Solid state lighting apparatus with compensation bypass circuits and methods of operation thereof

Patent metadata

Field	Value
Publication number	US-10264637-B2
Application number	US-70473010-A
Country	US
Kind code	B2
Filing date	Feb 12, 2010
Priority date	Sep 24, 2009
Publication date	Apr 16, 2019
Grant date	Apr 16, 2019

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.

First claim

That which is claimed is:

1. A lighting apparatus comprising:
a string of serially-connected light emitting devices; and
a bypass circuit configured to bypass at least one light-emitting device of the string of serially-connected light emitting devices based on a color point of the at least one light emitting device, to sense a current in the string and to individually vary a bypass current conducted by the bypass circuit in proportion to the sensed current in the string and concurrently responsive to a temperature sense signal.

2. The apparatus of claim 1 , wherein the bypass circuit comprises:
a variable resistance circuit coupled to 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.

3. The apparatus of claim 2 , wherein the temperature compensation circuit comprises a voltage divider circuit comprising at least one thermistor.

4. The apparatus of claim 3 , 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.

5. The apparatus of claim 4 , wherein the first resistor comprises a first thermistor and wherein the second resistor comprises a second thermistor.

6. The apparatus of claim 2 , 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.

7. The apparatus of claim 6 , 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.

8. The apparatus of claim 2 , wherein the variable resistance circuit comprises a bipolar junction transistor and wherein the control node comprises a base terminal of the bipolar junction transistor.

9. 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 and comprising a voltage divider comprising:
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.

10. 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 sense a total current in the string and to individually variably partially bypass at least one of the light-emitting devices based on a color point of the at least one of the light emitting devices and in proportion to the sensed total current of the string responsive to the sensed total current of the string.

11. The apparatus of claim 10 , 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.

12. The apparatus of claim 10 , wherein the bypass circuit comprises:
a variable resistance circuit coupled to the 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 of the variable resistance circuit; and
a bypass control circuit configured to vary the control voltage responsive to the total current.

13. The apparatus of claim 12 , 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.

14. The apparatus of claim 12 , 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.

15. The apparatus of claim 14 , 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.

16. The apparatus of claim 15 , 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.

17. The apparatus of claim 15 , wherein at least one of the first and second resistors comprises a thermistor.

18. 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, 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.

19. 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 of serially-connected light emitting devices and configured to individually variably partially bypass at least one of the light-emitting devices based on a color point of the at least one of the light emitting devices and responsive to a control voltage applied to a control node of the variable resistance circuit; and
a bypass control circuit configured to sense a total current in the string and to vary the control voltage responsive to the sensed total current through the string such that a bypass current through the variable resistance circuit varies in proportion to the sensed total current.

20. The apparatus of claim 19 , 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.

21. The apparatus of claim 19 , wherein the bypass control circuit comprises a voltage divider circuit coupled t

Assignees

• Van De Ven Antony P
• Negley Gerald H
• Harris Michael James
• Pickard Paul Kenneth
• Chobot Joseph Paul
• Given Terry
• Cree Inc

Inventors

• Van De Ven Antony P
• Negley Gerald H
• Harris Michael James
• Pickard Paul Kenneth
• Chobot Joseph Paul
• Given Terry

Classifications

• H05B45/48

  having LEDs organised in strings and incorporating parallel shunting devices · CPC title

• H05B45/24 Primary

  using electrical feedback from LEDs or from LED modules · CPC title

• H05B33/0854

  Electricity · mapped topic

• H05B33/089

  Electricity · mapped topic

• H05B33/0866

  Electricity · mapped topic