Is it generally advantageous (from a lifespan POV) to drive a LED at less than its maximum rating? I'm adding a power confirmation LED to a simple linear regulator. With the output voltage on this reg and the Vf and rated current of the LED I calculated a 405 Ohm matching resistor. It works fine and the LED is shining away at its (maximum) rated brightness. But will I be better off upping the resistor a bit so the LED is not running full tilt?
What matters is maximum current rating of the LED. As with anything else, the closer you push it toward its limits, the more likely you are to shorten life, not that it will shorten life - it's just more likely to happen. All things being equal, I tend to be somewhat conservative with voltage, current, and power ratings when I want to build something that will last a long time. I'll usually try to aim for around 70% to 90% of maximum ratings to stay within a "sweet spot" of value Vs performance.
Mike
Mike
Agree. And for indicators you rarely need to drive them hard. A few milliamps will usual be plenty bright.
The maximum current usually has other operational conditions attached.
Exceed any single of the group of conditions and rapid failure is likely.
A normal 5mm LED probably has a maximum of around 20mA.
But it will light up (very dimly) at 0.5mA.
Noticeable @ 1mA, getting bright @ 2mA. Probably very annoying as a constant indicator in a listening room @ 4mA
If you need a warning alarm then a flashing indicator is more noticeable.
Exceed any single of the group of conditions and rapid failure is likely.
A normal 5mm LED probably has a maximum of around 20mA.
But it will light up (very dimly) at 0.5mA.
Noticeable @ 1mA, getting bright @ 2mA. Probably very annoying as a constant indicator in a listening room @ 4mA
If you need a warning alarm then a flashing indicator is more noticeable.
I pulled the most convienent 1206 SMD I had and replaced the one that was on the PCB. The LED is now pulling about 11mA. Still plenty bright but derated to about 50%, which should give it a nice long life.
I recall seeing spec sheets from a major LED manufact which showed marked loss of 'brightness' over time as the current was increased.
As you need an indicator and not a spot-light running the LED at 1 or 2ma is fine.
I built an amp with a neon bulb power indicator, tweaked it so it flashed, and everyone thought it indicated a problem!
As you need an indicator and not a spot-light running the LED at 1 or 2ma is fine.
I built an amp with a neon bulb power indicator, tweaked it so it flashed, and everyone thought it indicated a problem!
Very generally speaking, maximum ratings will indicate the conditions that exceed what the die or wire bonds can handle.
After avoiding catastrophic damage, the next consideration is lifetime. LED intensity will degrade over time, at a rate that is roughly proportionate to the current. A hard-driven LED may take thousands or even tens-of-thousands of hours to noticeably change. If it is an always-on LED, then we are talking months or a few years for it to dim appreciably.
If operation is intermittent or kept to a fraction of absolute max current, then it will last at least as long as the rest of the components.
After avoiding catastrophic damage, the next consideration is lifetime. LED intensity will degrade over time, at a rate that is roughly proportionate to the current. A hard-driven LED may take thousands or even tens-of-thousands of hours to noticeably change. If it is an always-on LED, then we are talking months or a few years for it to dim appreciably.
If operation is intermittent or kept to a fraction of absolute max current, then it will last at least as long as the rest of the components.
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