SOLID STATE LIGHTING APPARATUS WITH COMPENSATION BYPASS CIRCUITS AND METHODS OF OPERATION THEREOF

• US 20110068701A1
• Filed: 02/12/2010
• Published: 03/24/2011
• Est. Priority Date: 09/24/2009
• Status: Active Grant

• Current Assignee: IDEAL Industries Lighting, LLC (Ideal Industries Incorporated)
• Original Assignee: Cree LED Lighting Solutions Inc (Wolfspeed, Inc.)
• Inventors: van de Ven, Antony P., Chobot, Joseph Paul, Pickard, Paul Kenneth, Negley, Gerald H., Harris, Michael James, Given, Terry
• Granted Patent: US 10,264,637 B2
• Time in Patent Office: Days
• US Class Current: 315/185.R
• CPC Class Codes: H05B 45/24 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices
• CPC Class Codes: H05B 45/54 in a series array of LEDs
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs

Abstract

A lighting apparatus includes a string of serially-connected light emitting devices and a bypass circuit coupled to first and second nodes of the string and configured to variably conduct a bypass current around at least one of the light-emitting devices responsive to a temperature and/or a total current in the string. In some embodiments, the bypass circuit includes a variable resistance circuit coupled to the first and second nodes of the string and configured to variably conduct the bypass current around the at least one of the light-emitting devices responsive to a control voltage applied to a control node and a compensation circuit coupled to the control node and configured to vary the control voltage responsive to a temperature and/or total string current.

Claims

1. A lighting apparatus comprising:

at least one light emitting device; and

a bypass circuit configured to variably conduct a bypass current around the at least one light-emitting device responsive to a temperature sense signal.

2. The apparatus of claim 1, wherein the at least one light-emitting device comprises a string of serially-connected light emitting devices;

and

wherein the bypass circuit is coupled to first and second nodes of the string and is configured to variably conduct a bypass current around at least one of the light-emitting devices responsive to the temperature sense signal.

3. The apparatus of claim 2, wherein the bypass circuit comprises:

a variable resistance circuit coupled to the first and second nodes of the string and configured to variably conduct the bypass current around the at least one of the light-emitting devices responsive to a control voltage applied to a control node; and

a temperature compensation circuit coupled to the control node and configured to vary the control voltage responsive to the temperature.

4. The apparatus of claim 3, wherein the temperature compensation circuit comprises a voltage divider circuit comprising at least one thermistor.

5. The apparatus of claim 4, wherein the voltage divider circuit comprises:

a first resistor having a first terminal coupled to the first node of the string and a second terminal coupled to the control node; and

a second resistor having a first terminal coupled to the second node of the string and a second terminal coupled to the control node,

wherein at least one of the first and second resistors comprises a thermistor.

6. The apparatus of claim 5, wherein the first resistor comprises a first thermistor and wherein the second resistor comprises a second thermistor.

7. The apparatus of claim 3, wherein the temperature compensation circuit is coupled to a node of the string such that the control voltage varies responsive to a current in the string.

8. The apparatus of claim 7, wherein the string further comprises a current sense resistor coupled in series with the light-emitting devices, and wherein the temperature compensation circuit is coupled to a terminal of the current sense resistor.

9. The apparatus of claim 3, wherein the variable resistance circuit comprises a bipolar junction transistor and wherein the control node comprises a base terminal of the bipolar junction transistor.

10. An apparatus for controlling a string of serially-connected light emitting devices, the apparatus comprising:

a variable resistance circuit coupled to first and second nodes of the string and configured to variably conduct a bypass current around the at least one of the light-emitting devices responsive to a control voltage applied to a control node; and

a temperature compensation circuit coupled to the control node and configured to vary the control voltage responsive to a temperature.

11. The apparatus of claim 10, wherein the temperature compensation circuit comprises a voltage divider circuit comprising at least one thermistor.

12. The apparatus of claim 11, wherein the voltage divider circuit comprises:

a first resistor having a first terminal coupled to the first node of the string and a second terminal coupled to the control node; and

a second resistor having a first terminal coupled to the second node of the string and a second terminal coupled to the control node,

wherein at least one of the first and second resistors comprises a thermistor.

13. A lighting apparatus comprising:

a string of serially-connected light emitting devices; and

a bypass circuit coupled to first and second nodes of the string and configured to variably conduct a bypass current around at least one of the light-emitting devices in proportion to a total current of the string responsive to the total current of the string.

14. The apparatus of claim 13, wherein the string further comprises a current sense resistor coupled in series with the light-emitting devices, and wherein the bypass circuit is coupled to a terminal of the current sense resistor.

15. The apparatus of claim 13, wherein the bypass circuit comprises:

a variable resistance circuit coupled to the first and second nodes and configured to variably conduct a bypass current around the at least one of the light-emitting devices responsive to a control voltage applied to a control node of the variable resistance circuit; and

a bypass control circuit configured to vary the control voltage responsive to the total current.

16. The apparatus of claim 15, wherein the variable resistance circuit comprises:

a bipolar junction transistor having a collector terminal coupled to the first node of the string and wherein the control node comprises a base terminal of the bipolar junction transistor; and

a resistor coupled between an emitter terminal of the bipolar junction transmitter and the second node of the string.

17. The apparatus of claim 15, wherein the bypass control circuit comprises a voltage divider circuit coupled to first and second nodes of the string and to the control node of the variable resistance circuit.

18. The apparatus of claim 17, wherein the voltage divider circuit comprises:

a first resistor having a first terminal coupled to the first node of the string and a second terminal coupled to the control node; and

a second resistor having a first terminal coupled to the second node of the string and a second terminal coupled to the control node.

19. The apparatus of claim 18, wherein the string further comprises a current sense resistor coupled in series with the light-emitting devices, and wherein the second resistor is coupled to a terminal of the current sense resistor.

20. The apparatus of claim 18, wherein at least one of the first and second resistors comprises a thermistor.

21. The apparatus of claim 18:

wherein the variable resistance circuit comprises;

a bipolar junction transistor having a collector terminal coupled to the first node of the string, wherein the control node comprises a base terminal of the bipolar junction transistor; and

a third resistor coupled between an emitter terminal of the bipolar junction transmitter and the second node of the string; and

wherein the second resistor has a first terminal coupled to the second node of the string.

22. An apparatus for controlling a string of serially-connected light emitting devices, the apparatus comprising:

a variable resistance circuit coupled to the first and second nodes and configured to variably conduct a bypass current around the at least one of the light-emitting devices responsive to a control voltage applied to a control node of the variable resistance circuit; and

a bypass control circuit configured to vary the control voltage responsive to a total current through the string.

23. The apparatus of claim 22, wherein the variable resistance circuit comprises:

a bipolar junction transistor having a collector terminal coupled to the first node of the string and wherein the control node comprises a base terminal of the bipolar junction transistor; and

a resistor coupled between an emitter terminal of the bipolar junction transmitter and the second node of the string.

24. The apparatus of claim 22, wherein the bypass control circuit comprises a voltage divider circuit coupled to first and second nodes of the string and to the control node of the variable resistance circuit.

25. The apparatus of claim 22, wherein bypass control circuit is configured to be coupled to a terminal of a current sense resistor coupled in series with the light-emitting devices.

26. A lighting apparatus comprising:

a string of serially-connected light emitting devices;

a variable resistance circuit comprising;

a bipolar junction transistor having a collector terminal coupled to a first node of the string; and

a first resistor coupled between an emitter terminal of the bipolar junction transmitter and a second node of the string; and

a bypass control circuit comprising;

a second resistor having a first terminal coupled to the first node of the string and a second terminal coupled to the base terminal of the bipolar junction transistor;

a third resistor having a first terminal coupled to the second node of the string; and

a diode having a first terminal coupled to a second node of the third resistor and a second terminal coupled to the base terminal of the bipolar junction transistor.

27. The apparatus of claim 26, wherein the diode is thermally coupled to the bipolar junction transistor.

28. The apparatus of claim 27, wherein the transistor is a first transistor of an integrated complementary transistor pair and wherein the diode is a junction of a second transistor of the integrated complementary transistor pair.

29. A lighting apparatus comprising:

a string of serially-connected light emitting devices; and

bypass means for controlling at least one of a color point, a lumen output, a temperature response and/or a current response of string of serially-connected light emitting devices.