How long will a 1W LED last without a heat sink?

[tperry724]

Folks, got a project here that uses a 1W LED.  I've got a power supply adjusted to just over the forward voltage of the LED - about 3.7V.  The LED definitely runs warm/hot.  How long will it last without a heat sink attached?  

Thanks,

Tony

[missdrew]

Anywhere from 1 second to forever. The datasheet MAY tell you.

[srnet]

Why dont you try it, in a suitable flameproof place of course ?

[tperry724]

Well, I'll just give it a go.  I bought the LEDs direct from China so no datasheet for these.  If it burns out, I'll find a heat sink around here and get some thermal glue.  

[Paul_KD7HB]

Folks, got a project here that uses a 1W LED.  I've got a power supply adjusted to just over the forward voltage of the LED - about 3.7V.  The LED definitely runs warm/hot.  How long will it last without a heat sink attached?  

Thanks,

Tony

The connections between the LED and the power are the heat sink in your case. There is always a heat sink. You may add other heat sinks by mounting the LED on a printed circuit board with large copper pads.
Paul

[DVDdoug]

I've got a power supply adjusted to just over the forward voltage of the LED - about 3.7V.

Does that mean you're using a regular power supply with no current control?   


High power LEDs (1W or more) normally use a special constant current (or controlled current) power supply.

If you don't know what the current is, you could be way-more or way-less than 1W.   It will probably last forever at 1/10th of Watt...     LEDs (like all diodes) are highly non-linear and small change in voltage makes a HUGE change in current.   On the other hand, with the proper constant-current power supply the voltage "magically" falls into-place.

With "regular little LEDs" we use a series resistor, and with a known-constant voltage drop across the resistor we can calculate/control the current.  You can use a resistor with high-power LED but it has to be a "high power" resistor (about the same wattage as the LED, depending on the voltage & current of course) and the resistor is wasting power & generating heat.

...Somewhat ironically, LEDs run a lot cooler than a regular light bulb of the same light output but an LED can't take anywhere the heat that a tungsten filament can take.  So, it it's running cooler but it still needs a heatsink.

[tperry724]

Thanks all.  Karma sent.

Best,

Tony

[tperry724]

Hi all.  The answer in my case is not long at all.  Ha.  Gonna need another solution.  

Tony

[SteveMann]

Hi all.  The answer in my case is not long at all.  Ha.  Gonna need another solution. 

Tony

And another LED.
show a picture of the LED. Is there a reason you can't use a heat sink?

[westfw]

uses a 1W LED.  I've got a power supply adjusted to just over the forward voltage of the LED - about 3.7V.

that's not going to work.  You need to limit the current.  Read some of the tutorials on LEDs (the same logic applies to 1W leds as to the normal 20mA LEDs, except that you design for a current of ~250mA to get the full watt.)

In the absence of a current limit, if the power supply voltage is slightly less than the actual Vf of the diode, you won't get much output, and if it's slightly more than the actual Vf, the diode will happily draw much more than 1W for as long as it lasts.

You should be safely able to drive a 1W LED with "small" currents (say, 0.3W @ ~100mA) for quite a while (but it wont be at maximum brightness.)