Granted Patent B2

US 9,161,415 · App. 14/177,673 · Granted Oct 13, 2015

Abstract

Claims (48)

1. A method for determining a temperature of at least one light-emitting diode (LED) in a circuit which includes a power supply for powering the LED, where the LED is operable to generate light, the method comprising:

providing an operating current and an operating voltage to the LED;

superimposing a current pulse on the operating current;

sensing a magnitude of a voltage pulse across the LED resulting from the applied current pulse superimposed on the operating current; and

determining an operating temperature of the LED at the provided operating current based on a magnitude of the current pulse and the magnitude of the voltage pulse.

2. The method according to claim 1 , further comprising:

before providing the operating current, providing an initial operating current and initial operating voltage at a known initial temperature of the LED;

determining at least one LED parameter based on the initial operating current, initial operating voltage, and initial temperature, the operating temperature being determined based in part on the LED parameter.

3. The method according to claim 2 wherein the initial operating current and initial operating voltage are provided at a time when the LED has reached a resting temperature that is essentially the same as an ambient temperature around the LED.

4. The method according to claim 3 wherein determining the operating temperature includes using the LED parameter in the ideal diode equation

I

=

I

o

⁢

exp

[

V

-

E

g

AkT

]

,

where I is the operating current, I o is a constant, V is the voltage applied across a diode junction of the LED, E g is the effective optical band gap of the semiconductor at the diode junction, A is the diode factor, k is Boltzmann's constant, and T is the operating temperature in degrees Kelvin.

5. The method according to claim 4 wherein the LED parameter is related to the effective optical band gap of the LED.

6. The method according to claim 4 wherein the LED parameter is used to determine a current to voltage curve for at least one temperature.

7. The method according to claim 1 wherein superimposing includes selecting a power supply that exhibits a ripple current and using the ripple current as the current pulse.

8. The method according to claim 1 wherein superimposing the current pulse on the operating current produces a temporary change in the light level from the LED that is imperceptible to humans.

9. The method according to claim 1 , wherein the LED is operable at a temperature less than a maximum temperature and is subject to thermal damage at a damage temperature exceeding the maximum temperature, the method further comprising:

comparing the operating temperature with the maximum temperature; and

reducing the operating current responsive to the operating temperature exceeding the maximum temperature.

10. The method according to claim 1 wherein the superimposed current pulse lowers the magnitude of the operating current to a value that is less than another value of the operating current that would otherwise be present without the superimposed current pulse.

11. The method according to claim 1 wherein the circuit comprises a thermistor electrically connected to the LED and positioned in a thermal pathway to receive heat from the LED.

12. The method according to claim 11 wherein the thermistor is electrically connected in parallel with the LED.

13. The method according to claim 1 further comprising receiving, with a ballast, a utility power in the form of a utility alternating current and a utility alternating voltage, the alternating voltage having a root-mean-square voltage over 100 Volts, and wherein providing the operating current to the LED includes converting the utility alternating current into the operating current using the ballast, the ballast having a size smaller than a volume envelope of a conventional single gang junction box.

14. The method according to claim 1 further comprising determining multiple operating temperatures at multiple different times and saving values of the temperatures and times at which the temperatures were determined to determine an overall operable lifetime of the LED.

15. The method according to claim 14 further comprising determining the overall operable lifetime of the LED based at least in part on the multiple operating temperatures and the multiple times at temperature.

16. The method according to claim 15 further comprising indicating the overall operable lifetime of the LED to a user.

17. The method according to claim 15 further comprising providing the determined overall operable lifetime of the LED to a system that monitors power usage.

18. The method according to claim 15 , wherein the operation lifetime increases when the LED is operated with the operating temperature below a maximum operating temperature, the method further comprising:

comparing the operating temperature with the maximum temperature; and

reducing the operating current to reduce the operating temperature below the maximum operating temperature.

19. The method according to claim 1 wherein there are at least two LEDs in the circuit and wherein the superimposed current pulse includes a frequency component at a predetermined frequency, the method further comprising passing the current pulse to a first LED while blocking the current pulse to the second LED based on the frequency component and wherein the determined operating temperature is the operating temperature of the first LED.

20. The method according to claim 1 wherein the determined operating temperature is a first operating temperature which occurs at a first time and further comprising determining a second, different operating temperature at a second, different time.

21. The method according to claim 1 wherein the provided operating voltage is between 1.5 Volts and 2.5 Volts DC.

22. The method according to claim 1 wherein the superimposed current pulse is a current ramp having a plurality of current magnitudes and the sensed voltage pulse is a voltage ramp having a plurality of voltage magnitudes corresponding to the current magnitudes such that the operating temperature is determined based on a curve relating a log of a plurality of the currents against a corresponding plurality of voltages.

23. The method according to claim 1 wherein superimposing the current pulse, sensing the voltage pulse, and determining the operating temperature are performed periodically.

Assignments (10)