# How do you make a LED to short itself?

Discussion in 'Electronic Basics' started by Mr. Man-wai Chang, Jul 5, 2013.

1. ### Mr. Man-wai ChangGuest

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2. ### Mr. Man-wai ChangGuest

I just want to know whether it could be done. Everyone said it's safer
to assume that LED would short itself.

Now, how could we prove that LED would really do it using experiments?

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3. ### Daniel PittsGuest

Yes, put an amp meter in line with the LED and start raising the voltage
across. You'll see the amperage raise rapidly as you approach the
voltage drop of the diode, indicating it acts like a short until it
burns out.

Another way to do this is to put a resistor and LED in series with a
variable voltage source. Measure the voltage across the Resistor as you
increase the voltage of the source. After you reach the rated voltage
of the LED, you'll see the rest of the going across the resistor, no
matter how much more voltage you add (until you burn them both out, of
course).

4. ### Jasen BettsGuest

I did that once, 100mA at 5V about 1 hour on a fairly ordinary red LED,
then it failed open. which if the semiconductor junctions is
responsible for 2V of the drop a inticates about 33 ohms ohmic
resistance.

5. ### whit3rdGuest

If there is a need for a diode to fail in short circuit, there ARE some
surge-protection diodes that do that (Zener types).
As for LEDs, the failure modes can include low light output
or fused (open circuit) bond wires. Or, presumably, short circuit.

But, I'm not aware of any LED types that can be expected to become short
circuits under any reasonable conditions. If you really WANT
the LED to be replaced with a short, use a relay.

6. ### Mr. Man-wai ChangGuest

Just wanna prove that LED could short itself under the right
conditions....

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7. ### Daniel PittsGuest

Did you read my earlier reply? It answers exactly why it should be
*treated* as a short, even if it doesn't fail as a short.

8. ### Mr. Man-wai ChangGuest

That's why I am interested in devising an experiment to make it
happen...

What all of you said is: do NOT treat a diode as a resistor or a fuse.

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9. ### Daniel PittsGuest

And I devised such an experiment. Did you try it? What did you observe?

10. ### Mr. Man-wai ChangGuest

Not yet... busy with something else. Relevant messages copied.

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11. ### Daniel PittsGuest

In other words, you've run out of steam to troll on the topic?

You've been obsessed with this since it was first mentioned, and once
someone gives you a 30 minute experiment to try, suddenly you've got no
time?

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