I remember something I struggled with in the beginning.
It’s supposed to have a fixed voltage drop, right?
But what if I force 3V across its legs with a 3V battery?
The LED seem to still work.
But does it now have 3V across its legs?
This is where it’s good to know how a real-world battery actually works.
A real-world battery will have internal resistance.
So when you connect a battery directly to an LED, you actually have a resistor in series with the LED.
It’s just inside the battery.
And this resistor is usually very small.
Maybe 20 ohms.
So what happens is that the LED still gets 2V across it.
And 1V drops across the internal 20-ohm resistor instead.
1V across 20 ohms gives a current of 50 mA.
So you get 50 mA through your LED.
Too much for most standard LEDs.
Probably enough to reduce the lifetime of the LED multiple times.
But not too much to make it burn and die in a spectacular way.
Keep On Soldering!
Oyvind @ build-electronic-circuits.com
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