Using An LED Die To Measure Temperature Inside Silicone That Encapsulates An LED Array

Abstract

A light-emitting diode (LED) device includes first and second LED dies with the same structure and that are both encapsulated by the same silicone layer. The first LED is supplied with sufficient drive current to illuminate the LED. Control circuitry supplies the second LED with a constant current, determines the voltage across the second LED, and calculates the temperature of the second LED based on the voltage across the second LED. The constant current has a maximum magnitude that never exceeds the maximum magnitude of the drive current. The LED device is able to calculate the temperature of a diode with a gallium-nitride layer (GaN or GaInN) that is receiving a large drive current and emitting blue light by determining the voltage across an adjacent similar diode with a gallium-nitride layer through which a small constant current is flowing. Preferably, the band gap of the LEDs exceeds two electron volts.

1 - 20 . (canceled) 
     
     
         21 . A device comprising:
 a diode that has a temperature;   an encapsulant that covers the diode, wherein the encapsulant contains phosphor; and   circuitry adapted to determine the temperature of the diode based on a voltage across the diode.   
     
     
         22 . The device of  claim 21 , wherein the diode has a gallium nitride (GaN) layer. 
     
     
         23 . The device of  claim 21 , wherein the diode has a band gap that exceeds two electron volts. 
     
     
         24 . The device of  claim 21 , further comprising:
 a second diode, wherein the encapsulant covers the second diode, and wherein the second diode emits light.   
     
     
         25 . The device of  claim 24 , wherein each of the diode and the second diode has a gallium nitride (GaN) layer. 
     
     
         26 . The device of  claim 21 , wherein the circuitry determines the temperature of the diode by supplying a constant current to the diode. 
     
     
         27 . The device of  claim 26 , wherein the constant current never exceeds ten milliamps. 
     
     
         28 . A device comprising:
 a first diode;   an encapsulant through which light is emitted, wherein the encapsulant covers the first diode, and wherein the encapsulant has a temperature; and   circuitry adapted to use the first diode to determine the temperature of the encapsulant.   
     
     
         29 . The device of  claim 28 , wherein the first diode has a gallium nitride (GaN) layer. 
     
     
         30 . The device of  claim 28 , wherein the first diode has a band gap that exceeds two electron volts. 
     
     
         31 . The device of  claim 28 , wherein the encapsulant contains phosphor. 
     
     
         32 . The device of  claim 28 , further comprising:
 a second diode, wherein the encapsulant covers the second diode, and wherein the second diode emits the light.   
     
     
         33 . The device of  claim 32 , wherein each of the first diode and the second diode has a gallium nitride (GaN) layer. 
     
     
         34 . The device of  claim 32 , wherein the first diode and the second diode have the same structure, and wherein the second diode emits light with a wavelength between 445 and 455 nanometers. 
     
     
         35 . The device of  claim 28 , wherein the circuitry determines the temperature by supplying a constant current to the first diode and by sensing a voltage across the first diode. 
     
     
         36 . The device of  claim 28 , wherein the first diode is supplied with a current that never exceeds ten milliamps. 
     
     
         38 . A device comprising:
 a first diode that has a temperature;   a second diode, wherein each of the first diode and the second diode has a gallium nitride (GaN) layer;   an encapsulant that covers the first diode and the second diode; and   circuitry adapted to determine the temperature of the first diode based on a voltage across the first diode.   
     
     
         39 . The device of  claim 38 , wherein the circuitry determines the temperature of the first diode by supplying a constant current to the first diode. 
     
     
         40 . The device of  claim 39 , wherein the constant current never exceeds ten milliamps.