Remote Living > Lighting

Voltage controlled LED drivers.

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Rembrant:
 You guys are amazing. I simply interred into a discussion that it seems you can't handle.

First, I have nothing to hide. my name is luke lucent, I live in Florida. I attended Pine Forrest High where I graduated(1999) with an B average. I later, attended the University Of West Florida where I graduated(2004) with a B average. The real kicker is? I actually paid for it my self, with a real job. Second, I am not so arrogant as to claim I am the MASTER of anything. Third, I never was rude or disrespectful to anyone. In fact, I didn't just burst on to the scene proclaiming anything. Perhaps it is true that some of you have become over emotional and broke out the instant blinders.

  I'll get right to the point. You are teaching the wrong information about LEDs. A current controlled LED driver will simply not do the job when powering an LED. It has a specification for a reason. The manufacturer of said product actually knows more about it than you all. Fourth,(I count pretty good too) The Point of this master class is what? to prove that you can power an LED with a current driver. You sure can, but efficiency and product life will suffer when you begin to drive the device with more voltage than it was rated for. Thats why it has a rating at all.
The truth about the LED is that if powered by a regulated source at the manufacturers voltage specification it will draw a predictable current and produce a predictable amount of light. If it doesn't, it is defective. It is true that if the voltage is steady the current is steady.
The benefits of an all parallel device are evident. Easy replacement, being the most notable and the fact that if one goes out, you don't lose a whole string. So now we have got all of the LEDs powered Correctly and we have maximized the use and regulation. All without an overcomplicated circuit that only regulates the current and forgets about the voltage.
Now what is left? I would suppose that we want our light to be efficient as well. Why not design a PWM circuit that will power the voltage regulated Driver and regain some of the power lost from a linear voltage conversion? Ever heard of a class D amplifier or maybe a computer power supply.
 To you all I am an idiot. So you can ready up on such dumb ideas from other "Posers" here www.rebelwolf.com/essn/ESSN-Jun2005.pdf

and here www.elecdesign.com/Articles/ArticleID/9254/9254.html

Or some other interesting things about PWM and LEDs that only Posers can get to by searching here http://www.google.com/search?q=LED+PWM+NASA

hell even some of us posers are directly controlling LEDs with PWM and making them brighter. Certainly, everyone at NASA is a huge poser.

BruceDownunder:
Rembrant,,,
I sort of got some interest in the middle of your posting ,,, the first paragraph must have been when you were finishing off your, "mrs Palmer and her 5 daughters act" ,,
anyhow ,most of us here are fairly stable ,,so keep in touch ,,you might make the grade..
fair dinkum ,,you are a first class wanker.
(I'll surely be banned for this,at 62 who gives a $#|+)
Sorry Admin--I've read this post for an hour and I'm furious
bruce

ruddycrazy:
OK Rembrant I think what Bruce said is the sentiment of the majority of us now just to shoot your theory on led's being voltage controlled heres a link to a Dallas application note where they state
 'LEDs are current-driven devices in which the light output depends directly on the forward current passing through them.'
http://www.maxim-ic.com/appnotes.cfm/appnote_number/1804/CMP/WP-37
Now do you think that a company that makes led's would lie to their customers
I think NOT
So if you can't be nice to the members of this great forum do us all a favour and dont bother coming back here
 Just my 2.2 cents worth and Admin's if your going to ban Bruce for fessing up what we all think that will be a dark day on feildlines.
Bryan
.

dinges:
"The truth about the LED is that if powered by a regulated source at the manufacturers voltage specification [...] "
Perhaps you've missed Amanda's explanation that there IS no set voltage; it varies, not only per batch but also by temperature. And that current varies a lot as supply voltage varies a little.
"It is true that if the voltage is steady the current is steady.". Yep. But it's a big 'if'. If temperature of the environment varies, Vf varies a little and If will vary a lot more. As the LED heats up its Vf and thus If (in a voltage source) will vary. In a current source, If will stay the same no matter the temperature, Vf of the LED, etc.
There's little doubt in my mind why others, with more electronics knowledge than I have (unlike you, I'm just self-educated on the topic) don't bother to answer you. Your statement is so wrong as to be looking like a troll post.
In fact, the way you behave in here (when newbies start throwing tantrums, I immediately assign the 'troll' label to them; call me a bigot), I think you are.
By all means, power your LEDs by a voltage source. But if you start exhibiting incorrect information in here, expect to be criticized. 'Truth' is written with a capital 'T' in here.
'Why not design a PWM circuit [...]'
I'd say, put your money where your mouth is. Amanda has given us some simple circuits; why don't you give us a much better one, a PWM driver for the LEDs?

ghurd:
I go through a LOT of LEDs.
"It has a specification for a reason. The manufacturer of said product actually knows more about it than you all."

LED data sheets are like toilet paper, only intended to be used once, then thrown away.
"The truth about the LED is that if powered by a regulated source at the manufacturers voltage specification it will draw a predictable current and produce a predictable amount of light. If it doesn't, it is defective."
Most of my data sheets for white LEDs say 3.6V and 20ma. One says 3.6V and 15ma.

If we find an LED that meets both those numbers at the same time (or even close), it goes straight into the trash.  It probably doesn't happen 1 in 5,000.
Maybe they are sending me 99.98% defective parts. Thank goodness.  

I would not want LEDs meeting the data sheet specifications.
Don't let us stop you.  By all means, build a white LED bulb with 50 parallel LEDs being fed 3.6V, then run it 24/7 for a few weeks.

G-

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