METHOD AND TESTING EQUIPMENT FOR LEDs AND LASER DIODES

• US 20080205482A1
• Filed: 02/23/2007
• Published: 08/28/2008
• Est. Priority Date: 02/23/2007
• Status: Active Grant

• Current Assignee: Epistar Corporation
• Original Assignee: CAO Group, Inc.
• Inventors: Cao, Desen, Lin, Zhao-hui
• Granted Patent: US 7,651,268 B2
• Time in Patent Office: Days
• US Class Current: 374/178
• CPC Class Codes: G01K 11/00 Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
• CPC Class Codes: G01K 15/00 Testing or calibrating of thermometers
• CPC Class Codes: G01K 15/005 Calibration
• CPC Class Codes: G01K 7/01 using semiconducting elements having PN junctions G01K7/02, G01K7/16, G01K7/30 take precedence
• CPC Class Codes: G01R 31/2635 Testing light-emitting diodes, laser diodes or photodiodes

Abstract

The present invention is a non-invasive method and associated apparatus for determining the junction temperature for an LED or laser diode (collectively “LED”). First a sample LED is placed in a heat chamber and the change of the LED'"'"'s peak wavelength is recorded over time, as is the change in the temperature in the heat chamber. Since the heat chamber supplies the major component to the junction temperature, dwarfing the other components, it is a reasonable proxy for true junction temperature. The data is compiled to determine change of peak wavelength as a function of temperature and that function can then be used to determine junction temperature of similar LEDs that are installed in a system or manufactured. The invention may also be used to measure other useful data, such as power, output power changing with the junction temperature and intensity of the LED over time and may be used to estimate failure rate.

Claims

1. A method of determining junction temperature for an LED, the method comprising:

a. Placing a sample LED in a heat chamber;

b. Powering the sample LED with a forward pulse current;

c. Heating the chamber and recording a temperature of the heat chamber as a function of time;

d. Measuring change in a peak wavelength of the sample LED as a function of time;

e. Determining the function of the change of the peak wavelength as a function of temperature

f. Using the function of the change of the peak wavelength as a function of temperature to determine junction temperature of a second LED, identical to the sample LED, by measuring a peak wavelength of the second LED for use in the function.

2. The method of claim 1 being used to determine the junction temperature of a white LED, wherein the measured peak wavelength is a spectral blue peak.

3. A method for determining the junction temperature of an LED, the method comprising:

a. Determining the peak wavelength emitted by the LED;

b. Comparing the peak wavelength to a given function relating the peak wavelength of an identical LED to junction temperature;

c. Determining the junction temperature based upon the temperature associated with the measured peak wavelength in the given function.

4. A method for continuous monitoring of an LED'"'"'s junction temperature comprising the method of claim 3 being continuously applied.

5. The method of claim 3, being utilized for a white LED, wherein the peak wavelength is the spectral blue peak.

6. A method for continuous monitoring of an LED'"'"'s junction temperature comprising the method of claim 5 being continuously applied.

7. A method of determining the power output of an LED as a function of temperature, the method comprising:

a. Placing a sample LED in a heat chamber;

b. Powering the sample LED with a forward pulse current;

c. Heating the chamber and recording a temperature of the heat chamber as a function of time;

d. Measuring change in the spectrum of the sample LED as a function of time;

e. Determining the function of the change of the spectrum as a function of temperature;

f. Integrating the function of the change of the spectrum as a function of temperature to obtain power output as a function of temperature for the sample LED.

g. Using the function of power output to determine the power output of a second LED, identical to the sample LED, based on an emitted peak wavelength.

8. The method of claim 7 being used to determine the power output of a white LED, wherein the measured peak wavelength is a spectral blue peak.

9. A method for determining the power output of an LED as a function of temperature, the method comprising:

a. Determining the peak wavelength emitted by the LED;

b. Comparing the peak wavelength to a given function relating the peak wavelength of an identical LED to junction temperature;

c. Determining spectral data and a resultant spectrum as a function of temperature from the given function;

d. Integrating the spectrum to determine power as a function of temperature

10. A method for continuous monitoring of an LED'"'"'s power as a function of temperature comprising the method of claim 9 being continuously applied.

11. The method of claim 9, being utilized for a white LED, wherein the peak wavelength is the spectral blue peak.

12. A method for continuous monitoring of an LED'"'"'s power as a function of temperature comprising the method of claim 11 being continuously applied.

13. An apparatus for determining junction temperature of an LED, the apparatus comprising:

a. An optical detector;

b. A spectrometer;

c. A computer, said computer being programmed with software for comparing peak wavelength data to peak wavelength data for an identical LED in relation to temperature.

14. An apparatus for determining an LED'"'"'s junction temperature in relation to spectral data, the apparatus comprising:

a. A heat chamber, said heat chamber further comprising a mounting structure for and capable of delivering electrical current to an LED and an observation window;

b. A power supply capable of delivering a forward pulse current, operatively connected to the mounting structure;

c. A thermocouple situated inside the heat chamber;

d. A spectrometer and optical detector situated to measure spectral data emitted from an LED;

e. A computer, operatively connected to the spectrometer and thermocouple;

Wherein the computer stores and compiles data obtained from the spectrometer and thermocouple to derive spectral data of an LED as a function of temperature.