claim 19 , further comprising a rectifier circuit configured to be coupled to a power source and having an output configured to be coupled to the string of LED sets.

24. An apparatus comprising:

a plurality of current diversion circuits, respective ones of which are configured to be coupled to respective nodes of a string of serially-connected LED sets and to operate responsive to bias state transitions of respective ones of the LED sets, wherein a first one of current diversion circuits is configured to conduct current to a first one of the LED sets while bypassing a second one of the LED sets and to be turned off responsive to a current through the second one of the LED sets, wherein each of the current diversion circuits comprises:

a transistor configured to provide a controllable current path between a node of the string and a terminal of a power supply; and

a turn-off circuit coupled to a node of the string and to a control terminal of the transistor and configured to control the current path responsive to a control input.

25. The apparatus of claim 24 , wherein current through one of the LED sets provides the control input.

26. A method of operating a string of light emitting diode (LED) sets coupled in series, each set comprising at least one LED, the method comprising:

conducting current from a first one of the LED sets while bypassing a second one of the LED sets using a first current diversion circuit coupled to a terminal of a resistor coupled in series with the string;

conducting current from a second one of the LED sets using a second current diversion circuit coupled to the terminal of the resistor; and

turning off the first current diversion responsive to a voltage at a terminal of the resistor.

27. The method of claim 26 , wherein each of the first and second current diversion circuits comprises a bipolar transistor providing a controllable current path between a node of the string and a power supply and wherein turning off the first current diversion responsive to current through the second one of the LED sets comprises varying an emitter bias of the transistor of the first current diversion circuit.