Lamp driver having a shutdown interface circuit

1. A lamp driver responsive to a control signal that is variable in a determined control range, comprising:

a first circuit operable in a first operational mode in response to a value of the control signal within the determined control range to develop a first lamp control parameter that controls a lamp dependent upon the value of the control signal; and

a second circuit operable in a second operational mode in response to a value of the control signal outside of the determined control range to develop a second lamp control parameter to control the lamp in a manner different than the first operational mode, and wherein the second circuit is operable when the control signal is outside the control range to sink current.

2. The lamp driver of claim 1 , wherein the first circuit comprises a constant current source.

3. The lamp driver of claim 2 , wherein the second circuit comprises a shutdown circuit.

4. The lamp driver of claim 1 , wherein the first circuit is operable when the control signal is within the control range to supply a constant current.

5. The lamp driver of claim 4 , wherein the second circuit comprises a shutdown circuit operable in the second operational mode to shut down the lamp.

6. The lamp driver of claim 5 , wherein the lamp driver initiates operation in the first operational mode when power is initially applied to the lamp driver and remains in the first operational mode until the value of the control signal is outside of the determined control range.

7. The lamp driver of claim 6 , wherein the lamp comprises at least one LED module.

8. A lamp driver responsive to a control signal that is variable in a determined control range, comprising:

a circuit operable in response to a value of the control signal within the determined control range to develop a first current and a lamp control voltage dependent upon the value of the control signal; and

a shutdown interface operable in response to a value of the control signal outside of the determined control range to develop a second current to turn off a lamp.

9. The lamp driver of claim 8 , wherein the circuit comprises a constant current source when the first current is developed.

10. The lamp driver of claim 9 , wherein the shutdown interface comprises a current sink when the second current is developed.

11. The lamp driver of claim 8 , wherein the shutdown interface includes an isolation element.

12. The lamp driver of claim 11 , wherein the isolation element comprises an opto-isolator.

13. The lamp driver of claim 8 , in combination with a lamp module.

14. The lamp driver of claim 8 , wherein the first current has a constant magnitude and the control signal has a variable voltage magnitude.

15. A lighting apparatus, comprising:

an LED module;

a control module that develops a control signal having a selectable variable magnitude within a determined control range to command operation of the LED module at a selected brightness and wherein the control module is further capable of developing a control signal having a magnitude outside the control range;

a circuit responsive to the magnitude of the control signal within the determined control range to supply a constant current magnitude and a variable lamp control voltage to the LED module dependent upon the value of the control signal; and

a solid-state shutdown interface operable in response to the magnitude of the control signal outside of the determined control range to sink current to turn off the LED module.

16. The lighting apparatus of claim 15 , wherein the shutdown interface includes an isolation element coupled to the circuit.

17. The lamp driver of claim 16 , wherein the isolation element comprises an opto-isolator.

18. The lamp driver of claim 15 , further including mutually linked inductors having a primary winding connectable to a source of AC power and a secondary winding coupled to a secondary control circuit.

19. A lighting apparatus, comprising:

an LED module;

a control module that develops a control signal having a selectable variable voltage magnitude within a predetermined control range to command operation of the LED module at a selected brightness and that further is capable of developing a control signal having a magnitude outside of the predetermined control range;

a circuit including a primary winding and a secondary winding and responsive to the magnitude of the control signal within the predetermined control range to supply a constant current magnitude and a variable lamp control voltage to the LED module dependent upon the value of the control signal; and

an isolated solid-state shutdown interface coupled to the primary winding operable in response to the magnitude of the control signal outside of the predetermined control range to sink current to turn off the LED module.

20. The lighting apparatus of claim 19 , wherein the circuit further includes a primary control circuit responsive to the shutdown interface and a secondary control circuit responsive to the circuit.

21. The lighting apparatus of claim 20 , wherein the shutdown interface comprises means for isolating the primary winding from components coupled to the secondary winding.

22. The lighting apparatus of claim 21 , wherein the isolating means comprises an opto-isolator.