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Topic: Myth - ALL LED'S require Resistors or.... (Read 23646 times) previous topic - next topic

liuzengqiang


Unless the voltage is able to rise from 3.2 to 4.2+

Nothing will happen, i'd be more worried about the voltage regulator being faulty... if you wish to prove me wrong please do so with actual proof


"Not using current limiting will damage the LED"

Wrong...  so if i take a 5mm LED supply exactly 2v until it glows you CLAIM  that it will one day fail because theres no current limiting action?

No it wont so stop telling me it will....

Me and Mike pointed to you multiple times fluctuating voltage supply was NOT what we meant. Voltage is constant!! Current is NOT!

I give you one last chance before I ignore you completely. Here is an undergraduate report done possibly in a minority-serving university. The author did some study of one diode at two temperatures. Please read this graph and answer one simple question to prove you actually an intelligent human and not a machine: at 0.3V fixed voltage (i.e. regulated), what are the currents through the same diode at 293K and 353K (FYI, the K is Kelvin temperature)? Hint: one is about 3 times the amount of the other. They ARE under the exactly same voltage, mind you.

Answer:
293K ______mA
353K ______mA

Help me ignore you, please!
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter

thepenguin

#91
Aug 03, 2013, 12:27 am Last Edit: Aug 03, 2013, 12:38 am by thepenguin Reason: 1

Quote
Some people prefer elegance to safety (there is a reason we don't all drive SUVs).

So simple equals elegant? You will love these elegant solutions
http://failblog.cheezburger.com/thereifixedit/tag/duct-tape
They are the same thing as you advocate.

I would consider a good deal of them to be elegant solutions (as long as the repair is functional, and the device continues to serve its intended purpose).  A good deal of ingenuity  is required to take a solution other than "it's broken, buy another one", and I greatly applaud the repair men for their efforts (as long as the device continues to work, not like that traffic light on the wrong side of the pole, which is by no means elegant).


Quote
Also, Mike, I don't think anybody here is building production electronics with their arduinos, as this is not what they are intended for.  We just pull out one LED and insert another.

I think you will find there are very few people here with that philosophy. Temporary functionality is setting the bar very low.

Temporary functionality is as high as I would be willing to set the bar for anything open-source, Mike.  I'm more of a fan of closed-source, because I have yet to find an open-source piece of software that measures up to its closed-source counterpart.  I am not saying that there isn't a single open-source program that beats out a similar closed-source program, but it would seem that there would be more incentive to create good software if you are actually going to control the software.  The same logic may be applied to hardware.  I would think that people would try to use a better system for production electronics, but whatever floats their boat is fine.


Quote
The fact of the matter is that LEDs work without a resistor in series.  I make no claim as to lifetime, performance, or other specifications, I merely state that they do, in fact, work.

Sure they do. What you fail to understand is that there has to be something that limits the current, that need not be a resistor although it is one f the simpler options. That something can be some explicit circuitry or some accidental factor of a specific setup, like the impedance of a battery.

As far as I can tell, resistors limit voltage, not current. I know that ?V=IR, or that the voltage drop across a resistor is equal to the current flowing through it times the resistance.  However, it effectively limits the current because the voltage across the LED keeps decreasing (eventually to zero), and thus the LED still dies.

cjdelphi

http://flashlightwiki.com/Driver#Direct_Drive

You religious resistor freaks need to understand that your piddly little LEDs which (wont die if stable voltage is supplied) and high powered ones are not the same hence direct drive!

liuzengqiang


http://flashlightwiki.com/Driver#Direct_Drive

You religious resistor freaks need to understand that your piddly little LEDs which (wont die if stable voltage is supplied) and high powered ones are not the same hence direct drive!


You are so forth ignored. You are also reported for language FYI.
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter

nickgammon


As far as I can tell, resistors limit voltage, not current.


I don't know about that. Since the LED is a non-linear device the voltage drop across the resistor will be constant and thus the resistor limits current, due to Ohm's Law.

Read this:

http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

nickgammon


If you supply the correct voltage and it's a clean voltage the LED does not require current limiting....


Try Wikipedia:

http://en.wikipedia.org/wiki/Led#Power_sources

Quote

Power sources

The current/voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can cause a large change in current. If the maximum voltage rating is exceeded by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies, or driving the LED at a voltage much below the maximum rating. Since most common power sources (batteries, mains) are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor.


My emphasis.

It clearly states that you require constant current, not constant voltage. Note the warning about "potentially damaging or destroying the LED".
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

liuzengqiang

Nick,

You're wasting your breath. Just lock the thread and walk away if you don't want to further waste your time. It's not like you didn't try or I didn't try or Mike didn't try. These people can't be reasoned with and now the OP has resorted to name calling. I urge you to lock thread and remove his posting right until he can speak politely again, as a good example we don't tolerate this behavior.


http://flashlightwiki.com/Driver#Direct_Drive

You religious resistor freaks need to understand that your piddly little LEDs which (wont die if stable voltage is supplied) and high powered ones are not the same hence direct drive!
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter

nickgammon

I think you might be right. Time to calm down and do some serious work.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

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