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Subject: Re: What is maximum current for LED?
Date: Wed, 02 Oct 2002 16:26:38 +0200
Organization: Ingenieurbuero Erckert
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Do you have any idea of the thermal properties of the package (Rth,
thermal capacity)? Pulses must be short enough to prevent exceeding the
maximum permissible junction temperature. If the thermal resistance of
the package is too high your diode must be operated with pulses short
enough that the thermal capacity can swallow the energy (usually below
Limit no. 2 is electromigration of the metalization. Typically life time
of the metal traces halfs at a temperature increase of 6K or at a
current increase of 10% (at constant temperature).
Normally metalization is designed for 10000h at 125 Celsius or 150
Celsius (at least these are the standards for automotive ICs. Some high
performance CPUs are designed for far less!).
Your stress is the peak current and the operation time multiplied with
the duty cycle.
Boris Nogoodnik schrieb:
> Interesting question. Specs give you constant current ratings that won't damage
> them. Damage is caused mainly by overheating. However, there is one human
> vision factor. If you use pulses instead of constant current, thy still will
> look as bright as on constant current, but will dissipate much less power. So
> here you can make them look much brighter by exceeding the maximum current in
> pulses, but still keeping the average current well under the specs.
> "Nelson Win" wrote in message
> > I bought a few high brightness 3mm LEDs (various colors: R,G,B,W) and
> > the specs mention a forward current (If) of 20mA and peak current (If
> > (peak)) of 100mA (160mA for red). The specs don't say anything about
> > the current beyond that, nor what the recommended maximum current
> > should be. There's not even a brand name on the LEDs so I can
> > approach the manufacturer. I want to squeeze the brightest light I
> > can from the LEDs without prematurely burning them out. Does anyone
> > have any experience here to recommend a maximum current? The LEDs will
> > flash on and off at a frequency of a few hertz, 50% DC, for a duration
> > of a couple or hours at a time. Any advice appreciated.
> > Regards,
> > Nelson
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