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I'm currently working on a project involving (I think 3mm, 1.5VDC) Infrared LEDs. However, due to my photoresistor, I think the current, voltage, or whatever (forgot) will vary greatly to minuscule amounts. So, do these LEDs need UVLOs? They are very, very sensitive and I've already wasted half the pack.

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3  
What are UVLOs? They need resistors. – Leon Heller Oct 15 '11 at 22:27
Google or Wikipedia works... – Francis Lau Oct 15 '11 at 22:30
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FL - Yes, Google does work. But too many answers like that to people who are attempting to assist is liable to do you no good. As Leon said, you need series resistors when driving LEDs OR to drive them with a controlled constant current. Dead LEDs are liable to be due to electrostatic damage, to which many LEDs are extremely sensitive, or to attempting to drive them from a voltage source. Google can provide vast amounts of information on the current way to drive LEDs. Use search terms LED constant current circuit. Then select images. – Russell McMahon Oct 16 '11 at 6:36
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@Francis, Russel - Google and Wikipedia do work, but suggesting that people use those sites instead of actually answering the question is unhelpful. It's much better if we can have the information right here. Directing people to Google is one (necessary but not sufficient) sign that you're behaving like a help vampire or like a generally helpful person who has been sucked dry by help vampires. – Kevin Vermeer Oct 16 '11 at 21:46
@Francis - You want us to help you, but if we ask for information you say "Hey, I'm not gonna tell you, you have to look it up." Arrogance. Do you still want us to help you? I don't know what UVLOs are, I'm not going to look it up, so I'm afraid I can't answer your question. – stevenvh Apr 17 '12 at 10:08

2 Answers

up vote 8 down vote accepted

No.

LEDs are not damaged by low voltages.

If you are damaging LEDs, you must be driving them beyond their rated currents. Show your circuit to receive advice.

In general, very few electronic components are damaged by undervoltage. Some microprocessors can mis-execute in a brownout condition, which could have undesirable effects depending on the application. And Li-Ion batteries should not be discharged to too low a voltage.

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up vote 1 down vote

LEDs cannot be damaged by "forward" voltages that are so low that they do not draw rated current.

They can be damaged by voltages that are low by normal standards.
An infrared LED may easily be destroyed by a 3V3 or 5V power supply if current in excess of its maximum rated current flows.

LEDs are intended to be driven by either a constant current source of by a voltage source and a resistor such that. In both cases, maximum current is less than rated current.

In your circuit, worst case current must NEVER be able to exced maximum rated value.

LEDs may be damaged by reverse polarity voltage. Current drawn will be small, even when there is enough voltage to kill the LED.

Many LEDs are prone to electrostatic damage from "static electricity". Handling LEDs without wearing an earth strap or taking equivalent precautions may be enough.

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