Why'd my LEDs pop?

"Anthony Fremont" <spam@nowherest.com> wrote in message
news:125s0p43ut6is70@news.supernews.com...
"Phil Allison" <philallison@tpg.com.au> wrote in message
news:4c6ckbF13vhdoU1@individual.net...

"Anthony Fremont"



** FUCK the HELL OFF you STINKING ASSHOLE .

I guess you tried it for yourself. Enlightening wasn't it?
Click to expand...
Anthony,
Consider you've got one over Philthy Allison.
As soon as he starts swearing, you know he's lost the argument.

Cheers,
Alan
 
"Alan Rutlidge" wrote:
"Anthony Fremont" wrote:

I guess you tried it for yourself. Enlightening wasn't it?


Anthony,
Consider you've got one over Philthy Allison.
As soon as he starts swearing, you know he's lost the argument.
Click to expand...
Oh, I know. :) I hope he really did try it for himself. I noticed it
quite by accident when I connected a blue LED to the output of an op-amp
to clamp the peak output to the Vf of the diode, letting the op-amp
limit the max current thru the LED. The op-amp was biased at 2.5V and I
was sort of surprised to see the LED start glowing as soon as I plugged
it to the breadboard. Not blindingly bright (indicating the obvious
self limiting of the current), but clearly on. Just can't understand
why Phil has to have a conniption fit over it.
 
On Sun, 7 May 2006 19:51:26 +1000, "Michael C" <nospam@nospam.com>
wrote:

"Brian Goldsmith." <brian.goldsmith@NOSPAMMecho1.com.au> wrote in message
news:zui7g.24366
***** You really haven't got an effing clue,have you.Do you think you
might
be able to getit through your thick skull that LEDs are CURRENT operated
devices,measure the current Luke,measure the current!!!!!

You may well be right, I am a bit confused about what's going on here,
although there's no need for your childish rudesness. The reason I'm asking
Click to expand...
Brian has always been an idiot. Add him to your kill filter, its the
best thing you can do.

here is because I'm trying to get a better understanding. Surely the voltage
across the LED affects the amount of current going through it, hence they
Click to expand...
YOu are correct. This is basic ohms law.

will light up once a certain voltage is reached? Why isn't a household
lightbuld considered a "current operated device", surely it lights after a
certain current is reached.
Click to expand...
A houshold lightbulb is very different. It is purely resistive
(theoretically) piece if wire where as an LED is semiconducter.

OK, the problem with putting a whole heap of LEDs in series is that
each one may be slightly different. A small imperfection cause go one
to go short circuit then the rest are going to get more current.

Add to this, if your power source varies, then so will the current
flow through your string of LED's

Before we can help you with the correct sollution, you need to tell us
all details. What is the use? What is the expected power source and
how much can it vary (tolerence). What brand LED's are you using and
what is there stated foward voltage and current.
 
"E d" <tosser@dfat.gov.au> wrote

there are a number of rude posters here, just like anywhere.
but anyway....





***** Including moronic top posters!!!

Brian Goldsmith.
 
"Brenden" <brendenede@hotmail.com> wrote in message
news:n4o7g.24608$vy1.446@news-server.bigpond.net.au...
Michael,
There is a possible explanation for what you've experienced.

All LED's do not have an equal operational voltage, even those of the
same type. It varies with manufacture tolerances, some higher and some
lower, hence the datasheet gives a range of operation.

Those with a higher operational voltage will at any current of
operation, dissipate more power, turning it into heat and light. Thus
some LEDs get hotter than others.
Click to expand...
That makes sense. I suspected the power supply was giving a dirty DC signal
when testing a voltage reg with it. I tried the reg with a 9V battery and it
gave a certain voltage out, with 4 AAs it gave the same voltage but with the
DC power pack the voltage was different. The peaks wouldn't have shown in
the LEDs as they actually put out less light after a certain voltage.

To solve your problems, make sure you have pure DC, as much as possible,
then measure current of your chain running it through various resistors,
start with a value about 1K and reduce the resistor value until you get
to about 20mA through the chain. The use this value to run the LEDs
permanently.
Click to expand...
I've changed the design a bit now so that each LED will have it's own
resistor and they will all be in parallel, that way if one dies the others
will keep working.

Michael
 
"E d" <tosser@dfat.gov.au> wrote in message
news:e3kjnv$ifq$1@news-01.bur.connect.com.au...
there are a number of rude posters here, just like anywhere.
but anyway....
Click to expand...
Its appears to be greater in this group than other's for some reason.

this appears to be an informative article you may want to read:

http://217.33.241.242/download/Firstsight%20Vision/Tech%20Tips/LED-lighting.pdf
Click to expand...

Thanks, I'll have a look at it now.

Michael
 
"Anthony Fremont" <spam@nowherest.com> wrote in message
news:125sds9oc4o9lb0@news.supernews.com...
"Alan Rutlidge" wrote:

"Anthony Fremont" wrote:

I guess you tried it for yourself. Enlightening wasn't it?


Anthony,
Consider you've got one over Philthy Allison.
As soon as he starts swearing, you know he's lost the argument.

Oh, I know. :) I hope he really did try it for himself. I noticed it
quite by accident when I connected a blue LED to the output of an op-amp
to clamp the peak output to the Vf of the diode, letting the op-amp
limit the max current thru the LED. The op-amp was biased at 2.5V and I
was sort of surprised to see the LED start glowing as soon as I plugged
it to the breadboard. Not blindingly bright (indicating the obvious
self limiting of the current), but clearly on. Just can't understand
why Phil has to have a conniption fit over it.
Click to expand...
Unfortunately the occasional flashes of brilliance PA exhibits are grossly
overshadowed by incessant ramblings of incoherent spasms of abuse and foul
language. Obvously there's a wiring mix up in his brain or needs
re-programming?

Cheers,
Alan
 
Alan Rutlidge wrote:
Unfortunately the occasional flashes of brilliance PA exhibits are grossly
overshadowed by incessant ramblings of incoherent spasms of abuse and foul
language. Obvously there's a wiring mix up in his brain or needs
re-programming?
Click to expand...

Maybe a "Hard reset" would work? ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
Michael A. Terrell wrote:
Alan Rutlidge wrote:
Unfortunately the occasional flashes of brilliance PA exhibits are grossly
overshadowed by incessant ramblings of incoherent spasms of abuse and foul
language. Obvously there's a wiring mix up in his brain or needs
re-programming?


Maybe a "Hard reset" would work? ;-)


Generally he refuses to answer his unit calling if the voice is
Click to expand...
unfamiliar ... however its not that hard to gain entry if you have time .
 
On 2006-05-07, Michael C <nospam@nospam.com> wrote:
"Brian Goldsmith." <brian.goldsmith@NOSPAMMecho1.com.au> wrote in message
news:zui7g.24366
***** You really haven't got an effing clue,have you.Do you think you
might
be able to getit through your thick skull that LEDs are CURRENT operated
devices,measure the current Luke,measure the current!!!!!

You may well be right, I am a bit confused about what's going on here,
although there's no need for your childish rudesness. The reason I'm asking
here is because I'm trying to get a better understanding. Surely the voltage
across the LED affects the amount of current going through it, hence they
will light up once a certain voltage is reached? Why isn't a household
lightbuld considered a "current operated device", surely it lights after a
certain current is reached.
Click to expand...
the voltage at which they light isn't certain, and varies...

--

Bye.
Jasen
 
"Michael C" <mculleyNOSPAM@optushome.com.au> wrote in message
news:445e8371$0$9697
http://217.33.241.242/download/Firstsight%20Vision/Tech%20Tips/LED-lighting.pdf

Thanks, I'll have a look at it now.
Click to expand...
I think I get it now. They are still similar to a standard light bulb in
that they use a certain current at a certain voltage but that current
changes very rapidly with small changes in voltage. It can vary greatly
between LEDs in the same batch. Hence you need to make a circuit to supply a
controlled amount of current, not voltage. And a plain old resistor is a
good way to do that. :) I'd always thought the resistor was just to get the
voltage down and could have been replaced with a reg.

Thanks for all the replies.

Michael
 
Michael C wrote:
"Michael C" <mculleyNOSPAM@optushome.com.au> wrote in message
news:445e8371$0$9697

http://217.33.241.242/download/Firstsight%20Vision/Tech%20Tips/LED-lighting.pdf

Thanks, I'll have a look at it now.


I think I get it now. They are still similar to a standard light bulb in
that they use a certain current at a certain voltage but that current
changes very rapidly with small changes in voltage. It can vary greatly
between LEDs in the same batch. Hence you need to make a circuit to supply a
controlled amount of current, not voltage. And a plain old resistor is a
good way to do that. :) I'd always thought the resistor was just to get the
voltage down and could have been replaced with a reg.

Thanks for all the replies.

Michael


there are articles on why you should not run a LED of a regulator.
Click to expand...
LED are supposed to be thought of as having a constant voltage drop
across them just like any forward biased diode.
 
On Mon, 08 May 2006 20:56:21 +1000, Mark Harriss <billy@blartco.co.uk>
wrote:

Michael C wrote:
"Michael C" <mculleyNOSPAM@optushome.com.au> wrote in message
news:445e8371$0$9697

http://217.33.241.242/download/Firstsight%20Vision/Tech%20Tips/LED-lighting.pdf

Thanks, I'll have a look at it now.


I think I get it now. They are still similar to a standard light bulb in
that they use a certain current at a certain voltage but that current
changes very rapidly with small changes in voltage. It can vary greatly
between LEDs in the same batch. Hence you need to make a circuit to supply a
controlled amount of current, not voltage. And a plain old resistor is a
good way to do that. :) I'd always thought the resistor was just to get the
voltage down and could have been replaced with a reg.

Thanks for all the replies.

Michael


there are articles on why you should not run a LED of a regulator.
LED are supposed to be thought of as having a constant voltage drop
across them just like any forward biased diode.
Click to expand...
What if your source voltage varies? It is hard to maintain a constant
current without using some form of regulation.
 
The Real Andy wrote:
there are articles on why you should not run a LED of a regulator.
LED are supposed to be thought of as having a constant voltage drop
across them just like any forward biased diode.


What if your source voltage varies? It is hard to maintain a constant
current without using some form of regulation.
Click to expand...


Simple: use a LM317 variable regulator as a current regulator.
In the NatSemi app notes you can find it, but it works by
having a resistor in series with the output terminal that
is selected to have a 1.25 V drop at the current you want to
regulate at: so 1.25/.02=62.5 Ohms. The adjust terminal is
connected to the opposite end of the resistor which is then
the output of the current regulator.

This works by having the LM317 keep a constant 1.25v across
the resistor which gives a constant 20 mA.
 
"The Real Andy" <will_get_back_to_you_on_This@b.c> wrote in message
What if your source voltage varies? It is hard to maintain a constant
current without using some form of regulation.
Click to expand...
I'm using an lm317 to regulate the voltage.
 
Michael C wrote:
"The Real Andy" <will_get_back_to_you_on_This@b.c> wrote in message
What if your source voltage varies? It is hard to maintain a constant
current without using some form of regulation.

I'm using an lm317 to regulate the voltage.


Have a look in lm317 datasheet at constant current source
Click to expand...
Tom
 
On Tue, 9 May 2006 10:47:56 +1000, "Michael C"
<mculleyNOSPAM@optushome.com.au> wrote:

"The Real Andy" <will_get_back_to_you_on_This@b.c> wrote in message
What if your source voltage varies? It is hard to maintain a constant
current without using some form of regulation.

I'm using an lm317 to regulate the voltage.
Click to expand...
This will essentially provide the same result. To provide a seperate
constant current source to each LED would be silly, when a resistor in
series with a regulated source voltage will do just fine in your
application.
 
You are looking for an explanation...
Another potential explanation is the effect of capacitance.
Rather than thinking about the static DC operation.... consider what happens
when the thing is first turned on....
A mass of electrons fly through the circuit, to build up the operating bias
point for each LED, this can be modelled as a capacitance for each LED, but
if one has less capacitance than the others, then it will reach this point
sonner, and hence become the soul resistive load in a chain of 'shorts' . Of
course, this all happens in a microsecond or so.

To the people in this group who are unfortunately exposed to the pointless
abuse from others...I suspect they are simply socially inept, oblivious to
their human defects seen by others, and continually thought of as sad,
angry, friendless people.

They get a cruel sense of fun when abusing / flaming others, so dont bother
arguing with them
 
"Simone Merrett"
You are looking for an explanation...
Another potential explanation is the effect of capacitance.
Rather than thinking about the static DC operation.... consider what
happens
when the thing is first turned on....

A mass of electrons fly through the circuit, to build up the operating
bias
point for each LED, this can be modelled as a capacitance for each LED,
but
if one has less capacitance than the others, then it will reach this point
sonner, and hence become the soul resistive load in a chain of 'shorts' .
Of
course, this all happens in a microsecond or so.
Click to expand...


** What utterly * bizarre * crapology !~!

This one deserves an honorary PhD in Crapology.





........ Phil
 
"Tom" <tom@nospam.net> wrote in message
news:KNR7g.1709$b6.47161@nasal.pacific.net.au...
Have a look in lm317 datasheet at constant current source
Tom
Click to expand...
I was considering that but I'm running 12 LEDs in parallel so if one dies
the others will get more current.

Michael
 
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