# Would a LED short itself?

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#### Mr. Man-wai Chang

Jan 1, 1970
0
Oh, now that things are getting real and you're losing face, you want
to bail in order to cut your losses?

"Face" was never my objective. I just want to use fewer parts.
Figures...
Do you even know how to use a current-limiting resistor?

V=IR?

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M

#### Mr. Man-wai Chang

Jan 1, 1970
0
That works because the current in a series circuit is everywhere the
same and if the LED drops a certain voltage with a peculiar current
through it, the current limiting resistor must drop the difference
between the supply voltage and the LED's voltage, across itself, with
that same current through itself.

Could I ignore the voltage drop at the LED and just use a resistor to
limit the current in the circuit to 20mA? That is,12V/20mA in your example.

The LED might be at its maximum brightness though....

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#### Jasen Betts

Jan 1, 1970
0
Could I ignore the voltage drop at the LED and just use a resistor to
limit the current in the circuit to 20mA? That is,12V/20mA in your example.

You can do that, you won't get full current, and thefore won't get full
brightness. many times full brighness isn't needed or even desirable,
and by running the LED at reduced power you increase its lifetime.
The LED might be at its maximum brightness though....

huh? It definately won't.

M

#### Mr. Man-wai Chang

Jan 1, 1970
0
huh? It definately won't.

Dammit.. I left out "not" in that sentence... T.T

--
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M

#### Mr. Man-wai Chang

Jan 1, 1970
0
As soon as you removed the short though, the drop across the LED would
take away from the drop across the resistor, causing less current
through the circuit than in the shorted case, making the LED less
bright.

Dammit.. I left out "not" in that sentence... T.T

--
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M

#### Mr. Man-wai Chang

Jan 1, 1970
0
Oh, now that things are getting real and you're losing face, you want
to bail in order to cut your losses?
Figures...

Have you ever studied seriously about LED and high current from the
perspective of material science?

Could current-limiting resistor for LED be nothing but a superstition
among electronic engineers? Objective is to sell more resistors?

--
@~@ Remain silent. Nothing from soldiers and magicians is real!
/ v \ Simplicity is Beauty! May the Force and farces be with you!
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T

Jan 1, 1970
0
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#### Daniel Pitts

Jan 1, 1970
0
By just applying 3V over the LED, it would draw whatever current needed?

Summarizing the replies from the answers, most said that the LED might
**NOT** always just blow like a fuse. And that's the main reason of
using a current-limiting resistor.

If LED would always die like a fuse without shorting itself, then there
should not be a need for a resistor.
You need to current-limiting resistor to *prevent* the LED from dieing,
unless you want your LED to die.

It is also possible that it will draw enough current to damage other
circuits *before* it finally lets out the magic smoke.

Resistors are *extremely* cheap. LEDs are only moderately cheap. If you
can save your LEDs by adding something that is 1/10th of the cost of

D

#### Daniel Pitts

Jan 1, 1970
0
continue the thread. There is a difference between being dense (as Mr.
Chang appears to be) and being a Troll (which by this post alone seems
to match you).

D

#### Daniel Pitts

Jan 1, 1970
0
Have you ever studied seriously about LED and high current from the
perspective of material science?

Could current-limiting resistor for LED be nothing but a superstition
among electronic engineers? Objective is to sell more resistors?
Ha.

No, I have actually burned out LEDs. I have also burned out chips which
were trying to power the LEDs. I have studied the fundamentals of how
diodes in general work, and LEDs are a type of diode.

Resistors are so cheap I can't imagine a large enough profit margin on
them to justify such a conspiracy.

M
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