LED lighting device with temperature dependent output stabilizer
A lighting device has a plurality of LEDs of at least two types connected in series. At least one of the LEDs of the first type and LEDs of the second type is connected in parallel to a resistor assembly, such that the temperature-dependent resistance of the resistor assembly stabilizes a ratio of luminous flux output at different junction temperatures of the LEDs.
1. A lighting device comprising a plurality of light emitting diodes, LEDs, the lighting device comprising:
a first LED assembly comprising at least one LED of a first type having a varying first luminous flux output as a function of its junction temperature;
a second LED assembly comprising at least one LED of a second type having a varying second luminous flux output as a function of its junction temperature different from the first luminous flux output of the first LED assembly as a function of its junction temperature,
wherein the first LED assembly is connected in series to the second LED assembly, and wherein at least one of the LEDs of the first type and LEDs of the second type is connected in parallel to a resistor assembly having a temperature dependent resistance, the temperature dependence of the resistance being adapted to increase a stabilization of, within a predetermined range, a ratio of the first luminous flux output to the second luminous flux output at different junction temperatures of the first LED assembly and the second LED assembly.
2. The lighting device of claim 1 , wherein the first luminous flux output decreases with increasing junction temperature of the first LED assembly at a first rate, and the second luminous flux output decreases with increasing junction temperature of the second LED assembly at a second rate lower than the first rate, a first resistor assembly being connected in parallel to at least one LED of the first LED assembly, and a second resistor assembly being connected in parallel to at least one LED of the second LED assembly, the resistance of the first resistor assembly increasing with increasing temperature of the first resistor assembly, and the resistance of the second resistor assembly decreasing with increasing temperature of the second resistor assembly.
3. The lighting device in claim 1 , wherein the LED of the first type is adapted to produce light having a first color, and wherein the LED of the second type is adapted to produce light having a second color different from the first color.
4. The lighting device in claim 1 , wherein the resistor assembly and the at least one of the LEDs of the first type and the LEDs of the second type connected in parallel thereto are thermally coupled.
5. The lighting device in claim 1 , wherein the junctions of the first LED assembly and the second LED assembly are thermally coupled.
6. The lighting device in claim 1 , wherein the LED of the first type is an AlInGaP type LED.
7. The lighting device in claim 1 , wherein the LED of the second type is an InGaN type LED.
8. A lighting system, comprising:
a dimmer having input terminals adapted to be connected to an electrical power supply, the dimmer having output terminals adapted to provide a variable current; and
a lighting device according to claim 1 , the lighting device having terminals configured to be connected to the output terminals of the dimmer.
9. The lighting device of claim 1 , wherein the first luminous flux output decreases with increasing junction temperature of the first LED assembly at a first rate, and the second luminous flux output decreases with increasing junction temperature of the second LED assembly at a second rate lower than the first rate, a first resistor assembly being connected in parallel to at least one LED of the first LED assembly, and the resistance of the first resistor assembly increasing with increasing temperature of the first resistor assembly.
10. The lighting device of claim 9 , wherein the first resistor assembly comprises a positive temperature coefficient, PTC, resistor.
11. The lighting device of claim 1 , wherein the first luminous flux output decreases with increasing junction temperature of the first LED assembly at a first rate, and the second luminous flux output decreases with increasing junction temperature of the second LED assembly at a second rate lower than the first rate, a second resistor assembly being connected in parallel to at least one LED of the second LED assembly, and the resistance of the second resistor assembly decreasing with increasing temperature of the second resistor assembly.
12. The lighting device of claim 11 , wherein the second resistor assembly comprises a negative temperature coefficient, NTC, resistor.
13. A method of producing a lighting device comprising a plurality of light emitting diodes, LEDs, the method comprising:
providing a first LED assembly comprising at least one LED of a first type having a varying first luminous flux output as a function of its junction temperature;
providing a second LED assembly comprising at least one LED of a second type having a varying second luminous flux output as a function of its junction temperature different from the first luminous flux output of the first LED assembly as a function of its junction temperature;
connecting the first LED assembly in series to the second LED assembly;
connecting at least one of the LEDs of the first type and the LEDs of the second type in parallel to a resistor assembly having a temperature-dependent resistance; and
adapting the temperature dependence of the resistance to increase a stabilization of, within a predetermined range, a ratio of the first luminous flux output to the second luminous flux output at different junction temperatures of the first LED assembly and the second LED assembly.