Apparatus and methods for the thermal regulation of light emitting diodes in signage

• US 20090013570A1
• Filed: 04/10/2008
• Published: 01/15/2009
• Est. Priority Date: 04/10/2007
• Status: Active Grant

• Current Assignee: Revolution Lighting Technologies, Inc.
• Original Assignee: Nexxus Lighting, Inc.
• Inventors: Grajcar, Zdenko
• Granted Patent: US 7,948,190 B2
• Time in Patent Office: Days
• US Class Current: 40/552
• CPC Class Codes: G09F 13/22 electroluminescent electroluminescent light sources per se H05B33/00
• CPC Class Codes: G09F 9/33 being semiconductor devices, e.g. diodes
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

Apparatus and methods for the thermal management of one or more light emitting diode (LED) modules disposed within a channel sign are disclosed. The apparatus, in various aspects, detects the ambient temperature generally proximate the LED module and regulates the current flowed onto the LED'"'"'s within the LED module based upon the ambient temperature. Methods for thermal management of the one or more LED modules disposed within a channel sign are disclosed herein.

Claims

1. A channel sign comprising:

a channel sign housing having a sign cavity therein;

a power distribution circuit disposed within the channel sign; and

a plurality of LED modules disposed within the channel sign cavity, wherein each of the LED modules is electrically coupled to the power distribution circuit and comprises;

at least one LED intended for operation within a normal temperature range;

a driver circuit coupled to the LED for supplying current thereto;

a control circuit coupled to the driver for regulating the current from the driver to the LED; and

a temperature sensor coupled to the control circuit and mounted on the LED module for furnishing a temperature signal to the control circuit indicative of ambient temperature about the LED;

wherein the control circuit is responsive to the temperature signal for reducing or cutting off current from the driver circuit to the LED when the ambient temperature exceeds the normal temperature range.

2. The channel sign of claim 1 wherein the control circuits of the respective LED modules operate independently of one another.

3. The channel sign of claim 1 wherein:

the control circuit is responsive to the temperature signal for regulating the driver circuit to supply a maximum forward current to the LED when the ambient temperature is within the normal temperature range; and

the control circuit is further responsive to the temperature signal for regulating the driver circuit to cut off current to the LED when the ambient temperature exceeds the normal temperature range.

4. The channel sign of claim 1 wherein:

the control circuit is responsive to the temperature signal for regulating the driver circuit to supply a maximum forward current to the LED when the ambient temperature is within the normal temperature range; and

the control circuit is further responsive to the temperature signal for regulating the driver circuit to cut off current to the LED when the ambient temperature exceeds a cutoff temperature in excess of the normal temperature range; and

the control circuit is responsive to the temperature signal for regulating the driver circuit to supply a derated current to the LED when the ambient temperature exceeds the normal temperature range and is less than the cutoff temperature.

5. The channel sign of claim 4, wherein the derated current inversely varies in a substantially continuous manner as a function of the ambient temperature.

6. The channel sign of claim 1 wherein:

a first one of the LED modules comprises a first LED having a first normal operating temperature range and a first cutoff temperature; and

a second one of the LED modules comprises a second LED having a second normal operating temperature range different than the first normal operating temperature range, and a second cutoff temperature different than the first cutoff temperature.

7. The channel sign of claim 1 wherein the temperature sensor comprises a thermistor.

8. The channel sign of claim 7 wherein the thermistor is a negative temperature coefficient thermistor.

9. An LED module useful in a channel sign, comprising:

at least one LED intended for operation within a normal temperature range;

a driver circuit coupled to the LED for supplying current thereto;

a control circuit coupled to the driver for regulating the current from the driver to the LED; and

a temperature sensor coupled to the control circuit and mounted on the LED module for furnishing a temperature signal to the control circuit indicative of ambient temperature about the LED;

wherein the control circuit is responsive to the temperature signal for reducing or cutting off current from the driver circuit to the LED when the ambient temperature exceeds the normal temperature range.

10. The LED module of claim 9 wherein:

the driver circuit comprises a driver transistor;

the control circuit comprises a bipolar control transistor having a base; and

the temperature sensor comprises a thermistor coupled to the base of the control transistor.

11. The LED module of claim 10 wherein the thermistor is a negative temperature coefficient thermistor.

12. The LED module of claim 9 wherein:

the control circuit is responsive to the temperature signal for regulating the driver circuit to supply a maximum forward current to the LED when the ambient temperature is within the normal temperature range; and

the control circuit is further responsive to the temperature signal for regulating the driver circuit to cut off current to the LED when the ambient temperature exceeds the normal temperature range.

13. The LED module of claim 9 wherein:

the control circuit is responsive to the temperature signal for regulating the driver circuit to supply a maximum forward current to the LED when the ambient temperature is within the normal temperature range; and

the control circuit is further responsive to the temperature signal for regulating the driver circuit to cut off current to the LED when the ambient temperature exceeds a cutoff temperature in excess of the normal temperature range; and

the control circuit is responsive to the temperature signal for regulating the driver circuit to supply a derated current to the LED when the ambient temperature exceeds the normal temperature range and is less than the cutoff temperature.

14. The LED module of claim 13, wherein the derated current inversely varies in a substantially continuous manner as a function of the ambient temperature.

15. A method for thermally managing a channel sign having a plurality of LED modules disposed within a cavity therein, each having at least one LED, comprising:

detecting a first ambient temperature proximate a first LED in a first one of the LED modules;

supplying maximum forward current to the first LED when the first ambient temperature is within a first normal temperature range for the first LED;

cutting off current to the first LED when the first ambient temperature exceeds a first cutoff temperature in excess of the first normal temperature range for the first LED;

detecting a second ambient temperature proximate a second LED in a second one of the LED modules;

supplying maximum forward current to the second LED when the second ambient temperature is within a second normal temperature range for the second LED; and

cutting off current to the second LED when the second ambient temperature exceeds a second cutoff temperature in excess of the second normal temperature range for the second LED;

wherein the detecting, supplying and cutting of steps for the first LED are independent of the detecting, supplying and cutting of steps for the second LED.

16. The method of claim 15 further comprising:

supplying a derated current to the first LED when the first ambient temperature exceeds the first normal temperature range and is less than the first cutoff temperature; and

supplying a derated current to the second LED when the second ambient temperature exceeds the second normal temperature range and is less than the second cutoff temperature;

wherein the derated current supplying step for the first LED is independent of the derated current supplying step for the second LED.

17. A method for thermally managing an LED module having at least one LED and useful in a channel sign, comprising:

detecting ambient temperature proximate the LED;

supplying maximum forward current to the LED when the ambient temperature thereof is within a normal temperature range for the LED; and

cutting off current to the LED when the ambient temperature thereof exceeds a cutoff temperature in excess of the normal temperature range for the LED.

18. The method of claim 17 further comprising supplying a derated current to the LED when the ambient temperature exceeds the normal temperature range and is less than the cutoff temperature for the LED therein.

19. The method of claim 18 wherein the derated current supplying step comprises varying the derated current inversely in a substantially continuous manner as a function of the ambient temperature.

20. The method of claim 17 wherein the detecting step comprises detecting ambient temperature with a thermistor mounted on the LED module.